How much is too much?(fire forming) Update

[K22]

I measure case head space with a bump gauge and caliper BUT, because measurement variations are possible, I always check the die setting by checking a sized case in the rifle chamber. This does not need to be done all the time but it's a good idea to do it on initial die set up then periodically after cases become hardened with repeated firings and sizings.

Removing the fire pin assembly greatly aids in obtaining a more precise feel of the case fit in the chamber. A sized case should chamber with slight (light) resistance, i.e. the bolt dropping down about half way then applying a light effort to close it. This is the way it was done before there were gauges. The rifle chamber is the ultimate gauge for assessing if the case is correctly sized in my humble opinion.

I'm still an advocate of measuring shoulder bump but I like to spot check the case fit in the rifle chamber to verify that my die setting is producing the desired shoulder set back. I prefer closer to .001" set back but .002" is not excessive and most of the time my set back measurements range from .001 to .002" in some rifles with some brands of cases.

I always carefully check cases after firing for initial signs of head separation which I've never encountered with full sizing using a slight shoulder bump.

 

[MUP]

Yes sir, I measured the factory ammo to the shoulder before firing, and the difference was between .006"-.008" from case base to shoulder. After a couple of firings, the shoulder had stretched out that far and was consistent on all the cases I had loaded and fired up until this point. I'm pretty sure they have reached the chamber dimension at this point, however I could not swear to it. I'll advise once I get the HS gage and check the clearance. Thanks again everyone for all the very helpful advice!

 

[Ned Ludd]

In my hands, cartridge base-to-shoulder (CBTS) measurements with Lapua brass increase .005" to .006" on the first firing with .308 Win Palma brass, and .007" to .008" with .223 Rem brass. I bump the shoulder back ~.0015" on all subsequent firings and have never had a problem with case head separation. So even though the CBTS dimension may increase substantially on the first firing, it doesn't seem to be an issue on subsequent firings as long as you only bump the shoulders back .001" to .002". Lapua brass seems to have a fairly thick case wall relative to Hornady or some other brands, which might be a contributing factor to better longevity. However, I am aware from anecdotal evidence that even Lapua brass can experience case head separation within 3-4 firings if the shoulders are bumped back to the original [virgin] dimension after each firing (i.e. bumped .004"+ each firing).

As has been mentioned, you may need a combination of being absolutely certain you are only knocking back the shoulders the minimal amount necessary to ensure proper chambering, and/or switching to a different brand of brass that can withstand that initial "stretch" a little better. The region where case head separation occurs is at the point where the thicker brass in the case head tapers/thins out rather abruptly to the much thinner standard wall thickness, which is a weak spot when repeatedly stretching and compressing the cases longitudinally. If you haven't already done so, it might also be worth checking to see whether you can easily re-chamber a piece of once-fired brass. If so, you might be able to get away from moving the shoulder at all on the first re-size. Regardless, whatever you can do to minimize the repeated stretching/compression of the brass after the first firing may be of benefit to help mitigate this issue.

 

[Uncle Ed]

I have headspace gauges for most of my rifles, "BUT" all they tell you is the bolt will close or not.

"BUT" you do not need a headspace gauge to find out how long your actual headspace or head clearance is.

1. Measure a new or fired case from the case mouth to the base of the case and write it down.

2. Now take a fired spent primer and start it into the primer pocket with just using your fingers.

3. Now chamber the case and let the bolt face seat the primer and eject the case.

4. Now measure the case again from the case mouth to the base of the primer and write it down.

5. Now subtract the first measurement from the second and this is your head clearance.

NOTE, the amount the primer is protruding is how much shorter the case is than the chamber headspace. If you use the primer method you can join the cheap bastards club and be a lifetime member.

If you look at a SAAMI cartridge and chamber drawings the headspace is listed as min and max, and the average rifle has .010 between min and max.

https://www.forsterproducts.com/product/rimmed-and-belted-headspace-gages/
If a rifle closes on a GO gage, the rifle chamber will accept any ammunition that is made within SAAMI (industry standard) specifications. If a rifle closes on a NOGO gage, the rifle chamber might have excessive headspace. Most gunsmiths chamber a rifle’s headspace between the GO and NOGO dimensions. If a rifle closes on a FIELD gage, the rifle chamber is dangerously close to or already over the SAAMI specified maximum chamber size.

 

[M-61]

lubricate the cases with something like Hornady One Shot Cleaner & Libricant, but loads should be more moderate if you are going to do that to prevent excessive bolt thrust

This is one step I would Not recommend.
Moderate load is a relative term and lubed cases will produce a dramatic effect on bolt thrust.
Proofing Lee Enfield's, the Brits fired normally, then doubled the load, and the final was a lubed case. If it held together it was stamped as good. Once the case can not 'grab' the walls of the chamber strange things happen.

