Muzzle erosion

[Merc]

I finally got around to ordering a .30 caliber muzzle erosion gauge and measured the muzzle diameter of my M1917 Winchester. It accepted the .3015 ring which was a little surprising since the throat erosion on this barrel is nearly zero. I have no trouble hitting targets at 100 yards with 150 gr. FMJ boat tails so the rifle is still very accurate even with a loose muzzle.

Merc

[Clark Howard]

Concentricity of the muzzle wear is more important than total wear. That is why muzzle damage caused by a cleaning rod is more damaging to accuracy than simple wear from shooting. Shoot all you want. Clean carefully. Regards, Clark

[Merc]

Clark,

Good point. Thanks. The accuracy is still there so I have to assume that the wear out to .3015" is shooting related. I don't allow the cleaning rod to come in contact with the barrel when cleaning.

Merc

[fguffey]

Good point. Thanks. The accuracy is still there so I have to assume that the wear out to .3015" is shooting related. I don't allow the cleaning rod to come in contact with the barrel when cleaning.

You checked the muzzle with a tapered gage; it is possible to check both ends of a barrel with a muzzle gage. Your rifle could have left the manufacturer with a barrel that indicated .3015". Rather that assume the rifle has ware from shooting and or cleaning I suggest you determine the diameter of the barrel; we all know the two diameters of the 30/06 is .300" and 308". And then there are reloaders that believe they have slow and or fast barrels meaning they can load their ammo with extra powder without raising pressure. Or; they have to reduce the powder change to prevent signs of excessive pressure. Problem: Once they determine their barrel is not the correct diameter they want their money back. Shooters assume their barrel has the correct diameter; they believe they live in the perfect world.

And then there is the picture that won awards in the art world but has never been seen by the arsenal in Aberdeen Maryland; if they saw the picture they are not sharing.

F. Guffey

[Merc]

[QUOTE=fguffey;471084]You checked the muzzle with a tapered gage; it is possible to check both ends of a barrel with a muzzle gage. Your rifle could have left the manufacturer with a barrel that indicated .3015". Rather that assume the rifle has ware from shooting and or cleaning I suggest you determine the diameter of the barrel; we all know the two diameters of the 30/06 is .300" and 308". And then there are reloaders that believe they have slow and or fast barrels meaning they can load their ammo with extra powder without raising pressure. Or; they have to reduce the powder change to prevent signs of excessive pressure. Problem: Once they determine their barrel is not the correct diameter they want their money back. Shooters assume their barrel has the correct diameter; they believe they live in the perfect world.

And then there is the picture that won awards in the art world but has never been seen by the arsenal in Aberdeen Maryland; if they saw the picture they are not sharing.

F. Guffey[/QUOTE

The gauge goes too far down into the receiver to be read. If there is wear, you usually see it at both ends of the barrel. I did the jump gap test which indicated there was a zero gap. That suggests the rifling in the throat of the barrel is showing zero signs of erosion. The rifle still shoots accurately which leads me to believe that the muzzle diameter is still concentric and the looseness probably isn't related to cleaning rod abrasion.

[fguffey]

The gauge goes too far down into the receiver to be read.

Are you saying the taper on the two gages are different? To determine ware the smith/reloader needs two readings, I would think one reading would be before and the other after. Without the 'before' reading I would think the smith/reloader would need a 'middle' of the barrel' reading. If the middle of the barrel reading is the same as the reading at both ends I would think there is no taper.

F. Guffey

[Merc]

I have a straight muzzle erosion gauge with graduated rings that increase in size from .3000" to .3030" in .0005" steps. Here's a pic of the gauge inserted into the muzzle of my 03-A3 Remington .30-06 and shows the barrel only accepting the first ring which is .3000" in diameter.

I measure the throat erosion by using a method taught to me by JB White. It's a simple method but indicates how much of the rifling has been shot away from the throat (jump gap) over the life of the barrel. It doesn't measure the diameter of the barrel at the throat where rifling lands are present.

Equipment required: One bare .30-06 bullet, one dummy .30-06 round and one 1/4" X 36" wood dowel rod. I use the same type of bullets and assemble the dummy round to the recommended COAL for that type of bullet. Be aware that different bullets will have different COAL.

First remove the rifle bolt and insert the dummy round into the chamber and hold it there with your finger. Insert the dowel rod into the muzzle until it touches the tip of the bullet and mark that spot on the rod as close to the end of the muzzle as possible. Remove the dummy round.

Next, insert the bare bullet into the receiver and use the dowel rod to push it into the throat until it engages the rifling. Hold in place with a short dowel or cleaning rod if needed. Insert the wood dowel rod down through the muzzle until it touches the point of the bare bullet and mark that spot on the dowel rod as close to the end of the muzzle as possible.

