PDA

View Full Version : Velocity test with barrel being shortened 1" at a time



Butch Lambert
02-02-2018, 09:50 AM
posted 29 January 2018 17:03 Hide Post
1. CCI STINGER 1545 FPS 0.6080 1.3968
1543 FPS 0.6682 1.7784
1558 FPS 0.7400 1.6696
1546 FPS 0.8796 1.7560
1539 FPS

2. FIOCCHI ULTRASONIC 1272 FPS 0.5946 1.5954
1239 FPS 0.5806 1.5268
1259 FPS 0.9088 1.6456
1294 FPS 0.6586 1.8978
1262 FPS

3. ELEY FORCE 1173 FPS 0.5338 1.3140
1188 FPS 0.4906 1.0982
1198 FPS 0.5276 1.2768
1191 FPS 0.5476 1.1766
1155 FPS

4. CCI MINI MAG 1192 FPS 0.5454 1.1414
1213 FPS 1.1400 1.7902
1222 FPS 0.9944 1.9086
1228 FPS 0.6502 1.7822
1220 FPS

5. SK STANDARD 1028 FPS 0.4446 1.3360
1033 FPS 0.5716 1.4686
1042 FPS 0.5280 1.0822
1059 FPS 0.4196 0.9898
1051 FPS

6. ELEY SPORT 1015 FPS 0.7156 1.4130
1081 FPS 0.7246 1.4260
1084 FPS 0.4806 1.2700
1047 FPS 0.5640 1.4052
1099 FPS

7. FIOCCHI SUBSONIC 1026 FPS 0.8764 1.7658
1027 FPS 0.6894 1.9966
1043 FPS 0.5572 1.4536
1061 FPS 0.8574 1.4620
1038 FPS

8. ELEY CONTACT 1074 FPS 0.6510 1.2918
1067 FPS 0.6198 1.3132
1070 FPS 0.6756 1.6334
1071 FPS 0.6672 1.3652
1976 FPS

9. LAPUA MIDAS PLUS 1045 FPS 0.5440 1.3748
1055 FPS 0.5858 1.5414
1084 FPS 0.5670 1.5556
1084 FPS 0.4938 1.0080
1111 FPS

10. ELEY TENEX 1052 FPS 0.6104 1.2084
1066 FPS 0.6814 1.4264
1074 FPS 0.5412 1.2210
1061 FPS 0.4982 1.1566
1095 FPS

These are the velocities after a further one inch was cut off.[/quote]

MilGunsmith
02-02-2018, 10:46 PM
More details. What was original barrel length?

Butch Lambert
02-03-2018, 09:22 AM
He is using a CZ452 and I believe the barrel length started AT 24.25"

Butch Lambert
02-04-2018, 10:17 AM
Butch,

Could you please give a little more detail? I can't figure out what these numbers mean.

Many have posted in the past that a rimfire burns all it's powder at about 17-18 inches. down the barrel, and the bullet coasts e.g. slows down. If this barrel was 24+ inches and they cut it one inch at a time this tells a very different story.

Please provide what information you can. Thanks!

TKH

Tony, All I can provide is the rifle is a stock CZ452. The shooter is the owner of the Accurate Reloading forum and is a very wealthy person. Saeed is a very serious hunter around the World. Dwight Scott is his gunsmith. He knew the test needed to be from a variety of ammo and all the same lot for each type. The first number beside the ammo is the starting velocity of the full length factory barrel. After it is chronographed an inch was cut off and crowned and shot again. Each velocity in number descending is the velocity of the shorter barrel. I believe the bottom number under each type of ammo is after it reached 20.25" I think. Saeed wil be in Canada for a couple weeks, so the test is on hold until he returns.
I will try to answer more of your questions if I can.

Bob1949
02-04-2018, 12:32 PM
The two additional numbers after the muzzle velocity are the group sizes at 50 and 100yds respectively.
The information was gleaned from the Accurate Reloading forum.

