What amount of throat erosion means barrel is toast?

[MarinePMI]

Just tossing this out there to see if any folks had info of their own to share.

My current 6.5CM AI barrel is up to about 3000-3100 rds down the tube. In preparation for the inevitable replacement, I ordered a replacement a few months back. For yucks, I pulled the comparator out and measured the old barrel, and then screwed on the new barrel (also an AI) and measured it and got a .083" delta in the throat. The old barrel still seems to shoot fairly well (not as good as it used to, but still hovering a little above 1/2 MOA), but I'm wondering if I'm starting to push it a bit.

Has anyone else measured their throat of a toasted barrel and compared it to a new one? If so, what was the difference when it finally gave up the ghost?

Really curious to hear everyone's responses (and yes, I know there is no hard and fast rule, just looking for a consensus of sorts).

TIA

 

[rijndael]

Years ago, a friend of mine had a 300WM with a throat that was burned out for inches in front of the chamber, it still shoot well.

I would go based off how it shoots rather than a number.

 

[lash]

I based mine on the ability to shoot well and maintain velocity. I had over 4400 on my .260 barrel before I replaced it. I made a mistake in taking it to a two day match when it had almost 4400 on it. Mid-day the second day it took a big crap and went from around 3/4 moa to well over 1 moa and velocity dropped. I learned a couple of things that day. I did not measure the throat erosion though.

 

[Fig]

That’s the danger. Some start wandering off, and others just let go within a few shots. You can chase it a little with OAL, but you usually run out of Mag room first.

 

[MarinePMI]

Yeah, I can still fit in the mag with the RDF's (and their liking of a jump helps some). I just wonder if I'm venturing into the gambling zone like Lash mentioned. Since I have just been shooting local matches lately (due to work commitments), I may take more of a gamble than I normally would.

I'm just wondering (also) if throat erosion with a certain case (6.5CM in this instance) and in a certain barrel brand (Bartlein in this instance) would show a trend towards accuracy wandering off, or just letting go suddenly.

I figured it was worth asking the question, just in case their might be a corollary across the user base.

 

[RTH1800]

I go by how the barrel shoots and velocity. Other indicators are how frequently cleaning is required. I also use a bore scope. The truth is in where the bullet lands. The other things just roughly indicate how long its going to be landing there. I have seen barrels that still look good that quit and others that look awful that shoot great.

 

[PFG]

I have seen barrels that still look good that quit and others that look awful that shoot great.

Yep. Barrels are funny. And another reason for letting the accuracy talk.

Throat erosion can also be a real teaching moment. I've seen shooters who swear up and down at the importance of getting that bullet in the lands. Then they lose mag room and do a little more shooting before getting a new barrel...only to find out that being in the lands didn't matter nearly as much as they thought.

Shoot straight ammo and a lot of accuracy questions disappear. IMO

 

[Black Bart]

I am one of those that believe in chasing the lands. When doing load development you should be testing seating depth and you should know at which jump your accuracy goes to shit. A given load WILL NOT shoot consistently well (3/8") from .005" all the way to .205" jump. Your requirement for accuracy does define how important this is to you. Given a sub 1/2 moa (3/8" ave) requirement chances are real good that you need to chase lands. This is important to note bc it causes two problems with throat erosion. Fitting in the mag and running out of neck.

I agree that accuracy is king and the ultimate judge of whether or not a barrel is still serviceable but if you run out of mag or neck you will be forced to either jump the bullet at a distance that isn't conducive to accuracy or you will lose accuracy bc of inadequate case neck grip on the bullet. You might be able to re-do load development and find a jump like 120 thou plus that the bullet begins to shoot well again.

