Specification Sheet for Inspections

Muzzle Face and Muzzle Crown Damage: When these get dinged up or too worn from use, they will need re- facing and/or re-crowning.

Muzzle Wear: Note: Muzzle Wear Gages were “Shop Made” at Arsenals and 5th Echelon Depot Repair facilities, but no Gauges to check this were generally issued to Armorers. In my experience, WWII Barrels were closer to between .300” to .301” land diameter when new and thus giving MW readings of 0 to 1 when new. Post WWII Barrels often ran at least .301” and larger, giving a MW reading of at least 1 or more on new barrels. I prefer a reading under 1 ¾ for a Garand Match and a reading of 1 or less on a NM Rifle.

Damage from Importer Stampings being struck too deeply. The average person won’t have a gauge for this, but you can sometimes tell when a tight patch hangs up in this area.

Follower Rod: Check to ensure the Rod is not bent and the hooks are not loose.

Operating Rod Spring: 19 ½ to 20 ½ inches when new. Minimum length 19 inches with NO flat spots on the coils of the spring and NO dog leg or other bends when at rest. Armorers frequently changed these springs when needed, though most G.I.’s never realized that. DO NOT use a spring over 20 ½ inches as I can almost guarantee it will cause the rifle to malfunction!!

Operating Rod Catch Pin: .154” to .155” when new. Believe it or not, there have been times when nothing else corrected Timing, until I used one in this size range.

Follower Arm: Measurements of the pivot studs vary from .004” to .006” in diameter when new. I like them .120” or larger. Replace if the studs are noticeably worn out of round or indented.

Operating Rod Catch: Though I have tried for decades, I know of NO way to measure these to ensure better timing with some than others. You just have to try different ones along with a Timing Gage, when you have Timing Problems. Check the wear on the Accelerator and the Pin is not loose.

Bullet Guide “Nose” Height:

WWII specs of .175”-.178” Tall. However, Post WWII Guides ran taller, sometimes from .180” - .184”, though the blueprint specs were not changed. Note: WWII Timing Gages seem to time sooner than Post WWII Timing Gages, but the latter generally works better for general operation. Armorers were taught to peen the nose out, so it would be longer and correct Timing, when the Nose was too short.

Follower and Slide: No specs for this part, but the Slide must move side to side freely and the Follower must not be damaged or cracked.

Operating Rod: I will break this down into three subsections.

1. Gas Piston. Minimum Diameter is .525” ALL the way around the diameter and must be checked with the G.I. Gage or Precision Micrometer for the best reading or at the very least a Precision Caliper. This because any small area that goes under .525” is going to cause function problems. Maximum Diameter is .528” and this is listed because an oversize Piston will hang up and not function in a G.I. Gas Cylinder.

2. The “Hooks” that engage the Operating Rod Catch must not be chipped or filed on, the latter because those who do that in an incorrect manner to correct timing, do not realize they are going through the surface hardness and it will cause more damage in use.

3. The “Lug” or Tab that rides in the Groove. Height .317”-.320”, Width .235”-.265”, and Most Importantly the Thickness .095”-.110.” I use .090” as a minimum thickness to ensure the lug won’t pop out of the receiver groove during operation, but in some receivers the Lug will work a bit thinner than that.

NOTE: Though I am not connected with them in any way, Columbus Machine Works, Inc. will fix Op Rods and they can be reached at: http://columbusmachine.com/oprod.htm

Bolt Group:

1. Firing Pin Protrusion: Minimum .044”, Maximum .060”. I have seen a fair number of short ones, though only one or two that were too long.

2. The Nose of the Firing Pin must not be chipped or damaged.

3. Firing Pin Hole in Bolt. Maximum .083”. The Smooth End of a Number 45 Drill Bit, .082” diameter, can be used as a Gauge. The Firing Pin Hole must not be chipped or worn out of round.

4. Minimum Length of Extractor Detent and Spring combined: 7/16” Minimum. This is not a G.I. Spec, but rather what I have found is the minimum that will keep the Extractor from Popping out of the Bolt in use.

5. The bottom of the Extractor Post, on the underside of the Bolt, MUST NOT protrude from the surface of the bolt or it will cause the Extractor to Pop Out during firing. I have ground shorter many dozens of these over the years.

Headspace using G.I. Gauges: I have seen enough CMP with TOO SHORT of Headspace that I most strongly recommend Headspace always be checked on inspections. Too Short Headspace can and will cause the case to rupture and throw gas and pieces of brass into your face and eyes. You really only need the GO and FIELD REJECT Gauges as they are the Minimum and Maximum Headspace. BTW, Headspace won’t “grow” more than about One reading in the entire life of a barrel.

