Gas sealing with PRBs in rifled barrels

[Vaino]

If the amount of gas pressure is sufficient to overcome the inertia of the PRB and propel the PRB up the bbl, some gas blowby becomes irrelevant.

If one calculates the thickness of patch mat'l in the grooves of even a "tight load", it's usually minimal and will allow gas blowby. In fact, many patch/ball combos don't even fill the grooves.

A .540 bbl land dia. plus .015 groove depth X 2 = .030 which equals a .570 groove dia. A .530 RB along w/ a .020 patch thickness X 2 equals .570 which is the same as the groove dia. This combo will not seal the groove dia. and blowby will occur.


A .535 RB and a .022 patch thickness X 2 equals .579 .....this combo yields .0045 excess patch mat'l to fill the grooves. Will this combo seal the grooves? I doubt it because it's only cloth. This combo would be very difficult to load.

I don't think there's a "useable" RB/patch thickness that will seal the grooves and allow no gas blowby.

I think a conical on average if shot in a shallow rifled bore that's sized for a conical will allow a lot less blowby than a PRB shot in a RB bore. If a conical is shot in a RB bore, the gas blowby would be tremendous and the gas cutting would destroy accuracy. Of course we could then blame this poor accuracy on too slow a twist?.....Fred

 

[ohio ramrod]

Clovis , I also use wads between powder and patched balls. Only mine are made from leather since I have an unlimited supply of leather scraps. I find the wads greatly improve consistency of velocity, and therefore accuracy. Plus they "power swab" the bore with each shot so I have consistency between shots with out having to swab between shots. I find using a tight wad makes loading easier with thicker patches since the wad acts to swab the bore before loading as well as when fired. :idunno:

 

[ohio ramrod]

Wes , while adding over powder wads is something new, adding corn meal over the powder was an old time way of sealing moisture from the powder on guns that would be left loaded for extended or unknown periods of time.I assume the corn meal would have some "sealing" effect at high pressures. :idunno:

 

[hanshi]

I've seen a few slo-mo videos of prb in action. There have also been a few other studies on the subject. It is apparent that a true seal does not occur with a lubed patched ball. High pressure gasses are simply too difficult to contain. A prb does act as a seal but not a perfect one. The prb is basically a compromise between ease/speed of loading and accuracy/power/ velocity of the ball.

A prb is certainly efficient enough for the job it does and, in fact, performs well beyond what should be expected. An op wad gives additional help but is far from a cure.

 

[Clovis]

Ohio ramrod, if I had access to suitable material and an accurate cutting tool I would maybe make wads for my rifles, but being a bit lazy it seems easier to buy wonder wads.

As to using corn meal, I don't know, the corn meal would hold some moisture on it's own, and would likely be pretty much burnt up on firing and not sure would seal much. Just guessing here, no experience. I do know I can recover the wads I use and they only show some singeing.

Interestingly, I found one pair of wads the patch had reversed itself and the wads were inside the patch.

And to reinforce your findings, the wads going down on the powder do clean the bore leaving the patched ball easier to load and as the fouling ends up on the powder it is either burnt or expelled with the wads and ball. Keeps me from having to swab between shots and risk filling the breech with wet/damp fouling and having trouble with the next shot.

 

[Viking78]

This video of a patched roundball exiting a flintlock rifle is pretty slow at 15,000 frames per second (when you get to around 0:30 the video hasn't stopped, it's actually that slow):

[youtube]oHF6BXhUzcA[/youtube]

I found the video at Larry Pletcher's excellent site: http://www.blackpowdermag.com/featured-articles/siler-high-speed.php

 

[Vaino]

Not too many years ago, a plastic cup wad was on the market. It had a "cup" for the RB and the other end was dished and acted like a "skirt" that expanded to seal the bore...something like the "skirt" on a mini-ball. I imagine this "wad" increased efficiency by eliminating blow by. Trouble was....the RB didn't stay in its cup and either rolled out of the bbl or upon firing was at some length down the bbl w/ possible disastrous results. It's marketing was very short lived.

Tight fitting OP wads might eliminate most of the blow by, but it's just another item to contend w/ and seeing that through the ages their use wasn't widespread or in fact was possibly non-existant, I prefer not to use them.

W/ all it's inefficiences, the unadorned PRB still manages to do an excellent job.....Fred

 

[Rifleman1776]

Ball exited before the flame. Same as the shirtless guy vid.
Kinda proves my gut correct. The lubed patch is a seal.
What are we talking about?

