Throat erosion ?

[jsthntn247]

My 308 has around 1800 rounds on it now. For the first 700 rounds the throat did not move and the gun shot extremely well .015 off the lands. When determining my base to ogive distance I would always see 5 land marks on the bullet and when I moved just a few thousandths off what I determined my base to ogive length to be I would no longer see any land marks on a bullet that I shined with steel wool. Now the gun has to be jammed .020 or more to shoot without getting horizontal stringing. It has also become really sensitive to slight variations in powder charge=small nodes. When determining my base to ogive I now get 2 pronounced land marks for .020 longer than the other 3 lands. Is it time to have the barrel set back or at least have the throat lengthened to square the lands back up? Could the uneven lands be giving me horizontal stringing ?

 

[mikecr]

Your post doesn't make sense.
How did you end up with 5 land marks on bullets .015 off?
Why don't you just determine best seating and leave it at that best?

 

[chkunz]

You did not state what the application for this barrel is, the loads you are shooting or details about the actual results you are getting and that would be helpful in giving a proper response. I have shot out my weight in M14 (308) barrels and normally I put a minimum of five thousand rounds thru them. I once took an M14 with eight thousand rounds thru the barrel to Perry and got leg points. If you are using this barrel for something more demanding then you may not want to go that many rounds but a 308 will go twice what you state yours has unless you have abused it with a cleaning rod or something unusual like that. There have been many barrels replaced when the barrel was not the problem; at 1800 rounds I would look elsewhere, not the barrel. If you are an experienced competitor ignore the following but if you are relatively new to the competitive shooting sports you will find that everyone claims to have a sub MOA gun and load. They may have to shoot many three shot groups (meaningless) and throw out the flyers to prove it but that makes all the normal folks think there is something wrong with their stull. I will stop and let you respond with more info so we can properly diagnose your problem if in fact you have one.

 

[mikecr]

if you are relatively new to the competitive shooting sports you will find that everyone claims to have a sub MOA gun and load

I'm not a competitor, and I don't know if you compete off rests or off hand, or with one hand tied behind your back. But IMO if you can't shoot sub-moa off rests, you're not ready for any competition.
'Sub-MOA' is a horrible thing to cling to.

 

[watercam]

Easy guys! We are all friends here! The original post was a tad confusing regarding whether you were jumping or jamming. If you have land marks on the bullet, it seems jam. When my Palma barrel gets finicky I pull out the JB cleaning compound and then polish it with the JB polishing cream. Does wonders for wearing barrels as long as one doesn't over due it. Every 500 rounds at the most. Beyond that, a look with a bore scope would tell you a lot.
In my personal experience, I jump my bullets and maintain the same jump where ever the throat takes me. I check it every 500 rounds.

 

[243winxb]

Could the uneven lands be giving me horizontal stringing ?

No, is my guess.

 

[chkunz]

if you are relatively new to the competitive shooting sports you will find that everyone claims to have a sub MOA gun and load

I'm not a competitor, and I don't know if you compete off rests or off hand, or with one hand tied behind your back. But IMO if you can't shoot sub-moa off rests, you're not ready for any competition.
'Sub-MOA' is a horrible thing to cling to.

Mikecr, The NRA/CMP High Power Rifle National Match Course consists of four stages, Standing slow fire at 200 yards and the ten ring is 7 inches, Sitting rapid fire at 200 yards with 7 inch ten ring, Prone rapid fire at 300 yards also with a 7 inch ten ring and Prone slow fire at 600 yards with a 12 inch ten ring. Competitors may use a U. S. Service rifle(M1 Garand, M14 or M16 civilian type rifles) or match rifles as defined in the rule book. The CMP competition if for service type rifles only. Sub MOA is desirable but not really feasible for the M1 or M14 type match rifles but near MOA accuracy for the AR service rifle configuration versions of the M16 is achievable. Many of the match rifles used in this type of completion are capable of MOA or near MOA accuracy. Anyway lets hear the response from jsthntn247 before we hijack his post. We need to address his question first. Take care, Clyde.

