Headspace Issues

[VarmLR]

Returning from a day on the range, I took back two .308 bullets from a batch of 40 using Lapua cases that failed to chamber, despite being full length re-sized.

 

I took the fire formed cartridges and using a Hornady headspace gauge comparator measured the twice fired Lapua cases, and compared those with some twice fired PPU cases. The PPU measured 1.624" average and the Lapua 1.6245 average.

 

I pulled the bullets and emptied the powder from the bullets that failed to chamber (Lapua 2F) and re-tried them in the chamber. One chambered with a little resistance felt and one did not. Before trying them I compared them on the comparator and they measured 1.625 and 1.627 respectively. Puzzled, I lubed the cases, and full length re-sized each (obviously after de-priming them!) but measurements were the same, if not about a thou more on one AFTER FL resizing yet they both chambered this time.

 

One still had some resistance (too much) on it so I decided (to write the cartridge off...that would not be used again) that the stiffer one, still measuring 1.627 on the comparator would be used to experiment. I turned the die in by 1/4 of a turn more (a full 9 thou in theory), re-sized the cartridge and measured again. STILL 1.627! This time though it chambered properly without any stiff resistance...as you'd expect with potentially a 6 thou headspace!.

 

Can I conclude then that the comparator gauge is not to be trusted as clearly, bumping the shoulders back on the die did result in a definite ease to chambering yet no difference at all was found on the comparator measurement? It's as though the comparator shoulder does not have the same profile as the chamber.

 

I would have suspected the exact opposite (ie the die was too long in the shoulder so not contacting the cartridge shoulder enough) as per this article, had the case not chambered easily after turning the die in. Anyone got any ideas? Looks like I'll need to be turning the Lee (pacesetter) FL die in by more than the recommended 1/4 turn from top of the ram position but as the comparator is not measuring any bump back I am not happy that I know exactly how many thou it's being bumped except that the die used a 14 TPI thread so from my quarter turn in to take up the slack perhaps I need to turn a further 5 or ten degrees? (ie up to 2 thou on the shoulder?). This all seems to assume too much though. Anyone had similar issues?

 

 

[bradders]

Sounds to me that you aren't actually bumping the shoulder but sizing the case sides (namely the base, and not enough at that)

If you put a case in a die it's the sides (body) that gets resized. As it reduces in diameter, and that brass has to flow somewhere....and that's towards the shoulder.

So it is common for cases headspace to grow until it contacts the dies shoulder, and that's when you can adjust the headspace

 

I hope that makes sense

[The Gun Pimp]

Headspace issues?

 

Your dies should be used to size YOUR brass so that it JUST fits YOUR chamber. Headspace is irrelevant - it is what it is - in YOUR rifle.

 

How do we do this? With a once-fired case (fired in your rifle) set up the FL die so that, with the firing-pin assembly removed from the bolt, the bolt will just 'kiss' a resized case when closed. Job done. May take two or three goes to exactly set up the die correctly.

 

Too many shooters try and use brass fired in another rifle and run into chambering issues.

 

I recently put a new barrel on for a guy who is an experienced FTR shooter. It was Match 1 of a GBFCA League shoot - he couldn't chamber the first reloaded round he took out of his box (using full-length re-sized brass from his old barrel).

 

He turns to me and says "What spec is that reamer you used - it seems a bit tight?") A fellow shooter was stood behind him and handed him a box of 308 rounds. "Try these - they are loaded with brand new cases."

 

They flew in - no resistance at all.

 

Moral of the story - new barrel - new brass - and never use brass fired in another rifle.

[VarmLR]

Thanks.

 

I had previously set the die up for my PPU brass (and set it up correctly) pretty much as per the Lee instructions as it happened. I admit that I hadn't re-set it for the Lapua brass as I wrongly assumed that as long as the outside dim's were the same (which they would be for fire formed brass) for the fired cases, then the die should be set ok but I guess the extra thickness of the Lap cases changes things as the expander has to force that extra brass somewhere. I'll re-set the die accordingly.

 

None of the above explains just why the shoulders bumped back didn't measure differently when I used the headspace comparison guage which was part of the original question. Not to worry, I'll sort it.

[VarmLR]

Sounds to me that you aren't actually bumping the shoulder but sizing the case sides (namely the base, and not enough at that)

If you put a case in a die it's the sides (body) that gets resized. As it reduces in diameter, and that brass has to flow somewhere....and that's towards the shoulder.

So it is common for cases headspace to grow until it contacts the dies shoulder, and that's when you can adjust the headspace

 

I hope that makes sense

 

Thanks for that.

 

I re-set it up today and it took a further 1/8th turn to bump back the shoulders. It's only the third firing (I said twice fired yesterday, but it's actually the third firing) so I was a little surprised that one or two hadn't chambered. However, all's sorted now. I usually check two different ways. First, I check using the bolt (firing pin removed) as per post 3 (have been doing this since I started reloading) so that only very slight resistance is felt on the bolt, then I check each one once sized using the comparator gauge to some fire formed cases. They're all now between spot on (ie to fire formed dimensions for shoulders) or headspace (max) is 2.5 thou. All lay between these values. 2.5 thou was the max turned in, and I've backed off so the average is now closer to one thou. Job done. That'll teach me to be complacent in future. Different brass, check settings!