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Posted: 9/15/2004 5:32:56 PM EDT
I'm looking to put together an AR pistol and I haven't been able to find any #s on the velocity for 55gr FMJ (XM193) from a 7.5 bbl. Specifically, I'm looking for muzzle velocity and max fragmentation range. I've found the #s for 10.5" and 11.5" and could probably extrapolate a 7.5" but if any can point me towards some real data, I would sincerely appreciate it. TIA.
Link Posted: 9/15/2004 5:52:12 PM EDT
some people will tell ya the speed will be in the 50 fps spitball range
Link Posted: 9/15/2004 5:52:44 PM EDT
Link Posted: 9/15/2004 6:03:23 PM EDT
Thanks for the info gents. I was afraid of that. From the data I've found, a 10.5" bbl won't do that much better (2700 FPS MV) and an 11.5" bbl will be in the 2800 FPS range. Seems like once you get into the 11.5" bbl, it's a pretty big pistol.
Link Posted: 9/15/2004 10:23:50 PM EDT
Link Posted: 9/16/2004 5:47:17 AM EDT
[Last Edit: 9/16/2004 5:48:05 AM EDT by PALADIN-hgwt]

Originally Posted By Matt_B:
Thanks for the info gents. I was afraid of that. From the data I've found, a 10.5" bbl won't do that much better (2700 FPS MV) and an 11.5" bbl will be in the 2800 FPS range. Seems like once you get into the 11.5" bbl, it's a pretty big pistol.

My actual measured results with reloads were even less impressive. Loads that nominally produce 3000 to 3100 fps in 20 inch barrels often lost 600 fps in my 10 incher. 2200 fps was a typical average velocity using 55's, but I did not chrony any full m193 spec loads.

Using 69's, a load speced for around 2700 fps chronied at 2225 fps, but had an outstanding ave. dev. of only 17 fps! This was a MAX load in the manual, BTW.

Energy wise, you are looking at around 700 to 750 ft.lbs. of energy at the muzzle, LESS THAN A 44 MAGNUM handgun...

Link Posted: 9/16/2004 5:32:52 PM EDT
I had an avg of 2382 with 3131A from my 7.5" DPMS. It was fairly warm dry sunshine day. Used a cheap green "Chrony".

Santa-Barbara SS-109 went 2340.

From my 11.5" Bushnaster 1x9 barrel, 3131A ran about 2785, SB ss-109 went 2690

From the std 20" 1x7 Colt barrel, 3234 (3131A) and 3096 (SS-109)
Link Posted: 10/14/2004 6:38:19 PM EDT
Link Posted: 10/14/2004 8:10:38 PM EDT
How about a ballistic tip? not much penitration, but lots of surface dammage (probally not the home defence round either)
Link Posted: 10/14/2004 8:23:14 PM EDT
The 5.56 is designed for rifles. The FN 5.7 is designed for pistols and short barreled SMGs. Don't even consider an AR pistol a good gun for self defense.
Link Posted: 10/14/2004 9:22:36 PM EDT
Link Posted: 10/15/2004 5:32:12 AM EDT
Noone raves about thte P90... everyone says it sucks.
Link Posted: 10/15/2004 6:32:52 PM EDT
Link Posted: 10/15/2004 6:37:25 PM EDT
Link Posted: 10/15/2004 7:35:03 PM EDT
I have taken my 7.5" and punched holes clean through a steel wheel at 50yd with a moderate handload of H-322 and a Speer 55gr SP. I don't think body armor is going to be an issue.

Link Posted: 10/15/2004 9:03:08 PM EDT
Link Posted: 10/16/2004 4:43:49 AM EDT
I've watched a guy fire the Oly AR pistol. There is a MASSIVE muzzle flash. Reason?....the round needs a longer barrel to complete the burn of most of the powder. The whole concept of this weapon is silly. For home defense or QCB, I don't want a stupid AR pistol. Pull out a real AR for that fight.
Link Posted: 10/17/2004 6:37:14 PM EDT
[Last Edit: 10/17/2004 6:37:50 PM EDT by MP906]
Link Posted: 10/17/2004 6:47:25 PM EDT
You are a moderator and you are asking newbie questions like that? For shame, for shame.... read the ammo oracle!

All ballistic tips and hollow points underpenetrate from all barrels in 5.56mm and the 75 and 77 grain run out of steam at 50m or under in a 10.5" barrel... though this would be OK for a dedicated indoor weapon if you had hearing protection on. 7.5" and 75 and 77 grain ammo has not been put in the jello to my knowledge. Perhaps someone knows better than I but I would assum a zero fragmenting range as the bullets will be below the frgmenting velocity floor.
Link Posted: 10/17/2004 7:02:15 PM EDT
Link Posted: 10/17/2004 11:04:54 PM EDT
Pistol hollow point perform like rifle soft points and simply expand. Rifle hollowpoints fragment into such small pieces they have too little momuntum to travel further than 6" or so deep into tissue. Arms and odd angles and mags stored on the chest will prevent the fragments from reaching vital organs. Also there is some testing which shows bad penetration through body armor on lightweight ballistic tips... that is to say they penetratre but penetrate very shallow. Pistol hollow points stay in one piece and have the momuntum to travel very far in tissue. That is the difference.
Link Posted: 10/17/2004 11:08:24 PM EDT
Pistol caliber 7.5. That would be very cool. 10mm or .45 Super maybe.
Link Posted: 10/17/2004 11:40:35 PM EDT
Just get a 9mm upper...

Who needs an MP5k when you can have an AR PDW ...

9mm out of a 7.5" barrel would be VERY effective...

Use the oly upper -> mags for cheap (STEN mags)
Link Posted: 10/18/2004 5:24:41 AM EDT
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