Bob

Butch Lambert
02-04-2018, 12:58 PM
The two additional numbers after the muzzle velocity are the group sizes at 50 and 100yds respectively.
The information was gleaned from the Accurate Reloading forum.

Bob

Yes Sir!

Fred J
02-04-2018, 01:36 PM
So how was the accuracy during these tests? Did it improve or was it a disaster?

Butch Lambert
02-04-2018, 02:38 PM
So how was the accuracy during these tests? Did it improve or was it a disaster?

Remember the group sizes are 5-10 shot groups average. Each velocity is the average of 5-10 shot groups. Saeed is shooting 50 rounds for each type ammo for each inch that he is trimming. He is right in thinking that a lot of groups from the same lot of ammo is the only way to really have a good test. I believe he said that he would need 1800 rounds of each type ammo from the same lot for the test to be effective. I wish he had measured all of the groups.
The CZ452 factory rifle is a good tincan shooter, but not a BR rifle.

MilGunsmith
02-05-2018, 07:02 AM
So it would appear that velocity is increasing as the barrel gets shorter.

Butch Lambert
02-05-2018, 09:13 AM
From the forum.



posted Jan 16, 9:45 AM Hide Post
Yes, I never realized how much shooting this is going to require!!?

The rifle has a 24.75 inch barrel.

My intention is to cut 18 inches off in one inch increments!

Shooting will be 5, 10-shot groups.

I have removed the open sights.

I have adjusted the trigger, and installed a Bushnell 6-24X scope on it.

I am going to check my ammo store and select the ammo. It seems I would need 1,800 of each type for the test!!!?


Hopefully this answers more of your questions.

todde
02-05-2018, 10:10 AM
Of the better ammo the groups looks to closed up as the barrel got shorter by the test. Todd

blades
02-05-2018, 10:28 AM
quite some time ago this same style test was run it was published in either Shooting Times or the American rifleman ( somewhere in the early 80's. Increments were one inch. It was controlled enough that Anshutz repeated it in their facilities. Upshot was that around 19-20 inches gave the optimum velocity and "accuracy" deemed acceptable to their standards at that time. There were a series of rifles produced with barrels in this length and a sight tube on the end( bloop tube was the common name in referance to the sound) the tube was there only to extend the sight radius for Irons so the clicks were the same as before ( although many other ideas were ascribed to the tube- they were not tuners nor there to keep wind deflection to a minimum at the time of projectile exiting the barrel). One little tidbit, Annie barrels are slightly choked. Many Annie barrels were promptly wacked off ( but forgetting the slight choke) so the response a bit later was that it was so much black magic. I have an acquaintance that did that and bitched about it forever afterwards. At the time I had a very rough 52c- bull barrel that had been unkindly treated- the barrel was shortened to 20" restocked and a Canjar LP trigger installed it became my heavy siilly-wet gun and still is. Putting it back in the original prone stock it would produce 100- mutiple x count on the A36 target @ 50 ft or at 50 yards outdoors, providing of course that this operator did his part. Primary ammo feed to this rifle was Elely Practice 100 , Club, or RWS Match it also did well with CCI standard of that vintage.

tim
02-05-2018, 12:25 PM
quite some time ago this same style test was run it was published in either Shooting Times or the American rifleman ( somewhere in the early 80's. Increments were one inch. It was controlled enough that Anshutz repeated it in their facilities. Upshot was that around 19-20 inches gave the optimum velocity and "accuracy" deemed acceptable to their standards at that time. There were a series of rifles produced with barrels in this length and a sight tube on the end( bloop tube was the common name in referance to the sound) the tube was there only to extend the sight radius for Irons so the clicks were the same as before ( although many other ideas were ascribed to the tube- they were not tuners nor there to keep wind deflection to a minimum at the time of projectile exiting the barrel). One little tidbit, Annie barrels are slightly choked. Many Annie barrels were promptly wacked off ( but forgetting the slight choke) so the response a bit later was that it was so much black magic. I have an acquaintance that did that and bitched about it forever afterwards. At the time I had a very rough 52c- bull barrel that had been unkindly treated- the barrel was shortened to 20" restocked and a Canjar LP trigger installed it became my heavy siilly-wet gun and still is. Putting it back in the original prone stock it would produce 100- mutiple x count on the A36 target @ 50 ft or at 50 yards outdoors, providing of course that this operator did his part. Primary ammo feed to this rifle was Elely Practice 100 , Club, or RWS Match it also did well with CCI standard of that vintage.

