7mm rem mag question

[Shootn4fun]

Looks like a bit of case stretch to me, Take a paper clip and straighten it out, make a point at the end and then bend an L at the end about an 1/8 of an inch long. Insert it in the case mouth all the way to the primer pocket. Bump the point against the case wall and slowly drag it up a bit. If you have case stretch you will feel the point dragging in that area of the case wall. IT WORKS Then re adjust the dies. If needed.

 

[Bob Wright]

To the OP. Buy and use the comparator as shown above and instructions. See a gunsmith or a buddy well versed in reloading.
The belt had one job. It was measured when the chamber was reamed in the factory. All "new unfired brass" rests there on the belt
For reloading fully form fired brass, that belt is meaningless. Just ignore all comments about the belt. No one measures the "belt to head" for reloading.
It IS measured from "shoulder datum to head" using this style of headspace comparator.
I'm getting FEENIX's popcorn now.

 

[archangel485]

BigBull beat me to it -- there is a bunch of incorrect information floating around here for a belted magnum case. As BigBull said, head space in a belted magnum is measured from the bolt face to the top of the belt. The measurement from the bolt face to the shoulder datum is used for head space measurement in non-belted cases.

This is not to say OP is not pushing his shoulders back too far, just that is not a measurement of "head space."

OP should compare measurement from case head to shoulder datum to know how much he is bumping the shoulder back, and not exceed .002 for that bump. More might lead to case head separation, but that is NOT head space he's measuring on a 7mm Rem Mag.

This is very interesting information, I didn't know much about this before today honestly. So it seems at the very least as far as the point of the OP's problem, we're all talking about the same thing, like @Bob Wright said. The issue you two are pointing out is a technicality, that I (and a few others) am incorrectly using the word "headspace" when what I'm actually talking about is the head to shoulder datum measurement. I had to do some reading on that to find out why they decided to define headspace that way on belted cases, and it makes a lot more sense to me now when I look back at history and consider back in the 375H&H days, cases didn't have shoulders, but they were also transitioning to cases that didn't have rims, so they added a belt in order to have something to measure headspace to. However, I will say, (not guaranteeing it is right, but I think @Bob Wright would agree) the article I was reading did state that the current known belted magnums (including 7mag, and most H&H based magnums) headspace off the shoulder not the belt, and the belt is "non-functional". https://gundigest.com/more/how-to/belted-magnum-cases-myth-dispelled

 

[jimbires]

here are the tools we're talking about . I use the hornady headspace tool . it is universal and will probably measure just about any case . the other is the RCBS precision mic . it is cartridge specific , so if you go this route you'll have a collection of them . I have both , and the hornady tool works just fine . everybody knows what we're talking about , don't let the spelling B champs confuse you . I'll call it the accepted slang term for measuring cartridge base to shoulder datum . as you can see both of these tools are marketed as a headspace tool . hornady list under insert E .420" the 7 rem mag , the 300 win mag , the 300 wby mag . oh my god , I just abbreviated all these cartridges . if anyone has troubles figuring out these abbreviations I'll be back in a couple hours , to help you out .

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[Bob Wright]

It was a "dangerous game round" as the 375 H&H which has about .019 clearance at the shoulder (on my 7mm RM) as "new unfired brass or ammo".
It was guaranteed to chamber in those double rifles and bolt guns when something was preparing to stomp you or eat you.
The belt was needed then. For reloading it's not used. The shoulder to head is now the "head space" one pays attention to. That .019 +/- is the first firing. That case moves that much as new brass or ammo.
You can just neck size fully fire formed brass for maybe 3 firings, but a reloader will at some point need to bump the shoulder back .002-.003. I used to do this but have learned from many guys that neck sizing only and having a bolt drag on reloads isn't helping at all.

 

[archangel485]

It was a "dangerous game round" as the 375 H&H which has about .019 clearance at the shoulder (on my 7mm RM) as "new unfired brass or ammo".
It was guaranteed to chamber in those double rifles and bolt guns when something was preparing to stomp you or eat you.
The belt was needed then. For reloading it's not used. The shoulder to head is now the "head space" one pays attention to. That .019 +/- is the first firing. That case moves that much as new brass or ammo.
You can just neck size fully fire formed brass for maybe 3 firings, but a reloader will at some point need to bump the shoulder back .002-.003. I used to do this but have learned from many guys that neck sizing only and having a bolt drag on reloads isn't helping at all.

