Full Length sizing die struggles

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Full Length sizing die struggles

Post by ropedrag » Mon Jan 20, 2020 9:18 pm

Well with roughly 500 once fired casings I figured it time to clean and resize.

My standard work flow is decap with my Forster Co-Ax press
Run through a 20 min cycle in my sonic cleaner using Hornady One Shot Sonic Cleaner solution
Dry in my food dehydrator
Lube using the home brew case lube, as described here and elsewhere https://ultimatereloader.com/2017/05/09 ... case-lube/
Resize using my Forster 300 BLK full lenght sizing die
One more cycle through the sonic cleaner to ensure the lube is fully removed

My goal was to bump the sholder back .004, 4 thousands as I've read a great number of times this works well for semiauto. I measured a dozen or so fired casings ready to resize with my hornaday comparator to get a good strong average number to subtract .004 from.

I grab a case insert it, grab the handle and cycle stoping for a 2 count at the bottom, pull the case and measure. I then adjust the die turning it down towards the shell holder in small increments locking it off each time until the sized case measures to match my target number. So far so good.

I then grab another case and cycle it but the number isn't the same as the first by .002. Ok I figure the 4 cycles on the fist case maybe overworked it a bit, seems reasonable I thought. So one more die adjustment and I hit my target number, cool, ready to get after it, or so I thought. I size 5 more and stop to measure, all are different and by as much as .005. What the ....? So now I'm playing... or actually chasing my tail making die adjustments until I give up and screw it down to make contact with the shell holder and lock it off. With this the cases are coming out consistent in length and within saami spec, also checking ok in my wilson case gauge, but my shoulders are pushed back much more than I wanted.

So while this isn't a crisis and I can make good functional ammo with these cases which are now sized to new unfired size, I'd like to figure out what the hell I did wrong, not being able to get the shoulder bump I was after.

Any insight would be appreciated!

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Re: Full Length sizing die struggles

Post by rebel » Mon Jan 20, 2020 9:38 pm

Once fired - in how many chambers?
Fire form them as supers and go from there. You can't expect uniformity with 500 once fired cases.
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Re: Full Length sizing die struggles

Post by dellet » Tue Jan 21, 2020 12:24 am

First, you should set your die based in the longest case, your chamber is longer than that. Sooner or later after multiple firings they should all be that long or as Rebel said, longer. If they only grow .004” each firing and you keep setting them back the same, they will never get to full length.

You will never get a consistent base to datum on randomly sized brass unless the shell holder touches the ram. You can prove this by inserting a feeler gauge between the ram and shellholder, that space will vary and is why die manufacturers instructions are contact plus. If you set your die at firm contact without a piece of brass in the press, then insert a piece there will be a gap between the shell holder and ram. This is flex and slop in the press.
The brass you are trying to size is likely mixed headstamps, mixed lots, fired at various pressure or a combination of all or more.

This is a good investment, you can get the headspace setting you want, and have the die set up to contact the ram as it was designed.

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