EXTENDING COMPETITION BARREL ACCURACY THROUGH BORE HONING MAINTENANCE

[jden]

Boyd, Im no metallurgist but when metal breaks down from heat and pressure as the throat does in a (fire cracking) barrel no amount of lapping will fix this. My procedure for extending a barrels life and avoiding fire cracking is scoping barrel after each match and look for early signs of throat erosion, Usually 500 rounds in a PPC, Jump the chamber enough to remove worn metal. With the poor steel we have today this method is critical for maintaining good groups. What I have said is meant for competition barrels only.

Good luck with your experiment.

JD

 

[jonbearman]

I think the original poster is saying his friend is just smoothing the sharp edges so it wont affect the jacket material so bad. I don't think he is making any real claims as a fix. There are people that come up with what we would view as a radical or even a crazy idea. If he proved it out to this fella it may work but you would have to no when and where to stop. I for one think it is interesting at very least. Keep an open mind as necessity is the mother of all invention.

 

[ebb]

Ive lapped barrels and got results on some and not on others, here is how I was taught then you can flame at will. First no valve grinding compound, Brownell"s makes several kits that are for this job. They go from 240 or 320 grit to 1000 grit. Ive never started with anything below 400. I use a Parker-Hale style jag and wrap a cloth patch around it till it is tight in the bore. Apply the paste to the patch and stroke the bore as you would JB paste. After 25 strokes clean and go to next high numbered grit. When you run out of grits it will either work or not. I have never used this on a name brand match barrel that is good, but have used it on factory barrels and some match barrels that have fouling trouble or don't want to shoot. The guy that taught me this method he and I, bought some Montana rifleman barrels that we got cheap. Most shot well from the get go but others needed work this helped all of them. Some factory barrels have so much bad chit going on, nothing can fix them, others improve to some extent or an other. If you don't believe in this by all means don't do it, but if you haven't tried I don't see how you can say much.

 

[johara1]

People worry about the .236 bore verses the .237 bore but will jump to run valve grinding compound diamond compound in a bore? First it would have to be a non imbedding compound. I never let mine get to the point of fire cracking so bad it would be detrimental to accuracy and at 3000 rounds and numerous rechambering they are ready to be regulated to fire forming or great 24" rifle varmint barrels……… jim O'Hara

 

[butchlambert]

Ive lapped barrels and got results on some and not on others, here is how I was taught then you can flame at will. First no valve grinding compound, Brownell"s makes several kits that are for this job. They go from 240 or 320 grit to 1000 grit. Ive never started with anything below 400. I use a Parker-Hale style jag and wrap a cloth patch around it till it is tight in the bore. Apply the paste to the patch and stroke the bore as you would JB paste. After 25 strokes clean and go to next high numbered grit. When you run out of grits it will either work or not. I have never used this on a name brand match barrel that is good, but have used it on factory barrels and some match barrels that have fouling trouble or don't want to shoot. The guy that taught me this method he and I, bought some Montana rifleman barrels that we got cheap. Most shot well from the get go but others needed work this helped all of them. Some factory barrels have so much bad chit going on, nothing can fix them, others improve to some extent or an other. If you don't believe in this by all means don't do it, but if you haven't tried I don't see how you can say much.

If you do a little research or call the barrel makers you will find that they lap with probably nothing any finer than 240-320. A high polished bore will foul much more than a 240-320.
Now if you doubt me do a little honest research before flaming.

 

[dmoran]

If you do a little research or call the barrel makers you will find that they lap with probably nothing any finer than 240-320. A high polished bore will foul much more than a 240-320.
Now if you doubt me do a little honest research before flaming.

+1.......... very true !.!.!

A barrel mfg told me he starts with 150 grit aluminum oxide powder mixed with a thin grease to dress the lap. Then 180 aluminum oxide to lay down the final finish end-to-end. And stated the compound breaks down very fast, almost to fast.

