A Slice of (Barrel) Life — Inside Look at Barrel Erosion
So what does a “worn-out” barrel really look like? Tom Myers answered that question when he removed a 6.5-284 barrel and cut it down the middle to reveal throat wear. As you can see, there is a gap of about 5mm before the lands begin and you can see how the lands have thinned at the ends. (Note: even in a new barrel, there would be a section of freebore, so not all the 5mm gap represents wear.) There is actually just about 2mm of lands worn away. Tom notes: “Since I started out, I’ve chased the lands, moving out the seating depth .086″ (2.18 mm). I always seat to touch. My final touch dimension was 2.440″ with a Stoney Point .26 cal collet.”
Except for the 2mm of wear, the rifling otherwise looks decent, suggesting that setting back and rechambering this barrel could extend its useful life. Tom reports: “This was something I just thought I’d share if anyone was interested. I recently had to re-barrel my favorite prone rifle after its scores at 1,000 started to slip. I only ever shot Sierra 142gr MatchKings with VV N165 out of this barrel. It is a Hart and of course is button-rifled. I documented every round through the gun and got 2,300 over four years. Since I have the facilities, I used wire EDM (Electro Discharge Machining) to section the shot-out barrel in half. It was in amazingly good shape upon close inspection.”
Tom could have had this barrel set back, but he observed, “Lately I have had to increase powder charge to maintain 2,950 fps muzzle velocity. So to set it back would have only increased that problem. [And] I had a brand new 30″ Krieger all ready to screw on. I figured it was unlikely I’d get another full season on the old barrel, so I took it off.”
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Tags: 6.5-284, Barrel, Leade Erosion, Throat, Tom Myers
I first heard about throat erosion when i bought a custom built 6ppc from clarence hammonds. A superbly accurate rifle but only for a limited round count. He said cutting it back would extend its barrel life. While i understand what erosion is and what cutting it back does. I dont understand why erosion effects accuracy so much. Its obvious it does so im not arguing that. Its just one of those thing i cant wrap my fingers around y.
My BR smith told me no problem cutting a new chamber to do a set back. Whether it is advisable depends on how much fire cracking remains in the rest of the bore. His opinion is that (in a 6ppc) I can expect to get maybe 600-900 accurate rounds after the rechamber.
I wonder how much of the erosion could have been seen using a borescope? I’m debating the purchase of a borescope for all it can reveal. This (using borescope) may be a way of determining how much to set back a barrel after it has eroded like this.
Ive never had one stop shooting before the throat was out .100 or more.
Can you recall how many rounds went downrange before you DX’d the barrel?
I am shooting a .308 match grade Australian Maddco barrel. At 4,500 rounds it is as accurate as the day I installed it.
EDITOR: Glad you are getting that kind of barrel life. Not unheard-of with the .308 Win catridge. However, you may want to start saving for a new tube. We have seen many cases where .308 Win barrels really lose accuracy between 4000-5000 rounds. It has happened to some notable F-TR shooters and Palma shooters. Recently at the SWN a well-known Lady sling shooter told us that he rifle was starting to toss shots — it ‘opened up badly’. When we asked the round count, she abashedly said “Over 4000, maybe closer to 5000. I know, I know… I thought I could get one more match out of it. But it’s toast now.”
If you’re just shootin’ steel for fun, no reason to pull a barrel that might still deliver 0.7 moa. But if you are shooting matches, it’s unlikely (not impossible) but unlikely the top-level accuracy will hold past 4500. YMMV.