6XC ... Is it toast?

[rijndael]

My 6XC is giving me some fits and I'm wondering if the barrel is toast. I'd appreciate some input.

The barrel is a Rock 5R. Round count is 1319. I wouldn't say it's had a hard life.

A few months ago, my known good load stopped working: 39.4 of RE17 w/ 115 moly DTAC.
I dropped it down to 38.5 and got it working again, shooting great & consistent.

In prep for a March match, I cleaned the barrel. Now it's not shooting again. It's between .5 and 1". I've given it about 30 rounds to settle back down and it's not cooperating. I've re-run a seating depth test around the last known good, no luck. The ES/SD is up a hair; the SD is hovering around 10 now, up from 5-6 (over 15 shots). The velocity is fine, no big drops.

Here's the throat, post cleaning:

 

[Laurie]

My one and only 6XC with a four-groove Bartlein was way past its best if not complete 'toast' at 1,100-1,200 rounds. It was loaded with Viht N550 for the first few hundred rounds, then was run exclusively on Alliant Re17/Reload Swiss RS60. This was with 105s which should produce slower throat wear than your 115s.

So I reckon you've done pretty well to reach 1,319. A friend who also tried the cartridge with this powder ran his at a bit higher velocities than me and failed to break the 1,000 round mark.

RS60/Re17 is a real performer in the cartridge, but is hard on barrels. I'd evaluate your borescope pic as 'pretty well shot out'.

 

[rijndael]

Ugh ... Thx. I was really hoping for a bit more barrel life.

 

[Catfur]

I've had 6XC barrels last 1600+ rounds, and I've had them go south at 1K. But ~1300 is in the range.

 

[Bob3700]

Our shooting group shoots about 4 rifles chambered in 6XC. Shooting 107 Sierra’s , bbl life rims right around 2000-2200 rds. The 115s u are running will shorten that . The picture of ur bbls throat looks like it is done.
If I were shooting the XC with 115s, every 200-300 rds I would work the throat with some diamond lapping paste to keep it smooth.

 

[SmokinJoe]

I don't know much about the 6XC but I have a 6-250AI that is pretty close. You have a bit of heat checking/fire cracking there but not nearly as bad as my first 30BR barrel at 9000 rounds, and it was still competitive but getting difficult to clean. If this barrel has been a good one you might consider setting it back and going again.

 

[Bob3700]

Our shooting group shoots about 4 rifles chambered in 6XC. Shooting 107 Sierra’s , bbl life rims right around 2000-2200 rds. The 115s u are running will shorten that . The picture of ur bbls throat looks like it is done.
If I were shooting the XC with 115s, every 200-300 rds I would work the throat with some diamond lapping paste to keep it smooth.

The throat looks pretty rough but have you looked at the Muzzle? If the bbl was still shooting good at that round count, I might look at setting it back. The word on the street is that if you are going to set a bbl back, don't wait till it stops shooting. Go about half the expected bbl life and then set back. The muzzle will also be enlarged so when setting back, cut at least 1/2 inch off the muzzle and recrown.
I think you are beyond that point right now.

 

[Pabs284]

Hi there..
have you tried cleaning with abrasives, such as JB or Iosso?
i had a 6xc. Arre. Which I thought is was cooked and it came back to life for a further 500 rds.

 

[NZ_Fclass]

Skip the JB. Give a clean with your favorite solvent and then polish with a fine diamond paste, using keronsene as a lubricant. A small amount on a dampened patch works wonders. Nothing to lose and you may get some extra life. Worked for me a couple of times

 

[PeteB]

Skip the JB. Give a clean with your favorite solvent and then polish with a fine diamond paste, using keronsene as a lubricant. A small amount on a dampened patch works wonders. Nothing to lose and you may get some extra life. Worked for me a couple of times

IMO from what you say i would scope the bore and land condition an 1" or 1.5" from the existing lead area, if the condition is better than what you have and not cracked i would do this. Cut of the thread or a bit more if required, re-machine tenon and thread then rechamber with your favourite 6XC reamer. Use some of the above mentioned diamond past to give the throat area a light rub, recrown and lap muzzle. I would try 37.5 to 38 grains of H4350 depending on freebore, seat your 115 dtacs .015 of and i think you will get another 500.

 

[rijndael]

Shooting 107 Sierra’s , bbl life rims right around 2000-2200 rds. The 115s u are running will shorten that .

2K is what I was expecting. What about the 115s makes it harder on barrels? I know my RE17 diet didn't help, but I didn't run them on the edge of pressure.

have you tried cleaning with abrasives, such as JB or Iosso?

Yes, this last cleaning it got a little JB. I think it was the first time I've used it in that barrel. I didn't go crazy with it.

IMO from what you say i would scope the bore and land condition an 1" or 1.5" from the existing lead area, if the condition is better than what you have and not cracked

It's much better.

Cut of the thread or a bit more if required, re-machine tenon and thread then rechamber with your favourite 6XC reamer.

