Barrel length

[NHmsj]

Is there a minimum length for a barrel with a slow twist, say 1:66 or slower? If so, what might it be? And why?

msj

 

[roundball]

I don't know if barrel lengths are as much twist oriented as they might be oriented towards combustion/pressure/velocity.

One observation is that T/C and GM make a lot of 1:60"-1:70" round ball twist barrels that are 30" to 33" long

 

[paulvallandigham]

NO. Originally, when nothing was know about the effect of ROT, the chosen ROT was the length of the barrel. So, for instance, if your barrel was 48 inches long your ROT was 1"48". Longer barrels got slower ROTs.

Later, as barrel makers began to understand what effect a given ROT would have on a designated caliber of ball, and then conical bullet, any correlation between ROT and length of barrel was coincidence, as that system was abandoned.

When you contemplate barrel length, turn your thoughts to pistol barrels. The .38 special revolver has a ROT of between 1:14, and 1:18" ROT. When was the last time you saw a .38 revolver with a 14 or 18 inch long ?

There is the " Greenhill " formula for calculating ROT for barrels:

ROT( T) = 150 X D/R
where T is the Rate of twist, D is the diameter of your bore, and R is the Ratio of the diameter to the length of the ball or bullet.

Find the R first. If you are shooting a RB of .490 diameter, you would divide the Diameter of the bore( .490") by .490 = 1. T = 150 times .490 x 1 =
1:73.5". Shooting a conical of 3/4 inches, you get 150 x .490 x .653 = 1:48 ROT!

I am advised by folks who know more about the Greenhill formula than I will ever understand that this works for a ball or bullet going at approx. 1500 fps. MV. If you are sending a ball or bullet faster or slower than that velocity, then alter the formula's multiplier accordingly. ( Ex. For 1800 fps.MV: T= 180 x D x R )

Another way to describe the formula is :

Caliber times Caliber times 150, divided by the length of your bullet = your RATE of Twist.

 

[almrl]

It has always been considered that three-fourths,[1:48] or a whole turn [1:36}, in the angle of a rifle in a barrel three feet in length, was the best for throwing the ball to a certainty. This mode of rifling is practised by the Germans, French, and Americans; and all the foreign rifles that I have ever yet seen are rifled according to that principle; and several English gunmakers are firmly of opinion, that one turn in four feet [1:48] is the best angle possible. With these angles of rifle I never could fire at a long range to any degree of certainty. If I apportioned the powder to make it range at three hundred yards, I found the ball go very random; and from this I judged that the ball stripped over the top of the rifle, which caused it to fire as random as a common musket. In order to find out the cause of this evil, I rifled a barrel one turn in four feet [1:48] , and, on trial, found that the nearer I came to the straight line, the more true and further I could range. I then cut it to one foot, one quarter turn [Still 1:48, but less rotation to the point when the ball leaves the barrel] , and found I could fire more true at a short distance than I could when more angle in rifle. From this conviction, I made a barrel two feet six inches, and rifled it one quarter turn [1:120] . The experiment succeeded to my most sanguine expectation. I was perfectly satisfied, that I could range further, and more true, than in any previous trial, and with less elevation. In loading, also, the friction is not so great, and the ball is not so much impeded in coming out of the barrel by the angle in the rifle more approaching the straight line. Mr. Robins, in his Treatise on Gunnery, page 339, says, " Whatever tends to diminish the friction in rifle barrel pieces, tends " at the same time to render them more " complete.for the service."

Ezekiel Baker
Remarks on the Rifle Gun
1834 ed.

Twist rates in brackets are mine. I think I got 'em right.

Apparently they measured "twist in terms of fractions of a turn in a given barrel length.

A thirty-two inch barrel with a full turn twist would be 1:32, with a half turn it would be 1:64, etc.

Note, this is 1834 and before so prb is the projectile.

Old Coot

 

[paulvallandigham]

Yes, I agree. That is because by the 1830s, rifling was much better understood. But folks had been playing with the idea for a couple of hundred years by then. So-called " straight rifling " was tried, with little success in improving accuracy. It did make reloading easier without cleaning between rounds.

Much development of rifling was done during the 19th century, and about all we have done in the past 100 years is retest these ideas with barrels made on machines that have higher precision. New cartridges, higher velocities, better steels, better bullets, jacketed bullets, copper,brass, and other metal bullets, etc. have been tested, but the basic principles remain the same.

I don't know anyone who thinks the Greenhill formula is the answer for all projectiles, BTW. Certainly not for RBs, which are short range projectiles, and can be shot accurately out of much faster twist rate barrels than the formula suggests.

The OP asked if there was a minimum length of barrel needed for a slow twist barrel, and if so, why? and I think the answer has to remain " No." The only restriction on barrel length is a given barrel's ability to burn enough powder to generate velocity to allow the PRB to perform accurately at a given range.

