Progressive rate of twist

I have a translated bit of info from German and I believe it's a calculation for progressive rate of twist. Can anyone verify??


The twist length was 12 feet (3.766 m) at a twist angle of 3 ° 45 '.

You would have to vary the angle to have progressive twist (old name GAIN TWIST)

Even with a 6 inch bore that angle would make less than half a full turn in those twelve feet

About the standard 1 in 10 for a .30 cal bore.

The 12 ft is my twist rate. But what is the 3. 45?

The 12 ft is my twist rate. But what is the 3. 45?

From the OP: "The twist length was 12 feet (3.766 m) at a twist angle of 3° 45'."

3° 45' is the angle the rifling makes with the bore center line, presumably. Perhaps we don't understand your original statement correctly. What do you mean by "The twist length was 12 feet ... ?"

Paulbryanpoq said:

I have a translated bit of info from German and I believe it's a calculation for progressive rate of twist. Can anyone verify??

Click to expand...

? Not without your posting the original German, no.

The twist length was 12 feet (3.766 m) at a twist angle of 3 ° 45 '.

Click to expand...

One turn in 12 feet. Thats heavy artillery 'gun', not 'howitzer' barrel (land-based) or "Naval rifle", (seaborne) length, if even the barrel is long enough to accomplish one full turn. Either way, a rate that is probably rather ancient as such things go.

Progressing from 'X' to one turn in 9 INCHES a number sometimes found in small-arms - even handguns.

More info than net twist per total length is needed for establishing 'gain twist' though.

Your degrees of departure would be progressively calculated from their moving base-line, not from a fixed reference, hence the term 'progressive'.

Heavy artillery has taken advantage of progressive twist to reduce stripping effect on driving bands when accelerating the angular velocity from rest of some astonishingly heavy projectiles.

Old idea, BTW:

Report of the Chief of Ordnance - United States. Army. Ordnance Department - Google Books

Others just use a lower rate of twist, 'coz the heavier the projo, the less spin it actually needs.

And then there is the Magnus effect, anyway, so some modern and highly accurate weaponry doesn't spin the projectile at all. "Fin stabilized" rather than "spin stabilized" and sometimes even "neither one".


Good idea to avoid being on the receiving end of 'any of the above', 'coz all work well enough, and the entity as saved the production cost of gain-twist probably spent it on more deadly shells. Or just more shells, period.

The Italians used gain twist rifling for their 6.5x52 rifles. Not sure how long that lasted. Would be interesting to see a sectioned barrel from one.

Yes this is 1860's tech. Most rifling numbers from that time I have seeen are just a full rotation to a determined length. Like 1:12 or 1:16 ft. It is a breech loading field piece. I am going soon to measure an original . I was thinking the 3. 45' was a sign bar set up or some bad translation. I will just have to see what the original is. I expect only a half rotation in a 6 ft tube

Gewehr 98 said:

The Italians used gain twist rifling for their 6.5x52 rifles. Not sure how long that lasted. Would be interesting to see a sectioned barrel from one.

Click to expand...

They also had the highest-velocity main battery battleship guns, and with some of the longest ranges, though not necessarily best accuracy nor longevity, War Two and just prior.

That didn't seem to do them a great deal more good than their choice of infantry rifles did.

More to all that than just 'technology'.