Author Topic: Another newbie question... does air get compressed in a loaded barrel?  (Read 3937 times)

Offline bones92

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So whenever I get to thinking about loading PRB, I get to wondering a bit.

When we load a tight-fitting PRB load and drive it all the way down, are we effectively pressurizing the powder?  This assumes, of course, that the vent hole on either a flinter or caplock is effectively blocked by powder, thus preventing air from escaping.

Something tells me that the air does probably slip out through the powder, otherwise it might be much harder to load a PRB if compressing the entire volume of the barrel.

« Last Edit: June 30, 2016, 07:00:25 PM by bones92 »
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Offline FDR

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Nothing in the system is "air tight".  The powder is granular and the ball/patch combo is not air/gas tight until ignition. If it were you could not load the gun with a ramrod!

Offline Mauser06

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When loading my Fowler with wads I can feel the air pressure if I don't nick the edges slightly to allow the air a way out...

But that's a smoothbore and tight wads that seal well...guessing the air doesn't come out of the vent because of the long heavily buffered and packed shot column...


In my rifles with 3f and an opened up touch hole I can see a few powder grains blow out the vent ...



Offline hanshi

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Offline Squirrel pizza

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Everyone has an opinion and a recipe. IMHO, with rifles .58 or larger, ff BP is recommended. I do like using (as a main charge), of 20-25grs. of FFF first followed by60+ grains of FF on top to that. A lot depends on if your hunting moose or shooting paper, and the range your shooting. Because BP burns and not "explodes" like a modern smokeless powder, you reach a point of diminishing return. Meaning you can only expect so much powder to actually burn and produce pressure, the rest is wasted after the ball or bullet leaves the barrel. Using the finer powder burns quicker, helping ignite the heavier powder. I don't know if with your rifle or conditions this will help much. A basic starting point is 1 gr of powder charge per caliber. Depending on your barrel(old antique, new, how heavy), counts a lot as to the pressures you want it to go through. Remember, with a RB, the patch takes the rifling. I use the thickest patch possible that I don't have to hammer down the barrel. I'm sure lubes are just as important, especially to the AR target shooters. But I've used everything from spit to mink oil. When rampaging squirrels threaten the homestead a man has to do what's nessisary, but I prefer bore butter, again, a personal preference.

Offline smylee grouch

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Squirrel Pizza, what do you mean when you say modern powder explodes ?

nosrettap1958

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Squirrel Pizza, what do you mean when you say modern powder explodes ?

If anything and comparing the burn rates its black powder that 'explodes' but a bad choice of words in either case.

Offline smylee grouch

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My thoughts also Crawdad. I know of one hunter safety teacher who demonstrates the burning of modern and black powder to his students by burning a table spoon full of each. The modern, H-870 I think, burns for about two or three seconds and the black flashes. This way he can show the students why you don't want to use modern powder in a muzzleloader as the modern is constantly building up pressure where the black is just a flash for an instant .

Offline bob in the woods

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Black powder does not "flash" in your barrel.  It burns . 

Offline smylee grouch

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You are right Bob, my choice of words for how black powder burns in the demonstration in an ash tray.

Offline SCLoyalist

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Air can get compressed:  Put a tight fitting, wet cleaning patch on a jag, plug the touchhole  and send the jag down the bore and sometimes (but not always) when it gets down towards bottom of the bore you can turn loose of the cleaning rod and see the rod come back up a couple of inches (until air pressure bleeds off around the patch & jag or out the touchhole).   There's been some speculation that you can, by a rapid and forceful push of the rod down on a ball, create a fire piston effect and raise the temp in the barrel high enough to set off the powder.  I kind of doubt it, but I've never seen either a convincing practical demonstration or paper analysis based on the beloved "Combined gas law" of Freshman Chemistry indicating how much force you'd have to be able to exert to heat the air to the ignition point for black powder.

Offline frogwalking

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What Mauser06 said. When ramming home the overshot wad, if I don[t nick the edge, the trapped air pressure will throw the ramrod right out of the barrel.  In a rifle, the air escapes through the flash hole or nipple, whichever your rifle has.  In a fowler, the air can be trapped between the overpowder wad and overshot wad.
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Offline Daryl

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What Mauser06 said. When ramming home the overshot wad, if I don[t nick the edge, the trapped air pressure will throw the ramrod right out of the barrel.  In a rifle, the air escapes through the flash hole or nipple, whichever your rifle has.  In a fowler, the air can be trapped between the over powder wad and overshot wad.

Exactly, however I'd have used different wording- perhaps, as in -  can throw to rod up and sometimes out the barrel due to the compressed air between the over powder wad and overshot wad.

Last rendezvous, I had no over powder wads for my choked 20 bore flinter, so used the thin overshot "B" wads - several of them as a barrier between powder and shot. These did not hold the air pressure, but allowed normal loading. I also was using a steel rod - and heard the rush of air out the vent, every time as I seated the overshot cards, including the overshot card.
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