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Old September 19, 2013, 09:30 PM   #1
NinjasHateCommies
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Overcrimped/Slamfire on M1A

Hi,

I am a beginner Reloader. Last Sunday had two instances of Slam Fire (doulble burst). Since I was in a match I shot 75 rounds single loaded by hand. This ammo I had loaded a week ago.

What I used was twice fired Remmington Brass from the original Factory Match Ammo 168 Gr. I loaded it after maticulous case preparation. i.E. Twice cleaned, Flash Hole Deburred, primer pocket uniformed, trimmed to 2.005, deburred.

I primed them with Winchester LR Primers via the RCBC strip Loader on an Ultramag Press. Primers were inspected to be all 0.006 under the case horizon.

IMR 4895 42 gr. with a Hornady 150Gr FMJ/BT with Canulure. The first time I reloaded them to OL 2.700 and crimped them right at the outside edge of the canalure.

This time was an Identical Load. 42gr., same bullet ONLY out to 2.730 which crimped in the canelure close to the bottom 1/4.

Velocities were around 2650 SD 13. I am very maticulous when I charge. I use a 10/10 scale and a Hornady Electronic just to check if endeed it was 42Gr.

After the match I cleaned and resized them and noticed that they really pushed harder then usual in the press. Further many of the primers had a lip and were quite flat...Oh,Oh. Then I looked at the cases and found 5 with clear cracks beginning to form.

My Question is has anyone had simmilar experience with crimping towards the bottom of the canalure. Perhaps overcrimping. Can Anyone explain or suggest what might be going on.

Thank You.
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Old September 19, 2013, 09:49 PM   #2
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Have you checked the inside of the cases with a bent paperclip? This will give you indication of incipient head separation. While the bright spot seems too forward, never hurts to check.

When you size your cases how much are you setting the shoulder back? Another way to ask is how are you adjusting your sizing die?

Seems to be less related to crimp and more related to other issues.

Flat primers can be more of an indication of excessive headspace as much or more than an indication of over pressure.
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Old September 19, 2013, 09:52 PM   #3
mehavey
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Quote:
"... resized them and noticed that they really pushed harder then usual in the press.
Further many of the primers had a lip and were quite flat...Oh,Oh. Then I looked at the
cases and found 5 with clear cracks beginning to form...."
Double fire aside, I'm thinking excessive headspace clearance between the sized case dimensions
and those of the actual chamber. That would be consistent with all the case/primer appearance
symptoms you describe.

The M14/M1A extraction process is very hard on cases. If I read you right, this was the
4th firing of that brass. Even with good case/chamber match, you're approaching case
life unless you are doing some advanced resizing techniques exactly tailored to the chamber.

If you haven't already, download and memorize this pamphlet's info:
http://www.zediker.com/downloads/14_loading.pdf

.

Last edited by mehavey; September 19, 2013 at 09:59 PM.
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Old September 19, 2013, 11:18 PM   #4
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Looks like there may be a "ring" in the chamber.
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Old September 19, 2013, 11:37 PM   #5
NinjasHateCommies
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Thanks for the replies.

I use Redding Full lenght sizing Die and competition seating Die. Brass was fired 3X including last time, twice Reloaded.

I check all cases with Wilson Chamber Tool, all fit perfect. Slide in very easy.
Dimensions perfect.

When I adjust the die I bring handle to max position screw Die in then have them touch with gentle resistance.

I also Loaded 175 SMK for my LWRC with N540 no issues at all. Same Chamber fit.

PS from 140 cases only 5 had the crack so "the ring" theory seems unlikely.

Yes on the paper clip: There is a dip on the inside on 4 out of the 5 with the mark, all others smooth.

I also looked with a Fiberoptic and saw crack circumpherencially on 4/5 cases with cratering / stretching of brass in the area. That was cool. Wish I could post a picture.

I am starting to think it is Extra Head Space since they sit closer to the Min in the Wilson Gauge.

Interesting Stuff.

Last edited by NinjasHateCommies; September 20, 2013 at 12:02 AM.
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Old September 20, 2013, 06:47 AM   #6
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As stated above and in the provided link, your brass life is coming to an end.

