New Rifle, barrel thou and a half too large

Varmit

Varmit

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A buddy of mine took his new 270 Winchester rifle to a gunsmith to have the trigger adjusted and the smith told him the barrel measured .2785 inches or a thou and half larger than .277. He asked the smith if this was a problem and was told it was half worn out and this is common with production rifles. The rifle shoots good but my buddy is disappointed that it is out of spec.

Do barrels on production rifles really vary this much? and is it really half worn out?
 
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Really ? ON A NEW RIFLE ?

The BORE diameter of rifling is from the lands, that is, the part of the rifling that sticks up and engages the bullet to spin it. The GROOVE diameter of a barrel is measured between the grooves, or largest diameter of the bore.

It would be interesting to see what method the Gunsmith used to measure this. A quick check of the rifling is to take a .270 bullet, oil it lightly, and put it into the muzzle of the rifle. A .270 bullet measures .277 and if the bore diameter is .2785 as the Gunsmith has told you, then a .277 bullet should be able to be pushed through the bore of the rifle from muzzle to the breech with not too much effort.

Another simpler way is simply take a loaded cartridge and carefully insert it into the muzzle of the rifle. Push it firmly but DO NOT FORCE IT IN. If the bore is .2785, the WHOLE of the bullet should enter into the muzzle up to the mouth of the cartridge case and not have any of the bullet showing.

Generally the rifling in a barrel is 4 to 5 thousands of an inch deep. For example, in a .308 rifle, the ideal BORE diameter is .300 and the GROOVE diameter is .308. The .270 has about the same depth of rifling, with the ideal of a bore of .270 and groove of .277. Many barrels vary in groove and bore diameter slightly and the .308 barrel can be .309 or .307 for instance and be within specifications.

If the rifle has a groove diameter of .2785 this is 1 1/2 thousands of an inch. Theoretically the bullet engages the rifling equally so this means that 3/4 of a thousands of an inch around the bullet will NOT engage the rifling. However since the rifling is three and a half thousands of an inch on each side, that means that 2 3/4 of a thousands of an inch WILL engage the rifling on each side of the bullet, assuming that the Gunsmith is correct in his measurements.

I think it might be a fairly safe bet that it will not fully enter the muzzle. If it does not fully go in, and leaves slight marks on the bullet where the bullet engages the rifling, then I would not worry too much about a "half worn out bore."

DO LET US KNOW HOW THIS ONE TURNS OUT.
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That smithy is confused. Like buffdog says, the bore is the hole that was drilled so the rifling could be cut(etc). The bore diameter of a .270 Win is .270" with .277" groove diameter. Don't think I'd worry about it.
The real question is why did the "smithy" slug the barrel if he was supposed to be adjusting the trigger(That your buddy could have done himself.)?
 
This gunsmith would not be seeing any more of my business. Sounds like he is putting one over on you. I'm sure he has a new barrel for a real good price sitting in the shop.
 
The Gunny would have measured the groove diameter and could have easily misread the result. If it "shoots good" it's moot.
 
Andy said:
The Gunny would have measured the groove diameter and could have easily misread the result. If it "shoots good" it's moot.
Click to expand...

yes, he must have measured the groove diameter. which would have to be at least .277, so I don't think it's anything to worry about.
 
buffdog said:
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Really ? ON A NEW RIFLE ?

The BORE diameter of rifling is from the lands, that is, the part of the rifling that sticks up and engages the bullet to spin it. The GROOVE diameter of a barrel is measured between the grooves, or largest diameter of the bore.

It would be interesting to see what method the Gunsmith used to measure this. A quick check of the rifling is to take a .270 bullet, oil it lightly, and put it into the muzzle of the rifle. A .270 bullet measures .277 and if the bore diameter is .2785 as the Gunsmith has told you, then a .277 bullet should be able to be pushed through the bore of the rifle from muzzle to the breech with not too much effort.

Another simpler way is simply take a loaded cartridge and carefully insert it into the muzzle of the rifle. Push it firmly but DO NOT FORCE IT IN. If the bore is .2785, the WHOLE of the bullet should enter into the muzzle up to the mouth of the cartridge case and not have any of the bullet showing.

Generally the rifling in a barrel is 4 to 5 thousands of an inch deep. For example, in a .308 rifle, the ideal BORE diameter is .300 and the GROOVE diameter is .308. The .270 has about the same depth of rifling, with the ideal of a bore of .270 and groove of .277. Many barrels vary in groove and bore diameter slightly and the .308 barrel can be .309 or .307 for instance and be within specifications.

If the rifle has a groove diameter of .2785 this is 1 1/2 thousands of an inch. Theoretically the bullet engages the rifling equally so this means that 3/4 of a thousands of an inch around the bullet will NOT engage the rifling. However since the rifling is three and a half thousands of an inch on each side, that means that 2 3/4 of a thousands of an inch WILL engage the rifling on each side of the bullet, assuming that the Gunsmith is correct in his measurements.

