TargetTalk

Can anyone tell me how to detect and correct a tight spot in a barrel?

You can check with a cleaning rod. Using a tight fitting patch you can feel the increased resistance from tight spots. At loose spots, and especially bulges, the patch will jump. Alternatively a bullet pulled from a cartridge can be used to "slug" the bore.

As for fixing a tight spot, I suspect it would have to be lapped out, but this is not a job for the DIYer, and I don't think it's a routine job even for professional gunsmiths.

Fire-lapping may be the way to go. At least it's cheap and easy.

While you can find large deviations in bore diameter with a rod and patch, smaller ones require slugging, as deviations as small as .0001" are detrimental to accuracy unless the tightest spot is at the muzzle. Barrel makers hand lap barrels using experienced people and an air gage. You can lap a barrel using a prodigious supply of slugs and a lot of time and patience and a .0001" mic. (unless you have an uneven number of lands/grooves). Best to practice on an old barrel. Even better to use a new barrel where the muzzle can be cut at the tightest spot.

beye wrote: Barrel makers hand lap barrels using experienced people and an air gage. You can lap a barrel using a prodigious supply of slugs and a lot of time and patience and a .0001" mic. (unless you have an uneven number of lands/grooves).

Where can I learn about air gages?
What does number of grooves have to do with it?

kkkayser wrote:

beye wrote: Barrel makers hand lap barrels using experienced people and an air gage. You can lap a barrel using a prodigious supply of slugs and a lot of time and patience and a .0001" mic. (unless you have an uneven number of lands/grooves).

Where can I learn about air gages?
What does number of grooves have to do with it?

The number of grooves will affect your ability to accurately measure the diameter of a slug. Most barrels have an even number of grooves, so the grooves are opposite. This makes it easy to measure across the widest part of the slug. Some barrels have an odd number of grooves, so each groove is opposite a land. If you measure the slug the jaws of the micrometer/caliper will touch across the top of two grooves on one side.

Air gauges are fairly serious pieces of kit.

It would help to know what type of gun we are talking about here?

If it's a rifle with a long barrel and the tight spot is near the muzzle the best option is to shorten it just behind the tight spot (don't do that if it's an air rifle with a choked barrel!).

Otherwise, if it's genuine tight spot then your barrel is basically scrap, get a new one. Amateur lapping etc. won't save it, especially if it's match quality accuracy you want.

Rover wrote:Fire-lapping may be the way to go. At least it's cheap and easy.

Take it from someone who has actually done it several times.

I think many smallbore rifles have choke as well, but am not positive. Never noticed, but I don't use very tight patches or have slugged my barrel either.

If you slug your barrel and it has an uneven number of grooves, to measure the bullet you need a "V" micrometer, not to be confused with a thread measuring micrometer with a "V" anvil. If you wish to buy a V micrometer, you will need to do some trig to calculate the angle needed to span the correct points on the bullet you wish to measure. This angle depends on the number, and width of the lands and grooves. Make sure to buy one with a tenths reading vernier.

Rover wrote:

Rover wrote:Fire-lapping may be the way to go. At least it's cheap and easy.

Take it from someone who has actually done it several times.

You've fire lapped 22 match barrels?

Can they be called match barrels if they are not perfect and you're not satisfied?

If they're good I wouldn't mess with them. If they're not you can't really mess them up. Your call.

But from what I've done and what I've heard, you won't hurt anything (though it does eat the throat on a high power rifle a bit).

patriot wrote:

Rover wrote:

Rover wrote:Fire-lapping may be the way to go. At least it's cheap and easy.

Take it from someone who has actually done it several times.

You've fire lapped 22 match barrels?

I've won a national championship and set national records with one!

Justin Tracy

an air gauge is definitely a very expensive piece of equipment. There is a web site

http://chesapeaketesting.com/services/g ... oC-Vzw_wcB

that claims their laser inspection is better than air gauging. I didn't see a post of the cost.

Justin Credible wrote:I've won a national championship and set national records with one!

Justin Tracy

Justin,

did that barrel have tight spots too? I hadn't realised the abrasive-coated bullets could be used for anything other than polishing rough spots.

Tim S wrote:

Justin Credible wrote:I've won a national championship and set national records with one!

Justin Tracy

Justin,

did that barrel have tight spots too? I hadn't realised the abrasive-coated bullets could be used for anything other than polishing rough spots.

I can't say I remember any tight spots, but it was over a dozen years ago that I did it... before I knew very much! The reason I tried it is that after it sat around unused for a bit and I pushed a patch through I noticed a slight rust. Uh Oh. So I just decided to give it a go and see what happens. I wasn't good enough of a shooter back then to tell if it made a difference one way or the other, but the thing certainly shot after my skills increased! The test target that came with the gun is probably the best Anschutz one I've seen, for whatever that is actually worth, and of course it shot well in the future.

I wouldn't do it again unless the gun just did not shoot and had nothing to lose.

I used the TUBB Final Finish system. I also used this on a factory centerfire barrel that would foul quickly and stop shooting, now it shoots great for much longer and most of the machining marks are gone.

Justin Tracy

A friend that didn't clean his 1913 after every session has primer hazing at 6 o'clock. My 1913 has more than twice the rounds down the tube but looks clean. I doubt his damage is effecting accuracy enough to matter in prone, not benchrest, but it might be an interesting experiment if he ever decides to replace the barrel.