None of this explains the "slam-fire" however. If I were you I would be more concerned with this than the brass. How are you crimping? With the seating die or a separate die like the Lee Factory Crimp die?

Over crimping with the seating die may cause the case to buckle and cause chambering issues. Is all your brass trimmed to the exact same length? If not this could cause inconsistencies in your crimp and maybe a buckled case.

If you are going to crimp, get a Lee Factory Crimp die.
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Old September 20, 2013, 08:53 AM   #7
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You don't need to crimp case mouths onto bullets for the M1A. Arsenal and commercial match ammo's never had crimped in bullets for several decades; it ain't as accurate as uncrimped case mouths.

If those cracks on the cases wer about 1/4 inch up from the case head, I think you're resizing the fired cases way too much. That causes head separation in all rifles, both semiauto's and bolt action.

If you want to resize cases fired in that rifle, you need to get a gauge to measure fired case dimensions from head to shoulder; RCBS Precision Mic or Hornady LNL case gauge are good ones. Measure a fired case, then set the die in the press to set the fired case shoulder back no more than .003". Any more and the case will stretch way too much at its back end when fired, then keep doing that for every time that case is reseized, reloaded and fired.

Regarding the slam fire. . . most of them are caused by the shooter "floating" his trigger finger barely off the trigger when the semiauto fires and it pushes back on the trigger as the rifle moves back forward coming out of recoil. Another popular cause is insufficient engagement of the hammer hooks and trigger sear that gets disengaged from the shock of the bolt slamming into battery on a new round. Very few slamfires happen due to soft or thin primer cups. And the inertia of the floating firing pins ain't enough to fire primers within decent specs. Do the primers in those slamfired cases have normal depth and shaped dimples from the firing pin's impact looking the same as normally fired ones?
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Old September 20, 2013, 09:21 AM   #8
NinjasHateCommies
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First of all: Thank you for all the guidance.


I use a Lee factory Crimper.
I noticed that most likely it is an excessive headspace issue, since the twice sized brass feels looser in the Wilson Gage.

Re: Slam fire it was likely my Trigger Finger since I was shooting OffHand.

The issue was this was during a Match so I have no way of knowing which primer was fired. I also did not notice it until I resized.

I will get a case Gage as you suggested and push back only 0.003.

Just got the RCBS one, Thanks for the guidance.

Thanks Again.

Last edited by NinjasHateCommies; September 20, 2013 at 09:40 AM.
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Old September 20, 2013, 10:24 AM   #9
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Different type of match than usual for HP Rifle if you're mag loading for the standing position.

In general, listen to what Bart B posts.

There's a difference between a slam fire and the various types of doubles that can happen. From the original post + additional information I would remotely diagnose (all dangers and disclaimers included!) just a bump-fire. You can possibly eliminate this with various semiautos by including holding your trigger finger back somewhat firmly as part of your follow-through. OTOH, the trigger group should probably be looked at for adequate engagement. A trigger job that leaves inadequate "overlap" between safety sear let-off and the primary sear catching the other hammer hooks can occasionally make those triggers act more like 8 ounces than 4.5 lbs.

Yeah, I used to size my semiauto brass to about midway between the Wilson min and max on those gages...until I discovered that as-fired, my cases were well above the max *ammo* headspace spec. The gunsmith "splitting the difference" between SAAMI and military headspace because of the 100% certainty of using DCM-issued USGI Match ammo at Leg Matches was why, but sizing that far for those chambers led to case life of only 4-5 reloads.

Completely unrelated to the doubling issue.

Excessive head clearance is also why your primers are showing a bit of mushrooming. Non-crimped primers back out on ignition, and then for full-power loads the case eventually slides back in the chamber and resumes contact with the boltface. The primer has time to expand radially before, essentially, being re-seated. This leads to false-positive "pressure signs", sometimes of alarming appearance. Lighter loads, especially with dirty chamber and/or not-polished brass, can leave high fired primers that weren't high when the rounds were loaded. Measure their protrusion and you can get an idea of how far back to unscrew your sizing die to give your ammo something more like .004 clearance instead of what you have now.

I predict that in YOUR chamber, min-headspace ammo has probably .010 head clearance.

