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rate-of-twist?
- Thread starter Daddybear
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Think you'll find your smaller cal's up to .45 will be 1-48 and heavier cal's 1-66, 1-70.
Yup, it's sorta caliber dependant. A lot of factory guns come with a 1:48 no matter what caliber and that works for balls okay. Typically, you'd expect to see a slower twist as the caliber get's larger. Say, 1:48 for a .32 up to a 1:70 for a .58.
I like Roy's comment. Don't worry about it too much. Well, as long as you don't mistakingly buy an MZ that's meant for conicals/sabot and try to shoot balls out of it.
I like Roy's comment. Don't worry about it too much. Well, as long as you don't mistakingly buy an MZ that's meant for conicals/sabot and try to shoot balls out of it.
paulvallandigham
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If there is a general rule of " thumb " for determine the best Rate of Twist for round balls, it would be 1.5 times caliber:
.32= 1:48
.36= 1:54
.40= 1:60
.45= 1:67.5
.50= 1:75
.54= 1:81
.58= 1:87
.62= 1:93
.69= 1:103.5
.72= 1:108
These are the optimum ROT for these caliber RBs. You cannot overspin a Round ball. However, using a ROT that is faster than optimum tends to affect the size of variation in powder charge used that will still send the ball to the same POI.
For instance, My brother has several .40 caliber rifles that have a 1:48 ROT, and they shoot just fine. But even that ROT is much slower than the 1:16 ROT used in his friend's conical bullet .40 caliber rifle. He can still shoot RB in the gun but the powder charge is about 35 grains, instead of the 50 grain charge used for accuracy in the other .40 caliber rifle barrels made to shoot RBs with the 1:48 ROT.
The slower ROTs(shown) are much more forgiving to small variations in powder charges- as occurs when you use a volume measure to measure the powder, vs. using a powder scale to WEIGH the powder charge. The faster the ROT, the more likely you are going to need to both reduce the powder charge, AND weigh the charges to get small groups.
This is the reason we don't recommend buying a fast twist barrel designed to shoot conicals and sabots. Its not that you can't shoot RB out of these barrels: instead, its just more difficult to get good groups out of such barrels with RBs.
Now, KEEP in MIND that when we are describing group performance, we are usually talking about shooting a rifle off a bench rest, not off-hand. And, we are talking about shooting at distances of 50 yards and further. Many BP shooters never shoot at distances further than 50 yards, and sometimes not even that far, either in practice, or when hunting, since they are shooting off-hand mostly.
.32= 1:48
.36= 1:54
.40= 1:60
.45= 1:67.5
.50= 1:75
.54= 1:81
.58= 1:87
.62= 1:93
.69= 1:103.5
.72= 1:108
These are the optimum ROT for these caliber RBs. You cannot overspin a Round ball. However, using a ROT that is faster than optimum tends to affect the size of variation in powder charge used that will still send the ball to the same POI.
For instance, My brother has several .40 caliber rifles that have a 1:48 ROT, and they shoot just fine. But even that ROT is much slower than the 1:16 ROT used in his friend's conical bullet .40 caliber rifle. He can still shoot RB in the gun but the powder charge is about 35 grains, instead of the 50 grain charge used for accuracy in the other .40 caliber rifle barrels made to shoot RBs with the 1:48 ROT.
The slower ROTs(shown) are much more forgiving to small variations in powder charges- as occurs when you use a volume measure to measure the powder, vs. using a powder scale to WEIGH the powder charge. The faster the ROT, the more likely you are going to need to both reduce the powder charge, AND weigh the charges to get small groups.
This is the reason we don't recommend buying a fast twist barrel designed to shoot conicals and sabots. Its not that you can't shoot RB out of these barrels: instead, its just more difficult to get good groups out of such barrels with RBs.
Now, KEEP in MIND that when we are describing group performance, we are usually talking about shooting a rifle off a bench rest, not off-hand. And, we are talking about shooting at distances of 50 yards and further. Many BP shooters never shoot at distances further than 50 yards, and sometimes not even that far, either in practice, or when hunting, since they are shooting off-hand mostly.
Like I said earlier its something I never gave any thought too. Just started to pay a bit more attention now that some customers ask. I am sure either choice will be equally as good as far as rate of twist. Now peoples choices my vary on what production gun. That is something that I really have no clue about :haha:
I think the important thing here is to get a barrel that has a twist that is 1:48 or slower.
