List of recommended twist rates per caliber

[Hobbyman2007]

I would be nice if we had a reference guide or a sticky that would give us an idea of what barrel to chose for our intended projectiles . Here’s an example .
.22 bullets
1:16” or faster
.22 pellets
1:18”or slower
.25/257” bullets up to .6”
1:18”or slower
.25/257” bullets over .6”
1:14” or faster
.25 pellets
1:20” or slower


Now this is subjective and the numbers posted are just an idea ,not necessarily “Gospel” . Once a list is made maybe we can add sources for said barrels in specific twist rates . We know our selections are pretty limited as far as barrels go without going through a custom mandrel process . Love to get some I put here .

[Back_Roads]

 Sounds handy, I am not sure if Bobs pellet weight list will include popular bullets as it develops ?

[Bob Pratl]

This looks like a good start, now we have to add .30, .357, and .45.

[Hobbyman2007]

Here’s a barrel list from TJ’s including his air rifle / pellet specific barrels . I haven’t seen it posted here before . Lots of choices .

[Hobbyman2007]

Sounds handy, I am not sure if Bobs pellet weight list will include popular bullets as it develops ?

You mean like this https://www.gatewaytoairguns.org/GTA/index.php?topic=153770.0

After a closer inspection of Bobs spreadsheet . He has included the list for recommended twist rates . THANKS BOB .

[KnifeMaker]

Good to see this Denis!


Mike

[rsterne]

The twist rates in my spreadsheet are using the Kolbe Twist Calculator, and are the minimum to have a stability of SF = 1.5 at 1000 fps.... That should mean it would still be stable at Mach 1 (which is the worst case scenario).... For most bullet shapes, the stability increases in the Subsonic range as the muzzle velocity decreases.... I think the required twist rate for boattails is conservative, they tend to work in slower twist rates than Kolbe says....

The Kolbe calculator cannot address Diabolo (waisted) pellets.... but from what I am seeing, they can use a much slower twist rate than most manufacturers are using.... This tends to show up only at long range, in the form of spiraling (corkscrewing) if the twist rate is too fast.... I think part of the problem is that the manufacturers simply don't test at 75-100 yards, and don't realize it's a problem.... 

Spiraling is cause by Dynamic Instability, which is virtually impossible to calculate.... but one of the causes can be too fast a twist rate.... Here is what it looks like and how it develops....



As the pellet loses velocity, it doesn't lose RPM as fast, so the result is the same as if you used a faster twist rate.... Since pellets slow down faster, they are more prone to spiraling than bullets.... and/or at reduced ranges compared to bullets....

Bob

[Hobbyman2007]

Maybe it would be easier to list the manufacturers and list the projectiles that work best. EG : Evanix  225-39 fn , 223-38rn , pellets over 25gr.

[Nvreloader]

Denis

Do you want OEM bbl's/twist rates, or just custom bbl makes?

Tia,
Don

[rsterne]

There was an extensive post about barrel twist rates, I think in the Airgun Gate....

Bob

[rsterne]

I found the thread I was looking for on twist rates....  https://www.gatewaytoairguns.org/GTA/index.php?topic=117383.0

Bob

[Hobbyman2007]

Thanks Bob , I do remember reading that a while back . Now to put it all in one place . I’ll start plugging all the info for .22 and .25 into a spreadsheet .