I sent my DPMS conversion in with a peened chamber and they replaced the chamber and gave me what I think is a shortened firing pin.

It was nearly flawless functioning.  Now a lot of rounds aren't firing.  

I put about a 1000 rds through it today and only probably 900 of those fired. Toward the end of the session it was getting dirty and the chamber was pretty fouled and I fired a round with the bolt apparently partly open and it blew out the side of the case and took out my extractor.  

I guess I should have stopped to clean it.  I didn't think that firing with the chamber open would be possible with the design.  I guess it is.  I'm glad that didn't happen when I was shooting left handed or I might have some nice schrapnel in the face/support hand.

Anyway now I need an extractor but I think I'm just going to replace it myself as to send it in requires about $10 and a month waiting for it.  

It's an accurate upper, it just looks like it could use a heavier recoil spring to close the bolt more reliable primer ignition.  

Quoted: I fired a round with the bolt apparently partly open and it blew out the side of the case and took out my extractor.

Welcome to the club. Same thing happened to me the first day I had mine.

Mine was caused by out of spec bulk ammo. It has not happened since, even when the gun is run hundreds and hundreds of shots between cleanings.

We have now had reports of ALL the rimfire conversions using the AR fire control system, including the R22, firing out of battery like this. ALWAYS wear your shooting glasses when shooting these things.

Does the 261 do that too then?

It seems that extractor tension and the charging handle are working against the mechanism.  It would be nice to see a kit with a cocking piece on the bolt.  

How does extractor tension affect whether it chambers fully?   And the charging handle doesn't move when it's fired, so how does that make a difference?  

Cocking handle on the bolt would prevent "drop-in" conversion on unmodified uppers.  (Unless the bolt travel is less than the length of the ejection port, but you'd have to install the handle after you inserted the kit.)   The CZ dedicated upper does use a side handle.

"How does extractor tension affect whether it chambers fully?"

The extractors are sprung with a range of motion is slightly greater than needed so they impinge against the little angled reliefs cut for them in the breech and this pushes against the bolt closing. I think the DPMS kit has two of them which makes it 50% harder to close than say the 261 conversion off the top of my head.

" And the charging handle doesn't move when it's fired, so how does that make a difference?"

The charging handle has a spring loaded latch that will not close with the .22lr spring so when you first cock the kit it fights against the bolt slamming home under full pressure.  Also in use the CH can sometimes if not consciously slammed forward slide slightly back and act like an anti-bounce weight which is not desired when the stupid bolt is barely closing as is.  Even if the spring loaded latch has no effect on the kit the handle moves under some resistance and has greater mass than a simple cocking piece which would not have and friction resistance.


"Cocking handle on the bolt would prevent "drop-in" conversion on unmodified uppers. (Unless the bolt travel is less than the length of the ejection port, but you'd have to install the handle after you inserted the kit.) The CZ dedicated upper does use a side handle."

Yeah so you'ld have to insert the handle- big deal.  It could thread in or be a simple detented pin.  The point is limiting these many factors that can effect reliability.  The less potential problems exist the greater overall reliability should be.  

Ah, I see now on the extractor.  I guess I see how the charging handle could be a problem on the first round, but I don't think it's a big deal on the rest of the mag.  BTW, I think it's the M-261 that has the double extractors.  Ciener has one.  Don't know on the DPMS.

I don't think I've ever had a problem with my Ciener not going into battery that wasn't related to the ammo.  In all of those cases I got a "light hit" FTFire, followed by a FTExt as the bullet stuck in the chamber and the extractor jumped the rim.  I tried running with the anti-bounce weight (it's a semi kit) on the thought that it would help bump the bolt the rest of the way closed but it made it worse instead, I assume because the extra mass slowed the cycling down.   I think a stronger recoil spring would help.

The 261 has a stronger spring and a lighter second extractor spring thing-- I would call it more of a round retainer than an extractor.  

I think the 261 should prove more reliable and less accurate.  

The extractor cost me $12!  a heck of a lot for a little piece of stamped steel.