ballistics question

[dlpowell]

Reviewing the load info for 54 cal in Lymans 2nd edition bp manual shows better ballistics from a 24" barrel with a 1 in 48 twist than a 32" barrel with a 1 in 60 twist. Exact load is 90 gr Goex FF, .535 rb, .015 patch pre-lubed.

I happen to own guns that match the test guns and know the 32" barrel does a better job at containing large loads of powder to burn. At the range there is a big difference in the sound of the guns when fired. The 32" is much louder.

I just don't believe that 24" barrel length is better than 32" barrel.

Can the better ballistics be due to the twist

 

[CoyoteJoe]

If you do a detailed study of the ballistics in Lyman's manual you will find many seeming misfits of that sort and even more if you compare the first edition to the second. I'm sure the Lyman staff did their best but unexplainable phenomena do crop up. Compare several different manuals for reloading modern cartridges and you will also find several different "max loads" and very different velocities for the same load.
I would expect the 32" barrel to produce a good 200fps more then the 24" barrel but this all goes to show that we really don't know what happens inside a gun barrel. We have theories that have come to be accepted as fact but sometimes things come up that don't fit the theory and we really don't KNOW. :grin:

 

[BrownBear]

It could be something as basic as a tight patch/ball fit in the 24" and a loose one in the 32". If you look again, they also use different powders from one gun to the next, and that is a significant source of velocity variation.

I use the Lyman manuals for frame of reference to get some idea of safe boundaries for my loads, but I never expect to get their exact results. When I'm serious about my own numbers I drag my chrony to the range, but mostly I'd much rather shoot than play with that.

 

[paulvallandigham]

The tighter ROT makes more resistence in the barrel, longer barrel time for the PRB, and you burn more powder in the barrel. The slower ROT allows the ball to move out easier, and you will be burning more powder outside the muzzle, and hence have a bigger sound when the gun is fired. The sound you hear is expanding gases pushing the air away, and then the air coming back in to fill the void. The bigger the amount of gas that expands outside the muzzle, the louder the noise. It is the same principle for muzzle brakes, and silencers, for BP and smokeless.

The Slower rate of twist allows you to shoot ROUND Ball loads without much concern about how much powder you pour down the barrel. At short range they are going to hit the same POI even if you are off by 5 grains one way or another. The Faster ROT is designed to allow you to shoot conical bullets, sabots, and modern, copper Jacketed Pistol bullets. With the Conicals, Sabots and pistol bullets, you increase the friction of the projectile to the bore, and with the fast ROT you also increase the barrel time for the projectile. All this allows for burning more powder, which also produces more recoil forces for your shoulder. Remember to add half the weight of the powder charge to the total weight of the sabot, and bullet, when calculating recoil, as BP does not detonate like Smokeless, but burns progressively, which means that part of the powder is being pushed down the barrel with the projectile. What every goes forward, produces and equal and opposite reaction( force). Hence more recoil. When someone tries to make a super Sharpes buffalo rifle out of a .50 or .54 cal. fast twist, short barreled rifle with one of those actions we don't discuss here. those large powder charge do become a problem. When reading those charts, pay particular attention to the differences noted for the guns and loads. Otherwise you might think you are driving a sports car, when instead you are stepping into the cab of a Semi.

 

Paul, I have to respectfully disagree with you that smokeless detonates. It is classed as a propellant and is progressive burning. Black powder is a class A explosive and burns quicker than smokeless. You can perform a simple experiment by pouring a small amount of black and your choice of smokeless on something safe and igniting them with a match. Get out of the way of black powder as it explodes and you will have a little trouble getting the smokeless to ignite. The difference between slower and faster burning smokeless powders is also readily apparant. I know this changes as pressure inside the chamber and barrel increases but the fact remains that smokeless is considerably more a propellant with controlled burn than black powder.

The size of the hole and length of the granules in extruded powders controls the rate of burn. In flake powders the thickness of the flake and size of the hole controls the burning rate. I have no idea how it's done in ball powders.

Maybe I misunderstand what you posted and if so....ignore this post....hehehe.

Vic

 

[Blizzard of '93]

Some dependence on type of smokeless powder, flake is used in both shot-shell and pistol cartidges. Extruded is rifle cartidge powder (crimped neck) and ball is generally a 'magnum' pistol or small rifle (.30 carbine, AK-47)powder, both with a 'crimp' generally tight, and pistol cartride uses a 'magnum' primer with ball. Also there is more resistance on the bullet (generally cooper jacketed) being driven down the barrel which generally has a much faster twist than a muzzler. This is why pressure peaks occur with smokeless. It's nearly impossible to blow a BP pistols chambers, but fairly common with a smokeless powder one, due to the rapid burn rate contributed to the pressure peaks.

 

[paulvallandigham]

Sharps 4590: Powder burns differently in the open than in a closed environment. I have had black powder both explode on touching it with a source of heat, and I have had it fizzle and burn slowly like a fuse. In an open air enviromment, smokeless powder burns slowly. Put it in a closed container, and its a different deal. The pressure spike is very immediates, and many times higher than Black powder pressure ever dreams of reaching. Black powder burns progressively in your barrel, so that the pressure curve looks like a Bell, and not a ski jump. The barrels on ML rifles are left heavy to the end of the forestock to take that pressure, while modern barrels are slimmed down in front of the breech, as all the pressure is taken in that brief area that is the chamber and maybe one inch of the bore of the gun. As the ball or bullet progresses down the barrel, in ML guns, the pressure is also reducing slowly, In smokelss guns, its already down within inches of the mouth of the casing. Of course the pressure is still adequate to propel the bullet down the barrel and down range, but Black Powder barrel pressure are relatively higher out to the muzzle than comparable modern guns.

