6 XC Freebore

[bobby]

Hi There,
What freebore do you guys ask for to shoot the DTAC 115 bullet in a 6XC chamber and what is the best rate of twist for the above bullet.
Thank you
Bobby

 

[rcw3]

It depends - if you are working with a 1 1/2 degree throat angle, a .165" freebore is about right for a 115 DTAC. If you go with Tubb's 3/4 degree throat angle, you would typically use a .123" freebore for the 115 DTAC. The 3/4 degree throat angle was used to try to mitigate the pressure spike when shooting the 115 gr bullet out of the 6XC because the 115 gr DTAC is frankly almost too heavy a bullet for that size case,i.e. not an optimum match) but they wanted to get it to work in there so the compromise was made so the 6XC could be used as the cartridge that can do it all. The only problem with throating a 6XC for the DTAC 115's is that when you go back to 105-107 gr bullets, the bearing surface of them is half way up in the neck to start before any throat erosion.

For barrel twist with the 115 DTAC, they say a 1:8" twist works, and it does with a true 1:8" twist, but I had a couple button rifled 1:8" twist barrels that were not true 1:8" twist and they would not stabilize in them. I just bought a Bartlein cut rifled barrel and had it made in 1:7.8" twist. When you start getting faster in twist than a 1:8", pressures can sometimes climb pretty fast,due to the extra twist) as you get too much faster than 1:8" twist, then you may have pressure issues and can't get the velocity up there with such a bullet without pressure problems and loose primer pockets, etc. The 115 DTAC is not the easiest bullet to work with because it's flaunting the limit of what a 6mm bore size can effectively handle. I know a lot of shooters who initially embraced them thinking they were the greatest new thing sincle sliced bread, but then a lot of them have dropped off from using them because they had a hard time dealing with the finer balance of things you have to in order to get them to consistently work well.

Robert Whitley