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Old October 14, 2000, 01:35 PM   #1
Charmedlyfe
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Just a note, but I recently played with an AR with 11.5" barrel (W/bbl extension for 17" OAL). I have read that .223 rounds depend on velocity for effect (breakup at cannelure, etc.)and that effectiveness of ball ammo is greatly reduced by shorter barrels.
I rounded up some Ballistic jelly and checked it out. Bal ammo did show quite a reduction in effectiveness with the 11.5" versus 16" and 20" barrels. More reading showed that the Military settled on the 14.5" barrel as the shortest effective length.
I also tried the last of my Hornady TAP Urban 55gr out of the 20" and 11.5" barrels. I couldn't really tell a big difference in performance from that round. TAP is an expanding round.
From what I can tell, Shorter barrels require a change in ammo. I would appreciate comments on this, and why (if this is true) many SWAT units still use standard ball in their short guns.
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Old October 14, 2000, 07:31 PM   #2
Jeff White
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George,
5.56 mm effectivness is tied to muzzle velocity. Army studies from the late '80s revealed that the bullet tumbles when it hits (all spitzer type bullets do this, it's just basic physics, the part with the most mass, the back tries to move to the direction of travel, it would do this in flight if the rifling wouldn't make the bullet spin) and at velocities above 2500 fps (most reliably above 2700 fps)the bullet breaks apart at the cannelure and the fragments cause additional permanent tissue damage.

The fact that the Army decided on the 14.5 inch barrel has nothing to with such things as terminal effectiveness. The 14.5 inch barrel was settled on because it was the shortest length they could mount a bayonet on.

What range did you shoot the geletin at? You should have gotten sufficient velocity for the ball ammo to be effective out of the 11.5 barrel at very close ranges. Even out of full size rifles velocity drops rapidly. A 14.5 M4 with M855 (62 gr steel penetrator) only will have the ideal velocity out to about 120 meters. The 20" M16A2 with M855 will only have this ideal velocity out to a little more then 200 meters. These are far short of the published max effective ranges of 500 meters for the M4 and 600 meters for the M16A2.

I don't know what SWAT teams you know that are using 11.5 barrels. Most that I know of are using 14.5 or 16.1 on their AR type weapons. Even an 11.5 inch barrel should generate sufficient velocity for good terminal effects at the 15 foot CQB range they operate in.

Jeff
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Old October 15, 2000, 09:18 AM   #3
WalterGAII
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Bushmaster had a bunch of 11.5" barrels that nobody wanted. One of their creative distributors came up with the idea for a "Y2K Special Edition" rifle, to take cheesy advantage of the Y2K silliness. They used an A-1 upper, which nobody wanted and matched that with the 11.5" barrels, with a longass welded-on muzzle brake.

The Y2K Special Edition is probably the only almost worthless Bushmaster ever created.
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Old October 17, 2000, 08:32 AM   #4
Chris Orndorff
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George,

What kind of penetration were you getting with the TAP rounds?
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Old October 17, 2000, 09:56 AM   #5
Charmedlyfe
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A friend owns a couple hundred acres and built himself a rifle range.
As to the penetration, it was around 9.5". The TAP expanded nicely (came apart)once it got inside the jelly about 1.5".
The ball ammo didn't do the damage the TAP did, but I wouldn't call it 'ineffective'. No, it didn't break at the cannelure.
Guys, I appreciate the information. There's an awful lot of swag out there on the 223, and I'd really like to understand the round better. I forget where I read about the 14.5" barrel, but I'll try to find it again.

***Does anyone know an inexpensive source for ballistic gelatin? The stuff I got cost a FORTUNE.....
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Old October 17, 2000, 11:29 AM   #6
John/az2
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I saw a recipe for ballistic jelly somewhere... maybe a search would bring it up.
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Old October 19, 2000, 10:08 PM   #7
.
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George,
Do a search on "barrel length" in this forum.
You should turn up a couple of early threads that provided both .308WIN & .223REM velocity drops based on cutting increments off test barrels.
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Old October 20, 2000, 09:53 AM   #8
DaMan
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George, Bushmaster.com has info on velocity from different barrel lengths. Here it 'tis!
http://www.bushmaster.com/faqs/techdatafaqs.html

Here is info on Hornady TAP, also from Bushmaster (LE site) http://www.bushmaster.com/le/tests/h...ammunition.htm

Regards! DaMan

[This message has been edited by DaMan (edited October 20, 2000).]
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Old October 24, 2000, 02:08 AM   #9
boing
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As an aside, the jacket material also plays a role in fragmentation. I picked up a case of S&B .223 at a gunshow, only to find out that the jacket is steel (or bi-metal, at least). The stronger steel jacket will keep the bullet from breaking up, even at higher velocities.
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Old October 26, 2000, 10:22 AM   #10
Jeff White
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Erick,
I've heard that too The only problem with that story is that the Army and Marines had very little to do with the development of the M4.

The M4 was originally a Colt commercial model produced for the government of Abu Dhabi(sp). Colt presented it to the US military in an attempt to increase sales. Outside of small purchases for special units the US military didn't field a short M16 type in any quantity since the old XM177 series of the Vietnam era.

Colt produced several commercial carbines during the 70s and 80s. Just about all of them had the 14.5 inch barrel (except for the ones produced for civilian sales in the US which had 16.1 inch barrels to comply with the NFA of 1934). The BATF designated the muzzle device on the XM177 as a silencer and the Carter administration made silencers non exportable this effectively ended the XM177 as a commercially viable product for Colt. It was after this that the 14.5 inch barrels were placed into production. I'm just guessing here, but I think the length has more to do with decreasing the muzzle blast and flash to an acceptable level then it does with malfunctions or muzzle velocity. After all, barrels as short as 7 inches work on the AR pistol varients.

Jeff
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