There is one correction/addition I would offer.
A lot of the Anschutz work resulted in the first generation on the 2007 series actions and back then a very desirable feature was the barrel clamping that afforded one to reset headspace, back when rims were all over and everybody had rim thickness guages and sorted rims.
This was all published as a cover story in the old Precision Shooting with testing done by a couple California guys that brought in the first 8-10 of those barreled actions.
I was able to buy one of those first 2007 barreled actions and they did, indeed have very short barrels, on the order of 20".
It also came with a bloop tube. It was slotted and the CM barrel had a small pin about an inch behind the muzzle, the bloop seated on this and then clamped much the same as today's devices.
It did not have any other points, grooves, screws, of any kind to mount sights, and was noticably shorter and considerably heavier than anything that now supports sights.
I can only deduce that this first generation device was supplied only as a tuner with no other use and never heard anything in regard to further production 2007's ever including such a piece of equipment.
It was somewhat useful, however, I mostly shot this with an additional tuner developed back in the 50's-60's by a well known prone guy whose name I long since forgot.
It involved an adhesive backed tape you mounted on your barrel and then a very strong ceramic magnet between two iron plates that went on the barrel.
The theory was that once you attached it a set distance from the action, you could then rotate it's position on the barrel axis. You could, by doing this, move groups around on paper a good 1/2"-3/4" from previous print. Soon thereafter the Time units and the Hoehn 4000's came out.

GordonE
02-05-2018, 06:16 PM
Choke or Twist rate? I can measure Groove dia. with a Diatest split ball indicator that measures in tenths. The tightest place in the muzzle and the round place is easy. Head space with a clamped barrel doesn't amount to much with ignition like STILLERS 2500x. Twist rate makes or breaks a great rimfire barrel. You can make washers out of a barrel and the only thing you will get is a lot of pieces. A cz isn't much of a platform.

Butch Lambert
02-05-2018, 06:43 PM
Gordon,
Saeed has a couple or 10 accurate BR type rimfire rifles. He is just doing a comparison test of velocity of a barrel as it is shortened only. He is going to measure the muzzle blast (sound) also. It is a playtoy thing for him, but he tries to have certain controls to make his test information accurate. He has used Bleiker, Walther, and Anschutz factory rifles to test ammo for speed and accuracy. Fortunately Saeed has plenty of funds to play as he likes and some of his tests are fun to follow even if it may mean nothing to you.

GordonE
02-05-2018, 07:01 PM
If he has all the funds that you keep touting. Why in hell would he use a CZ. Makes one wonder.

tim
02-05-2018, 08:15 PM
If he has all the funds that you keep touting. Why in hell would he use a CZ. Makes one wonder.

He has always played with all kinds of stuff like this. Apparantly interested in anything that goes bang and time to do whatever.
His facility in the desert is like disneyland, and apparrantly a heart of gold, used to take two gunsmiths from the USA on African Safari for like 3-4 weeks, and I mean Safari. One year I have no idea how many of the big 5 they shot but it involved something like 5 elephants alone at about $150,000 a pop. One of the guys got bit, got denge fever, and he had him picked up and sent back for proper treatment. Very generous guy.
Gordon, we gotta find friends like this.

GordonE
02-05-2018, 08:45 PM
bobbing a CZ barrel one inch at a time is meaningless. This is a benchrest accuracy forum. Where you may get all soft and fuzzy about how much money he may have. A CZ is still a poor platform for a test of any kind of accuracy. S&it Barrel,S&it Trigger,S&it ignition. Hope you get to go on one of those big money hunts.

tim
02-05-2018, 08:56 PM
No argument from me.