For your continued education, there are two types of slam-fires: locked-bolt and "out of battery", which from the evidence I've seen is almost always a half-locked bolt. The second is the dangerous rifle-destroying type. There is a *belief* arising from the incidence of OOB slam-fires with Service Rifles and even at DCM and NRA HP matches with USGI Match ammo, that the minutely-longer ammo combined with a tight "match" chamber in those rifles with aftermarket or replacement barrels makes an OOB event more likely. I'm not convinced of that.

My belief now is that OOB firings with USGI ammo have been most likely caused by firing pin bounce in rifles with either worn firing pin tails, receiver bridges, or both, which allows the FP to contact the primers early in the bolt closing rotation rather than only the last little bit. Wear in this critical FP-retraction function (not only on bolt opening but especially as the bolt stops forward motion just before rotating closed) can even let a hammer jar-off fire the round, despite the hammer's own bolt-rotating camming surface.

There remains some suspicion that OOB firings with a worn parts situation* can even result in a round firing from only the firing pin bounce in the feeding cycle. This is partially because otherwise unexplained grenade (term from Wolf Publishing's writers) events were far more common with Garands than with M1As.

Sadly, the only PROVEN way to make an OOB slam-fire on demand is to load a round with spherical powder AND combine that with a primer seated high enough for the bolt face to light it up on bolt closing--IF enough powder has moved under the primer to hold it back for that impact to make the primer act as if it were at the bottom of the primer pocket. This is why anyone loading for a semiauto should NEVER, EVER use a case which accepts primer seating with less than the usual resistance. I have personally seen and inspected ammo that looked just fine, but the primer would back out dangerously when the case head was tilted 30° and tapped against a tabletop. Believe me, the feeding cycle when the bolt strips the round out is more vigorous than that.

Anyway, be careful and scrap out your brass when it gets those internal rings. My bench has a couple of dedicated spring-steel tools for such inspections.

Be safe.


*And especially with the unknown number of aftermarket receivers with receiver bridges placed or machined too close to the chamber--I had one with it actually too far back, which pulled the tail of the FP too far on opening and again on feeding--broke the FP after only 3,000 rounds or less--AND the whole bolt path was almost 1/8-inch too low to the magazine, preventing a full mag from fitting under a closed bolt.
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Old September 20, 2013, 10:40 AM   #10
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The rifle is new has spit out 375 rounds.

Yes, HP Match I used two rounds for sighting in durring Fast Fire.
After that loaded one at a time with mag in place.

It would appear that I have to separate issues.

Thanks Guys for all the great info.

Now I wonder if I did not ruin the primer pocket with the Lee pocket primer Uniformer.......hmmmm will watch that a little closer.

Great info, Thank you very much.
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Old September 20, 2013, 01:22 PM   #11
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I do not understand how you could a double in a match where you fired 75 rounds single loaded into a magazine but only fired sighting shots from the magazine.

What type of match were you shooting in? I does not sound like the Highpower Across the course match I am familiar..

Were you shooting the rifle on a bench? Did the doubles occur when shooting from the bench, or off a bipod, from the magazine?

If you were shooting from a rest or a bipod, shooting rounds from a loaded magazine, then the most probable explanation is a double due to bump firing.
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Old September 20, 2013, 05:02 PM   #12
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80/ 50 round NRA High Power Modern Service Rifle M4/M6/M1A/M14/Garand.

Stage 1: During sighting in I loaded 2 rounds into 10 round mag.

Bam/Bam with one trigger pull. Then I released the Trigger. I have long follow .

Then I decided for Safety to shoot the rest with single Loading.

Mag in place, Chamber round, off seat mag, Bolt release, Mag Back.....X10

Durring Stage 2: one mag had 8, the other 2. After Single fed sighting in.

put mag with 8. One pull doubble burst. Took Alibi. checked barrel. Shot rest of match via manual single feed. For Safety reasons.

High Power Service Rifle (NRA) Rules.

STAGE 1: 10 (20 for NRA) shots Standing Slow fire + 2 sighters, 12 minutes, SR-1 target.

STAGE 2: 10 (20 for NRA) shots Rapid Fire + 2 sighters, Sitting or Kneeling, 60 Seconds, SR-1 target.

