Rifling Angle to Bullet?

[Bart B.]

Here's three barrels:

22 caliber (.224" groove diameter), 1:8" twist.

30 caliber (.308" groove diameter), 1:11" twist.

44 caliber (..448" groove diameter), 1:16" twist.

Which one has the greatest angle the rifling presents to the bullet?

 

[knights_armorer]

anyone?

 

[briansmithwins]

Think of it this way: A rifle with a 1/1000 twist would have an angle that's almost 0 degrees. One with a 1/1 twist has almost 90 degrees.

The tighter the twist the steeper the angle. BSW

 

[Sport45]

I believe the angle is the same for all of them.

It's not the answer I though I'd come up with but that's what my ciphering tells me.

 

[RS14]

I'm not a gunsmith, but I thought about the problem.

The circumference of the barrel is

pi*cal

In making one revolution, the bullet spins by this amount while traveling the distance given in the twist rate.

Thus the angle made with the bore axis is

ArcTan[pi*cal/dist]

As it turns out, all three barrels you listed present precisely the same angle (5.027 deg), because the ratios between the bore diameters are the same as the ratios between the twist rates.

 

[knights_armorer]

very slick.

i didnt have the answer but i knew it was trickier than just rate of twist.

would it be correct to say that rifling in a barrel 1" in diameter with a twist of 1/10 would be the same angle of a barrel 1.5" in diameter with a rate of twist of 1/15?

 

[RS14]

would it be correct to say that rifling in a barrel 1" in diameter with a twist of 1/10 would be the same angle of a barrel 1.5" in diameter with a rate of twist of 1/15?

Yes.

 

[Maverick223]

The tighter the twist the steeper the angle.

I think what he is asking is what is the twist relative to the bore size...as Sport45 and RS14 said in the above statement the difference is negligible (but there is a small difference between the calibers mentioned), and for practical purposes the same relative to the diameter.

Bart, I know I am being nit picky but the bore diameters that you quoted are incorrect per ATF definition, the bore is measured from land to land, therefore .22cal is .220in., .30cal is .300in. (with the exception of most European .30cals which are actually .303), the bullet diameters for these are as you stated...but your really off on the .44cal as it typically uses .429in. bullets, similar to the .38Special which isn't even close to .38. Go figure?

 

[Sport45]

Bart, I know I am being nit picky but the bore diameters that you quoted are incorrect per ATF definition, the bore is measured from land to land, therefore .22cal is .220in., .30cal is .300in. (with the exception of most European .30cals which are actually .303), the bullet diameters for these are as you stated...but your really off on the .44cal as it typically uses .429in. bullets, similar to the .38Special which isn't even close to .38. Go figure?

There aren't any hard and fast rules here. 38 caliber handgun bullets are normally .357 to .358 diameter. Those diameters would describe 35 caliber rifle bullets. 38 caliber rifles normally use bullets that are .375 to .376 inches in diameter.

Bart may have taken some artistic license with his .448" bore (unless we're talking muzzle loaders), but it makes the math work out nice. With his stated diameters I found no difference at all in the approach angle.

 

[rangerruck]

what about 5r rifleing, which supposedly has a purpose built increase angle to the rifleing?

 

[knights_armorer]

the way i started seeing it as being a very deceptive little question was when i imagined a 16 inch bore like the ones on battleships, then invisioned the angle of attack required to get one revolution in 8", lol. the projectile would look more like a screw than a bullet!!!!!

i would have never thought about it before this, but a barrel of exactly .22 caliber with a twist rate of 1/8, and a barrel of exactly .44 caliber with a twist rate of 1/16, will have identical angles of rifling. that is cool.

cool thread bart

 

[Maverick223]

what about 5r [rifling], which supposedly has a purpose built increase angle to the rifleing?

Would be the same, the rifling itself is angled but the bullet diameter/twist rate relationship would be identical. It does however make cleaning easier (or so I have heard), due to reduced fouling, whilst maintaining equal purchase on the bullet to impart spin.

 

[Bart B.]

For those who caught my "bore" word that should have been "groove," I tried to edit that earlier. Some crazy electron in the wires between me and you jammed up three attempts.

I finally changed it to "groove." Thanks for the alert, Maverick223.

 

[Bart B.]

rangeruck asks:

what about 5r rifleing, which supposedly has a purpose built increase angle to the rifleing?

Barrett (Boots) Obermeyer, cut rifled barrel maker in Wisconson, designed his 5R rifling shortly after the 7mm Rem. Mag was introduced. Sierra's .284 diameter 168-gr. Match Kings that came out in early 1970(?) had a pretty thin jacket compared to their 30 caliber bullets. Conventional rifling shapes cut deep enough in jackets that when bullets were spun really fast, they would come apart shedding their jackets. Sierra has since used slightly thicker jackets on their 7mm bullets.

Boots took his design from the AK47's bore which had a similar design to his. He called his 5 (for five groove) R (for Russian from whence commeth the AK).

My post is about the angle the rifling is at caused by the groove diameter's ratio to the twist rate, not the shape of the lands and grooves.

 

[Art Eatman]

Based on the wording of the OP, the tighter the spiral, the steeper the angle with respect to the axis of the bore and the axis of the bullet.