View Full Version : Headspace one more time
November 15, 2012, 05:58 PM
I have an old Spanish Mauser in 7X57 I use as a trunk gun when traveling the backwoods of Utah. I have checked the headspace and it is barely acceptable. After test firing some rounds carefully I have checked the primers and they are protruding about .008 to .010. I am somewhat worried about a blown primer but they seem to have quite a bit of primer body left before exiting the case and no signs of excessive pressure. I am using the old Federal 175 g. RN. I would appreciate your take on this problem as it is a good do all rifle.
November 15, 2012, 08:32 PM
It sounds like your reloads might actually be too light and the case is not coming back over the primer. You might also be setting the shoulder back too much when resizing the case. If your rifle headspace gauges OK, I wouldn't worry about it.
November 16, 2012, 11:42 AM
Bob Thompson, concerns? Your concerns warrant attention and an explanation, the failure of the primer to seat when fired means there is a difference in length between the chamber from the bolt face to the shoulder of the chamber and the length of the case from the head of the case to its shoulder. Reloaders do not have a term for this anomaly (Anomaly: something that does not ‘nomaly’ happen).
I measure the difference in length between the case and chamber, I want to know what effect the chamber will have on the case when fired, reloaders fire first to form, I form first then fire. You have low pressure loads, if the pressure was higher the primer would not protrude, it would be flush with the head of the case.
I am the fan of reducing travel time, I off set travel time with the length of the case, With reduced loads you can not form a case, the story goes something like, the bullet, case, powder and primer run to the front of the chamber to avoid the primer strike, once the shoulder hits the shoulder of the chamber the firing pin is said to crush the primer. With the shoulder of the case against the shoulder of the chamber things get serious, hot, high pressure metal cutting gas builds up and expands the case, the case when expands it locks onto the chamber wall, when this happens the case head is not supported until it hits the bolt face, and there is the problem, you case head is not being driven back to the bolt face, if it was!!!! your case would be stretching between the case head and case body, allowing the case to stretch between the case head and case body leads to incipient case head separation.
Remedy: reloaders can not get the concept of moving the shoulder forward, bump? They are all bumpers, they never talk about moving the shoulder forward without firing, and that is a bad habit, as I have just described “I am the fan of cutting down on all that case travel” and firing a case that is shorter than the chamber results in the case stretching between the case head and case body.
Case forming: I form 7MM57 cases from 30/06 cases, I form 7MM57 cases from 8MM57 cases, I form first then fire. Or I could form 30/06 cases that would chamber in my 7MM57 chambers, THEN THROW THE TEST CASES AWAY! The most important information I need to know is the length of the 7MM57 chamber from the bolt face to the shoulder of the chamber, once I know the length of the chamber I can adjust my dies to my shell holder in my press to avoid excessive sizing (reducing the length of the case from the head of the case to its shoulder), Yes I could purchase a go-gage, I could purchase a no go-gage, I could purchase a field reject gage, I choose to take advantage of the design of the press, it has threads, my dies have threads, my dies are adjustable, I am not hard headed, I use the companion tool to the press, the feeler gage (thickness gage) to adjust my die off the shell holder when adding length to the case.
Again, I have an Eddystone M1917 that has a chamber that is longer by .016” that a minimum length case, that would be the same thing? as being .011” longer than the perfect go-gage length chamber, not a problem, I form 280 Remington case to 30/06 cases, with an additional .051” case length added to the 280 Remington a good reloader can not miss, the rest? (the M1917 chamber is .002” longer than a field reject gage). It is possible to measure the length of the 30/06 chamber in the M1917 with a 280 Remington case.
I went to Alabama, knowing there was a prblem with ammo chambering I had to devise a way to check it out. I left with the instructions I was not going to fix, repair or build any computers, I was told I was not going to build and or repair engines, I was not going to build and or repair a rifle, I was told I was going for a visit. So I purchased a new box of Winchester 7mm57 ammo, every round in the box chambered, I brought back 4 boxes that would not chamber. After returning home I dug out 2 7mm57 rifles and a barrel, I attempted chambering the 4 boxes of ammo that would not chamber in the rifle in Alabama, 1 round of the 40 offered resistance to bolt closing, the rest chambered. The rifle in Alabama has a chamber that is shorter by .002” than a go-gage length chamber, I will measure the length of the cases that would not chamber in the Alabama rifle, no, I do not use a head space gage, I do not use a case comparator, back to the extra barrel, no matter the hype about the tools, it is about understanding the tool, I can use a barrel to measure the case head protrusion to determine the length of the case.
I returned home with a computer, I had to sneak up on that one to get it started.
