Sizing die adjustment

[memilanuk]

So... this one is kind of a head scratcher at this point. Either I'm missing something fundamental here, or something is wonky.

Cartridge is a .308 Winchester, specifically a 2013 US FTR chamber (essentially a '95 Palma with .170 freebore) in a 30" Kreiger heavy Palma contour barrel on a Savage Target Action. Cases are once-fired (in this chamber) Lapua Palma (small primer) brass.

The only die I had on hand equipped with a small PPC-sized decapping pin was a small base Redding Type 'S' F/L bushing die with a Wilson .335 bushing and Redding floating carbide expander ball. Nothing exotic, and essentially the same setup I've used for many thousands of rounds in various .308s (other than the small base). I got the die a couple years ago to attempt to handle some issues I was having with brass fired in one chamber not playing nicely in another, and haven't used it in some time. It was last set up in my Forster Co-Ax press and hasn't been touched since, so I expected headspace to be 'close'.

Fired case headspace measured 1.5610" using Sinclair 20 degree insert in a comparator body (all my barrels are set using the same Forster headspace gauge, so that is a very common and expected reading) on my Mitutoyo digital calipers.

Lubed up the case with Redding/Imperial sizing die wax and ran it thru the press. Headspace measured 1.5585". Great, no biggie. Going for more like 1.560", so I loosened the die ring and backed it off a bit, locked it down and lubed another case and got 1.5590"... not what I was expecting. Backed off some more, next case read 1.5585". Backed it off a bunch more... 1.5585". Backed off a full *revolution*... 1.5590". And yes, I was going the right direction as you could visibly see the change in the amount of neck sized by the bushing at that point. I returned the die to the original setting and locked it back down.

Now for the fun part. The cases are actually a bit *harder* to chamber after being sized than straight out of the gun.

I'm not quite sure what to make of this... whether I'm doing something wrong (kinda doubt it, but its happened once or twice before ;p ) or if something is wrong with the die. The easy solution is to try a different die - I've got enough of them around here but I'll have to swap some parts around because of the PPC-sized flash hole - but I'm curious as to whats up with *this* die in particular.

Any suggestions?

TIA,

Monte

 

[Rtheurer]

I bet your not even getting contact with the shoulder and the Chamber is quite a bit larger than the Small base FL sizing die. Thus squeezing the shoulder in and that in turn is pushing the shoulder of the case OUT ward or stated diffrently making the case longer. kinda like rolling bread dough on a counter top.

Just Curiuos. Measure the sized Case right at the shoulder Body Junction and the Sized case in the same spot.

Squeezing it down in the body and making the cases longer.... ( Maybe)

RT

 

[22BRGUY]

Might be reading this wrong but is the die touching the shellholder?

 

[memilanuk]

RT,

If the body is getting squeezed (most definitely) by the SB die and moving the shoulder forward... why is the headspace dimension not showing it? Not arguing, just askin'...

22BRGuy,

Its a Forster Co-Ax... there is a two-piece shell plate, not a shell holder as you might be thinking of... but no it's not *quite* touching as near as I can tell. Definitely not when I screwed the die out a full revolution!

Thanks,

Monte

 

[BoydAllen]

First of all did you survey the "headspace of all the fired cases that you sized? Secondly, it has been my observation that cases to not reach their maximum "headspace" with only one firing. I suggest that you do another test with some new brass of the same type, and the same die. Number each case with a permanent marker, and make a chart, showing the unfired, and fired "headspace" of each case. If your cases got tighter after sighting the shoulder probably moved forward during sizing, because it was short of full chamber potential and then got squeezed by the die, but the die was not low enough to locate the shoulder during the process. Personally, I do not like headspace comparitors that have inserts cut to shoulder angles, much preferring something designed to make line contact around the shoulder, such as the Stoney Point, now Hornady design. If your shoulder was telescoped slightly by sizing that did not fully move it back and determine its angle, it may have ended up at a slightly different angle than the insert. What I like to do is to fire a single case, neck sizing only, with relatively hot loads, until its datum to head dimension ("headspace") does not increase. At that point, I record the datum to head dimension for that rifle, and set bump in reference to that dimension. Most of the time, when I have to work with once fired brass, I set the die so that the shoulders are where they came out of the chamber when fired, and since they will vary, I check several, try the longest in the rifle, and if it is not tight, use that dimension.

 

[memilanuk]

Hello Boyd,

You might be onto something there... I've got a Hornady/Stoney Point headspace comparator around here somewhere; I'll dig it out and try it when I get home tomorrow. Should be interesting to see if it shows the same story for headspace fired vs. sized.

Monte