Some days ago on this forum, I proposed a new cartridge, for the AR platform.
This new cartridge, would be the standard .223 case, necked up to 30 caliber; and it would launch a 125 grain cast bullet to around 2500 fps.
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Humm... it rather seems that somebody has beaten me to it.
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Wilson Combat has a new round; 7.62x40WT.
The 7.62x40WT, is the .223 case, ...necked up to 30 caliber, ..and it launches a 125 grain jacketed bullet to 2400 fps.
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Were we to take "Wilson's," new "necked up" .223 case;
and combine it with a .....a Ballard type, .......deep cut rifled barrel, using a long twist;
I suspect a shooter could launch a 125 grain hard cast, ..gas checked bullet, of Lavern style, from the AR platform, ....using standard AR magazines, to around 2500 fps.....
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The result:
Acceptable accuracy, acceptable velocity, acceptable trajectory, and full ability to cycle cast bullets through the standard AR gas system.
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This is just food for thought.
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I would add, the 223 case, and 7.62x39 case hold just about the same amount of water, with the 223 case just a few grains more, and the 7.62x39 is a very able to launch a 125 grain bullet to 2400 fps;
so a 30 caliber/.223/125 grain cast bullet/2500 fps , in a long rifling twist, should actually be quite do-able.