HuskerP7M8
02-05-2018, 10:16 PM
No offense to Saeed because I greatly admire those that attempt to test and gather data that may be helpful, but I've followed his testing for many years and looked at the data he's presented numerous times on various subjects, and it doesn't usually take me long to realize there are more problems with his methodology than I'm willing to explain or devote to a forum post.

In this particular test, if he's only using 5 rds to gather velocity data, as he reported, the usual outcome is a mish-mash of confusing results that make no sense and can't be statistically analyzed successfully because it bears no resemblance to the same testing I and many others have done over the years when investigating the same matter using sample sizes that "will" give repeatable results.

It also doesn't help that I see at least one typo (Eley Contact showing an increase in V from 1071 fps to 1976 fps) when the barrel was shortened from 21.75" to 20.75"!
It don't take any special smarts to see that's impossible! LOL

I've posted a summation of sorts below that may be easier to comprehend if this thread continues, and it also illustrates some numbers that can't possibly be correct because they show both V's increasing and decreasing with the length of the barrel.

Being really anal about collecting quality data, I and most others of my ilk will use a minimum of 50-shot samples in gathering velocity data....not 5!
Fact is we don't even know if he threw out the 1st rd fired with every 5-shot string, and if he didn't....that 1st rd would totally screw the V stats!

50-shot samples may be overkill, and not practical for say CF, but like I said, I'm obsessed with this stuff and I want it to stand up to peer review and the usual criticism of so called internet expurts.

https://farm5.staticflickr.com/4767/26233569948_6d08529a23_o.jpg (https://flic.kr/p/FYaUo9)2018-02-05_1859_02 (https://flic.kr/p/FYaUo9)

Let's also touch on what Tony posted in this thread because it's something I've seen mentioned more times than I can count.

Tony posted this:
"Hence many believe a longer barrel on a rimfire allows the bullet to coast and stabilize its velocity, and that perhaps, makes the barrel less sensitive to ammo variance."

Sorry Tony, but it's highly possible it's just the opposite.
As friction becomes a more dominant/significant factor from about 6" barrels on, friction robs the bullet of a given amount of energy per unit length travelled up the barrel. But, the energy of the bullet goes as the velocity squared, so slower bullets will slow down quicker than faster bullets. This will lead to an increase in the V SD and V ES as the barrel lengthens.

So, should we all use the shortest barrels possible to enhance this advantage?
I don't know for certain because there's another factor that may dramatically affect the results one way or another.
Among the small community I collaborate and share data with privately, we've had several discussions concerning muzzle pressure and how it affects precision.
It boils down to gaining an advantage with shorter barrels in RFBR, but possibly giving it back because the increased muzzle pressure (Transitional Ballistics) with shorter barrels may cause an unknown adverse effect on precision.

Let me know what happens when you campaign a 6" barrel on your rifle this next year. LOL

A dumb but very curious farmer,
Landy

MilGunsmith
02-06-2018, 08:06 AM
The shorter barrel may also be stiffer and therefore less affected by harmonics. We tested an M16/M4 with 20", 14 1/2", and 10" barrels in 5.56mm (.223) at 300 meters in a rail mount. Using the same lots of ammo, the 10" barrel consistently shot tighter groups but always had a lower velocity. I know this is a rimfire discussion, but some things can carry over.

Butch Lambert
02-06-2018, 09:11 AM
No offense to Saeed because I greatly admire those that attempt to test and gather data that may be helpful, but I've followed his testing for many years and looked at the data he's presented numerous times on various subjects, and it doesn't usually take me long to realize there are more problems with his methodology than I'm willing to explain or devote to a forum post.

In this particular test, if he's only using 5 rds to gather velocity data, as he reported, the usual outcome is a mish-mash of confusing results that make no sense and can't be statistically analyzed successfully because it bears no resemblance to the same testing I and many others have done over the years when investigating the same matter using sample sizes that "will" give repeatable results.

