Questions on headspace with new brass

[Sogan]

So I’ve got a question in regards to headspace with new Lapua brass and my gun which is a AI MKIII:

I use the Hornady headspace gauge on some old Lapua brass that has been fired by me several times (bought it as once fired so I don’t know exactly what length the headspace started at). The old Lapua brass measures 1.630 with the headspace gauge after being fired in my gun - I then bump the shoulders back .002 etc etc. I recently purchased some new .308 Lapua brass which will be used for the same gun and its current headspace measurement is 1.618 as it sits today, brand new. Will using my normal load really stretch the brass all the way to 1.630 on the first firing or is it going to take multiple times to get my “Fire formed” brass? Is there anything else I need to be concerned with in regards to having that large of a headspace difference? I’m assuming I can’t be the only one who has this big of a headspace difference starting out.

 

[308pirate]

You'll have a one time stretch then you'll be back to normal. There's 60 KSI of pressure in there, that brass will stretch in all directions to fit your chamber in one go. But that one-time expansion isn't going to create a dangerous situation like a case head separation. You'd have a problem if you did that every time you resized the brass, which you won't.

 

[spife7980]

It might take a couple firing to get it all the way there but I wouldnt fret it too much. You can go to a middle charge instead of a minimum and hopefully get a more compete blow forward. Some people also jam to make the additional pressure to fully push the brass forward and the case head against the bolt face. Myself, I do the middle of the road load when Im firing new brass but make sure you are aware of your pressure signs. After they are fired I would go ahead and bump them back .002 even if they arent actually all the way extended, it will be close enough to begin load testing as the majority of the difference has been resolved. Just check them on the third firing and see how much more they grew and adjust appropriately. You should be checking your settings on every firing though as good practice.

 

[Milo 2.5]

It might take a couple firing to get it all the way there but I wouldnt fret it too much. You can go to a middle charge instead of a minimum and hopefully get a more compete blow forward. Some people also jam to make the additional pressure to fully push the brass forward and the case head against the bolt face. Myself, I do the middle of the road load when Im firing new brass but make sure you are aware of your pressure signs. After they are fired I would go ahead and bump them back .002 even if they arent actually all the way extended, it will be close enough to begin load testing as the majority of the difference has been resolved. Just check them on the third firing and see how much more they grew and adjust appropriately. You should be checking your settings on every firing though as good practice.

I think you are right on needing more than one firing to get brass to chamber dimensions, but why bump the shoulders .002" ? Just run the brass in his setup die for his chamber, if a couple get bumped, so be it, most wont.

 

[MtnCreek]

If you have a FL die that's on the tight side, FL sizing prior to firing may push the shoulder a little forward. It would be worth trying a couple to see if they move.

 

[Milo 2.5]

If you have a FL die that's on the tight side, FL sizing prior to firing may push the shoulder a little forward. It would be worth trying a couple to see if they move.

I would not worry about it, shoulders on new brass rarely defined as fired brass, figure in the tool used to measure, usually the outer edge of the shoulder, and now the problem is non existent.

 

[MtnCreek]

^ That's a good point.

 

[spife7980]

I think you are right on needing more than one firing to get brass to chamber dimensions, but why bump the shoulders .002" ? Just run the brass in his setup die for his chamber, if a couple get bumped, so be it, most wont.

How do you set a die up for the chamber if you dont yet have a piece of brass thats at the maximum dimension to set it up with? I figure that by setting it up for .002 shoulder set back on once fired may actually be .004 from the absolute maximum chamber dimensions but it ensures a little more equal and uniform treatment of the brass which is what I value most.

Though now upon rereading he has already had stuff set up for his old brass so it shouldnt be too different and the same setting will very likely be adequate. He could probably see that his soon to be once fired is at say 1.626 as opposed to the old 1.630 measurement and know that he wont need to size it enough to move the shoulders. He could also see if it chambers without too much resistance and feel more comfortable by not bumping that .002. But I expect that some brass will vary from 1.625-1.629 so setting it up to bump the long ones back to 1.627 wont have any detrimental effects on brass life and will bring them back towards the same benchmark as the other pieces.

 

[JCCinOhio]

My experience has been what spife7890 said.. A mid load will get you most of the way, need an almost max load to get full expansion of the case. I started off with new Lapua .308 (1.618-1.621" HS) and went up in charges. I should have documented it, but I didn't... but what I saw was at the lower end the case barely grew, had to get into mid-upper range for better expansion, and max load (just before pressure signs) usually fully stretched it out. Haven't done this in a while, and just so happens I have some new Lapua loaded up, ready to shoot once it warms up a little (<10 degrees today).. I'll measure them along the way and see what happens. However I am starting off at 42.7gr (175 SMK) of IMR 4064 since I know that is a safe load from before. My max headspace is also right at 1.630".

 

[Sheldon N]

How do you set a die up for the chamber if you dont yet have a piece of brass thats at the maximum dimension to set it up with? I figure that by setting it up for .002 shoulder set back on once fired may actually be .004 from the absolute maximum chamber dimensions but it ensures a little more equal and uniform treatment of the brass which is what I value most.

I find that if you creep up on the shoulder bump setting slowly with once fired brass there's a point where the shoulder actually gets pushed forward and a case that previously would chamber with zero resistance will start to have effort on bolt close. I note that measurement and back off 0.001 or so, until there's no resistance on bolt close again. My personal thought is that hitting the right headspace or as close to it as possible is preferable to having everything the same but 0.004 back.

As to the original question as to whether 0.012 is too much headspace, my general opinion is that it's probably going to be okay if you treat it well after the first firing. I think the last couple chambers I've run virgin brass in were around 0.006-0.008 headspace from virgin brass and I didn't do anything other than load and shoot. Now if you're super OCD and you care about having the brass last 20 or 30 firings as opposed to 15 firings then jamming a bullet into the lands with a moderate charge to fireform will minimize case stretch and postpone any case head separation down the road. I don't think I've heard of anyone bothering to do that with 308 brass before though.

 

[918v]

I I think something is wrong with your rifle or your headspace gauge.

 

[Marksman10x]

Load the new brass, shoot it, then FL size it with your die that is already set-up. This is easy, too many on here want to overcomplicate everything!! Who cares how many firings it takes to completely fireform your brass--THAT DOESN'T MATTER EVEN IN THE SLIGHTEST!!! You already have your headspace info from the old brass, the new brass won't magically measure differently.

 

[308pirate]

OP, take you new brass and load it like you normally would. Nothing will happen to it, you, or your rifle.

I have to just wonder at how people here over think every single thing about this hobby.