I am banging away with a 308 M1A and have read that brass life is only 3-4 reloads. Considering the gauge to possibly prolong brass life. Good 308 brass isn't cheap. When I bought the M1A I also bought a few hundred factory loads to hold me until I got 308 set up on the loading bench and to give me brass to start out with. I already have (4) reloads on some of this brass and I see no sign of case head separation. Maybe reload these a few more times to see if these rifles really are the case eaters folks say they are.
First of all, with any Garand based mechanism, load for safety first. For safety's sake, just ignore all the the vast amount of bench rest, F Class reloading advice. The last thing you want is a tight case to chamber fit.
My advice for reloading for M1a’s is to
1. Full length resize in a small base die
2. Trim cases
3. Clean primer pockets, ream to depth
4. Prime all cases by hand, verify that all primers are below the case head, and use the least
sensitive primers you can find.
5. Use IMR4895/AA2495/H4895 powders.
6. Seat the bullets to magazine depth, no longer than 2.8 for the 308, shorter is fine.
The M1a has a free floating firing pin, like this M1 carbine. The M1 Carbine and the M1a have a firing pin retraction cam. This cam pulls the firing pin back during extraction. Some claim it is a safety device, I am going to claim the firing pin retraction cam was never meant to be a
"firing pin block", and it is easily defeated by tight or long rounds. If you sized your round smaller than the chamber, and you are going to have a slamfire, making sure the case is smaller than the chamber will increase your odds to have an in battery slamfire instead of an out of battery slamfire.
Only at final cam down is the firing pin retracted. Up to then the firing pin is totally free floating and tapping the heck out of the primer.
This is a M1 Carbine firing pin retraction cam.
Due to picture limitations I had to remove the M1 Garand firing pin retraction cam image, but the M1 carbine and M1 Garand firing pin retraction cam are functionally identical, just the carbine is easier to visually understand.
This is the location where out of battery slamfires occur.
If the bolt has to stop here to crunch fit a long case or a fat case that firing pin is rebounding off the back of the primer at its highest velocity and the lugs are not engaged. There are many of out of battery slamfire reports in these mechanisms. When I asked those who had out of battery slamfires, the most frequent things I heard were standard sizing dies, brass fired in a different rifle, match chambers, Federal primers, and setting up die by sizing to the shell holder plus a quarter turn.
It is important to full length, small base size cases used in these rifles and to set up the dies with a case gauge and size to gauge minimum. (Assuming you don’t know the headspace of your chamber, if you do, always be 0.002 to 0.003” less) You want the bolt to close without resistance. This will reduce the risk of an out of battery slamfire.
Take all the neck sizing advice, the bench rest, and F Class reloading advice, and throw it on the ash heap. None of it applies to the M1a. Safety and function first.
I purchased a set of reamer cut gauges by Sheridan Engineering. I love gadgets like this.
These case gauges are dimensionally correct for a SAAMI chamber. You can drop a sized round or a loaded round in the thing and see if there is an interference fit somewhere. The Wilson gauges only measure base to shoulder distance, they are cut large in the middle. The Wilson gage won't tell you if the round is fat. The Sheridan gauges will.
There are some who say small base dies are not needed in these rifles, the Gunwriter Mike Venturino has been one. For years he has been saying in print that only standard sizing dies are need. But in the July 2012 issue of Guns Magazine, he is testing an M1a and a AR10 and his reloads are too tight. I find it humorous to read of him beating the bolts open with scrap lumber. Ha, Ha. He is darn lucky he did not have an out of battery slamfire in that M1a.
Small base sizing requires good lube. Attempting to small base size cases with they typicl spray on lube will result in cases stuck in the die. I recommend RCBS water soluble or Imperial Sizing wax. These are excellent lubes. Mink Oil has to be a copy of Imperial Sizing wax, worked great.
I am assuming that the chamber on your M1a is correct, that is the Go and No Go are within SAAMI specs. If that is so, then using a SAMMI spec case gauge will allow you to set up your dies such that sizing to gauge minimum means that case headspace will not be longer than chamber headspace. Comparator's will work for cases fired in bolt guns, but they will not work for any semi automatic mechanisms. The reason is, these actions unlock while there is still pressure in the barrel.
