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Shoulder bumping .308 cases

A

AZgeek

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Sep 30, 2014
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Tucson AZ
Hey guys.

I've got a FL .308 RCBS resizing die that does not bump the shoulder back far enough for use in multiple .308 rifles (2 bolt, one gasser). So two questions:

Can you recommend a good adjustable shoulder bump die?
Are there FL residing dies with shoulder bump adjust ability for a single step process?

Thanks!

AZ
 
Why not just use a regular FL die, and adjust it up and down like most do?

Edit: either your chambers are very short across all three rifles(unlikely), your shell holder is too tall, or your die is out of spec(long). Your die is likely the issue. Fix or replace your die. Add Redding comp shell holders, and easily switch the effective setting of the die, without actually having to screw it up and down.
 
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Yeah I think my die is defective or just worn out. I just measured some once shot, resized brass vs. a new piece of LC. The FL sized brass is 25 thousands longer measuring from the shoulder.
 
Forgot to add that I'm already up against the base of the die at the shell holder. No more adjustment is possible.
 
No. Got it second hand years ago. Going with a new small base body die and Fl residing die. They just happen to be on sale at Midway.
 
AZgeek said:
Yeah I think my die is defective or just worn out. I just measured some once shot, resized brass vs. a new piece of LC. The FL sized brass is 25 thousands longer measuring from the shoulder.
Click to expand...

This tells me its not just the die but your chamber too. (or possibly your measuring)

If you sized brass down and it is still .025 longer than a new piece of 308 brass you have some serious issues somewhere. My virgin brass usually only grows maybe .010 or so max. Your brass is growing 2.5x more than the max Ive seen mine move.

Soo.... Just for a baseline that cant be screwed up by someone else along the line: I would take a piece of factory loaded ammo, measure its shoulders unfired, and then measure it fired. How much did it actually grow?

Then size it down to where your shoulders measure .001-.002 shorter for a bolt or .003-.004 for a gas gun.

If you want to use the same brass in all guns, then youre going to have to make some sacrifices. You will have to size all the brass down to the level of your shortest chamber. That means that they will have shorter life when fired in the longer chambers. For best results use the brass only with the same rifle it was fired in. They will also almost assuredly not be the same load. Maybe youll luck into something special where it works great in all of them but I highly doubt that.
 
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Hey Spife. Thanks for your input.

That 25 thousands was from the resized gas gun vs the virgin brass. Just for S&G's, I tried to chamber the sized gas brass in my 700 SPS tactical. Tight, very tight to the point of stopping. The I took that same brass and tried it in 700 R5 Milspec. Bolt would not even begin to close. Clearly different size chambers between the bolt guns. That said, I have more work to do here to properly quantify what's going on. I'll do that measuring on all three guns in the next day or so per your suggestion so I have good data to share.

I have already been separating the gas brass from the bolt guns. I'll deal with that later. Hopefully the new small base dies fixes the problem with the bolt gun situation. Whatever is going on with the old die, it has gotten progressively worse. Strange.
 
AZgeek said:
Hey guys.

I've got a FL .308 RCBS resizing die that does not bump the shoulder back far enough for use in multiple .308 rifles (2 bolt, one gasser). So two questions:

Can you recommend a good adjustable shoulder bump die?
Are there FL residing dies with shoulder bump adjust ability for a single step process?

Thanks!

AZ
Click to expand...

If you're going to buy dies from Midway, I'd pick up this as well: https://www.midwayusa.com/product/5...set-1-308-winchester-30-06-springfield-45-acp

You just read the directions and adjust your die once. Then change shellholders to increase the bump to the shoulders if needed. I used to notice that my brass would grow using an RCBS FL die and require trimming more often with the stock sizing button.
 
Thanks Mike! These look like a great way to fine tune. I already place my order with Midway, but its good to know these are out there just in case.
 
AZgeek said:
Hey Spife. Thanks for your input.

That 25 thousands was from the resized gas gun vs the virgin brass. Just for S&G's, I tried to chamber the sized gas brass in my 700 SPS tactical. Tight, very tight to the point of stopping. The I took that same brass and tried it in 700 R5 Milspec. Bolt would not even begin to close. Clearly different size chambers between the bolt guns. That said, I have more work to do here to properly quantify what's going on. I'll do that measuring on all three guns in the next day or so per your suggestion so I have good data to share.

I have already been separating the gas brass from the bolt guns. I'll deal with that later. Hopefully the new small base dies fixes the problem with the bolt gun situation. Whatever is going on with the old die, it has gotten progressively worse. Strange.
Click to expand...

