M1A Short Stroking Mystery--only works good when hot

[Cosmoline]

Last week I had a ton of short stroking, almost to the point of being a straight pull. I cleaned out the gas system on my Springfield M1A Squad Scout, kept it dry and returned to the range today. I also made sure the gas plug was tight this time. Both the bolt assembly and the pistol passed the tilt test fine.

Unfortunately, it was still short stroking. Not as much as last time, but still enough to be annoying.

However, and here's the odd part, when the rifle heated up after about 50 rounds all short stroking ceased and the thing worked beautifully. So go figure. I've pulled it apart again and the only thing I can see potentially off is that the barrel gas hole doesn't seem to line up perfectly with the piston chamber. So you can look through the access hole and see light, but more of a waning moon than a full moon if you know what I mean. I have no idea how to adjust that and don't have those tools anyway. And that may have squat to do with the issue.

Any ideas on what's getting fixed when it heats up?

 

[Robbins290]

How many rounds have you put down range with it. How long have you had it? I know with my m1 garand (kinda the same design) the action spring will cause that. When i go to replace it, the old spring is about 3-4 inches shorter where it was compressed passed service life. I would try that. Brownells or e gun parts should have one in stock

 

[madcratebuilder]

You may need to "shim" the gas cylinder. The gas hole in the gas cylinder is larger than the gas hole in the barrel by about .040, you have some room the play with.

Do you have a gi piston or a coated piston from Sadlak?

I would check the bore diameter of the gas cylinder, make sure it's in spec.

Is the op-rod guide greased up?

Op-rod rubbing on hand guard?

How to shim the M14 (click this)

However, and here's the odd part, when the rifle heated up after about 50 rounds all short stroking ceased and the thing worked beautifully.

I would look real hard at the gas piston and gas cylinder. When these heat up and expand you have a better gas seal. You need .0025 to .0036 piston to cylinder clearance cold.

This link well give you piston and cylinder specs.
http://www.sadlak.com/si_rifle_parts_pistons.html

 

[Jason_G]

Sounds like a gas problem to me as well, but I'm not a smith. Shimming might allow you to get everything back in line and tight, and will improve your accuracy anyway, so it might be worth a shot. The other alternative would be to send it to SAI and have them make it right, and maybe ask nicely for a few goodies for your trouble.


Jason

 

[Cosmoline]

Thanks!

You mean these shims?

http://www.fulton-armory.com/gascylindershimsetstainless.aspx

There is some play between the gas cylinder and the gas cylinder lock. It can be rotated about 1/4 a turn more and as I understand it, the shims lock it down when it's in line. Would too much play here cause the short-stroking?

Everything is lubed up, and the cylinder is running dry apart from a finger-touch of CLP

I'll check the dimensions. This rifle hasn't been shot much, certainly not enough to wear out the spring. In fact I'm hoping this is just a teething issue.

 

[VA27]

It sounds like the gas cylinder isn't lined up correctly.

Pull the gas plug, screw the gas cylinder lock (the figure-eight looking thing) all the way down until it's snug. Then back it off just far enough to line it up with the gas cylinder and install the gas plug and tighten it up. If everything is right you shouldn't have to back the lock off more than half a turn. If it takes more than three-quarters of a turn you probably need a shim.

 

[emmett dunham]

Sometime the gas ports looks clean and it is not. I used a drill bit to clean mine out by twisting it with my fingers. I would also check the specifications of the pistion and the cylinder to make sure they are with inn spec, the parts when they are heating up could be closing the specifications. The shim sounds like a good idea but I wonder about the improvement after some ammo is shot with the alignment as is.

Emmett

 

[asia331]

Shoot the M-1A every weekend; only short stroking I've experienced has been with Pakistani milsurp.

 

[Cosmoline]

Well I did some measuring and the piston, while not exactly perfect, seems to be within tolerances. I think the problem was an improper alignment of the holes. I rotated the locker around one more turn and the light down the bore now shows a "full moon" so the maximum gas should be vented with less chance of debris hanging it up.

Of course that doesn't explain why it was working when hot, but we shall see. One step at a time.

Even as a sometimes straight-pull I'm really liking the way this rifle shoots from the stances. Rock solid platform and very comfortable in the hand.

 

[madcratebuilder]

I rotated the locker around one more turn and the light down the bore now shows a "full moon" so the maximum gas should be vented with less chance of debris hanging it up.

This should give you full gas. You can make or buy a stepped pin that inserts through the bottom hole of the gas cylinder. The small end, .062+/- fits in the gas hole of the barrel and the larger diameter .112+/- fits in the cylinder's gas hole. If the pin seats then you correct alignment. You have about .025 tolerance in either direction.

Using your lights achieves much the same results.

Ideally you want the cylinder lock to be hand snug at the 5 O'clock position and wrench tight at 6 O'clock alignment.

Install the gas piston oil free and add a drop of #9 after assembly. Any kind of oil in the cylinder/piston well cause excessive carbon build up. Under normal conditions you should be able to shoot all year without cleaning the gas cylinder unless you are using incredibly dirty ammo, ie Russian or Packy.

Of course that doesn't explain why it was working when hot,

As the piston and cylinder heated up the clearances decreased creating a tighter, more effective seal.

 

[Cosmoline]

That would explain it--it also points to my next upgrade on this rifle.

 

[Jeremy2171]

If it doesn't work..Call Springfield Inc and have them fix it...warranty for life...y'know...I wouldn't spend any money to "repair" it....upgrade sure but not to "fix" what they cover..