This is the timing of a T44 rifle, this T44 had a Garand receiver modified for a 20 round magazine, a 7.62 Garand barrel, gas cylinder, and operating rod installed. The M14 gas system has different peaks and pressure duration's, but both of these mechanisms unlock while there is pressure in the barrel. And it is deliberate, it is called the residual blowback effect. The designers are trying to increase the amount of time there is useful energy to push the mechanism.
Blowback actions do the same thing, images from Chin Vol IV Machine Gun
this is probably the Oerlikon action, an advanced primer ignition system, (retarded blowback), and the WW2 mechanism used pre greased ammunition. Post WW2, Oerlikon’s were fitted with oilers. Each round received a drop of oil before entering the chamber.
I took a set of 308 cases 22 reloads before the primer pockets expanded too large for my comfort. The thing was, these cases were lubricated before firing. That meant, on ignition the case slide to the bolt face without the case adhering to the chamber walls. And then at unlock, instead of the case neck adhering to the chamber, case lubrication prevented the case from adhering to the chamber walls, and thus, no sidewall stretch.
But, something that can be seen, is that due to the residual pressure left in the barrel, pressure was causing the shoulder to fold out to the chamber front, even as the case is being extracted.
These cases were full length sized, typically 0.003” less than chamber headspace, and yet when the case head to shoulder distance is measured after ejection, the cases measure above the No Go.
Something you also see in
@thump_rrr post #25
It should be noted that the FN90 chambered in 5.7 X 28 is a straight blowback weapon. But the cartridge operates at high pressure, and that required case lubrication. (Probably sintered Teflon) If the case was not lubricated, it would rip apart. I understand from posts, that there are reloaders who did not understand the importance of keeping a lubricant layer on their 5.7 X 28 cases and there have been serious out of battery incidents because part of a previous case was left in the chamber. I have no doubt that 5.7 X 28 cases were never intended to be reloaded, so if the sintered teflon is removed by a reloader, that is going to cause a serious malfunction in a straight blowback mechanism.
As you can see in
post #25, the shoulder moved forward during case extraction. If someone with a comparator was setting up their die based on a fired case, they would not be sizing the case enough to chamber. A comparator is not the proper gauge to use on semi auto mechanisms.
For Garand mechanisms, and the M14 is product improved Garand, it is safety critical to ensure that all primers are below the case head. Reaming primer pockets to depth is a good idea. Seat the primers by hand, and verify that all of the primers are below the case head. There is a chance that a cocked primer, with the anvil firmly seated on something, will cause a primer initiated slamfire. One poster swaged his primer pockets, which shaved brass donuts into the pocket. He left the donuts in the pocket, which resulted in high primers, and his AR10 slamfired in battery. Clean those pockets! A high primer can cause a slamfire but only if the anvil is firmly seated.
High primers are one of the most common cause of misfires because the primer won't fire unless the anvil is seated and is pushed up into the primer cake.
Mysteries and Misconceptions of the all important primer.
However, given a shallow pocket it is theoretically possible that high primers could slamfire, or given debris in the pocket, you can get a slamfire.
When I bought my SuperMatch M1a’s, Springfield Armory provided a copy of Wayne Fattz’s article “The Mysterious Slamfire” which was printed in the American Rifleman in Oct 1983.
Mr. Faatz had an out of battery slamfire, from the clip, with Federal primers. He wrote an article trying to understand why it happened to him.
First on his list of slamfire causes is a sensitive primer.
1. Sensitive Primer (included under this category is a high primer)
2. Minimum headspace chamber and inadequate case sizing (leading to the firing pin hitting the primer with excessive force)
3. Hammer following the bolt
4. Fouled bolt face
Any and all service rifles which have a free floating firing pin have slamfire reports, and they all can slamfire at any time if sensitive primers are in the primer pocket. The in print guys don’t talk about this, but slamfire frequency in all semi auto mechanisms with free floating firing pins, is “controlled” by primer insensitivity. The most sensitive the primer, the more slamfires. The use of commercial factory ammunition or reloads that use “soft” or more sensitive primers often create slamfires.
