I have a question about forming cases for the 7RM. I know it sounds stupid as there are zillions of inexpensive good quality brass available for this calibre, but I want cases that fit my chamber like a hand in a glove.

My ”problem” is that my chamber is quite long from base to shoulder, new cases have the shoulder moved about 0,5 mm (0,02 inches) forward when fired. And the maximum case length my chamber allows is 64,2 mm (2.527 inches), wich is 0,9mm (0.035 inches) longer than the length of new cases. The chambers is normal, or even a little tight ( its actually perfect) in diameter, so its only the length that is a little generous.

I have my full length resizer adjusted to bump the shoulder of fired cases back about 0,05mm (0.002 inches). I want to use my full length sizer to reform cases from a larger calibre so it will fit my chamber more or less like a once fired case. I also want a case that, once reformed, is at least 64 mm (2.520 inches) long. I reckon I will need to turn the necks of these cases, and I don�t mind. I have some .300 Win Mag cases that I will try first, and I have ordered some .308 Norma Magnum cases to try later. I think the .308NM would be perfect, since the shoulder on this case is slightly forward of a 7RM, and since the case is longer to begin with. The Win Mag is even longer in both respects.

Does anyone have any experience with this? Any recomendations about the best case to start with? (I believe the .308 NM must be the perfect candidatehave, the .338 Win Mag has the same length and base to shoulder dimensions prior to reforming as the 7RM) Can anyone tell me what problems I can expect or pitfalls I need to be aware of? Any feedback would be welcome. Thanks.

Tron

It is truly disgusting how sloppy manufacturers are with chambers for belted cases. They simply assume that the case will headspace on the belt and therefore "hog" out the chambers nice and big so there won't be any fit problem with factory loads. As a cost benefit, the oversized reamers the factory uses last a lot longer before wearing down below minimum tolerances.

At any rate, Tron, you're on the right track. Your "fit" when beginning with longer cases such as the .300 Win may not be as good as you assume, since your FL sizing die will likely be somewhat smaller in shoulder diameter than your chamber, but at least you will have cases that come much closer to fitting (and the die can be set to headspace the cartridge firmly on the shoulder rather than relying on the belt). I doubt that you will need to thin the neck walls, even if using something like the .338 as a source case, since your chamber is likely somewhat generous in neck diameter as well. Load and fire a formed case with a light load and then try inserting a bullet into the unfired case by hand. If the bullet goes with a "slip" fit, the your neck thickness is fine. Be sure to properly chamfer (bevel) the inside neck walls after trimming your .300 Win to proper length.

This problem is in the drawings of the chambers of belted cases. They are different than rimless cases and have more clearance at the shoulder as they headspace on the belt.

I found out about this 33 years ago when my second "magnum" had a chamber made to the limits of this defective design.

Your on the right track. Make cases out of something bigger. I used .300 Win Mag brass.

Also make a feeler from a 6" length of coat hangar wire. Bend the end to a tiny hook and file it to an edge. Use this to look for insipiant head separtions in belted cases. You won't have to do this in rimless cases fired in front locking actions unless of course their headspace is way out of spec.

Stonecreek
Thanks for the reply. I also find it annoying that chambers and cases for belted magnums seems to be void of even the slightest care during manufacture. My chamber is actually not that bad, its even minimum spec at the neck, exactly 8 mm. But it seems all cases are well below minimum dimensions when it comes to base to shoulder length and shoulder diameter.

If I use Norma 7RM cases and US bullets in my gun I have 0.002 inch clearance between the neck and the chamber, wich is ok with mild loads and when I can keep the chamber really clean. I tried some european (german) bullets with a slightly larger diameter (.286-287 inches)and primers started popping out of my cases. For hunting loads I need to keep loaded rounds to a neck diameter of about 7.90 mm, so I guess neck reaming could be necessary.

I will have a go at the .300 win mag cases tonight and see if I can reform them without the cases collapsing. I hope to get a case that will headspace properly on the shoulder to start with, and to get good case life as the major benefit. Maybe in time I can gain some wisdom to share with you..

Tron

trb,

It seems that you were typing and posted after my comment above was made.
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Each cartridge has a drawing with tolerances and so does each chamber. They are not the same dimensions! There must be a clearance. However as I pointed out above the belted chambers have more clearance than rimless chambers. Also things are not always made to their tolerances!

There is a thread here by John Ricks that explains this.

These belted cases were never designed to be reloaded and are dangerous. But almost everything can be dangerous so just take more care and extra steps.

