Just got a barely used 9mm asa upper etc. I used winchester 9mm and it fired and cycled each and every time. Using 25 round Uzi Mags

then I used blazer alum caseed 9mm had many stove pipes and all kinds of problems.

FOund a guy at the range that had some tan boxed "nato:" marked 9mm that did the same........

Qustion.

Is there a break in period for new uppers?

In the ammo listed above esp the blazer have any of you had any problems?

I think you may find the Blazer to be a little lame. I have not fired any personally, but I do have 3 range pick-ups that I could try.

Mine is a custom made barrel, and no break in  there, cycles fine.  Did you actually inspect the so-called NATO ammo? Verify that it was factory ammo, and not lame reloads in a NATO box?

will the NATO stamp be on the bottom?

From 115gr wally world to 145gr silver bear, no stove pipe anymore.

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