Barrel internal design

[Ole Cowboy]

In my engineer's minds eye: RIFLES

1) Increase the depth of the throat (no rifling) to about .75+/- in.

This should increase the velocity of the round.

2) Use progressive twist rifling.

This more slowly develops the twist which keeps velocity high and insures the needed stability.

Thoughts???

 

[Lunyfringe]

1) increase as compared to what? And the trade off is that the bullet is going faster when it reaches the rifiling, which is more violent and can destabilize and/or deform the bullet.

2) Progressive rifiling (aka "gain twist") can cause more deformation of the bullet which can lead to less stable flight.

3) How about polygonal rifiling? I've seen several barrel manufacturers offer it.

 

[robertc1024]

2) Progressive rifiling (aka "gain twist") can cause more deformation of the bullet which can lead to less stable flight.

School me. I'm not sure I understand why you'd think this. I would think that a gain twist would deform the bullet less. My reasoning is that as soon as it hits the lands, it would be accelerated into a twist more slowly than conventional rifling which would cause lower forces initially on the bullet.

 

[Lunyfringe]

School me. I'm not sure I understand why you'd think this. I would think that a gain twist would deform the bullet less. My reasoning is that as soon as it hits the lands, it would be accelerated into a twist more slowly than conventional rifling which would cause lower forces initially on the bullet.

With the gain change, the angle of the rifiling changes, so rather than 1 set of grooves all at the same angle, the rifling marks on the bullet "wipe" a larger area on the jacket.

In some cases it works well, (like S&W 460xvr)... but on some bullet designs it can adversely affect accuracy.

https://www.americanrifleman.org/articles/2017/5/15/back-to-basics-rifling/

What is the problem you're trying to fix with gain twist rifling?

 

[Ole Cowboy]

We are talking rifles:

When the bullet exits the case it goes from, zero to over 2000 fps in a near instant. The optimal barrel would be a smooth bore, but the down side is stability, so lands and groves were added to provide that and works quite well.

But in the windmills of my mind I think if we start the lands and groves later into the process we can optimize the velocity. The progressive rifling provides a more gentle twist approach this 'scrubing off less velocity while provides the needed stability.

polygonal rifiling: Seems to be going with a deeper throat to optimize the velocity and combine that with possibly polygonal - 5R could provide some advantages in both increased velocity and the solid stability required for accuracy.

 

[orbitup]

Some guys use a progressive twist in rimfire barrels. I couldn't tell you why.

 

[motorcarman]

I have a Carcano 91/24 in 6.5mm.
It is the only rifle I own that has 'gain-twist'.
When I was a kid and learned about 'rifling', I thought it was all 'gain-twist' because it seemed normal to me to start the spin gradually and not try to spin from none to ultimate spin speed.

I found out I was wrong and it is 'normal' to 'slam' the bullet into the rifling at a constant pitch.

What did I know, I was just a kid????

bob

 

[grasshopperglock]

We are talking rifles:

When the bullet exits the case it goes from, zero to over 2000 fps in a near instant. The optimal barrel would be a smooth bore, but the down side is stability, so lands and groves were added to provide that and works quite well.

But in the windmills of my mind I think if we start the lands and groves later into the process we can optimize the velocity. The progressive rifling provides a more gentle twist approach this 'scrubing off less velocity while provides the needed stability.

polygonal rifiling: Seems to be going with a deeper throat to optimize the velocity and combine that with possibly polygonal - 5R could provide some advantages in both increased velocity and the solid stability required for accuracy.

Thoughts on micro rifling?

 

[Ole Cowboy]

Thoughts on micro rifling?

MR seems to have a solid fan base in the Marlin .22 guns and those that have seem to think it provides better accuracy but has a downside on cleaning since there are so many groves.

If I was in the gun-barrel business this would be my approach: using a /308 and 5.56 std NATO config:

1) Take match grade ammo and fire it out a smoothbore to ascertain the max attainted velocity. At some point in time you gain no more velocity due to the length of the bbl, the smoothbore only gives you the nominal friction loss of rifling. Take away: What is the best velocity we can attain with the least friction...2837 fps +/- 4 fps over a 100 rd trial.

2) Now we play the land n groves game from Micro to 5R and everything in between all other things being equal let look at velocity vs rifling

3) Throat depth: I would take the speed at which the powder formulation burned and how far that would be in bbl throat depth. DuPont XYZ Fast Burn, burns at X per millisec = throat depth of .748 in of smoothbore

4) Progressive rifling vs standard twist rate.

5) Accuracy: 100 yds, machine rest 20 rds

Goa: identify MAX velocity/MAX accuracy and where the X-Y points cross

Yea, lot of $$$, lot of time to do the analysis and then the results are only linked to 2 calibers, your gas mileage may be different for other grades of ammo, other bbl lengths etc etc.

 

[grasshopperglock]

There's seems to be a bunch of profiles.

 

[Ole Cowboy]

There's seems to be a bunch of profiles.

View attachment 144156

and there are more, the Ballard and the Micro and ++ is my guess.