50y BR with Thomas HPX

michaelthomas said:
Hi Pedro.... hope all is well with you. I had heard about the addition of 50m air rifle. I agree that they won’t allow the use of slugs...will be too much to swallow right off.

My hope is to get some participation here in the US for 50y BR with slugs. If they can be made competitive with the unlimited rimfire guns...I think that could spark some interest since the long term cost will be much lower and the problem of finding good ammo would go away. Not going to likely save any money on
the initial investment.

After getting a good setup with slugs...it’s hard to muster much desire to shoot at 50y with pellets.?

Mike
Click to expand...

Hi Mike, good to hear from you!
I totally concur with your say
 
I can understand the point about pellets vs slugs- level the playing field a bit, but that does put one back on relying on the MFG QC again. Almost the same as rimfire - luck of the draw. The whole precision BR pretty much died out at my club, Although some other form of Bench shooting was started up, more on the order of off the shelf RF. I have not participated in it as yet - time constraints are best excusei can give.
 
michaelthomas said:
Hi Landy...thanks.

The targets were shot horizontally. It’s a lot of vertical.

The wind was averaging 6mph and bouncing between 5 and 7 o’clock.

I’m not able to hold a good velocity spread with this barrel no matter how I valve tune the gun. If I replace the barrel with a Shilen ratchet, the velocity spreads go from over 20fps to less than 10 for 25 shots. I also gain about 40fps on average. If I could get the velocity spread under 10 with the Muller I believe I could improve my scores significantly. The Muller is more precise and predictable in the Horizontal plane.

I thought I might be able to use a barrel tuner to help with the vertical.... but the muzzle blast and the overhanging bloop tube make about 2” groups at 50. I’m considering edm cutting some ports about an inch back from the muzzle to vent the muzzle pressure before the bullet leaves the barrel. Doing so might allow me to use a standard barrel tuner. The other option is to make a tuner that doesn’t extend past the muzzle.

The TDS target comparisons are dubious. The 2150 would have plugged a 249 on the WRABF target...with a lot more xs. Over the last 21 WRABF cards I have shot I have averaged 247.5 in winds up to 15 mph and as low as 2-3.

Mike
Click to expand...
Mike,

A few more random comments, thoughts and questions:

You mentioned in post #11 you were observing a 30 to 40 deg slant due to "Aerodynamic Jump".

Through live fire testing with RF projectiles having a Sg (Stability factor) of 1.5, I measured a 36 deg slope at 25 yds and a 30 deg slope at 50 yds. The differences in slope for the 2 distances in my testing are likely due to the "Aerodynamic Jump" being angular while the horizontal wind drift is not, and should cause the slope to shallow out at longer distances.

The 1.5 Sg I used with RF projectiles is based on a projectile length of 0.460" in a 16" twist barrel. Have you tried taking a stab at calculating the Sg for your slugs bases on the length of them?
I guess what I'm wondering is if your slugs might be longer and may be contributing to a lower Sg that should induce more "Jump"? Just a thought.

I'm not a bit surprised you had different scores than the TDS screenshot for the WRABF target. The image you posted didn't have the resolution needed to do other than a coarse plotting of the shots, but was entirely adequate for distinguishing the ARA scoring rings, matching the 2150 score, and illustrating the shape of the distribution. It was also helpful there weren't any shots I call line lickers on the scoring rings that would hinder my attempt at calculating the score.

I don't have a clue as to why velocity SD would be higher with the Muller than the Ratchet. I'd have to dig thru my data to be certain, but I don't believe I ever see that with RF ammo and the dozens of barrels I've compared unless the data sample sizes are too small. Perhaps looking at V SD only and/or plotting the shots and looking at Excel's statistical "Slope" function for the "y" point data would reveal something different.
BTW, I hate fishtailing head and tail winds! LOL

Many years ago while having a discussion with Dr Geoffrey Kolbe who used to own Border barrels and is a physicist, he mentioned his next project was going to be an attempt at minimizing muzzle blast by employing a method similar to what you're contemplating. I don't presently know if he ever made the attempt, but if I get the chance to visit with him again....I'll ask.

I do know I'd love to get the chance to compare one of my better barrel/ammo combinations in my ballistic tunnel before and after the modification....hint....hint! LOL

Landy
 
Hi Landy,

The original post from a while back was using manufactured slugs. They behaved oddly and did not fare well in a variety of wind. At that time, I would have still shot pellets in a 50y BR match. What I’m using now is a homemade slug that is performing reliably and predictably without the radical jump that was common with the others.