 

[George]

Wes , while adding over powder wads is something new, adding corn meal over the powder was an old time way of sealing moisture from the powder on guns that would be left loaded for extended or unknown periods of time.I assume the corn meal would have some "sealing" effect at high pressures. :idunno:

I've never run across that one, can you tell me where you found that info?

Spence

 

[Billnpatti]

Using cornmeal to seal out moisture from your powder just doesn't sound right to me. :hmm: I don't say that it wasn't done by some folks but they may have been wrong in doing so. Corn meal will absorb moisture pretty well and it would seem to me that it would add to any moisture absorption problem. It could possibly absorb enough moisture to cause a serious rust problem over time. I can understand its use as a sealant to keep the hot gasses away from the patch or to give more consistent MVs but not as a moisture sealant. I think that those who were using it as a moisture sealant were likely making a mistake. Just my opinion for whatever it's worth.

Having said that, I wonder if cornmeal may have a somewhat greater affinity for moisture than the black powder and tend to draw moisture from the powder much in the same way that people use rice to pull the moisture out of a wet cell phone or other electronics that have gotten wet. Perhaps that was their thinking. Still, I am not sure that it was a good idea for that purpose since it would have been drawing moisture from the air into the bore as well as from the powder. Oh well, just a thought.

 

[Stumpkiller]

I found the video at Larry Pletcher's excellent site: http://www.blackpowdermag.com/featured-articles/siler-high-speed.php[/quote]


He was the third poster in this thread. ;- :hatsoff:

 

[galamb]

Just thinking out loud - could cornmeal have simply been used as a buffer if it was in fact used and have nothing to do with sealing or moisture prevention etc?

 

[cynthialee]

when I have used cornmeal in a long gun it was to protect the thin patches I sometimes use

in revolvers I use it to push the ball closer to the forcing cone

I imagine after an afternoon of my shooting the revolver the ants enjoy a nice roundup of toasted cornmeal.

 

[Larry Pletcher]

Referring to the video I did, mentioned by Viking and Stumpkiller, I need to mention that I did not use a heavy load for that shot. I don't recall the exact amount but my standard load was 40 gr of fffg behind a .395 ball. As we were shooting in my garage, I was more likely to cut that down. If a stiff load was used the outcome might have changed. Would there have been gas in front of the ball with 90 grains for a load? I don't know. 90 grains in that gun is over 2200 fps. It seems to me that a STIFF load could support both sides of the discussion.
1 high pressures are more likely to bump up the ball
2 high pressures are more likely to leak ahead of the ball

Regards,
Pletch

 

[ApprenticeBuilder]

Nice Find, pretty clear in that video what exited first.

 

[Viking78]

Here are two more that shows gas before the ball exits:

[youtube]yQv8Oy_NPVs[/youtube]

[youtube]EYjyxAVYMZA[/youtube]

It looks like the same things happen in modern guns as well:

[youtube]otpFNL3yem4[/youtube]

 

[Rifleman1776]

Thanks for those interesting vids.
But :shocked2: , my gut it talking to me again. And, it is saying what we see there is compressed air and barrel crud being forced out ahead of the projectile. The burning gasses follow.
I believe they disprove the 'patch is not a seal' theory to be :td:

 

[roundball]

:rotf:
Yeah, that's what's talking to you...your gut...LOL

Knowing Physics, I'm pretty sure "compressed air" has to have something to be forced against in order to become compressed...not an open empty pipe.
And conversely the "compressed air forcing out barrel crud" theory would mean a video like that of the first shot out of a clean barrel would not show the same thing then.

But I think it's quite safe to conclude that the people with the smarts, the high tech equipment, and the know-how to make such technologically superior videos know all about such basic physics and test conditions.

I get that you believe a simple fold of cloth we can see through when we hold it up to the light can magically seal & hold back 7000-10,000 PSI of hot flame and pressure...and you're certainly entitled to your belief.

The problem is real life examples show that not to be the case...IE: if a simple patch 'was all that' there would never be any need to also consider adding wads, corn meal, and other things to try and seal a rifled bore better.
:hmm:

 

[Wes/Tex]

Yeah I laughed at the 'gut' comment too. We experienced similar all those yeas ago. Hots from the front angle appear different than the side shot that more clearly reveals what exits the muzzle face first. I'm not convinced that what's being seen first is necessarily 'compressed' air of barrel debris, etc. Obviously, different patch thickness or materials showed some minor variations but the ball was never first in our efforts.

 

[nchawkeye]

Why would we think a greased, cloth patch would seal all gases when we know in a modern, internal combustion engine the rings don't seal all gases???

This is why you have to change your oil in your truck as it gets dirty from carbon...