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ReedG said:I have a 6BR with 1:14 twist and it shoots up to 75-gr. HPs very well. Really hums with 57-gr. also. The normal 62-, 65-, 68-gr. bullets will work great in it ... enjoy if you decide to get it. If not, let me know how "cheap" it is ...
RonAKA said:You may want to try playing around with the calculator at the Border Barrels site. I put in the measured dimensions of a Berger 68 grain and got the following.
http://www.border-barrels.com/cgi-bin/barrel_twist.cgi?diameter=.2426&length=.840&nose=.487&meplat=.078&base_diameter=.2426&angle=&boat_tail=&twist=14&secant_radius=&unit_length=inches&temperature=59&humidity=0&local_pressure=29.92&pressure=29.92&altitude=0&density=11.4&custom_density=
This calculator is suggesting a required twist of 12.5 to get a 1.5 stability factor. The graph at the bottom is suggesting a 14 twist will give you a stability of 1.2.
Berger says you need a twist of 13. That gives you a stability of 1.4 which is good. I think 1.5 is a little overkill.
The question is what can you get away with. I found out that in a hunting gun I had less twist than I though and had a stability of about 1.1, but when the temperature drops it goes close to 1.0, and groups open up to 2-3 times the size.
My thoughts are that you are on the edge with a normal flat base 68, but probably can get away with it.
Berger makes a high BC 69 grain that is quite long. That one may not fly for you. It works in my 12 twist, but I suspect is getting close to the limit.
Not sure if you have the means to measure it but throat length is the other issue. With a 14 you will be stuck with the lighter bullets. Did they shorten the throat so you can still make the lands with the lighter bullets? It is a bit of an issue in my Savage. That 69 grain for example is seated so far out in the neck that I can easily pull it out of the neck of a loaded round with my fingers. It still shoots quite well, but certainly is on the limit of what I can do with this gun.
Hope that helps some.
jo191145 said:Don't believe those twist rate calculators too much.
Normal twist in a PPC is 14. We know they shoot right
My PPC does just fine with 68gn fare. Thats exactly what its designed for.
JBM twist calculator says it can't shoot. My targets disagree.
I have a 6BR 14 twist Pac-Nor barrel on a Savage action. It also shoots the 68's just fine. Just as accurate as my PPC, maybe even better.
It does like those 58 V-Max too. Ugly, short, squat bullets shoot better than they look ;D
DCRYDER said:You fellas having trouble reaching the lands need to give the 75gr Sierra varminters a try. I used to load for a friends Cooper 6br and they shot lights out. They are flat base with a long bearing surface, prrobably go halfway down neck.
If it were my gun i would set it back and rechamber with less freebore. I have a reamer with just .030" freebore and it works fine even with the 58gr vmax.