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Old June 10, 2007, 07:34 AM   #1
k Squared
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Slam/Double Fire

I recently experienced what I believe was a slam/double fire in my M-1 Grand.

I always count the trigger pulls when I shoot and on the seventh pull I believe there were two firings and the clip was ejected. I was quite surprised and thought I must have miscounted the trigger pulls, but I was relatively sure of the two firings.

I already had a couple dozen empty cases on the ground and could not immediately identify the offending case. I suspected a high primer and looked at all the brass. I identified one primer that was significantly different from the rest. I have attached a picture of the different primer next to one that looks normal. The different primer is on the right and shows a raised rim around the indentation, but it does not appear to be a "high primer".

I also noticed that the mouth of the case was split, but a couple of the "normal" cases also had split mouths. The brass had been reloaded several times, but I don't know how many times.

I inspected my unfired ammunation, then fired a couple more clips. Everything seemed normal.

Can anyone give me any ideas of what actually happened?

Thanks
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Old June 10, 2007, 07:51 AM   #2
VaFisher
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slam fire

Looking at your pic's it looks like it indead would have to do with a raised primer. In the pic on the right you can see the dimple around the firing pin cone. This dimple was caused because the primer was raised and on impact it slam fired. You can see where the dimple fire formed inside the firing pin hole only because it was sticking out that amount. The fiing pin cone is smaller because it was formed inside the firing pin hole when slam fired occured. Hope this help you understand, explaned as simple as I could.
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Old June 10, 2007, 07:57 AM   #3
Mal H
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Welcome to TFL!

Since you put this in the reloading forum, can we assume you were using reloads in your Garand? If so, what was the load? bullet/powder type and weight/primer

The picture of your primers certainly does look like an overcharge in the right casing. Whether there was a high primer or not is almost impossible to tell after the firing. I wonder if you mistook a firing with much more than average recoil for a double firing.
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Old June 11, 2007, 03:23 AM   #4
k Squared
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Thanks

VaFisher and Mal H,

Thanks for taking the time to look at my posting.

To answer Mal H's question, I had reloaded this ammunition a few years ago with an IMR power suggested for the Grand in the American Rifleman. I had 150 gr soft point bullets. I can't remember which IMR power I used. I doubt that I could have fit a double charge in the case, but it could have been more then the specified amount.

I can see that I need take a closer look at my primer seating and get back in the habit of marking my ammo containers with the load information. I'll also get a fresh load of brass and start tracking the number of times it's been reloaded in case the cracks in the mouth are an indication of excessive wear.

Thanks again,
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Old June 11, 2007, 04:48 AM   #5
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Slamfires are very real phenomena with semiautomatic mechanisms. People will acknowledge that mechanical things, like stuck firing pins, grease in the firing pin hole, hammer following the bolt, all will cause a slamfire, but when it comes to primer sensitivity, folks just will not acknowledge this as a factor, instead you get absolute denial.

If you have a primer and a firing pin with sufficient energy to ignite the primer, the primer will ignite. If you have a free floating firing pin attached to a rapidly moving bolt carrier you have a condition which a slamfire can occur. If that fast moving firing pin hits a primer with sufficient energy to ignite the primer, you will have a “slamfire”. If the primer goes off before the bolt is in battery you have an “out of battery” incident. That is likely to be a destructive event. In your case, the lugs were engaged. Next time you could have the back of the receiver blown out.

From your pictures, it looks as though your were using WLR. Back in 1999 Winchester redesigned their whole primer line to make the primers more sensitive. Based on your experience, I guess they are too sensitive. Federal primers have been known for years to be too sensitive to use in a Garand and have caused lots of slamfires. CCI is the only manufacturer who claims to make a “Mil Spec’ primer. When talked with CCI, I was told that these primers are less sensitive than commercial and are magnum primers.

For you, it would be prudent too change primers. But this is not a cure all, there are process changes you need to be aware of to prevent that free floating firing pin tapping the primer before the lugs are fully engaged. Purchase "Wilson" type cartridge headspace gages. Purchase a small base die, especially if you have a commercial barrel on your rifle. Size your cartridges to gage minimum. This will ensure that your cases will never be overlength in the chamber which would delay bolt closure. Small base dies will ensure that your case is not "fat", which also delays bolt closure. Following this advice, and using less sensitive primers will reduce your risk of an out of battery slamfire to a low level.
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Old June 11, 2007, 06:34 AM   #6
VaFisher
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Well put Slamfire.
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Old June 11, 2007, 10:37 AM   #7
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Huh! Mine does that a lot, but I think it's caused by the trigger/sear engagement. I haven't been reloading for my garand, I got a big bunch of korean surplus ammo from midway, I've been shooting that. I would doubt it has "high" primers. It was loaded by PMC for the south Korean military.

It ONLY happens when I'm gently squeezing the trigger off the bench, a garand expert said it could be fixed, BUT it's NOT firing out of battery, and I'm not competing with it, just fun shooting.

I don't doubt that slamfires do happen. Especially with high primers, or loose primer pockets allowing the primer to back out of the pocket. Sometimes though, I suspect it could be a worn sear that causes the trigger to double.
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Old June 11, 2007, 04:35 PM   #8
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Quote:
It ONLY happens when I'm gently squeezing the trigger off the bench, a garand expert said it could be fixed, BUT it's NOT firing out of battery, and I'm not competing with it, just fun shooting.
Snuffy: Yours is most likely a mechnical out of tolerance issue. What you are describing happened a lot in the days when the M1a ruled the Highpower firing line. Typically it was due to a trigger pull job that removed too much material from the hammer hooks and the sear surfaces.

Change out your hammer and trigger, do that first. Your hammer is following the bolt and that is a dangerous condition. The firing pin is sticking out through the face of the bolt as the bolt rams the cartridge home. If that firing pin sets off a primer before the lugs are engaged, you will blow the back end of the receiver off.
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Old June 12, 2007, 09:29 PM   #9
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Quote:
CCI is the only manufacturer who claims to make a “Mil Spec’ primer. When talked with CCI, I was told that these primers are less sensitive than commercial and are magnum primers.

Switch to MilSpec primers. They have a thicker, harder cup. Remington 9 1/2 are MilSpec, and I think you can special order one from CCI that's MilSpec.

According to the NRA, Remington 7 1/2 SR and 9 1/2 LR have always been MilSpec.
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Old June 13, 2007, 08:33 AM   #10
TimRB
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"It ONLY happens when I'm gently squeezing the trigger off the bench, a garand expert said it could be fixed, BUT it's NOT firing out of battery, and I'm not competing with it, just fun shooting."

I would bet good money that your rifle is doubling, not slam firing. Doubling happens when you don't have a firm grip on the rifle with your trigger hand, and the recoil causes you to hit the trigger twice, like bump firing.

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