throat erosion

[AKSavage]

I just checked the distance to the lands of one of my 6.5 mm barrels and found that it has crept out 15 thousandths (.015") since the barrel was new.

My questions is, how much throat wear is typical before a barrel is toast? I realize that there will be barrel to barrel differences, some barrels will still shoot with more throat erosion than others, so I'm just looking for a ball-park figure here. Am I near the end of the life of this barrel?

Thanks!

 

[WeiserBucks]

The targets will tell you all you need to know. It just depends on the level of accuracy degradation you're willing to accept. Chase the lands and get your money's worth out of the barrel.

 

[Mikecr]

Unless best of testing had you seated into the lands, don't chase lands. Keep your seated CBTO where it originally tested as best.
If you haven't tested for best, then you really should.

There are folks out there shooting as well as ever with several inches of erosion. Throat erosion is not actually the killer of barrels. Bore constriction(carbon constriction) is what ends it. This is a point where removing the constriction ruins the bore anyway. Moly constriction is another similar killer.

 

[AKSavage]

Thanks for the replies guys. Accuracy is still decent, right at or below MOA, but it does seem like I had more consistency early on. By consistency I mean fewer flyers within groups, but also that it seemed like earlier the barrel was less picky and would shoot good groups with a wider variety of powder and bullet combinations.

Since I just found out that my throat had eroded, my first test will be to see if "chasing the lands" improves accuracy. My best groups early on (1/2 MOA) were with bullets lightly jammed, and I haven't been able to get that level of accuracy for a while now. Maybe this explains why.

I don't have access to a bore scope, and I haven't ever shot out a barrel before, and there was no sudden decline in accuracy. I was just wondering if .015" of throat erosion was a lot or a little, thinking that if it's a lot then I might want to start the process of ordering a new barrel.

 

[WildRose]

Thanks for the replies guys. Accuracy is still decent, right at or below MOA, but it does seem like I had more consistency early on. By consistency I mean fewer flyers within groups, but also that it seemed like earlier the barrel was less picky and would shoot good groups with a wider variety of powder and bullet combinations.

Since I just found out that my throat had eroded, my first test will be to see if "chasing the lands" improves accuracy. My best groups early on (1/2 MOA) were with bullets lightly jammed, and I haven't been able to get that level of accuracy for a while now. Maybe this explains why.

I don't have access to a bore scope, and I haven't ever shot out a barrel before, and there was no sudden decline in accuracy. I was just wondering if .015" of throat erosion was a lot or a little, thinking that if it's a lot then I might want to start the process of ordering a new barrel.

As long as you have adequte twist to stabilize them you can step up to a slightly heavier/longer bullet seated further out to stretch the life of your barrel.

You can also have it cut off and set back a few turns if the rest of the barrel is still in good shape.

Typically when it's "shot out" you'll know it because accuracy goes to hell in a handbasket rapidly.

My .204 went from .3's to 2.0 in about twenty shots.

 

[AKSavage]

Both magazine length and seating depth have enough wiggle room to allow me to seat bullets further out. As a matter of fact with the added distance to the lands my bullets now seat with the bullet's body/tail junction right at the neck/shoulder junction of the case, and the COAL is still just below magazine length. In some ways, if the accuracy is still there then the added throat length has actually gotten me closer to where I want to be in seating depth. Now if it would just stay there!

The barrel is on a Savage action, there's still some extra room on the barrel threads, and I own the chamber reamer. All that to say that if/when accuracy does go south, could just have the barrel set back by, say, 1/4"? Or would the throat beyond 1/4" probably also be ruined by then, so setting the barrel back 1/4" would just be a waste of time? I mean, a barrel being shot out is not just about where the lands start, right?

I appreciate the responses. Great discussion. I'm learning a lot!

 

[Mikecr]

If best with your load was actually jammed, then you'll need to maintain that, or your pressure peak will drop away from your best. However, an added factor here is that you had bullet bearing seated into donut area. This is not a condition you should have relied on, and the only way to get jam + donut tension back is constant setting back of the barrel.

