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Old 05-30-2012, 02:11 PM   #11
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Yes thats what he is saying. Basically, any powder that burns after the bullit leaves the barrel is wasted. The shorter the barrel the less time for the powder to burn. Conversly, any barrel lenth added past the point of powder expansion, slows the bullit down. So the trick to maximising bullit energy is to have the bullit exit the barrel at the instant before, max pressure.

You can clock your round, using diferent barrel lenths and as you shorten a barrel, velocity will drop off, conversly as you lenthen a barrel to far velocity will drop off.

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Old 05-30-2012, 02:21 PM   #12
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I think a 12 in barrel will be adequately long enough to keep velocities above the optimum fragmentation speed for 5.56 at cqb distances. If you are going to rebarrel, look into .300 blackout.

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Old 05-30-2012, 02:50 PM   #13
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That seems to be the thing these days is the 300 BO. Haven't checked the price difference on the ammo .

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Old 05-30-2012, 04:43 PM   #14
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I need to get the BLK out again. Ammo is down to $10.99 a box which is good for what it is.

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Old 05-30-2012, 05:10 PM   #15
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Quote:
Originally Posted by MikeJK View Post
I need to get the BLK out again. Ammo is down to $10.99 a box which is good for what it is.
where? link! link!
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Old 05-30-2012, 06:06 PM   #16
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going shorter than 14.5 on a 556/223 rapidly drops that cartridge somewhere around 22magnum levels. if your going to go shorter than 14.5 i would go 9mm 40sw or 45acp
I wouldnt say its at .22 mag levels the difference between a 7.5" barrel and a 20", both .223 is roughly 430 fps at the barrel and roughly 600 fps at 80 M, sighted in at 50 yards still hits 10" steel plates at 100 yards . Now further than that its lost a ton of velocity and falls off pretty quick . I need to run it thru my chrono with some 5.56 and see how much difference there is between it and the standard .223 FMJ ammo on the velocity. Shortys have their special place of use and most cant justify the need or the want to spend the $200 for the stamp when they can get basically the same thing in a pistol with out jumping through the hooplah and the wait
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Old 05-31-2012, 03:16 PM   #17
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where? link! link!
Here you go. $10.36/box + shipping.

http://www.cheaperthandirt.com/2AACO102860-1.html
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Old 05-31-2012, 03:40 PM   #18
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The .300 BLK guys posted some 125gr for $10.50 on FaceBook a couple days ago as well. I thought it was from CTD but can't find it now. I'll check FB.

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Old 05-31-2012, 04:16 PM   #19
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I wouldnt say its at .22 mag levels the difference between a 7.5" barrel and a 20", both .223 is roughly 430 fps at the barrel and roughly 600 fps at 80 M, sighted in at 50 yards still hits 10" steel plates at 100 yards . Now further than that its lost a ton of velocity and falls off pretty quick . I need to run it thru my chrono with some 5.56 and see how much difference there is between it and the standard .223 FMJ ammo on the velocity. Shortys have their special place of use and most cant justify the need or the want to spend the $200 for the stamp when they can get basically the same thing in a pistol with out jumping through the hooplah and the wait
I'm not really agreeing with the numbers you are posting here.
Optimally fragmentation occurs at velocities above 2700 fps.
Muzzle velocity for M193 55 gr fmj is in the 3200 fps range with a full length barrel.

430 fps is a really fast paintball.
250-1000+ for pellet guns.
230 gr fmj .45 acp shoots in about the 900 to 1000 fps depending on barrel length.

Um here you go....
http://www.ar15.com/content/page.html?id=213

Once you go under 2700fps, fragmentation gets really spotty so for the most part you are just punching holes. But much deeper holes than a .22 magnum.
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Old 05-31-2012, 04:29 PM   #20
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They have developed 300 BLK that is designed to work at subsonic levels.

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