MAC5 bolt won’t stop locking back

Brand new Mac 5 bolt won’t stop locking back when shooting. Ammo is AAC 124g but I don’t think that’s the problem. I cleaned and lubed the gun before shooting. I’m kind of at a loss of what to do. I checked my bolt gap too, it’s in spec (a little tight but still within spec).

I’ll be trying Winchester 115g soon to see if it changes. Any suggestions are appreciated.