Home Forums Reloading Big Game Rifles 7mm RM headspace

I was doing some OAL measuring with some bullets for this rifle (Rem 700) which I haven't handloaded for yet, and while I had the comparator out I did a comparison between some fired Federal cases and some new Nosler brass. 2.147 vs. 2.125 respectively. I don't have any Go-No-Go guages, but I had some factory Federal and Winchester loads so I measured them too with the stoney point tool and they measured 2.127 and 2.122 respectively, which brackets the Nosler brass pretty closely and points to a possibly long chamber? To me .020 -.025 inch is a lot of headspace, even for a mass produced factory rifle even if the cartridge headspaces on a belt. This can't be good for a multitude of reasons (like case life maybe?) and I'm debating how much effort to put into load development without first getting the chamber more compatible with "correctly" formed standard brass. Or, do I just shoot 'em once and press on now that they're "fire formed"? What do y'all think?

If they were fired in your rifle I would try to size on the shoulder,if not re-size and shoot away.

Shoot them once to fire form then set your dies up to headspace off the shoulder. By doing that the case will only stretch on the first firing, on subsequent firings you'll have minimal case stretch if you set your dies up correctly. A set of go/no go gauges isn't going to tell you anything about the shoulder dimensions, they only index off the belt in a belted magnum. Just to clarify, you don't have .020-.025" headspace because the headspace isn't measured there on a belted magnum, it's measured from the belt. Once you fire form to the chamber you can use the shoulder to set the headspace.

I was going to aim for .002 or so of shoulder bump when I re-sized (as best i can measure with a digital caliper and the case shoulder comparator tool).
It still appears that my cases will get stretched, .022 or so first time, no big deal?

That's about normal for most belted magnums. As long as you don't keep setting the shoulder back then the brass will last. .002" is a good number to shoot for, it'll keep the case stretching to a minimum.

Thanks, Crow. That's somewhat comforting. I'm a little surprised that it's not particularly unusual for a mass produced belted magnum to allow .020"+ of lengthwise case expansion from factory formed brass. Assuming the chamber's shoulder and belt counterbore were reamed in the same operation, I would have thought that the dimensional relationship could be kept uniform and reasonably close to the "standard". Maybe it's intentionally "loose" to insure that it will digest practically any ammo?

I've got the same thing going on with a new 7RM barrel on a 700.
I loaded up some new WW brass to try it out, and every round I fired smoked the entire case.
I checked some of the new brass from the same bag and it was way short of the specs in the manual.
I had a fired case the smith sent with the gun, and it measured spot-on with book specs, and some once-fired brass I had bought for the gun measured spot-on too.
My smoked-up fired brass still measured short, so apparently it isn't fireforming to the chamber like it should??

707, How are you measuring your brass? I find that the only measurement that I can make with any confidence is "relative" case length. That is, one case vs. another. I'm using the stoney point comparator for a digital caliper and an appropriate adapter that indexes consistently on a straight portion of shoulder. I find it difficult to draw any conclusions regarding whether the chamber is long or the cartridge is short with respect to any established spec, particularly given their choice to specify length at readiused shoulder transitions and the like. Even though three brands of unfired factory brass all measure within .005", that doesn't mean they are "standard". I suspect that in my case both the brass and the riflemaker both take advantage of a cartridge that headspaces on the belt and err on the side of a "loose" fit for compatibility vs. precision (and case longevity for handloaders).

You sound like a benchrest shooter, I was for a long time. first time I made the measurements you speak of, I thought that my head was going to explode. My advise is to go and shoot the darn gun, work up a load, decopper every 15-20 rounds till you get a feel for the barrel's fouling tendency.

Throw the fed in the garbage...soft.

Since you have a factory rifle, work up a load in the Nosler brass...
I'd like to know how long the primer pockets last on the Nosler brass. I shoot very tiny groups with Rem and Win brass.

Unless you are willing to spend a good chunk of change on a custom barrel with a custom min spec reamer, you just need to enjoy the rifle for what it is. My 700's shoot very small groups with bedded stocks(not plastic) and tuned or replaced triggers.

Best wishes!

fw707, often I have found win brass on the small side.

Also, sounds like you are shooting a light load or a load that is light for your rifle...barrels are all different. Never use a light load to fireform bass..case stretching is the result.

I would expect you to get early case head seperations on the "smoked" brass.

Good luck on your new barrel, I'm sure that you just have a lot of brass on the small side.

Actually Keith, just a hunter afflicted with an engineering background. Curious, and tend to try to improve performance on things... I'm a bit leary right now because I (actually my buddy) just finished with a painful episode of load development for another rifle of mine, and encountered headspace issues. The vendor of the custom cases (.375 Hawk/Scovill) were .026" short of what was needed which caused all sorts of problems. Broken case inside the sizing die, etc. That rifle was not a belted mag, so it was less forgiving. I ended up eating the brass and making my own from .35 Whelen (PITA). Not having fooled with belted mags much (except just feeding 'em factory fodder), I'm learning. You seem to be reading my mind as I come along and begin to think "just shoot the darn gun" and toying with a custom barrel. In keeping with your thoughts regarding working up a load with the Nosler brass, I guess I will need to regard the first rounds to be a pseudo-fireforming exercise and expect somewhat more consistent accuracy with subsequent re-loads... Like I was alluding, I already have one rifle to fire-form for and the notion that my factory rifle will be better the "second time around" kind of nags me... I hope that sheds some light on my equivocal position which seems to be showing through Thanks for the subjective input, it's helpful to hear from others that "have been there".

BTW, my Nosler brass seems to be kind of short in the neck which also irks me. Like 2.480". My chamber will handle 2.535". The neck is already short on the 7 Rem Mag. Just makes it that much harder to work with the long bullets in a hunting rifle.

Reno,
I measured it with a Sinclair bump gauge on digital calipers. I'll try to get the exact measurements tomorrow.




keith,
I didn't expect to be fireforming cases. I just ran the new brass through a FL die and loaded it up like regular (non-belted) brass.
I think I'll trash the smoked brass and start over. Maybe next time load the bullets out to the lands to seat the case back against the bolt face, with a decent load of a faster burning powder