Best method to use to see if a rifle barrel is shot out?

[DocMedic]

Just curious on what methods that most are using to determine if their barrels are starting to be shot out, I have a sneaking suspicion that my Light weight 18" JP might be heading that way with +12k down the pipe, my groups at 300 will start under MOA but 5 or 6 groups later open up. So what is your method?

[Flatland Shooter]

I don't really have a "method" to determine when a barrel is shot out.

What I do is shoot an occasional group with ammo known to be accurate with that barrel and keep records of group size. To get the best accuracy possible, I install an 18X scope and shoot from sandbags.

Its not a case of doing it every 1000 rds or so, but more of a case where either I just feel like a range day shooting from sandbags or I feel I may have a barrel that is not performing as well as it has in the past.

What I find interesting about your post is that the first group is MOA but follow up groups are opening up. Sounds like you have issues other that a worn out barrel. Is heating up the barrel causing problems? Is it possible your rifle likes to be shot with a clean bore and just a little fouling causes problems? (Possibly changing your ammo would solve the problem.)

Bill

Edited August 19, 2015 by Flatland Shooter

[lwink]

Yes, the fact that you're getting good groups out of it early may point to some other issues. The easiest way is to find a friend or friendly smith with a bore scope and take a look at the throat of the chamber, that's the part that will go first in normal wear.

[bushmeat]

If it's shot out, it wouldn't do MOA on the first few groups. It's a lightweight barrel. Probably just heating up.

[MarkCO]

Cold bore accuracy over the life is the best determination.

[kurtm]

I disagree. Hot barrel groups are the determiner. Both Sechiotano and I have had barrels that would group well under an inch when cool, but run a magazine through it and then try a group and it was scattering wildly. My last J.P. barrel when cold would give nice 3/4" groups at 100. get it hot and it would only put two or three bullets on a FULL SIZED IPSC target. What Curtis is describing is not that uncommon, at least in my little world! This seems to be related to Stainless barrels. I know of at least 7 barrels that were like this. They didn't look too bad with a bore scope either, but the proof is in the results!

Edited August 22, 2015 by kurtm

[MarkCO]

Kurt, you need to read what I wrote.

Sure, as a barrel ID increases, at some point, less engraving results in more skidding and thus less rotation imparted to the bullet. Soo in effect loss of stability earlier in the flight path. However, that also occurs when cold, and the cold bore shots are still a better determination and you get that when the thermal drift and barrel harmonics are not heat affected.

[kurtm]

Then please explain the phenomenon I have personally experienced. My barrel when cold would easily do 3/4" groups, every day. It never showed any signs of scattering. When hot it wouldn't hold a 20 M.O.A. group. And on the very same day, with the very same ammo when it had cooled completely it would once again shot a 3/4 M.O.A group.

I am not the only one to experience this as noted. So please let me know how a cold group would indicate that the barrel is good or bad. Curtis is experiencing the very same problem, so please let him know that if it groups good cold, the barrel is just fine.

[MarkCO]

Tracking groups...if it shoots 1/2 MOA cold when new, and 3/4 MOA hot, then at 10K it shoots 1 MOA cold and 20 MOA hot, sure, you have a shot out barrel.

But, if you have 1/2 MOA new and 1/2 MOA at 10K that opens to 20 MOA hot, you have a barrel extension/barrel nut issue.

[openclassterror]

Kurt- I don't think you and Mark are talking about the same phenomenon. You are talking about a barrel that won't group when hot, even though it isn't worn out as seen through a bore scope. He, I think, is trying to answer the OP's question about whether the bore is shot out. If the throat is badly eroded, it probably won't group as well as it did when new. It is easiest to see the difference when the rifle is being shot in conditions that give the best accuracy, thus the cold bore group. If you are getting a 20 MOA group when hot (even if the throat is still OK) then when the bore is shot out, you may not even be able to tell the difference with a hot barrel group. The OP was not explicit about HOW the groups were shot- IE allowed to cool in-between, back to back, etc. So we don't know if thermal cycling is the problem, or bore wear, or possibly other factors, without a little more info from him. I think MarkCo was simply suggesting removing one of the possible variables from the equation for determining the SPECIFIC question "is it shot out" without the use of a bore scope. It very well could be that the bore is NOT shot out, but is still struggling to group well when warm for a different reason, as in your case. The question as posed was not "Do I have a bad barrel?", but rather "Is it shot out?". The two are not necessarily one-in-the-same.

[kurtm]

I guess it is all in the way you read Tom. The O.P. stated that it would START (read cold here) under 1 M.O.A. at 300 yards, but after 5-6 groups it would start to open up (read hot here). So lets assume 3-5 shot groups, so it started COLD and then after 15-30 rounds (hot) it would open up. Now remember it is stated that this barrel has around 12,000 rounds on it. I was replying to the specifics of the post.

Now in all fairness I could see how someone could reply to the more general TOPIC post which stated " Best method to use to see if a rifle barrel is shot out?, but I would proffer this.

If it wouldn't group well cold it is shot out (or if new a bad barrel, which this one seemed to be fine for the first 12,000 rounds)

If it won't group well when hot it is shot out (unless the group wonders due to heat, which would have been noted when new, not at 12,000 rounds) BTW Curtis is a darn fine shooter.

I really doubt that this issue has anything to do with the barrel nut, or extension, I know for certain in my case as well as Chris's that it had nothing to do with it.