 

[Uncle Ed]

This is one step I would Not recommend.
Moderate load is a relative term and lubed cases will produce a dramatic effect on bolt thrust.
Proofing Lee Enfield's, the Brits fired normally, then doubled the load, and the final was a lubed case. If it held together it was stamped as good. Once the case can not 'grab' the walls of the chamber strange things happen.

The British proof-tested the Enfield rifles with two "lubed" proof cartridges. If the rifles headspace increased .003 or more the rifle failed proof testing. The European CIP to this day still uses two proof cartridges when testing new firearms.

And my point like M-61 stated is a lubed cartridge can double the amount of bolt thrust of a dry cartridge and chamber.

For any of you who doubt what has been said the British used the base crusher system. Meaning the actual pressure and force delivered to the bolt face.

Cartridge Pressure Standards​

http://kwk.us/pressures.html

Under the British base crusher standards described below, proof loads ran 30 to 45% above normal. To maximize breech thrust, proof cartridges were oiled before firing.

In Britain, a third set of crusher standards were developed, using a "base" crusher. The crusher was a short, thick tube placed behind a piston at the base of the cartridge, and the firing pin passed through the center. The cartridge case was well oiled before firing, to minimize cling to the chamber walls

Below from the 1929 British Textbook of Smaal Arms.

 

[Webster]

The point I'm driving at is, that if the goal to increase loadings per case is by bumping the shoulder back .001"-.002" to keep from working the brass too much, is it feasible that this initial stretching of up to .008" may have been a key factor in these case failures?

I'm experiencing early signs of case head separation in my Ruger Precision Rifle in 6.5 Creedmoor. 2x loaded from factory brass and pronounced ring and groove just above the base. I checked my other fired cases to the shoulder and compared them to some of the factory ammo dimensions and found a difference of between .006"-.008". That seems to me a huge stretch initially for fireforming, isn't it? Anyway, I checked my headspace and it's right at .003" using the primer/bolt method. Part 2 of the story: I've shot some 140 gr ELD-Ms with no issues so far, 3x fired, but the issues I'm having are happening with the 153 gr ATips at Hornady max recommended load data (42.9 gr Hornady Superformance, started mid range and worked up). Am I pushing these too hard, or is the extreme length the brass is stretching at fireforming playing more into this, or a combination of both? Any insight appreciated.

MUP

Sounds like you are using the max load from the Hornady data and you think it's OK because of easy extraction and no signs of pressure on the primers. Did you measure case head expansion .200" above the extraction grove? You want to continue shooting max loads and solve the problem by bumping the shoulders? If it was me I would back off at least 1 grain of powder and see if the problem goes away. I would always assume it was excess prressure until proven otherwise. You cann't blow off the fact that you are shooting max loads. If the cases had insufficient hardness other people would be complaining about the problem. You are probably the only one. You should be loading for best accuracy and not trying to put as much powder in the case you can get away with. I get over 20 reloads from my cases with good speed and accuracy for GH hunting.

 

[Brians356]

This is one step I would Not recommend.
Moderate load is a relative term and lubed cases will produce a dramatic effect on bolt thrust.
Proofing Lee Enfield's, the Brits fired normally, then doubled the load, and the final was a lubed case. If it held together it was stamped as good. Once the case can not 'grab' the walls of the chamber strange things happen.

I only lube cases when Ackley improved fireforming bulletless, with about a 15% capacity charge of Bullseye and a pistol primer. No case filler. The lube induces the shoulder points to fully form on first firing. Unfortunately my AI chamber is cut a little long, not providing a crush fit on unfired parent 22-250 cases.
-

 

[MUP]

Sounds like you are using the max load from the Hornady data and you think it's OK because of easy extraction and no signs of pressure on the primers. Did you measure case head expansion .200" above the extraction grove? You want to continue shooting max loads and solve the problem by bumping the shoulders? If it was me I would back off at least 1 grain of powder and see if the problem goes away. I would always assume it was excess prressure until proven otherwise. You cann't blow off the fact that you are shooting max loads. If the cases had insufficient hardness other people would be complaining about the problem. You are probably the only one. You should be loading for best accuracy and not trying to put as much powder in the case you can get away with. I get over 20 reloads from my cases with good speed and accuracy for GH hunting.

Ok, here's my update guys. First off, this load IS producing .5" groupings at 100 yds, and I worked up in .3 gr increments. That said, I've made more measurements and have more info to share. First off, I was using COAL to the tip (2.800") as my starting length, without measuring the actual distance to the lands in this particular rifle. Secondly, I AM a card carrying member of the CBC(cheap bastage club) and did use the spent primer method initially to measure the headspace. Now, I received my FIELD headspace gage and was unable to close the bolt on it, so my question about headspace has been satisfied. Also, I finally measured my actual distance to the lands, and found that I was at a .075" jump with the 2.800" oal cartridge measurement. So, I've set my seating depth for a .020" jump, and will now begin again, starting midrange of the powder charge scale, and searching for accuracy nodes. Still a work in progress. I appreciate all of your comments and advice guys, it's helped me get to this point and I'm grateful for your help!