New Build, persistent jamming

[montana]

My thought - it's your barrel throat. Replacing the barrel with the same barrel, means it still has the same throat.

For whatever reason, it's common for manufacturers to short throat a Grendel, so that mag length rounds with an agive that's forward of the case neck much any at all, will jam into the throat. Like - REALLY common; to the point of basically standard. 123 H's at mag-length are close on this already. Who's barrel are you using?

Try different ammo to see if they can seat and be withdrawn. Do the sharpie test (which isn't definitive). Maybe this is or isn't your problem - maybe it's just how this manufacturer cut the chamber. But with Grendel, it's so common to be short-throated, that on almost any issue be it reliability or accuracy, I pretty much auto-advise to always start looking there, at the throat depth.

I agree, but he stated :

And yes, with the bolt out a load can be pushed in and then it falls out.

If he did this correctly, then the bullet would have jammed in the throat preventing the cartridge from falling out..