November 16, 2012, 12:02 PM
“I have checked the headspace and it is barely acceptable”
“If your rifle headspace gauges OK, I wouldn't worry about it”
Head space gages, we all know the go-gage when chambered will allow the bolt to close by .005”, barely acceptable would mean the chamber is short, meaning??
If the gage is a no go-gage and the chamber is ‘barely acceptable’ the chamber is longer than the case by .009” FROM THE USUAL PLACES! Back to my M1917, a field reject gage will chamber and allow the bolt to close by .002”, again, not a problem, I have a 30/06 form/trim die, I form 280 Remington cases to fit my chamber, and all the rest of the 30/06 chamber in the world, I form cases from –.012” shorter than minimum length cases, I form cases out to infinity, or a more practice .016” longer than a minimum length case in thousandths, again, that is 26 different length cases from –12 to a +16.
November 17, 2012, 02:03 PM
Bob, I've seen that same thing happen with .270's, .308's as well as .30-06 and 8x57 Mauser rounds. Each and every time was caused by not enough powder in them; I had reduced my starting load too much.
I've also seen it happen with factory and military ammo loaded to normal max safe pressures but fired in an M1909 Argentine Mauser whose barrel had been reamed with a .30-06 chamber. Its .303 bore and .312 bore diameter didn't cause enough pressure for the .308" diameter .30-06 bullets.
While your barrel may be OK headspace wise, I'd have it checked for excessive throat erosion and bore wear which can cause the problem with factory ammo.
November 17, 2012, 05:40 PM
I have checked the headspace and it is barely acceptable.
What's "barely acceptable"?
I'm trying to figure out what all this extraneous discussion is about.
Did it pass a field gauge test, or not?
If the rifle has excessive headspace- usually worn bolt lugs/receiver- don't shoot it. It's mechanical wear of the lugs and mating surfaces on the receiver that increase headspace over time- not throat erosion/chamber dimensions.
You can try swapping bolts to decrease the distance from the boltface to the cartridge datum line.
November 17, 2012, 05:49 PM
If you're checking headspace by examining fired cases, you're not doing it right.
Remove the extractor from the bolt and insert a "go" gauge into the action. It should close.
Now try the same with the "no go" gauge. If it closes, it's probably over SAAMI specs.
If it closes on a "field" gauge, the barrel shank must be shortened to reduce the headspace and that means lathe time by the gunsmith.
November 21, 2012, 11:57 AM
Update: thanks to all who replied. I do not have go-nogo guages but after checking and measuring very accurately the fired and unfired cases I find with these Federal Blue box 175g. cartridges they are well under what four of my reloading manuals call on shell specs. Here is my findings:
From the manuals: OA length: 2.235 My cases both fired and unfired: 2.225
" " " Head to neck: 1.895 " " " " 1.875
" " " Base diameter: .471 " " " " .464
Naturally the neck is slightly bigger after firing.
Now my measurements are pretty accurate but even if I was off slightly they show a consistant difference and I believe Federal produces these cartridges well under reloading specs and pressure to chamber easily in the many different chambers of mass produced military rifles yet still be safe. I will be checking some other cartridges from Midway in the near future but I believe what is happening is when firing, with a fairly heavy firing pin spring in most military rifles, the case is moving forward the .010 I'm seeing in the primer extrusion. As you can see in my fired cases the base show no signs of high pressure but just the opposite, a case that feeds easily. With my AR and M1 Garand I'm reloading for I use RCBS small base dies to accomplish the very same thing. I believe I'm safe here but am I assuming too much and thanks again guys?
November 21, 2012, 07:47 PM
You're correct that the case is driven forward by the fp, this is in all rifles, not just military ones...
Also correct in that primers become partially unseated at detonation. However, your primers should reseat after detonation and case head stretching.
The fact that your primers are not reseating is indicative of excessive headspace in my opinion. Too much air between the end of the case and the boltface.
Your fired case head dimension is almost .01 larger than unfired brass- too excessive.
The fact that the brass didn't blow up doesn't mean excessive headspace doesn't exist- get a no go gauge. Brass is very forgiving- it can stretch a lot, and return to dimensions that can mask a problem- for a bit, anyway...
Good article on internal ballistics at Hornady:
November 23, 2012, 11:29 AM
“it can stretch a lot, and return to dimensions that can mask a problem- for a bit, anyway...”
Not fair, I chamber a round, pull the trigger, then bang, I eject a case that has absolutely no memory of what it was before I pulled the trigger. I have 257 Roberts cases with 30/06 head stamps, 8mm57 with 30/06 head stamps, 243 Winchester cases with 308 W head stamps, I even have 30 Gibbs cases with 30/06 head stamps. I have 30/06 fired cases with 280 Remington head stamps.