Because SKS’s slamfire so often, there are lots of slamfire reports with SKS’s, Murray’s has a firing pin modification to reduce the chance of slamfires. Also, the SKS boards has this excellent “A primer on primers”
http://www.sksboards.com/smf/index.php?topic=56422.0
Springfield Armory M1A Manual, page 4
Ammunition
The M1A is designed and built to specifications to shoot standard factory military 7.62 NATO ammunition. The specifications for standard military ammunition include harder primers to withstand the slight indentation from the firing pin when the bolt chambers a cartridge. This slight indentation is normal. The use of civilian ammunition with more sensitive primers or hand loads with commercial primers and/or improperly seated primers increase the risk of primer detonation when the bolt slams forward. This unexpected "slam fire" can occur even if the trigger is not being pulled and if the safety is on. Use of military specification ammunition will help avoid this.
Every shooter should use extreme caution when loading this or any other firearm. See page 17 for instructions on proper loading to help avoid a "slam fire". Also see enclosed article on “Slam Fire” written by Wayne Faatz
Federal primers are the most sensitive primer on the market and the most "slamfiring" primer in Garands/M1a's. I have lots of web accounts of slamfires with Federal primers. Don’t use them. I recommend CCI #34's and Tula7.62 primers as they are considered "Mil Spec" primers. Which means they are less sensitive than commercial primers, Federal being the most sensitive commercial primer on the market. CCI claimed their standard rifle primers were made to commercial specs, but everyone considers them “harder” than other commercial brands. Don’t use Winchester, they made their primers more sensitive in 1999 with the issuance of the brass finish WLR.
When firing single shot, load from the magazine. Do not put a round in the chamber and drop the bolt. Lots of inbattery slamfires, and a few out of battery, have happened because of this. You want to slow the bolt down. When rounds feed from the magazine the friction between cartridges slows the bolt a bit.
I disagree with the Springfield Armory Manual that using mil spec ammunition will prevent slamfires, inbattery or out of battery. I have talked to a number of shooters, USMC and AMU who shot the M14 with NM ammunition. In battery slamfires and out of battery slamfires happened with miltary ammunition with mil spec primers. Mil spec primers are on the average less sensitive than commerical primers, but that does not mean that a sensitive primer will not come off the military primer production line.
Use powders that are close to IMR 4895 in burning rate or just use IMR 4895. High port pressures are the concern. High pressures will create excessive operating rod acceleration. The NRA used to recommend powders that have burning rates between IMR3031 and IMR4320. This includes powders such as IMR 4064, and Winchester 748. I believe the first choice of powders are IMR 4985, H4895, AA2495. In the 308 I have used a load of 168 grain Sierra Match, 41.0 to 41.5 grains IMR4895, LC cases, and CCI #34 primers OAL 2.800 for years. Basically I am looking for 2550 to 2625 fps with a 168 grain bullet.
Here are actual chronograph values at 200 yards. The muzzle velocity was probably 2600 fps. I was surprised to see how fast the velocity drops.
M1a Super Match
2-Sep-23 T = 70-76 °F
Velocities measures at 200 yards with target chronograph on electronic target.
168 Hornady BTHP Match
41.5 grs AA2495, lot 2-14-1995 (loaded 5/23) LC90 CCI#34 OAL 2.800"
Ave Vel = 2216 fps
Std Dev = 28
ES = 174
Low = 2128
High = 2302
Number rounds registered = 84
Note: Hornady BC =0.450
Calculated Muzzle velocity 2600 fps
200 yard velocity 85% of muzzle
I was more or less blown away finding that my rounds had dropped that much velocity in 200 yards. And there is not much you can do in a gas gun to increase velocities, at some pressure level, the action will rip off case rims. That is very hard on extractors!
Check cartridges for case head separation. Gas guns are hard on brass: the bolt unlocks while there is still significant chamber pressure. Because of this the case gets stretched on extraction. Carefully inspect cases for stretch ring marks at five reloads. They occur about .4” of an inch ahead of the base.
no sidewall stretch when firing lubricated cases
You can verify if the cases are internally necking by inserting a bent paperclip in the case, and feeling for an edge. A number of shooters claim various dry case lives in the M1 or M1A. Some firing dry cases have case head separations about the fifth reload, others have taken their cases up to ten reloads. The useful lifetime of a case is determined by case head separations, case neck splitting, or primer pocket enlargement. When any one of these failure mechanisms happens to a case, it has exceeded its operational lifetime. In my experience, US military brass holds up better than commercial cases. But this is a broad generalization. You want to use heavy cases over light cases.
