Hi all I just finished my first sbr build and I was checking the barrel flash hider alignment before my can gets here. Im using a suppressor alignment rod and it wont fit im my barrel. The rod is 0.299 thousands and the barrel is 300blk. Could my barrel internal diameter be to small? Im not sure how to measure to check. Im planning on shooting it next week and i dont want it to have any problems.

Thanks
jayson

The definitive answer for the actual bore diameter of your barrel might come from the barrel maker, but 300 Blackout barrels are supposed to have the same bore and rifling diameter as .308 Win/7.62x51 barrels, which is 0.300" bore diameter, with a 0.3080" groove diameter.

Where does the alignment rod stop?  In the flash hider, at the crown, or somewhere else?  If the flash hider isn't perfectly aligned, the rod could stop at the crown...

Frist thing I'd check is the barrel with out the flash hinder.  If the guide does not fit then you have either a defective guide or a defective barrel.  If the guide fits then the problem is in the flash hider and barrel alignment.