Once Fired LC Shoulder Bump

[Afkirby]

I’ve got about 2,000 pieces of mostly matching headstamp LC brass that I’m planning on using for a variety of AR’s and a Nucleus action that I have preordered. I just got a Sinclair comparator to see how far I’m bumping back the shoulders and it seems to be taking them back about .020. Does this seem normal for a first time sizing on surplus brass? I’m curious to see what the brass is going to expand to in my chambers. I’ve got 3 dies, a Lee, a Forster, and a RCBS small base and each one bumps the shoulders the same amount on my Dillon with a small amount of cam over.

Thanks,
-Kirby

 

[spife7980]

Why are you moving them back that far? You know you can change it by unscrewing the dies, right? Moving them that far is gonna cut your brass life short.

 

[rijndael]

With that much brass, I'd just set aside a few hundred per rifle and keep them dedicated to a gun.

Yes, a .020" shoulder bump is excessive.

 

[Afkirby]

That’s the plan, I’m hoping they’ll only blow out a few thousandths from where they are now.

 

[supercorndogs]

From .02 some of them will probably case head separate on your first firing. You are looking for .002-.003. With once fired that may or may not fit your chamber.

 

[MtnCreek]

Measure fired cases from your AR's. Assuming they're all with a couple thou, reduce headclearance on the tightest by about 0.004 and size to that.

 

[Precision Underground]

Unscrew die a bit, resize case, try to chamber case, case still tight, screw die in a tiny bit more, try to chamber case, still a little tight, screw die in a tiny bit more, case chambers nicely, screw die in a tiny tiny bit more, you have your bump. Measure a few to make sure they are consistent.

 

[Afkirby]

When my Nucleus and barrel get here I’ll try to size a few so they just barely fit so I’m not oversizing them. Just to be clear I don’t plan on bumping them .020 every time, just seeing if LC brass is that oversized often.

 

[rijndael]

I've had many batches of LC (LR) brass and none required .020" bump, but none of my brass was MG fired.

 

[Afkirby]

Also the “through hole” on the Sinclair comparator is really tight. The unsized neck of the case will stick in it. I’m assuming the chambers these were shot it were fairly loose.

 

[MtnCreek]

What comparator are you using?

 

[Afkirby]

Sinclair shoulder bump comparator.

 

[MtnCreek]

If it's making contact with the case neck, you are likely using the wrong insert.

 

[Afkirby]

It’s the correct one on their website, and the shoulder angle matches up nicely. Once sized it clears fine.

 

[MtnCreek]

I use some sinclair inserts in my hornady gage. The ones I use space off the shoulder, very near the junction with the body as apposed to the hornady inserts that space off the datum line more near the middle of the shoulder. It sounds odd that they'd touch the neck.

 

[spife7980]

The sinclair headspace bushing should be "749-011-473WS #23, 23 degree shoulder (17-6mm)" so it shouldnt be dragging on the necks, it can fit a 6x45 after all.

If this brass is larger than a 6mm and .020 longer than normal I would scrap it or figure out what exactly it is that you have because everything so far says that its wrong.

Just to be clear I don’t plan on bumping them .020 every time, just seeing if LC brass is that oversized often.

Wait, in reading this now, over sized as compared to what? Whats your point of reference to say its oversize?

 

[MarinePMI]

Sounds like brass that's been run through SAW.

 

[Afkirby]

The sinclair headspace bushing should be "749-011-473WS #23, 23 degree shoulder (17-6mm)" so it shouldnt be dragging on the necks, it can fit a 6x45 after all.

If this brass is larger than a 6mm and .020 longer than normal I would scrap it or figure out what exactly it is that you have because everything so far says that its wrong.



Wait, in reading this now, over sized as compared to what? Whats your point of reference to say its oversize?

All three of my .223 dies are bumping the shoulders back .020 with a full cam over, I was just wondering if that was normal for LC brass. I figured there might be slightly larger chambers in the military guns that would result in larger than normal fired brass.

 

[Afkirby]

The comparator is a Sinclair #23 and has an ID of .255”. I measured 5 pieces of LC09 brass which measured

.2545
.2525
.2535
.2535
.2535

The brass slides in but will not fall out from gravity unless it has been sized.

 

[spife7980]

Well I would just hold off on potentially ruining anymore brass until you get your chambers measured and then size appropriately instead of just screwing them all the way in.

 

[MarinePMI]

The comparator is a Sinclair #23 and has an ID of .255”. I measured 5 pieces of LC09 brass which measured

.2545
.2525
.2535
.2535
.2535

The brass slides in but will not fall out from gravity unless it has been sized.

Perhaps (as I stated) it was fired from a SAW. The SAW fires from an open bolt (which really doesn't mean anything), and at a high rate of fire. In some cases, the chamber being overly large in conjunction with extraction happening while the case is still expanding, will bloat the case slightly at the neck juncture. If the bottom of the neck is blown/rounded forward, it would cause you cases to stick in the comparator (essentially they'd pinch at the junction between the neck and shoulder). After putting a piece of brass in the comparator, are there any marks down at the bottom of the neck? IMHO, that would be a clear indicator that the case has a slightly ballon'ed shouder. If that makes sense to you....

Just neck size a couple cases (down to the shoulder, but without bumping the shoulder back) and then try them in the comparator.

 

[Afkirby]

I used a Lee neck collet die on the brass before using the comparator, I’m getting much better numbers now. I emailed Sinclair and their answer was to drill the hole out myself, not exactly thrilled by that. I’m getting 1.460 now on the unfired LC brass, I have to bump the shoulders to about 1.452 to get them to chamber in my white oak barrel.

 

[DRAM40A1]

The whole point of the gauge is to set your dies up to size for your rifles chamber. Until you know how much to bump the shoulders to fit your rifles chamber, there is no point in sizing the brass. Shoot some to fireform to your chamber and see what you need to do instead of speculating.....

 

[poptart4YALL]

The whole point of the gauge is to set your dies up to size for your rifles chamber. Until you know how much to bump the shoulders to fit your rifles chamber, there is no point in sizing the brass. Shoot some to fireform to your chamber and see what you need to do instead of speculating.....

If he already knows the measurement for his chamber there’s no need to fire form. He’s full length sizing and the brass is clearly longer/larger than what he needs. He just sets up the die to give him the correct shoulder clearance and load them.

 

[DRAM40A1]

If he already knows the measurement for his chamber there’s no need to fire form. He’s full length sizing and the brass is clearly longer/larger than what he needs. He just sets up the die to give him the correct shoulder clearance and load them.

Reread the thread and point out to me where he knows what his headspace is......One of the rifles he plans on using the brass in does not even exist! The rest is a variety of ARs. None of his brass has been fired in a rifle owned by him. Unless I'm missing something? LOL

 

[Afkirby]

The whole point of the gauge is to set your dies up to size for your rifles chamber. Until you know how much to bump the shoulders to fit your rifles chamber, there is no point in sizing the brass. Shoot some to fireform to your chamber and see what you need to do instead of speculating.....

I’ll fireform them after my first loading, I was just messing around with my new (and apparently faulty) comparator. Wondering if other people were getting similar readings at full cam over. I think this brass is slightly oversized, but not too much. After rectifying my comparator issue I’m having to bump the shoulders back about .008 to get them to fit in my chamber.

 

[DRAM40A1]

Just load a few and fire them, then you have something to measure and set the die for the proper headspace for your chamber.