Home Forums Hunting & Shooting Gunsmithing 7mm RM headspacing

I am going to install a new XCaliber 7mmRM barrel on my Savage 110.
I know the belted mags will headspace on the belt for the first firing, and after the first shot, the brass should headspace off the shoulder.

I have alse read the SAAMI chamber vs brass dimensions may differ a little, allowing extra headspace. I am not sure about the chamber dimensions for the XCaliber reamer, but would it make more sense to use go gauge vs a piece of brass (assuming dimensions are smaller on brass) to avoid the extra headspace?
I know brass has more spring than steel gauges, and I have changed Savage barrels before, but not on belted mags.

What are your thoughts?

Thanks

Yes, a guage...we`ve done this, not on a savage, but no quessing involved. You`re comfortable it`s correct. IMHO

Thanks

Chambers, dies, etc ALL have TOLERANCES...what you want to do is set up the headspace for YOUR RIFLE not someone else's or what all the krap you read online or off says.

Fire a round, measure the headspace on THAT round..then size it and measure AGAIN. You want YOUR rifles headspace to MATCH the sizers dimensions so you don't have to mess about when reloading or overwork the brass.

USE THAT CASE TO SET YOUR RIFLES HEADSPACE. It's just so easy to then set the headspace and lock it in AND CHECK IT AGAIN. The lock ring will cause the barrel to move slightly sometimes either backwards increasing headspace or forward decreasing headspace.....I've had BOTH happen on my Savages...I have 3 LA and 3 SA receivers and a ton of barrels from 17 Rem to 338 Lapua to 50 cal wildcats.

Forget all the hokum about brass VS Steel gauges...you can feel when the barrel hits the gauge as long as you're not ham fisted or a gorilla...be gentle but firm. Do it a few time to get the feel.

This is how I do all my Savages and also the way I cut any rifle chamber I do and I've been doing this a very long time...with savages since they first came out in the very late 50's.

Set up this way and polishing my reloading dies to match sizer to chamber, I can get over 15 reloads out of some of my belted cased rifles and 40-50 out of the smaller or straight walled cases.

I only use 5 times or less reloaded cases for hunting, depending, and over that number for working up loads.

NONE of this is locked in stone...you have to use your head and keep your eyes open. This is GENERALLY what I do but it also varies in and among all my shooters.

I have brass that is 40-45 odd years old for a few rifles done this way that is the original 50-100 rounds I set up way back then and rifles that have 2000+ firings with that brass.

Believe it or not.

Good Luck

When you size it. Do you size to the max the die will allow? It is my understanding that loaded 7mm RM ammo or brass is generally still shorter than minimum SAAMI, which means still some extra headspace. Using brass to set headspace would minimize that

In practicality it won't matter if you use a go gauge or a case, you're still going to get case stretch on the first firing. Using a case isn't going to fix that because when you're screwing in the barrel the belt on the case will stop you just like the go gauge would. You're not going to be able to use a new case and get it to headspace on the shoulder like a beltless case.

I've headspaced savages both by using a case and a go gauge, with belted mags and non belted cases. My preference is to use the gauge if I have one available but I've done too many using a new case to believe that it can't be done or is dangerous.

Using a case isn't going to fix the issue like you think though, you're still going to have the shoulder expand forward on first firing and need to set your dies up to headspace off the shoulder after that.

Melloyello,
How do you fire a case in a gun you haven't yet assembled?
Or, am I misunderstanding your post.

7mmRemMag is like a lot belted magnums:

Sammi registered range for chambers is from 0.220" minimum to 0.227" max
Sammi registered range for cartridges is from 0.212" minimum to 0.220" max


https://saami.org/wp-content/upload...CFR-Approved-2015-12-14-Posting-Copy.pdf
go to page 44


Here I have build a fixture for measuring the distance on brass from the front of the belt to the rear of the case head. It is being used to measure a piece of bass with a layer of masking tape on the head.

I own a number of factory 7mmRemMag rifles and a number I have chambered and headspaced.
The factory rifles are all between 0.220" and 0.227" like SAAMI says to do.

I have many brands of 7mmRM, 300WM, and 338 WM brass.

Very little or none of the brass I have is greater than 0.215". [I have ~ 2000 pieces and have just measured ~ 100 samples]

Why would I headspace my own rifles less than 0.220"?
I do not like unnecessarily stretching the brass.

Clark, It's hard to get nuances of written "speech" and I couldn't quite understand if you are questioning the decision to headspace at less than 0.220" or to pose the question and answer it, suggesting to do so.

If the belt is what will determine headspace, whether gauge or new unfired brass, then it is truly a moot point, as stretching will happen?

The firing pin pushes the cartridge forward until something stops the case from going any further forward.
The firing pin then dents in the primer and the cartridge goes off.
The powder burn makes expanding gas pressure that pushes outward on the case walls.
The case walls stretch radially and press against the chamber wall.
The case walls grip the chamber walls with a force needed to drag F = coefficient of friction [area] pressure = 0.5 [2 sq in] 50kpsi = ~50,000 pounds to drag the brass back to the breech face.
The cross section of brass area = pi diameter [thickness] = 3 [0.5"] 0.04" = 0.06 sq in of brass.
Strength of cartridge brass = 62 kpsi
Strength tension yield of a case lengthwise = 0.06 [62kpsi] = 3,720 pounds

50,000 pounds force is greater than 3,720 pounds strength so the case has going to stretch until the case head touches the breech face.

There may be 0.001" or 0.002" of elastic deformation, but after that it is plastic deformation.

Once it starts to have plastic deformation in stretching, that part gets narrow and all the stretching will be there. That can lead to case failure.

Can this happen with sloppy SAAMI dimension tolerances? Yes. Just keep reloading with the firing pin pushing the case forward further than 0.002", and that brass will wear out.

I know the sequence of events and reasons for stretching, but that was even harder to understand... hahaha
My question is, headspace at less than 0.220? or moot point cause it will happen once and then size to shoulder ?

Generally speaking, I prefer to chamber to .220" and , after the first firing, headspace on the shoulder. This is simply because a customer's rifle must be able to chamber any factory cartridge and there is always the possibilty (unlikely though it may be) one might find a piece of brass which approaches maximum dimensions. Since I have never seen such, I chamber my own rifles to .218" but still headspace on the shoulder after the first firing. GD

You'll still have to bump the shoulders back on the fired brass.

I think Clark is advising that you headspace at 0.220, the minimum end of the chamber spec, or even slightly less (like 0.218) as his experience with numerous examples of brass is that brass headspace dimensions (head to belt face) do not exceed 0.215 across manufactures.

I'm gathering that you're seeking an ideal brass to chamber fit, where you'd have maybe 0.002" headspace at both the belt face and the shoulder. Is that what you're getting at?

Yes
Trying to avoid unnecessary stretch, as described most factory ammo and new brass is 0.215 and headspace gauges 0.220. If no way around it, then no big deal. For my needs, it is likely a negligible difference and effect.

Belts vary all over so the shoulders should still be used. Belted magnums are going away. I never used go-no go gauges. Layers of masking tape on case heads showed me head space. It is not rocket science.

Masking tape is too soft to use on a bolt action, it compresses too much. One time I tried checking the headspace of a Mauser with tape and got about 9 layers on a cartridge. Same cartridge with a steel shim would only take 3 thou.

You can't use force, just feel. Some resistance with 2 layers and the bolt should not close with 3. I am sure you can force it to close as there is camming power with the action. Just a gentile pressure on the bolt.