twist rate vs velocity

[TrapperDan]

all things being equal, powder , bullet, primer, brass etc. With an 11 twist, will the velocity be slower, faster or the same,than with a 12 twist .( 204& 20 vt)

[TwentyBore]

Very slightly slower. The question is whether that tiny difference is of any consequence.

[Bill K]

all things being equal, powder , bullet, primer, brass etc. With an 11 twist, will the velocity be slower, faster or the same,than with a 12 twist .( 204& 20 vt)

There are more than one poster on this and other sites, that show targets and verbally say the 11 twist, even if ever so slightly different, seems to stabilize and give better groups. At least that is something I have picked up on. Bill K

[TrapperDan]

The reason for the question is as follows. I used a load from the 20 VT load map on accurate shooter.com which was 32 grain v max over 19.4 grains of 8208 with cci br4 primers. It showed a velocity of 3760 from a 1:12 barrel. I used the same load but with R 71/2 primers otherwise the same. Best I could get was between 32 and 3300 from my 1:11 barrel. That’s over 400 fps slower. At first I thought the crony was bad or the light was wrong. I shot 30 rounds over the next few days under varying light conditions and still 32-3300.I then used a load for my 204 that published 4130 with a 1: 12 twist. That’s almost the exact speed I got from my 204 1:12 .Hence, crony must be accurate. Why am I not getting the published speed with my 20 VT? Dan

[futuretrades]

Why am I not getting the published speed with my 20 VT? Dan

If you have access to a powder burn rate chart, Check the burn rate for 8208 powders against other powder like RL7 or H4198. These 2 powder have a faster burn rate and are more suited to calibers like your VT. When I was having problems with my VT, I called Cooper. They told me all testing for 20VT, 204, and 223, was done with H335 powder. I tried H335 in my VT and even using a charge just over what Cooper used, I could not achieve velocities over 3200fps, but using RL7 and H4198, the velocities were about 400fps faster. I would suggest saving your 8208 powder for your 204. Oh, by the way, H335 powder has a faster burn rate than 8208.
Keep in mind, larger cases use slower powders, and vice versa, smaller cases use faster powders. Also keep in mind that we are shooting and testing in "The Real World". Not in a computer program.
Also, I would go to Todd Kindlers web site, The Wood Chuck Den, and order a copy of The Terrific Twenties. He is the man that wildcatted the 20VT!

[Jim White]

What I've found is a few FPS more/less compared to each other does very little to extend the range, especially in energy. Try a ballistics program and input the max range out to 1000+ yards. As far as velocity, some guns shoot loads lower than others. Additionally, things like altitude come into play. Velocities would be faster at higher elevations. Temperature, barometric pressure also come into play. Other things such as light, bullet placement placed over the chronograph sensor, distance between chronograph and muzzle and any turblance generated by the walls or muzzle blast has an effect.

When I chronograph, I always try to do it from the same spot on the range for consistency purposes.

HTH,

[wirelessguy2005]

Dan

as noted above the 8208 xbr powder is a bit slow burning if you are looking to get top speed out of the 20vt. Your best option for speed and accuracy is H4198 or Reloader 7. I usually like to use Ramshot xterminator in many of the small caliber cases and it typically gets me great speed, the 20 vt is an exception to that rule. I have used H4198 with great success in the 20vt case and it typically produces 3700 -3800 fps with great accuracy.

As a side note some barrels just end up producing more speed or less than other barrels, this is something i have discussed with Bob Green on a couple of occasions about a 17 Fireball he built for me. The 17 fireball was producing speeds that were easily 200 fps faster than they should have been. Bob explained that some barrels are just "faster" than others. He went on to explain the reason why but I have since forgotten the details.

Brad

[RAMOS]

Jeepers, Brad, you gett'in old on us? Might have to change your handle from CRT to CRS. I probably should not give you a hard time, since your such a good guy. Oh well, I'm sure you will forget about it soon enough!
Jon

[wirelessguy2005]

Yep i am getting old and forgetful.

Jeepers, Brad, you gett'in old on us? Might have to change your handle from CRT to CRS. I probably should not give you a hard time, since your such a good guy. Oh well, I'm sure you will forget about it soon enough!
Jon

[TrapperDan]

Thanks guys for the great replies. They were all very helpful .I was worried that I had spent a lot of money for a 20 vt build and screwed up by getting a 1:11 twist. Although 32 grain z max over 8208 shoots consistently in the 2s and 3s with 2 out of the last ten groups were .162 and .170(tried to post pictures but can’t figure it out) it’s just slow. I have been trying to get some 4198 for several months to no avail. Out of 8 different powders that I have, the hottest is 322 but can’t find any work ups for it. Haven’t bought Todd’s book yet because I am a “grass is greener on the other side of the fence” guy and I would want one of each. That may not be a bad thing tough. Thanks again Dan

[TrapperDan]

WOW !!!! This is just unbelievable. Just loaded up one round using 322. Got 3639 fps. That’s 300 fps faster than the 8208. Went in and loaded that same brass again and got 3668,but in almost the same hole, .171 . went in and loaded this same brass again and shot 3681 and .424.I,m really getting excited now so tried it one more time. Again unbelievable. This one was 3674 and in almost the same hole as shot # 2.Shots 1, 2, & 4 were .247.Can’t wait to get some 4198 and see what it does.

[wirelessguy2005]

Dan,

sounds like you are on the right track. To be honest with the speed and accuracy you are getting from the 322 i would just stick with that. The additional 100 fps you get from 4198 won't make a bit of difference in the real world. Looks like Bob Green built you one heck of an accurate rifle.

[TrapperDan]

Yes, he sure did Brad. I was not expecting it to be this accurate. I can’t believe that I can shoot this good! Bob also did something to the action as it was never this smooth before. He did an excellent job. Need to get one of the grandkids to help me post pictures. I am also going to send Bob pictures of the targets along with another big thanks. Thank you for the referral Brad. I am really looking forward to next march and another squirrel season with this new 20 VT.