I had a 6.5x47L Bartlein barrel erode real fast shooting 130's and Varget last year. About 60 thou in 800rds. It was a hammer to start out. I had to re-do load development at 450rds and ran out of case neck at 800. I set it back and it never regained the original accuracy. Since then I have been anal about measuring throat erosion. I pull my barrels when I clean them (every 100 to 200rds). I re-measure the lands at that time. I have since shot two dasher barrels and a 6SLR barrel. The 47L barrel eroded at a cumulative rate of 7.5 thou per hundred (36.7gr Varget). Both the Dasher barrels (K&P and Krieger) eroded at .004" per hundred (32grs Varget). The 6SLR is averaging at 2.8 thou per hundred (43.8gr RL26, QL says less than 50K psi chamber pressure, 115DTAC at 3000fps). The neck on a 6SLR is .300". The COAL is 2.85". Using an ARC or AW mag I have 100 thou of erosion before I hit the end. The neck is as long as the day. The barrel accuracy will go before I am limited by neck or mag length. I had to switch to 115 DTACs on the first Dasher barrel bc the Hybrids ran out of neck.

While you could lose accuracy from large pits and broken off steel from fire cracking long before you run out of mag or neck (300WM) there is a pretty good correlation between the rate of erosion and how fire cracked your barrel gets. .002" per hundred is awesome, 3 -4 thou is good, 5 plus is going to crack up a barrel within 1500 rds to the point most folks retire them from inconsistent accuracy.

I have seen many 300WMs shot out as an Instructor. When you true and chrono a firing line of 20 identical rifles (aside from use) and one the rifles is chrono'ing the same ammo 100fps slower it will also not maintain consistent dope or true data. So, what I mean is that while the rifle may shoot sub-moa at 100 it will not consistently shoot data at distance. Just going off 100yd groups for accuracy is inadequate.

I would have never thought the 6.5x47 would out burn the dasher with its midget short neck. I wonder if that 40 degree shoulder is helping?

 

[MarinePMI]

I think the key to that is he's using Varget. Great powder, but eats throats with the 6.5x47....

 

[V-Ref]

I am one of those that believe in chasing the lands. When doing load development you should be testing seating depth and you should know at which jump your accuracy goes to shit. A given load WILL NOT shoot consistently well (3/8") from .005" all the way to .205" jump. Your requirement for accuracy does define how important this is to you. Given a sub 1/2 moa (3/8" ave) requirement chances are real good that you need to chase lands. This is important to note bc it causes two problems with throat erosion. Fitting in the mag and running out of neck.

I agree that accuracy is king and the ultimate judge of whether or not a barrel is still serviceable but if you run out of mag or neck you will be forced to either jump the bullet at a distance that isn't conducive to accuracy or you will lose accuracy bc of inadequate case neck grip on the bullet. You might be able to re-do load development and find a jump like 120 thou plus that the bullet begins to shoot well again.

I had a 6.5x47L Bartlein barrel erode real fast shooting 130's and Varget last year. About 60 thou in 800rds. It was a hammer to start out. I had to re-do load development at 450rds and ran out of case neck at 800. I set it back and it never regained the original accuracy. Since then I have been anal about measuring throat erosion. I pull my barrels when I clean them (every 100 to 200rds). I re-measure the lands at that time. I have since shot two dasher barrels and a 6SLR barrel. The 47L barrel eroded at a cumulative rate of 7.5 thou per hundred (36.7gr Varget). Both the Dasher barrels (K&P and Krieger) eroded at .004" per hundred (32grs Varget). The 6SLR is averaging at 2.8 thou per hundred (43.8gr RL26, QL says less than 50K psi chamber pressure, 115DTAC at 3000fps). The neck on a 6SLR is .300". The COAL is 2.85". Using an ARC or AW mag I have 100 thou of erosion before I hit the end. The neck is as long as the day. The barrel accuracy will go before I am limited by neck or mag length. I had to switch to 115 DTACs on the first Dasher barrel bc the Hybrids ran out of neck.

While you could lose accuracy from large pits and broken off steel from fire cracking long before you run out of mag or neck (300WM) there is a pretty good correlation between the rate of erosion and how fire cracked your barrel gets. .002" per hundred is awesome, 3 -4 thou is good, 5 plus is going to crack up a barrel within 1500 rds to the point most folks retire them from inconsistent accuracy.

I have seen many 300WMs shot out as an Instructor. When you true and chrono a firing line of 20 identical rifles (aside from use) and one the rifles is chrono'ing the same ammo 100fps slower it will also not maintain consistent dope or true data. So, what I mean is that while the rifle may shoot sub-moa at 100 it will not consistently shoot data at distance. Just going off 100yd groups for accuracy is inadequate.

