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Old January 25, 2013, 09:37 AM   #26
Slamfire
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I have more slamfire posts on Garands than any other mechanism, but combined, the posts on all other mechanisms, including M1a’s, M1 carbines would be at least as long, but I thought the posting of them redundant.

Now one thing I note from your posts, and all of your posts that I have seen on this subject, is a lack of discussion or acknowledgement of primer sensitivity. That is something I have noticed from shooters from “back then”. They only attributed causes are mechanical, shooter misconduct, high primers. And yet, the elephant in the room is primer sensitivity. It has always been the elephant in the room, it has always been known.

That is why people have been told to feed from the magazine or to use SLED’s. It is to reduce the kinetic impact of the firing pin on the primer. I find it humorous that primer sensitivity deniers give this advice without making the connection why this advice is good.

It is also why most designs with free floating firing pin have springs around the firing pin. I know from a member of an Armalite design team, that their AR10’s were tested with military LR ammo, without a firing pin spring, and the rifles slamfired. So Armalite put the firing pin spring in the mechanism.

There are very good later designs have features that radically reduce the chances of an out of battery slamfire, a failure mechanism that has plagued Garand type mechanisms since day one. Even the Russians put in design features that reduce the chance of an out of battery slamfire as you can see in this video from Murray’s Guns.

http://www.youtube.com/watch?v=xj3QtnUWCwQ

I think what Murray did was crazy dangerous, but if you managed to wedge a Garand type firing pin in the forward position, such as Murray did with the SKS, you would blow it up.

The Garand mechanism was one of the first semi automatic military rifles, the M14 is a product improved Garand, but the mechanism dates back to the 20’s and back then Americans accepted death and dismemberment as a normal employment risk.

If you notice, AR’s don’t slamfire out of battery, neither do HK91’s. These are 50's vintage designs. In fact, HK91’s don’t have firing pin initiated slamfires. There are very good reasons for that. The Germans designed out that possibility by putting a firing spring so stiff that it takes two hands to compress the bolt.



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Old January 25, 2013, 09:49 AM   #27
Hummer70
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In loading Garand as indicated by others stay off the hot loads. You might even drop to 46 gr 4895 with 150. There is a gas port pressure window you need to be in and if you have Quick Load program look for a load that will give you about 10,000 lbs muzzle pressure.

The Match M1s that were rebarreled to 308 has less problems with op rod warping.

What you will probably run into is finding FL dies that will size base dimension down enough to allow you to load 8 into the clip. I have like five sets of 30.06 dies that size base dimension as measured .200" up from rim to .466" (new cases come .465") and they run from there up to .469".

Garands have big chambers thus working the brass from say .472 fired down to .466 to get them to load easily is rough on brass. Gov't surplus brass lasts longer than commercial in my experience. It is also thicker and thusly heavier.

You have to remember the acceptance accuracy for Garand was 5" at 100 yards which is not very demanding.

Last edited by Hummer70; January 25, 2013 at 09:55 AM.
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Old January 25, 2013, 09:58 AM   #28
Bart B.
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Great post, Slamfire. Thanks for sharing your information.

I'm well aware of the late 60's Fleet Match slamfire issues. I asked folks at the All Navy matches that year from the east coast if anyone checked the primers on those cases to see how much they were dimpled; nobody had done so.

But yes, over sensitive primers can detonate from minimal dimpling. But I've never seen one; that's my point.

