I set up my Hornady dies on my Dillon 550 to re size my once fired LC .308 cases. I followed the die instructions, re sized 500 cases. While shooting these cases at the range I had two headcase separations. Bought the RCBS precision mic to get a precise measurement on my case head space. My cases were measuring 1.610, I know the minimum head space is supposed to be 1.630, I was shooting these through my AR-10. I now have 500 cases with shoulders bumped back to far. Can I safely shoot these out of a bolt gun?
- Thread starter Mojo Daddy
- Start date
Nope, according to SAAMI/STANAG, the dimensions are: Shoulder to head with 7.62x51 is 1.560, .308 is 1.5598 inches. SAAMI is a reference at best. There are no laws or rules governing the exact measurements. I have the SAAMI drawings and several different 7.62X51 chamber crawings. That measurement is head to shoulder which is what you headspace on.
First off, I'm stunned your die/shellholder arrangement is even capable of getting cases .020" undersize. That's huge.
Secondly, I'm glad you bought a suitable tool for measuring this dimension in the future. Use it every time you setup your sizing die.
Are they safe? Textbook answer is "no". Once you've identified ammo as questionable, you shouldn't use it anymore. Is it going to be blow your face off? Probably not, provided the vent holes in your action aren't clogged. Sounds like either way, your brass is ruined, so firing this stuff will only "save" you the time spent loading and then pulling it down.
Secondly, I'm glad you bought a suitable tool for measuring this dimension in the future. Use it every time you setup your sizing die.
Are they safe? Textbook answer is "no". Once you've identified ammo as questionable, you shouldn't use it anymore. Is it going to be blow your face off? Probably not, provided the vent holes in your action aren't clogged. Sounds like either way, your brass is ruined, so firing this stuff will only "save" you the time spent loading and then pulling it down.
What does fired brass from the bolt gun measure? Perhaps you got lucky and have a tight chamber and it is close enough. Kinda doubt it though, you would be having problems with factory ammo if it was that tight. Probably best to pull them down and trash the brass so you know nobody gets hurt with it. Even if the action vents like its supposed to saving that brass could cost you a messed up chamber. 60,000psi inches from your face...
So I ask, whats the worst that could happen ?
The chamber is still the correct size? The powder charge is the same, the bullet weight is the same. Provided the distance from the shoulder to the throat is maintained the bullet will not contact the lands.
If the undersize brass fires (Probably will) it will blow the shoulder out to match the chamber. Being .020" further down the chamber can effect things like firing pin strike and extracting loaded rounds. Beyond that and the accuracy loss I dont see this as the problem people are making it to be.
If you are still not convinced then I ask you this. Why when a standard cartridge is fired and formed to a Ackley Improved Chamber does it not expirence overpressure ? Many Ackley Improved's blow out the shoulder quite a bit more then .020"
If it were my brass I would shoot it
The chamber is still the correct size? The powder charge is the same, the bullet weight is the same. Provided the distance from the shoulder to the throat is maintained the bullet will not contact the lands.
If the undersize brass fires (Probably will) it will blow the shoulder out to match the chamber. Being .020" further down the chamber can effect things like firing pin strike and extracting loaded rounds. Beyond that and the accuracy loss I dont see this as the problem people are making it to be.
If you are still not convinced then I ask you this. Why when a standard cartridge is fired and formed to a Ackley Improved Chamber does it not expirence overpressure ? Many Ackley Improved's blow out the shoulder quite a bit more then .020"
If it were my brass I would shoot it
I just measured another box of brass that I had stored away. This brass is measuring 1.623, .007 below minimum. I am going to load and fire these through my bolt gun and use the paper clip method to check for case bulge. If no bulges I will keep this brass.
The worst that could happen is that a case would rupture just ahead of the case head, thereby venting all the gasses immediately. If that happens,you will most likely blow up your firearm, and would risk very serious injury like blindness or death.
It simply is not worth it.
How many rounds have this set back?
It simply is not worth it.
How many rounds have this set back?
I agree with turbo. FL sizing dies are designed to bottom out before producing undersized brass. I didn't think the RCBS mic would make a headspace measurement without using a once fired case.
I think your opinion is not realistic. Remember this is once fired, 7.62 thick LC brass.
By the time pressures reach a point where the brass has gripped the side of the chamber, the cartridge will be expanded to fit the chamber. The shoulder will grow pushing the head against the bolt. The expansion will be moving the shoulder forward, not stretching the case above the head. It just doesnt work like that.
If your theory is correct, I again ask, why do Akley Improved Cartridges not rupture above the case head during fire forming ?
While PO Ackley never reworked the .308 Offically, his design was applied to a .308. The .308 Improved is 1.6950" from base to shoulder as oppsed to 1.5598" for the standard .308. Thus it blows out the shoulder .1352" This caliber improvment is based upon firing the standard caliber to fired form. This is obviously more then .020"
Rprecision...with all due respects, you are wrong. The firing pin drives the case forward. The burning of the powder and pressure occurs AFTER the case has head spaced on the shoulder. The case walls are thinner forward, expand to grip the chamber walls, and the base is driven toward the bolt face...stretching the case at the base/case wall junction. The reason that a properly dimensioned Ackley Imp doesn't ruin brass is the same...the case is head spaced on the original datum line at the junction of neck and shoulder. That allows the shoulder and forward part of the case to expand to fill the IMPROVED chamber, without the base being driven back. If the op wishes to save the shortened brass...simply get a .32 or .33 expander die from K&M and expand the neck. Then size the case back to the proper dimension. That will give him a "FALSE SHOULDER" that the case can headspace against and allow it to expand to fit the chamber without stretching too much. JMHO
Formal naval person, that .32-.33 ex pander die sounds like a good plan. I'll check it out.
Just remember to wire (bronze) brush the inside of the neck and lube it before expanding.
Turbo54:
It is possible to oversize a case on a 550B by screwing the die in too far. When setting up dies on a 550B the use of a comparator or case gauge is required.
The RCBS Precision Mic is a good tool and have a bunch of them but before chunking your sizes brass compare against fired brass for the difference in headspace. If as great as you say it is, probably best to pull the bullets and discard. Point in passing the difference between new Norma 300WM brass and fired brass through my McMillan ranges between .015 and .017.
It is possible to oversize a case on a 550B by screwing the die in too far. When setting up dies on a 550B the use of a comparator or case gauge is required.
The RCBS Precision Mic is a good tool and have a bunch of them but before chunking your sizes brass compare against fired brass for the difference in headspace. If as great as you say it is, probably best to pull the bullets and discard. Point in passing the difference between new Norma 300WM brass and fired brass through my McMillan ranges between .015 and .017.
good info gentleman. i dont mean to highjack but its relevant. is using the dillon or LE Wilson case gauge an accurate way to set up FL dies just as well as using the stoney/hornady headspace gauges? i set up all my dies using these and seeting them to the max step up on the gauge and havent had any issues yet. woulda tool like tht helped the OP in the beginning better?
Case gauges are very accurate when setting up your dies but it depends on what you are attempting to do. For my bolt and single shot rifles I try to set the shoulder back .001 to .0015 when sizing and requires the use of some type of comparator such as the Hornady. By doing so, I am sizing the cases to headspace to that particular rifle and not potentially oversizing the case. Case Gauges will just indicate whether the sized case is within SAAMI spec.