The base may be giving issues in chambering but that still doesnt explain the massive differences in your shoulder measurements if they really are .025 different even after sizing. Im thinking there has to be an error somewhere in either your measurements or just transcribing what you wrote down.




This is the saami print. Notice that the case tolerance is 1.634-.007" so anywhere from 1.627-1.634 would be expected.

The chamber tolerance is anywhere from 1.630-1.640. Thats .010 total, you have .025 for 2.5 times the allowance.

Now, a gas gun thats over gassed and starts unlocking early may allow for some additional growth over those specs but still... .025 is a hell of a lot of difference.


1548104288767.png




Your personal measurements with case comparators most likely will not be exactly these numbers, your comparator has a beveled inside edge and its not the most perfect. Its a relative measurement for your equipment and not a nasa level absolute measurement but the difference between min and max should still only vary by .007 or so. This post does a good job of showing how the number the hornady returns doesnt match the actual headspace gauge spec. But the comparators will give you an accurate measurement of your fired case relative to your sized case.
 
So I found my primary issue. My FL sizing was NOT bumping back the shoulder. Reason unknown at this point. Just for S&G's, I took out the decap rod, cleaned the die and did some resizing with the Gasser brass. I have two types of brass - cheap PPU M80 ball and good GG&G m80 ball that I originally used when testing the gun after the build. I worked with the GG&G brass first.

In order to get the shoulder to bump, I have to make sure there is ram preload (to some degree) or the die simply does not bump. I get results that are close but can vary by 5 thousands or so. Difficult to adjust and maintain consistency. I then moved on the the PPU without touching the die. That resulted in WAY to much bump (30 to 40 thousands too much!) so apparently not all brass bumps the same. Is this true or am I just losing my mind?

The factory Lake City measured here is the baseline for my tightest chamber. That measurement using my Sinclair bump gauge is 3.635. That number is dead smack in the middle of the number Spife highlighted above! I can't go anymore 5 thousandths over that or it starts to bind/drag. So I have a baseline measurement that works and is within the SAAMI spec. Hopefully the new dies will be more precise on adjusting.

Now on to root cause as to how I screwed all this up!

1548115218984.png
 
Your variance of .005 in shoulder set back seems strange. Do all of your brass from that lot measure 3.683-3.684? If so then something is amiss if they are that inconsistent.

Also, with the gauge on the calipers close the jaws and zero it so we don’t have those dumb wrong digits. Just makes it easier to interpret.

What is your lube process? Could be under lubed causing it to stick and resist sizing that’s leading to the .005?

Differences between brass types can vary but not .030-.040.

What press?
 
spife7980 said:
Your variance of .005 in shoulder set back seems strange. Do all of your brass from that lot measure 3.683-3.684? If so then something is amiss if they are that inconsistent.

Also, with the gauge on the calipers close the jaws and zero it so we don’t have those dumb wrong digits. Just makes it easier to interpret.

What is your lube process? Could be under lubed causing it to stick and resist sizing that’s leading to the .005?

Differences between brass types can vary but not .030-.040.

What press?
Click to expand...

The PPU brass could have been made worse by an incomplete stroke or not enough pressure during FL sizing I just don't know and probably not worth spending anymore time on without the new dies and the controlled measuring before and after that you mentioned. Went back however and did some measuring of new PPU rounds. Un-fired, they are either 3.6840 or 3.6845 with most of the sample at 3.6845 or out of spec!

Those calipers are brand new and holding zero every time i checked them. I use light Royal Purple as my lube. Press is a Lee 50 BMG single stage.
 
Ok so besides me reading the wrong decimal place on a digital micrometer, I have this figured out. First issue is the "play" on my press. The shell holder tension ring (on the press) accounts for at least .002 of variability. I confirmed this with a feeler gauge. This is why the preloading (over just the touching of the die and shell holder) in my case is required. Second issue is possibly die itself. I can now "feel" when the shoulder is or is not bumped. Precise control the amount of bump is really difficult. No matter how a fiddle with preload, the bump is a minimum of .002, typically ends up at a .003 increment.

Fixed all my brass, now know how to properly measure the shoulder and understand the variability introduced by the press. Miracles do happen!

Thanks everyone for all your help!
 
Some final comments:

I got my new dies today and moved over to a Dillon 650 press. With a little practice, I'm now able to keep the shoulder bumps to under .002 in variation! I found that after the die hits the shell holder/base plate, just a very slight application of torque is required to get the job done. The Lee press was the biggest contributor to the problem, followed by the worn die.
 
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