M1a Issue

[lngrng]

Have an M1a that has been rebarreled and worked-on by Smith Enterprises of Tempe, Arizona. He is a well known M1A specialist who builds rifles for the military. Recently, I have been plagued with fail to feed issues. Fire a round, and it short cycles, bolt closes, but nmo new round is chambered. I have since replaced the spindle valve and spring, cleaned the rifle, including de-carbonizing the op rod chamber.....nothing seems to fix the problem.
Now I know that you specialize in Bolt rifles, but I'm wondering if you can shed some light on the problem or perhaps suiggest someone local who can fix the problem. Thanks in advance. Mark Van Beek, aka LNGRNG.

 

[GeneT]

Have an M1a that has been rebarreled and worked-on by Smith Enterprises of Tempe, Arizona. He is a well known M1A specialist who builds rifles for the military. Recently, I have been plagued with fail to feed issues. Fire a round, and it short cycles, bolt closes, but nmo new round is chambered. I have since replaced the spindle valve and spring, cleaned the rifle, including de-carbonizing the op rod chamber.....nothing seems to fix the problem.
Now I know that you specialize in Bolt rifles, but I'm wondering if you can shed some light on the problem or perhaps suiggest someone local who can fix the problem. Thanks in advance. Mark Van Beek, aka LNGRNG.

First, verify that it's short cycling.

Check a mag to make sure that it holds the bolt open when empty (insert empty mag, cock - bolt held open? If yes, proceed...

load a single round in the magazine, chamber it, and fire. Does the bolt hold open? If it does, it's probably not short cycling - just not picking up the next round.

Does ammo cycle through the rifle when cycled by hand? If not, there's probably an issue with round pickup. Likely the magazine is to blame.

If that all check out, can you hear the gas piston slide to and fro when you tip the rifle muzzle down then stock down?

If all that seems good, I'm going with a gas port too small or misaligned.

GsT

 

[Asa Yam]

Lngrng,

1 key point not mentioned in your post. What load are you using? An M1A is VERY preferential in what it shoots. Designed for a 147 grain bullet Fired around 2650 FPS, the gas system is limited to sub-180 grain bullets at velocities below 2600 FPS. Combined with the requirement to full length size the case to a uniform length, and using a powder with a specific burn rate (evtruded powders in the burn range from IMR-4475 to 4064). Seating of the primer is also important: It must be below flush, and the primer is required to have a hardened cup to prevent "slam fires", occasions where the round discharges after closing the bolt, without actuation of the trigger. This is because the design of the M1A DOES NOT include a spring to hold back the firing pin when the bolt is closed. (Ever open the bolt of an M1 or M1A and see a "dimple" in the middle of a primer of a chambered round? Now you know the reason why it is there.)

In summary, the requirements for ammo that cycles the rifle are:

• Brass resized to a uniform range: Allows for COMPLETE cycling of the gas mechanism and operating rod;
• A uniform dose of an appropriate EXTRUDED powder: One of the -4895 clones by IMR or Hodgdon is a good starting point;
• An appropriate primer, seated at or below flush: Federal 205Ms work, but so do WLRs, and CCI_34s, and;
• An appropriate bullet. Sierra makes 150, 155, a68, and 175 MatchKings, all of which work with appropriate charges of -4895.

If in doubt, the words of the Sierra Bullets Ballistics Department should always be remembered:

A semiauto rifle is NOT a benchrest rifle. Practices which improve accuracy in benchrest can be hazardous or dangerous in a military type semiauto. DON'T DO IT.

Hope this helps.

Asa

 

[MilGunsmith]

After trying the above with a magazine, check the following:

1. Gas piston must be between .4968" and .4980" in diameter. The inside must be cleaned also, use a long #14 drill bit and either a 5/16", Letter O or Letter P drill bit, depending on who manufactured the piston, all turned by hand to clean the carbon out. Make handles for them and keep in cleaning kit.
2. Gas cylinder internal diameter must be between .4980" and .5009". Gas piston should move freely inside cylinder, any binding is a sign of warping or other damage.
3. Gas port in barrel should be .062" in diameter, and properly aligned. Check alignment by using a .062" dia. rod and going through the vent hole in the bottom of the gas cylinder, it should freely go through the spindle valve and into the barrel through the gas port.
4. Gas plug should be cleaned internally also using the same drills as the gas piston. Gas plug should be tight. Mark with paint pen to verify that it hasn't come loose during match.
5. Check for binding in the op rod by removing the op rod spring and spring guide. Then tip the rifle back and forth, the bolt and op rod should move freely back and forth without touching them.
6. Reassemble and shoot the rifle with proven ammo such as GI M80, M118, M118LR, M852, or a good M14 reload such as 168gr Matchking with 41.5gr IMR-4895. This was our standard match load.
7. Make sure that the rifle is properly lubed. Use GI rifle grease, or an equivalent like Lubriplate or TW-25B, not oil or CLP. Lube the op rod and the spot in the receiver that it rides in, the bolt roller and its recess in the op rod, and the groove inside the receiver that the bolt lug rides in. M1's and M14's are dependent on proper lube and are kind of messy to shoot when lubed right.
8. Make sure that the action is not loose in the stock. Also the rifle must be shot with it firmly in the shoulder. I used to fill the holes in the buttstock with lead shot to add weight and balance to a heavy barreled rifle.