Regards
Donovan

 

[clowdis]

Butch,
I don't disagree with what you're saying. What I have used is a green (1800 mesh) or blue (1200 mesh) lapping compound, from Gesswein, just for throat maintenance, I don't do the whole bore. I have been in a popular barrel manufacturers shop and seen their compound in a brown color (325 mesh) on the lapping bench. Now I do not know if it's the same company's compound or if the color meant anything at all, but the makers do need to remove cutter marks and other things that the shooter isn't trying to remove. Also looking at new barrels they are not "polished" to a high finish, but to a consistant smooth finish. You and johara1 are probably bench shooters and maybe ya'll can afford to set back a barrel every 300-500 rounds or so, but for prone of F-class shooters we will shoot maybe 150 rounds a weekend and maybe 2 matches a month. That's a lot of setbacks going down in a very short time if we follow johara1's schedule, so we aren't/can't use the same bore maintenance techniques. On my 7RSAUM I've done it twice, once at about 850 rounds and again at about 1200 and it's still going strong at near 1400 rounds. On my Palma rifles I won't touch the throat until about 2500 rounds so we're not talking about diamond lapping the throat every few times we clean. Guess we're talking apples and oranges about cleaning. I assumed the OP was shooting F-class but don't know for sure. I think a smart, cautious lapping of the throat will extend the life of a barrel by a few rounds but I'm not sure it will bring one back to life. That's for someone else to experiment with.

 

[BoydAllen]

When barrels start to show the first signs of fire cracking, they begin to tighten up in that area, and copper more, in proportion to how rough they become. I would imagine that the fine diamond paste work, confined to that area only , would tend to dull the edges that grab copper, and relieve the slight constriction. Of course I would never use that material any farther forward in a bore. I am careful about that, even when using IOSSO to deal with hard carbon, that is why I use a nylon brush, so that I can short stroke, and confine my work to the areas where it is needed. In the barrel that I was given, the difference that I saw was subtle. The pattern was still there, but the edges of the fissures were not sharp. If I do an experiment, it will be with a barrel that has stopped shooting at a level that would be competitive. Like a lot of shooters, I do not have a lathe, so the economics of setting back are not favorable. In any case, I enjoy experimenting. Some of them turn out as expected, others are simply a learning experience.

 

[butchlambert]

Butch,
I don't disagree with what you're saying. What I have used is a green (1800 mesh) or blue (1200 mesh) lapping compound, from Gesswein, just for throat maintenance, I don't do the whole bore. I have been in a popular barrel manufacturers shop and seen their compound in a brown color (325 mesh) on the lapping bench. Now I do not know if it's the same company's compound or if the color meant anything at all, but the makers do need to remove cutter marks and other things that the shooter isn't trying to remove. Also looking at new barrels they are not "polished" to a high finish, but to a consistant smooth finish. You and johara1 are probably bench shooters and maybe ya'll can afford to set back a barrel every 300-500 rounds or so, but for prone of F-class shooters we will shoot maybe 150 rounds a weekend and maybe 2 matches a month. That's a lot of setbacks going down in a very short time if we follow johara1's schedule, so we aren't/can't use the same bore maintenance techniques. On my 7RSAUM I've done it twice, once at about 850 rounds and again at about 1200 and it's still going strong at near 1400 rounds. On my Palma rifles I won't touch the throat until about 2500 rounds so we're not talking about diamond lapping the throat every few times we clean. Guess we're talking apples and oranges about cleaning. I assumed the OP was shooting F-class but don't know for sure. I think a smart, cautious lapping of the throat will extend the life of a barrel by a few rounds but I'm not sure it will bring one back to life. That's for someone else to experiment with.

clowdis, At a weekend match I fire about 250 rounds which includes practice at the match.

 

[clowdis]

That's a lot of shooting Butch. Is that benchrest? I know little to nothing about bench shooting other than what I've read over the years. Maybe I should attend one somewhere

 

[butchlambert]

Well,
We shoot 10 5 shot groups a day with unlimited sighters. That is 100 rounds without any sighters . I looked over several of my targets and I average 3 sighters per target minimum and that would be an additional 60 rounds. The Friday before a match is practice and you can shoot a lot learning conditions and confirming your load. Remember that at least 98% of BR shooters reload during the match. Not many folks preload.

 

[clowdis]

That's enough shooting to make it worthwhile to do a bit of travelling to get to a match. I'd hate to drive 3 or 4 hours to shoot 50 rounds and that was it.