I’ve played with the Kolbe twist calculator quite a bit...but it’s not intended for hollow nose projectiles like all the manufactured slugs seem to have. I guess it was also not designed for use with rebated boattails....which are the most common variety for us too. I don’t feel like I got to much useful information from my time with it. I don’t really know. The slug I’m using now with the Rimfire barrels is .465” long. I have tested lengths from about .380” to .500” and these shoot the best scores for me. I have always been under the impression that a higher Sg creates more jump than a lower one.

I have never shot a good rimfire rifle in the wind, so I don’t really know how they behave. I’m only assuming that my current setup is similar. It may not be at all. I’m a decent pellet BR shooter, but it’s been tough for me to shoot slugs because my mind has been trained for pellets. Pellets rise in a L to R wind...and fall in a R to L. Whatever is happening on the range with pellets is an automatic process for me....but it’s very slow when I’m shooting slugs right now because I have to actually think about what to do. Even when I do think about it, I’m often wrong. At this point, I really just need to take sighters every time something changes a little. With pellets I can make a good adjustment on the fly and be correct most of the time.

I think you live in Nebraska based on your forum name. I live in Colorado...but not on the Nebraska side of the “hill”. What part of the state do you live in?

I think the Muller just has a lot more bore drag compared to the Shilen. With greater drag, there will be greater fluctuations...I think. An interesting note is that after cleaning either of the barrels I will lose 100fps of velocity or greater. It will slowly come back over 25-50 shots. Luckily I don’t need to clean to maintain accuracy. It hangs in there for thousands of shots.

Mike
 
Thanks for the info Mike.

Yup, I had a brain fart on the Sg! Self taught amateur ballisticians have a tendency to do that. LOL

I live almost dead center of the State in Cozad, NE on I-80. You can even see my tunnel from I-80 if you know where to look. Neighboring States but still a very long drive between the two of us. Maybe someday the two of us will have a chance to meet.

Landy
 
I would like that. I’m not necessarily opposed to an 8 hour drive if I can learn something. I’ve done a lot more for a lot less. ?

Mike
 
michaelthomas said:
I have never shot a good rimfire rifle in the wind, so I don’t really know how they behave. I’m only assuming that my current setup is similar. It may not be at all. I’m a decent pellet BR shooter, but it’s been tough for me to shoot slugs because my mind has been trained for pellets. Pellets rise in a L to R wind...and fall in a R to L. Whatever is happening on the range with pellets is an automatic process for me....but it’s very slow when I’m shooting slugs right now because I have to actually think about what to do. Even when I do think about it, I’m often wrong. At this point, I really just need to take sighters every time something changes a little. With pellets I can make a good adjustment on the fly and be correct most of the time.
Mike
Click to expand...

Mike you just touch my biggest issue...
I'm the opposite, I think rimfire, and went wrong when shooting pellets... many times just forgot they are the opposite...
 
Very interesting topic, Mike I know you have been working hard to have Airguns compete directly with Rimfire 50yd BR, and would like to believe they can and will! Very excited to see this play out, I need to find a local RF Benchrest shoot to watch and take notes. A couple shooters I’ve had the pleasure to compete with this summer in 25m will take note as well!
 
Hi Joe, I’m really hoping this goes somewhere. The Rimfire guys seem open to letting us shoot with them as long as we shoot the same target and distance. Makes perfect sense to me. You have shot Rimfire, so you know where air needs to be to keep up. We have our work cut out for us if we want to claim
equality on the target. It’s exciting to me.

Mike
 
6 Target Unlimited Tournament 12/12/20 Piney Hill Indoor range Luray Va.

It has been all talk up until now!

But here is the first chance for the Air Gunners to show up and shoot with Rimfire shooters in a 50 yard tournament.

The target will be the IR 50 target, 25 scoring bulls, and a 20minute time limit.

The Larry "The Legend" Harrison tournament will be held at Piney Hill indoor range Luray Va. start time 0900hrs. 12/12/20.

Air Rifles shooting .22 cal. are welcome.

This tournament is being put on by Scot Whystell to honor Larry Harrison, a much loved rimfire competitor that has past on.

This is a money match and awards will be given out for target winners, and the top three places.

Entry fee for the tournament is $50.00. Lunch will not be served so bring your own.

Hope to see some air gunners there.

TKH
 
Last edited:
HuskerP7M8 said:
Mike,

A few more random comments, thoughts and questions:

You mentioned in post #11 you were observing a 30 to 40 deg slant due to "Aerodynamic Jump".

Through live fire testing with RF projectiles having a Sg (Stability factor) of 1.5, I measured a 36 deg slope at 25 yds and a 30 deg slope at 50 yds. The differences in slope for the 2 distances in my testing are likely due to the "Aerodynamic Jump" being angular while the horizontal wind drift is not, and should cause the slope to shallow out at longer distances.

