7 mag headspace problem


February 21, 2011, 03:34 PM
i think i have a headspace problem with my 7 mag.im getting case seperation ahead of the belt and its hard to open the bolt.i got some virgin brass to reload.can i put 10 grains reddot,some filler and then wadding to fireform mycases.then can i set my die to headspace on the shoulder instead of the belt?


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February 21, 2011, 03:53 PM
Expand a few unfired cases to 308, and then adjust the FL die down till you feel a little resistance as you close the bolt, then load and fire them. .then can i set my die to headspace on the shoulder instead of the belt? Yes you may, the crush fit works here also.

February 21, 2011, 04:32 PM
I use 15 grains of Unique, corn meal filler over 1/4 sheet of toilet paper and a wax wad to make 338 into 358 Norma Mag. It works for me.


February 21, 2011, 05:56 PM
7mm rem. mag. is my pet cartridge so I'm going to see if I can help you here.
1. Are the cases that are separating factory rounds?
2. What powder and charge are you loading with?
3. With said bullet and powder charge what is your COAL ?
4. What do your primers look like?
5. How many times has the brass been loaded?
6. What bullet and weight are you using?
7. What primer are you using, brand, and magnum or standard?
8. What sizing die are you using, FL, or neck die?
The reason I'm asking these questions is, belted magnums headspace at the shoulder after the initial firing. Headspace is of little importance if your hand loading, and especially if just necking the brass. I load absolute maximum listed charges in both of my 7mm mags. and have shot a bunch through both and never had head separation, except when the brass has expired after 12 or cycles and then it will only show mild signs, but never problems with extraction being dificult. So, I would venture to guess if the brass has not reached it's number of cycles limit, you may be dealing with a powder weight problem, or seating depth driving pressures way up.
Review my questions and that of the rest of us, and let us know. Head separation is a very serious matter.

February 22, 2011, 02:23 AM
SAAMI spec 7mmRM chamber is .220" to .227" to the belt.

I have built (3) 7mmRemMag rifles on Mausers actions and set headspace at .215".


Because SAAMI specs brass between .212" and .220", and I can't find much brass bigger than .215".

February 22, 2011, 07:32 AM
Headspace is of little importance if your hand loading

Are you sure this is good advise to a new reloader?

Jimmy K

February 22, 2011, 09:27 AM
Not very clear, is it Jimmy. :)

We understand what he meant, but how about the casual reader?

February 22, 2011, 10:11 AM
Headspace is of little importance if your hand loading, and especially if just necking the brass. "Cartridge Headspace" is of little importance if your hand loading. This can be adjusted by the full length resizing die. Its a brass thing. "Chamber Headspace" is a Mechanical Thing set by a gun smith or at the factory on Manufacturing/assembly of the firearm. :) The Chamber Headspace is very important.

February 22, 2011, 11:52 AM
A reloader who knows how to properly FL size his cases to match the headspace will be fine no matter what that headspace really is. And, that's NOT a confusion factor to noobs, it should be an asset in working though the BS frequently posted on the web about the "need" to FL size to SAAMI specs each cycle. If it's rimmed, rimless or belted doesn't matter to a reloader using bottle neck cases, just size off the shoulder to obtain a snug chamber fit.

It is NOT neccessary to "fireform" virgin cases any way other than using a normal load. AFTER firing, measure the head-to-shoulder length and restore that length when FL sizing; all will be well.

February 22, 2011, 12:14 PM
no matter what that headspace really is. You sure about that statement?

February 22, 2011, 02:37 PM
Yes he is.

We can size brass to fit our chamber, eliminating built in mechanical headspace. Out actual "working" headspace will be just fine, despite the fact that the rifle, by SAMMI specs, has excessive mechanical headspace.

February 22, 2011, 02:47 PM
I've got a 6 PPC that has 0.018 head space MORE than SAAMI specs. Yes 0.018!!

I found this out firing it the first time and having insipid case head separation. It turns out the chamber was cut for a "Tall Dog" 6 PPC that is made up using 7.62X39 brass with the shoulder further forward.

I found that by fire forming I could get usable cases to work with. So far I formed 100 with zero case loss and have fired all 100 of those five times so far.

Custom fitting those cases is a pain but it is a fun rifle to shoot on an AR platform.


February 22, 2011, 04:45 PM
When you have excess chamber headspace, you can have case head separations on the very first firing. You can be loading with new brass or factory ammo, dont matter. Seen it right here on THR . See > :neener: http://i338.photobucket.com/albums/n420/joe1944usa/th_reloading_2.jpg (http://s338.photobucket.com/albums/n420/joe1944usa/?action=view&current=reloading_2.jpg) Unless you fire form the brass first like i said in post #2 :banghead:

February 22, 2011, 05:50 PM
"Yes he is."

