Issues barreling receiver

[conju]

Got my 18" barrel this week and mocked up my receiver this evening for install. When I tried to insert the barrel into my MA-TEN upper receiver, I managed to insert the extension about 1/2" to the receiver, but it would go no further, even with gentle taps from a deadblow. Was curious if this was by design and that I just need to give more force or take an emory cloth to the extension or what. 

I have done ar-15 barrels before and remember that there was some wobble (maybe .005") between the extension and the receiver, but thought maybe its different with the 308 AR's being non-standard.

Thanks for the input!

[Deleted]

I have seen this on several of the large uppers. I polished the barrel extension and also the inside of the receiver. I have even lapped the inside of the receiver, to get the clearance. If you use the lapping method go slowly and be careful not to remove to much material. You can also heat the receiver and freeze the barrel and they will slide together.

You want a tight fit for maximum accuracy. The .005 you mentioned is in my opinion on the excessive side. But you also don't want to hammer them together.

[conju]

I had kinda thought that all that might be the case, good to hear it from someone in the know. The .005 number was a WAG from my recollection. I'l just take some 320 grit to the barrel and see if I can just knock down the blasted surface and see if that does it first. Thanks for your help!