My firing pins are mechanically operated, all of my firing pins are driven forward by a spring, again, not fair, I pull the trigger, the shoulder of (some) my fired case never make it to the shoulder of the chamber until the pressure inside the case erases the shoulder of the case meaning some of my shoulders on some of my fired cases never get to the shoulder of the chamber, not fair, time is a factor.
“The fact that the brass didn't blow up doesn't mean excessive headspace doesn't exist- get a no go gauge. Brass is very forgiving- “
‘OR’ become a reloader, get a press, die and shell holder and the companion tool to the press “THE FEELER GAGE’: STUDY the mechanical advantage of the “INCLINE PLAIN’, Again, I have long chambers, I have short chambers, I do not use go-gages, I do not use no go-gages, I do not use field reject gages (I did not say I do not have chamber length gages, I said I do not use or need chamber length gages), because! I have a press, die and shell holders for everything I load for, and I have the companion tool to the press, the feeler gage.
30/06 chamber length gages? I have 280 Remington cases, lots of them, I have a 30/06 forming die, the shoulder on the 280 Remington case is ahead of the 30/06 shoulder .051”, the 280 case will not chamber in a 30/06 chamber, with the forming die I can form the shoulder on the 280 case .051” back to 30/06 dimensions by mindlessly raising the ram, or I can THINK, I can adjust the die off the shell holder and form the shoulder anywhere between .000” to .051” by erasing the shoulder and forming it where I want it. Where I want ‘it’? Again, I have and use the companion tool to the press, the feeler gage.
A reloader can off set the length of the chamber with the length of the case from the usual places, Again, I have an Enfield M1917, the length of the chamber from the bolt face to the shoulder of the chamber is .016” longer than the perfect go-gage length 30/06 chamber. Not fair, because I am a reloader with an adjustable die and press I do not insist on chambering minimum length/full length sized cases in the M1917 chamber, I do not fire to form, I form to fire. forming a 280 Remington case to chamber in the 30/06 LONG chamber is a matter of adding .014” to the length of the case from the head of the case to its shoulder by forming the 280 Remington case, I know, it sounds complicated, I erase the 280 Remington shoulder, part of the 280 Remington shoulder becomes part of the neck, part of the case body becomes part of the shoulder, I would ‘BUMP’ the shoulder but , back erasing the 280 Remington shoulder, by .037” comes closer to being described as wreck when compared to bump, I do not know when bump? starts and erase begins, seems there would be a fine line between case body support and no case body support. I am the fan of case body support.
I have rifles that are different than the rifles used by reloaders on this forum, I know, most do not believe that is fair, I am the fan of preventing case travel, knowing the length of the chamber allows me to form sizes to off set the length of the chamber.
November 23, 2012, 03:44 PM
F. Guffey, thanks for a very informative bit of info. I must agree with all you have said because its make a lot of sense and I will not debate any of it. I will just add; Because this particular rifle does not warrent any great amount of money spending I will not be reloading for it and just using factory ammo. Being older and retired now I have reloaded for many different cartridges and know exactly what you are saying. I agree feeler guages, mikes, venier calipers and other, some home made, measuring devices are invaluable in good reloading practices and I use many myself.
Remember this first ammo (Federal) has way under sized cases before and after firing, evidently, as I said earlier, to promote easy chambering and still be safe in "most" older, and maybe some rifles, with not much quality control.
Using these cases I recently did my own headspace check buy adding to an empty case, no primers, small round pieces of masking tape until the cartridge became somewhat diffucult to chamber. Remember that with a Mauser bolt you can close and open the bolt, in the middle position, with the firing pin cocked so there is no resistance to the bolt other then the round being chambered. Now I understand there is a small amount of tape crush doing this but it gave me a fair reading of bolt head to case measurement. I ended up with about .015. Probably out of Saami specs and why I am seeing some primer extrusion.
I will be doing some headspace checking, using this method, when I get some new ammo from Midway and will post the results.
Tobnpr said " Your fired case head dimension is almost .01 larger than unfired brass- too excessive." Respectfully but If you look closely you will see the case before and after firing measured, at the base, not the rim, just north of the extraction groove, .464. My reloading manuals all call out for a case to be .471 which shows mine are undersize even after firing. It could be also that when firing, the cases, which are all measuring the same, are not expanding enough, maybe light loaded for older rifles, to keep it from moving and therefor the primer extrusion.
New ammo will give me more info but might be closer to Saami specs for modern rifles but could be more powerful also so I'll be advancing very carefully. These older military rifles are somewhat a challenge to use safely.
Thanks for everyones input, I have learned a lot. And the quest continues.
November 25, 2012, 02:58 AM
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