It also doesn't help that I see at least one typo (Eley Contact showing an increase in V from 1071 fps to 1976 fps) when the barrel was shortened from 21.75" to 20.75"!
It don't take any special smarts to see that's impossible! LOL

I've posted a summation of sorts below that may be easier to comprehend if this thread continues, and it also illustrates some numbers that can't possibly be correct because they show both V's increasing and decreasing with the length of the barrel.

Being really anal about collecting quality data, I and most others of my ilk will use a minimum of 50-shot samples in gathering velocity data....not 5!
Fact is we don't even know if he threw out the 1st rd fired with every 5-shot string, and if he didn't....that 1st rd would totally screw the V stats!

50-shot samples may be overkill, and not practical for say CF, but like I said, I'm obsessed with this stuff and I want it to stand up to peer review and the usual criticism of so called internet expurts.

https://farm5.staticflickr.com/4767/26233569948_6d08529a23_o.jpg (https://flic.kr/p/FYaUo9)2018-02-05_1859_02 (https://flic.kr/p/FYaUo9)

Let's also touch on what Tony posted in this thread because it's something I've seen mentioned more times than I can count.

Tony posted this:
"Hence many believe a longer barrel on a rimfire allows the bullet to coast and stabilize its velocity, and that perhaps, makes the barrel less sensitive to ammo variance."

Sorry Tony, but it's highly possible it's just the opposite.
As friction becomes a more dominant/significant factor from about 6" barrels on, friction robs the bullet of a given amount of energy per unit length travelled up the barrel. But, the energy of the bullet goes as the velocity squared, so slower bullets will slow down quicker than faster bullets. This will lead to an increase in the V SD and V ES as the barrel lengthens.

So, should we all use the shortest barrels possible to enhance this advantage?
I don't know for certain because there's another factor that may dramatically affect the results one way or another.
Among the small community I collaborate and share data with privately, we've had several discussions concerning muzzle pressure and how it affects precision.
It boils down to gaining an advantage with shorter barrels in RFBR, but possibly giving it back because the increased muzzle pressure (Transitional Ballistics) with shorter barrels may cause an unknown adverse effect on precision.

Let me know what happens when you campaign a 6" barrel on your rifle this next year. LOL

A dumb but very curious farmer,
Landy

Landy, I wouldn't call a "farmer" stupid. If you reread his post, he is shooting 5-10 shot groups of each ammo after cutting an inch off the barrel, not 5 shots. Saeed is making no claims, just reporting his results.
Ask Dwight Scott how he was taken care of after contacting "sleeping" sickness in the bush.
If I had known that this thread would be attacked with asinine posts I would not have posted it. This forum has been pretty stagnant for a while.

tonykharper
02-06-2018, 09:47 AM
No offense to Saeed because I greatly admire those that attempt to test and gather data that may be helpful, but I've followed his testing for many years and looked at the data he's presented numerous times on various subjects, and it doesn't usually take me long to realize there are more problems with his methodology than I'm willing to explain or devote to a forum post.

In this particular test, if he's only using 5 rds to gather velocity data, as he reported, the usual outcome is a mish-mash of confusing results that make no sense and can't be statistically analyzed successfully because it bears no resemblance to the same testing I and many others have done over the years when investigating the same matter using sample sizes that "will" give repeatable results.

It also doesn't help that I see at least one typo (Eley Contact showing an increase in V from 1071 fps to 1976 fps) when the barrel was shortened from 21.75" to 20.75"!
It don't take any special smarts to see that's impossible! LOL

I've posted a summation of sorts below that may be easier to comprehend if this thread continues, and it also illustrates some numbers that can't possibly be correct because they show both V's increasing and decreasing with the length of the barrel.

Being really anal about collecting quality data, I and most others of my ilk will use a minimum of 50-shot samples in gathering velocity data....not 5!
Fact is we don't even know if he threw out the 1st rd fired with every 5-shot string, and if he didn't....that 1st rd would totally screw the V stats!

