As an extension of A BETTER WAY TO DETERMINE ROUND COUNTS ON BARRELS thread I pulled some of my historical barrels out and did some detailed photographs of just what goes on in a barrel.  There was another thread of whether you could really burn up a barrel and this proves it.

You can and will ruin a chrome lined barrel at a given point.  Just a matter of the firing schedule you submit it to.  The barrel manufacturers love to see guys buy the drum mags.

The lower barrel was a test conducted to determine what 20,000 rounds of M193 would do to a barrel.  The upper barrel was a SAW experimental barrel wherein they rigged three 30 shots mags in parallel for fast changing and attached the bipod.  THE SAW BARREL GOT HOT AND I MEAN HOT ! ! ! ! !

http://www.geocities.com/binarybytes/1.jpg

Pull it up at large scale at:  http://www.geocities.com/binarybytes/1.jpg

picture dont work.

tag for home.

I can't see shit!

Get the pic up.  I wanna see

I'll fix it here:



Enjoy.

Thanks for FIXING IT.  Did I do something wrong?

I found when you see the RED X it is waiting to load and takes a while as it is a big photo.

If anyone wants to see them in more detail:

http://www.geocities.com/binarybytes/1.jpg  

I nominate Humpy70 as "best new user of the twentyfirst century".

Quoted: I nominate Humpy70 as "best new user of the twentyfirst century".

I second the motion.  Many thanks for your posts Humpy70!!!

Would the erosion/wear look the same if the 20,000 rounds were spaced out over twenty years? In other words, no rapid fire, no smoking barrel, and plenty of maintenance.

I would say yes.  Gov't 30 cal accuracy barrels went for 15,000+.  I have seen a barrel (30 cal) with no rifling 3 inches in front of chamber.  Looked like glass to naked eye.
Would have loved to got my borescope in that one.  At any rate it shot 1.5" at 300 yards with Fed Match.
It was shot a few rounds slow fire and cleaned well before they put it back in storage.
Name of the game as far as I am concerned is clean and clean well.  In my humble opinon you have two enemies. Heat and carbon.  If that is true and my testing tends to confirm it on three guns and a total of 2000 rounds, I am going to be a cleaning fanatic the rest of my shooting years.

For instance a couple months ago I pulled a 30.06 out.  I set it back at 2500 rounds and now has 4200 rounds on it.  I did a thorough cleaning on it and went back to shooting it.  The rifle shoots better now than when it was new ! ! ! !   All the wear was in the throat.

I also understand the M24 Sniper Barrels at the school at Benning have about 15,000 on them now and still shooting acceptance accuracy.  They are shot slow fire and cleaned thoroughly.

Now all this can go up the tubes so to speak if you damage the muzzle crown. A guy I used to work with said he was convinced GI cleaning rods took out more barrels than were ever shot out and I agree with that 100%.

If you follow the Garand line you will see them talk about muzzle gages.  That is not from shooting but cleaning as no one told the kids not to let the cleaning rod touch the muzzle.

The military now routinely "rod" rifles coming off line to make sure they are empty.
They are ruining more than they think.
One tiny little nick on a muzzle and groups will open 300+%.

You have absolutely got to protect that muzzle crown.

This is one reason I was glad to see them do away with bird cage as it was a carbon trap.  Carbon traps moisture etc.  It is all but impossible to remove and you don't want to be unscrewing it and screwing it back on.

Bottom line, AR barrels are pretty cheap and easy to change. I know that heat kills em, but who cares? I'm going to have fun with mine and just replace them as needed.

It's gonna be a while before I hit 20,000 rounds anyway.

The military now routinely "rod" rifles coming off line to make sure they are empty. They are ruining more than they think. One tiny little nick on a muzzle and groups will open 300+%.

If this is still happening, those units are in violation of an Army "Safety of Use" message that directs all Army personnel to stop rodding barrels. Units are supposed to use published clearing procedures instead. It's been out now about 2-3 years.

