PDA

View Full Version : garand slam fire?


bamaranger
March 8, 2010, 02:21 AM
I am experiencing slam fires in my Garand, after changing the op rod from GI to heavy duty after market. My ammo is properly headspaced, primer pockets uniformed, and uses mil-spec hard skinned primers. I think my ammo is OK. I have reinstalled the GI spring, but have not made it out to shoot again since the slam fire experience. (hey, I always wanted to shoot a BAR!)

My diagnosis is the heavy spring 'caused the prob. I thought I'd made a change to ease wear and tear, but believe I have created a (dangerous) problem. B..B..Bang , PING, what a trip.

Questions:
-Has anybody else experienced a slam fire after an op rod spring change?

-Is there a std for the weight of an op rod spring (lbs pull) The GI spring seems weak, the heavy duty very stiff. What's "right" and how is it determined?

-Tell me what else I should consider, firing pin protrusion, disconnector.....?
I think these parts are OK, as the problem occurred AFTER the spring change, but, can I check them for spec, at home. I do have another trigger group that I can swap out.

dmazur
March 8, 2010, 02:36 AM
My understanding is that these are GI spec (and stainless, too) -

http://www.m1garandrifle.com/Garandparts.htm

The part you want is G28a.

As the timing in the Garand is critical, I could never understand why someone would make an "extra power" spring. I'd get the correct spring, then make sure the rifle is lubed properly.

(You're lucky you're not getting OOB firing. That's more excitement than you want. :) )

stubbicatt
March 8, 2010, 10:23 AM
You might replace the firing pin.

Generally slam fires in the Garand are really caused by hammer follow. You might replace your "disconnector" or secondary sear.

My $.02 worth what you paid for it.

Slamfire
March 8, 2010, 11:41 AM
My diagnosis is the heavy spring 'caused the prob. I thought I'd made a change to ease wear and tear, but believe I have created a (dangerous) problem. B..B..Bang , PING, what a trip.

I would agree. I do not have the URL, but I recall reading of another Garand slamfire after the owner installed an "extra duty" recoil spring.

I have read of AR slamfires when owners hard mounted hardware to the bolt carrier in a gas piston conversion.

I believe that either increased weight to the bolt carrier, or an increased strength recoil spring increases the chance of a slamfire.

I believe the forward speed of the bolt is increased, which increases the momentum of the firing pin as it rebounds off the primer.

You must fix this. You are running the real risk of an out of battery slamfire.

I took three stripped Garand receivers and found the point at which the receiver bridge starts to hold back the firing pin.

http://img.photobucket.com/albums/v479/SlamFire/M1a%20and%20Garand%20Receiver%20Pictures/ReducedDSN6756SAM1areceivershowingb.jpg

http://img.photobucket.com/albums/v479/SlamFire/M1a%20and%20Garand%20Receiver%20Pictures/ReducedSCN6746HRReceivershowingbrid.jpg

http://img.photobucket.com/albums/v479/SlamFire/M1a%20and%20Garand%20Receiver%20Pictures/ReducedDSCN6749IHCReceivershowingbr.jpg

The firing pin is totally unobstructed in the forward travel of the bolt up to this point on these receivers. If the next slamfire occurrs just .00X" earlier, the lugs are not engaged and you will have an out of battery slamfire.

Mechanical malfunctions tend to empty the magazine. When I have seen M1a's and AR's malfunction due to following hammers, a whole clip will be shot up at once.

It is good that you are using "thick skinned primers" (CCI#34's?), but are you using case gages in setting up your sizing dies?

A combination of fat cases sized in a standard sizing die, and a overly long case, will create a condition favorable for a slamfire. For a fat or long case, the bolt has to stop while the cocking cams crush fit the case to the chamber.

http://img.photobucket.com/albums/v479/SlamFire/Reloading/ReducedWilsongagemeasuringnew308bra.jpg

If you are not using a case gage, like this Wilson gage, then you should get one and verify that your ammo is below the No Go of the gage.

http://img.photobucket.com/albums/v479/SlamFire/Reloading/Wilsongagebetweengoandnogage308bras.jpg

For gas guns, I recommend sizing cases with a small base die, and sizing the case to gage minimum.

Please report back when you finally figure out the cure.

