6mm barrel twist?

[Matt_3479]

just about to order the barrel for my 6mm build. 90% sure I'm going with a 6x47lapua. Medium palma, 28" and either 1:7.5 or 1:7 twist. I'm thinking my main bullet will be the 105 hybrids but definitely want to test the 115 dtacs in this little caliber! Who knows if they get a decent velocity I could be using that bullet as my primary. Don't want to get the 7.5 and it be on the slower side for the 115 and get a 7 and be too fast for the 105?

 

[Rob01]

7.5 is plenty fast enough for a 115. People have been using 8 twists with them for years. I shoot 105 BTHP from my 8.5 twist .243 and they are very accurate. I wouldn't go any faster than 7.5.

 

[swd]

7.5" will do pretty much everything. No need for a 7".

 

[Matt_3479]

Main reason for asking is when checking Bergers stability chart/program, it shows the 1:7 twist is optimal for both but the 1:7.5 only marginally acceptable for the 115's.

My gunsmith also recommended the 1:7 twist. I had almost purchased the 7.5 until my gunsmiths recommended the 7 twist as that's what they use and have had the best luck with

 

[Rob01]

I shot a .243 for 5 years with 115s and the 7.5 worked fine. Very accurate.

As a side note my team mates also used a 7.5 and they had troubles with some 105 AMAX blowing up on them. Not saying the 105s you are going to use will do that but just a thought before you go 7 twist if you plan on using the 105s mostly.

 

[mikecr]

How fast will you drive the bullets?
It doesn't matter for stability but for reliability.
What elevation will you be shooting?
This matters for stability.

 

[Matt_3479]

How fast will you drive the bullets?
It doesn't matter for stability but for reliability.
What elevation will you be shooting?
This matters for stability.

Well I'm hoping to be around 2950-3050 for the 115's and 3050-3150 for the 105's.

I'm only 800feet for elevation

 

[Rob01]

I was running the 115s at 2990fps at sea level and no issues with stabilizing in a 7.5 twist.

 

[Matt_3479]

I was running the 115s at 2990fps at sea level and no issues with stabilizing in a 7.5 twist.

Okay well that's good news. Cause the gunsmiths have 5 7.5 twists barrels in stock and only 1 left in 7 twist. I'm nervous about purchasing a 7 twist and think I'm going with a 7.5 twist barrel.

 

[mikecr]

You'll be fine with either, so I'd go 7.5tw

 

[rcol317]

I'd second the recommendation of 7.5, I have several 6XC's and 6x47L's with 7 twist and had a couple 7.5. Seems to me that the 7.5 work fine with the 115's and are easier to develop loads for. For some reason the 7's seem to be more finicky the get accuracy out of. I doubt I build any more 7 twist 6mm's.

 

[cmillard]

i would give the 7 twist a try, then give the 110 sierra a try

 

[Dgd6mm]

7.5

 

[JBT47]

Ditto on the 7.5"

 

[calib]

7.5

 

[savagedasher]

7.5 Larry

 

[Mickey D]

7.5 Larry

I too say 7.5 Have one on order from Rock Creek.

 

[Zero333]

Either one will work good for 105-115 grainers.

If your smith wants you to get the 7" then get the 7" since there is no problem either way you choose.