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Posted: 12/15/2005 8:35:38 AM EDT
Has anyone ever tried 75 or 77gr OTM in a shorty? What kind of velocity do you get? Does it make the fragmentation threshold? Does it spin up fast enough to stabilize in that short a barrel (1:7 or 1:9)?

Also, what do you guys with SBRs keep around for SHTF ammo?

Thanks all.

CO
Link Posted: 12/15/2005 8:51:25 AM EDT
Unless I'm mistaken MSTN has built plenty of these SBR 1/7 twist barrel set-ups for the mercs over in Iraq providing security details for various purposes......

IIRC, they are all mostly using 77 or 75 ammo. Which is why the 1/7 twist SBR set-up is so popular, especially for getting in and out of vehicles.

Mike

ps - there's good data tacked to the top of the Ammunition Forum and the www.ammo-oracle.com should provide ya w/ some good reading too.....
Link Posted: 12/19/2005 9:12:20 AM EDT
[Last Edit: 12/19/2005 9:14:21 AM EDT by yellowjacket]
I didn't find a whole lot of specific info in the ammo oracle about velocities from SBR's except that M193 barely makes frag velocities and M855 isn't appropriate at all. I got the following information from Keiler (a member here):

Mk262Mod1

M193


Note these are purported to be 5.56 pressures so .223 ammo will not reach even these velocities. According to the Ammo Forum FAQ the minimum frag velocities are:

77gr OTM: 2300fps
75gr OTM: 2300fps
M193: 2700fps

mr_wilson also pointed out this chart from Bushmaster's website:


The heavy bullets are really your only choices for effective SBR use.

-yj

Edited to fix picture.
Link Posted: 12/19/2005 1:39:43 PM EDT
[Last Edit: 12/19/2005 2:37:13 PM EDT by NoAim]
Just as an aside, Fulton Armory is having their Black Hills sale right now until the end of the year.

I just picked up two cases of the 75 grain. It's cheaper and has the cannalured bullet.

The 77 grain, while it uses the same Sierra Matchking bullet, is not loaded nearly the same as Mk262.

From a 24" test barrel, these reach about 2750-2800 fps.

EDITED: corrected errors.
Link Posted: 12/19/2005 2:27:43 PM EDT
.
Link Posted: 12/19/2005 3:12:47 PM EDT
tag
Link Posted: 12/19/2005 5:03:13 PM EDT

Originally Posted By NoAim:
Just as an aside, Fulton Armory is having their Black Hills sale right now until the end of the year.



And another aside - so no one misses on the Fulton Armory sale - it runs runs until Noon EST, Saturday, December 24th.
Link Posted: 12/19/2005 6:12:05 PM EDT
I've shot some of my home-rolled 77 gr. Noslers through my 11.5" and it shot very well. I didn't have the chance to chrono it, but accuracy was excellent out to 200 yds.

Pic of 11.5" SBR

Link Posted: 12/21/2005 2:43:00 PM EDT
Thanks for all the info, gentlmen. Particularly you Yellowjacket, the graphs are very helpful.
Link Posted: 12/22/2005 5:43:27 AM EDT
You're welcome. I also got this from a fellow SBR shooter in GA:



Ed chrono'd the BH 77 SMK (BLUE BOX) through his 10.5" JN Rifleworks (PAC-NOR 1:7 Poly rifled) barrel, and had a six shot average of 2336 FPS.



You can see the velocity drop between Mk262Mod1 and blue box Black Hills.

-yj
Link Posted: 12/22/2005 5:47:16 AM EDT
tag
Link Posted: 12/22/2005 10:35:52 AM EDT
MK 262 Mod 1 and TAP 75 grain 5.56 will have a fragmenting range in excess of 100 yards from a 11.5" barrel. With a quality barrel they will shoot sub .5 MOA groups.
Link Posted: 12/22/2005 11:06:23 AM EDT

Originally Posted By DevL:
MK 262 Mod 1 and TAP 75 grain 5.56 will have a fragmenting range in excess of 100 yards from a 11.5" barrel. With a quality barrel they will shoot sub .5 MOA groups.


You got any clue what it would be for the non 5.56 spec ammo in those weights? should be around what maybe 70 or so as it's generaly like 100 or so FPS slower in .223spec ammo.....
Link Posted: 12/22/2005 12:32:45 PM EDT
Link Posted: 12/22/2005 3:57:09 PM EDT
[Last Edit: 12/22/2005 4:00:26 PM EDT by DevL]

Originally Posted By photoman:

Originally Posted By DevL:
MK 262 Mod 1 and TAP 75 grain 5.56 will have a fragmenting range in excess of 100 yards from a 11.5" barrel. With a quality barrel they will shoot sub .5 MOA groups.


You got any clue what it would be for the non 5.56 spec ammo in those weights? should be around what maybe 70 or so as it's generaly like 100 or so FPS slower in .223spec ammo.....



About 50-60 yards depending on manufacturer if I recall correctly. I dont know about 10.5" barrels because I just bought an 11.5" and did all my recent research on 11.5"ers. The velocity differences I have heard were in the 125-150fps range. It difficult to tell though as people seldom give ambient temp, etc when they chrono. Ny custom 11.5 should be mailed by Friday but I still cant test velocity till I build her up after the new year.
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