 

[lngrng]

Smithing help

Lngrng,

1 key point not mentioned in your post. What load are you using? An M1A is VERY preferential in what it shoots. Designed for a 147 grain bullet Fired around 2650 FPS, the gas system is limited to sub-180 grain bullets at velocities below 2600 FPS. Combined with the requirement to full length size the case to a uniform length, and using a powder with a specific burn rate (evtruded powders in the burn range from IMR-4475 to 4064). Seating of the primer is also important: It must be below flush, and the primer is required to have a hardened cup to prevent "slam fires", occasions where the round discharges after closing the bolt, without actuation of the trigger. This is because the design of the M1A DOES NOT include a spring to hold back the firing pin when the bolt is closed. (Ever open the bolt of an M1 or M1A and see a "dimple" in the middle of a primer of a chambered round? Now you know the reason why it is there.)

In summary, the requirements for ammo that cycles the rifle are:

• Brass resized to a uniform range: Allows for COMPLETE cycling of the gas mechanism and operating rod;
• A uniform dose of an appropriate EXTRUDED powder: One of the -4895 clones by IMR or Hodgdon is a good starting point;
• An appropriate primer, seated at or below flush: Federal 205Ms work, but so do WLRs, and CCI_34s, and;
• An appropriate bullet. Sierra makes 150, 155, a68, and 175 MatchKings, all of which work with appropriate charges of -4895.

If in doubt, the words of the Sierra Bullets Ballistics Department should always be remembered:


Hope this helps.

Asa

Asa, I am using Lake City 19 Factory Ammunition in my M1A. I have checked everything provided as answers to my original p[ost, and everything checks out as it shoul.
Mark, member at Tri-County.I would encourage you to call me at 503-819-3411

 

[Asa Yam]

Asa, I am using Lake City 19 Factory Ammunition in my M1A. I have checked everything provided as answers to my original p[ost, and everything checks out as it should.

What LOAD w/LC brass? The answer to this question matters, big difference between the 175 grain load, and the 147. Rifle should cycle w/ the 147, it may or may not with the 175. You are aware that LC changed the powder in the 175 grain load? A year or two after Winchester took over management of LCAAP, they changed the powder in the LR load from RE-15 back to something similar to 760. Wrong powder (overgassed) for the M1A.

 

[lngrng]

Smithing help

What LOAD w/LC brass? The answer to this question matters, big difference between the 175 grain load, and the 147. Rifle should cycle w/ the 147, it may or may not with the 175. You are aware that LC changed the powder in the 175 grain load? A year or two after Winchester took over management of LCAAP, they changed the powder in the LR load from RE-15 back to something similar to 760. Wrong powder (overgassed) for the M1A.

Asa, are you willing to look at my rifle and perhaps offer some suggestions to fix the problem? I have noted my phone number and identified myself as a member of the same local club as you.........I know that you are knowlegable about the rifle in question, and I would really like it if you would be willing to offer help. If $$$$$ is an issue, I would be willing to grease your palm for a fair amount. I am aprehen
sive to send the rifle back to Smith Enterprises due to concerns regarding shipping issues. I hope that you will be willing to offer some assistance.
Mark 503-819-3411

 

[MilGunsmith]

What LOAD w/LC brass? The answer to this question matters, big difference between the 175 grain load, and the 147. Rifle should cycle w/ the 147, it may or may not with the 175. You are aware that LC changed the powder in the 175 grain load? A year or two after Winchester took over management of LCAAP, they changed the powder in the LR load from RE-15 back to something similar to 760. Wrong powder (overgassed) for the M1A.

Our All Guard load back in the day was LC Match brass with 168gr Sierra MK and 41.5gr IMR-4895.