Neck Sized 7mm Rem Mag issues

[lennyo3034]

I have a 7mm Rem Mag in a Bighorn TL3. I have been neck sizing only on the brass based on recommendation of the smith who built it so that it headspaces off the shoulder instead of the belt. This has worked fine for me for 5+ firings on my first lot of brass.

On my second lot of brass, I have only fired them once. After first firing, neck sized and loaded them all, just as I had done previously. Now I have extreme difficulty getting the rounds to chamber. I have to push forward with significant force to get the bolt to turn down. Once it turns down, it drops into batter quite easily. Likewise when unloading (I have not fired any like this), the bolt lifts easy, however requires force to pull back and eject the live round.

Any ideas on what the issue is? I have measure base to ogive and I am not jamming bullets into lands. I have cleaned the chamber/throat area out with carbon cleaner with no effect. Virgin brass still chambers easily.

Would I be safe to fire these rounds? I have loaded quite a few so pulling them would be a bit PITA.

Brass is Nosler. Bullets are 180 ELDm loaded to 3.495" OAL. .010" jump.

 

[918v]

Different lot, different case hardness, different capacity, different pressure. Could be any or a combination of the above.

 

[spife7980]

Exactly, we cant tell you, you have to measure and see for yourself.

After the first firing you can headspace off the shoulder just like normal brass. Neck sizing is for dolts.

That said I bet 100 bucks that your base diameter is too big now.

Full length size and you wont have these issues. You have the means to measure your bullet ogive, replace that bushing with a case bushing to measure the shoulders and then measure the diameters of the brass right above the belt.

 

[bax]

Captain Obvious Says, "Something doesn't fit".

Do whatever you do to clean and resize a fired case. Skip the primer for now. Magic-marker the entire case - case head, rim, everything. Put the case into the chamber and close the bolt. Raise and lower the bolt knob a few times without extracting the case. Remove the case and look for shiny spots. (0) the case mouth, (1) the neck itself, (2) the radius when the neck turns to the shoulder, (3) the shoulder, (4) the radius where the shoulder turns to the case body, (5) the case body, (6) the case body just above the belt, (7) the top edge of the belt, (8) the outer edge of the belt, (9) the outer edge of the rim, (10) the case head.

If you had trouble closing the bolt handle, the base will probably be partly shiny because that is what the bolt face was pushing against. The question is - where is the other end that you were pushing against?

That action looks to me like a hunting receiver so you might expect that you will get water and dirt in there. You might give some thought to full-length sizing. You don't have to give up headspacing off the shoulder but you have to be as careful about it as you would with any other gun.

I have a 300 Winchester Magnum. Some brands/batches of brass expand just above the belt and I can't (that is, won't) size it enough to make it right again. I decided to stop shooting brass that does that. I full length size every case after every firing using a Redding button die set to headspace off the shoulder. I have brass that has been fired a lot, I also anneal my cases. The current barrel has about 2,400 rounds through it. A friend recently shot a 1/2 MOA 5-shot group at 100 yards with 230 grain Bergers, he had never fired that gun before. The ammo fits in the magazine. Not great but it is sufficient for my needs.

 

[davidb187]

If your full lenght sizer's not sizing enough just above the belt try Larry Willis collet die. Some brass need it some don't. But if you're a belted mag afficionnado like me you need one in your tool chess.

 

[lennyo3034]

I took some measurements with one of these rounds, some fired rounds from an older lot and some virgin brass.

These rounds and the older lot of fired rounds were essentially the same. However both had significantly larger dimensions than the virgin brass. Headspace measured .019"! longer on fired brass compared to virgin. Is that not ridiculously excessive? Or is that common with the belted magnums?

 

[MtnCreek]

Large clearance between shoulder and chamber is normal for belted brass.

Personally, I'd use a FL die set up properly rather than neck only.

 

[918v]

My belted magnum has .025” shoulder clearance.

 

[lennyo3034]

Wow, I did not know that. Thanks for the info.

With that being said, I will absolutely start full length sizing.

However for the rounds I already have loaded, would they be safe to fire? I seat with a fair amount of neck tension and I'd hate to have to pull all of these.

 

[918v]

I would run them through a Redding body die and apply an appropriate amount of shoulder bump.

 

[lennyo3034]

I can run loaded rounds through a body die?

I already have a redding body die so that helps.

 

[918v]

Sure can.

 

[MtnCreek]

First you should think about why these are tight in the chamber and the other brass was not. Are you dealing with over pressure?

 

[NineHotel]

Neck sizing does not just effect the neck. Still headspacing off the shoulder not the belt, bump the shoulder back .002" and your problem will go away. Neck sizing only for a field use rifle is not a good idea.