Upper receiver compatibility?

[Coz]

Will non 9mm uppers function with 9mm specific lower receivers? Want to know if anyone has built or used SBR with this set up?

 

[Nick Leduc]

When you say non 9mm upper, are you talking rifle, say 5,56? You may have luck with other handgun cartridges like 40 and 45.

 

[Coz]

Yes. Exactly like 5.56. I saw a guy on utube build one and he used a 5.56 upper receiver and seemed to have a few issues with buffer tube but not related to the upper.

 

[teamRR]

The magwell is probably the limiting factor with a 9mm lower.