Powder charge & twist rate as functions for accuracy?

[Naphtali]

As I was writing Steve Zihn, a question popped into my head I have not considered before.

Forsythe rifling, as I understand it, is an extremely slow rate of twist. It is intended to allow the shooter to hugely increase his propellant charge behind a round ball for substantial increase in velocity.

I have .72-caliber barrels with 1:72 inches twist - definitely faster than would be Forsythe rifling. Has anyone confirmed an upper limit on amount of FFg that can be used to shoot RBs above which the ball strips the rifling and accuracy goes to pot?

Or a little differently, has anyone confirmed a upper limit on muzzle velocity for .72-caliber (.715 + .015) patched balls above which the ball strips the rifling and accuracy goes to pot?

 

[Rifleman1776]

Yours is a gigantic question and the basis of many other ml issues often cussed and discussed. Something on the order of: "Why is light light"?
I don't know anything about Forsythe rifling, but the essence of your question really has nothing to do with Forsythe, or Einstein or Joe the tobbacco spitter.
Best charges and/or velocities with any given twist boil down to what finds the 'X's the best. Some claim with a .45 cal. rb and xx grains of bp in a 1:48 twist will strip the patching. Others say you can't strip the patching no matter what charge you use. As the jug rounds the campfire for the fifth or tenth time a comment will be made about .72 cal. and what charges will strip the rifling.
I really don't know what charges it takes to strip the prb in any given twist.
For the .72 you are wondering about, I'll take an experienced guesstimate that, if it is possible to strip the patching with a round ball that size, shooting the charge required would possibly put the shooter in the hospital with a ruined shoulder.
Bottom line: don't sweat it, the ball/patch/charge combo that does the best job of finding the 'X's is all you need be concerned about. Excepting, of course, safety issues.
OK, now is the time for somebody to jump in with the arguments about rifling styles and groove depths and phases of the moon. :shocked2:

 

[aeatwood]

Some of the guys with .72 Kodiak doubles were using up to 170gr of 777 to get them to regulate. I had one for a while, and now I have the Pedersoli .72 Gibbs African. I have never actually gotten a blown patch. I had some cut patches 'til I radius'ed the sharp edges off the crown w/ emery paper. The Pedersoli's are _almost_ forsythe barrels. The twist is a little fast, but they use narrow lands and shallow grooves, and seem to react well.

I have gone up to 140gr of 2F, and 150gr of 1F and not blown the patches. Don't forget that ball diameter and patch thickness are also in play. I started w/ a Lyman .715 mould that was actually casting .719" out of my alloy. I couldn't load over a .10" patch with that combination.

I have since moved to a Jeff Tanner mould listed as .710 and casting .714, and can go to a .015" patch, which is still a little thin to suit my tases. (I'm casting up range scrap for the most part, with a bit of tin to help the casting characteristics of the melt.) I'm using ToW mink oil or olive oil, or spit for patch lube.

 

[paulvallandigham]

Large balls tend to upset quickly in the rifled barrels, even at low velocity, because the mass( ie. weight)is so great to overcome.

The 1:72 rifling came about in the late 18th century when it was thought that the best accuracy came from rifled barrel where the ball rotate one complete turn in the length of the barrel, and 6 foot long barrels( 72 inches) were not unusual.

Then, it was next thought that the rifling should be equal to the caliber. That allowed barrels to be shorter, and the guns to weigh less.

Remember that at the time, there was "Cannon" powder, and musket powder- not the grading we experience today.

I don't know how much powder a given 72 caliber barrel can safely soot behind a lead ball. I don't WANT to know. I have fired an 8 gauge(.835" caliber) smoothbore loaded with 6 drams( 165 grains of FFg Goex powder, and pushing 3 oz.(1312.5 grains) of shot! That gave as much recoil as I want to experience. I have also fired a .50-140-550 Sharps rifle, using a full case(140 grains FFFg Goex) powder behind a cast, 550 grain bullet.

Both guns say "HELLO" with authority. :shocked2:

Loading the big bore guns is not an issue of velocity. Its more an issue of felt recoil forces for a given powder charge. The 12 ga. ball will weigh between 1 ounce ana 1 1/8 ounce, depending on actual diameter. There are 437.5 grains to the ounce][7000 grains to the pound], making the analogy to shooting a freight car out of a gun a very real description of what happens on the receiving ends-both the target, and the shoulder behind the butt.

Accuracy is much more important than Muzzle velocity when sending such a large diameter, HEAVY lead ball at a target- especially living flesh.

Start with light powder charges, and work up from there, shooting 3 to 5-shot groups until you find a load that produces the smallest groups. The second edition of the Lyman Black Powder Reloading Manual has some loading data for these large bore calibers. Most people start out using loads of 60 grains of FFg powder, and work on up. Hunting loads are often 100-120 grains of FFg powder, but some are finding that using Fg powder in these large guns gives less recoil and better accuracy.

That's the best advice I can give regarding working up loads in your gun. NOT all barrels are the same design, the same thickness, nor made of the same steel alloys. Keep that in mind when looking at loading data in any book or website. Unless you have the money and the desire to find out how much powder it takes to blow up a gun barrel, there is no point to putting more powder in a barrel than will reasonably shoot accurately in the gun, with recoil that the shoot. :hmm: :hatsoff:

 

[nkbj]

I have a .696" bored Fremont with shallow three groove minie rifling that will let a patched ball sail down the bore as though it were smooth. Which only makes sense when you think about it seeing as in essence it is a smoothbore with imperfections. To get it to behave you stick a lube soaked 14 ga. fiber wad under the patched ball. The wad expands into the rifling, conforms to the ball, seals the bore and everything is ducky.

