PRB flight question

[roundball]

[quote
Are you saying that your round balls don't flatten out when you fire them into something, or am i misunderstanding you? [/quote]

...questions about obturation, since I never get any land & groove marks on my RBs...

 

[roundball]

I can't believe a roundball doesn't obturate to some degree but have precious little evidence to back up my belief.

I understand the physics of course and agree that theoretically there could be obturation.

But it may be, that in the case of a "light for caliber projectile" like a round ball, and the fact that it's sitting in a slippery lubed patch on a set of rails (lands), it simply has comparatively little resistance...dunno

 

I don't think I have ever found a ball that was still round. The few I have found in deer were flattened to some degree - most punched all the way through - and I have never fired any into water. I also will admit I can't recall seeing any patch markings from the rifling but I probably wasn't looking either.

 

[Gametracker]

How does rifling affect a prb? I understand the stabilizing twist rifling imparts to my modern bullets, but does it stabilize a round projectile? If so, how?

My guess is that, like a flywheel, top, or bicycle wheel, the rotating sphere tends to keep its axis in a constant direction in space. 'Course the next question is "why slow twist and not fast". That's something I'd like to know. Does a fast twist cause the axis to wobble?

Also,

What about air flow and air pressure? A spinning roundball would have more air flow than a non-rotating ball (I assume). Is that reduced air pressure enough to significantly reduce drag, making the rifled shot not only straighter but longer?

 

[Curly James]

One simple way to "see" how a roundball may appear as it exits the barrel is this. Measure a ball and a patch with a micrometer. Seat the ball as normal. Use a ball puller (scewing it into the ball causes the ball to obturate to the bore) to remove the ball from the bore. Measure the ball and patch again. Each one of my rifles are different simply because they are rifled differently and use a different patch and ball combo. Take a close look at both patch and ball. In my experience the patch will have rifling marks on the cloth itself. The ball will be imprinted with the weave of the cloth. This is not very scientific, but it is also cheap and simple way to ake some observations about your ball, patch fit, and bore conditon to some degree. :m2c:
Take care, CJ.

 

[roundball]

I don't think I have ever found a ball that was still round. The few I have found in deer were flattened to some degree - most punched all the way through - and I have never fired any into water. I also will admit I can't recall seeing any patch markings from the rifling but I probably wasn't looking either.

Oh yes, mine are pushed out of shape after impact too...but what I was referring to and as a case in point, last year I shot a 6 pointer at 55yds with a .440 ball...hit a rib on it's way in through the heart and stopped, bulging out the hide on the far side...and while it was flattened on one half so it looked like an "igloo"...the other round half of it didn't have a mark on it...no patch weave marks, no land/groove marks, nothing...looked like it had simply dropped out of the sky.

90grns Goex 3F
Oxyoke wonderwad
.018" pillow ticking
Hornady .440

 

RB,

I also shoot a .45 but only with 70 gr of 3F so I should experience even less ball deformation than your load. I get patch burn-out above 80 gr but I am not using a wad over powder/under ball.

When I was growing up, we shot all of our deer with 12 ga, #1 buckshot. This was my uncle's farm and even though it was pretty remote, that was all he would let anyone use due to his fear of a projectile going where it shouldn't. Subsequently, I saw a lot of .30 cal pellets cut out of deer. I cannot recall ever seeing one that was still round but some of the deformation may have come from being fired. A lot of the balls were in pieces, especially if they hit bone and one thing I hated about buckshot was the bloodshot tissue that was always present. A single PRB seems to result in much less meat damage and still kills quickly.

 

Well, my memory did fail me in my other post in this thread and I am compelled to correct it. The drift of a 500 Gr., 45 cal. bullet when fired at approximately 1100 fps from a 1-20 twist is 20 inches at 1000 yards, not 500. At least I got to correct my own error and my apologies for same.

Also, after digging thru some of my books on both muzzleloaders and BPC rifles, and based on my own experiences, I'm going to have to say that obturation to some degree is a fact with both PRB from muzzleloaders and bullets from cartridge rifles. The amount of obturation obviously depending upon the powder charge and weight of projectile.

Vic

 

[Joel/Calgary]

Arrgghhhh!!!!

<exasperated pedant mode>

Obturation is the sealing of something, not the mechanism of that sealing. It could be achieved by piston rings in a motor cylinder, by a packing gland around a ship's propeller shaft or a water-cooled machinegun barrel, by the expansion of a shell's driving band or a mini

 

[robinghewitt]

If a ball (or bullet) happens to upset to only partially fill the grooves of the rifling (whether Whitworth, Brunswick, Metford, Forsyth, or other), if it hasn't formed a seal, it hasn't obturated the bore.

Surely a bullet or ball that upsets to partly seal the bore has still obturated to a degree. There's nothing in the dictionary definition to indicate that a perfect seal must be achieved, all things being relative :thumbsup:

 

[Birddog6]

Arrgghhhh!!!!

I realize some of y'all have heard some form of this rant before, but imprecision in technical usage is a sore point with me.

Joel

Well, you may as well get over it Joe.......... Most of us are normal guys enjoying some ML'ing shooting & not trying or wanting to be rocket scientist. We do the best we can with the info we can retain, even tho it is a lil inaccurate & distorted at times... ::

 

[roundball]

Arrgghhhh!!!!

I realize some of y'all have heard some form of this rant before, but imprecision in technical usage is a sore point with me.

Joel

Well, you may as well get over it Joe.......... Most of us are normal guys enjoying some ML'ing shooting & not trying or wanting to be rocket scientist. We do the best we can with the info we can retain, even tho it is a lil inaccurate & distorted at times... ::

Yeah, life is complex enough as it is...I use the KISS principle:

I look at a fired ball...see that "it ain't got no land or groove marks on it"...and conclude "that it didn't obtur...obfur...obscur...that it didn't squeeze out into the lands and grooves" !!

:: :crackup: ::

 

Just as long as they shoot accurately....

 

I had a question occur to me on this subject. If the round ball remains more or less unmarked when fired and the patch does all the work, is there any reason why we can't be using wheel weights or other hard lead to mold balls? Would sure narrow the search on those of us that cast our own.

 

[roundball]

I had a question occur to me on this subject. If the round ball remains more or less unmarked when fired and the patch does all the work, is there any reason why we can't be using wheel weights or other hard lead to mold balls? Would sure narrow the search on those of us that cast our own.

Excellent question...I personally don't see why not...Hornady has been making a 'hardball' in a little sabot for a few years now so I asume the accuracy piece is probably OK...and a good pillow ticking patch should provide all the protection needed

 

[Stumpkiller]

I use scrap lead that has all kinds of oddments in it. One batch of pipes had much solder. The balls were very hard when cast. I fould that they were a b!#ch to load, but shot well. They weighed about four grains less than pure lead, and shot a little low. You might tear patches too, depending on your bore & their toughness/thickness.

I save ALL lead. If I can use pure I do, if I don't have pure I use what melts. With muzzleloaders, if you can get it down the barrel with the ramrod the powder can get it back out, no problem.

I just pulled a ball last weekend and it had the woven pattern of the patch pressed into the lead where it contacted the lands and was decidedly flattened in those spots. I figure that's a plenty tight fit (.530" & 0.017" tick patch)

 

Well - that's outstanding information! I have all sorts of scrap lead laying around but pure lead is sometimes hard to find.

 

[Rebel]

If you have a smoothbore it doesn't matter if you use hard lead rd balls. There is no rifling for the patch to compress in to.