GO: 1.940” NO GO: 1.946” FIELD REJECT: 1.950”

Gas Cylinder Lock Screw: If the Poppet is cracked at all, replace it, as it will cause function problems.

Gas Cylinder: It is difficult to completely check the serviceability of Gas Cylinders without a Gas Cylinder Gage and one that fails this check will not work, even when it looks fine otherwise. Other things to check for:

1. When looking at the front of the Cylinder, make sure the top of the Cylinder is perpendicular to the holes. Terrible copies are out there where the top of the Cylinder (where the Front Sight rests) is at an angle and these should be thrown away. Also, there should not be excessive wear on the face of the cylinder as that will cause too much gas to escape.

2. Threads for the Screw worn out.

3. Excessive pitting or grooves in the rear of the Cylinder.

4. Reamed out rear ends of Cylinders for Oversize Pistons. Though a properly matched Oversize Piston and Reamed Cylinder will function correctly when used together, they won’t work with G.I. Spec Parts.

Barrel Threads for Gas Cylinder Lock: If these are worn too much, there is nothing you can do but replace the barrel.

Gas Port Hole:

For .30-06. - .078” minimum. Use smooth end of 5/64” Drill bit to check, though it may not go into some properly drilled Ports.

For .308/7.62 mm. The G.I. minimum for 7.62 mm was .106”. HOWEVER, a Number 31 Drill Bit, sized .096”, provides plenty of Gas Pressure and is what I use for .308/7.62mm M1’s. NOTE: Many, if not most new commercial .308 barrels come with an undersized .078” gas port and must be drilled out to .096”, so the rifle will function properly.

Throat Erosion: G.I. Specs called for rejecting a Barrel with a reading of “6” or more for barrels on rifles that were to be shipped overseas. The idea was the didn’t want to ship a rifle overseas that did not have enough serviceable life left in it before it had to be re-barreled.

NOTE: I cannot more strongly recommend you take the Rear Handguard OFF the Barrel to inspect the top of the Barrel under it. Over the years I’ve been able to identify two piece and other Junk Barrels this way, or in one case, an Idiot cut a dovetail into that barrel that ruined it and that was hidden by the Rear Handguard. This was not part of a G.I. Inspection, but they usually didn’t need to do it.

Clip Latch: The Latch must rotate freely. It can hang up due to a bent Clip Latch Pin or “stuff” that has gotten inside of the hole in the Latch. I clean the hole with Pipe Cleaners and Bore Solvent, then oil afterwards. Replace bent Pins. If the Latch is not indented, it will normally work fine, though I had to replace a couple that caused a rifle to malfunction.

Clip Latch Spring: I cannot even begin to relate the Timing and Function problems I’ve seen due to these springs being too worn. I replace at least half of them on CMP Rifles and a higher percentage on other Rifles. I suggest if this spring doesn’t look new or nearly new, replace it and then you will never have to worry about replacing it again for most or all of your lifetime.

Receiver: I have inspected many hundreds of Receiver Bridges with the G.I. Gage and have never seen one fail that was not deeply indented by the tail of the Firing Pin or the Bridge was already cracked. I inspect the serrations for the Elevation Pinion closely and if worn too much, I won’t use that receiver on a “Shooter” M1, other than perhaps with Lock Bar Sights.

I MOST Strongly Recommend you check the Receiver Drawing Number against the Serial Number to ensure you don’t have a Welded Up Receiver. Then you should still inspect the Receiver closely for it having been Welded anyway, because sometimes the numbers match on Welded Receivers. I cannot recommend anyone use a Welded Receiver for Concerns.

Finally a note where Gremlins attack some Garands; causing the Rifle not to function properly even in a Perfectly Timed and lubricated Rifle, where all parts are serviceable and one is using good clips and Ammo. Yes, it can happen and it cannot be exorcized even with The Armorer’s Cross. I had worked on HUNDREDS of M1’s before I saw this and it bewildered me at the time. I have run into it four more times since.

The worst case I’ve dealt with was when I corrected the Timing and the owner said it did not function correctly. OK, I gutted the parts affecting Timing and used other parts to Time it again. Still didn’t work. OK, I took the rifle from the owner and had my parts and Timing Gage at the Range. I went through THREE more sets of parts before the third set worked!! The interesting thing was that rifle did not have another Timing Function problem for the rest of the life of that barrel.