Neck Sizing 7mm RM


June 25, 2013, 06:03 PM
I know I've read places where folks neck size after fire forming belted mags like the 7mm RM. I've even seen dies for it.

My mentor, says not to neck size belted mags like the 7mm RM. He highly suggests FL sizing only for belted mag brass.

Just trying to find the general census among the reloading community, and then make my own decision on the matter.

What say you?

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June 25, 2013, 07:28 PM
Neck size. Most belted magnum loaders believe the opposite. I do for my 300 Mag. I adjust the FL die out so it only gets the neck. Takes some adjusting to find the right adjustment. I use a sharpie and color the entire neck, then adjust until it smudges about 3/4 or more of the neck. Lock it down and size away.

That's how i do it.

June 25, 2013, 08:04 PM
In my mind, I figured, the cases are already the size of my chamber, no sense in overworking the case by FL sizing especially in a magnum.

Plus I'm hoping it'll be one of those small little things that'll add a little to tightening up the groups.

June 25, 2013, 08:23 PM
I neck size 7mm RM brass that I fired in my rifle, FL size brass I got any other way. With a tight chamber, FL resizing to fit can take some effort.

June 25, 2013, 08:25 PM
I neck size 7mm RM and have been doing so for a long time. The one thing that I think is important to understand, is that regardless of being a belted cartridge, or not, necking is not an exclusive method of sizing for any shouldered cartridge. In other words, you will always need to use another die intermittently to reposition the shoulders, as well as the walls. This is because each time you fire a case, the shoulders and walls get pushed out more and more each time, thus causing the brass to eventually reach a point in which it simply won't fit the chamber. There are various methods of accomplishing this, but the FL die is a less expensive and common method of bringing the brass back into proper dimension.

I generally get 2 - 3 neckings before having to put them through the FL die. But this number can vary depending on the loads and brass being used too. I find that RP brass doesn't spring back as much as Win brass and usually get 1 necking before having to FL size. And by not keeping the brass properly maintained in this respect, can lead to the web getting pushed out, as well as damage to the bolt lugs.


June 25, 2013, 08:27 PM
After firing virgin brass, I neck size only in my 7 RM. Doing so you are using the shoulder to headspace. Others my disagree with me, but have had longer caselife by just neck sizing. Just keep an eye out for head separation on your cases. This occurs just above the belt area. Make yourself a feeler gauge with a paperclip. Scrape the inside of the case and you can feel a crease or valley forming in that area, chuck those cases.

June 25, 2013, 08:27 PM
GS, you're right of course. I have yet to fire a piece enough times to need FL sizing, but I don't have any with more than two firings.

June 25, 2013, 10:28 PM
I think I've made up my mind. Just have to figure out how to deprime, while only neck sizing with a FL sizing die now.

June 25, 2013, 10:42 PM
I suggest a universal decapping die. It's just a wide open die with a decapping pin that will accommodate anything over .17 or .20 caliber (except 50 BMG) without doing any sizing of any kind. It doesn't touch the case at all, just the spent primer. Lee makes one for about $12 bucks.

June 25, 2013, 10:47 PM
Ill have to get one of those. I was kind of hoping to make up some loads and try it out this weekend.

Would a thin small punch work if I put the case in the shell holder, and them just slightly tap the punch with a small hammer? Or would this mess it up? Or is there an easier way?

June 26, 2013, 06:19 AM
Anyone know if using a punch is ok to knock the primer out, at least until I can get a universal decapping die?

June 26, 2013, 06:31 AM
Sure, as long is it fits through the neck without touching. It might be a little fiddly to align, and you of course have to set the case on something to provide clearance (some place for the spent primer to go), etc.
June 26, 2013, 06:36 AM
A punch will work as long as the body of the punch will fit in the case neck. That is what the lee loader kits uses to deprime.

June 26, 2013, 07:08 AM
Sweet thanks guys. I tried out a few this morning, and it worked great. I did have to fiddle with it a bit to make sure it was touching the primer, but all in all in worked great. Something I can file away for later reference.

I figure it'll work for now, until I can get me a universal decapping die ordered and delivered. Never thought I'd need one. LOL. That's what I get for thinking. It'll at least let me neck size only on my 7mm RM brass.