Considering that we have short( 6-10") pistol length barrels that shoot RB very accurately, It would be very difficult to argue that there is much of a minimum barrel length, as he asks about, IMHO. While barrels made for BP pistols are often given faster ROTs, I have seen many pistols made from the ends of rifle barrels that were cut off barrel stock, and these pistols give good accuracy.

 

[CoyoteJoe]

Is there a minimum length for a barrel with a slow twist, say 1:66 or slower? If so, what might it be? And why?

msj

As your question is worded, I'd say yes! The real issue is the RPMs given the ball and that depends on both the rate of twist and the velocity. That is why barrels made expressly for pistols will have a faster twist, to keep RPMs up at the lower velocity usually expected of handguns. Many people have built pistols from cut off rifle barrels and generally are disappointed in the accuracy. So yes, there is a minimum velocity and therefore a minimum barrel length for any given twist, although it would be hard to say just what that length may be. :grin:

 

[JOHN L. HINNANT]

Good Afternoon NHmsj

Paul V. and Coyote Joe gave some good answers to your question, I will direct my reply in another direction.

As a rule 3FFF or 2FF black powder is most frequently used in rifles. 2FF will generally give a better burn-to-pressure-to-velocity ratio, in barrels 36 inchs and longer in the larger calibers, than will 3FFF black powder.

This is particularly true in calibers 50 and larger with barrel rifling twist 1-54" and slower.

The choice of using the most efficient burning powder (2FF or 3FFF black powder) in slow rifling twist barrels, usually breaks at 36 inch long barrels in 50 caliber.

That is not to say 3FFF should not or cannot be used in longer barrels of 50 caliber and larger. I have some very favorite 3FFF target loads for 25 and 50 yards in my 50 caliber Hawkens with 1-66", 1-70", and 1-72" twist rifled barrels.

These low pressure/low velocity loads are not the most accurate loads at 100 yards.

IN GENERAL, slow twist rifled barrels require higher velocities to obtain the best grouping accuracy past 50 yards.

Higher velocity comes only with higher breech pressures. That is a law of physics.

Grain weight for grain weight, in the same caliber and same barrel, the breech presuure curve of 3FFF black powder will spike higher and faster than 2FF black powder. For this reason, in calibers larger than 50 and slow twist rifling, 3FFF black powder may not develope the the higher velocity required to attain best accuracy (past 50 yards) without generating unsafe breech pressures.

Are there any exceptions to these general rules of thumb?

Certainly!!!! But I am not willing to trust my safety to exceptions.

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!!! US Freedoms Die!!!!

 

[NHmsj]

IN GENERAL, slow twist rifled barrels require higher velocities to obtain the best grouping accuracy past 50 yards.

Higher velocity comes only with higher breech pressures. That is a law of physics.

Grain weight for grain weight, in the same caliber and same barrel, the breech presuure curve of 3FFF black powder will spike higher and faster than 2FF black powder. For this reason, in calibers larger than 50 and slow twist rifling, 3FFF black powder may not develope the the higher velocity required to attain best accuracy (past 50 yards) without generating unsafe breech pressures.

Everyone, thank you all for such in depth and interesting information regards the question of slow twist and barrel length.

John, it's interesting that you should bring up the matter of powder grade - 2f vs. 3f. That is an issue I have been wrestling with as of late. I've read where a lot of guys swear by heavy loads of 3f, but the manufacturer of my rifle (T/C) discourages the use of such. However, I am not carrying the original short (27"), 1:48 twist barrel in the stock any longer. As one might guess from my original post, I replaced the stock barrel with a 31" 1:66 roundball barrel. As regards velocity, I have read that with a PRB one needs to be concerned with pushing the ball too hard, to avoid (triping over the rifling??) I have yet to load higher than 80 grains, but I am also not satisfied with the groups I am getting - yet. I have considered 3f, but whereas I have no way of knowing what's going on in the chamber pressure-wise, I am quite reluctant to use the 3f. T/C's max load restriction of 120 grains of 2f for a .54 cal PRB is given in conjuction with the use of the 27" 1:48 barrel. I have no manufacture guidelines for max load with the replacement barrel. From reading what you wrote I think I will stick with the 2f for now and push the load up closer to, or perhaps beyond, 100 grains. As it is, my patches have been showing absolutely no damage whatsoever. In fact, I've been a bit curious regards how little damage they display - no cuts or tears and only minimal "browning" of the patch; and I mean minimal. So, I guess from that fact alone, I am not yet near the max load for the present barrel. To get the accuracy I want I am hopeful, of course, that it is as you seem to indicate, simply a matter of the barrel wanting a heavier load, more velocity, to place those PRBs tighter together.