The main reason M1 and M14 slam fires have full dimple depth in the primer cup is their hammers drove the firing pin that far deep into them. There's not enough inertia of the firing pin itself to do that; even with a soft cupped large pistol primer in a .30-06 case. Jammed firing pin from debri wedging it in place is another one.
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Old January 25, 2013, 12:11 PM   #29
Slamfire
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Quote:
The main reason M1 and M14 slam fires have full dimple depth in the primer cup is their hammers drove the firing pin that far deep into them. There's not enough inertia of the firing pin itself to do that; even with a soft cupped large pistol primer in a .30-06 case. Jammed firing pin from debri wedging it in place is another one
I can see how you interpret deep primer strikes on slamfire cases as evidence for a mechanical malfunction. Given how rare slamfires are even seeing seven cases to inspect is most unusual. But a slamfire is a dynamic event, and weird things happen with bodies under motion, I had two out of battery slamfires with Federal primers and both primers had nice deep indentations, and the trigger groups have never followed (I still use them) and I have never bumped fired a rifle ever. (I have had ND's with the 6 ounce triggers on my small bore rifles, oops!) Subsequently I don’t believe the theory that they were hammer caused. Also, I had a slamfire, standing stage, in a AR15, and so did the bud on my firing point. I examined all the cases we picked up and all 223 cases had nice deep firing pin indentations, including those we identified as the slamfire rounds. The rifles have never followed and my bud stopped using Federal match primers after his second AR slamfire.

As I said earlier I don’t know why this is so, it would take a lot of money to figure the mystery, and no one is looking.
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Old January 26, 2013, 09:42 AM   #30
Bart B.
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I'd like to know what the inch-ounce force is for a service rifle's firing pin smacking a primer when the round's chambered; both form single loading to stripping a round from a clip as well as with a normal strike from the hammer.

I'd also like to know what Federal's inch-ounce force numbers are for their large rifle primers for both the no-fire and always-fire situations using standard test methodology.

Interesing info about this is at:

http://riflemansjournal.blogspot.com...t-go-bang.html
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Old January 26, 2013, 02:41 PM   #31
Slamfire
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Quote:
I'd like to know what the inch-ounce force is for a service rifle's firing pin smacking a primer when the round's chambered; both form single loading to stripping a round from a clip as well as with a normal strike from the hammer.
If we had the bolt velocity we could figure out the KE with the mass of the firing pin. KE = 1/2 MV**2

Quote:
I'd also like to know what Federal's inch-ounce force numbers are for their large rifle primers for both the no-fire and always-fire situations using standard test methodology.
I would like to see primer test data. I called Winchester and was told that was proprietary. I have seen primer test data on DTIC, but it was for large, like grenade, primers. It was totally frightening because primers fired all the way down to the "Non-Fire" limit. Lets say the "Non Fire" limit was an 8 inch ball drop. Well out of a lot of 100 primers all would fire at the all fire limit, like 20 inches, and as the drop height became less than the "average" drop height, out of a 100 primers, 55 would fire, a little lower, 35, but as I recall one inch above the "non-fire" limit (say 9 inches), something like 27 would fire out of 100. Then zero at the non-fire limit of eight inches. Well that does not provide a lot of margin in my opinion.

And then there is this chart



This is the current "mil spec" primer formulation. This looks to be primarly a manufacturing chart, primer cake is kept wet at the factory, it is also a 3 D chart and we are only looking at the 2D. I am going to assume red means 100% bang and green means zero percent bang, and the colors inbetween are some percentage chance of bang. But just look at the probabilities of ignition below 1 joule. There is always some probability of ignition according to the color bar.

Frisco Pete, at the SKS boards, put a lot of time and energy into studying primers, and his post "CHOOSING THE RIGHT PRIMER - A PRIMER ON PRIMERS" is well worth looking at.

http://www.sksboards.com/smf/index.p...6422.msg646510

Mr Humphreville’s article : “IT DON’T GO BANG: FIRES, HANGFIRES, MISFIRES AND SHORT ORDER COOKS IN JERSEY.” was very interesting to read and shows the shortsighted nature of corporations. Corporations no longer train or retain expertise. It is a lot cheaper to contract out everything, in house expertise is expensive, and since slavery is illegal, if they train/retrain someone that person might leave for a higher salary. I hear Corporations complaining in the media all the time about how they can’t hire because but no one has the "job skills". Corporations expect the public to forecast what skills are needed in the future, then Joe Public is to go into debt to the tune of $100K getting that education/training, so the Corporation years hence can pick up the phone and hire an expert for an afternoon.
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Last edited by Slamfire; January 26, 2013 at 03:00 PM.
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