June 26, 2013, 07:33 AM
I think the important thing with most any rifle caliber, not just belted magnums is to resize to the minimum amount. True neck sizing uses a special neck size die whereas the advice given to adjust your dies to resize the bare minimum amount using a marker pen as in post #2 leads to much less brass working & longer case life. Checking for case stretching with a feeler (#6) is good advice too which hopefully shouldn't happen if you've adjusted your dies correctly.

June 26, 2013, 08:08 AM
You can deprime with a punch or anything really, just be cautious that the instrument you use doesn't enlarge the flash hole. An enlarged flash hole can cause serious problems by causing excessive primer blow outs, which can damage the bolt face.

And using a FL length die will work quite well without having to buy a separate decapping die. The decapping pin can be adjusted down far enough to push the spent primer out without the shoulder making contact with the die. But only adjust it enough to accomplish that or you might break or bend the decapping assembly, and or damage the case web area surrounding the flash hole.


June 26, 2013, 08:23 AM

How do I go about adjusting my FL sizing die? Do I lower the arm all the way, then screw my die in until I feel in make contact with the shoulders, then back the die off, then lower the decapping pin down far enough to decap the case?

Sorry for all the questions, this will be the first time I have neck sized only.

June 26, 2013, 02:04 PM
RCBS #13630 is the neck sizing die for the 7mm RM, I have one and only neck size my 7mm brass and have for over 30 years. Works great in MY 700BDL

November 7, 2013, 09:49 PM
I used to reload a lot for my 7mm RM range gun. I only neck sized and I never had one problem. The loads were also supremely accurate. Someone mention the shoulder moving forward until the reload would no longer chamber. I don't see how a case can expand larger than the chamber. I don't think that is possible. I did notice the brass did flow and trimming took off a bit of brass each time so I would suspect the brass would become thin over time so if you shoot and reload a LOT I would take care of how many times you reload each case.

November 8, 2013, 01:59 AM
I have done experiments to see how many firings of 7mmRM I could get.
I bought the innovative technologies collet die.

But in the end I got a lifetime supply of once fired 7mmRM brass. I resized it with a Bonanza FL die with the neck honed out to .307". I set the shoulder back .002" more than I need with my reamer. I run it between 9 and 11 gr over max published Hodgdon loads. I never use the brass again. I have easy bolt lift, but that collet die cannot fix brass that has seen that pressure.

The other thing I do is headspace the rifles at 0.215", well below the SAAMI minimum of 0.220".
Almost all the belted magnum brass I have ever seen will fit in a .215" gun.

November 9, 2013, 04:01 PM
I use the RCBS 1630 Neck Die, but if you want to use your FL die to work similar in function it's very easy to do. But it won't provide you with true neck sized brass though. And the necks will very likely only get partially resized, which isn't usually an issue as long as you are getting enough neck tension.

First thread the die into the press with the ram at full extension. Adjust the die down to where it is roughly .010"-.015" from the shell holder, that is plenty to avoid shoulder contact. If that touches the shoulders, then that chamber is excessively out of spec.. Then adjust the de-capping pin down another 1/16" or so and make sure it is centered, it should be if it hasn't been previously bent.

Check your cartridge with a gauge prior to, and afterward to make sure the shoulders didn't get bumped, just to be sure. If the first one got bumped at all then continue adjusting the die up another .010"-.015", but I've never seen a chamber that sloppy before.

But, because you are using a FL die the case body is still going to get sized some. And because of this it can push the shoulders up some, this is due to the brass being displaced, it has to go some where.

Don't forget to trim follow all of this. PM me if you have any other questions or concerns.


November 9, 2013, 05:17 PM
Neck sizing with a FL die will soon or later get you hunting ammo that will not chamber. Unless you try to chamber each case before loading, its not a good idea. IMO. Neck sizing, with a neck only die, will cause the case to become unsupported in the belt/web area. May not be good for full pressure loads. Looking at the drawings & head clearence may help you see the unsupported area of belted magnums when letting neck sized brass grow to fully fill the chamber. You will notice the bolt becomes a little harder to close.

November 10, 2013, 12:06 PM
I used to only neck size untill my cases got tight to chamber then full length. Now I just bump the shoulder enough to chamber smooth. I have brass with 15-16 loadings on it and not one issue. I run Winchester brass.

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