headspace variance on fired brass

[TackDriver284]

I felt several chamberings that felt real snug on the .308 and fired all loaded rounds. When I measured the headspace on the fired brass ( to bump .002" on the Redding body die ) and there was a variance of .003" I have not experienced that before and so I put the whole batch of brass through the body die and bumped back .002" and neck sized for the next loading.

What would be the issue of the .001" - .003" variance between fired brass?

 

[TackDriver284]

Side note, all brass is same lot, its Lapua brass and all fired 6 times.

 

[Dwh7271]

Same headstamp brass?

 

[TackDriver284]

Same headstamp brass?

Yes, same lot of Lapua.

 

[desertcj]

How are you measuring? What tools? 6 loading may be time to anneal if you haven't.

 

[TackDriver284]

How are you measuring? What tools? 6 loading may be time to anneal if you haven't.

Measuring with the Hornady headspace gauge and I just annealed this batch prior to firing It was never annealed until the 5th firing.

 

[desertcj]

What type of calipers? Some are much better than others.

 

[ElmerThud]

Brass even from the same lot, as it's extruded will have variations of 'springback' right from new, so it's quite normal to have .001-.002" variation in fired case headspace measurement.
Especially if you're using an averagely inexpensive vernier.
.003" does seem rather a lot of variation though.

Are you measuring with fired primer in or after decapping?
After decapping is the correct way.

The Hornady measuring tool is OK, the RCBS Precision Micrometer is better.
I haven't tried others, but I'd bet Sinclair is good too.

Take an overall average of the fired case headspace dimension then F/L resize to that dimension.
Good luck.

 

[TackDriver284]

What type of calipers? Some are much better than others.

Digital RCBS, its pretty much accurate and consistent to me when I tested the caliper's consistency on the same fired brass so I don't believe the issue is with the calipers.

 

[TackDriver284]

Brass even from the same lot, as it's extruded will have variations of 'springback' right from new, so it's quite normal to have .001-.002" variation in fired case headspace measurement.
Especially if you're using an averagely inexpensive vernier.
.003" does seem rather a lot of variation though.

Are you measuring with fired primer in or after decapping?
After decapping is the correct way.

The Hornady measuring tool is OK, the RCBS Precision Micrometer is better.
I haven't tried others, but I'd bet Sinclair is good too.

Take an overall average of the fired case headspace dimension then F/L resize to that dimension.
Good luck.

I decapped all the brass with a Lee Decapper, then measured it. I measured them several times to make sure and the measurements are as I noted above.

I chambered 3 pieces of fired brass to see which would chamber easy and smooth without a snug fit. The one that chambered perfectly was 1.622", the 1.623" chambered a teeny snug, but not much. The 1.624" was a bit snug, so I bumped to 1.621"

 

[greenheadcaller]

I felt several chamberings that felt real snug on the .308 and fired all loaded rounds. When I measured the headspace on the fired brass ( to bump .002" on the Redding body die ) and there was a variance of .003" I have not experienced that before and so I put the whole batch of brass through the body die and bumped back .002" and neck sized for the next loading.

What would be the issue of the .001" - .003" variance between fired brass?

Tack ... I think you likely gtg here imo as it relates to variance of fired brass....that variance isn't bad imo if that is your extreme spread and most were in the middle. So I am going to ignore those for this response.

But that typed, one thing you typed did catch my eye and might be worth thinking about...and is what I will focus my answer on.

That is, your first sentence suggests they weren't all the same headspace or size going in (and the snug chambering of some but not all would have more of my attention then your close measurements coming out).

First place I would look is your expander ball (or whatever your die uses to resize inside neck) and consistent lube inside neck. Assuming you used your new FART before annealing as you stated.... your necks are cleaner (less slick) than they have been, and brass is more pliable....so making sure inside necks are consistently lubed matters a bit more. My guess (and it's just a guess)...is a few of them might have gotten stretched when expander drug back out.....causing the snug chamber.

