Long Barrels And Round Ball

[nkbj]

This is just something wondered about.
Everybody knows that soft lead bullets expand somewhat inside the barrel as a function of pressure versus inertia. When they get hit from behind their resistance to movement is expressed in a swelling of their profile. It doesn't happen at once and loads are adjusted accordingly to avoid gas cutting and to achieve accuracy. Engineering of a 19th Century weapons system had to include all those considerations. So, to get back to my thoughts about this, with a really long barrel like the forty some odd inch lengths of yesteryear... In longer barrels did those light weight bullets (round ball) have time to start expanding and filling out the rifling grooves for better shooting?

The most accurate shooting round ball gun I've ever had is an unwieldy booger* with a 43" long barrel, something that makes no sense at all if you're talking about a cloth patch skidding down a length of machined steel. I've begun to suspect that perhaps the accuracy is a function of the longer barrel dwell time allowing the bullets of low mass (of low resistance to acceleration) sufficient time to conform to the rifling in a uniform manner.

*Dixie Gun Works, early 1980's.

 

[TreeMan]

I can’t answer your question directly but I do dig a lot of shot roundballs out of the dirt and most of them are still perfectly round. Some could be loaded and shot again.

 

[Johnny Too-Tall]

Round balls don't or shouldn't touch the rifling ever. Thats the job of the patch to grab and sink into the rifled grooves and spin the ball. If you have ever recovered a round ball that "sunk or swelled into the groove of rifling there would be grooved cuts into the ball and that's not the case.

 

[Phil Coffins]

My thoughts on long barrels are the longer sight radius allows finer aim hence better accuracy. Also peak pressure and obturation of the ball happens in the first few inches of the barrel.

 

[oldwood]

Only Time I ever noted any obturation in my .50 round balls shot out of a "C" wt. Getz 44 " barrel , is when the ball smacked into some object. 80 gr. fffg.

 

[Tumbledown]

Everybody knows? Everybody knows you are quite wrong. Lead does not expand to fill rifling grooves. Bullets are made slightly larger than the bore so they engage the rifling. That was a big reason muzzleloading rifles were so slow to load. The Ferguson (sp?) and Hall rifles were attempts to overcome this by loading the ball from the breech. In cartridge guns, bullets were "patched" (jacketed) with paper or copper to get a better gas seal and reduce obduration in the barrel, particularly as velocities increased.

One exception to this is the Minnie ball, which has a thin skirt designed to flare out and engage the rifling, which is VERY shallow. In this case, the bullet and barrel are designed to work together. But the body of the bullet does not expand.

Patched round balls do not go skidding down the barrel. The patch engages the rifling from the start. The slower twist helps ensure the patching engages the rifling and does NOT skid by.

 

[Phil Coffins]

Reading “The Bullets Flight” by Dr. Mann can be an eye opening experience to the individual that doesn’t understands what happens when a projectile is launched by the explosion of gun powder.

 

[nkbj]

Round balls don't or shouldn't touch the rifling ever. Thats the job of the patch to grab and sink into the rifled grooves and spin the ball. If you have ever recovered a round ball that "sunk or swelled into the groove of rifling there would be grooved cuts into the ball and that's not the case.

Not that a ball could expand enough to fill the rifling grooves as do heavy bullets but rather could expand sufficiently against the bore (the rifling lands) to produce more consistent accuracy. My accuracy load in the 43" long fifty caliber barrel is 90 grains of FFg. When started into the bore the .49" ball has compression grooves pushed into it (imprinted with the warp and woof of the ticking patch) by the rifling lands. Perhaps it experiences some expansion when spanked by 90 grains and maybe it doesn't, but that's the conjecture stated above.

 

[Johnny Too-Tall]

Not that a ball could expand enough to fill the rifling grooves as do heavy bullets but rather could expand sufficiently against the bore (the rifling lands) to produce more consistent accuracy. My accuracy load in the 43" long fifty caliber barrel is 90 grains of FFg. When started into the bore the .49" ball has compression grooves pushed into it (imprinted with the warp and woof of the ticking patch) by the rifling lands. Perhaps it experiences some expansion when spanked by 90 grains and maybe it doesn't, but that's the conjecture stated above.

Sorry I started to laugh a bit.. Not at you but I envisioned the prb coming out the barrel looking like one of the Frito Lays Honey BBQ Flavor Twist I am currently snacking on.

 

[nkbj]

Reading “The Bullets Flight” by Dr. Mann can be an eye opening experience to the individual that doesn’t understands what happens when a projectile is launched by the explosion of gun powder.

Yes indeed. A maker of muzzleloading rifle barrels surprised me years ago by mentioning that shallow grooves aren't needed for guns shooting heavy bullets, that deeper grooves will shoot accurately also. I was taken a'back by that because I'd thought shallow would naturally be better because the less the bullet had to expand then yeah, the more consistent it could be from shot to shot.

And then I realized oh duh, what about all those people shooting round sized and lubed bullets in their Whitworth's with fast twist hexagonal cross section bores. With the bullets expanding to fill the corners on the hexagon that's about as "deep" of rifling as you're liable to see!

