RIFLING questions

[Dusty Stevens]

Maybe a slight thread drift, but just something to think about. FX air rifle company came up with a novel barrel design called the SMOOTH TWIST. It was smooth bore for the first four-fifths of the barrel, then had a progressive twist. They shot great and had just one drawback, they had to be cleaned about every 20 shots to maintain accuracy. They have a different one now the details of which I am not familiar.

Now they impart the rifling onto the outside of the barrel and it makes the inside smooth rifling

 

[PigButtons]

Now they impart the rifling onto the outside of the barrel and it makes the inside smooth rifling

Thanks @Dusty Stevens , as usual you are a wealth of knowledge.

 

[Luisyamaha]

I once did the exercise of adding up the dimensions of all the different segments of the rifling and they added up to the circumference of the bullet. The jacket or lead has to have someplace to go as it obturates (?) into the barrel. And it seems to do so radially, not longitudinally.

Now, this was a long time ago, and I may be remembering it wrong, but that is my best recollection.

Luisyamaha

 

[Walt Schmidlin]

A VG friend of mine was an excellent pistol shooter and pistol smith. Made custom barrels for HS & SW M41 pistols.
Asked him about Marlin Micro Groove barrels, he said the rifling was too shallow, not accurate enough for 50yd SF.
He did mention he used several brands of barrels for his custom barrels, apparently more than one brand was successful.
He found Federal 711 22rf was the most consistent, I’m not sure 711 is still available.

 

[darkangel_r2]

My PacNor 3-groove barrel has wide grooves and lands, and the grooves appear shallow relative to the height of the lands. In other words there isn't that much diametrical difference between lands and grooves, at least as seen by the eye through the borescope. This configuration has delivered significantly more velocity with a 6BR cartridge than is typical. With the same charge weight and bullet, the 3-groove runs about about 20-25 fps faster than my 6-groove cut-rifled barrel that is 1" longer. Every barrel is different of course. But I discussed this with John Krieger and he believed that a 3-groove might well be faster than other configurations.

Do they appear shallow or are they actually shallow? Do you have the dimensions? Have you noticed a difference in throat wear with the 3 vs 6 groove? See any bullet blow ups?

Only one edge of each land imparts the actual turning force on the bullet so reducing the number of lands increases the force per area. So even with the same volume of metal composing the lands a reduction in number of lands and grooves will increase pressure on the faces of the lands and on the new edge of the bullet.

But reducing the number of lands also reduces the total friction on the bullet going down the bore because the surface area in contact is less (with total lands volume the same) than with more lands. So in theory fewer lands should result in more speed at the same pressure with less heat transfer as well. Only potential downside being possible jacket failure due to increased local pressure on the bullet on the faces that contacts the face of the lands that imparts the spin force. This may be offset somewhat by fewer overall jacket deformations (3 vs 6).

I am not sure of the impact of varying the volume of the lands.

Simulation Study on the Impact Response of Barrels with Different Rifling Profiles during Bullet Engraving

Gun barrel bores are prone to ablative damage and stress concentration under high temperatures, pressures, and dynamic load impacts during bullet engraving, which may result in barrel failure. A dynamic stress analysis during bullet engraving is a prerequisite for barrel life analysis and...

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