Twist Rate

[MudRunner2005]

so if i wanted to end up with an end twist rate of 9:01, and started with (just guessing) a 6.5:01, the lands would put more drag on the bullets ?

No, you got it backwards... It starts slower, then ends faster. Say you wanted a 9 twist for your final twist. Your starting twist at the chamber end would be a 10 or 11 twist, and it would gradually tighten up to a 9 twist towards the muzzle.

The faster your twist rate, the more pressure it creates in your bore...Which is why you put the slower twist rates at the beginning (to help keep pressures lower), and the faster ones at the end.

 

[elkaholic]

Grooves in bullet get progressively wider as twist increases....

 

[tim_w]

Grooves in bullet get progressively wider as twist increases....

That is why IMO for conventional designed bullets gain twist is best kept moderate say 1-2.5 inch per rev increase depending upon barrel length. Now when you get to banded bullets specifically designed for gain twist or to have the bands removed by the lands you can see some more extreme increase rates.

It also seems to help hold thinner jacketed bullets together when pushed harder with faster twists.

I think GT has a place when you get to these longer bearing surface heavier high bc bullets that are at the top end for caliber. Then in combination with OB cases.

 

[elkaholic]

I ALMOST did s moderate gain in my 30/375 S.I. but changed my mind the last minute. Kind of glad I did because the rifle is one of my best shooters!

 

[tim_w]

Yeh you never know. It does add complexity. But consider that Rock has been adding small amounts say .5 to many of his barrels for years. The only company I would consider getting one to a specific gain would be Bartlien at present. They have the equipment to hold to very tight tolerances which certainly helps if the skill is there.

The ones I know of winning BR ( I think it was 1K IIRC) were moderate around 1" gain

 

[elkaholic]

Bartlein was the barrel I had ordered with a 10.5 to 10