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Old 02-20-2014, 8:58 AM
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ar15barrels ar15barrels is offline
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Originally Posted by LynnJr View Post
The bullets were slugging up do to a short throat?
The bullets were obturating while they were still in the neck and transistioning into the bore.
A traditional drawn jacket is strong enough that you can push the bullet from behind (via the 40k psi+ gas) and the front of the bullet will get obturated in the throat/lead while the rear of the bullet holds it's diameter until it fully enters the throat where it is fully supported.
The cast bullet with copper plating is NOT strong enough to do this at typical 40k PSI pressure and the result was the shearing off of material during each firing.
By extending the throat about 0.107", they were able to get more of the bullet supported in the throat before obturation began and the cast/plated bullets would go down the barrel without leaving any of their parts behind.
Randall Rausch

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