STAGE 3: 10 (20 for NRA) shots Rapid Fire + 2 sighters, Prone, 70 Seconds, SR-21 target.

STAGE 4: 20 shots Slow Fire Prone + 2 sighters, 22 Minutes, MR-31 target.


Retr: Should have just quit.

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Old September 21, 2013, 10:33 AM   #13
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The slam fire maybe avoided by using CCI military type primers. No. 34/7.62MM
Military large rifle primer with NATO sensitivity.
The line on the brass is start of a separation from to much Head Clearance or to many loadings. Some gas guns stretch the brass on opening early. The fired brass maybe longer, head to datum, then the chamber. From what i read. I dont own one. Good reading, the Service Rifles. http://www.exteriorballistics.com/re...sgunreload.cfm

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Old September 22, 2013, 11:53 AM   #14
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Based on what I understand, I think the most probable explanation is that your doubles are due to bump firing.

Both the M1a and Garand kick and if you do not have a firm hold on the things they will move enough that your trigger finger will bump the trigger, even though you did not expect to.

I always shoot my standing rounds with one round in the chamber and thus have never had the opportunity to see if the rifle would double. Standing offhand is not the most braced position, as you are trying to your utmost to precisely pull the trigger at the right time without disturbing your sight picture.

As for slung positions. With Garands/M1a’s you must always ensure that the sling is tight. You should have to put your hand on the buttplate and push the rifle forward as you move it into your shoulder. Lesser rifles can be held loosely but these full power service rifles have to be slung tightly or they will move during recoil and a bump fire is possible.

Most unintentional bump fires with 30 caliber rifles occur on the bench. Shooters have these things on sandbags and a rest, loose in the shoulder, the rifle recoils back, goes forward, and the trigger finger bumps the trigger.
I do not consider this safe at all as you could loose control of your weapon and the hammer is following the bolt down. The only thing preventing an out of battery slamfire is the hammer nose and bolt notch interlock. Garand designed a mechanical interlock to prevent the hammer from touching the firing pin until the firing pin has cleared the bridge notch. The hammer nose will rotate the bolt to an inbattery position before the hammer can touch the firing pin.

Hammer nose notch to left of firing pin.







But the firing pin is able to go fully forward well before the lugs are fully engaged, the pencil mark shows just when the firing pin clears the receiver bridge notch.




Safety devices can fail, mechanical interlocks are not necessarily 100% positive , I would not trust this interlock time and again from to prevent an out of battery slamfire and if the rifle only goes off in battery, there is the very real possibility that the lugs are not fully supported.


My advice for reloading for Garands/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 3.3” inches for the 30-06, 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, M1 Garand and M1a have a firing pin retraction cam, often called the "receiver bridge". This cam pulls the firing pin back during extraction. It also has limited utility as a safety device, but is easily defeated by tight or long rounds. If you sized your round smaller than the chamber the odds would will be in your favor to have an in battery slamfire.

Due to the longer and heavier firing pin in the Garand, it has always had more inbattery and out of battery slamfires than the M14/M1a. The primer sensitivity specifications were the same, logic, based on physics, provides the understanding that given KE = M * V**2 that the greater the mass, the greater the kinetic impact energy on the primer. I have not weighed the M1 carbine firing pin, but it may be the heaviest of them all. Examining M1 carbine primer specifications, the all fire limits were inches above the large rifle primers, so carbine primers are even less sensitive than the primers used in Garands/M14's.

Only at final cam down is there any firing pin retraction and the firing pin is never fully retracted behind the bolt face. For almost three inches of travel the firing pin is totally free floating and tapping the heck out of the primer. Static pictures give a false impression of a smooth and linear movement. Based on reports of people who have seen high speed camera images, the actual movement is not smooth and there is bouncing and back and forth oscillations. I believe the dynamics of firing pin movement to be chaotic and given the right conditions, it will rebound hard off the primer before bolt lock. Given a sensitive enough primer you will have primer ignition.

This is a M1 Carbine firing pin retraction cam.




The M1 Garand/M1a firing pin retraction cam are functionally identical, just the carbine is easier to visually understand.


