6XC Throat Life

[reid308]

I just measured the throat in the 6XC barrel on my T2K. It is the original 25” Polygon barrel they supply.
When new, an 85 gr Sie was 3.065” after chambering a long round and letting the Lands soft seat the bullet.
I was using the Sinclair Nut Thingy to check the length.

At 1047 rounds the same was 3.085” so I had .020” erosion.
At 1560: I just measured it @ 3.096”. So I have a .031” increase based on soft seating. I am using the same bullet in the same case I had set up on the shelf for this very purpose. Seems a bit small to me but I repeated it several times and it was the same.
Note that a lot of the rounds were the 70 gr Sie for 200 yd XTC: @ 35.0 gr Var. The 85 gr Sie for 300: @ 34.0 gr Var- and the 107 @ 600 with 39.0 gr IMR 4350. If I were running all the rounds with the 107’s @ 2900 I believe the throat would be out a good deal more than it is.
YMMV.
Reid

 

[mikecr]

Thats good to here. I just recieved my T2k/6xc in 28" and haven't fired it yet. Have you found that the rifle groups well at 100yds?
It came with a 5 shot group of .491", but my barrel being longer may have effected normal results from McMillan's test load.
Keep us posted on your barrel life findings. I bet one day, it takes off. But not for awhile.

 

[reid308]

I can't tell anything about accuracy @ 100 yds. How do I evaluate 7 shots in one hole, 1/2" in diam? I do all my incremental load development @ 300 yds. The test I did with a new 30" Lilja in 6XC on the T2K resulted in the last 3 shots from each of the two 7 shot strings cutting the same hole. I overlayed the two targets and the last 3 shots from both strings made one hole 3/4" in diam. End of load development for that barrel. Tested the high end of the incremental load,39.5 gr H4350, Tubb 6XC brass Russian primer and the SSS 115 gr bullet @ 2975 f/s) at 600 yds the following weekend and had a 199-15X and a 200-15X. The 9 on the first string was me overestimating the effect of the wind on that 115 and it went right where I pointed it. The T2K shoots everything I feed it about 1/2 moa. Don't matter, it just shoots. It has been the most accurate and least pickey about loads of any rifle I have ever had over the last 40 years of HP/LR shooting. I have already sold off one of my M70
XTC rifles and will be doing the same on another M70 308 XTC
as well as a 40X Palma gun and using the T2K instead. I have a 30" Krieger 308 Palma barrel that I just screw on and go shoot Palma. Screw it off and stick on the 25" 6XC and go shoot XTC. Take that off and put on the 30" 6XC and do LR. I shot a 2,3 & 600 yd xtc match a while back on Sat and took off the 25" and screwed on the 30" palma 308 barrel using the forks of a tree to hold the barrel clamp. Shot a 10 @ 9 the next morning on the first sighter @ 800 yds. I had a previous zero on that barrel and just lined up the front RPA with the locator ring that was on the 308 Palma 30" tube. Get the Action wrench and a couple extra barrels and go shoot. Screw the load development. Add enough powder to get the V you want and forgetaboutit.
Reid