The 1.5 Sg I used with RF projectiles is based on a projectile length of 0.460" in a 16" twist barrel. Have you tried taking a stab at calculating the Sg for your slugs bases on the length of them?
I guess what I'm wondering is if your slugs might be longer and may be contributing to a lower Sg that should induce more "Jump"? Just a thought.

I'm not a bit surprised you had different scores than the TDS screenshot for the WRABF target. The image you posted didn't have the resolution needed to do other than a coarse plotting of the shots, but was entirely adequate for distinguishing the ARA scoring rings, matching the 2150 score, and illustrating the shape of the distribution. It was also helpful there weren't any shots I call line lickers on the scoring rings that would hinder my attempt at calculating the score.

I don't have a clue as to why velocity SD would be higher with the Muller than the Ratchet. I'd have to dig thru my data to be certain, but I don't believe I ever see that with RF ammo and the dozens of barrels I've compared unless the data sample sizes are too small. Perhaps looking at V SD only and/or plotting the shots and looking at Excel's statistical "Slope" function for the "y" point data would reveal something different.
BTW, I hate fishtailing head and tail winds! LOL

Many years ago while having a discussion with Dr Geoffrey Kolbe who used to own Border barrels and is a physicist, he mentioned his next project was going to be an attempt at minimizing muzzle blast by employing a method similar to what you're contemplating. I don't presently know if he ever made the attempt, but if I get the chance to visit with him again....I'll ask.

I do know I'd love to get the chance to compare one of my better barrel/ammo combinations in my ballistic tunnel before and after the modification....hint....hint! LOL

Landy
Click to expand...

Is there a chance that the Muller SD issue may come as a result of different rifling (shallower) and/or bore dimension possibly presenting less bore sealing of the slug ?

Michael, understanding these are still early days, with your present slug configuration, has it been possible or worthy to alter slug dies to yield some variations of slug diameters that might be barrel specific to see SD imact?
Just thinking out loud here a bit.
 
Hi Tim, I think the larger SD is due to the muller having more taper and more overall friction. I can make my slugs from .222-.224”...and have tried them all. Any smaller than .2225 and accuracy deteriorates...and anything over .2230 with throw fliers.

I have gotten the Muller to hold a SD of 2 lately. With air rifles...we can use a longer valve duration to drive the bullet all the way down the barrel. It uses more air, and makes more muzzle blast....but it does keep the spread down.

It’s been shooting well. I would like to be able to use a tuner...but have not been able to use anything that overhangs the muzzle. The muzzle blast inside the tuner throws the accuracy into the toilet. All I can do is move weight behind the muzzle...but have not tried that yet.

Mike
 
Mike, I know 0 about air rifles but the recent threads have been enlightening. A question, what differs from the blast of an air rifle opposed to a rimfire that throws the accuracy off when the tuner is installed? The huge rush of air?
Could you experiment with your own tuner design with a larger i.d. to mitigate that perhaps?
Thanks for posting!

Keith
 
Unfortunately....I really don’t know what’s exactly different. I can only make assumptions based on things I do know about the two.

The Rimfire cartridge makes a very small volume of very high pressure. I have read that it’s up to 20,000 psi. Your bullet accelerates very quickly and then coasts down the last 8 inches of barrel or so.

We get about 2500-3000 psi to work with and have to drive the bullet all the way down the barrel as hard as we can to get up to speed. I suspect the actual muzzle pressures to be very different between the two.

I wonder if a Rimfire tuner would disrupt your bullet out of a very short barrel?

I have tried air strippers and even porting the barrel 1 1/2 inches back from the muzzle to vent pressure before the bullet left the barrel. I was hoping this would let me use a tuner. So far, it has not.

It may work to have a larger ID...but I’m guessing it will not. If I place a 4x16 plate vertically 6 inches to the right or left of the muzzle...it will string shots diagonally. If I put it flat below the muzzle...it will string vertically. I wish I could see what’s happening.

Early on....my air tube extended past the muzzle. I saw lead tracks on the air tube and cut it back. That was the first big step to finding the accuracy it has now.

If I could remove the vertical, this thing would be killer.

Mike
 
Quite a few years ago I decided to compare about a dozen barrels with the same lot of ammo in varying lengths from 6" to approx 25" and found a fairly strong indication that shorter barrels had a lower V SD than longer ones. Kind of the opposite of what you hear from most RFBR shooters when they usually say a benefit of longer barrels is that they allow for a stabilization of velocities because the bullet is just coasting after 14" to 16" and chamber/muzzle pressures are diminishing.

