50y BR with Thomas HPX

[tim]

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

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.

[michaelthomas]

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

[linekin]

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

[michaelthomas]

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

[HuskerP7M8]

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

[tim]

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

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.

[BillBrawand]

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.

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]

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

stock.

[tim]

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

Billy, for the record, we ‘re pretty much talking post Vietnam war era here.

[BillBrawand]

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

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.

[BillBrawand]

billy, for the record, we ‘re pretty much talking post vietnam war era here. :d

it was about that time,

[BillBrawand]

billy, for the record, we ‘re pretty much talking post vietnam war era here. :d

it was when they held n b r s a . Rim fire natls. In tnn. Dublin ga. At shamrock range

[BillBrawand]

it was about that time,

way back then european barrel were chocked which made them more acc than american

[BillBrawand]

way back then european barrel were chocked which made them more acc than american

if you remember i was first to make jacketed bullets for 22 rinfire and and lead swaged one ihad reloading dies madefor press they shot very well that milt cook outlawed them got scared he would get beat.with center fire barrel.

[BillBrawand]

if you remember i was first to make jacketed bullets for 22 rinfire and and lead swaged one ihad reloading dies madefor press they shot very well that milt cook outlawed them got scared he would get beat.with center fire barrel.

made a few for clay spencer he liked for squirle.