50-shot samples may be overkill, and not practical for say CF, but like I said, I'm obsessed with this stuff and I want it to stand up to peer review and the usual criticism of so called internet expurts.

https://farm5.staticflickr.com/4767/26233569948_6d08529a23_o.jpg (https://flic.kr/p/FYaUo9)2018-02-05_1859_02 (https://flic.kr/p/FYaUo9)

Let's also touch on what Tony posted in this thread because it's something I've seen mentioned more times than I can count.

Tony posted this:
"Hence many believe a longer barrel on a rimfire allows the bullet to coast and stabilize its velocity, and that perhaps, makes the barrel less sensitive to ammo variance."

Sorry Tony, but it's highly possible it's just the opposite.
As friction becomes a more dominant/significant factor from about 6" barrels on, friction robs the bullet of a given amount of energy per unit length travelled up the barrel. But, the energy of the bullet goes as the velocity squared, so slower bullets will slow down quicker than faster bullets. This will lead to an increase in the V SD and V ES as the barrel lengthens.

So, should we all use the shortest barrels possible to enhance this advantage?
I don't know for certain because there's another factor that may dramatically affect the results one way or another.
Among the small community I collaborate and share data with privately, we've had several discussions concerning muzzle pressure and how it affects precision.
It boils down to gaining an advantage with shorter barrels in RFBR, but possibly giving it back because the increased muzzle pressure (Transitional Ballistics) with shorter barrels may cause an unknown adverse effect on precision.

Let me know what happens when you campaign a 6" barrel on your rifle this next year. LOL

A dumb but very curious farmer,
Landy

Landy,

I don't know what information is available from your private community but here is what the public domain says about Transitional Ballistics.

Transitional ballistics, also known as intermediate ballistics,[1] is the study of a projectile's behavior from the time it leaves the muzzle until the pressure behind the projectile is equalized,[2] so it lies between internal ballistics and external ballistics.

Transitional ballistics is a complex field that involves a number of variables that are not fully understood; therefore, it is not an exact science.[3] When the bullet reaches the muzzle of the barrel, the escaping gases are still, in many cases, at hundreds of atmospheres of pressure. Once the bullet exits the barrel, breaking the seal, the gases are free to move past the bullet and expand in all directions. This expansion is what gives gunfire its explosive sound (in conjunction with the sonic boom of the projectile), and is often accompanied by a bright flash as the gases combine with the oxygen in the air and finish combusting.
The propellant gases continue to exert force on the bullet and firearm for a short while after the bullet leaves the barrel. One of the essential elements of accurizing a firearm is to make sure that this force does not disrupt the bullet from its path. The worst case is a muzzle or muzzle device such as a flash-hider that is cut at a non-square angle, so that one side of the bullet leaves the barrel early; this will cause the gas to escape in an asymmetric pattern, and will push the bullet away from that side, causing shots to form a "string", where the shots cluster along a line rather than forming a normal Gaussian pattern.
Most firearms have muzzle velocities in excess of the ambient speed of sound, and even in subsonic cartridges the escaping gases will exceed the speed of sound, forming a shock wave. This wave will quickly slow as the expanding gas cools, dropping the speed of sound within the expanding gas, but at close range this shockwave can be very damaging. The muzzle blast from a high powered cartridge can literally shred soft objects in its vicinity, as careless benchrest pistol shooters occasionally find out when the muzzle slips back onto their sandbag and the muzzle blast sends sand flying.

This seems to favor a slower bullet leaving the barrel rather than a faster bullet given the crowns are square.

But to prevent a he said, she said, I'll leave it there.

But I for one, would still like to know what happens to velocity once the barrel gets cut shorter than 17-18 inches.

TKH

HuskerP7M8
02-06-2018, 11:12 AM
Landy, I wouldn't call a "farmer" stupid. If you reread his post, he is shooting 5-10 shot groups of each ammo after cutting an inch off the barrel, not 5 shots. Saeed is making no claims, just reporting his results.
Ask Dwight Scott how he was taken care of after contacting "sleeping" sickness in the bush.
If I had known that this thread would be attacked with asinine posts I would not have posted it. This forum has been pretty stagnant for a while.