Chris_B
March 8, 2010, 12:46 PM
Bamaranger-

What were you trying to correct with the heavy-duty oprod spring? Am I correct in guessing that the first round was not being stripped out of the clip when you loaded a fresh clip? There's nothing "wrong" with that

If the rifle never slam fired with the GI oprod spring, and it will with the ehavy duty spring, while not conclusive proof, I would start suspecting the new spring

Tim R
March 8, 2010, 04:36 PM
How many rounds are squirting out? 2 or the entire 8?

I have a tuned 308 M-1 which uses a Wolf extra power op rod spring. The only time I have problems is when I "milk" the trigger which produces doubles. Milking the trigger is when you try to shoot the M-1 like you would a pistol. This is not a slam fire because of your light trigger pull the trigger gets tripped again under recoil.

Since you are using mil-spec primers, I doubt you are getting true slam fires.

A M-1. M-14/M-1A and the M-16/AR-15 series of rifles the firing pin all "dimple" the primer when a round is chambered. I have not seen a dimpled primer fire when shooting from a clip or Mag. I've shot 1,000's of CCI large rifle and CCI BR primers in the gas guns with no problems. Federal primers have a reported history of slam fires however.

enstorm
March 8, 2010, 05:29 PM
I think Tim R is on track. A slam fire is an out of battery experience, I believe, but it sounds as though that is not the case in your situation. My Garand with LC ammo will full auto a couple of rounds every so often when I am gentle on the trigger. And, this happened both before and after putting in a Wolf op rod spring.

bamaranger
March 9, 2010, 01:40 AM
I am setting my cases up using an RCBS precision mic. Fired "like" cases in my LMR M1 run +.09. I set my dies up to size to +.06+ My other M1 has a different Prec. Mic reading. I am steering by an article written by the guys at Fulton Armory (I think). I've got to look the article and #'s up everytime I load for the Garands. I am not using a Wilson gauge, but....doesn't the use of the RCBS Prec Mic accomplish the same task regards headspace/setting cases up for correct headspace?

As far as a "long" case goes, I am trimming to 2.485, never over 2.490. That is just over the "trim to length" and safely under max case length according to my Speer manual. Not ruling out an ammo problem, but I think I've got a handle on the ammo situation. But.......if I absolutely need a Wilson gauge to load for Garands, I'll get one.

My purpose for a heavier spring was to reduce bolt slam on the receiver at the shot, ie lower bolt speed rearward. What I think I've done is INCREASE bolt speed/energy forward in the return to battery/chamber fresh round stage, and the free floating firing pin is striking the primer hard enough as the bolt locks, to fire the next round in the chamber. No good deed goes unpunished. What I probably should do (in hindsight, and more educated now) is to get an adjustable gas plug. The spring was in fact a Wolfs HD from Brownell's.

I have not dumped an entire clip, double and triple when it occurred.

I am familiar w/ "floating" a trigger stroke and am guilty of same occassionally w/ M1, M14 and AK off bags/bench when I am REALLY caressing the trigger.
No follow through. No pull trigger to rear and hold. This was different.

I have also experienced doubles and trips when a priming tool pooped out and began seating primers high. A new tool, mil spec primers and uniforming primer pockets have solved this former problem I believe.

I am going into my days off and will shoot the LmR m1 w/ the GI op rod spring installed and report back.

Slamfire
March 9, 2010, 09:34 AM
I am setting my cases up using an RCBS precision mic. Fired "like" cases in my LMR M1 run +.09. I set my dies up to size to +.06+

As far as a "long" case goes, I am trimming to 2.485, never over 2.490. That is just over the "trim to length" and safely under max case length according to my Speer manual. Not ruling out an ammo problem, but I think I've got a handle on the ammo situation. But.......if I absolutely need a Wilson gauge to load for Garands, I'll get one.

Based on this, your cases are sized to the proper length and trimmed to the proper length.

My purpose for a heavier spring was to reduce bolt slam on the receiver at the shot, ie lower bolt speed rearward. What I think I've done is INCREASE bolt speed/energy forward in the return to battery/chamber fresh round stage, and the free floating firing pin is striking the primer hard enough as the bolt locks, to fire the next round in the chamber.

Could be but don't ignore a bad trigger group.

I have not dumped an entire clip, double and triple when it occurred.

EEK!. I really hope that you do not have a trigger group problem. Messed up trigger jobs also do this. It is very unusual to have mulitiple slamfires due to primers.