.308 Win - Setting Setback Part 2

[Multi-Tool]

My previous post explained issues I had with getting any appreciable setback in resizing some once-fired Lapua brass. After calling the die manufacturer, I swapped out the expander ball with one for a smaller caliber, removing the expander from process, but keeping the de-priming pin in place. My plan is to use a mandrel expander in a separate step.

So today, I went back to adjusting the sizing die. I previously took measurements, using a Stoney Point case comparator, from a group of cases fired from a bolt action Rem 700. However, it should be noted that the cases I am resizing were fired from both the bolt gun and a gas gun.

After making more adjustments, I sized 10 clean but un-resized cases. The result was that half of them resized to with a setback of .003”. Three had a setback of .007”, one was at .004” and one was at .006 “.

I had hoped to get more consistent results. Does the group have any suggestions? Am I overlooking anything or overthinking the process?

Thanks!

 

[Evintos]

Add a little bit of dwell time in the sizing process. Raise ram and pause for a few seconds before lowering.

 

[pfl338]

Are you depending on the stroke of the press to establish the setback of the shoulder? If so ,that could cause a lot if inconsistencies in shoulder bump. Get a set of redding competition shell holders, that way you can reference the amount of the shoulder setback off of the bottom of the die consistently.

 

[Doom]

You mention that the cases are from different guns. Did you check the dataum dimension prior to resizing?

 

[Multi-Tool]

You mention that the cases are from different guns. Did you check the dataum dimension prior to resizing?

Yes, and my plan was to base the setback on cases that I knew were fired from the bolt gun. Raw data from a 10 round sample that were fired in the Rem 700, as measured using my Stoney point case comparator, has 9 cases at 3.637” and one case at 3.636”.

Out of curiosity, I also measured 10 rounds from the cases that were mixed-bolt gun and gas gun:
3 cases measure 3.639”
5 cases measure 3.638”
2 cases measure 3.637”

 

[Precision Underground]

Yes, and my plan was to base the setback on cases that I knew were fired from the bolt gun. Raw data from a 10 round sample that were fired in the Rem 700, as measured using my Stoney point case comparator, has 9 cases at 3.637” and one case at 3.636”.

Out of curiosity, I also measured 10 rounds from the cases that were mixed-bolt gun and gas gun:
3 cases measure 3.639”
5 cases measure 3.638”
2 cases measure 3.637”

Sizing brass from 2 different guns, especially from a gas gun, can create variations when resizing. The shoulder may be close on the fired brass but the rest of the case may not be. I bet if you try to close the gas gun brass in the bolt gun the bolt won’t close half way. More variation going in can make for more variation coming out. Also if your lube and press stroke aren’t consistent you can get more variation. Some of this stuff is 60% art and 40% science.

That being said, I’d be willing to bet you won’t be able to tell the difference between .003 and .007 on target. I don’t get bogged down over a few thousandths either way. Open your calipers to .004 and ask yourself if that’s going to change anything when the powder violently burns and forces the bullet down the barrel. If you’re a bench rest shooter or something like that then maybe go to town. But for tactical shooting just spend those hours dry firing and you’ll get much more out of them.

 

[ma smith]

3 cases measure 3.639”
5 cases measure 3.638”
2 cases measure 3.637”

What cartridge cases for 308 are 3.6" long? The magazine length for 308 Win is 2.8 to 2.95 depending on your standards.

I think you need to re-zero your caliper. (Or, please correct me if I'm not following correctly).

 

[CK1.0]

I went back and read your other thread...

You're going to drive yourself crazy trying to use an average for the shoulder datum... and also by mixing brass that was shot/formed in different guns/chambers.

I'm going to assume you're resizing these cases to be fired out of the gun with the longer chamber (the bolt gun I'd guess?). Measure enough of the cases to know what your longest ones measure out to, that's your number, set the die to then bump those ones 1.5-2 thou, done. Run all the cases through the die regardless of what they measure (the longest ones getting bumped back is all that matters).

Fire them all again.... after a couple/few firings they'll all come out measuring about the same give or take a thou.

 

[R_A_W]

What cartridge cases for 308 are 3.6" long? The magazine length for 308 Win is 2.8 to 2.95 depending on your standards.

I think you need to re-zero your caliper. (O,r please correct me if I'm not following correctly).

He just didn't zero with the calipers once the Hornady Lock n Load headspace gauge thing was on.

My fired .308 brass measures 1.630 or 1.632", I'd have to double check

SAAMI is 1.634-1.637 to the midpoint of the case shoulder

https://i0.wp.com/www.theballisticassistant.com/wp-content/uploads/2021/01/308-Win.jpg

To @Multi-Tool - If you're using the Hornady tool, you should re-zero your calipers after. The play between the bushing and the red anodized clamping piece can throw off your measurements, not to mention how consistently you attach it to your calipers

 

[Multi-Tool]

He just didn't zero with the calipers once the Hornady Lock n Load headspace gauge thing was on.

My fired .308 brass measures 1.630 or 1.632", I'd have to double check

SAAMI is 1.634-1.637 to the midpoint of the case shoulder

https://i0.wp.com/www.theballisticassistant.com/wp-content/uploads/2021/01/308-Win.jpg

To @Multi-Tool - If you're using the Hornady tool, you should re-zero your calipers after. The play between the bushing and the red anodized clamping piece can throw off your measurements, not to mention how consistently you attach it to your calipers

Exactly,

I am using the case comparator for relative measurements; not absolute measurements.

 

[Multi-Tool]

Thanks to all for your input. I don’t like resizing rifle brass, but sometimes it has to be done. I sent some brass off for resizing a couple of years ago, but was not about to do that with Lapua brass, so I am sorting out these details of precision resizing. The feedback gives me assurance that even with the variations in measurements, it seems I am on the right track.

 

[MarkyMark007]

use search function. i already wrote about it.