Wow, the government finally did something right.  This calls for an investigation of how such would happen. I mean I saw the Army do it for what 20 years ! ! ! !Well it is high time they did after ruining maybe a million or two barrels in the process.  They used to do it at Camp Perry Small Arms School and I couldn't stand it.  Every M16 at the small arms school has had a jointed rod run in it numerous times and I have seen that. I haven't been on a active army range for years but you don't know how glad I am to hear that one.

Now if you could just get them to quit completely submerging M16 system in Brake Free we would be doing fine.  That I am told was seen as little as a month ago at a facility in South Carolina.  A former armorer for 82nd told me he had visited a facility as he was trying to join up and saw them completely submerging them. I first saw complete submergings in 1979 and per my contact is still going on.

So they still got a ways to go.  Thanks much for the heads up.

Break free, hell, they had us line up to get our chambers and barrel extensions roto-rootered out by an NCO with a chamber brush chucked into an electric drill, and then put the uppers (sans handguards) into a parts cleaning tank with some sort of super-nasty solvent that did Bad Things to the anodizing.  Made it about the same color as the thread backgrounds on here.

This was about 7 years ago, though.

Quoted: Break free, hell, they had us line up to get our chambers and barrel extensions roto-rootered out by an NCO with a chamber brush chucked into an electric drill, and then put the uppers (sans handguards) into a parts cleaning tank with some sort of super-nasty solvent that did Bad Things to the anodizing.  Made it about the same color as the thread backgrounds on here. This was about 7 years ago, though.

You, too, eh?  

Pacetime and Wartime are two differnet matters entirely.  Peacetime is all about style.  Wartime is all about substance.

please help me understand the point of this thread.

what i see from the pics is "some" erosion to what i have scaled to be the first 1.5 inches of the bore. the rifling does not appear to be totally gone. so the bullet still has to traverse 13 inches of well-rifled barrel. these last inches are the most important to accuracy.

i see no info determining the effect of this condition on accuracy. the fact that rifling is still in good (better) shape thru the rest of the barrel would lead me to believe the erosion would have minimal effect on accuracy. doesn't look bad for 20k rounds.

the original post made mention of a chrome-lined bore so i would have to determine that the "damage" would be more severe on a chrome moly or stainless barrel.

how does barrel cleaning relate to the pictured conditon?

i trust everyone is in agreement that this is a good pic after 20k rounds.

Quoted: Now all this can go up the tubes so to speak if you damage the muzzle crown. A guy I used to work with said he was convinced GI cleaning rods took out more barrels than were ever shot out and I agree with that 100%.

Don't ever go to a Marine Corps armory while jarheads are cleaning or you'll have an anuerysm.  The only thing we are allowed to use to clean is the the .gov issue cleaning kit, CLP, patches, and wood handled Q-Tips.

The problem, is the armorers are crazy stupid about carbon anywhere on the rifle so Marines end up taking one piece of their cleaning rod and using the threaded end to scrape the hell out of the muzzle in an effort to get their rifle "clean".

Yikes.  God knows what the does the muzzle crown after a couple of times.

Quoted:
Quoted:
Marines end up taking one piece of their cleaning rod and using the threaded end to scrape the hell out of the muzzle in an effort to get their rifle "clean".

quote]

That sux, I kinda cringed when I read that...

- Clint

I guess the best way to explain it is when chrome flakes off it leaves a rough condition that will strip bullet jacket material.  Once you start stripping jacket material from the first round you get a build up of copper that keeps on taking copper from follow on bullets.
The bullet has a separate core.  Best accuracy requires that the core stay centered in the bullet jacket.
Once you start cutting grooves in the jacket which removes instead of engraving the bullet you will unbalance the bullet and regardless of what the rest of the barrel looks like you have already ruined the bullet before it clears the muzzle.  You still have plenty of rifling to impart spin only problem is you are now spinning a couple hundred thou rpms with a unstable bullet because center of gravity has shifted off center.
I have pics of wear on barrels with far less wear (6000 rounds) and the dispersion was approximatley 8 feet at 600 meters where it should have been two feet max.
It is kind of like balancing a tire.  I am sure you have had cars/trucks pass you on interstate and you see a wheel hopping so to speak.  If the vehicle stops and you go up and examine the tire you won't actually see anything wrong with it.  Placed on a balance machine and weights applied the same tire will appear to go to sleep rolling down the road.