This supports my experiences as well.

Pressure, barrel temperatures, firing string length/intensity, barrel to barrel steel variation, and cleaning regimes are all factors regarding barrel life, that can move the chambering known for barrel life into the barrel burner column and vice versa.

 

[lash]

<snip>...
I agree that accuracy is king and the ultimate judge of whether or not a barrel is still serviceable but if you run out of mag or neck you will be forced to either jump the bullet at a distance that isn't conducive to accuracy or you will lose accuracy bc of inadequate case neck grip on the bullet. You might be able to re-do load development and find a jump like 120 thou plus that the bullet begins to shoot well again. <snip>...

<snip>... So, what I mean is that while the rifle may shoot sub-moa at 100 it will not consistently shoot data at distance. Just going off 100yd groups for accuracy is inadequate.

Agreed that accuracy is not just at 100 yards. We are, after all, on the Sniper's Hide, where most of the discussion is centered around long range shooting. I do not have time to chase the lands, so I use projectiles that are as forgiving of jump as I can find. That does mean that I often don't use the most recent projectile with the highest BC, but it also means that I can focus on shooting with what little time I get to enjoy my shooting. If I had more time available and was competing on more than a casual level, I might spend more time doing what you do. Not sure I would, but it's a possibility.

 

[rijndael]

I do not have time to chase the lands, so I use projectiles that are as forgiving of jump as I can find.

Same here. Not only is it a time issue, but I'm running a factory chamber. If I chased the lands I'd have to single feed.

 

[samb300]

This is all great info. I have been shooting 6.5x47L for the past few years, and love it as an overall cartridge (accuracy/consistency, velocity, recoil, barrel life). My go-to load is 36.5gr Varget with a 140 Hybrid at 2725fps out of a 24” barrel. The majority of my shooting is PRS-style matches, and practice where my time is limited so the barrel stays hot.

I have found that about 0.040” of throat erosion per 1000 rounds is normal for me. I generally chase the lands to move back to a 0.010” jump every 1000 rounds or so. What I find happens with the Hybrids is they still shoot great with the jump, but I gradually lose a little velocity (like 10-20 fps).

In my opinion, if you’re at 3000 rounds and wondering how much more you can push it, you certainly do so knowing the risk is the barrel takes a crap in the middle of a match. I’m of the mindset that I’d rather toss the barrel with a little life left on it and put a new one on. I don’t shoot every weekend and I like to know at a match I’m not going to be dealing with possible barrel issues trying to eke out an extra couple hundred rounds.

If you think about it, if your AI barrel was $800...
$800/3000rnds = $0.267/rnd
$800/3500rnds = $0.228/rnd

The potential $0.04/rnd savings TO ME aren’t worth the risk with the costs associated with shooting a match.

 

[lash]

I do not change my load and do not lose velocity like crazy because I also am not shooting a hot cartridge to start with. Mine is a .260 that I run at or around 2750 and it's as consistent as can be. I do know where my lands are when I start and I do load development to find a forgiving node with the shortest jump sweet spot that will give me a consistent results when things change. I do not shoot bench rest and also do not chase true 1/2 moa groups, so your earlier statement regarding expectations is accurate. I've seen good shooters do well and then get so caught up in chasing perfect loads, at the highest speeds possible, that they begin to digress in their progress and get very frustrated. They get to changing things like load, bullet, speed and even cartridge, over and over again in an attempt to eke out the nth degree of perceived improvement and they lose sight of the real goal of improving skills and practicing what actually matters in these matches.

I'll admit to even heading down that rabbit hole myself for a while until I came to my senses and started re-focusing on quality practice and consistent reloading practices.

 

[samb300]

I do not change my load and do not lose velocity like crazy because I also am not shooting a hot cartridge to start with. Mine is a .260 that I run at or around 2750 and it's as consistent as can be. I do know where my lands are when I start and I do load development to find a forgiving node with the shortest jump sweet spot that will give me a consistent results when things change. I do not shoot bench rest and also do not chase true 1/2 moa groups, so your earlier statement regarding expectations is accurate. I've seen good shooters do well and then get so caught up in chasing perfect loads, at the highest speeds possible, that they begin to digress in their progress and get very frustrated. They get to changing things like load, bullet, speed and even cartridge, over and over again in an attempt to eke out the nth degree of perceived improvement and they lose sight of the real goal of improving skills and practicing what actually matters in these matches.