Intuitively, that always kind of made sense to me and I was a little surprised with the results I got. Geoff Kolbe was also a bit surprised when I shared the data with him, but he came up with an answer that might explain it.

Quote:
"As for the increase in SD in the longer barrels, I think that well be because friction is a significant force on the bullet from about 6" 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 fast bullets. This will lead to an increase in the SD with length of barrel"

How this may or may not jibe with Mike's thoughts? I don't have a clue, but just thought I'd throw it out there.

More food for thought. I'm thinking the BHN of Mike's slugs and the amount, if any, of obturation to the bore with the slugs at reduced chamber pressures may be of importance.

As is usually the case, more speculation than any real answers,
Landy
 
HuskerP7M8 said:
Quite a few years ago I decided to compare about a dozen barrels with the same lot of ammo in varying lengths from 6" to approx 25" and found a fairly strong indication that shorter barrels had a lower V SD than longer ones. Kind of the opposite of what you hear from most RFBR shooters when they usually say a benefit of longer barrels is that they allow for a stabilization of velocities because the bullet is just coasting after 14" to 16" and chamber/muzzle pressures are diminishing.

Intuitively, that always kind of made sense to me and I was a little surprised with the results I got. Geoff Kolbe was also a bit surprised when I shared the data with him, but he came up with an answer that might explain it.

Quote:
"As for the increase in SD in the longer barrels, I think that well be because friction is a significant force on the bullet from about 6" 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 fast bullets. This will lead to an increase in the SD with length of barrel"

How this may or may not jibe with Mike's thoughts? I don't have a clue, but just thought I'd throw it out there.

More food for thought. I'm thinking the BHN of Mike's slugs and the amount, if any, of obturation to the bore with the slugs at reduced chamber pressures may be of importance.

As is usually the case, more speculation than any real answers,
Landy
Click to expand...

Landy,
i don’t know where you got the “ most” re longer bbls/ vs SD.
Frankly, I heard it rarely, don’t happen to believe it, etc.
What I have heard extensively and believe whole heartedly is that longer barrels often tend to yield a more stable slug on exit, and some pretty good smiths/ shooters are in this camp. It allows a slug to , perhaps, “calm down” for 8”-10” after combustion. Not a big stretch here to assume that’s logical.
Like lots of this stuff, not easy to prove but my belief.

Michael, I believe, sub sonic match ammo is around 12000-13000 psi with combustion done @ about 16”-18”.

P.S. SD around 2 fps.... I’d call that damned impressive.
 
tim said:
landy,
i don’t know where you got the “ most” re longer bbls/ vs sd.
Frankly, i heard it rarely, don’t happen to believe it, etc.
What i have heard extensively and believe whole heartedly is that longer barrels often tend to yield a more stable slug on exit, and some pretty good smiths/ shooters are in this camp. It allows a slug to , perhaps, “calm down” for 8”-10” after combustion. Not a big stretch here to assume that’s logical.
Like lots of this stuff, not easy to prove but my belief.

Michael, i believe, sub sonic match ammo is around 12000-13000 psi with combustion done @ about 16”-18”.

P.s. Sd around 2 fps.... I’d call that damned impressive.
Click to expand...
went to johnson city tnn some yrs ago and broke worldrecords in light custom class in rimfire with 18 inch barrel on 40 x later went to dublin ga; and broke world records in sporter class with win. 52 with 18 inch barrel on jim stekls knowege. 8.5 pound class the i made mysef for weight
 
billbrawand said:
went to johnson city tnn some yrs ago and broke worldrecords in light custom class in rimfire with 18 inch barrel on 40 x later went to dublin ga; and broke world records in sporter class with win. 52 with 18 inch barrel on jim stekls knowege. 8.5 pound class the i made mysef for weight
Click to expand...
stock.
 
BillBrawand said:
went to johnson city tnn some yrs ago and broke worldrecords in light custom class in rimfire with 18 inch barrel on 40 x later went to dublin ga; and broke world records in sporter class with win. 52 with 18 inch barrel on jim stekls knowege. 8.5 pound class the i made mysef for weight
Click to expand...

Billy, for the record, we ‘re pretty much talking post Vietnam war era here. :D
 
billbrawand said:
went to johnson city tnn some yrs ago and broke worldrecords in light custom class in rimfire with 18 inch barrel on 40 x later went to dublin ga; and broke world records in sporter class with win. 52 with 18 inch barrel on jim stekls knowege. 8.5 pound class the i made mysef for weight
Click to expand...
both guns were hart barrels also i was setting in the unlm. A recordwith a 22 centerfie barrel with fiocchi till i ran out of that lot on last group.
 
You must log in or register to reply here.
Back
Top