Velocity test with barrel being shortened 1" at a time

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.
 
HuskerP7M8 said:
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.

2018-02-05_1859_02

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
Click to expand...

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.
 
HuskerP7M8 said:
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.

2018-02-05_1859_02

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
Click to expand...

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
 
Butch Lambert said:
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.
Click to expand...

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
 
tonykharper said:
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
Click to expand...

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
 
GordonE said:
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.
Click to expand...

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.
 
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!!!?
 
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
 
HuskerP7M8 said:
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
Click to expand...



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.
 
Similar Test

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.
 

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