The barrels with twist rates that are faster than that like 1:28 etc are designed for shooting slugs or sabots.
It isn't the rate of twist in these barrels that makes roundballs work poorly in them, but these barrels seem to always have very shallow rifling grooves. These shallow grooves don't work particularly well with patched roundballs.
The barrels with twist rates that are faster than that like 1:28 etc are designed for shooting slugs or sabots.
It isn't the rate of twist in these barrels that makes roundballs work poorly in them, but these barrels seem to always have very shallow rifling grooves. These shallow grooves don't work particularly well with patched roundballs.
paulvallandigham
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What distance, and for what purpose?
In my 1:48 .50 caliber rifle, with a .39 inch barrel I use: a target load of 60 grains, good to 50 yards; and a hunting load of 75 grains, FFg Goex, to 100 yds for deer.
If I had a slower rate of twist, I would more likely be using 80-85 grains of FFg powder for hunting. But, everything would depend on what the barrel likes the best. I certainly have enough velocity to kill a deer out to 100 yards with what I am using now.
In my 1:48 .50 caliber rifle, with a .39 inch barrel I use: a target load of 60 grains, good to 50 yards; and a hunting load of 75 grains, FFg Goex, to 100 yds for deer.
If I had a slower rate of twist, I would more likely be using 80-85 grains of FFg powder for hunting. But, everything would depend on what the barrel likes the best. I certainly have enough velocity to kill a deer out to 100 yards with what I am using now.
ohio ramrod
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For target shooting Ilike to start about five grains below the caliber and work up until I get minimum sized grouping. So for a fifty I would start at 45 grain. The one thing about this sport is each gun has its own best charge due to many factors including but not limited to barrel length,location of mounting pins ( or wedges), full or half stock, lube and patch fit/thickness etc. In fact if you read all of the articles effecting group size you start to wonder how we ever hit anything.
Tom Compton
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Daddybear, a PRB has very little engagement with the rifling (one of the reasons a tight ball and patch combo is needed). Seat a ball and then pull it to see the narrow band around the ball where the rifling has marked the ball. If you are shooting a high velocity (relative to ML so 1500+ fps) the slower twist or a gain twist keep the projectile from stripping the rifling and therefore losing spin and accuracy. Also better to have deeper rifling. RB target barrels are generally 1:66 w/ .012+ rifling depth. Barrels for heavy hunting charges run 1:70 to 1:72 twist. Caliber has little importance as the required twist is based on revolutions per second and length in calibers. All RBs are 1 caliber long. Rate calculators I have seen come up with 1:70 for RB. Smaller calibers are less likley to strip the rifling as the mass of the ball is less and requires less engagement to spin it.
That being said, my .50 Douglas barrel likes 60 gr FFg at 25 and 50 yards w/ .495 ball and .017 patch. It still shoots real well w/ 90 gr FFg and same point of aim at 100 yards. That is my hunting load.
Sight picture, trigger control, follow through,
TC
That being said, my .50 Douglas barrel likes 60 gr FFg at 25 and 50 yards w/ .495 ball and .017 patch. It still shoots real well w/ 90 gr FFg and same point of aim at 100 yards. That is my hunting load.
Sight picture, trigger control, follow through,
TC
The best rate of twist for a given caliber depends on the caliber and what you want to use it for. An older barrel maker friend of mine says to use 120 time the caliber. There are very few commercial barrel companies that use that rule consistently, except for, perhaps, Numerich Arms Co. There are a number of custom barrel makers who will make a barrel with any reasonable twist rate you might want. For the smaller caliber target rifles, the rule may change to 100 times the bore size to impart a faster spin to the RB for fine offhand target work.
Using the first rule, and .45 caliber barrel would use a 1 in 57.6 inch rate of twist, while you will fine barrels with a 1 in 56 inch twist for this caliber. Other makers use 1 in 66 inch for all calibers, including the .45.
If you want a fine .40 cal. target rifle, you might use a 1 in 40 inch twist, understanding that with the faster twist rates, you will use less powder and the accuracy will be more sensitive to powder charge than the slower twist rates barrels would be. Typically the .40 caliber RB rifle barrel come with a 1 in 48 inch twist rate, meeting exactly the first rule.
