Budget 1st Grendel upper build

[LRRPF52]

With the scope rings on two separate planes, you will end up with walking groups, since there is considerable flex between the upper and handguard. I would strongly consider getting a mount that only attaches to the upper receiver.

Also, make sure the carrier key is attached securely on the bolt carrier, as this was a notorious problem for Bushmaster before they were bought by Freedom Group. It also might be an old DPMS bolt carrier group, and you might be able to tell if there is a "D" on the left side of the carrier.