Barrel Extension Fit?

[Pugsbrew]

I have two Grendel barrels. One has the barrel extension finished/blued, the other one is not blued. When fitting in to an Aero Precision M4E1 upper, the blued one fits great. The un-blued goes in about 1/8 of the way and seems to stick.

I have measured the extensions, and they are they same. It seems that the blued extension is slicker, if you will, and slides in with hand pressure.

So, I'm concerned about FORCING the un-blued barrel in.

Any techniques of getting the barrel seated?

Thanks.

edit I should have included that both are from the same manufacturer. Both were purchased on a group buy here.