A .50 cal RB rifle would ideally have a 1 in 60 inch twist, but most barrels are made with 1 in 66 inches for that caliber or even slower pitches like 1 in 72 inches. These slower twist for full length barrels allow the shooter to use more powder and burn it efficiently, but then you have a longer barrel and more weight.
As other people have stated, don't worry too much about the twist rate. The barrel must be straight, meaning the bore must be drilled and reamed straight, with very little runout from one end to other. Generally above .45 caliber, this is not a problem with boring straight holes. There should be no reaming marks on the lands, although anything at the breech end will have little effect on accuracy no matter what the lands and grooves look like in that area. The grooves, if cut should have no significant marks in them either. I do shoot a barrel that I've lapped and the bottom of the grooves still show the cutting marks, but it doen't seem to effect accuracy -- the cloth patch rubs against that part of the groove. I know the Rice Brothers make fine barrels, and I have barrels from several makers - Green Mtn, Douglas, for instance, incluing custom ones. If you are looking for a good quality barrel, you could choose either from the Rice Brothers or a Green Mtn barrel and not go wrong. The other barrel available commercially are also good for the value. How the barrel is crowned and the rifle is cleaned may have more to do with its goodness than what manufacturer you choose.
I'm getting ready to make a barrel in .38 caliber with a 1 in 38 inch twist, if the tooling will allow it. This is a target rifle barrel.
Good luck!
Using the first rule, and .45 caliber barrel would use a 1 in 57.6 inch rate of twist, while you will fine barrels with a 1 in 56 inch twist for this caliber. Other makers use 1 in 66 inch for all calibers, including the .45.
If you want a fine .40 cal. target rifle, you might use a 1 in 40 inch twist, understanding that with the faster twist rates, you will use less powder and the accuracy will be more sensitive to powder charge than the slower twist rates barrels would be. Typically the .40 caliber RB rifle barrel come with a 1 in 48 inch twist rate, meeting exactly the first rule.
A .50 cal RB rifle would ideally have a 1 in 60 inch twist, but most barrels are made with 1 in 66 inches for that caliber or even slower pitches like 1 in 72 inches. These slower twist for full length barrels allow the shooter to use more powder and burn it efficiently, but then you have a longer barrel and more weight.
As other people have stated, don't worry too much about the twist rate. The barrel must be straight, meaning the bore must be drilled and reamed straight, with very little runout from one end to other. Generally above .45 caliber, this is not a problem with boring straight holes. There should be no reaming marks on the lands, although anything at the breech end will have little effect on accuracy no matter what the lands and grooves look like in that area. The grooves, if cut should have no significant marks in them either. I do shoot a barrel that I've lapped and the bottom of the grooves still show the cutting marks, but it doen't seem to effect accuracy -- the cloth patch rubs against that part of the groove. I know the Rice Brothers make fine barrels, and I have barrels from several makers - Green Mtn, Douglas, for instance, incluing custom ones. If you are looking for a good quality barrel, you could choose either from the Rice Brothers or a Green Mtn barrel and not go wrong. The other barrel available commercially are also good for the value. How the barrel is crowned and the rifle is cleaned may have more to do with its goodness than what manufacturer you choose.
I'm getting ready to make a barrel in .38 caliber with a 1 in 38 inch twist, if the tooling will allow it. This is a target rifle barrel.
Good luck!
"I was looking at a lymans greatplains with a 1 in 60 or a traditions pennsylvania with a 1 in 66"
I would look no further than the LGP, its has a good twist and depth of groves and even looks a lot like an original ML, probably the best all around production ML made right now. the adjustable sights that come with it are pretty funky but they also send a good set of fixed sights, the front blade is a bit thick to suit most but a bit of filing will fix that.Good luck with whatever you choice may be and enjoy the journey.
I would look no further than the LGP, its has a good twist and depth of groves and even looks a lot like an original ML, probably the best all around production ML made right now. the adjustable sights that come with it are pretty funky but they also send a good set of fixed sights, the front blade is a bit thick to suit most but a bit of filing will fix that.Good luck with whatever you choice may be and enjoy the journey.
JOHN L. HINNANT
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Good Morning Zonie,
I never thought that I would read these words written by you.
"Those shallow grooves don't work paticularly well with patched roundballs".
