Typically as I wear out a barrel I’ll see it shoot fine, fine, fine, start to open up, plateau, fine at plateau, open up more, open up more, open up more and it’s all downhill from there. After the plateau if it doesn’t quickly plateau again it’s getting there and it’s time to start planning my next pipe. I’ve already started planning my next pipe, a 6XC to match an identical one we’ll put on Coach’s gun. Nonetheless, this barrel is still good. Question is, for how long?
I know from prior experience that I get a little longer barrel life from the polygonal rifling that CRA uses. I’ve not burned out enough of their barrels to get a useful statistical value for how much longer but I can speculate based on the limited data I do have. Right now, given the throat wear and grouping we’re getting on Coach’s existing 6XC; which is at 1500 rounds so far, and the expected life of that Shilen barrel being around 2200-2300 rounds, I’m estimating; and trying to be extremely conservative in that estimation, that I’ll make it to 1800 rounds or further before this .243AI pipe is really done for match work. (See update below).
That’s almost 40% longer barrel life than I initially anticipated, if it gets there. We knew that the HBN coating on the bullets would help barrel life but probably only marginally so I’m confident it’ll get to 1500rds. We knew the CRA polygonal rifling means no sharp edges for the burning powder plasma to ablate would help too. We knew the Ackley shoulder angle would keep the flame vertex inside the case neck and that that would help too.
It’s just with all those things helping, we have no idea where this train is going to stop. If I go on throat erosion alone, calculating how far until the boat tail is up inside the case neck, then I’m looking at almost 3000 rounds of barrel life. That’d be 230% of anticipated barrel life and I just don’t see that as being realistic given the amount of powder being burned and the rapidity with which I shoot in matches. I’ll get that barrel pretty hot sometimes.
I get higher velocities than one might expect from less powder than one might expect. I get longer barrel life than one would expect. I get amazingly accurate and consistent performance, moreso than one might expect (especially for a drop-in pre-fit). The thing turned out sub-MOA groups with fire forming loads. It did not like 55gn varmint bullets at all though. No surprise on an 8 twist. The chamber on it is very tight. It’s meant for someone who’s willing to turn necks if necessary (my inside neck diameter on a fired case is .2435). Thankfully I don’t have to neck turn. Lucky me, everything just fits perfectly. When I ordered it I specified that I would not be put off by a possible requirement to neck turn brass if that were what their reamer would require.
Much of this situation was and is by design. When I initially decided I wanted a fast 6mm I found what my options were and then picked a chamber that would maximize performance, brass life and throat life. I picked a powder that would give maximum velocities without pressures being tall or a lot of flash. I picked projectiles that had very high BC’s and would be routinely available in boxes of 500 (including a primary and backup bullet). I set up a load that performs identically with both bullets and shoots to the same point of aim, just in case I’m unable to re-up on one I can use my backup supply of the other. I bought all of the brass, powder and primers I expected to ever use in this barrel ahead of time (8lbs of powder, looks like I might need another 8lbs). Everything about the gun except the optic I’d settle on was decided before the barrel even arrived. Best of all, the barrel was set up to CRA’s rigorous standards which means it was done perfectly and it was under $400.
So why am I building a 6XC now? Well Coach and I shoot together. It’s best if we have one set of ballistics DOPE and shoot the exact same load through identical chambers. It’s actually best if we share a gun but I like mine and he likes his. We find that when we can use drop and wind corrections from each other that we win more matches. Duh. If I run a stage and miss 2 of 7 shots on wind, I can tell him what the adjustments would have been and what the wind was for those misses then he can adjust accordingly and pick up those points and vice versa. (Update: Coach has left the BallisticXLR team.)
So, I’ve got 2 new barrels on the way from CRA, 27″ 6mm 8-twist unprofiled blanks which we’ll have a local gunsmith chamber, thread and profile for us in 6XC with a .264 neck (CRA doesn’t have a 6XC reamer or I’d have them do it). We’ll set them up for zero head space to minimize brass growth and then we’ll use my new ExactShooting.com Custom Collection sizing die to perfectly set the head space and neck tension of our reloaded ammo. We’ll be as close to shooting the same rifle as two guys can possibly get. If you want faster velocities, longer barrel life and one heck of an accurate barrel, you could do a lot worse than to drop Columbia River Arms a line.
UPDATE: November 2019
Hot Dog Gun’s barrel finally gave it up. Throat erosion made it to the point that ammo was longer than mag length and if I made the ammo fit in the mag then group sizes opened up to almost 2MOA with tons of flyer action. The final round count was 1800+. So I took that barrel off and had my gunsmith gauge it. He found that the bore was still .239 which is exactly what it was when it was brand new. So we’ve cut the chamber off and run my 6XC reamer into it as well as cutting the tenon for M26x1.5 to stuff into my new Howa 1500 receiver. It’s got a new crown as well. We’re going to shoot this rifle till it starts key-hole-ing. Right now I’m betting that I’ll get a full 2000 rounds from this barrel. Probably a little more as we’re using HBN coated bullets. Let’s see.