6.5mm twist rate

[Brad Y]

Chasing a bit of user experience if anyone is shooting 6.5mm cals.

Do the Berger 140 VLD and hybrid bullets stabilize in a 8.5 twist at sea level? Velocity will be around 2900fps mark. I know a straight 8 twist is recommended but trueflite only have 8.5 twist option available at the moment. If not I will have to look at another maker.

[bruce moulds]

brad,
when i shot a 6.5/284, we all used 1:8 barrels.
toward the end of the 6.5/284 era, some americans were using 1:8.5 barrels.
they were running 140 bergers at 3000.
if i were to go back to 6.5 i would stick with1:8 to play it safe. berger recommends this twist for both 140 and 130. but that is the devil you know.
we believe we have seen problems with 1:9.5 twist 7mm barrels shooting 180 vld bullets at lower light (sea level) while 1:9 is ok. no tumbling, just random accuracy questions.
if you had trouble with an 8.5 twist you could investigate the length of the 142 sierra and the 139 lapua.
keep safe,
bruce.

[Dave P]

Used a 8.5 twist in a 260AI without issues mv was around 3150fps with 123 Lapua and 3000fps with 139 Lapua.
I also found that the 123 shot better than the 139 at least in my rifle

[macguru]

what era are we in now Bruce ?

7mm ?

[AlanF]

Brad,

I had a pair of Krieger 1 in 8.5 twists, which I used at sea level in winter (down to about 10C here), at velocities around 2930 fps. There were no obvious stability problems with 142gn SMKs. One of them was quite good, the other just a barrel.

I think you're right to prefer an 8 twist, but you'll probably have no problem with the 8.5

Alan

[Brad Y]

Yep I think a straight 8 is going to be my preference. Just in case.

[Matt P]

Brad
I use a 8 twist T/F with my 6.5x47 with 130's, goes pretty good.
Matt

[Brad Y]

Thats why I wanted to go with another trueflite Matt- had a great 20 cal varmint barrel from them and a great 7 twist 22BR from them as well. They said they cant do an 8 twist for a couple of months. Still another 10 weeks or so til the reamer arrives so still a bit of time left.

[Brad Y]

Done a bit more research. JBM calculator and also the calculator on the SA Fclass site both listed the 140 hybrid as stable (factor 1.4) at 2900fps in a 8.5 twist.

I know it is always a gamble but I think Im going to try it out. Worst case I do have to go back to shorter 139 and 140gr bullets than the hybrid.

[Brad Y]

Update:

Ive been in conversation with Walt Berger via email- top bloke! He said 8.5 will be sufficient for 140VLDS at that velocity (but its not leaving much room for error). Not the hybrids. I looked and looked for more info and to get those bullets shooting at sea level it looked as though it really does need the 8 twist to be open to shooting bergers. 8.5's are perfect for the shorter 139 scenars and 142SMK's.

Just got off the phone to one Nev Madden and have a 6.5mm maddco 30" 1:8 twist being done up for me. So that is that part done. Just waiting for the reamer (10 weeks away), barrel block and tax return now. Fingers crossed in that tax return there is enough for a new pierce action to go with it

[bruce moulds]

brad,
why not get both barrels, and use the 8.5 at canberra?
keep safe,
bruce.

[Brad Y]

I aint nowhere near Canberra Bruce! Im in the wait awhile state where bugger all people shoot FO!

[bruce moulds]

so if you get the 8.5, and the chance arises to go to canberra, or raton, then you will have a fresh barrel and this will be good.
if not for that reason, then think of science. who knows, your experiment could benefit many of us. i personally am thinking of trying a 6.5 super lr with an 8.5 barrel and would love to know the truth of this in the real world.
if the 8.5 were to be stable, its accuracy would be excellent.
it's guys like you who are pioneering open over there. good on you and don't give up.
when you remember at christmas time that it is hard to find 3 wise men from the east, westnos doesn't sound so bad after all.
we even have that problem in common with you here in s.a.
keep safe,
bruce.

[Brad Y]

Bruce

This is the reamer on its way
http://6mmar.com/260_Imp_30_.php

Not quite the 6.5SLR but very similar. I know the 6.5x47L is accurate as heck but this extra boiler room for the 140's will hopefully help out without the 6.5x284 barrel burn factor- but only time will tell.

8.5 was a gamble I wasnt prepared to take with the first barrel. Next one possibly, especially if the 139 or 142 ends up the better bullet. But bergers are my first choice for now.

Definitely not pioneering FO, just wanting to shoot something different because I can. Theres a few people over here that have flown or are flying the 6.5mm flag higher than me at the moment.

[bruce moulds]

a good and interesting choice.
hope you have a pimping plan for the rifle.
i have found good stickers at auto supply shops if that helps.
keep safe,
bruce.