This is a M1 Garand receiver and the firing pin is fully forward and just touching the firing pin retraction cam. As you can see there is only thousand's of an inch of forward movement left in bolt cam down and yet the firing pin is out about 0.064" of the bolt face.







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.

That is why it is important to small base size cases used in these rifles and to set up the dies with a case gage and size to gage 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.




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.

If you attempt to small base size with a spray on lube you will stick the case in the die. I recommend RCBS water soluble or Imperial Sizing wax. These are excellent lubes.


For these rifles 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 primer pocket. 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. It actually turns out that high primers are 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. http://www.shootingtimes.com/2011/01...motaip_200909/ However, given a shallow pocket it is theoretically possible that high primers could slamfire, given debris in the pocket, you can get a slamfire.

Mr Faatz stuffed an extra anvil in his primer pockets as he was unable to get unsupported high primers to ignite. Reference A.

Just examine the back of the ammunition you have and see if there are high or cocked primers.

It is also safety critical to use the least sensitive primer around because these rifles will slamfire in battery or worse, out of battery, given a sensitive enough primer.

Federal primers are the most sensitive primer on the market and the most "slamfiring" primer in M1a’s and Garands. 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 considered "Mil Spec" primers. Which means they are less sensitive than commercial primers. The military chose the characteristics of its primers after careful analysis of test data. The military spec primers are the appropriate primers to use in these mechanisms because they reduce, but do not eliminate, the risk of an slamfire. These primers are insensitive enough that the risk of a slamfire is in the magnitude of 1:10 million and yet the mechanism has enough energy to reliably ignite these primers at -40F. The chance of slamfires go up the more sensitive the primer.

When firing single shot, always 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 clip the friction between cartridges slows the bolt a bit. Firing pin initiated slamfires are all about primer sensitivity, you want to reduce the kinetic energy of the firing pin as it rebounds off the primer.
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Old September 22, 2013, 08:54 PM   #15
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slam fire

my ole man stick's to cci primers they have a thicker shell thus less sensitive ,since using no more slam fire's in his m1a .
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Old September 23, 2013, 10:08 AM   #16
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@Slamfire: Thanks for all the great info.

I did something unusual I had a long follow through, held the trigger for about a second after the shot broke. Perhaps that combined with the recoil created the double burst.

I have ordered about two months back 2000 CCI #34 and hopefully one day soon they will arive.

Re Separation: I think my mistake was I over-resized them thus generous headspace.

Also I noticed that 43.2 grains is MAx for Service Rifle.

I think I will back off to 40 grains, toss the brass batch.

Ironically with the muzzle break (CA BS legalization) it really does not kick mush at all.

Also I looked at my notes I used RSBC Hand Priming tool so it is possible those two were less then Ideal.

Again, Thanks for the wealth of info.
Happy Shooting!

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Old September 25, 2013, 04:24 PM   #17
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Well, I think I figured out what occured.

Prior to the Match I cleaned the rifle really well.
I also cleaned the bolt with some Hops #9 with a soacked pad.
Some of the Hops #9 must have gone into the firing pin thus lubricating it just enought to cause a bump fire.

Has anyone disassembled the bolt on an M1A. Is it worth the effor? Can it be done? Should it be done? The manual seems to discourage such attempts.
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Old September 25, 2013, 06:11 PM   #18
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Gluing the firing pin forward is not a good idea.

There is a UTube video on bolt disassembly, but I do not take it apart the same way.

http://www.youtube.com/watch?v=FWhvvTm1cLk

I have a GI bolt disassembly tool, makes life very easy. This is Brownells' copy:

http://www.brownells.com/gunsmith-to...l-prod917.aspx
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Old September 25, 2013, 06:46 PM   #19
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Many Thanks.
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Old September 26, 2013, 09:24 AM   #20
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I don't think Hoppe's No. 9 is an adheisive nor bonding agent. It will not "glue" a firing pin to the bolt of a semiauto.
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Old September 26, 2013, 02:03 PM   #21
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Quote:
Has anyone disassembled the bolt on an M1A. Is it worth the effor? Can it be done? Should it be done? The manual seems to discourage such attempts.
I was in the last class of Small Arms Repairmen the Army trained on the M14 rifle at USAOC&S (Aberdeen Proving Grounds). Graduated second in my class and was promoted for it. Almost 38 years ago (sigh).