 

[dcali]

Erosion is not going to lead to horizontal stringing. As others said, if you're jumping, you won't see land marks, so something is amiss there. How many rounds are you shooting? When you see stuff all over the place like this, I find that the usual culprit is statistics - people thinking their rifle is more accurate than it really is based on only shooting a couple three shot groups, a ladder test, OCW, or some such thing. Sometimes "horizontal", "vertical" or "flyers" is just another word for "my rifle isn't as accurate as I think it is".

 

[chkunz]

Erosion is not going to lead to horizontal stringing. As others said, if you're jumping, you won't see land marks, so something is amiss there. How many rounds are you shooting? When you see stuff all over the place like this, I find that the usual culprit is statistics - people thinking their rifle is more accurate than it really is based on only shooting a couple three shot groups, a ladder test, OCW, or some such thing. Sometimes "horizontal", "vertical" or "flyers" is just another word for "my rifle isn't as accurate as I think it is".

damoncali You make an excellent point about needing more information and that is why I recommended that we get additional information so we can solve the real problem rather that hijack the post and get a bunch of side issues going. As you say the specifics about the number of groups fired and the number of shots in the group is critical to the solution. Groups do not get smaller as more shots are fired and a 20 shot group will, on the long run average, be almost two times as large as a three shot group. Take care, Clyde

 

[jsthntn247]

I must have made no sense at all to begin with. The gun is a 308 custom action 30" Bartlein I shoot comps with. I use a hornady oal tool to find the distance to the lands then I seat a dummy round .010 longer than that measurement, chamber the round, check for land marks, seat it .005 deeper and repeat until marks are gone to make sure the measurement from the tool is correct. When the barrel was new I could do this and I would get. 5 equal marks on the bullet when jammed. As soon as I seated the dummy round deeper that what the oal gauge said was the distance to the lands, I would no longer get lands marks on the bullet when chambering the dummy round. However, now when doing the exact same thing, I'm only getting 2 lands showing at 2.333 which is the measurement I get with the oal gauge. I have to seat the dummy round to 2.353 before all lands show when chambering the dummy round. Juggernauts shot extremely well .015 off the lands until my throat started to lengthen unevenly. Now, if i seat any bullet off the lands groups string horizontally. It doesn't matter if it's .005 off or. .050 off, they all string. I have to jam all bullets .020 or more now to get rid of the horizontal.

 

[243winxb]

The jam just aligns the round in the chamber. Have you tried just sizing 1/2 of the neck with a bushing? This will align the round without the jam. Without a jam, you will need to work up the load again.

 

[chkunz]

I must have made no sense at all to begin with. The gun is a 308 custom action 30" Bartlein I shoot comps with. I use a hornady oal tool to find the distance to the lands then I seat a dummy round .010 longer than that measurement, chamber the round, check for land marks, seat it .005 deeper and repeat until marks are gone to make sure the measurement from the tool is correct. When the barrel was new I could do this and I would get. 5 equal marks on the bullet when jammed. As soon as I seated the dummy round deeper that what the oal gauge said was the distance to the lands, I would no longer get lands marks on the bullet when chambering the dummy round. However, now when doing the exact same thing, I'm only getting 2 lands showing at 2.333 which is the measurement I get with the oal gauge. I have to seat the dummy round to 2.353 before all lands show when chambering the dummy round. Juggernauts shot extremely well .015 off the lands until my throat started to lengthen unevenly. Now, if i seat any bullet off the lands groups string horizontally. It doesn't matter if it's .005 off or. .050 off, they all string. I have to jam all bullets .020 or more now to get rid of the horizontal.

If you were experiencing "gilt edge" accuracy and now that is gone something has definitely changed. 1800 rounds is not insignificant but normally a 308 will go well beyond that. But most of my experience is with the M14 and they are not tack drivers so my expectations and experience may not be directly applicable to what you are doing. It would be helpful to know more about the groups you were getting originally and what you are getting now, number of groups, number of rounds per group, size of groups, etc. Like was said above if you are not shooting enough shots to define the group size you may just be seeing variations within the group. Are you careful with the cleaning rod? Some folks have been know to have destroyed accuracy with a cleaning rod. It is educational to look at a sectioned barrel with a new chamber cut in it. These things we call lead, lands, etc. are tiny things and easily damaged by improper cleaning methods. It is amazing that they last as long as they do. The Hornady OAL gages are very inaccurate, if you make ten measurements using the same bullet and do the best job you can you will see a large variation in the measurements relative to what you are trying to set as jump but it is the best tool I am aware of to make these measurements. You additional checks you describe after finding the starting point with the OAL gage sounds like good practice. Are you careful with keeping a round count on the barrel? It is easy to underestimate the number of rounds thru the barrel. This is very interesting.