I'll admit to even heading down that rabbit hole myself for a while until I came to my senses and started re-focusing on quality practice and consistent reloading practices.

Yes, great points. I myself have stuck with the 6.5x47L at "slow" speeds lol, and tried not to get sucked up in the latest and greatest 6mm's and barrel burners. On a good day I shoot better than a lot of guys with my slow and consistent 140 Hybrids, even though on a ballistic app their 6mm at 3100fps crushes mine. I won't even say I am a better shooter or practice more, but I will say that I have the utmost confidence that my load is consistent, accurate, and precise. I don't worry that in a 200 round match my load will go out of tune, or that the barrel will become shot-out.

The other factor for me is TIME. My club range isn't even that far away (30min), but to tweak a load even every 200 or 500 rounds means: loading, gearing up, driving, shooting, and coming back home to clean up and assess the data. That's a lot of hours that are at a premium at this stage in my life. I would love to have a backyard range where I could lay down on the porch and shoot, but unfortunately that's not the case. So I put a priority on shooting a caliber that allows me the flexibility to go 1000 rounds and only have to true the velocity by 10 or 20fps as it slows down a bit.

 

[47guy]

in the last 10-12yrs ive shot out 6 300wm barrels
11 260rem barrels...counting the bad ones ive had...8 not counting the bad ones
5 6mm CM barrels and 1(just switched to #2)6.5x47 barrels

i chase the lands and adjust powder as needed...normally when the throat moves .010-.020 i adjust seating and when the barrel starts to slow down i adjust powder...ive only RE-load-developed a couple of times because the small adjustments were not getting it shooting again.

ive shot shilen,bartlein,kreiger,criterion,hawk hill and 1 factory barrel-s...of all the barrels ive shot ive never gotten the round counts i see ppl claim.
as far as how they stop shooting only the 300wm barrels just faded away all of the others just quit from one shot to the next basically and most in matches.

for instance my first 6.5x47 barrel...april 27th i went out to the range i was shooting a match at to check me dopes...i shot 30 rounds from 200yds to 1000yds(the match distances)and a few at 1320yds...they were stacking and all distances barrel at 2100 rounds after...saturday april 28th(shooting prone)i shot the 200yd 5 outta 6...shot the 300yd and cleaned 6 outta 6...400yds not one impact..barrel now at 2118 rounds...500yds... shot 5 and 5 misses last round i shot a coyote(not part of the stage)i held on the right side...his ass and the impact was in his lower jaw/neck on the left .7mils high and .5 right...i made adjustments and shot the 600yd first round 7ft low and right next one over the top and left...i finished with one more impact on the 800yd.

i know my round count because i keep a strict record and record ever round...95% of this barrels life was with 36.9g of varget and 140g berger hybrids it only dropped 10-15fps and im not sure where the throat is but at 1700 i move the bullet out .020 closer to stay at .020 off the lands.
my new barrel(184 rounds threw it) im running 130g berger hybrids with varget at 2950-2960...at load development this load was at 2930 at 61 rounds so its sped up 30fps.

so now im curious to see how long this barrel goes with 2g more varget.

 

[47guy]

This thread is about throat erosion not why you choose to not to deal with it although I understand how the two topics are intrinsically linked. Regardless of why you choose to load the way you do, erosion is still a thing.

I was of the same mindset as lash and the other post'r but my mild 47L load wouldn't let me "set it & forget it " as much as I tried. No matter how limited a person's time is, wasting a day at a match bc you can't figure out what you're barrel/ load is doing isn't fun.

It isn't a choice, shoot well thru practice or shoot well thru good loading and attentive rifle maintenance. At some level, both are required

i got a little off topic there....to add to my post ive never really seen the big throat erosion ppl claim either...when i get home tonight ill measure the throat on that first 47 barrel i just pulled but im pretty sure it only lost .020-.030 in 2175 rounds.

as far as gauging when a barrel is done i gauge by how it shoots...when it starts throwing unexplainable flyers that tells me its done and most times i will try to have a known good shooter shoot it as well to verify its not me having a bad day.

