I know it's an uncommon caliber, but what's an appropriate rifling twist rate a .26 cal rifled barrel? Also, safe BP load for it?

[Warsong]

I'm modifying a piece of 0.50" x 0.120" DOM 1026 tubing for a personal rifled barrel project, the endgame is to make a little squirrel rifle for shooting patched #4 buckshot. The barrel will be have about 30 inch of working bore length and I plan to groove it with DIY single-cutter rifling jig to a depth of 0.005". I just need to know what's an appropriate twist rate for the rifling and safe "max" load with black powder?

Given the issues with DOM tubing as gun barrels, I don't plan to push this homemade barrel for everything it's got, but I do want a MV of at least 900-1000 fps with the 20 gr buckshot RB. By my calculations, the finished tubing barrel should be able handle at least 25,000 psi of peak pressure before "yielding". I know the original 22 LR cartridge had a 5 grain "fine" black powder load , so I guess that 5-6 grains of 4Fg will be a good place to start off?

 

[44Bro]

If it were me,,,I'd ditch the DOM and use 4130. 1026 has an top ultimate tensile of~71000 PSI. 4130 normalized has a MINIMUM ultimate tensile of ~72000 psi. Most batches of 4130 normalized run 85000 or higher. I have some that the Test Report shows to be over 115000 psi Ultimate. The other problem with DOM is the weld seam CAN be a weak point. (won't always be) 1 in 48 could be an appropriate twist as it is what a lot of the early rifles ran. (some barrel makers only had a 1-48 mandrel/guide) Barlow's formula can give an approximation of the max safe pressure, just figure that Most black powder loads will stay under ~15000 psi.

 

[Sean E Bug]

I just got a 25 cal barrel made by Rayle. his standard twist for that caliber is 1:48 but he will also do 1:36. I have found for low velocity in my 32 cal 1:32 works well so I would probably go with that. the smaller the bore the faster the twist generally speaking but not a whole lot is done looking into the best twist for such small calibers.

 

[Grimord]

I have a rifle I built using an old .22 rim fire barrel. I shoot .234 Air rifle cup based slugs (30 grains) with 5 grains of 4f. I am getting 1000+ FPS out of the 20" barrel and 1" accuracy at 30 yards. I believe the twist is 1:24 based on a tight patched jag and measuring the twist at the muzzle.

 

[Rifleman1776]

You asked about twist for caliber. A 1:48" will work fine. But a faster twist might also. I had a friend who built a .22 cal. ml rifle using the barrel from an old .22lr britch loader. I believe those were often in the 1:12" twist range. He loaded bare ball using buckshot. It worked just fine for him and was his favorite squirrel gun.

 

[44Bro]

Most .22 rimfire barrels are 1-16. Some of the older short only bbls were 1-20 or 24, very few of those left.

 

[Warsong]

Thanks for the input guys, going by the suggestions here and the numbers from a rifling twist calculator I found online, I'm going to go with a 1:48 twist - which will nicely carry over to the .36 cal rifle I also I have planned .

If it were me,,,I'd ditch the DOM and use 4130. 1026 has an top ultimate tensile of~71000 PSI. 4130 normalized has a MINIMUM ultimate tensile of ~72000 psi. Most batches of 4130 normalized run 85000 or higher. I have some that the Test Report shows to be over 115000 psi Ultimate. The other problem with DOM is the weld seam CAN be a weak point. (won't always be) 1 in 48 could be an appropriate twist as it is what a lot of the early rifles ran. (some barrel makers only had a 1-48 mandrel/guide) Barlow's formula can give an approximation of the max safe pressure, just figure that Most black powder loads will stay under ~15000 psi.

My supplier specs on the DOM 1026 are 70,000 psi yield and 80,000 psi UTS, which matches the specs for as-is, non-stress relief/normalized DOM 1026 from other sources. The normalized DOM 4130 I got from a local hobby aircraft supplier for a pistol build had 40,000 yield and 90,000 UTS as the specs. Since this is a rifled barrel, I'll like a little more hardness to reduce wear on the rifling grooves. From working previously DOM 4130, I find it harder it work with and it tends to "stick" and grab when drilling or filing, so I'm going to stay with the DOM 1026 for now until I iron out my rifling setup.

After doing some napkin math last night, for a 20 gr .25 cal projectile at 1200 fps I doubt the barrel will see any more than 4000 psi of peak pressure worst case. I might run some loads from a 12 or 6 inch test barrel through my chrono just to have a better idea.

 

[Grimord]

Most .22 rimfire barrels are 1-16. Some of the older short only bbls were 1-20 or 24, very few of those left.

Thanks 44Bro. The barrel i used to make my .22 BP rifle came from an old .22 RF Stevens single shot rifle. I only wish I could have found a usable octagon barrel but every one I examined was too far gone to be used to make the gun I wanted to make.

 

[Codger Craig Wilcox]

Sounds as though you are really doing your homework. I think your 1/48 wills work just fine. Just be sure to use non-hardened buckshot.

I have long wanted to make a small rifle using a .22 barrel. A match-grade barrel is not overly pricey, and a breechplug shouldn't be too difficult to make.

 

[Grimord]

Thanks for the input guys, going by the suggestions here and the numbers from a rifling twist calculator I found online, I'm going to go with a 1:48 twist - which will nicely carry over to the .36 cal rifle I also I have planned .



My supplier specs on the DOM 1026 are 70,000 psi yield and 80,000 psi UTS, which matches the specs for as-is, non-stress relief/normalized DOM 1026 from other sources. The normalized DOM 4130 I got from a local hobby aircraft supplier for a pistol build had 40,000 yield and 90,000 UTS as the specs. Since this is a rifled barrel, I'll like a little more hardness to reduce wear on the rifling grooves. From working previously DOM 4130, I find it harder it work with and it tends to "stick" and grab when drilling or filing, so I'm going to stay with the DOM 1026 for now until I iron out my rifling setup.

After doing some napkin math last night, for a 20 gr .25 cal projectile at 1200 fps I doubt the barrel will see any more than 4000 psi of peak pressure worst case. I might run some loads from a 12 or 6 inch test barrel through my chrono just to have a better idea.

I'm curious. Where do you find a 20 grain 25 cal projectile?

 

[Warsong]

I'm curious. Where do you find a 20 grain 25 cal projectile?

Technically a .24 cal with a #4 lead buckshot, which Google is telling me is about 20 grains. A #3 buckshot will closer to .25.

 

[Grimord]

Technically a .24 cal with a #4 lead buckshot, which Google is telling me is about 20 grains. A #3 buckshot will closer to .25.

Thanks for the info. Don't know how you can handle that tiny ball with a patch. With my sausage fingers, I am lucky to be able to handle the .311 balls and patches for my .32's. I use 30 grain air gun slugs in my .22 built rifle and those are pretty small too. I always manage to drop several during the course of shooting.