Wanting headspace opinions

[Ackman]

I guess it just surprised me how much more the Lapua brass stretched compared to the Hornady. Thought I pretty much had my headspace dialed in already with the Hornady brass. Made some adjustments, and we'll see how they do. Hell I might just be going back to my original bump and say to hell with it. If it ain't broke, don't fix it kinda thing. SD's were in the mid single digits and it was shooting pretty good. It's that OCD side to me that just can't leave it alone.

if the fired caes chamber without having to lean on the bolt handle, you're fine. Don't get carried away with bumping shoulders.

 

[philip brousseau]

On a shorter fired case you could do the trick with setting a old fired primer long in the primer pocket and then close the bolt with it in your chamber, then eject it andmeasure it against the proud fired primer.

If you do fhis and it takes good effort to close the bolt headspace will be a few thousands less than the measurement you get on this case in my experience. I use this method when I need to.

 

[philip brousseau]

Just reduced headspace until you get a good fit

 

[D-4297]

You won't get a consistent "Bump" length on new Lapua cases , until around the third firing , if you are using a load comparable to , the load you'll be using normally . Even if you have some slight variations in case lengths , fire them at least twice , preferably three times from your "TEST GROUP" . Bet you'll find eight or nine out of ten have exactly the same datum measurement .
Since I shoot .308 TR and use Lapua cases , I also have a very good chamber , thanks to a slightly modified Manson 2017 TR Reamer , and I only Bump , .001 after the second firing . I don't even pay attention to the length on first firings , but I do anneal after every firing !

 

[Wild Bill IV]

To give a back story. The gun is a Bergara B-14 6.5 Creedmoor. I ran several boxes of ammo through the gun to break in the barrel, get some fired brass to check headspace, and just to see overall how it shot with different factory ammo. I then loaded up a ladder test using some of the once fired Hornady brass just in testing. Found a couple of charge weights I wanted to explore more, so I loaded up some additional rounds using the same, now twice fired Hornady brass to test these charge weights. Shoulder measurements were pretty consistent on the once fired Hornady brass, as well as some of the other brass I tested including Sig and Federal with the majority falling in at 1.4850. There were a few that 1.4855 and even a 1.4860.

With that being said, I close to bump my brass to 1.4835. I figured if the headspace was actually 1.4850, it would give still give 0.0015's clearance. And in the chance that most of the brass just didn't have enough pressure to fully fire form with the exception of a small handful. And that the 1.4860 was closer to the actual headspace. It would still only put me out like 0.0025. All was fine and dandy through the next couple of loadings on the Hornady brass I had picked to use for testing because I had more of it.

Where the questions appear was when I decided to test VV N555 in the gun. I had always planned on using my normal Lapua brass anyways, so I figured I'd go ahead and get new Lapua brass to test this powder. Loaded up a ladder test on it in 0.3 increments like I normally do from maybe a half grain over the books starting charge to 0.6 over the maximum charge weight so I could get an idea of where pressure was starting. Yes I know new Lapua brass can camouflage pressure signs pretty good, so yes I was checking everything closely. Brass looked good on the two max loads. No ejector marks, primers looked good, no heavy bolt lift, etc. All good.

Found a charge that looked promising, so I was going to load up a couple dozen at this charge weight to do more testing. Specifically at 300 and 500 yards. But before I loaded these I decided to check the shoulders on the once fired Lapua brass. The first one I tested came in at 1.4875. So I started testing all the Lapua brass that I had shot and ended up with a variety of results. The vast majority came in at 1.4860, but there were several as you can see in the photo that came in at 1.4865 all the way thru 1.4875.

I know this is long, so bear with me. My question is, do you think the 1.4875 is likely closer to my actual headspace? Like these are likely those rounds that were at max load or above? It's obvious I need to adjust my initial headspace I was using, but how far? I'm thinking that if the 1.4875 is the actual headspace, then make a dummy round at 1.4855 and verify that it chambers well. What are y'all's thoughts?

And y'all don't beat me up too bad in the comments. I normally use the cheap brass to get my headspace on other guns because it seemed to just expand easier than Lapua after a firing. This is the first time that I've had once fired Lapua actually stretch more than the cheap stuff. And sorry for the long post.

Let the rifle/case combo tell you the true headspace!!! After all, the true test is how we want the case to conform to the true chamber cut of the rifle!!!!

I find the true headspace by working up to finding the max pressure loads (2 reloaded cases each with 0.1 grain increments in powder charge at or past max depending upon pressure signs) and using the bump comparator at the range with cheap brass!!! There is a point of true headspace (continuous respectable measurements without some changes in bolt lift) and compression headspace (+0.0005" change in previous repeatable measurements)!!! The difference of 0.0005" (physical property of the compressiblity factor of 70/30 brass or limits of true physical spring back of cartridge brass after compression)!!! The slight increase of bolt lift is the start of the compression factor!!! Use the slightly compressed, fired brass to set your FL die!! Move the die down, without the deprimer/expander stem, until the heavy bolt drop is gone, that is your max free headspace!!! Set one empty die formed case at max headspace aside for reference and calibration purposes (zero or minimal bump setting for the comparator)!!!!!!!!!!!!!!!!!!! I know quit a little bit of measurement rules and techniques and induced error of analog to digital electronics (Physics level, not technical level)!! Periodic checks of calibration are required for precision of measurements (especially with analog to digital measuring devices)!!!!

I don't know what type of curriculum of shooting you are reloading for, but I prefer the old, BR modified neck size only approach (using high end FL dies) for precision, long range hunting (also called beanfield shooting in the days done by)!!! Therefore, I prefer 0 bump or a slight compression on the bolt drop (</~ +0.0005) for those long range, one shot kills on big game, using Hunter's Ethics for taking, or passing the shot!! After all, they are God's gift to man!!! Treat them with respect, and minimize their pain for your God given bounty!!!!

Words from a retired Industrial Physicists that has been reloading for over 50 years!!!