Yep. And a tip of the hat to Walkalong.

It takes MASSIVE headspace to incur a seperation on the first firing of virgin cases and that's REALLY uncommon, to the point of being virtually irrelivant except as a marginal matter.

February 23, 2011, 11:27 AM
thanks to all who have replied to my 7 mag. problem.the rifle was built in the late 60's on a '98 action.it hadnt been shot for about 10 years.i decided to restock it with a lighter composite stock.the only ammo i had was some old reloads. thats all that was ever shot in it (my reloads) so i knew what they were.two trips to the range and two separated cases.the couple that didnt separate were very hard to open the bolt on. figuered maybe old and tired brass was the problem so i ordered new.used the same load ive always used.tried three shells.no separation but bolt was hard to open.tried putting fired cases back into chamber and bolt was hard to close.thats why i asked about the charge i listed in my first post to fireform the case then set my fl die down until the case would chamber.figuered light charge and wadding would be cheaper than regular loads with bullets.maybe headspace isnt the problem.i dont know.dont give up on me, im still here.

for 243winxb---been kicking it around but why expand cases to .308?


February 23, 2011, 03:29 PM
why expand cases to .308?

It creates a "false" shoulder on the case to fit the chamber so that when the case is fired the shoulder will be blown out to the correct dimensions for your chamber.

Look at this link....http://bulletin.accurateshooter.com/tag/false-shoulder/

Jimmy K

February 23, 2011, 03:58 PM
why expand cases to .308?

JimKirk answered it well. To create a "false" shoulder. If done correctly, this will keep the head of the brass against the bolt face. The brass can no longer stretch on firing. The stretching/thinning of the brass is what causes the case Separations in the head area or the body. .the couple that didnt separate were very hard to open the bolt on. Hard opening of the bolt is 1 sign of high pressure. You may want to reduce your load. Changes in powder lots, or age of powder may have an effect on the bolt opening. Head separations are not caused by high pressure, but it does not help the problem any. Another method to fire form > You could try seating bullets with a long COL, so that you jam the bullet into the rifling. This may help when fire forming without expanding the necks to .308

February 23, 2011, 11:47 PM
Excellent suggestion to seat the bullets into the lands to form the brass! I wonder if that may be a factor contributing to my case life being so many cycles as I load up to the lands as a regular practice, just not into the lands. And regarding his extraction issues, I'm also thinking pressures resulting from one of the factors you mentioned, a powder problem of some sort, or seating depth too deep.
An interesting problem I've consistenly experienced with several of my rifles is the bolt is extremely difficult to open after factory is fired thorugh them, and they have all done it from the day they were bought brand new. Never one single repeat of the problem with reloaded rounds.

February 24, 2011, 07:51 AM
Another trick is to very lightly oil the cases when fire forming so they will get pushed back against the breech before the forward portion of the case grabs the chamber walls so tight the case stops moving and then starts stretching just above the case head as the case head is pushed against the breech face.

Hope that made sense. Not quite awake yet. :)

February 24, 2011, 09:31 AM
Excellent suggestion to seat the bullets into the lands to form the brass! Some experts say this does not work. Pressure may rise as much as 10,000 psi when seating into the rifling. The neck tension has to be a lot greater than the weight of the firing pin spring. When the firing pin strikes the round, it slams the case forward, pushing the bullet in to the case. So this may NOT work. Light Oil like Wallkalong said works, but some experts say it makes the Bolt thrust or breech pressure to high. Personally, i dont know???

February 24, 2011, 09:38 AM
On those 6 PPC cases I form with BE and corn meal I lube the snot out of the case with STOS, like RCBS Case Lube, and this seems to give better forming. The bolt rust is not an issue using the pistol powder approach.


February 24, 2011, 10:53 AM
but some experts say it makes the Bolt thrust or breech pressure to highExcellent point, and I should have mentioned it. There is some debate in that area. Many folks do it though.

February 24, 2011, 11:33 AM
Bad Habits? Knowledge should be accumulative, beats me why some insist on starting over in a new world every day.

Slide and glide goes back to the mid by 1910s with the military firing bullets called Cupio Nickel, an accident by design.

Then there is the firing pin launching the case, powder, bullet and primer before the firing pin crushes the primer?? I believe more thought should be given to the question before answers are made up or worst, repeated over and over and over, if more thought was given to answers it would seem someone would realize accuracy would go to #%** if anything as slow, mechanically, as the firing pin was a factor.


F. Guffey

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