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5.56 SBRs - terminal ballistics

SMS

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Yes! Awesome. Great info.

My summary: it seems even the Mk 262 stuff wasn't fragmenting as well as they'd like out of the 10.5" barrels so they went to an expanding bullet "optimized" for SBRs with a lower velocity expansion threshold hold. Great.

My understanding is that while Mk262 might offer better terminal performance than M855, it is still more of a match round than a terminal performer. Saying something does better than something that sucks isn't really an endorsement.

Feedback from some former coworkers running 14.5in 416s/M4s is that they are getting better results with the newer M855a1 than they had with Mk262. One went so far to say that he was 'less than impressed with the Mk262' when it came to putting people down.

Take that FWIW, very small sample.
 

MBB

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My understanding is that Mk262 is still more of a match round than a terminal performer.

Feedback from some former coworkers running 14.5in 416s is that they are getting better results with the newer M855a1 than they had with Mk262. One went so far to say that he was 'less than impressed with the Mk262'.

Take that FWIW, very small sample.

Interesting, thanks!
 

Hump66

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Hump66

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I've got one. A good basic rule is subtract about 125fps per inch off of a 16" barrel, so if velocity is 3000fps in a 16", then 1900ish for a 7" barrel.
 

Hump66

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Not according to my choronograph. My buddy and I were working up some .223 loads, shot them through his 16" and my 11.5" at the time, it was an average of around 125fps per inch(i.e. if his were at 2800fps, mine were around 550-575fps slower.) Dropped an average of another 125fps when I went to the 10.3" barrel. I'm not saying it is definitely 125fps per inch, but that's an average of what I experienced with all powder brand/grain combinations. YMMV.
 

HiredHand

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That's interesting data. I would have expected a 25-50 fps loss per inch. Have you thought about trying trying a standard 5.56 Nato or LE duty round to use as a baseline? Where your reloads full power or reduced loads?
 

Hump66

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Some were full power, some reduced, mainly testing for any accuracy changes between loads. Wanted to get the most accurate, highest velocity, with lowest recoil. I should try and put together a better test, like you said with a baseline and then compare other loads to that.
 

Glocktogo

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That's interesting data. I would have expected a 25-50 fps loss per inch. Have you thought about trying trying a standard 5.56 Nato or LE duty round to use as a baseline? Where your reloads full power or reduced loads?

Once you get shorter than 12.5", the velocity loss is going to be exponential. Anything under 10.5" is going to be a poor performer past CQB distances. With standard type ammo, a 10.5" is going to be good out to 45 yards, premium ammo, 85 yards or so. Obviously the 5.56 optimized has been covered in a previous post. This is not to say that 5.56 isn't lethal past these ranges, but it's overall effectiveness is dramatically reduced past these ranges.

I use TAP T2 in my 11.5" for HD and the Mark 318 Mod 0 SOST round for my 14.5", which is more for duty and outside the home use.
 
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