So Tom, with a bit of thread drift here, how can a rifle shoot a 3/4 MOA group when cold, then group around 20 MOA after a 30 round mag dump, and then again group at 3/4 MOA when cooled back down with the cold bore groups (5 rounds ) landing exactly on top of each other, same ammo, same rifle rest, same day, same shooter, etc. The barrel I am talking about had around 5000 rounds on it and it looked good under a bore scope. The extension wasn't cracked it was properly torqued as was the barrel nut. There was no bind on the gas tube, it didn't string it scattered! I sent it back to J.P. and they couldn't figure it out either. anyway a new barrel and it is back to fine, so all is good. But I really would like to know how you think this happens....and once again, I'm not the only one!

Mark both your statements seem to say the same thing with different conclusions. I am not trying to pick a fight, but could you clarify it for me a bit.

[MarkCO]

So Kurt, tell me why when a shooter has good cold groups and poor "hot" groups, on a factory rifle built by JP, I can take it apart and put it back together and make it shoot the same POA with the same group size hot or cold. Hint: It is the assembly process that allows thermal drift.

Basic fundamental in mechanical engineering on systems is differential expansion. Aluminum clamping steel to aluminum...yeah that can move with heat flux.

Unless YOU built the rifles in question, you do not know the torque levels, fit, etc. Sure, JP used to thermal fit and has since gone to shims...but the shims are not performing as well as their old style of assembly. Yes, better than most of the others, but there are some that don't group hot, especially after the flood of locktite (which never oxidized the passivated metals) runs out leaving islands in the mating surfaces.

[kurtm]

I understand that Mark, but we are not talking new rifles here. I can see what your saying for a brand new rifle, but in my case it shot great until about 4800 after that, cold good hot bad....it was a thermal fit barrel. I don't think taking it apart and putting it back together would change it. John yanked the barrel put it in a different receiver and it did the same thing as it was doing to me. So we are back to the same place. BTW I have shot several ARs that the nut was loose on, one you could even move the barrel in and out a few thou and even then they were much better than 20 MOA. So yes fit is important, but it doesn't explain what I have first hand experienced!

[MarkCO]

Great. but the OP questioned the "Best" method to use. The best method IS tracking performance over the life of the barrel cold bore, bar none. That is what I answered. You took a divergent path, and while I agree a shot out barrel can open up due to what I explained prior, I still don't think you provided Curtis with a better method. All barrel certainly do not behave the same due to a lot of factors, to to toss all barrels that open up when hot would not be a "Best" method by any stretch of the imagination.

[kurtm]

I think I could agree to that if we tracked both cold AND hot groups, just to catch those divergent few! From the sounds of it Curtis has been tracking it, after all why would a shooter at his level even bother with groups at 12,000 rounds if it weren't to track it, but I still maintain that you need to see what they do hot much more so in our game than not.

BTW I think you mean deviant path instead of divergent path.

Edited August 22, 2015 by kurtm

[MarkCO]

FWIW, I have found that somewhere between 10 and 15K, stainless barrels take a dive and that it is more abrupt than chrome-moly barrels.

[Religious Shooter]

On a new barrel I take a baseline groups after I have put 200 rounds through it.

Do one cold group. Fire 30 rounds in about a minute. Then do a "hot" group. Keep the targets filed away.

Down the life of the barrel, I'd do the same procedure and see what it does. Compare it with the initial targets. If I don't like what it does... time for a new barrel.

[MarkCO]

On a new barrel I take a baseline groups after I have put 200 rounds through it.

Do one cold group. Fire 30 rounds in about a minute. Then do a "hot" group. Keep the targets filed away.

Down the life of the barrel, I'd do the same procedure and see what it does. Compare it with the initial targets. If I don't like what it does... time for a new barrel.

If you had just written that at about 8am, we could have saved some bandwidth here.

[kurtm]

Are you KIDDING???? What else do I have to do while waiting on rocket fuel!

[MarkCO]

Are you KIDDING???? What else do I have to do while waiting on rocket fuel!

You could make a n f o I guess.

[ericm]

If I have too much rocket fuel, my barrel acts like it's worn out.

It takes several quarts of Mountain Dew to get it shooting like new again...

This is all on the same day, same ammo, same giant pink bunny motioning me to follow...

ericm

[toothandnail]

I changed mine when I started seeing key holes in paper at 7 yds , funny thing I was still getting reasonably consistent hits out to 350-400 yds .

My hit factor did go up some after changing barrels though.

[Alaskapopo]

Just curious on what methods that most are using to determine if their barrels are starting to be shot out, I have a sneaking suspicion that my Light weight 18" JP might be heading that way with +12k down the pipe, my groups at 300 will start under MOA but 5 or 6 groups later open up. So what is your method?

When the groups open up beyond a point you can accept. For me that is 2 moa with ball ammo and 1 moa with match. Once its beyond that point I start looking to replace the barrel or make it a back up rifle.

Pat

[Stlhead]

Barrels are a wear item, just like pants. Some people were the pants till the knees have holes and the crotch is gone, others replace them when they get the slightest bit threadbare. If you think your barrel may be shot out, it probably is. Get a new one, or not and keep shooting it, only thing it hurts is your scores, not that important in the long run.

[DocMedic]

Just had this happen at me at the Noveske Multi-gun Championship.

Target size is 5 MOA. I had no issues hitting the targets beginning out the string despite being in a non stable position. As I get to the last target I'm holding were I'm suppose to be. I think my Barrels done.

Edited August 31, 2015 by DocMedic