I immediately went into shock and had to be rushed to the hospital emergency wing. It took a plate of fine San Antonio Mexican Food to effect a quick recovery. Otherwise, I would probably still be on life support (there are probably some folks who wish I still was).
It was not that long ago that I critized shallow groove 1-48" twist rifling as having a narrow velocity range to achieve best accuracy and were also more finicky than slower twist, deep groove rifled barrels.
This, of course applies only to shooting the patched round ball.
For my critism of shallow groove rifled barrels, I was scathingly denounced, had my library card taken away, condemned and banished to a far-a-way land to shoot undersize balls with a black powder substitute in shallow groove rifled barrels for the next ten years.
I am in fear that by mentioning this subject again, my parole will be revoked and I will be sent back to complete the rest of sentence.
Hope that you had a great Thanksgiving. Part of my parole conditions requires me to sit in an empty deer camp on that day with a shallow groove rifled muzzle loading rifle, undersize balls, thin patch material, a black powder substitute, and no caps.
I guess it could be worse. The sights might be taken off of the rifle or reversed.
Best regards and good shooting,
John L. Hinnant
If you are not an NRA or NMLRA Member, why not? I am carrying your load.
Liberal politicians LIE!!! usa Freedoms Die!!!!
I never thought that I would read these words written by you.
"Those shallow grooves don't work paticularly well with patched roundballs".
I immediately went into shock and had to be rushed to the hospital emergency wing. It took a plate of fine San Antonio Mexican Food to effect a quick recovery. Otherwise, I would probably still be on life support (there are probably some folks who wish I still was).
It was not that long ago that I critized shallow groove 1-48" twist rifling as having a narrow velocity range to achieve best accuracy and were also more finicky than slower twist, deep groove rifled barrels.
This, of course applies only to shooting the patched round ball.
For my critism of shallow groove rifled barrels, I was scathingly denounced, had my library card taken away, condemned and banished to a far-a-way land to shoot undersize balls with a black powder substitute in shallow groove rifled barrels for the next ten years.
I am in fear that by mentioning this subject again, my parole will be revoked and I will be sent back to complete the rest of sentence.
Hope that you had a great Thanksgiving. Part of my parole conditions requires me to sit in an empty deer camp on that day with a shallow groove rifled muzzle loading rifle, undersize balls, thin patch material, a black powder substitute, and no caps.
I guess it could be worse. The sights might be taken off of the rifle or reversed.
Best regards and good shooting,
John L. Hinnant
If you are not an NRA or NMLRA Member, why not? I am carrying your load.
Liberal politicians LIE!!! usa Freedoms Die!!!!
Tom Compton
54 Cal.
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- Oct 21, 2008
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- 1,893
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Required revolutions per second (RPS) is based on the length of the projectile in calibers or, said another way, length to diameter ratio.
Same reason there are different twists for .223 (5.56 NATO) and other modern calibers depending on the bullet weight to be stabalized. Muzzle velocity is a little slower and bullet is longer (diameter stays the same so to get more weight the bullet is longer) and requires a faster twist.
A relatively small caliber RB can work in faster twist barrels because there is less mass to start spinning and therefore less of a tendancy to strip the rifling.
If you plan on accuracy at a low velocity with a RB, like using 40 gr charges with a .50 or .54, you will need faster twist than 1:66 to get the needed RPS to stabalize the ball. Has nothing to do with the caliber. If you use a bullet - pistol in a sabot, maxi or other conical - a faster twist is required due to the length of the projectile.
Sight picture, trigger control, follow through.
TC
Same reason there are different twists for .223 (5.56 NATO) and other modern calibers depending on the bullet weight to be stabalized. Muzzle velocity is a little slower and bullet is longer (diameter stays the same so to get more weight the bullet is longer) and requires a faster twist.
A relatively small caliber RB can work in faster twist barrels because there is less mass to start spinning and therefore less of a tendancy to strip the rifling.
If you plan on accuracy at a low velocity with a RB, like using 40 gr charges with a .50 or .54, you will need faster twist than 1:66 to get the needed RPS to stabalize the ball. Has nothing to do with the caliber. If you use a bullet - pistol in a sabot, maxi or other conical - a faster twist is required due to the length of the projectile.
Sight picture, trigger control, follow through.
TC
