I just got my SA basic piston kit the other day which I plan to build on an X-Products non-reciprocating side charging upper


I went to drop the Bolt Carrier (no bolt or pins just the carrier) into the upper to see how they fit and it got stuck about 1/3 of the way into the upper! I had to pull on it pretty hard to get it out, I've never had a BC do this before in an upper.  I don't have a calipers to check measurements, and didn't have time before going to work to see if the BC would slide in my DI upper, so I'm not yet sure if the BC or the upper are out of spec or both. I know these are both  companies with some cool products but this is not acceptable. Has anyone run into this issue with either a Superlative Arms Bolt carrier or an X products upper?

I have the MAS Defense side charge upper with the SA kit and it works fine. I also have the MAS upper with POF one piece bolt carrier and with that I had issue with the one piece gas key sliding into upper so I had to radius the upper where the trap door is slightly to get the carrier into the upper. The MAS defense looks like the same side charging upper as the x products.
https://m.imgur.com/a/1l5mn

Sounds like the same issue, hopefully I can apply the same fix.

So I actually took the inverse solution and took the dremmel out and shaved down the carrier key around the side and top of the shoulder.  The main reason is that my standard DI carrier and key hand no issues with fit, so it seems that the upper was within spec.  Though the SA piston carrier does fit in my other upper it does have noticeably higher and slightly wider shoulders on it's integrated piston key than a DI key.

I finished building the upper for it last night, and the results at that it works, though I may have to shave a hair more as it hangs up when cycled all the way to the rear. Seems it still pinches a little at the back of the upper. A good old slap up on the bottom of the lower receiver seems to get it free.  Alternatively I may just try to wear it in with some dry cycling.  I still have to build the dedicated lower for it to finish off the rifle before I can take it out to the range.

https://drive.google.com/open?id=0B8dU70Uady76V0p3ZmRRbG9DdzA

https://drive.google.com/open?id=0B8dU70Uady76YnY5ZjlBSlItZ0E