M1 Rifle short stroking

[Grizzman]

I'll take my M1 Rifle short stroking experience as an opportunity to create the first thread in the Help Me Fix My Gun category.

The M1 passes the tilt test, and the op rod moves smoothly with no binding or contact with the stock or sling swivel band. I also replaced all springs with ones from Orion 7.

I had been trying between 45.5 and 48.0 grains of IMR4064 and Varget with 168 grain Hornady A-Maxes in LC Match brass set off by CCI #34 primers seated to 3.240" to 3.330" COAL.

The supplier of the M1 sent me a different op rod and gas cylinder, which made no difference. I then bought some Greek HXP mil surp ammo, which ran fine. Since it runs with mil surp, he says the problem is my handloads, not the rifle, and will not assist with any more troubleshooting.

I bought a pound of H4895 which should have the ideal burn rate and used between 45.5 and 47 grains with the above mentioned details with the same short stroking results.

I then switched to 150 grain Sierra GameKings, thinking possibly it just doesn't like the 168s and loaded 8 each with 47.0, 47.5 and 48.0 grains of H4895 (with the above details). I experienced multiple short strokes with the 47.0 and 47.5 grain loads, but made it through the clip with 48.0 grains....but that was a fluke as it didn't work in a 2nd test.

I tore down a few of the Greek cartridges, and they had 52 grains of a ball powder with 150 grain FMJs. I loaded 49.5 grains of the Greek powder with 168s (and the above details) with success.

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I decided to get a McCann gas regulator to try with IMR 4350, figuring I could get it to run properly in that configuration. I tried it with 51 to 53 grains, and even with the smallest gas venting aperture, I got the same results as before. I fired a few rounds of the 51 grain load with stock gas cylinder screw, and it cycled them fine (brass was flying to approx 12:30 to 1:00.

I then bought some somewhat faster H414, and loaded up some test rounds with between 50 and 52.5 grains. It fed every time with all the loads, and the brass was going to between 1:00 (most between 1:30 and 2:00) and 2:30, which is more appropriate.

My current idea is to locate someone local with an M1 so I can meet them at a range to try their op rod and/or gas cylinder in mine, with 46.5 grains of Varget driving 168s. Hopefully this will allow me to determine if the gas system is the cause of the failures. I use Varget in my 308 Win loads, so would really like to use it in my M1 also. H414 may work, but it's not appropriate.

Do I have an volunteers that are local to KC. I've loaded up 104 rounds of ammo for the test, and can make up some more.

Does anyone have an M1 gas cylinder gauge I could borrow?

Does anyone have experience with Columbus Machine Works in case the op rod piston is to blame?

Does anyone have any other ideas on what else to check?

[Dave Waits]

Okay , since you changed the springs and it didn't help the next logical culprit is the gas system.
1.) Gas-Cylinder Lockscrew.
A.) Stupid question but, is the screw on tight and the threads Clean?
B.) Is the valve damaged or cracked?

2.) Gas-Cylinder.
A.) is the Gas-Cylinder cracked at the screw?
B.) Is it oversized, take an empty Remington 7mm magnum case and stick it in after cleaning the Gas-Cylinder, base-first(Secret!!!! The belt on a Rem.7mm mag. measures .530). Now,look in the other end of the Gas-Cylinder where the Op-Rod enters, can you see light around the case? If so, you need another gas-cylinder.

3.) Op-Rod Piston.
A.) It should measure no less than .5256" with a 0-1" Micrometer.
B.) Are any of the rim-edges chipped?
C.) If you answered yes to either query, you need a new piston, Call Columbus Machine, they'll install a new one very reasonably.

4.) Barrel port.
A.) Clean out the cruddy carbon with a toothpick and mike it with a #47 drillbit, should enter the port.
B.) Try again with a #45 drillbit. This is the No-Go gauge for the port. If this bit fits the port is too big, only answer is another barrel.

Good luck and let me know what you find, maybe I can help.
Dave

[Grizzman]

Okay , since you changed the springs and it didn't help the next logical culprit is the gas system.
1.) Gas-Cylinder Lockscrew.
A.) Stupid question but, is the screw on tight and the threads Clean? Yes, and yes.
B.) Is the valve damaged or cracked? This is a subject that has me confused. The gas cylinder screw seems to be a solid plug with no valve, orifice, etc.

2.) Gas-Cylinder.
A.) is the Gas-Cylinder cracked at the screw? The gas cylinder is mechanically sound.
B.) Is it oversized, take an empty Remington 7mm magnum case and stick it in after cleaning the Gas-Cylinder, base-first(Secret!!!! The belt on a Rem.7mm mag. measures .530). Now,look in the other end of the Gas-Cylinder where the Op-Rod enters, can you see light around the case? If so, you need another gas-cylinder. I'm able to insert the case up to .50" of the shoulder. Looking at a bright light bulb in this condition shows slight light leakage around less than half of the belt.

3.) Op-Rod Piston.
A.) It should measure no less than .5256" with a 0-1" Micrometer. In most places, it measures between .5245" and .5255" with my standard RCBS caliper. I don't own a micrometer. The replacement op rod sent me measured the same as the one that came with the M1, and I told him what the original one measured......which annoys me somewhat.
B.) Are any of the rim-edges chipped? There aren't any chips.
C.) If you answered yes to either query, you need a new piston, Call Columbus Machine, they'll install a new one very reasonably.

4.) Barrel port.
A.) Clean out the cruddy carbon with a toothpick and mike it with a #47 drillbit, should enter the port. A #47 bit goes in, but not with finger pressure only......light persuasion is required.
B.) Try again with a #45 drillbit. This is the No-Go gauge for the port. If this bit fits the port is too big, only answer is another barrel. A #46 won't fit, so it's definitely not too big.

Good luck and let me know what you find, maybe I can help.
Dave



So from this it seems that the gas port is on the small end of the acceptable range, the op rod piston is too small, and the gas cylinder is at least acceptable.

I can easily ship the op rod to Columbus machine to have a new piston installed.

Thanks for your help with this.

[NAMVET72]

See I told you Dave, could help you........

[Grizzman]

Yep, you were right about that, and I had a feeling he'd stumble across the thread eventually and give some helpful info....which he did in spades.

[Dave Waits]

Okay , maximum runout on the piston is .00035 so, it's small, send it to Columbus Machine, while you're at it it would be good to have them check and set the bends. Jim Swartz, when he quit doing this, sold them his equipment which included a $1,500.00 bend-gauge for the M1 Op-Rod.
Your Gas-Cylinder sounds servicable.

If your gas-screw has a single screwdriver slot it's solid, otherwise it's a poppet-valve type(Slot looks like a big lipshead). If it's cross-slotted, turn it upside down, put a 1/8th punch into the slot-center and push down onto a hard surface. The face will rise up. There could be grit or carbon stuck in it holding it partially open. Scrub the inside good with a toothbrush and Hoppes'. Then let it soak in Hoppes' for about 1/2 hour and scrap off the face with a penny until the black(Carbon buildup) is gone. Now, you can check the face for a crack. If you find a crack in it let me know, I have some extra servicable screws.I'll send you one.

Barrel-port- Chuck up the bit(#47) in a variable-speed batterydrill or better yet a Dremel or foredom tool and slowly run it into the port, making sure you run it straight in. It sounds like there's a carbon buildup around the hole.
Dave

[NAMVET72]

,
Hello wait to Dave Waits sees this Thread and hopefully he will be able to answer your questions and help you out...........