barrel twist rate for 20AB 20KB and 20VT

[chuckshooter]

I need to order a couple of barrels from Kreiger for some upcoming projects and I can't make up my mind. they will be for a 20 ackley bee/ 20 killer bee. my current ones shoot 32gr zmax at about 3600fps. I was going to order 12t. is there any reason to order 11t? any toughts? thanks Jim

and as long as we are talking twist rate, what about 20 vartarg 12t or 11t? same bullet 32 gr zmax

[Rick in Oregon]

In my humble experience with the .20 cals, if you only intend to shoot 32gr bullets, not much need for going to the 11-twist. That faster twist really shines when you move to 40gr bullets for better stability, but the 32's do just fine in all five of my .20's with the 12 twist.

When I want to shoot 40's, I grab my 11-twist M700 204R. You could always do the 11-twist and leave the 40gr bullet option open though......

[Hotshot]

I look at it this way. The 11 twist will never hurt you with 30-35 grain bullets, but a 12 twist(especially at lower velocity) will most likely hurt you with the heavier bullets.

[Bill K]

Day in and day out, with whatever bullet weight you go with, from 30-40 grain, go with a 1/11 twist and never look back. It will have you covered for any of those bullet weights and the one, if you settle on one, better than the 1/12. Bill K

[TAJ45]

If you want to give up 8-10 fps and be able to shoot every bullet profile being currently manufactured plus whatever may come along. Also remember and consider the ugly, gratuitous increase in SPLAT with any faster twist.
Now, with my tongue removed from my cheek, considering that some of your chamberings aren't fps screamers, the splat will increase the smile factor during launches - absolutely giving up nothing with that 11 TW while keeping all roads open.

[Ratbuster]

If you believe Berger's Twist Rate Stability Calculator an 11 twist is sub optimal and reduces the BC of the bullet, even for a 32 grain pill. 10T calculates better for both 32 and 40 grain. All future barrels I buy in 204 will be a 10 twist.

Parameters:
32 Grain Hornady Vmax 204
BC .210
Bullet length .638
Velocity 3650
Temp 59
Altitude 4200 feet (where I shoot)

This combo results in a SG of 1.47, (slightly marginal stability) and BC is reduced 1%. At sea level the SG is 1.26 and BC is reduced 7%. For those of you who are not familiar with SG it means Gyroscopic Stability Factor and that number should be 1.5 or higher.

With a 40 grain (hornady vmax) bullet it gets worse. An 11 twist barrel at 3850 fps (20P or 204R) shows a dismal 1.01 SG with resulting 15% loss of BC and 1.17 SG at 4200 feet altitude losing 10% of valuable BC.

Of course this all assumes the Berger calculator is accurate. As far as I know it seems to be the most respected out there.

[L.Sherm]

IMHO hotshot hit the nail on the head!

[chuckshooter]

[quote=Ratbuster;254373]If you believe Berger's Twist Rate Stability Calculator

I did look at their calculator. but I wanted to see what other thought as well.
1 have four barrels here waiting to go on remington actions as I wear them out and they are all 11t.. some of my 20p and 204's I will shoot 40gr but these 20AB, 20KB and 20VT I don't see myself ever shooting anything but 32's

It's an interesting thought, if the bullet is spinning faster, is it going to cause more aerobatic action on the squirrels that I shoot?

[Hog Patrol]

Another vote for the 1-11 twist. If you ever want to change chamberings to a hotter 20 cal to shoot the 40s faster, you'd be good to go with that twist.

[GrocMax]

The Berger calculator should be trusted for meplat or shallow HP bullets only. For all plastic tip bullets or a bullet with a deep hollow point the length of the tip comes into play, you basically eliminate it in the calc to get a more realistic result.

Use this calculator instead, it is closer to real world results-

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Here is a page with bullet OAL's-

http://www.shootforum.com/forum/bulletdb.html