I do not own an AR-15 rifle, I may.....
I read articles, and watch videos of guys endlessly trying to get cast bullets to shoot through the .223 AR platform.
It's always the same:
Ping ping ping, ......They turn their AR rifle, into a very finicky .22 magnum, or the lead the hell out of it trying to duplicate jacked bullet velocities, with cast bullets.
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The reason why the AR/.223 platform is not practical as a cast bullet rifle, is simple:
1.
The rifling twist is way too fast.
To shoot cast bullets fast, and accurate, a rifle needs a long twist, ...maybe 1/16, or better 1/18, ..not the "*** tight," 1/7 twist like we see in modern AR rifles.
Tight rifling twists simply "strip out" the lead bullet as it passes down the barrel.
You end up with a leaded barrel, a leaded gas port, a leaded chamber, and... the accuracy is ruined.
2.
The low powder charges needed at achieve accuracy, not only limit velocity, but, they also will not allow the action to cycle properly.
In the end, a guy shooting the "AR," with cast bullets, turns his rifle, into a finicky, bolt action 22 magnum, or he "leads" the hell out of it.
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OK, an answer to the problem:
Maybe folks should consider, ....... a custom cast bullet wildcat cartridge , .....especially designed to shoot "cast" through the AR platform.
Folks could start with the existing .223 case, neck it up to .30 caliber, ..then cut the case back,,,, and push the shoulder back,,, until a 125 grain+/- cast bullet ( when seated ) will function through the standard AR magazine. That establishes overall cartridge length.
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Next the bullet:
It needs to be long in the body, with a short pointed nose,, Lavern style, which has proven to give the best accuracy at high velocity.
The chamber throat:
It should to be made to fit that specific bullet, and only that bullet.
The rifling twist:
We look to the ...green hill formula..., that formula will tell us rifling twist for a specific bullet at a specific velocity, ...the longer the twist better, ...so maybe a 1/16 twist, or better 1/18...
Powder:
Would be case filling, and slow burning, ..and enough to cycle the action.
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Velocity /accuracy/capability:
If properly done, a wildcat, on the AR platform, using the .223 cartridge case, could deliver velocities of around 2400/2500 fps (using quenched WW cast bullets) , ... have sufficient gas to properly cycle the action, ... deliver energy about equal to the AK-47, ......and do it accurately, out to and even beyond 200 yards.
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OK, well, that is just my 2 cents, on shooting cast bullets using the AR rifle platform.