I have seen bullets blow up going down range because of jacket failures.  Other than having you continue to shoot your barrel until you decide it isn't accurate any longer and then cutting it as in picture and taking a look for yourself I really don't know what to say to convince you.

Just thought of a quick and dirty test you can perform to prove it yourself. Load up 50 rounds of your best load.  First 10 rounds load them as normal.  Next ten take a file and make a pass on one section of bullet.  Next ten make a pass on two different sections of bullet say 45 degrees from that one. On the next 10 make another pass 90 degrees from the first one.  On the last ten make a pass anywhere else on the bullet bearing surface you like.  Make all your passes take off about .004" of metal.  Do not cut all the way through the jacket.
Rifling is about .004" high depending on caliber.  Shoot these in a new or perfect barrel and examine your groups.  You might also weigh your bullets before and after jacket filing and record the amount of material you take off.

A cheaper test is to take a 22 target rifle with scope and shoot it for groups at say 100 yards.  Determine what the ammo is capable of. Then start shaving off very small slivers of lead and shoot the same number of groups with that.

The term shot out has more to do with bullet distruction due to surface roughness causing copper build up than just removing rifling.  On bolt rifles you can sometimes cut off threads on barrel, rethread and rechamber an inch down bore and the accuracy will come right back.  All you have actually done is remove the roughness in front of the chamber because as you observe  there is plenty of good rifling left in the bore.

Then again your definition of shot out and my definition may be worlds apart.  My definition of shot out is the dispersion is unacceptable regardless of what the rest of the barrel looks like.

Unfortunately in the AR family we don't have the luxury of being able to set barrels back and you have three conditions in these barrels.  New,  in process of being shot out and shot out.  The gov't standard of rejection is 7.2 inches at 100, the acceptance is 4.5" at 100.
A match shooter's rejection  is 1 1/4" at 100 maybe 1.5" depending on his skill level.

It is well documented with photographs in various publications of bullet deformation causing enhanced dispersion.  Basically you can deform the meplat and not get a very noticable effect on target but there are two things a bullet will not tolerate.  Bearing surface deterioration (not to be confused with engraving from lands) and bullet base deformation.

Load say ten rounds of the load you use in the 50 round test above.  On the base rim file one small spot off and load these and see what your results are.

And finally barrel manufacturers charge a enhanced price for lapping barrels.  Lapped barrels have smoother surfaces, remove less jacket material which retains center of gravity and produces smaller group sizes.

All I can tell you is if you keep shooting your rifle barrel the groups will at some point start to get bigger and will keep on getting bigger.   It is your decision when you decide that enough is enough and you want smaller groups  again.  If it gets bad enough you will see deterioration in bullet stability in as close as 25 yards.  It will take you awhile but sit down and shoot a 3X5 parallel card for ten shots at a dot on the card. At 5000 rounds do it again and 10,000 do it again.  At some point you will see bullet holes become elongated (egg shaped).  Your group sizes will get larger even at 25 yards.

You just have to decide what is acceptable for you.

Lol, when my barrel wears out i'll buy a new one.

Buying a new barrel is the only option you have with AR.  Can't set them back and if you don't give it TLC it will be like momma and we all know when momma ain't happy, no one is happy.haha.

That is the beauty of a bolt gun for highpower.  You just clean well and set it back occasionally.  Theoretically you could get a 28" target barrel (Winchester long range length)  shoot it maybe 5000, cut off threads and rechamber so now you have a 27" (Remington 40X length) barrel, then do it again and you have a 26" Palma length barrlel and so on.  You can cut barrel off four times and still have a 24" tube which was original barrel length of Mod 70 Target.

Now if you really wanted to save bucks you could get a 26" tube that is .875 at muzzle.
Put it on a bolt gun for a couple set backs and when you get down to 22" get it recontoured for AR and shoot it one last hurrah.

The name of the game is take care of the barrel.