Upper too tight for barrel?

[Herk308]

I bought a DPMS stripped (well, sorta; it had the e-port cover and forward assist installed) .308 upper a while back and I just today got my Faxon .308 barrel in the mail.  The problem is that the barrel is so tight that it can't even fit into the upper!  I've build AR15 uppers before and found that those barrels pretty much just fall into the upper with no resistance at all.  If I push kinda hard (hard enough to actually do something but not hard enough to make me nervous about causing damage) then the barrel might go in as much as 1/8" or so but it's tight enough that I don't want to push it any harder than that.

I not only can't find any reference to such a problem as this anywhere on the internet, but there actually seems to be a plethora of videos, articles, and forum topics addressing barrels that are too loose for an upper!  I guess I either really lucked out or I really didn't!

I looked up lapping the upper and there are references to lapping the face/"muzzle end" of the upper to make it more true but many of those articles admonish people to avoid getting any lapping compound into the inside diameter of the upper.

I'm not really sure what to do here; is either my upper or my barrel out of spec?  Is this a problem that anyone else has had to deal with before?  I don't want to force anything and get something broke or stuck.

[jtallen83]

Might be worth warming up the receiver and freezing the barrel then give it a try, not to warm on the receiver though. Do you have measurements on the parts?

[shepp]

49 minutes ago, jtallen83 said:

Might be worth warming up the receiver and freezing the barrel then give it a try, not to warm on the receiver though. Do you have measurements on the parts?

There was a post on this not long ago, I would try what JT said

[Herk308]

1 hour ago, jtallen83 said:

Might be worth warming up the receiver and freezing the barrel then give it a try, not to warm on the receiver though. Do you have measurements on the parts?

Good idea!  I shoulda thought if that.  About what temperature should I heat the upper to?  I don't want to get that wrong, I don't think... 

I just measured the upper and the barrel with my calipers and got 1.188" for both.  No wonder they don't fit!

I thought it was a little odd that I couldn't find another example of this problem anywhere on the web.  Is it really that rare?

[survivalshop]

  I like them tight , much better than loose . Put he Barrel in the Freezer & the leave the Upper at room temp & it should go in . A very light coating of Grease might help also. I usually just tap the Barrel In with a Rubber mallet , but the cold barrel & warmed up Receiver , it should slip right in . 

[shepp]

18 minutes ago, Herk308 said:

Good idea!  I shoulda thought if that.  About what temperature should I heat the upper to?  I don't want to get that wrong, I don't think... 

I just measured the upper and the barrel with my calipers and got 1.188" for both.  No wonder they don't fit!

I thought it was a little odd that I couldn't find another example of this problem anywhere on the web.  Is it really that rare?

 

2 minutes ago, survivalshop said:

  I like them tight , much better than loose . Put he Barrel in the Freezer & the leave the Upper at room temp & it should go in . A very light coating of Grease might help also. I usually just tap the Barrel In with a Rubber mallet , but the cold barrel & warmed up Receiver , it should slip right in . 

This, if they measure the same size I would do what SS said and go from there 

[jtallen83]

If you heat it I would try something like a blow dryer, shouldn't be able to get too hot like that. SS has the best idea, try just freezing the barrel first, should be enough with that measurement.

[Herk308]

The barrel is now in my freezer.  Should be nice and cold by tomorrow afternoon when I get home from work.  Thanks a bunch for your suggestions, guys; I'll let you alls know how it pans out!

[mineralman55]

I needed to use a paint stripper heat gun on an upper that would not accept the barrel. A few minutes heating and the barrel slipped right in.

[98Z5V]

18 hours ago, survivalshop said:

  I usually just tap the Barrel In with a Rubber mallet

I've done this routinely on AR15s.  One needed some pretty forceful "tapping," but it turned out to be one of the best-grouping ARs I've ever assembled.  I'm certain the tight barrel fit had an influence in that.

[Herk308]

So threw the barrel in the freezer around 9:00 last night, right before my last post.  I got up at 4:30 this morning, as usual, and as I was making breakfast I tried putting the barrel (which was between 19° and 21° according to my laser thermometer) into the upper (67°) and it still wouldn't go.  The barrel went back in the freezer, as I didn't have time to mess around with it before leaving.

I got home this afternoon and started heating the upper in a toaster over that I have for Kydex bending.  I got it to about 150° (that's not really that hot, I know, but I wanted to be kind of conservative about this) and then tried the frozen barrel.  The barrel went in maybe half an inch and then got stuck!  I started getting concerned at this point since it was really seized up and then decided that I ought to grab my heat gun and start heating the receiver threads while the barrel was still cold.  I started applying heat to the threads while pressing down on the barrel with the rear of the upper on the floor.  After a bit, the barrel slid in fairly easily.  I made sure that it was seated all the way back against the receiver face and then set it aside to cool.

It looks like this problem is solved; thanks for your help guys!  

[shepp]

Awesome!!! Glad it worked