Today, most M1A rifles, while very similar, are not "just" semi auto only M14s. Many, if not most are intended as match class rifles, and the factories do not recommend taking them all the way apart for cleaning, as this increases wear and can reduce accuracy, over time. Those with glass bedded stocks should not be constantly stripped for cleaning the way the Army taught with "rack grade" service rifles.

Stripping the bolt is not difficult, but requires a special tool in order to be done correctly and easily. This tool is found in the handle section of the regular GI cleaning rod. If you don't have a set of GI cleaning rods for the M14, get one. The handle section is a combination of special tools for servicing the M14, worth having, even if you never need to actually use it.
(if you want to know the details, do's and don'ts, PM me)

M14s M1`Garands and M1A rifles are well known for "doubling" if held and shot in just the right way. Completely releasing the trigger following the shot prevents this (although it might not be a match winning practice).

The other thing is slamfires. The floating firing pin actually taps the primer when the bolt shuts. With everything in GI spec (rifle and ammo), it does not fire. The weight and inertia of the firing pin is not enough to fire a GI spec primer when the bolt shuts.

BUT, commercial primers vary from the GI spec. Some have proven to be much more sensitive. Load a round, and then pull it out and look at the primer. Often you will see the small dent where the firing pin bounced off. Particularly with commercial primers, which are generally softer than GI spec.

CCI primers (standard large rifle) have been fine in my rack grade M1A for 30 years, never a slamfire, but they do show small dents from the pin. Each gun is a bit of an individual and the best thing is to use commercial primers made to the GI spec, if you can get them. IF not possible, I would recommend CCI over other brands, as being least likely to slamfire. Not saying other brands of primer WILL be problems only that they are slightly more likely.
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Old September 26, 2013, 04:27 PM   #22
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Great, Thanks.

I think that the cleaner might have acted as a lubricant and increased the pin movement. This combined with the commercial Winchester LR primers...
Bam.Bam.

At the Range yesterday I asked a regular who is there all th time with a bunch of Garands. He said that another guy had a slamfire because some gun oil got into the bolt......Bing..Bing ...Bing The light went on in my head as I realized that I was Guilty of the same mistake. I did not use oil but Hops #9 is pretty darn close to it....


RE: Flatened Primers and ICH Separation. After I got The RCBS MIC ran a bunch of fired cases.

They are all +5 +/- 1/2 thousands of an inch. After being fired in the M1A.
New unfired Factory Ammo (SMK 168-175Gr.) PNW, Remmington Match and Aussie Outback all run: -2 to -3 thousands of an inch.
After I measured the batch that separated they all came in at -10 to -12 thousands of an inch. SCARRY.

Each time they are fired they have expanded by +15 to +17 thousands of an inch. I believe that offers a goood explanation as to why the cases were destroyed.

Since the chamber is +5 I think I will adjust my Die to +1 to + 2 that way they will only expand by 3-4 instead of +15 to +17.

what do you guys think?????

Last edited by NinjasHateCommies; September 29, 2013 at 11:34 AM.
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Old October 11, 2013, 10:02 AM   #23
Grump
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Your seriously overly-sized (as in sized too much = too short) reloads don't fit into the long case/short chamber theory, but that one is more for the out of battery slamfires anyway.

Your long follow-through on the trigger *tends* to go against the bump fire/trigger caused double theory. BUT you have not reported the level of overlap your trigger group has between safety sear letoff and the primary sear picking up the other hammer hooks. Back when you had almost as many Garands on the line as M1As and military teams with M14s, the most common cause of doubling as I recall was marginal trigger jobs. Inadequate sear engagement can cause both micro-trigger-movement bump firing AND jar-off of the hammer.

Jar-off is the hammer being held back by either of the sears (or even both if the metal removal leaves them able to "sandwich" the hammer with the safety sear fully rocked forward), the feed cycle continuing to at least bolt fully forward, and then the impact of the bolt stopping, or maybe the op rod stopping a tiny bit later, providing a "jarring" impulse that knocks the hammer off of the sear(s).

