When my two friends and I made 6mms to shoot the 115 DTAC a 1 in 7.5 twist was recommended. A few said they could get the 115 to stabilize with a 1 in 8 but it was not the norm.
We also discovered that there were issues with the 115 Berger VLDs not being able to withstand the twist when pushed hard with a 6mm-284. That left the DTAC as the only viable 115.
1 in 8 will do fine up to 107 gr. Quite frankly I don't see an advantage in any of the 115s now that Berger offers the 105 match target hybrid with a BC higher than their 115 offering. .547 vs .545
I will admit that the DTAC has a higher BC which is generally reported as .585 but the velocity is quite a bit slower.
I get 3250 fps with the 115 DTAC and 3445 fps with the 105 Berger hybrid from my 6mm-284. The Berger's drift at 500 yds (10 mph crosswind) is 8.2" while the DTAC is 9.1" with same conditions of 4000 ft 59 degrees etc.
I have a new Bartlein 5R 1 in 8 twist which will replace my current Bartlein 5R 1 in 7.5 twist when it begins shooting poorly. Round count is close to 1000 with good accuracy.
I'll switch to the 1 in 8 and intend to shoot the 105 hybrids exclusively. FYI some hunters are reporting that the hybrid is working well as a hunting bullet. Go to bottom of the page:
7WSM 180 Berger takes down two Grizzlies!