bore gauge question part 2
Edited heavily for clarity.
If a government 30 cal barrel should have .300 bore and .308 grooves, then measuring the end of a bore gauge should say how much land you can lose before the throat is considered worn at that point.
If you measure between the one and the ten, you should have a rough idea of how deep that wear can go before you're likely to experience inaccuracy.
Now if I had a Mosin, I would know roughly how much life the barrel had if I knew how far up the bore the wear went. The wear would NOT be measured with the GI gauge. The bore would be slugged and the chamber cerrocasted and I would see how far up the throat I could measure wear equal to (GI gauge tip measurement minus .300).
I know I can just shoot it, but I want to know if it's worth working on, or if I'll shoot it out after a spam can or two.
So does anyone have a GI gauge and a caliper to measure it with?
If a government 30 cal barrel should have .300 bore and .308 grooves, then measuring the end of a bore gauge should say how much land you can lose before the throat is considered worn at that point.
If you measure between the one and the ten, you should have a rough idea of how deep that wear can go before you're likely to experience inaccuracy.
Now if I had a Mosin, I would know roughly how much life the barrel had if I knew how far up the bore the wear went. The wear would NOT be measured with the GI gauge. The bore would be slugged and the chamber cerrocasted and I would see how far up the throat I could measure wear equal to (GI gauge tip measurement minus .300).
I know I can just shoot it, but I want to know if it's worth working on, or if I'll shoot it out after a spam can or two.
So does anyone have a GI gauge and a caliper to measure it with?
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thats not exactly how it works, the 'lands' get worn much more than the 'groves'. also especialy with military barrels there is a 'tolerance'; bore dia. might be from .298" to .302", grove depth might be .004" to .006" (not these exact figures but close). you could measure 12 different 'new' barrels and get 12 different readings with the same gage. there are gages to measure throat erosion on m-1 garands but these are rifle model specific. the ONLY way to tell how a specific barrel will shoot.......is to shoot it.
EDIT; the old 'rule of thumb' is a rifle barrel will be worn out after shooting 40 lbs. of powder (with a .30/06 this comes out to about 5600 rds., a 7.62x54r would be similar). the russians never were conserned with stellar accuracy.0 -
Quality of ammo, could be a big factor in establishing accuracy potential. In the past I broke down a bunch of 7.62 X 54 ball for the components.
The Czech Silver Tip 147 grain was good clean stuff. The powder was clean and free flowing. Looked like it was made last week, not 30? years ago.
The Hungarian?, 181 grain, yellow tip, heavy ball, on the other hand. The powder was a solidified mass in the case. It wouldn't pour out. Make me nervous, just think about shooting it.
Use high quality commercial ammo if you want to check the basic accuracy of your M-N. The old ex military stuff, might have been stored in a flooded warehouse for the last 20 years.0 -
I want to try to get some clue about how much life is left in the barrel.
The Soviets had rifle clubs. Lee Harvey Oswald was on one. They tried to teach their people to shoot and provide recreation in one shot. There's a chance a bore could be shot out.
If the grooves are nonstandard then there's no telling how much wear it could withstand in the grooves because they're already out of spec, but I think mine is right on the money. Besides, they didn't accept sloppier tolerances because they wanted to, but because there was a war on and they had no choice.
Throat gages are only specific to one weapon because of the way they fit in that weapon, and maybe because rifling of a way different configuration would withstand wear differently. The length between the zero and the ten mark is the length the throat can deepen with acceptable accuracy.
I think if one weapon can withstand a certain amount of wear with a 30 cal barrel with four .004 deep grooves with 1-10 twist, then another weapon will probably go bad with roughly the same amount of wear even if it's 31 cal and has .005 deep grooves. They are both designed for roughly similar bullets.0 -
quote:Originally posted by SoreShoulder
Now if I had a Mosin, I would know that if I cerrocasted the throat and the bore had expanded .002 vs. the rest of the barrel, the "good part," then I would know the throat was eroded. The configuration of that rifling is roughly like other milsurps except the two-grooves and the Lee-Enfields.
I know I can just shoot it, but I want to know if it's worth working on, or if I'll shoot it out after a spam can or two.
So does anyone have a GI gauge and a caliper to measure it with?
Mosin takes .312 not .308 rounds, and a standard USGI gauge will be effectively useless.
To answer the question, there are 440 rounds in the standard 7.62x54R Mosin "spam" can, and no, by itself that's not nearly enough to wear out a barrel.
As mentioned, with the standard .308/30-06/7.62x54R/8mm Mauser/303 Enfield you're looking at several thousands of rounds downrange to "shoot out" a barrel.