Second place I would inspection of the sizing die (neck or otherwise, whatever you used). Clean her up good and go at it again.

Lastly...I would anneal them all again before you size them the next time. IMO (as you know I anneal every reload so I have a bias), your 5 fired 308 were hardened and needed it....some may have annealed and some may not of quite gotten there (which is ok, you would rather under than over anneal)....so they sprung back from sizing just a touch differently. Again, this is not a big issue as over time, if you anneal more often (not waiting for 5), you will catch those that didn't quite get there the next time. ((Conversely, over annealed brass will also cause sizing issues amoungst other things, because it will stretch all over the place....likely not the case here, as I know you used tempilaq and stayed on the conservative side....just saying))

hope this helps ... and again, all just guesses

(Ok, lastly lastly this time ..lol... If the snug chamberings were at the end of the session, a long shot possibility could be chamber was simply getting dirty..but I am reaching a bit on this possibility)

 

[ElmerThud]

Brass even from the same lot, as it's extruded will have variations of 'springback' right from new, so it's quite normal to have .001-.002" variation in fired case headspace measurement.
Especially if you're using an averagely inexpensive vernier.
.003" does seem rather a lot of variation though.

Are you measuring with fired primer in or after decapping?
After decapping is the correct way.

The Hornady measuring tool is OK, the RCBS Precision Micrometer is better.
I haven't tried others, but I'd bet Sinclair is good too.

Take an overall average of the fired case headspace dimension then F/L resize to that dimension.
Good luck.

I decapped all the brass with a Lee Decapper, then measured it. I measured them several times to make sure and the measurements are as I noted above.

I chambered 3 pieces of fired brass to see which would chamber easy and smooth without a snug fit. The one that chambered perfectly was 1.622", the 1.623" chambered a teeny snug, but not much. The 1.624" was a bit snug, so I bumped to 1.621"

I'm assuming Mark, when you chambered these cases you mention above, you did so before resizing and after decapping. So electing to bump to 1.621" is your chosen nominal resizing dimension. You can always adjust after the next firing if you think appropriate.

A good move as has been suggested, is to bronze brush the inside of case necks and ensure there's a touch of lube there to ease the process when resizing. Not teaching you to suck eggs here, but its definitely worthwhile when you want to work to close tolerances.

There's other stuff can be done if you want to get supercritical with brass prep. but I for one cannot shoot any better for all the brass prep and care I utilise.
But it does make me happy knowing I produced the best cartridge I can.

Now, I must go, I have an appointment with some stags in Scotland tomorrow & for the next 2 1/2 weeks. (Driving the 300 miles in an hour so time) The rut is about to start so my friends and I are going to use some well prepared ammo to take few. We're hoping to pull 1 1/2 tons of venison off the hills.
Cheers, ET

 

[greenheadcaller]

(Good luck Thud, have fun and be safe...we want pics)

 

[TackDriver284]

Greenhead, Thud and all, thanks for your advise and I'll keep ya'll posted. I'll make sure all cases are annealed, prep and headspace are correct before loading and clean the barrel and chamber on next trip out there. Hopefully fix this minor issue, its not much of a big deal but I love to straighten out the little wrinkles.

Forgot to add, Thud,,,good luck on your trip and stay safe out there and bring home the meat.

 

[drakehammer]

As was mentioned previously...anneal every time. I bet things will get tighter for you.


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[TackDriver284]

As was mentioned previously...anneal every time. I bet things will get tighter for you.


Sent from my iPhone using Tapatalk

I'll do that, thanks Drake.

 

[kraky1]

Medium to light loads will also get you varying headspace. At least it has for me. Near max gets me a more consistent headspace but certainly is not a reason to do it...lol

 

[ElmerThud]

Ha well thanks for the good wishes for hunting. Just got back home & the final weight check was 1.2 tons of dressed venison with seven stags down.
No decent heads on them to speak of, but it was magic to listen to them roaring their challenges out.
Truly wonderful.
Cheers ET