The final detail of the event can be, but is not necessarily, jarring the trigger rearward to release the hammer.

Jar-off is almost always an otherwise safe double, as the bolt does have time to rotate fully locked by the time the hammer completes its fall to the BOOM position.

Regardless of whether your firing pin retraction and clearance of the receiver bridge functions are properly timed, I seriously doubt that lube in the firing pin channel, or lack thereof, could ever have an effect on the firing pin bounce and the force of its impact on the primer.

And think about it (this includes a few of our helpful posters in this thread)--if the firing pin is stuck forward, its ability to fire off a primer after or as the extractor is snapping over the rim depends on the FP staying forward the last 1/8-inch (really 2mm) of bolt forward movement, which is well before the bolt starts to rotate and lock. For that to fire off the primer, either the firing pin must be broken so the tang getting retracted in that same instant does nothing to the tip, OR the FP tang/receiver bridge interface has to be very, very badly out of spec. Whether by bad manufacturing or by wear or by both, this out of spec situation *at that point of the cycle* seems to be very rare.
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Old October 11, 2013, 10:26 AM   #24
Slamfire
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Quote:
The other thing is slamfires. The floating firing pin actually taps the primer when the bolt shuts. With everything in GI spec (rifle and ammo), it does not fire. The weight and inertia of the firing pin is not enough to fire a GI spec primer when the bolt shuts.
I hate to be argumentative about this, but primer sensitivity varies by the lot. GI primers are less sensitive on the average than commercial, but there are GI primers that were sensitive enough to slamfire in Garands/M1a's. The probability is less than commercial, but it happens, and I have slamfire accounts of Garands/M14's with GI ammunition. I have a paper copy of a early 60's test report wherein a Springfield Armory M14 slamfired out of battery with GI ball. It is exceedingly rare, but, sometimes it happens.

One should never assume that any mechanism with a free floating firing pin won't slamfire due to primer insensitivity. Every military mechanism with a free floating firing pin has a posted report of a slamfire. Just Google it. The danger with a Garand type mechanism is that they slamfire in battery, and out of battery, given a sensitive enough primer.

For safe operation of these rifles the shooter must follow certain loading practices and reloading practices. One must never load a round in the chamber and drop the bolt. One must always size the case smaller than the chamber.

This guy used a CCI #34 primer, but put a case in the chamber and dropped the bolt. Given his own description, the brass was either too fat or too long. It is highly likely that if the case was sized smaller than the chamber, all he would have had was an in battery slamfire. As it was, he blew the back of the receiver off.


http://m14forum.com/m14/120119-out-b...ire-today.html


Quote:
After 15 years of shooting and reloading for this rifle, I blew it up this morning. Out of battery slam fire. Receiver came apart to the rear of the rear sight. Bolt is destroyed and op rod is tweaked. Near as I can figure, my once fired LC brass should have been run through a small base sizer, I think the loaded round chambered about 90% of the way, bolt and firing pin wanted to keep going and kaboom. Case head separated and turned into a frag grenade, remainder of case remains stuck in the chamber….
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Old October 11, 2013, 11:19 AM   #25
Bart B.
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Slamfire's comments are worth noting.

It would be nice for me to see the primers from cases that slamfired. If they've got a normal, full depth dimple, your may have bump fired the rifle as it came out of recoil moving forward and your trigger finger stayed in place firing another round as the bolt closed on it. A proper, firm grip on the stock by your trigger hand's the best thing to do, then don't let your trigger finger forward to reset the hammer-sear engagement until the rifle's stopped moving from recoil.

If the sear-hammer engagement's been changed to below safe minimum engagement, that will sometimes cause slamfires from the shock of the bolt closing disengaging the hammer and letting it fall.

I don't see enough evidence of all stuff involved to say for sure what happened.

Anyone reloading fired cases from US made 30 caliber semiauto service rifles needs a case headspace guage so they can measure sized cases after sizing then compare them to fired ones. Sized case shoulders should be no more than .003" closer to the head than fired ones are. Otherwise, excessive stretching of the case about 1/4 inch forward from its head will cause the case to crack; or come completely off when fired and let a bunch of hot gas push metal parts into your head.
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