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I want to push some .243 projectiles FAST (as in 4300+ FPS, in my 1-in-10 twist barrel, that's 309,600 RPM!)
What's the best jacket material for this kind of speed? Or, am I just screwed? Is it the velocity or the rotational speed (RPM) that causes jacketed projectile disintegration?
I might be in the market for a slower-twist barrel. What's the RPM limit of a copper- or brass-jacketed bullet?
Thanks!
jkpq45
JUST DO IT!! Sounds awesome! I just picked up a 9 twist Criterion 243 barrel. I'll be watching yoru results and may have a few of mine to post soon too.
Maybe a sized down thick 30 cal jackets. I got some of those around here some where. I imagine your bullet must be about what? 40-50 grains?
Tell you what. Soon as I put the gun together I'll test some 55 grain bullets at max loads with 22LR jackets. See if any of them make it to the target.
Good shooting and Swage on! You'll never know till you try!
BT
I'm trying to achieve these results with 55 gr. projectiles. I have some Nosler Varmaggedons, but the folks over at Nosler have only pushed them to 3800 FPS (which is typical .243 Win performance).
I'm just worrying about spraying jacket material all over the chronograph.
Load about 20. Fire the first 10 at a target. If none of them explode, shoot the rest over the chrony.
Depending on the degree of desire you have to make this happen you may not be opposed to the extra step of core bonding.
Keep in mind that speed isn't always the straight and narrow path to accuracy. It very much more has to do with TUNING the speed of the projectile to the harmonics of the barrel. A speed much lower than you suggest might give you quantum benefits in accuracy.
Also consider that the higher the velocity of your bullets, the more throat erosion you will see in your chamber, the higher the recoil you will see in the gun, and the faster the wear and tear on the equipment, which will have a reducing effect on your accuracy.
My suggestion is to avoid your plan for light-speed bullets. Start at the nominal end of the speed spectrum, work up a development for the caliber you like, and watch for the best accuracy. That will happen at speeds MUCH LOWER than you are talking about.
Quote:
Originally Posted by jkpq45
I can't give you an exact RPM but it is WAY higher than you can achieve. Don't worry about it.Quote:
Originally Posted by jkpq45
the break-up of bullets in flight is usually caused by the jaxket being cut by the rifling.
use a jaxket thick enough to overcome the cutting.
Another thing to think about. Some barrels do this at much lower velocity than others. The jacket cutting runriver mentioned can happen more so in barrels that are not so smooth. If you are using a hand-lapped match barrel, you will be able to get away with more velocity than you will with a not so smooth factory barrel. So, in other words, there is no velocity limit accross the board. It is dependent on multiple factors such as jacket thickness, and/or grip on the core, and condition of the barrel.
310,000 rpm is fast, but a half-decent bullet should be able to handle it.
I've done a lot of work studying bullet rpm and its affect on accuracy, bore fouling, and optimal stability. However.... most of that work has been with .224 projectiles. (Where optimal stability is found between 175,000 and 275,000 rpm, depending on bullet weight and strength.)
With .243 and .224 projectiles, I've found that exceeding 325,000 rpm is nearly always a death sentence for the projectiles. Even if they don't self destruct all the time, they still tend to suffer from decreased accuracy. And, they may still self destruct under different atmospheric conditions (example: 40 gr HP at 4,200 fps from a 1:9 twist -- just fine in warm weather, but grenaded in flight in sub-freezing temperatures ).
I have not yet found a bullet that can handle more than 340,000 rpm. (Not that much higher than his goal, williamwaco ;))
Pushing anything that hard really kills the bore, anyway, though.
I'd say a 0.025" to 0.030" thick jacket would be the absolute minimum. Perhaps a Corbin VB jacket, with the thinner mouth trimmed off, would work?