I think it might be a fairly safe bet that it will not fully enter the muzzle. If it does not fully go in, and leaves slight marks on the bullet where the bullet engages the rifling, then I would not worry too much about a "half worn out bore."

DO LET US KNOW HOW THIS ONE TURNS OUT.
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Click to expand...

I will check this out the next time we get to the range and report back.
 
I have a problem with describing a new barrel as "half worn out". Out of spec, ok.

If it shoots acceptably don't get twisted in a knot.

Acceptable tolerances will be looser on factory hunting rifle barrels,
that's how they can sell them significantly cheaper than "custom" match rifles.
 
rodregier said:
I have a problem with describing a new barrel as "half worn out". Out of spec, ok.

If it shoots acceptably don't get twisted in a knot.

Acceptable tolerances will be looser on factory hunting rifle barrels,
that's how they can sell them significantly cheaper than "custom" match rifles.
Click to expand...

Yeah, I guess I thought the groove diameter would be right on at .277
 
the gunsmith is an idiot. Who would call a new rifle half wore out. And who would do a job to improve someones rifle and then tell him its no good for some other reason when he has no idea if this is true or not.
 
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There is also another factor here that comes into play and that is Bullet Upset.. When fired, a bullet enters the bore of a rifle through the forcing cone. When the front end of the bullet enters the rifling it basically comes into contact with an obstruction, that is, the smaller rifling. The rear end of the bullet, still in the larger forcing cone, is still travelling forward and expands slightly in the larger diameter forcing cone. As the bullet moves forward, it overcomes this resistance, and the rear end of the bullet is swaged down slightly as it enters the rifling BUT it can only be swaged down enough to fill the bore itself. In the case of the .270, the .277 bullet with it's lead core and copper alloy bullet jacket, will surely expand 1 1/2 thousands of an inch to completely fill the bore if normal hunting bullets are used. Even if a steel jacketed bullet is used, it can expand slightly at the base of the bullet when fired.

Also, rifling, because it is smaller and has more "twisting" force applied to it as the bullet travels down the bore, wears much more quickly than the grooves of the barrel. In some of the older military rifles, you can see the rifling as only a small twist in the barrel, where it is well worn down from the erosion of hot gases and steel jackets.
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In shooting a lot of .303 ammunition over almost 60 years, I have come into contact with SMLE and Lee Enfield rifles with a groove diameter that are supposed to have a nominal groove diameter of .311-.312 but actually have diameters of .314 - .316, and they shoot the Mark VII Ball ammunition just fine with good accuracy.

You have to find out what your rifle likes. Rifles are like fingerprints, each is a bit different. You can have two rifles made the same day, one after the other, and possibly have them shoot differently. If you do not reload, you should try different Manufacturers and Bullet Weights on the range and see what each one will do. A bit of experimentation with reloads can cut factory groups in half.
 
buffdog said:
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There is also another factor here that comes into play and that is Bullet Upset.. When fired, a bullet enters the bore of a rifle through the forcing cone. When the front end of the bullet enters the rifling it basically comes into contact with an obstruction, that is, the smaller rifling. The rear end of the bullet, still in the larger forcing cone, is still travelling forward and expands slightly in the larger diameter forcing cone. As the bullet moves forward, it overcomes this resistance, and the rear end of the bullet is swaged down slightly as it enters the rifling BUT it can only be swaged down enough to fill the bore itself. In the case of the .270, the .277 bullet with it's lead core and copper alloy bullet jacket, will surely expand 1 1/2 thousands of an inch to completely fill the bore if normal hunting bullets are used. Even if a steel jacketed bullet is used, it can expand slightly at the base of the bullet when fired.

Also, rifling, because it is smaller and has more "twisting" force applied to it as the bullet travels down the bore, wears much more quickly than the grooves of the barrel. In some of the older military rifles, you can see the rifling as only a small twist in the barrel, where it is well worn down from the erosion of hot gases and steel jackets.
.

In shooting a lot of .303 ammunition over almost 60 years, I have come into contact with SMLE and Lee Enfield rifles with a groove diameter that are supposed to have a nominal groove diameter of .311-.312 but actually have diameters of .314 - .316, and they shoot the Mark VII Ball ammunition just fine with good accuracy.

You have to find out what your rifle likes. Rifles are like fingerprints, each is a bit different. You can have two rifles made the same day, one after the other, and possibly have them shoot differently. If you do not reload, you should try different Manufacturers and Bullet Weights on the range and see what each one will do. A bit of experimentation with reloads can cut factory groups in half.
Click to expand...

Yes, this makes sense to me. We are working up handloads for the rifle and it has shown good accuracy so far. Playing with seating depth right now and have some kg12 on order to get some copper out before the next range session.
 
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