 

[butchlambert]

We do a lot of shooting and ranges are from 1hr. to whatever for registered matches.

 

[dedogs]

I think I'm missing something(or just ignorant) but how does 10 x 5 = 100 and 10 x 3 =60?

 

[butchlambert]

I guess that you have not shot a competitive BR match. It is 2 days of 4 matches of 20 total targets.

 

[dedogs]

There you have it, I WAS showing my ignorance. Thanks for the info and no I have not shot a BR match.

 

[fgregorio]

Hi all,
If I can throw in my 5 cents...
I shoot palma quite seriously and I have a true flite barrel, 30 inch, 1 in 12 T that has been running hbn since new. As it reached 6000 RDS, it's accuracy started declining gradually, until by the time that I got to 7500 RDS, I couldn't hit a barn door ( grouping at 2 moa in elevation/ 2 moa in windage). The last 100-10x came at 6500 RDS at 500y.
As I was cleaning after each 12 rds, I could feel that the first 8 inches of the bore were rough like high grit sandpaper.
This is what I did to those first 8 inches from the chamber:
1/4 gallon of boiling water down the bore.
Bore guide on receiver, patch on bronze brush.
I used 100 strokes (50 each way) of low grit valve grinding paste, then another 1/4 gallon of boiling water, then patch to dry.
100 strokes of high grit valve grinding paste, then another 1/4 gallon of boiling water down the bore, then patch to dry.
100 strokes of Autosol metal polish, then 1/4 gallon of boiling water down the bore, then patch to dry.
Coated the bore with hbn.
Results: 100- 5x at 330y, 1moa elev spread in group
100-6x at 770y, 0.5 moa elev spread in group.
Cleaned barrel and got 99-2x at 770y, 2 moa elev spread in group.
Then 100-8x at 770y, 0.3 moa elev spread in group.
Pass 1 wet patch and 1 dry patch.
3 days later. 330y held 2 groups of ten shots at 0.3 moa with a dirty barrel. Poor scores due to my ability shot a 98.5 and a 95 on a 4 inch bullseye at 330y. Reason being that I corrected on a very bad 8 ring shot and got another 8 on the other side.
Nevertheless, the honing of the barrel really worked for me. Temporary fix though...

 

[ebb]

Butch I have no illusion that Ive polished the inside of my barrel to 1000 grit smoothness. I would never try to do a barrel that was lapped by some one that knows what they are doing. I believe that lapping a factory barrel or a barrel that has never been lapped is only knocking down the burrs and rough stuff that will eventually be removed by putting bullets down the barrel. I believe that doing without wasting bullets and coppering up a barrel is getting me further down the road faster than letting nature take its course. I don't think I can make a silk purse out of a sows ear, I do think I can find out which is screwed in to my receiver quicker and do what is appropriate.

 

[fgregorio]

Hi all, just a heads up on this subject.
I use a bloop tube that extends my sight radius, which, somehow causes a "chamber effect" at the muzzle that allows the combustion gas to dwell around the muzzle for a bit longer.
Before the honing: the crown/muzzle would be completely covered on an even layer of powder fowling.
After the honing: the crown/ muzzle has barely any powder fouling on it and it is just around the crown in 4 tiny triangular shapes. It looks like , because the bore tapers in towards the muzzle, I don't have gas overtaking the projectile in the last 22 inches of the barrel.
Thoughts?

 

[johara1]

Hi all, just a heads up on this subject.
I use a bloop tube that extends my sight radius, which, somehow causes a "chamber effect" at the muzzle that allows the combustion gas to dwell around the muzzle for a bit longer.
Before the honing: the crown/muzzle would be completely covered on an even layer of powder fowling.
After the honing: the crown/ muzzle has barely any powder fouling on it and it is just around the crown in 4 tiny triangular shapes. It looks like , because the bore tapers in towards the muzzle, I don't have gas overtaking the projectile in the last 22 inches of the barrel.
Thoughts?

The bullet upsets and will fill up the big hole you created….. no big deal unless you are looking the ultimate in accuracy. My barrels have lasted to the 3000 rd. range and will still shoot a 1/4 minute, but in 1000 BR. i don't think that is acceptable, they regulate to FF. and fun stuff……… jim