Sabre Defense & Mega Machine Shop specs question

[Mr. Ed]

I just purchased a CMMG upper and it will not mate with a Sabre Defense or Mega lower. The holes for the retaining pins do not line up properly and there is no way to get the takedown pins in. However, I have no problems with Bushmaster uppers, Mega uppers, RRA uppers, etc. Is it safe to assume that CMMG gave me an out of spec upper?

[jandmtv]

could be, but i have 2 cmmg uppers, and they mate fine with spikes lowers, and bushmaster lowers. could just be a bad upper, but then again, they do test shoot those so they must have mated with their lowers over at cmmg.

[rksimple]

May have some tolerance stacking issues, may be out of spec all together. Give em a call. Or take it to Randalls place. He'll set you up.

[PIRATE14]

May have some tolerance stacking issues, may be out of spec all together. Give em a call. Or take it to Randalls place. He'll set you up.

Had this happen w/ a lower and upper recently.......those two were in "SPEC" but they just didn't like each other but worked well with other uppers and lowers.........**** like that kills me....rare but it does happen....

You could try another upper or a little metal removed would work but I would give CMMG a call first.......

[Sgt Raven]

May have some tolerance stacking issues, may be out of spec all together. Give em a call. Or take it to Randalls place. He'll set you up.

Tolerance stacking can be a great big PITA. Even more so when you're building a engine for your Race car.

[Mr. Ed]

CMMG said that it was my lower that was out of spec because all of their uppers are test fired on their lowers. This ensures that they are in spec. I don't believe this because I tested another CMMG upper on my lowers and they fit. I really believe the one I got is out of spec.

I dont think they are going to fix it. So, how do I fix this. If i put the front take down pin in, the back one near the stock does not line up...and vice versa. I'm not good with tools or machines or stuff.

Any suggestions?