Setting Shoulders Back?

[sadderday]

Could someone please explain to me the concept/function of setting the shoulders back on a bottleneck cartridge?

I'm reloading .223 for a Bushmaster AR-15 using a set of RCBS Precision Dies on a RCBS Rock Chucker. After lubing and resizing a cartridge, I wipe off the lube, and then place it in a dillion case gauge. If it apperas to chamber in the gauge then I assume that I have my resizer set up correctly, and move on from there.

So, when I resize a case, is the die "setting the shoulders back" automatically?

[WIL TERRY]

Now this assumes it was shot it a rifle with correct headspace. If it was not it may set back the shoulder to about the middle of SAAMI specs with most FL sizing dies.

[Bullet94]

You might check this out -

http://ar15.com/forums/topic.html?b=1&f=9&t=408368

I use this to check headspace and set my FL dies -

http://www.sinclairintl.com/cgi-bin/...83X&type=store

so I don't over work my brass.

"So, when I resize a case, is the die "setting the shoulders back" automatically?"

I think the answer is yes, if you have your die set all the way down to where it sizes your case as much as it can and probably more than you need.

PS sadderday Welcome to the FiringLine

[sadderday]

I still don't completely understand.

I guess what I'm asking is: if the sizing die already sizes the cartridge back to its SAMMI specs, then why are some people bumping their shoulders further back by .002 (such as in the link you posted)? What function does it serve?

Not only am I asking why they are doing this, but how are they doing it as well? I'm bottoming my dies out on my shell holder so that the entire cartridge is resized. Are they doing this with some other tool/die?

I'm just really lost on this whole thing, and not sure if I'm missing out on some crucial measurement/specification.

Its the first time I've reloaded a rifle cartridge and I guess I'm afraid of blowing my gun (or face) up.

[Bullet94]

What this means is that if you fully resize your brass you are sizing it more than necessary. You use your same die just don't screw it into your press as much or just back your die out a little from where it is. You need a gage to measure your cases (headspace) to determine where to set your die so that you don't resize your case more than necessary.

Check your Private messages.

[30Cal]

You need to get a value from gaging several fired cases. Then adjust your seating die (screw it in or out) so that the sized cases come out 0.002-0.004" shorter at the shoulder. This ensures that the case is small enough to chamber reliably. It also is not excessively working the brass which will lead to premature case head separations.

SAAMI specs are great and all, especially if you don't know anything about the rifle chamber or are loading for several different rifles. But if you've got a gage, you may as well set up the die to optimum for your particular rifle.

[LHB1]

Sadderday,
When a bottleneck cartridge is fired, the brass expands to fill the chamber. If the chamber is longer than the original case dimensions, the brass will stretch and can move the shoulder forward slightly. If this case is then reloaded without moving the shoulder back to it's original position the case may be a tight fit when chambered again. This is especially true when the action is a "soft" action (i.e., lever action) or when fired in another gun with slightly tighter chamber. Excessive working/movement of the shoulder can lead to early brass failure or case separation. Really excessive headspace can lead to more catastrophic gun failure.
Check a fired case against a sized case for shoulder movement. Test a sized case for fit in your rifle. The idea is to move the shoulder back as little as possible, preferably none.
If your sizing die is screwed down to firm contact with case head and the shoulder is not moved back enough, you can file/grind a "little" off the top of shell holder or bottom of die. Then try again. Remember that shell holders cost less than dies.

Good shooting and be safe.
LB

[sadderday]

Thanks everyone. I'm pretty sure I understand it all now.

It looks like I'm going to have to purchase one of those RCBS Precision Micrometers.

[Tim R]

I set the shoulders back .002 to .003 on my 308 match M-1 gun and on my '06 M-1. This saves over working the brass and still get good feeding. I have the Stoney Point tool which you place on your calipers and measure the shoulders from base of the case. I found you have more uniformed cases using lots of case lube. I use RCBS Case Lube II on a lube pad as it wipes off with a damp rag. I also turn cases 180 degrees and hit them a second time with the sizing die. I took several unfired cartridges with the same brass as I was going to reload and took measurements from them after fired in my rifle to arrive at die settings. Once you have the proper depth on your sizing die, lock the lock ring and don't move it, this is where you want it.

When I got my match AR (WOP upper) I tried setting the shoulders back like I did with the 30's. I found the loaded brass would not always chamber fully and was hard to extract sometimes needing lots of force on the charging handle. No problem if the round was fired, it was getting a chambered round out that was a PITA. This was a problem I had not run into with the 30's. I figured I needed rounds that chambered 100% over the rule of setting the shoulders back a known amount of .002 to .003. I ended up setting the Hornaday Match bushing die down to kiss the shell holder with slight resistance at cam over. Feeding and extraction problems went away. I've got some L/C 223 brass at 10 reloads so brass life is fine for me with my rifle. And it shoots, boy does it shoot.