Savage99
Thanks for your tips, I have realized that I need to take a lot of care when feeding my 7RM. Based on how much original 7RM cases stretch in my chamber when first fired I have decided to stop reloading them and go for "custom made" instead. Hopefully this will give me safe and durable cases. Tron

trb,

From what I read of your posts I think you understand this very well. Compared to someone who will make "custom loads" who I don't know I would rather shoot your ammo!

Just make the cases from .300 Win Mags and you will be fine.

I had a go at the .300 win mag cases last night, took me a couple of cases to realize how little lubrication I need to use to avoid crumpling the case. I got ten cases that look really nice, but a couple of them has slight evidence of crumpling, just a few small creases at the shoulder/neck junction, will it be safe to fire them?

Compared to once fired 7RM brass my reformed cases have the neck length I want, I trimmed the cases to 64mm. Base to shoulder length measured with a stoney point gauge is 0.001 inch shorter than once fired cases. Shoulder diameter is smaller than once fired cases, but I am very satisfied so far. With a bullet seated the necks are 0.002 inch smaller than the neck of my chamber so I will try them without reaming the necks. Tron

Small dents from excess lubrication will "iron" out nicely when you fire the loaded ammunition. They are safe and will likely group just like the undented cases.

Sorry, should have mentioned to be sparing with the lube. Congratulations on some well-prepared ammunition.

Some dents may not iron out but they are safe and only a cosmetic problem. Put the case lube near the base of the case. This is where you need it as that's where they stick in the dies.

Before you size another case remove the decaping assembly and wipe out the inside of the FL die with a cloth or paper towel on the end of a pencils eraser end. I do this before sizing a new batch of cases every time.

Put very little or no lube on the case near the shoulder body junction or above it.

Clean the necks of all residue (on fired cases) to prevent scratching of the dies.

Measuring with Stoney Point tools etc is fine but nothing beats fitting the case to the chamber by actually puting the case in there and closing the bolt with the striker assemby removed or in the middle position in a M70 or Mauser.

"Put the case lube near the base of the case. This is where you need it as that's where they stick in the dies." "Put very little or no lube on the case near the shoulder body junction or above it."

Don, remember that Tron is sizing down .300 to 7mm, so he will have to have at least some lube on the neck and shoulder area, although very little on the shoulder. Also, he said that the shoulder diameter is coming out smaller than his chamber, so he will continue to have to have a bit of lube near the shoulder (and just below) even for the next trip through the die. At the same time, it's doubtful that the new .300 brass he's starting with will even contact the die near the base, and may or may not expand enough on firing to do so.

Not intending to be agrumentative, just wanted to clarify what his situation is.

Your right Stonecreek. I was thinking of FL sizing fired cases.

There is a fine line of how much lube to put on the case and where to put it. I have just made up a lot of brass for my .224 wildcat from 6.5 Rem Mags and they require lube in the form dies just as I have described. A case with a fold at the shoulder is really scrap so very little lube is needed there. Perhaps more on the first case with a clean die.

These will be good cases if made from the longer 300 WM brass.

I really appreciate the feedback, none of my shooting/reloading friends here in Norway go this far down the road.

After the first few crumpled cases I found that if I lubed sparingly from the base up to 0.1 inch from the shoulder of the .300 WM and then again a little on the neck itself the cases turned out fine. It requires a firm push on the press handle but they don�t stick. My press is a co-ax wich has good leverage, and as long as the cases don�t get stuck and the rims are straight I guess I�m in business.

The new cases don�t contact the die from the base and 3/4 way up, my fired brass rezises to appr. 0.05 above the belt. By the way, I only use new cases for reforming, its impossible to know anything about a case someone else left for you, how many firings its gone trough and in what kind of chamber etc.

My stoney point gauge give excellent readings, I resized two cases to 0.002 above zero headspace and my action wouldn�t close, its a break open single shot, no help from a bolt to force the case in. I will load up my reformed cases with a mild (not to mild)load (65 grains of Norma N-15, a reloader 22 equivalent, behind a 140 gr Sierra) and shoot them next week, keep you fingers crossed.

Tron

I finally got around to shooting my reformed cases, and they are just excellent. Very easy to resize after firing and they did not stretch at all. Last night I reformed a new batch and this is the routine I found gave the best results:

I start with neck annealing new Remington .300 WM brass. Then I lube them sparingly and run them trough my full length 7RM sizer. Then I neck them up slightly with a Sinclair expander iron, trim them to 64,1mm and ream the necks to 0,014 inches neck wall thickness. After cleaning I prime and load, these cases fit my chamber so well that except for the necks they seem to expand very little after firing, with no stretching. I think, and hope, they will last a long time. Tron

You do good work Tron. I hope others who load belted cases read and understand this.