I read the article by Dave Fortier in SOF this month about shooting Aguila's Sniper Sub Sonic ammo and figured, "I gotta get some". The article said that the 60 grain bullets work best in a 1:9 barrel. So I got my AR-15 and the .22 cal adapter and went to the range today. Took 2 shots then "pop!" and lots of smoke coming from the AR. Cleared the shell, everything looking OK, continued to shoot. 10 rounds later pop/smoke and hot particles blasted on my face. You'd think I would stop there, but I went on testing fate. 5 shots and pop/smoke/particles. Yuck. See the pic. This Aguila stuff can't be good. For the record I also fired Winchester .22lr and Federal with no problems as usual for that adapter.

I should add that I was shooting at 100 yards with the little faux-Colt 4x scope with a Bushmaster 20" A2.  Accuracy was not good.  about a 6 inch spread in slightly breezy conditions.  I was using the USAF .22 adapter and cycling worked most of the time with this ammo but I did have about 5 failures to eject out of 40 rounds.

Good thing it wasn't the GP 458 socom, That would have been really ugly. Good thing you were not hurt!

Aquila SSS does say "use only in a bolt action rifle" doesn't it?

It worked fine in my Ruger MKII pistol, hell it even cycled it!! I shot a box with no problems, but now you got me thinking. Damn this is starting to hurt!

After looking a little closer at your pics, it almost seems as though your firing pin is "breaking" the case where it strikes. Do you have any good pics of just the bottoms of the brass?

Quoted: After looking a little closer at your pics, it almost seems as though your firing pin is "breaking" the case where it strikes. Do you have any good pics of just the bottoms of the brass?

It does look like the case is splitting at the firing pin hit on two out of the three cases pictured.  Can't really see the third very well.

Thanks for the replies.  Here's a better pic:

You can clearly see the firing pin dent is next to - not on - the crack.  Also the one case is only cracked on the side of the case.  Fortier's article said that the SSS was designed to reliably cycle a full auto rifle so I didn't figure a semi-auto would be any problem.

I would still bet your FP is what is causing it. If it hits too hard it will weaken the metal around it enough to let it rupture. What kind of hammer and spring are you using with the .22 conversion kit? If your have one of those highspeed hammer/spring setup that woulld be my first guess.

I've shot some, but only from a bolt action rifle.

No  kB's, only lousy accuracy.

It WAS real quiet, tho.

There's nothing wrong with it...you just can't use it in a .22 conversion kit..the bolt doesn't have enough mass to stop it from opening too early.  Subsonic rounds are loaded with a small charge of extremely fast-burning powder, and the recoil impulse spikes immediately after ignition.  

You need one of these to shoot them effectively.:

hey quiet shooter I shoot sub sonic stuff out of my custom 10/22 and it shoots them very effetively like 3/8 inch 5 shot groups at 50 yards effectively and little over an inch at 100 yards. by the way that is a nice rifle you got there I like it alot. also I used to shoot just plain junk ammmo out of my stock 10/22 and then when i first started shooting subsonic stuff (CCI standard velocity)I thought it was so quiet but after awhile you get used to it I bet your rifle is super quiet huh quietshooter. what kinda hoops would I have to jump through to get a supressor on my .22

There's nothing wrong with it...you just can't use it in a .22 conversion kit....  Subsonic rounds are loaded with a small charge of extremely fast-burning powder, and the recoil impulse spikes immediately after ignition.

Does that apply to all subsonic ammo, or just the SSS?  

I picked up a box of the SSS a while back to try it.  At 50 yards 1 or 2 went through the target sideways and the rest weren't even on the paper.  Dad's gun put them all in the paper sideways.  No KBs, but both were bolt-actions.   I'd wondered how they'd work in the 1:7" and 1:9" AR barrels, but forgot about the rest of the box until I saw this thread.  Maybe I won't try it after all...