Pellet Size, Type, and Barrel Twist Rate

[Joe Shooter]

So, I've come to learn that there are certain barrel twist rates appropriate for certain caliber pellets; I also discovered that there are even more specifics to twist rates when it comes to diabolo pellets vs. slugs. Is there a chart available that breaks down these relationships for all calibers and types? Also, are swagged cast pellets/bullets categorized along with slugs in this regard?

 

[JamesD.]

http://www.geoffrey-kolbe.com/barrel_twist.htm



Have fun with all the info you need to know. Hope you have micrometers & are decent at math. This is allegedly the only calculator that will get twist rates right for subsonic ammo be it a Diabolo pellet or slug. There’s Ballistics experts around who have proved the calculations aren’t always the true optimal twist for air gun slugs rate. 

The Texan .257, why they use a straw barrel & too slow of twist I’m not sure. I’m hoping that Air Force & RAW technology merge (along with Uragan size tanks) and RAW makes a .257 with a heavier contour faster twist barrel. That would be my dream gun

 

[JamesD.]

Notice the I’m supposed to be shooting JSB 34.95 at 635 FPS to be “optimal” with a most common 1:16 air gun barrel twist rate. Until recently that is. Well, Sumatra’s, Evanix, have used rates from 1:16 to 1:28 and my 190 yard dead on shot is from a .253 Sumatra with a 1:18 spitting a 34.95 going 950 FPS if my BC is correct at 0.455. Let’s see what The Greenhill calculates for my specs.

1:19.6” isn’t far off from 1:18. Now the calculator already thinks subsonic is an error. The specific gravity should probably be a bit higher as this formula isn’t accounting drag stabilization from Diabolo skirt. 

The poop gets complicated. Here’s the one I just used for simplicity http://www.kwk.us/twist.html but, I’m told The Kolbe/Miller is best for subsonic correct returns for air guns specifically slugs. In pellets you have A LOT more forgiveness if twist isn’t perfect for diameter/length/weight/speed/SP.

 

[Arzrover]

I'm really not sure you can hard dictate twist rate for pellets. It seems as if the 1 in 16 or 17 is most common and there are plenty of examples of good and bad shooting barrels with a variety of pellet weights and calibers. I have Career 707 barrels in 22 and 177 that are 1in 22 and shoot extremely well with a variety of pellets and LW recently started offering a 1 in 30 that has had mixed levels of success. The diabolo form is self stabilizing and will even shoot fairly well with no rifling. In testing a pile of barrels in the last year in 25 cal, we ended up selecting some 1 in 30s as the best overall for 25 and 33 gn pellets. These theoretically will not shoot slugs and some of the 16s and 17s were very close and might shoot slugs. Anyway, the barrel internal form seems to have more to do with the accuracy than the twist from our testing and from my experience over many years of shooting ag's, so I'm not so sure you can formula-ize the twist rate for pellets. 

I guess what I'm suggesting is that you look to the barrel finishing and not worry much about twist.

FWIW, I had a good time on Wednesday shooting some long range with my friends near Flag in fairly constant wind. I think I hit 10 of 20 on a 4 inch triangle at 200 yards and very consistent on a 3 inch spinner at 160 with my RW in 22 w factory 1 in 16 barrel. For some reason I had a tougher time on a 5/8 spinner at 60 but fun day for sure. 

Hth

Bob

 

[Joe Shooter]

As a general contention, it appears that diabolo pellets shoot fairly well in slug barrels/liners, but not vice versa...at least shooting slugs in barrels engineered for diabolo pellets is not recommended. Is that fair to say?

And I ask again, are swagged cast pellets/bullets categorized as slugs in this converstion? How about the Benjamin Nosler 145gr. bullet?

 

[bandg]

Seems so. Common theory is that a diabolo pellet is "drag stabilized" by virtue of shape/weight distribution. Slugs (non wasp-waisted shape?) need spin to stabilize, whether swaged/cast/milled.

 

[mtnGhost]

Twist rate is a bit overhyped. 

 

[Joe Shooter]

@mtnGhost Please explain your premise for that statement.

 

[mtnGhost]

@mtnGhost Please explain your premise for that statement.

Sure. You can have a perfect twist rate in a poopty barrel and not shoot too well. The rate is just a factor in a larger equation.

 

[Joe Shooter]

@mtnghost One can also put cheap, poopty tires on a car and it will not drive as well as it could. What are going to do, change the tire size hoping that will help, or get a better quality tire? You see what I'm getting at? One doesn't change the prescribed ideal tire size for your car if the car is not drive comfortably; you get a better quality tire. Same holds true for a barrel...one doesn't change a prescribed ideal twist rate for a given style pellet if your not getting proper results, you look to a better barrel or gun. Ballistics have prescribed elements that have been proven over time.