Hmmmmmm...I suppose I could call T/C and ask them what a max load would be for the replacement barrel.

msj

 

[JOHN L. HINNANT]

Good Afternoon NMmsj,

Some of my points need clarifying and a bit more detail.

Paul V. is very good at detail, so I will leave it to him to fill in my blanks. For now, let me try to add some detail to my previous post.

By way of beginning, my muzzle loading PRB shooting experience covers 55 years, come this mid August. This experience covers BOTH the hunting field and the competitive range. Ten years ago, my hunting ceased. There was just no longer any interest in killing animals.

Competitive AND informal ML rifle shooting is the main thrust of my ML shooting now.

Competitive PRB shooting 55 years ago at age 14 was my first ML shooting experience, and the ML rifle has always been my first love in the firearms field.

With all of that said, let us move on to some more explanation about my post.

To begin with, everything is relative, subject to the change of the variable components and conditions. So....what else is new or different?

In your particular case, with the 50 caliber 31" long barrel, my recommendation is 3FFF black powder with a max load of 85 grains. High velocity loads do not necessarialy equate to accuracy. That reference to slow twist rifling needing higher velocity to achieve maximum accuracy(ne:larger powder charges) is one of those relative situations.

The 3FFF powder will produce a, more efficient, cleaner burn in barrels shorter than 35"-36" long. With a 1-66" rifling twist, 80-85 grains will develope all of the velocity needed to maximize grouping accuracy.

More 3FFF black powder than this tends to accelerate and spike breech pressures quite rapidly, regardless of rifling twist.

3FFF black powder is the best choice for a damp, rainy day, giving better, faster, and more reliable ignition.

My accuracy testing starts at 25 yards, off the bench rest. (Be fore-warned; my quest and procedures for match-grade accuracy greatly irritates a number of ML Forum members).

The right combination of patch and ball diameter will produce a repeatable three shot group that will overlap and cluster into one large hole at the aforementioned 25 yards. In my 50 caliber rifles, the PRB combination is a .500" diameter ball with 0.017"-0.020" thick patch material.

Patch lubricant is of secondary importance to the right PRB combination.

Depending on the range and rifling twist, the powder charge will vary from 55-65 grains at 25 and 50 yards to 80- 120 (2FF powder only) grains at 100 yards. Both 2FF and 3FFF black powder is used.

It has been my long-time observed experiences that shooters who start using the Teflon coated patch material and suddenly improve their rifle's accuracy do so, because the patch material is of a more correct thickness and better grade of material, not the Teflon coated patch lube.

My personal favorite patch material with the proper ball size produces match grade accuracy regardless of what the lube is, be it spit, Windex, Black-Solve, some other commercial patch lube, or Teflon. Other may have experienced different results, but I do not and have not.

The purpose of any lube is to facilitate ease of loading. Any other lube benefits are secondary to ease of loading.

My .500" size balls are hand cast and weighed. I suggest, that if you are not casting balls, use a commercial swaged ball of 0.495 diameter for your 50 caliber barrel. The balls in the yellow box have always been the best choice for me.

With the 0.495 size ball. the 0.020" thick patch material will probably be the best choice.

If you have tried all of the various, powder/ patch/ball combinations, and are still unable to produce that tight, overlapping 3 shot group time after time at 25 yards, then other factors must be considered, and there are a number of them.

My loading recommendations for the PRB is a very tight combination. Many ML rifle shooters have an intense dislike for this tight PRB fit and prefer to accept a lesser standard of accuracy in exchange for ease of loading.

This is a decision you might want to make. Everybody sets their own parameters, and this is not a problem for me.

In the meantime,

Best regards and good shooting,

John L. Hinnant

If you are not an NRA or NMLRA Member, why not? I am carrying you load.

Liberal Politicians Lie!!! US Freedoms Die!!!

 

[paulvallandigham]

John is correct. What he wants in accuracy is considerbly different than what the vast majority of MLers desire. But, the vast majority shoot BP simply as another way to enjoy hunting, and plinking. Making small groups in bullseyes at measured distances just doesn't do it for most shooters.

Having said that, there are very few shooters who don't appreciate the value of the work done by target shooters. Its the target shooters who have demanded better barrels, better molds, better quality control in making powders, percussion caps, better locks, and even better lubricants. All this has allowed the vast majority of Mlers to shoot better, with less practice, than our ancestors could possibly dream of doing.

The wonderful thing about shooting is that it allows the FREE EXERCISE of your Right To Choose what you do. For many people, this is about the only truly FREE WILL act they ever do.

Think about that. I believe its just one more reason its so important to maintain and keep alive our Full Second Amendment-guaranteed rights, and not allow Governments to turn them into " privileges".

 

[roundball]

I suppose I could call T/C and ask them what a max load would be for the replacement barrel.

