M1 Muzzle Repair Counterbore Diameter

[JRD]

Back after WWII, ordnance repaired M1's with damaged crowns by counterboring the muzzle. On these "blunderbuss" muzzles that were worn into funnels by abusive cleaning rod action, what diameter was that counterbore?

I'm thinking something in the .350-.375 diameter would be appropriate, but was hoping to get some corroborating information from the brain trust here.

[Der Gebirgsjager]

That's interesting. Are you sure it was OUR ordnance? Muzzle counter-boring is common in some European nations, but I've never seen it on a U.S. rifle by U.S. Ordnance. I guess anything is possible. Don't forget that we gave away/loaned many, many M1s to such nations as S.Korea, Denmark, Greece, Italy, etc. and perhaps you have encountered one of these. At any rate, I would think that if one wanted to follow that path rather than to re-barrel the piece it wouldn't have to be hugely over the original bore size of .308. Perhaps .312 would do.

[SOFMatchstaff]

I have used a standard 5/16 piloted counter bore on several 30 cal barrels, the really bad ones need the .328 (21/64), usually .375 to .500 deep. I have a 95 Win in 30 US with a russian bore, had to go to .328 dia .375 deep to get to good rifling. It now shoots well with 303 Brit ball bullets..

.3125 to .328 is the smallest jump I could find in std counter bores , about $25 each

[samari46]

Think Manson may be making the crowning tool for M1 Garand. Frank

[JRD]

The rifle in question is a reimport from South Korea from the early 90's. I checked last night and the muzzle flares open to .320 and the rifling is completely worn away to approximately 3/8" inside the muzzle. This rifle probably missed every Nork it was ever shot at, but no doubt it kept some recruits busy with a cleaning rod.

I can't find it again, but I did find a reference to counterbored muzzles in a post-WWII US technical manual the other day. I couldn't find any dimensions though. I've read about counterbored muzzles as a repair for many years on the internet.

Manson does make a recrowning tool, but not a counterbore tool. I'm going to make a custom counterbore tool using the pilot from a 30 cal chamber reamer and go with .350 ID. Wish me luck. If it doesn't work, I will still have a Garand that doesn't group and needs a new barrel. I'm not looking to make a match rifle. If I can turn a minute of basketball shooter into a minute of baseball shooter and make it useful as a water jug buster and steel gong ringer, I'll call it a success.

[Der Gebirgsjager]

Oh--you're talking depth of counter bore, not diameter. Well, how could one give a hard and fast answer, as it would depend on the individual rifle's condition and how enthusiastically it had been cleaned by how many. That is why TOE gauges have different markings on them, to assess different stages of wear. If you want to follow this path, then you'll have to determine the depth at which the size of the bore enlarges past acceptable. If it's one of those into which a bullet will completely disappear when inserted from the muzzle, then it's obviously going to have to be deeper than that. Perhaps you could insert a .308" diameter rod into the muzzle and when it gets tight mark it and measure to the end of the rod. I'll predict that, if the barrel was bad enough to be counter bored, the rest of the bore is shot out as well, and even a .310 diameter rod will go in deeply and perhaps completely through. Firing tens of thousands of FMJ rounds over many years will do that to any barrel. Here's how I know:

When I went through Army Basic Training at Ft. Ord in 1961 I anticipated shooting Expert with the issued M1, but trying my best was only able to qualify as Sharpshooter. On the last day of the rifle program, "Trainfire" I found a perfect .30 cal. bullet lying in the sand at the range. It didn't even have rifling marks on it. I dropped it into the open breech of the M1 and it rattled down the barrel and fell back into the sand. I brought this to the attention of the Range Officer and asked to shoot for qualification again with another rifle. He said not to worry about it, that when I reached my assigned unit I would have to requalify anyway. That statement was true and I easily fired Expert with a rifle in much better condition. The rifles at Ft. Ord had been continuously issued to every Basic Training cycle since WW II, and were just about shot out.