I recall years ago, in the Buckskin Report, seeing a burst barrel on a hawkin styled rifle, ruptured where the first barrel keyway was cut. The dovetail notch was too deep, and the pressure in the barrel ruptured the barrel at that point. It is located many inches in front of the breechplug, about where they figured the peak pressure of the rifle was delivered in the bore! The gun in question was made by a foreign maker where they were totally new to Black powder guns.

 

Paul: The realization that both powders react differently in the confines of a cartridge and a chamber was the last sentence in my first paragraph. I'm fully aware of that and so stated.

The most recent transducer derived oscilliscope time/pressure curve readings I saw, within the last year, indicated that black and smokeless were a lot more similar in the chamber and barrel than previously believed. I believe Double Gun Journal published the results of considerable testing. Black definitely had a longer curve after ignition and initial spike, but nothing that resemebled a bell. The initial spikes were quite similar in time. Obviously the peak pressures were considerably different.

I took exception to you calling black powder progressive burning, which it isn't, and saying smokeless powder detonates, which it doesn't. Smokeless is a progressive burning propellant and the higher the pressure the more progressively it burns, so much so that it burns incredibly faster than black, thus the much higher chamber pressures, velocities, et al. You observations of the thickness of a smokeless powder rifle chamber and the area immediately in front of the chamber are spot on. Even tho the barrel after that is thinner than a muzzleloader the pressures until the bullet exits are considerably higher than muzzleloaders. That the barrel holds the pressure is a function of the metallurgy of the barrel and time, (there, I've said ALL I know about that part of it).

Black powder is an explosive. It is an explosive that ignites at a low temperature and it "all goes at once", unless the powder is contaminated by moisture. I've never seen black powder that was dry or of the grain size used in firearms do anything less than ignite immediately. Maybe you have, but I haven't. The "all going at once" takes a while with black powder as compared to the progressive burn of smokeless, so yes, it continues to burn/explode some of the length of the barrel. Perhaps the entire length of the barrel depending on barrel length, bore size, powder charge and projectile weight. And yes, the increase of pressure helps it to burn more COMPLETELY, (cleaner), and that does impart more power to the projectile. I'll agree to that in a heartbeat. But to call it a progressively burning powder is incorrect. There's nothing progressive about it, as compared to smokeless, except that it "progresses" down the barrel as it is exploding. Why do you believe the haz-mat charges are so high on black as compared to smokeless?


Vic

 

[paulvallandigham]

I suspect that our disagreement is only a function of semantics, Vic. The industry has made the term " progressive burning ", a term of art, while it also has a generel meaning to readers. Detonate is the term I was given years ago to describe how smokeless differs in its burning rate from black powder. The Ski Jump look to its pressure curve, where the pressure rises to its peak, and then quickly falls off to lower levels as the powder completes its burning, and the bullet moves down the barrel, increasing the size of the chamber that has to control and hold back the pressure. No doubt that smokeless powders give considerably more pressure in the barrel, and that is why modern barrels are made of steel alloys, and heat treated for best use. I am convinced that in some black powder rifles the powder completes its burn before the muzzle and that explains why more debris, and powder residue are sometimes left near the muzzle.

 

[Blizzard of '93]

Or when using too much powder you will see a big flame in front of the muzzle and unburnt powder blown out in front.

 

Paul, I'll agree to that! Another thing I've noticed is that the lighter the powder charge and to some extent the length of the barrel determines how far back from the muzzle that....uhhhh....."peak fouling", (for lack of a better word), area is

 

[faw3]

Well all this has been over my head, dont know about you. All the pics Ive seen lately show BP to burn in the first 24 to 26 " of barrel a fast high peak right back down to about nothing, two test run had a 40 something " barrel with the same load everytime cut back 50 or more " each shot and the 40 down to 24 or 26 " was around 150 fps. Not much of a loss. Fred :hatsoff:

 

[paulvallandigham]

Fred: I have a double barreled 12 ga. percussion shotgun with 28 inch barrels, and my fowler has a .20 ga. 30 inch barrel. Both shoot well, and I don't perceive any measureable or useful loss in velocities in either. I say that because all the tables on down range velocity and energy per pellet indicate that most of the velocity is lost in the first 20 yds. The real difference is the percentage of velocity that is lost with the high velocity loads compared to low velocity loads. When You shoot loads at 1300 fps, you can lose up to 40% of the velocity in the first 20 yds! At 40 yds, difference in velocity between the 1300 MV load, and the 1050 MV load is less than 100 fps. And, the time to target difference is so small that you can't hold that close. All the higher velocity loads give is blown patterns and more recoil. Only if you are using a gun that is choked, and you are also using the modern plastic shot cups and wads to protect the shot in the barrel from rubbing against the inside of the barrel and developing flats can you take advantage of that extra velocity by still holding tighter patterns at longer yardage. And, I believe that shooting the lower velocity loads with those extras( choke, and plastic wad) give even better patterns, based on my observations and experience.

So, I will continue to recommend lighter loads for better patterns. In open cylinder guns, I recommend using heavier sized shot for hunting to deliver the energy needed to kill. And, I keep the shots under 30 yds, which is about as long a range as most of, if we were truly honest, would admit we are most likely to kill birds.