 

[nkbj]

Sorry I started to laugh a bit.. Not at you but I envisioned the prb coming out the barrel looking like one of the Frito Lays Honey BBQ Flavor Twist I am currently snacking on.

That's kinda what long bullets coming out of my TC New Englander resemble, just not so tight of a twist. It was a .54 with that gosh awful "quick load" counterbored muzzle. Got it relined in 2011 to .458" bore with 24" twist. I shoot .45-70 molds in it cast from straight lead, sizing them to .457" diameter after lubing or paper patching, which ever way I'm shooting them.

 

[oldwood]

In the mid 1970's , discussed the physics of patched round balls , and rifling , vs. black powder rifle barrels w/ **** and Donnie Getz in their shop. They said a patched round ball works due to the slow pressure gradient encountered with black powder when ignited. Modern cartridge powder is more violent in a shorter time , and a patch would burn up , shread , just as the lead bearing steel of a modern m/l barrel exploded due to too high pressure , applied too quickly. Black powder is lower pressure , and ideal for the patch ball combination. No initial obturation can be noted. A properly fit patched ball , if unloaded with a CO2 ball remover , will show the imprint of the rifling , including the imprint of the patch fabric weave , if the lead is dead soft.

 

[Kevin]

Oldwood is correct

 

[snakebit]

Sorry I started to laugh a bit.. Not at you but I envisioned the prb coming out the barrel looking like one of the Frito Lays Honey BBQ Flavor Twist I am currently snacking on.

 

[longcruise]

My thoughts on the ball upsetting to the bore are like illustrated in the drawing below. Since the ball is round, the pressure is being applied around the ball rather than straight forward as on the base of a flat based or hollow base bullet.

Bullets do upset immediately and obturate the bore in black powder loadings. BP is lower pressure than smokeless but it burns faster than smokeless. The pressure is lower but immediate and it immediately expands the bullet which is essentially a stack of soft lead. The taller the stack the more it expands at the base.

This is the concept applied to the maxi ball. The front driving band is ideally the same diameter as the grooves while the base is ideally the same diameter as the lands. The base aligns with the bore and the front band also aligns. With a proper fit, the base immediately upsets evenly and the front band less because it's at the top of the lead stack.

The fly in the ointment with the maxi and I'm sure other conicals is that not all molds cast the same exact size AND not all barrels meet exact specs. So, some combos might shoot lights out and others 8 moa.

When the 1873 TD and it's ammo went through development it was eventually realized that bullets for the 45-70 cartridge could be undersized and still shoot well because the BP would expand the bullet before it left the case. OTOH, shooting lead bullets in suppository guns and modern powders need a bullet slightly over groove diameter because even though the pressure peak and max pressure are higher, they occur too late to adequately bump the bullet up and serious leading can occur.

 

[boberator]

My thoughts on long barrels are the longer sight radius allows finer aim hence better accuracy. Also peak pressure and obturation of the ball happens in the first few inches of the barrel.

I agree with the longer sight radius Phil. Even with the rear sight set a little more forward than usual for those who need that because of older eyes, the sight radius is long enough to increase accuracy. I can’t really shoot any of my unmentionables with iron sights because trying to keep the rear sight in focus as well as the target because of shorter barrels.

 

[nkbj]

The acceleration (ft/sec/sec) applied creates the reduction in length of a bullet.
The softer the bullet the less resistance it has to being shortened.
The longer the bullet the greater the reduction in length for any given amount of acceleration.
The further back from the nose then the more so the lateral movement of metal.

Said all that to say this.
Accelerating a round ball to 2000FPS quicker than you can appreciate Bridget Bardot does inevitably produce a shortening of a soft lead round ball and therefore it does try to increase in diameter at 90 degrees to the direction of the acceleration. The question is how much. Is it enough to put a little extra outward pressure on the patch and rifling lands? I don't know.

 

[Phil Coffins]

The acceleration (ft/sec/sec) applied creates the reduction in length of a bullet.
The softer the bullet the less resistance it has to being shortened.
The longer the bullet the greater the reduction in length for any given amount of acceleration.
The further back from the nose then the more so the lateral movement of metal.

Said all that to say this.
Accelerating a round ball to 2000FPS quicker than you can appreciate Bridget Bardot does inevitably produce a shortening of a soft lead round ball and therefore it does try to increase in diameter at 90 degrees to the direction of the acceleration. The question is how much. Is it enough to put a little extra outward pressure on the patch and rifling lands? I don't know.

Yes, Mann’s book documents that even with jacketed bullets. He spent years measuring and testing in a very detailed manner.

 

[longcruise]

Accelerating a round ball to 2000FPS quicker than you can appreciate Bridget Bardot does inevitably produce a shortening of a soft lead round ball

Given that those same forces are being applied to the bottom half of the sphere then there is a powerful force keeping it round.

 

[Gordoncourtney]

Given that those same forces are being applied to the bottom half of the sphere then there is a powerful force keeping it round.

I must read this string again friend told me a round bullet loaded into a hexagonal whitworth barrel ended up at the back stop clay like an hexagonal whitworh bullet , such was the force of the explosion

Long and short barrels, ok. It’s a •5 bp 1880 unmentionable Good photo. Not by me