Having problems that are theoretically unlikely does happen.
Back off the load, try a heavier bullet, etc. It is just a possibility to test.
- Thread starter Taylorbok
- Start date
Back off the load, try a heavier bullet, etc. It is just a possibility to test.
I personally don't think it is stability. An sg of 1.0 will typically shoot a sub half moa group at 200 yards if the gun is chambered well and the barrel blank is good. The bc and stability at distance will suffer.
One thing I do have a fair amount of experience with is bullet failures. I like to shoot 68 grain bullets out of 7 twist 223. It doesn't always go so well when things get hot or dirty. I also like to shoot 105-115 grain bullets from a 243 Ackley. You need a 7.5 twist to stabilize 115s in the cold. 105s at 3200 start to get interesting.
(3200x720)/7.5=307,200 rpm
Anything over 300k can, but won't necessarily create problems.
You sir, are at (3175x720)/7=326,571 rpm.
If you do not scrub the ever living fuck out of your throat to keep it clean, you are in disappearing bullet territory.
Shooting a 243AI I have to clean every 200 rounds or so to keep from having fliers. It is likely you have a large carbon ring if you are not doing something to control it. (You need a borescope to see if you have a clean gun). That, combined with the rpms, is likely the cause of your problem.
Good luck figuring things out. Shooting stupid overbore cartridges with heavy bullets is fun, but it is on the ragged edge of not working with cup and core bullets.
One thing I do have a fair amount of experience with is bullet failures. I like to shoot 68 grain bullets out of 7 twist 223. It doesn't always go so well when things get hot or dirty. I also like to shoot 105-115 grain bullets from a 243 Ackley. You need a 7.5 twist to stabilize 115s in the cold. 105s at 3200 start to get interesting.
(3200x720)/7.5=307,200 rpm
Anything over 300k can, but won't necessarily create problems.
You sir, are at (3175x720)/7=326,571 rpm.
If you do not scrub the ever living fuck out of your throat to keep it clean, you are in disappearing bullet territory.
Shooting a 243AI I have to clean every 200 rounds or so to keep from having fliers. It is likely you have a large carbon ring if you are not doing something to control it. (You need a borescope to see if you have a clean gun). That, combined with the rpms, is likely the cause of your problem.
Good luck figuring things out. Shooting stupid overbore cartridges with heavy bullets is fun, but it is on the ragged edge of not working with cup and core bullets.
@MakeSawdust i really appreciate your experience. I am currently giving it a heavy duty clean. It’s going back to bare steel. Upon further inspection I did have a bit of a carbon ring so that could have been the culprit.
Will report back, and thanks again
Edit:
P.s. I had sworn off solids from shooting Barnes and the copper they leave but due to shortages on cup and core may move to lathe turned
Will report back, and thanks again
Edit:
P.s. I had sworn off solids from shooting Barnes and the copper they leave but due to shortages on cup and core may move to lathe turned
I mean they wouldn’t produce a bullet that’s going to destruct when properly stable. Also it didn’t explode before so something else is causing it.
I think you will find better results after the thorough cleaning back to a known condition. At speeds like that you may want to really clean well before 500 rounds.
There is more to it than that. Many things can contribute to jacket separation like crimp, a carbon ring, damage from cleaning rod or an aged barrel.
Bullet makers do not typically state do not spin these faster than x RPMs and design more around typical firearms and ammunition.
When you take a fast twist barrel and push velocity to the edges RPMs get high. Over 300k RPM and things get unpredictable. Also, things like a crimp that damages the jacket a little starts to matter.
It is the high velocity that causes the problem. That bullet moving 2900 fps would be fine, likely. (2900x720)/7=298,286 rpm
Slow the load down and the bullet is stable and won't self destruct. The bullet manufacturers can't control every variable.
I like to run 7 twist barrels in 6 Dasher. I run it slow for consistency. The extra twist usually results in better consistency at long range and more bc. I have a heavy 243AI barrel that I shoot in matches for fun. I like to step on the gas. A 115 DTAC at 3140 fps is an animal, but not as consistent. I run 7.5 twist for that to keep from having bullet failures.
Knowing how to do a little math can save a lot of headache. This stuff has become more mainstream. When it was more of a niche thing, most of the people doing it knew the line they were walking and were well aware of the possible consequences. Now, with the popularity of long range shooting, cartridges like the 22 Creedmoor, and high bc bullets this has become common.
You have an overbore cartridge running cup and core bullets on the edge of failure. Throat wear, fouling, heat, and a number of other variables can push things over the edge. The solutions are keeping the gun clean and running lathe turned solids if you start losing bullets.
With the quality of factory stuff these days, people can buy a 6.5 Creed with factory ammo and shoot long range with no issues. 308 is even more forgiving to shitty maintenance practices, etc. I've not tried it, but I think you could almost run the whole life of a 308 barrel without a serious cleaning depending on the powder you run. The same is not true when the bore size gets smaller and you get into 6mm and .22.
As oldmanwithagun said. A piece of paper close will show you something. My guess is its going to be signs the bullet is coming apart. Since my experience with fast twist 22 cal hotrods shooting long heavy bullets. I have been expecting to see a lot more threads like this as they get popular. Hot rods are finicky, they get hot and dirty fast.
same issues here with 22gt in 7 twist. 90 SMK at 3150 poof. 85.5 at 3175 - better but goes poof after about 80ish rounds down tube lol. I talked to Berger and Sierra - both said same thing, try to keep it at 300k or less. The 320k mark is where shit goes sideways according to what they have been testing. Probably going to go to a 7.5 twist with the 85.5s and call it a day. And there is a discussion that speaks to this, I think it is in the 22GT thread.
It came up in some of the older fast twist 22-250 threads also.
Berger claims BC is suffering at those speeds and twist...?
I knew the math but I wasn't aware that 320k rpm was the danger zone,
I'm just going to do a better job at keeping the rifle clean... if that solves the issue. If not I'll slow the round down, it just shoots so damn good here.
I've got a ton of these bullets so I wanna be able to shoot them.
I think next time around I will likely go to a 22 Dasher and 85.5gr if I can find them
Thought I should report back, finally got out shooting, been snowy and cold here plus other activities and responsibilities.
After a good hard clean down to bare steel and a throat scrubbing the issue is resolved, must have been blowing up projectiles. Thanks for everyone’s input.
After a good hard clean down to bare steel and a throat scrubbing the issue is resolved, must have been blowing up projectiles. Thanks for everyone’s input.
Keep us posted, curious to see if the issue rears its ugly head again after x rounds etc.
Will do but I am going to try and keep the carbon ring from forming to avoid this.
Wish I had seen this months ago - vaporized some 145 match burners a while back after talking with Barnes about their speed limit (they said 315K) - and sure enough they started blowing up around 320-325K. When on the verge, especially if due to carbon ring pressure increase, only a few blow up, so the frustration must be off the charts...
