I have a U.S. Army 22LR conversion kit for my AR. I believe it is called a M261. For some reason it wont work on my AR. I have both pre-ban with no sear block and post ban AR's. The magazine (20 round USGI) with the insert wont lock in my post ban. In my pre-ban it locks, but will only fire one shot. Any help would be greatly appreciated.

Thanks in advance.

It took me several weekends of tweaking to get mine running well.  These things are sensitive to the carrier mag.  I have found that orlites work best in my bushie.  That the unit won't lock may mean that the mag is not properly fitted in the carrier mag.  I have had bad luck with USGI, better luck with western or USA steel and great luck with orlites.  Every now and then the mag insert slips causing a malfunction, but hey, this is a training device and what better tool to teach failure drills.  I do love mine and shoot it more than anything else I own. FWIW my I am currently using it in a Oly A1 upper with 16" 1 in 14 barrel Bushmaster lower.  Soon to be replaced by Cavarms lower whenever it arrives.  I get 1" goups rested at 50 yards.  Also, these things are ammo sensitive, so far the only really cheap stuff that seems to feed reliably in mine is Remington Thunderbolt.  Also works well with CCI minimags.  It will not feed hollow points worth a damn so avoid them.  Hope this helps.

Also, spare parts and mags are available from SARCO.