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April 29, 2014

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drew458

2600fps is a conservative estimate for the JJ's Brit round when loaded to the same pressure level but to the longer OAL, and fired from a 'normal' 24" test barrel. I know; I did the calculations for him. And he'll tell you how I told him a million times "you want it to be 2.55 inches, not 2.25!" :-)

john jay

drew, friends:

you did indeed tell me a million times that i wanted it to be seated to 2.550" and not 2.260".

laughing.

and, drew did indeed do the quick load analysis for such a loading, using 140 grain flat based .284" bullets, if i remember correctly.

i believe quick load & drew suggested velocity substantially in excess of the 2600 fps muzzle velocity in question.

i prefer conservatism here, as elsewhere. but, i think that figure can be exceeded, and stay within relatively cautious pressure levels.

when i started the "plywood gun" is was envisioned to fire such a round as drew proposed, and at the length of at least 2.550". the length of the magazine well was designed to shoehorn a .308 magazine into an ar-15 receiver length, which, can be done, if you omit the bolt hold open.

the ak-47 got along for nearly 50 years without a bolt hold open, and it is not something i consider essential.

but, just as i got a .308 magazine fitted, dpms announced the dpms gen ii ar-15 in .308 winchester, ... , so what was the point of putting my "jj's brit" into the "plywood gun."

that's when i decided to put a .375" caliber bullet into a modified .30 remington/6.8mm remington spc case at about 1.500" in length, and build a very nice compact ar-15 pistol, with a very potent round, which in essence is a short & rimless & modified .38-55 winchester.

drew has done the pressure analysis on that, as well.

he is a talented cartridge designer, and his help has proved invaluable to me in my efforts.

he keeps my enthusiasms in reign, and also has been central in providing a good solid theoretical footing for cartridge performance levels, and powder and pressure analysis.

i owe him lots of thanks for the work he has done during all of these "wildcat" experiments.

john jay

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