This, of course, assumes that your barrel is in good shape to begin with; many/most of the surplus Mosin's have really lousy worn barrels from wartime neglect after being fired with corrosive ammo.
And no, since so far as I know there is no current supply for new Mosin barrels, its really not cost effective to rebarrel Mosin Nagant rifles at this time. Yes it "can" be done, but it effectively requires custom barrel fabrication and fitting and doing both things will cost several times what the actual rifle cost.
Not incidentally, I've heard that removing Mosin barrels can be exceptionally difficult. They're typically screwed in super tight, much tighter than many other older/surplus bolt actions, and getting the barrels out can require special tooling, heating with torches, etc.0 -
quote:Originally posted by beantownshootahMosin takes .312 not .308 rounds, and a standard USGI gauge will be effectively useless.Most of the bore doesn't wear, only the ends. So I could find what the original dimensions were by slugging, then I could cerrocast the chamber and throat to see how much and how deeply they are worn.
The GI gauge would never enter the bore, except I would know how much the bore has to wear away, and how deeply, to affect accuracy, if someone gave me the measurements of the gauge. Namely the diameter of the tip and the length between the zero wear and 10 wear marks.
I don't want to rebarrel a $150 rifle. I want to know how much wear I have left in the barrel.0 -
"if someone gave me the measurements of the gauge."...........we are trying to help you but there is no sutch gauge, especialy for the russian rifles. The m-1 garand does have throat and muzzel wear gauges but they are specific to the m-1, a 'new' barrel might gauge out at a 2 or 3 using them. Your rifle might fire 500 or 5000 rounds accuratly no mater what any guage says. ammo also will play a BIG part in how it will shoot and for how long. Some russians can have a grove dia. as tight as .309" or a 'loose' as .315" and still be in 'new' condition. rifle barrels don't wear much at the muzzle, any wear there is from bad cleaning technique ( the m-1 garand has to be cleaned from the muzzle).
"The muzzle may shoot out btw, I think all the gas rushes past it. I'm pretty sure they expand from erosion as well as from cleaning rods."..............no, the muzzle is the last place you will see any wear from shooting, many target rifles have had the chamber end of the barrel cut off, rethreaded, and rechambered to return them to match quality standards with no changes to the muzzle. they do make bore inspection devises that allow you to visualy inspect the bore. to make a guage like you want you would have to have the diemensions of that individual bore when new. even a gauged m-1 bore of say 7 might shoot well if all else is ok. with your mosin, even if the throat is worn you could seat the bullets out farther to compensate.
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quote:Originally posted by MIKE WISKEY
"if someone gave me the measurements of the gauge."...........we are trying to help you but there is no sutch gauge, especialy for the russian rifles. I want the measurements of an M1 or an M14 or an M1903 gauge.quote:The m-1 garand does have throat and muzzel wear gauges but they are specific to the m-1, a 'new' barrel might gauge out at a 2 or 3 using them. Your rifle might fire 500 or 5000 rounds accuratly no mater what any guage says.yes but it probably wont; it will probably shoot well until the throat wears out then it will shoot poorly. And if the wear extends half as deep or less than the distance between the wear marks on an M1 gauge then it probably has plenty of life.quote: ammo also will play a BIG part in how it will shoot and for how long. Some russians can have a grove dia. as tight as .309" or a 'loose' as .315" and still be in 'new' condition. rifle barrels don't wear much at the muzzle, any wear there is from bad cleaning technique ( the m-1 garand has to be cleaned from the muzzle).
I do plan to slug the bore, both to know what bullets to use and to use my plan to tell if the throat's worn. I don't think you read my plan.
Here's the plan: this part is pencil and paper. You get the measurement of the tip of a USGI 30 cal service rifle throat gauge, and subtract .300 from it. That gives you the value of how much the bore can expand before it's considered worn.
Then you measure between the wear marks of the gauge, and you know how far the gauge can enter the throat before it's considered worn.
Then you bust out your Mosin. You measure the bore by slugging or cerrocast, and you take a cerrocast of the throat. You see how deeply the throat is expanded equal to the value of (M1 throat gauge tip minus .300)
The rifling is about the same as M1 rifling and should respond to wear about the same, or in other words when the throat erodes the same amount, you're close to the end of the accuracy life, assuming you've found a bullet that fits the barrel as well. It's likely a little deeper so if anything you will get a conservative reading. The steel may be different but if you're halfway to the wear out point then you've got plenty of life.
The muzzle may shoot out btw, I think all the gas rushes past it. I'm pretty sure they expand from erosion as well as from cleaning rods.0
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