Hi Butch,

As I said, I really do admire the amount of work Saeed puts into his testing and I have no doubt he's sincere as well as trying to be helpful. On the other hand, I do see problems with his methodology that generally leads to suspect results.

Regarding the 5 shots samples I mentioned, maybe I'm confused but Saeed said this:

"I have fired 5 shots of each ammo, to get the velocity.
I am doing this because I found that the chronograph tends to misread if the targets being shot are at the top and not center of the sky screens."

I took this to mean he was forced into using only 5 shots to capture velocity data because the problems with his chronograph prevented him from doing it while he was shooting all the 10-shot groups.
I actually think he made a very astute observation concerning the sensitivity of shot placement thru the screens and most people don't realize how big a problem this can be with certain chronographs.

In my case, when I calculate drag coefficients in my ballistic tunnel, I shoot thru a 1" square area at both the muzzle and the downrange chronograph to combat noisy data from this potentially serious problem.

After looking at his results, what I saw suggests he must have been using only 5 shots because that's what I'd expect to see with inadequate sample sizes.

Could I be wrong? Of course!

I'll gladly delete my post if you feel it's asinine....just say the word. I have absolutely no desire to stir the pot or cause any controversy.

Landy

HuskerP7M8
02-06-2018, 11:18 AM
Landy,

I don't know what information is available from your private community but here is what the public domain says about Transitional Ballistics.

Transitional ballistics, also known as intermediate ballistics,[1] is the study of a projectile's behavior from the time it leaves the muzzle until the pressure behind the projectile is equalized,[2] so it lies between internal ballistics and external ballistics.

Transitional ballistics is a complex field that involves a number of variables that are not fully understood; therefore, it is not an exact science.[3] When the bullet reaches the muzzle of the barrel, the escaping gases are still, in many cases, at hundreds of atmospheres of pressure. Once the bullet exits the barrel, breaking the seal, the gases are free to move past the bullet and expand in all directions. This expansion is what gives gunfire its explosive sound (in conjunction with the sonic boom of the projectile), and is often accompanied by a bright flash as the gases combine with the oxygen in the air and finish combusting.
The propellant gases continue to exert force on the bullet and firearm for a short while after the bullet leaves the barrel. One of the essential elements of accurizing a firearm is to make sure that this force does not disrupt the bullet from its path. The worst case is a muzzle or muzzle device such as a flash-hider that is cut at a non-square angle, so that one side of the bullet leaves the barrel early; this will cause the gas to escape in an asymmetric pattern, and will push the bullet away from that side, causing shots to form a "string", where the shots cluster along a line rather than forming a normal Gaussian pattern.
Most firearms have muzzle velocities in excess of the ambient speed of sound, and even in subsonic cartridges the escaping gases will exceed the speed of sound, forming a shock wave. This wave will quickly slow as the expanding gas cools, dropping the speed of sound within the expanding gas, but at close range this shockwave can be very damaging. The muzzle blast from a high powered cartridge can literally shred soft objects in its vicinity, as careless benchrest pistol shooters occasionally find out when the muzzle slips back onto their sandbag and the muzzle blast sends sand flying.

This seems to favor a slower bullet leaving the barrel rather than a faster bullet given the crowns are square.

But to prevent a he said, she said, I'll leave it there.

But I for one, would still like to know what happens to velocity once the barrel gets cut shorter than 17-18 inches.

TKH

Hey Tony,

Not surprisingly, I'm confused! LOL

Are we arguing about something? I don't see where we disagree about anything and we pretty much said the same thing.

Landy

George Atkins
02-06-2018, 12:13 PM
If he has all the funds that you keep touting. Why in hell would he use a CZ. Makes one wonder.

bobbing a CZ barrel one inch at a time is meaningless. This is a benchrest accuracy forum. Where you may get all soft and fuzzy about how much money he may have. A CZ is still a poor platform for a test of any kind of accuracy. S&it Barrel,S&it Trigger,S&it ignition. Hope you get to go on one of those big money hunts.

