I just had my 7mag rebarrelled, and brass that would not chamber due to a lack of headspace (.002") when the barrel was unfired, now chambers (if barely). Seems logical that threads would "seat" a little when exposed to 65,000 PSI, 25 times or so. Does anyone have any measurements that they have taken on this subject? Dutch.

Dutch, have you thoroughly cleaned the chamber of your new barrel, then wiped it dry?

I ask this because I once had a new barrel that was hard to chamber, only to find that there was some dried oil and gunk inside that was, in effect, decreasing headspace. I'd clean the bolt lugs and lug seats thoroughly as well for starters........

AD

My first impression, is to say, if you got that much change in headspace, there is something loose.
I've screwed on a lot of barrels, and have never experianced what you have.

What you say seems very possible, but not that much change.

Dutch, my first 30/06 grew .007 headspace over a period of about 8,000 rounds. So, yes, I think it will change over time. And would likely depend on the loads fired thru it. A lot of mine were cast bullets at reduced loading.

Allan, it's not dirt. The rim on my Norma brass is just about exactly at max headspace dimensions, and would not chamber before, but I can strong-arm it in, now. From what I can measure (I'm hardly a wizard with calipers), the change seems to be somewhere in the .001 to .002" range. I just found it an interesting observation. Of course, the change could be due to seating the lugs, as well, rather than in the threads. The smith did square the action, so perhaps that had an effect? Dutch.

Dutch,

Did your smith lap the bolt lugs after truing the action?

If he did not this can often raise a small burr on the bolt lugs and when the rifle is fired, it will flatten these burrs out under pressure. This is not a good thing as it can result in a gauled lug recess over time.

I have also seen this from not putting a chamfer on the rear outer edge of the bolt lugs and they bear on that outer edge. Again when fired they are compressed until the lug itself bears on the recess.

Are you using virgin brass or once fired brass? The chamber should not be that tight using virgin brass on the 7mm Rem Mag round.

Good Shooting!!!

50

Fifty, it's fired brass. The chamber is not "tight" in the usual sense. It's tight in the distance between the edge of the rim and the bolt face. Winchester and Federal brass have about .002 to .003 clearance, but the Norma rim is "wider". I'd have never known if I had only shot domestic brass.... FWIW, Dutch.

This barrel job wasn't done by pac-nor, by chance, was it? If so, my experience is that their smith goes with very tight headspacing - usually tight enough to make chambering even factory ammo quite difficult. When I complained, they told me what you said: the threads will "shoot in" a bit. I tried "shooting it in" (which increased my faith in solder-on bolt handles, I must say), but it didn't make a detectable difference, so I had my local smith set the headspacing properly - now it's amazingly accurate *and* easy to load.

Im wondering what it was rebarreled "from" and if the lugs were lapped in. If they wernt making full contact and it used to be a less intense chambering...

I think the guy is on to something. I have rebarreled a number of match rifles and usually keep a print of H'space, thread diameter over wires, etc. Need to do this when fitting a barrel to a sleeved, glued action. On a hunch once, I checked the headspace on the takeoff barrel and the headspace had actually stretched by .005". I am sure it was not an error on my original chambering because I normally do them with minimum headspace. I have also made it a habit to check the headspace on the takeoff barrel and have found this situation to be true. Like the guy said, if you hammer enough 65,000 psi loads through it is bound to stretch.

Jim

To answer the questions, the barrel job wasn't done by Pac-Nor. I have a pac nor barrel, and that thread was cut so tight, I had to use an action wrench to spin it on. This rifle was a 7mag with about 1,000 rounds through it (shooting hot loads eats barrels.... ), rebarreled with a Douglas I bought out of an estate. I don't know what the smith did to fix it all up -- I just asked him to make sure everything was square before he spun the barrel on and dunked it the blueing tank. I know, you are supposed to have long, soul searching conversations about the work to be done...... We usually talk about Pheasants Forever, instead, or Elsies!

I appreciate the feedback on the measurements. Seems logical, even though .005 to .007 is more than I would have guesstimated.

She shoots in the .7's and .8's for four, so I'm a happy camper. That'll kill my sheep this year, if I can find one....! If I can use my preferred Norma brass, that'll be even better. FWIW, Dutch.