ever see a bad upper reciever?

[dammitman]

has anyone ever heard of this situation, you have a new upper reciever and new barrel and all new upper reicever parts like bolt and bolt carrier, basicall totally new build. long short, after assemble the bolt wont go in battery or wont lock up . tried another all different bolt carrier group with same results. installed a completely different new barrel and again no change, just wont lock up. wish i had a set of go-no go gauges but i do not have that caliber. i am going to try a different brand new upper reciever. i have plenty of parts to see but this isnt for me its a buddys build. now i gotta know whats happening. just never have seen a bad upper reciever if thats possible. your 2 cents?

[montana]

Yes. The barrel index pin could be off that clocks the barrel, the bolt carrier bore is not the correct size (you need pin gauges to gauge), dimensions not milled correctly,etc. Here is Chad from the school of the American rifle giving a quick explanation and check of upper receivers..https://www.youtube.com/watch?v=GDQ7-rkMNq4

[LRRPF52]

What upper receiver do you have? Do you have another upper receive to try your parts in?

There are a lot of upper receivers that aren’t within spec on the market due to the costs associated with maintaining tight standards, though issues with them don’t really show up in assembly.