About 3 years ago I re-barreled 5 M1 rifles for personal use. I used new Criterion barrels, and the process was not at all difficult. You would need to buy or rent a pull through chamber reamer, as these come short chambered, and have a set of .30-06 headspace gauges. Saving a Garand is always worth it, in my opinion.

I have (last count) about a dozen M1s. Four of them were "Blue Sky" S. Korean returns, and I re-barreled three of them. None had counter bored muzzles, but all were in about the same bore condition as my Basic Training rifle. As I said in my earlier post, I've never seen an M1 counter bored by U.S. Ordnance. Your rifle, do as you will; but the results are going to be much less satisfactory that if you re-barrel.

Good luck with your project.

[Outpost75]

Don't know about the ROKs, but in the PI they simply ran a .30-'06 chambering reamer into the barrel muzzle until the shoulder just barely kissed the muzzle crown.

The .343 neck diameter on the '06 reamer works fairly well if the reamer pilot is a good fit in the barrel.

[KenT7021]

The Army counterbored carbine barrels.I don't believe they did it to the M1 rifle due to the location of the gas port.In 1963 I looked at a number of carbines in a rack at Surplus City in Colo Springs.All were counterbored.

[john.k]

I counterbored a M1 muzzle 3/8 dia,and about an inch deep.....Gun looked like new ,but fired with out properly cleaning the bore.Lapped out the bore with steel wool and coarse valve grinding paste,counterbored the muzzle ,and it hit what it was aimed at ,and cycled properly.

[samari46]

Might need a few piloted reamers to do this.311,308,304 and 300 and ream it out in steps. And about a qt of the black heavy sulferized cutting oil. feed the barreled action completely stripped pf course. You could do thes under power. Starting with the smallest size reamer Of course it goes without saying feed the barreled action through the huse the tool post boring bar on the headstock to hold the reamers. Feed in slow and oil heavily. Frank

[nicholst55]

I knew an old-school gunsmith who had sporterized a large number of milsurp rifles in the late 40's, 50s and 60s. His regular procedure involved either cutting 1" off the muzzle and recrowning the barrel, or else running an appropriate sized throating reamer down the muzzle 1". In the case of an M1 Garand, I would stop just short of the gas port.

[JRD]

Thanks for all the constructive advice guys. I have crossed the Rubicon. I had a piloted .350 counterbore tool made up and bored my muzzle last night.
I lubed the flutes with Vaseline to catch the chips and cleaned frequently. I stripped the gun down to the bare barrel and clamped the barrel in a padded vice. For lack of a lathe I did it by hand.
I did learn some lessons. First is that a .300 pilot is great but when the muzzle is flared open to .320 there is lots of play in the pilot. I held the tool as straight as I could and cutting got better as the pilot got down to ride on the lands. I bored in about .35 and have verified with a bore scope that there is rifling at the crown.
I hope to be able to shoot it Sunday afternoon to see if accuracy improves or is just as bad as it was before.

[JRD]

Well folks. I got the answer. Turns out if you have a Garand with a pitted and worn bore and a flared muzzle from cleaning rod damage, and then you counterbore the muzzle by .35 back to where there is rifling, you still have a rifle with pitted bore and worn rifling.
It still didn’t group worth a darn. It still cycled just fine though.
So nothing lost because I still have a Garand that needs a new barrel and I have experience gained.

[SODAPOPMG]

Yep the blue sky marked imports were south Korea's wore out garands, friend of mine bought one in the 90's it shot 6ft groups at 100 yards we pulled a bullet from a round and dropped it into the muzzle it went in over 1 inch then he put it in the chamber and it went in to the barrel about 5 inches
He had it rebarrled and it was a track driver when it came back

[john.k]

Counterboring by 3/8 deep is just a recrown ,and very unlikely to have any result....min counterbore for a worn/rusted muzzle would be 1",and I would have to see even rifling at the sharp cut edge.