 

[dcali]

Now that I think about it a little more, uneven wear could cause horizontal. If the bullet gets a crooked start, it will shoot off in a predictable direction based on which way the bullet was pointed. It might just happen that that direction is left or right. jamming hard gives you a chance at overcoming that initial tipping. Now, what I don't get is why you would get such a big asymmetry in erosion to begin with. This is mostly speculation, of course, but it's a theory. Sounds like you might need to rechamber.

 

[jsthntn247]

I just saw your post Damon and that's exactly what I was speculating. I also just read a post in another forum that hinted toward the same thing. I have no idea why my throat is eroding more to one side than the other, but it is.

"considering some people find that after .050 of wear a barrel can go south at anytime, it might be considered fast wearing. The bigger factor is that the wear is even on all the lands/grooves, if it's even the barrel can last very long compared to uneven wear. some say that double based powders like RE15 can cause more wear".

 

[rminut]

I just saw your post Damon and that's exactly what I was speculating. I also just read a post in another forum that hinted toward the same thing. I have no idea why my throat is eroding more to one side than the other, but it is.

"considering some people find that after .050 of wear a barrel can go south at anytime, it might be considered fast wearing. The bigger factor is that the wear is even on all the lands/grooves, if it's even the barrel can last very long compared to uneven wear. some say that double based powders like RE15 can cause more wear".

I didn't reply to this posting about wear because you seem to be experiencing a very certain pattern and from the guys I know through service rifle shooting that state that if a land wears at a different rate than the others you will lose accuracy overall, not specifically horizontal stringing. I would copy the posting but it's a site you have to join to access. The author has shot his weight in krieger service rifle barrels and states for certain if a land/groove wears at a different rate the accuracy will drop in a hurry. if they wear evenly the barrel life can go much longer than expected. Since most barrels are made from the same 416 stainless I don't know if there is a way to explain why a land would wear unevenly. luck of the draw??

There is a in depth article about erosion by Bruce Woodford by doing a google search you can find it.

 

[rminut]

here is a quote from the guy:

My krieger barrels tend to move about fifty thou when they hit the 3500-5000 round range and that is when I stop trusting them for big matches. Those barrels generally shoot really well for reduced course matches for a long time though.

The bigger culprit is UNEVEN wear and that is almost impossible to check without the aid of a bore scope. I would rather compete with a barrel with 1/2 inch of even wear than one that has .020 with uneven wear.Lots of things can cause uneven wear and most of it is improper cleaning, but even under the best circumstances, and careful cleaning, I have still owned some barrels where one side or one land is considerably more worn than the others. Barrels seem to really stop shooting well at 600 quick when this happens.

I also think that barrel wear and accuracy are also proportionate to the amount of bearing surface you have on any given bullet. My theory is that long bearing surface = long bullet. As the bullet leaves the case mouth is it going to have any free bore before it hits the rifling? Bullets like 77 SMKs are tolerant to long throats because they can travel damn near 1/2 an inch of free bore yet still have bullet inside the case neck and that means there is some support. Bullets like JLKs even in a new throat with a Wylde or CLE reamer are only going to be supported in the case by maybe .40 or .50 to start.

Some barrels may shoot well beyond .050 but I don't trust them much and I view barrels as a consumable much like powder, primers and bullets.

Just an FYI the USAMU did at one time, and still might, rip their barrels at 2500 rounds. That would be considerably less than .050 wear.

 

[mikecr]

rminut, this is what Tubb's TMS is for.

 

[rminut]

please explain to me exactly how that will fix uneven wear to lands?

 

[mikecr]

Well it may be too late for you,, but TMS is all about dressing up the lands.