Maybe he could not find a 10/22 at the time. Why not a CZ ? You might be right on the barrel, but he may have not wanted a taper lapped one for this test. Now the trigger is far better than most OEM triggers, very adjustable. Now the ignition is not a PoS, if it is, then every Turbo and 10X is as well. Its PAS and everyone knows, NOTHING beats PAS, its the most consistent ignition available.

Just another opinion from the peanut gallery.

Butch Lambert
02-06-2018, 02:57 PM
Landy, this is his post that I was referring to.

osted Jan 16, 9:45 AM Hide Post
Yes, I never realized how much shooting this is going to require!!?

The rifle has a 24.75 inch barrel.

My intention is to cut 18 inches off in one inch increments!

Shooting will be 5, 10-shot groups.

I have removed the open sights.

I have adjusted the trigger, and installed a Bushnell 6-24X scope on it.

I am going to check my ammo store and select the ammo. It seems I would need 1,800 of each type for the test!!!?

HuskerP7M8
02-06-2018, 06:53 PM
Butch,

I understand how he said he would be collecting the accuracy data, but what he said earlier concerning velocity is what concerns me.

If I'm correct in understanding what Saeed said, he's only going to be able to make an attempt at gathering accuracy data, and the velocity lost per inch will likely be lost in the noise due to so few shots.
I may be wrong, but I suspect even the accuracy data will be compromised due to the poor shooting rifle he's using. If I were doing this testing, I'd want to use a rifle that averages in the range of 0.26" to 0.28" for 10-shot groups and we're not close to that.

There's a slight possibility we may learn something if we only look at the stats using the match ammo (Midas+ & Tenex) because the Standard Deviation of both is so much better than the other ammos which will almost certainly be very bad. I've seen some of that ammo produce Extreme Spreads in velocity in excess of 100 fps!

With only 5 shots, I hope everyone realizes just how badly a single slow or fast round can totally screw the results.
This ain't CF where you can manage the Standard Deviation in velocity and still get useful results with just 5 rounds.

Very good ammo, like very good rifles, will improve the odds of learning something but I'm not optimistic.

Maybe you can get this sorted out after Saeed returns. We need to know how many rounds he's using for velocity and we need to know for certain that he never uses the 1st round fired in any of the velocity testing.

Landy

Butch Lambert
02-07-2018, 09:23 AM
Butch,

I understand how he said he would be collecting the accuracy data, but what he said earlier concerning velocity is what concerns me.

If I'm correct in understanding what Saeed said, he's only going to be able to make an attempt at gathering accuracy data, and the velocity lost per inch will likely be lost in the noise due to so few shots.
I may be wrong, but I suspect even the accuracy data will be compromised due to the poor shooting rifle he's using. If I were doing this testing, I'd want to use a rifle that averages in the range of 0.26" to 0.28" for 10-shot groups and we're not close to that.

There's a slight possibility we may learn something if we only look at the stats using the match ammo (Midas+ & Tenex) because the Standard Deviation of both is so much better than the other ammos which will almost certainly be very bad. I've seen some of that ammo produce Extreme Spreads in velocity in excess of 100 fps!

With only 5 shots, I hope everyone realizes just how badly a single slow or fast round can totally screw the results.
This ain't CF where you can manage the Standard Deviation in velocity and still get useful results with just 5 rounds.

Very good ammo, like very good rifles, will improve the odds of learning something but I'm not optimistic.

Maybe you can get this sorted out after Saeed returns. We need to know how many rounds he's using for velocity and we need to know for certain that he never uses the 1st round fired in any of the velocity testing.

Landy



Landy, I'm not a rimfire guy. I do have 3 custom 40X RF custom tincan shooters and only 3 mod 37 Remingtons and my 1922M11 Springfield. I posted this for the interest of the BR.COM RF guys. I personally don't care. Why don't you go to the AR forum and voice your concerns there. I won't post any more of the results here.

Fred J
02-07-2018, 01:17 PM
I did a similar test, only using four different barrels, different lengths.
These were all 5 shot groups. I fouled the barrels with 5 shots, prior to each test.