03-31-2017, 04:34 PM
(This post was last modified: 03-31-2017, 04:37 PM by explorecaves.)
In the closed 12" GB thread, BFT wrote this:
And LRRPF52 posted this regarding the 12" barrel:
And if I remember correctly, switching to the 129 gr ABLR with its lower required expansion velocity, you will be good significantly farther.
Quote:Regarding barrel length, as I've studied the issue and tried to see a pattern and figure out rhyme or reason, I see SBR barrel lengths all over the place. AA has their 10.5 echoing what the SEAL boarding parties use. But why did the SEALs choose 10.5? In the industry, 11.5 and 12.5 are common. Why 11.5? Why 12.5? When the Army tried to develop the XM8 carbine, they settled on 12" as the optimum standard length. Why? LaRue sells a 12". Lilja sells an 11.5" and a 12.875". Is there some magic in 12.875"? What I see, in the final analysis, is guys just pick a length and run with it.
So my thinking is to split the difference between the common 11.5 and 12.5. I know the claims are that a 10.5 on a carbine gas system is just fine for reliability, but I like a little more barrel, a touch more dwell time, in front of the gas block. For a product line, I like that 12 is different enough from 16 to make the SBR a different animal. If I start creeping up in length, then the whole point of an SBR becomes moot and why not just make it a 14.5 or a 16?
So that brings us to 12".
And LRRPF52 posted this regarding the 12" barrel:
Quote:With 123gr factory AMAX, SST, and ELD-M, you'll be in the low/mid-2300's for speed.
Supersonic out to 975yds at 2340fps mv.
Expansion out to 350yds with 123gr SST with 887ft-lbs of energy.
0yd 2340 1495 -2.5
100 2178 1295 0
200 2023 1117 -4.9
300 1874 959 -18.2
350 1803 887 -28.5
400 1733 820 -41.5
500 1601 700 -76.4
600 1477 596 -124.9
And if I remember correctly, switching to the 129 gr ABLR with its lower required expansion velocity, you will be good significantly farther.