 

[47guy]

My load of 36.7gr Varget and 130 Hybrids was going 2850, pretty mild. I would also agree that particular barrel just went exceptionally fast. I switched to 6SLR bc I wanted a cartridge that doesn't use Varget and doesn't require mag kits to run well.

And the 115 DTAC is the most jump insensitive bullet I've shot. Hybrids have only been somewhat less sensitive than VLDs IMO.

i shot a 6CM and 115g DTACs for 2+ years...5 barrels at 3050 with H4350...i went back to a 6.5 because of barrel life and spotting impacts...i had 1 6CM barrel go 1700 rounds the others between 1400 and 1600.i went with the 47 because of the barrel life claims...i have a buddy back east says he was at 3000+.

regardless of barrel life i am a 47 lover now and is what im going to stick with...this is the easiest cartridge to load for and ridiculously accurate.

 

[samb300]

i shot a 6CM and 115g DTACs for 2+ years...5 barrels at 3050 with H4350...i went back to a 6.5 because of barrel life and spotting impacts...i had 1 6CM barrel go 1700 rounds the others between 1400 and 1600.i went with the 47 because of the barrel life claims...i have a buddy back east says he was at 3000+.

regardless of barrel life i am a 47 lover now and is what im going to stick with...this is the easiest cartridge to load for and ridiculously accurate.

6.5x47L has spoiled me as well. A lot of my local matches are 600 yds max, so I've contemplated a Dasher or straight BR for those, but in general the x47L has done me very well out to 1200 yds.

Do you feel like spotting impacts is that much better with the 6.5 vs. the 115 DTACs? Only have experience with the 140 Hybrids and 175 SMKs out of a 308, and have never really had an issue with impacts except in grassy/shadowy berms. I'm not good enough to not miss haha, so a BR shooting 105 Hybrids at 2850fps makes me a little worried that I would struggle with wind calls beyond 600 yds.

 

[47guy]

6.5x47L has spoiled me as well. A lot of my local matches are 600 yds max, so I've contemplated a Dasher or straight BR for those, but in general the x47L has done me very well out to 1200 yds.

Do you feel like spotting impacts is that much better with the 6.5 vs. the 115 DTACs? Only have experience with the 140 Hybrids and 175 SMKs out of a 308, and have never really had an issue with impacts except in grassy/shadowy berms. I'm not good enough to not miss haha, so a BR shooting 105 Hybrids at 2850fps makes me a little worried that I would struggle with wind calls beyond 600 yds.

i do think spotting impacts is much easier...not so much on smaller targets at closer ranges but on bigger targets out farther...especially when the paint is shot off them and the mirage is up.

at our local range we have 650 and 850 coyotes and a few guys shoot smaller 6mms..dasher and a couple of BRXs and when they shoot at the 650 and/or 850 coyotes we look for dust from misses not impacts on steel because you cant see the impacts on steel unless the target is clean...same goes for the guys shooting bigger 6s with 105s.

i shot a match saturday with 130g berger hybrids at 2950-2960 and when they hit the 850 coyote there is no doubt in your mind that it was a hit or miss...i had several miss calls last year with the 115s that i saw as impacts...if the 115s hit center mass it did not move the target much.
i know its only 15gs difference but it does IMHO make a huge difference and 140s...we all know how hard they hit.

 

[Billiam1211]

Lots of great information here! It's been helping me validate what's been going on with my rifle. I have a factory Tikka with about 1,600 rounds down the pipe. Accuracy is still phenomenal, however my velocity took a dump. I was at 2,742 fps and now after I had to redo my load development to chase the lands I'm at 2,613 fps.

Sounds like based on everyone's experience - velocity takes a dump prior to accuracy going away. Groups below were shot today @ 200 yards, even with my velocity having dropped. Luckily I have a backup barrel ready to go.

 

[nexusfire]

Just add a little more powder until your velocity comes back. No need to chase the lands.