 

[Naphtali]

Many thanks for your reply. My first loads through my Kodiak Safari was 150-grains Goex FFg with my custom 775-grain bullet. Accuracy was excellent. Recoil blooded and bruised my left arm (shooting shoulder) from clavicle to just below my elbow. Two things happened: I had a Pachmayr simulated leather Decelerator® (sp??) pad installed, and I regulated the rifle to shoot 110-grains FFg. Unfortunately, the projectile, being a squat conical, furnishes no information pertaining to the effect of large quantities of powder when shooting patched RBs as it furnishes a great deal of useful information about the quality of Kodiak Safaris.

What I do know is that Kodiak Safaris are capable of efficiently shooting anything that moves in North America - to 85 yards - and dropping it like a sack of potatoes falling off a table. And when regulated, such loads will shoot clover leaves at that distance. The downsides are that each barrel takes about five minutes to load, and the loading rod is useless for loading such projectiles.

 

[Rifleman1776]

Recoil blooded and bruised my left arm (shooting shoulder) from clavicle to just below my elbow

I have been there and experienced that. Saying "it hurt" is an understatement.
I once bought an experimental original CW rifle musket from a Gettysburg dealer. It was .72 cal. with a 12 grove, round lands and bottoms. The breech was a very long, Nock type, that was much smaller than the bore. That meant I had to load a minimum of 120 grains of bp, I used 2Fg. to avoid an air space. (BTW: it paid to take it to an ml expert gunsmith for checking out before it shot it. That was 'Ole Pefesser Wilford Shaw at Friendship, In. He discovered the potential for disaster if I underloaded.)
Back to topic. :redface:
The .715 round ball weighed about a full ounce. When I shot the recoil was notable. I could shoot three shots before the flinchies started because I knew the pain was coming. Those first (only) three shots were very accurat.
Sold it. That was a misteak. Pain and all, it was a neat old gun and would have made a great hunter.

 

[aeatwood]

Actually, the .66 (16-bore) weighs an ounce (437 gr.). The .715 weighs 545 gr.

The Kodiaks were designed to shoot ball. I would NEVER trust a conical to stay put on a double rifle. I doubt you could get a 725 gr conical much over 1000fps and stand to shoot it.

The .72 Gibbs is stocked WONDERFULLY. A 9.5 lb rifle that kicks less than the 10.5 lb double. And the 530+ gr. .710 ball will shoot through anything in N.A.

 

As I was writing Steve Zihn, a question popped into my head I have not considered before.

Why not ask "Steve"?

 

[Loyalist Dave]

Part of the question is based on the style of rifling as well, depth plus round or square bottom, for how the grooves are shaped will effect how the patch is gripped by the barrel.

At the very beginning of the 19th century, it was thought, in British military circles, that at least 1/4 turn was needed on a round ball to stablize it enough to warrant the added cost of a thicker barrel, and the added step of rifling. (Instructions for The Formations and Exercise of Volunteer Sharp-Shooters by Barber 1804) If this is applied to a Baker rifle of the period with a 30" barrel..., that's a 1:120 rate of twist. :shocked2:

The problem with this observation is that it was made regarding combat rifles, with less need for precise accuracy, and greater need for multiple shots prior to cleaning, than in a civilian target or hunting weapon. You don't have to hit the enemy soldier in the heart at 300 yards..., anywhere from knees to forehead will do. :wink:

So in common, modern, muzzleloading, rifle barrels we find that anywhere from 1/2 turn on up to almost a full turn may be found. The TC Hawken with 1:48 gives just slightly more than a 1/2 turn with a 28" barrel, while the Pedersoli Jaeger has a 1:24 twist in the same length barrel so gives slightly more than a full twist. A barrel with 1:56 gives a bit more than a 1/2 turn from a 38" barrel, and when you stretch that to a 42" barrel you get a 3/4 turn. Even a "slow" twist of 1:70 gives you more than a 1/2 turn in a 42" barrel.

So it appears that somewhat more than 1/2 twist will work for calibers out to .62. Beyond that who can say for as pointed out, the mass of the projectile starts to really influence the rifling.., AND..., what about gain-twist rifling to overcome the bullet mass as well as the Forsythe rifling?

:hmm:

LD

 

[Rifleman1776]

Although it was belived so, barrel length has nothing to do with rate of twist or ball spin. A one foot barrel will put just as much spin on a ball as a six foot barrel.

 

[Naphtali]

. . . I would NEVER trust a conical to stay put on a double rifle. I doubt you could get a 725 gr conical much over 1000fps and stand to shoot it. . .

Alan:

I wish I still had access to a chronograph to identify MVs for 110, 120, and 150 grains FFg with the squat conical (30:1). The tests that we did were comparative penetration tests. Our "control" was Barnes Triple Shock 150-grain bullet at 3100 fps from a .30-06. Tests were conducted at 15 yards into duct taped dry Encyclopedias. Tested also were LFN GC 425-grain 45-70 bullets (WW + 2). One variation was air dropped. The other was heat treated for hardness.

Regarding reloading safety - that is, having the unfired bullet dislodge forward during recoil - that was my first test. Two of us fired 20 rounds of 120-grains Goex FFg from right barrel while leaving the left barrel charged. One hundred twenty grains was my first step toward sanity after the shoulder breakers. The unfired bullet did not move - as measured by witness marks on my loading rod.

I would have been surprised if it had moved. Loading force required is high. That's the reason why it takes so long to load each barrel. That's the reason why I'm investigating RBs. The Kodiak Safari shooting my loads is a first-class tool. But its reality is: Two shots and you darn well better not need another.