Small bore rate of twist.

[GANGGREEN]

I've always heard that small bores should have a faster rate of twist than large bores to accurately shoot patched round ball. I'm considering ordering a .32 and a .40 barrel from FCI this week, both with round-bottom rifling, but wanted to know what rate of twist would be recommended. 1 in 48"? 1 in 56"?

 

[Grimord]

For the .32 I would suggest a 1:30 or 1:36" twist for roundball use. You won't need more than 20 grains of BP (probably less) to get great groups at 25-35 yards. I am not familiar with the .40 caliber so I can't make a suggestion there.

 

[Erwan]

A twist rate of 1:48 is more than largely sufficient for the patched round ball. With too short rate of twist and not deep enough rifling the bullet can "jump" the groves with a charge a bit strong…

 

[Bassdog1]

If you are having the rifling cut I recommend 1 in 30 for a 32 cal If you want to use it with light charges of powder for small game hunting. That is what the TC 32 Cherokees and Senecas were designed to do shoot accurately at a lower velocity. Some on this site get great accuracy with as little as 10 grains. I have shot a couple of CVA Squirrel rifles that shot well with 20-25 grains they were 1 in 48. I also shoot a 36 TC Seneca with a 1 in 48 twist that shoots an excellent group with 20 grains of powder and a PRB also just has a little more power than I need for a squirrel. So depending on what you want to use it for 1 in 30 up to 1 in 48 for the 32. I would stay with 1 in 48 on a 40 cal.

 

[Sidney Smith]

When I bought my .32 barrel from Rice, iirc the only rate of twist they listed was 1 in 48. Shoots roundballs fine.

 

[GANGGREEN]

OK, thanks guys. The FCI page says that all barrels can be purchased with twists from 1 in 18" to straight, so I presume I can request 1 in 30" for the .32 and 1 in 48" for the .40, which is what I'm inclined to do.

 

[GANGGREEN]

OK, just ordered them. 42" X 3/4" .40 barrel with 1 in 48" twist and round-bottom rifling and a 34" X 3/4" .32 barrel with 1 in 36" twist and round-bottom rifling. 6 month wait at the present, which is fine by me (too many other things going on right now), but I'm anxious to get them and get started on more projects.

 

[Pete G]

Ask the barrel maker. He has more experience than all the rest of us put together.

 

[Billy Boy]

I've always heard that small bores should have a faster rate of twist than large bores to accurately shoot patched round ball. I'm considering ordering a .32 and a .40 barrel from FCI this week, both with round-bottom rifling, but wanted to know what rate of twist would be recommended. 1 in 48"? 1 in 56"?

Most factory ‘standard’ small bores, 32s, 36s, have a 1 in 48 twist. My 32 and 36 are rifled so. I wish the 32 had a faster twist so I could load it down to
for less carnage on little, edible things and still retain excellent accuracy.

 

[Col. Batguano]

The general formula for RB twist rate is more complicated than this, but for (hunting load) rounding purposes, it is 1: 1 1/3x caliber. It's also a function of imparting sufficient rpms on the departing projectile to stabilize it, so, practically speaking, for guns intended to be shot with very light loads, you will need a higher twist rate than those intended to be shot with faster exit velocities.

There are others on this forum with better grasp of these formulae than I am, and hope they will chime in here with a more complete answer.

 

[SDSmlf]

Can’t speak to other twist rates, but the 1-48 in my Pedersoli Scout 32 caliber works great with the light charges I typically use, although with limited testing I remember it performing well with heavier charges. With 12 grains of Swiss fff and a patched 1-1/2 buckshot it is deadly on squirrels and targets out to the 30 or so yards I shoot it. Not quite an inch high at 25 yards, about inch low at 50. Squirrels aren’t that big, tough or aggressive around here so I stick with lighter charges.

 

[Loyalist Dave]

Ask the barrel maker. He has more experience than all the rest of us put together.

Agreed!

Look the barrel making companies or individual makers who have companies that bear their names, have a very good rep and want to keep it that way, so...,
They are going to give you something that works well.
My .40 is a 1:48
My .54 1:56
So ask about the .32. The maker may be happy to give you what you ask, but would it be the same if the barrel maker was to choose?

LD

 

[SDSmlf]

So ask about the .32. The maker may be happy to give you what you ask, but would it be the same if the barrel maker was to choose?

You also have to let the barrel maker know what type of shooting you will be doing. Some folks like to push heavy for caliber conicals to great distances, while others want to shoot patched roundballs short distances at squirrels. Don’t assume the barrel maker will know what you intend to shoot out of your new barrel.

 

[Pete G]

Squirrels aren’t that big, tough or aggressive around here so I stick with lighter charges.

You keep shooting off the easier ones and the tough aggressive ones will breed more.
Be careful out there.

 

[hanshi]

My .32 & .36 are both 1-48", and so was my .40. It's 1-56" for my .45 & .50. The .54 is 1-66" and is accurate with any load. Given decent rifling depth a 1-48" twist will work from .32 through at least .54.