different headspace measurements on fired brass

I felt several chamberings that felt real snug on the .308 and fired all the 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?

Is it all the same head stamp (same brand and lot)? It could be a small variation from piece to piece. It could also be a slight variation on the case head. I've had some pieces of brass that had the rim ever so slightly bent, and would throw off a head space measurement by a few thousandths.

I've seen .001"-.002" variation. I size to the shortest one. I'm not worried about 1 or 2 thou, though. Size it to the shortest piece you are measuring, and call it good. Just chamber check your brass after sizing to make sure it chambers smooth.

I'm new to the reloading game, but I will say that from an engineering standpoint, .001" is just absolutely nothing. It's hard to control anything to that level. Some of this reloading equipment is really capable of top-notch precision, but it's very difficult to understand how small that type of distance really is. I'm amazed that you guys can control this stuff as well as you do.

If you think about, the typical max to min headspace on a go, no-go gauge is .006" (sometimes .007"). A few thousands difference in the head space area is VERY important.

I believe it. It's just very impressive to me that they've created affordable tools that can control dimensions to that type of precision.

Yes Chad, its all the same headstamp, its Lapua brass, all the same lot, fired the same number of times. Fired 6 X's. Most are .001 to .002 off, a few are .003"

Well, after so many firings, you can get some brass flow in various areas. I'd call it good if it was within .002", honestly.

I understand where you're coming from. I've been reloading for nearly 20 years, and 10-20 thousandths of an inch doesn't sound or look like much of anything. But when you're dealing with firearms and ammunition, it might as well be miles. It's amazing how much difference a couple thousandths will make, be it a round chambering or not or the difference in safe or unsafe.

Thanks Chad.

TD, have you annealed? That would be by first thought. After several firings the malleability of the brass will not be as consistent and you can get differences in spring back after sizing. One other thing to check if your are loading up near max, particularly if you have been shooting in hot weather. A slight ejector swipe can give you inconsistent measurements depending if your caliper is on the mark or not. A few thousands isn't much but examining the case head through a magnifying glass will allow you to see it.

Yes, I annealed prior to firing them and they were under max load with 44.4 grains of Varget at 2,770 fps with no pressure signs at all, no ejector swipe. The weather was cooler this time out at 75 degrees compared to 90 prior to that. Even did all case prep prior to firing. That bugs me.

Were you measuring head space on a fired primer, or after decapping?

If with a fired primer in the pocket, and if there is any flow back, on the primer, around the firing pin strike it will throw off your head space measurement.

One other idea...if this is new brass, it may not yet be fully fireformed to your chamber.

I used the Lee decapper first and decapped all primers and measured after.

Brass is on 6th firing.

How clean is your bolt face, and how clean is your chamber?

sounds weird but this is a good idea when you are talking thousands of an inch.

Boltface was clean, barrel was cleaned and not sure about the chamber being clean, I'll take a look at it. I'll run a mop thru the chamber next time out.

Long shot reason but worth asking.

Clean all the case lube off the cases? Or were some more slick than others?

Depending on the rifle When the cases are sized say with a .002 shoulder bump, when the firing pin hits it can drive the case forward that amount or a little more since brass is springy there might be another thousandth or so in the head space. Ignition starts and pressures build. With a slick case it gets pushed back harder against the bolt face and can stretch a little more than a case that grips the chamber tightly.

Cleaned necks prior to loading as well.

Reading your posts it sounds like you are pretty thorough. If you are using a comparator with headspace bushing on your caliper, there may have been a little slack when you tightened things down. .003 is not much slack. Good luck working it out. It would gnaw on me till I figured it out too. In the end better consistency and chambering is why a lot of reloaders seeking precision, go with a partial full length size with a minimal shoulder bump every cycle. That is an old debate among loaders with pros and cons to both methods that I am not trying to get started.

It's seven weeks until deer season. We got time.

LOL. I'm an old guy that's walked both paths.

What caliper do you have? Are you 100% sure the instrument is accurate?

Yes Fireman, I tested it several times and right to the point. RCBS digital.

Ok, just throwing darts at this problem hoping for a bull eventually.

Thanks FM for helping out. I'll figure it out sooner or later.

Ok Tack Driver, one more stab at it. It sounds like the .002-.003 difference was there before you shot. The hard to chamber cases were already at a crush fit in your chamber. So either to many cycles between a shoulder bump or if you were neck sizing with an expander ball and the inside of the necks were not lubed, combined with nice soft brass after annealing, let the shoulder come with the expander ball a few thousandths on some of the cases. Or a combination of both. I think that was my last dart.

Pretty sure the whole batch was annealed and neck sized. I have not gone to fire them yet, but full sized them all and bumped .002", but maybe I have not annealed it hot enough to get it to 700 -750 degrees to properly anneal after 6 firings. The brass indexed about second right after the paint cleared up with the 650 degree Tempilaq, maybe it has not annealed them hot enough that some cases are still hardened and not properly annealed. Not sure. If I anneal them each firing and I will get the 700 degree Tempilaq to check to see if I am spot on. I may have indexed a tad too fast. Hopefully find out soon.