TC makes no distinction between load data for their 28" x 1:48" and their 30-32" x 1:66" barrels...I've lived by their load data charts for years in my TC 1:66's and GM drop-in 1:70's/1:72'...several calibers and gauges using Goex 3F hunting loads in all of them...not a problem

 

[NHmsj]

Hey John, thank you for your load advice concerning my T/C 1:66 31" RB barrel. However, the barrel isn't a .50 cal., it's a .54. I am sorry if I somehow gave the impression I was dealing with a 50. As it has been pointed out by Roundball, I now understand T/C makes no distinction between it's shorter, 1:48 twist barrel and their longer, 1:66 twist barrels - regards max loads, anyway. So, it would appear that T/C's suggested max load for the barrel in question is 120 grs of 2f when loading a PRB. Would you again make a recommendation as to what you might feel could be a possible accurate load, a reasonable starting point, for this .54 cal barrel with either 2f and/or 3f? I'll be pushing a .535 RB wraped in .018 ticking down the bore - probably lubed with Crisco from my lovely wife's kitchen cupboard.

msj

 

[paulvallandigham]

At 100 yds, a load of 80 grains of FFFg powder, or 90 grains of FFg should be more than adequate, and within the range of best accuracy for that gun. Starting loads can begin at 50 grains of FFg, using a OP wad to help improve burning speed, and chamber pressure using FFg powder. That will work for 25 yard shooting, and small game hunting. 60-70 grains will usually produce the best groups out at 50 yards. Work up to the load that is most accurate for your gun. Understand that you will lose 25% of the Muzzle Velocity of your PRB at 50 yds, and 45% of the MV at 100 yards. YOu aren't going to change that fact. But those big, 235 grain RBs pack a huge punch, inside 100 yards, where most deer are shot. When you consider your ability to shoot off-hand, and to shoot iron sights, a 100 yard shot is a very long shot. When in doubt that you can make a clean kill, DON'T SHOOT! Its far better to have a story about the one that got away, than the wounded one that you lost.

 

[JOHN L. HINNANT]

Good Evening NH,

My apologies for not replying sooner. Have been away from the old homestead for an extended time.

My comments about a 50 caliber would apply equally to a 54 caliber with a 31 inch long barrel or a 36 inch plus long barrel.

Paul's recommendations about 2FF and 3FFF black powder are good.

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!!! US Freedoms DIE!!!!

 

[roundball]

"...a lot of guys swear by heavy loads of 3f, but the manufacturer of my rifle (T/C) discourages the use of such..."

I've been a TC user for 17+ years...I can't agree with that statement the way you wrote it...what TC has done for over 30 years is publish a manual with 2F load data...as most manufacturers do because 2F is sort of the baseline reference standard.
But blackpowder is blackpowder...2F and 3F granulations are made at the same time off the same manufacturing run, with the different sized particles being screened off to be sold as 2F, 3F, 4F, etc.
A common rule of thumb if you want to use 3F is to just reduce a 2F load data by 10-15% to keep pressures in the same ballpark...ie: if you wanted to substitute 3F in place of a 100grn 2F charge, just use 85-90grns of 3F.

As regards velocity, I have read that with a PRB one needs to be concerned with pushing the ball too hard, to avoid (triping over the rifling??)

Old wives tale left over from a poor quality, shallow 3 land/3 groove military import back in the 50's...I've driven my TC .45/.50/.54cal 1:48" barrels with TC's max PRB loads and get groups as small as 1+7/8" to 2+3/4" at 100yds with 62 year old eyes.

I am quite reluctant to use the 3f. T/C's max load restriction of 120 grains of 2f for a .54 cal PRB is given in conjuction with the use of the 27" 1:48 barrel. I have no manufacture guidelines for max load with the replacement barrel.

No difference in TC's barrels regarding load data...and just reduce that 120grn 2F load data 15% and use 102grns 3F...(I just round it off to 100) and use Goex 3F that way...I use 3F all my calibers, .40/.45/.50/.54/.58/.62.

 

[NHmsj]

Hey guys,

Thanks for the advice regards powder granulations and loads for my .54 and for enlightening me concerning some misconceptions on my part regarding such. The advice I have received on this forum is remarkable, indeed. Great stuff that is proving to be spot on! I am now to the point of occasionally cutting one ragged hole with three, and sometimes four, shots off the bench at 50yds using a 85gr ffg load behind a .535 PRB using .018 patches. I am quite pleased, to say the least. My offhand groups are, of course, a bit more spread out, but I am equally pleased to say I am at least getting most on the black (a large black admittedly, but smaller than the vitals of a Whitetail.) I thank you men for your most generous and experienced guidance here with your kind advice. What a stroke of good luck it was for me to find this site. :grin:

msj