Nebie needs help with twist and free bore????

[Never Forget]

First off I'd like to say what a great site, I've been lurking around for months doing searches and am amazed by the wealth of information on this site.

So I’ve decided to build my first 6BR, I have a 223, 308, and 300 win bolt guns that I currently load and shoot with 1/4 MOA accuracy if I do my part but I'm looking for more.

I’m going with a Defiance action, McMillian F class stock, jewel trigger, and a Krieger 30” 1 ¼ straight contour barrel. Only going with a 30” so I can cut it off and rechamber it again down the road. Most of my shooting will be 300 yard benchrest but plan on doing some club level matches at 600 yard benchrest (maybe 2 to 3 times per year) and 1000 yard F class (maybe once a year). I realize the F class stock may not be the best option for bench shooting but I'm 6' 3" with monkey arms, I want the LOP adjustable and cheek rest as well.

I’m leaning toward an 8” twist, plan on shooting some 87 grain plinkers but focusing on 105’s for precision and distance. I see some people saying they have good luck with a 10” twist with these bullet weights but my past experience has shown me I am better off to over spin a bullet vs under spin. Any opinions on 8 vs 10 given the bullets I plan on shooting?

My main question is on free bore, what is the best for a 105 grain and some 87? I plan on doing a .272 neck and running Lapua brass with no turn.

Thanks, John

 

[TAJ45]

I've never heard of anyone on here (limited to having read the post) shooting a 105 with a 10TW. Here is what Shilen gives as a guide. With the VLD bullets, there will be modifications of course. I think Berger publishes suggested tw rates and I'm sure other mfrs do too.

6mm/.243
- 8" Special for VLD bullets over 100 gr.
- 8" * Ratchet rifled 4 groove
- 10" For bullets up to 95 gr. and VLD under 100 gr.
- 12" for bullets up to 85 gr.
- 13" * for bullets up to 75 gr.
- 13.5" * for bullets up to 70 gr.
- 14" * for bullets up to 70 gr.
- 14" * Ratchet rifled 4 groove
- 15" * Special for bullets up to 70 gr.

I agree it is easier to have a bit extra rpm - w/o getting goofy- than to be on the ragged edge of stabilization. I hope to run 115s through my 7.5 tw 6XC as well as 87s. If it will shoot lighter, fine but don't really plan on it. I have PPC and BR to cover those wgts.

 

[Sniper338]

8 twist!

 

[snowpro440]

Go to Bergers website for the twist calculator and you can get your info there on stability.

 

[Never Forget]

Maybe it was another site that I got the info from on a 10" twist with 105's but I remember seeing it more than once and was surprised that they were not running a 8".

Any advice on the free bore for 105's?

 

[OIF/OEF]

1/4 MOA accuracy is nothing to sneeze at Sir hell id pack up and go to the nearest match and give it a whirl. Ill be honest if I had to start alllllllll over again Id start out buying a used fully built rig off of this site. Im not ashamed to say it publically I have taken out a loan to buy a rifle completely built I couldn't afford to build and it saves possibly years of time. They will almost always be sold with load data also.

 

[NorCalMikie]

8 twist, freebore around zero so you can start off with 50 grain bullets and go heavier as the throat wears, a no turn neck chamber so you don't have to mess with brass. Load to the lands and watch those bug holes form. 8) 8)

 

[comagutsa]

im running a krieger HV barrel 1:8 twist 30" barrel .272 no turn neck on my 6BR shooting 105gr Berger hybrids and hunting VLDs and about to try 108gr Berger BT as trying to get any berger 105gr in Australia is like trying to find rocking horse crap.. but thats another story from berger in the US not sending us any

but i'm running a .105 freebore on mine and i know another 3 blokes shooting the same running the same freebore with great success shooting .2-.3 moa at 500 meter

a 1:8 will be able to shoot the 87gr with no problems at all

 

[noload]

I'll second the 105 freebore, I have had great success with 104" FB on many 8TW barrels, shooting 80gr to 105gr.

 

[Drop Port]

Mine is a .272 neck with .097 FB. Its a field gun that goes to the occasional G-Hog match and is competitive in LT gun at 100, 300 and 500. I shoot 107's don't know if it could improve with another bullet, these have filled my needs.
Older Broughton 1-8
Stiller Diamondback RBLP Drop Port