The distance between these two marks on the dowel rod represents the jump gap distance, or the distance the bullet must travel in the throat before engaging the rifling. If the gap is too long, a fired bullet could go airborne for an instant and possibly enter the rifling at the throat at an odd angle.

I would expect that new rifles would have a zero jump gap and the muzzle matching the caliber. The following is what has me scratching my head:

My 1917 M1917 Winchester has a zero jump gap (like new) but has a muzzle that accepts the .3015" ring (moderate wear).

My 1943 03-A3 Remington has a .062" jump gap (slight wear) but has a muzzle that accepts the .3000" ring (like new).

My 1944 Savage Enfield No. 4 Mk1* has a .250" jump gap (worn) but has a muzzle that only accepts the .3025 ring (actually smaller than .303").

All three can still shoot nice groups at 100 yards. Go figure.

My 1931 M1916 Spanish Mauser has a jump gap of .635", shoots poorly and now hangs on the wall. I'm guessing this was a well-used Spanish Civil War vet.

37439

[PhillipM]

I would expect that new rifles would have a zero jump gap and the muzzle matching the caiber

37439


Assume at your peril. It could have left the factory at that dimension. The best gauge is a target.

[Merc]

I would expect that new rifles would have a zero jump gap and the muzzle matching the caiber

37439


Assume at your peril. It could have left the factory at that dimension. The best gauge is a target.

Phil,

Expect, not assume, (don't know if there's a difference - trying not to split hairs here) but I agree with your target analogy. It would be helpful to know what the original factory manufacturing tolerances were for each barrel. Is it muzzle/throat erosion I'm seeing, or were they originally built that way? How much muzzle/throat erosion can each one sustain before they are no longer accurate shooters?

The No. 4 is a real puzzle. The barrels/receivers were built to extra spacious tolerances. How is it the .303 caliber muzzle only has a .325" lands diameter? I might ask the guys on the SMLE page if anyone knows anything about the barrel's dimensions and tolerances.

[fguffey]

I measure the throat erosion by using a method taught to me by JB White.

And then there are new rifles that have a problem with accuracy and no one knows why. A smith built 4 magnificent 7mm wildcats. He made the reamer meaning it was more like a 7mm/06 Ackley Improved chamber than a 7mm/270 improved. One of the rifles came back, the smith took the rifle to other smiths, and then came the bore scope. He took it to a smith with a bore scope, the smith could find nothing in the bore that would cause the problem with accuracy. And then; he called me, he wanted to know where I would start when determining the problem. I told him where I would start.

He got onto the Internet and Googled: He found the JB White technique?/method. After a while he called me and explained to me what he did and tried to explain what he discovered. And I said; "YOU USED A STICK! ?" Basically I suggested if he wants to talk about it for the rest of his like use a stick, but if he wanted to know what was wrong with the chamber bring the rifle to me with formed cases. And then I suggested we make a chamber case unlike any other chamber cast anyone has ever seen; the chamber cast was not necessary because the other method/technique was so convincing. And then he ask me: "How did this happen?" He built the rifle, he made the reamer, he cut the chamber, and I said; "I do not know".

Anyhow, to give the rifle the benefit of the doubt we loaded 120 rounds in 5 round groups and then test fired it. There was a very small window of accuracy where the rifle stacked the bullets in one hole.

F. Guffey

[fguffey]

And then there is the tapered gage. Reloaders have been know to use a throat erosion gage for the throat and then purchases another gage for the muzzle. And then there is the illusion the tapered gage is stepped. I have gages that are so old they are labeled go/not go, the go/not-go gages are stepped or one end of the gage is go and the other end is 'not go'. That was long before the Internet, after the Internet the name was changed to 'go or no-go.

The difference in length between a go gage and a no-go gage is .004" for the 30/06. I had rather measure the length of the chamber in thousandths than increments of .005". And then there is no-go gage length. The difference in length between a minimum length/full length sized case and a no-go gage length chamber is .009" meaning the difference in length between a minimum length/full length sized case from the shoulder to the case head is .005" shorter than a go-gage length chamber.

F. Guffey

[PhillipM]

I put my micrometer (not caliper) on my Stone Axe gauge. It is spot on.

[RC20]

Ok, first there is mfg tolerance and that was more so back in the day. New barrel could read 1 or 2 on the MW.

Next, Steven Mathews carries on the Stone Axe gauge under his own name. Its a great tool and not too costly ($54 or so)

TE is so close on the 1917 as not to matter, per Steve not calibrated but we are not looking at close. different between 2 and 3 is not a problem

Difference between 3 and 8 is.

One tool does both measurements and is good for a number of different rifles (1903, 1917, Garand version with bent handle, 308 version.)