Thank you for the info. And I completely agree about bumping shoulders back, I bump shoulders every single reload, even on my 6.5 creed the cases get too tight. I want my cartridges to turn with the bolt face when I drop my bolt handle. Anyways, thanks for all your insights @Bob Wright

 

[L.Sherm]

Trust me I bump .002-.003 on 7 mag and 300 mag cases all the time using a comparator and have never had a case seperate. The guys saying the belt sets the headspace only are the ones incorrect.
If your in a pinch for a comparator a 45 ACP case will work.

 

[bigbull]

BigBull beat me to it -- there is a bunch of incorrect information floating around here for a belted magnum case. As BigBull said, head space in a belted magnum is measured from the bolt face to the top of the belt. The measurement from the bolt face to the shoulder datum is used for head space measurement in non-belted cases.

This is not to say OP is not pushing his shoulders back too far, just that is not a measurement of "head space."

OP should compare measurement from case head to shoulder datum to know how much he is bumping the shoulder back, and not exceed .002 for that bump. More might lead to case head separation, but that is NOT head space he's measuring on a 7mm Rem Mag.

epolenta is Correct

Lets back up a little because this topic started to go sideways at post #5 when the word head space came into the conversation and some people jumped on board, it was a fast walk over the cliff after that hahaha.
I assumed that we all practice good loading practice and have a reasonable knowledge of all the variables that must be controlled in order to reduce the possibility of head separation. I made a mistake in assuming this.
bobwright and others gave very good accurate information without sticking head space back into the issue since using guages to check headspace on belted cases will not answer your question on separation.

I will repeat that headspace in head separations is only a valid term with rimless cartridges where the head space is from the bolt face to the datum of the shoulder, period, guages can be used to validate these dimensions.
On belted and rimmed cases the head space is not important since these cartridges measure head space to different references and not to the shoulder datums, therefore they have no bearing on head separation even when you use a head space guage to validate that the firearm is within safe specs.

Some will try to state that all cartridge headspace is mesured to the shoulder datums this is not true for belted or rimmed cases.
To reinforce what I am saying, When we re-barrel a rifle, a head space guage is used to set the chamber location from the bolt face, on belted cartridges the headspace guage sets this dimension to the forward edge of the belt and not to the shoulder datum.
On rimless cartridges the dimension is set to the shoulder datum.
On rimmed cartridges it is set to the thickness of the rim.
Nothing new here.
BB

 

[blacktail 8541]

A belted case is sized to fit the chamber the same as a non belted for reloading. 2 to 3 / 1000 set back of the shoulder.

 

[L.Sherm]

On belted and rimmed cases the head space is not important since these cartridges measure head space to different references and not to the shoulder datums, therefore they have no bearing on head separation even when you use a head space guage to validate that the firearm is within safe specs.

That is exactly correct, so a soon as you size your brass on the datum of the shoulder the belt becomes a moot point no matter if the headspace is correct on the belt or not.

 

[MOOSE39465]

There's way to much over thinking to this topic. IMO Just annealer your brass and size it to fit your chamber. If your bolt closes with very little friction after fl sizing brass your good. If your hunting dangerous game and you feel the need bump the shoulder back, but don't over do it.

 

[bigbull]

Forgot to mention that this is only the third time these cases have been fired.

Sheephuntr, Sorry but I never really answered you directly.
I would like to know if you got your answer to your question?
What did you understand from all of this?
BB

 

[Sheephuntr]

Sheephuntr, Sorry but I never really answered you directly.
I would like to know if you got your answer to your question?
What did you understand from all of this?
BB

Well I did take the gun to a gunsmith an he told me the headspace was right on. What he found was the chamber was really rough so he is going to polish that out an I'll start my load over by resetting my dies an start from scratch.

 

[Scott E Ames]

I will bet this solves your problem. Although this really is not a problem as much as a cosmetic issue. You do want your case to be able to grab the chamber (or vice versa) to prevent too much bolt thrust. Carefully moving up on your RL 26 loads will hopefully get you to "bug hole" accuracy.