 

[Billiam1211]

Just add a little more powder until your velocity comes back. No need to chase the lands.

I tried that and I actually hit pressure. My load before was at 42.5gr and I worked up to 43 grains. Accuracy was acceptable, however I started noticing ejector marks on the brass. That's why I decided to do a complete load workup again. 41.5gr had stellar accuracy, however the velocity is now slower than my 308 Win gas gun by 100 fps?

 

[sinister]

Precision drop-offs with rifle barrels has a lot to do with the degree of erosion and advancement of the rifle's throat, the barrels' metallurgy, and the way the tube was rifled/manufactured (buttoned, cut, etc.).

Highpower rifle shooters may notice changes quicker in that they shoot and document their short-range (200- and 300-yard) and mid-range (600-yard) group performance in their shooting logbooks, whereas it seems many-most PRS-style shooters don't keep data books based on groups (if at all), tending more towards hits.

Traditional highpower and long-range shooters will note more off-call shots at 600, and wider groups or groups with two group centers at 300 before they notice any difference at 100 and 200 yards. This is a function of gas blow-by and some minimal degree of bullet yaw as the projectile ogive has some free-bore jump from the case mouth to the rifling (which is reflected in some of the noted velocity drops).

If you borescope a well-used rifle you might find that you have bore erosion/corrosion at the throat (either smoothed or with gas-cracking), while further down the tube the rifling is still sharp. Benchrest shooters can rejuvenate a rifle and get a few more hundred rounds by shortening say an inch from the back end, re-threading and re-chambering, and driving on.

I imagine a lot of shooters don't want to shoot groups to check their rifles, in an attempt to squeeze the most life out of them that they can -- but this might be a quick way for you to check, especially if you start at mid-range (say 500 and 600 yards) since you may not see much difference at closer ranges.

If you are a dedicated long-range prone-sling shooter you might retire a 1,000-yard barrel between 1,200 and 1500 rounds when it no longer holds an X-10 ring, while a PRS shooter might go longer if their standard is a hit anywhere on a steel IPSC target or plate.

 

[Gunfighter14e2]

Long ago I had a 300wm that had 5440rds down the tube. The last HardRock match that barrel shot when I got back to the 600 aftre shooting the 1K 9 &800 yd it opened to over 1.5 moa @that range. Thinking the barrel was gone after the way I shoot, when home I started stripping it for a new tube, an found the rear ring loose. Put her back together, took to the local range an see printed 3 five shot groups less than .5 moa. took it to another place close an at 700 yds it was under .5 moa, driving back home debating what to do, I said, new with a Kenyan president about to take over we better do this. Sent the barrel back to Rock Creek an Mike posted his finding on here back then. First 1.5" of the rifling was gone an heat cracked badly, but the rest of the tube was good. Long short lots of internet myth about shot out tubes.
The 308 I sold last year had 16K + down the tube (Pac-Nor) still to this day it will print .5moa groups at distance. The new owner said he never would have believed it until he seen /did it his self, That barrel had be cyro'ed right after birth before I owned it.

Guessing only the older guys here will remember Mikes post about the 300, as it long before the move to scout. The target never lies, but make sure everything else is right before blaming the barrel. BTDT

 

[47guy]

Ive never seen a coyote on a tpost hanger not move when hit by a 6mm at 800

not on T post hangers at our club....and i have seen coyotes not move enough to see the movement at our club and on T post hangers...when you center punch them the movement is hard to see.

 

[47guy]

I was kinda serious and kinda fesecious at the same time. "I've never seen a target not move..." . Lame joke. Sorry.

We've never had problems with JC Steel coyotes bc they're fairly small. But another match I shoot we will shoot 3 moa plates at those distances and out to 900-something. Last match guys shooting 6 BRXs and Dashers center-punching it wouldn't move it. You could hear it and see no movement through glass. We had to shoot a couple of times to verify what we thought we were perceiving. But it would move when I hit it with a DTAC going 3000fps.

I’m shooting a 6CM right now...105 hybrids at 3220 and when I hit center there it not a lot of movement and harder to see in the mirage...our club targets are life size.

My personal varmint targets are a little smaller and same thing on my coyote at 850...if hit center there’s very little movement.