I would start over with new bullet seating depth testing (Berger's recommended). Find a CBTO that would not ever rely on a starting pressure condition. That is, plenty clear of land contact.

 

[WildRose]

Both magazine length and seating depth have enough wiggle room to allow me to seat bullets further out. As a matter of fact with the added distance to the lands my bullets now seat with the bullet's body/tail junction right at the neck/shoulder junction of the case, and the COAL is still just below magazine length. In some ways, if the accuracy is still there then the added throat length has actually gotten me closer to where I want to be in seating depth. Now if it would just stay there!

The barrel is on a Savage action, there's still some extra room on the barrel threads, and I own the chamber reamer. All that to say that if/when accuracy does go south, could just have the barrel set back by, say, 1/4"? Or would the throat beyond 1/4" probably also be ruined by then, so setting the barrel back 1/4" would just be a waste of time? I mean, a barrel being shot out is not just about where the lands start, right?

I appreciate the responses. Great discussion. I'm learning a lot!

It all depends on how far forward the erosion is showing.

I've burned up several .220 Swifts and a .204 Ruger shooting prairie dogs and all of them had different amounts of erosion when they finally went south.

 

[Frank in the Laurels]

Chances are with today's modern cartridges producing high velocity, throat erosion can happen fairly quickly, the more you push the limit the faster it happens. I think you'll run out of magazine length long before you can't touch the rifling anymore, that will be the limiting factor.

 

[AKSavage]

I just got back from the range and three out of the four loads I was testing shot 5 shot groups under 1.5" at 200 yards, with two of them at 1.25". One of those loads was not jammed, but the best two were lightly jammed at .008". It is a custom barrel, but considering it's a fairly light barrel on a factory action and factory tupperware stock, that's plenty good. It's also right about as good as the rifle shot when the barrel was new, so I'm satisfied.

I'm going to do one more test with 8 rounds each of the best two loads to determine my final load, and then I think I'm going to baby this barrel from here on out. I still have some room left in the magazine. Gotta love the long (2.99") magazine of Savage short actions, which is actually one reason I choose to build on a Savage. It looks like I'm good for a few more seasons.

 

[bigngreen]

A throat moving .015 is nothing, once you find your seating depth all you need to do is load a few .005 longer and see if it brings you back into the node every once in a while. I do regular throat matanance with an abrasive cleaner so my throat stays smooth while moving forward so when I shoot one out the first thing I'll see is a drop in velocity then it'll stop shooting VLD's and in the last stage of death I'll only get bullets like ballistic tips to shoot at low velocity, there will be several inches showing extreme wear and the throats move close to half an inch.

 

[Mikecr]

Have you completed full seating testing?
http://www.longrangehunting.com/for...accuracy-berger-vld-bullets-your-rifle-40204/
You could do this, and load develop again from a better position.
There is just no reason to lock yourself into a jammed load, and essentially reduce your shooting because you can't maintain that condition.
Nobody can maintain that condition without at least melonite treating the barrel from new.

 

[AKSavage]

Mike I actually have gone though the Berger process of testing, going back .01" at a time all the way back to .05" off, but the most consistent and accurate was still lightly jammed. I could of course repeat the process, but I really don't feel like starting over at this point. Another part of the equation is that I'm shooting a slower powder, so the case is pretty full. Before I got any throat erosion this was a fairly compressed load. I start compressing powder at .02 off the lands, and the deeper I go the more resistance and spring back I get when seating bullets. Now, with a little more room to seat bullets out, I'm not crunching powder at all. I've shot plenty of compressed loads before, but it's one less complication to worry about.

Also, I don't have any trouble with the donuts. I anneal and neck turn my brass, and if I feel anything other than easy, smooth pressure when seating bullets I fix it. Seating the bullets with the base of the bullet right at the shoulder/neck junction of the brass has never produced any problems for me. I do appreciate your input, but I think I'm with bigngreen on this one. It seems like I still have plenty of barrel life left, and when I run out of magazine length I can either rebarrel or go with bullets that have s shorter nose than the Berger VLDs, such as Amax or SMKs.