I'd have to send it off, and with shipping and gunsmith costs, I'll just call it dead.

 

[Lefty Trigger]

Using a cooler burning powder would extend the life a bit, maybe 1500-1600 rounds. All things considered remember the barrel is the expendable part of the tool.

 

[Matt_3479]

I would of expected slightly more life but I know rl17 is hard on barrels

 

[AckleymanII]

A friend gave me a 6 BRA barrel with 1400 rounds on it. The barrel had started throwing flyers, and would not group well after adjusting the load, H4895 was the powder.

Our high quality barrels will usually be uniform from front to back. The muzzle measured .2360 so when the barrel was new, the breach would have measured .2360. Notice the wear in Dia of the bore. Most think of the leade getting shot out or extended, but few ever consider that the bore dia wears from heat/pressure.

Muzzle dia:


Throat dia has increased by 0.0022 in 1400 rounds, this is the accuracy killer


Bore dia changing, rapidly


At .2370 the bore looks new, but the bore dia is still .001 over muzzle dia. It is a shake of the dice to start the bullet in a throat that is .001 over muzzle dia for accuracy work. For varmints, this may work out, but still a shake of the dice in my experience. For accuracy work, the bore should be uniform from front to back.

It takes time and effort to determine bore dia changes in the bore, and few if any gunsmiths do this kind of thing. I am not a gunsmith, just a hobbyist.

As you can see, it is a huge MISTAKE, thinking that you can just cut the threads off, plus a little bit to get a barrel shooting again.

Muzzle Dia:


Breach Dia at the throat that has worn .0022 since new, this is the accuracy killer!


Dramatic bore dia changes in front of the throat


Bore dia continues to change


10" from Breach, the bore dia is still not muzzle dia


I hope this illustration will cause anyone that is considering a "set back" reason to pause.

 

[rijndael]

All things considered remember the barrel is the expendable part of the tool.

It's the timing I'm irritated at, not the expense. I have a barrel blank on the shelf, I just expected to need it much later in the year.

I don't want to toss away a box of bullets, and wasted range trips, trying to get another 200 rounds of life - and it sounds like I may be there. I'll give it one more attempt today and see how it goes, with my old 4350 load.

 

[Laurie]

2K is what I was expecting. What about the 115s makes it harder on barrels? I know my RE17 diet didn't help, but I didn't run them on the edge of pressure.

The heavier the bullet, the faster the throat wear at same peak pressures and with the same powder. This is because the greater mass of a heavier bullet increases its inertia so it takes longer to get moving after ignition, then accelerates more slowly into and down the lands. Meanwhile, pressure is increasing behind it and the throat/leade are subjected to peak pressure and heat for a longer period. Same thing with Re17. It gets most of its extra performance from its patented 'EI' deterrents infusion process (as opposed to simple surface coating in other powders). They work better - ie for longer - so modify combustion for a longer period. Again, the throat, leade, and first inch or two of the barrel are subject to peak pressure and heat for a longer period.

 

[rijndael]

seat your 115 dtacs .015

Your .015" comment made me rethink seating depth because when I first developed these loads it was happy at .014". The load never really changed much, maybe .003" longer here and there, but it was mostly stable - I let the targets drive it and I never re-measured the chamber.

This morning I lightly cleaned the bore (carbon only) and re-checked the lands. It's lost about .070" of throat over 1100 rounds. I loaded up my old faithful H4350 load of 39.0, plus a few warmer ones, while moving the seating depth out .070", so it's jumping about .014" again.




I guess need to re-check this much longer seating depth with RE-17, to make sure it just didn't stop liking RE-17 .... or stop wasting my (probably limited) barrel life and continue on. Continuing on is probably what I should do, but it'll eat away at me if I don't retest with RE17.

My only guess is that the recent cleaning, the one where it never recovered from, must have really changed something.

Regardless, I need to start planning for that next barrel.

 

[FeMan]

That is pretty short life but as stated, I think the high burn temp of RL17 will shortened it.

It hasn't happened often but on a few barrels that started having a mid-life crisis, I found that switching powders made an amazing difference. The last one was a 6.5CM that shot 156 EOLs under 0.2 with H4350 until 1200 rounds. Then, it wouldn't stay under 1.0 no matter what I tried. I did extensive seating depth testing, powder ladder, even tried different primers. I then tried 4831sc and it immediately jumped back to 0.2 or less.

 

[rijndael]

I hope this illustration will cause anyone that is considering a "set back" reason to pause.

Very informative, thank you.

 

[mongo chicago]

Not an expert, but there are so many variables concerning barrel life, powder, bullet wieght, bullet design, velocity etc. that when you lose accuracy, just replace it. I did that when my 6mm rem. bbl. went south after 2400 rounds. Replaced it with a 6 XC. I don't waste time, money and aggravation on trying to get a few extra rounds out of it. It'll be cheaper and you will be happier in the long run.