Windage and Rifling

[DoktorD]

Hey there guys,

Ok, I was wondering about windage and rifled barrels like on scale Parrotts or Ordinance rifles... In the smooth bores, there should be a windage of 1/40th the bore diameter...

SO my question is, how does this scenario change when dealing with tubes with rifling? Obviously with the 1/40th windage, a "bullet" for lack of a better term wouldnt "bite" into the rifling... Or doesnt that matter?

Sorry about my naturally inquisitive nature 

Trying to learn as much as I can... What can I say when fascination borders obsession 

[gary michie]

Hi:
As far as I know the rounds are made with the same radius but have differant types of ingagements that expand against the bore and into the rifling.

[subdjoe]

The simplest form was a cup of soft metal that was bolted to the back end of the projectile.  When the propellent charge went off it expaned the cup into the refling.  There were also various bands of lead that were somehow forced into the grooves, some by the expanding gases, some by using a two part projectile that would crush the band and cause it to expand.  Some had lugs that rode in the grooves.  Our ancestors were most inventive.  Check out civilwarartillery.com for some photos. 

[DoktorD]

Ahhh I gotcha... I saw the pictures and assumed that the viod at the base of the lead projectile was to keep the weight closer to that of a ball load.

Just seems like that would increase the pressure by quite a bit?

[GGaskill]

You need the shot to be smaller than the lands enough that it is reasonably easy to load the shot in a fouled barrel.  You don't want the shot to stick with a charge in place.  Any more windage is wasting powder.

[subdjoe]

Ahhh I gotcha... I saw the pictures and assumed that the viod at the base of the lead projectile was to keep the weight closer to that of a ball load.

Just seems like that would increase the pressure by quite a bit?

Just a bit, yes.    And, most were iron or steel, not lead.  Lead projectiles that size would have been around 15 pounds if solid.  And I don't think you could make shell out of lead, it would likely have crushed and blown apart as it came out the muzzle.

A 12 lb. Napoleon had a standard service charge of, I believe, 2 1/2 pounds.  A 10 lb (3 in.) Parrott or Ordnance Rifle had a standard service charge of 1 pound. 

[GGaskill]

Actually a solid lead shot the diameter of a 12 lb cast iron shot would weigh 19.6 lbs and (I think) the Napoleon powder charge was 1 1/4 lbs.  You can let your web browser calculate the shot weights by using the Spherical Shot Weight Calculator.

[Artilleryman]

Actually a solid lead shot the diameter of a 12 lb cast iron shot would weigh 19.6 lbs and (I think) the Napoleon powder charge was 1 1/4 lbs.  You can let your web browser calculate the shot weights by using the Spherical Shot Weight Calculator.

You have the 6 pdr charge confused with the 12 pdr charge.  As post earlier the 12 pdr Napoleon has a 2 1/2 lb service charge.  Lighter charges were used for cannister and for special purposes.

[seacoastartillery]

A 12 lb. Napoleon had a standard service charge of, I believe, 2 1/2 pounds.  A 10 lb (3 in.) Parrott or Ordnance Rifle had a standard service charge of 1 pound. 

     Subdjoe,   You are correct on both items here.  

You need the shot to be smaller than the lands enough that it is reasonably easy to load the shot in a fouled barrel.  You don't want the shot to stick with a charge in place.  Any more windage is wasting powder.

      We have found by actual practice with our scale Brooke Rifle, 1.167" bore diameter, what George has stated is absolutely true:
"Any more windage is wasting powder".  Since we are not fighting a war, we don't have to put up with a "fouled bore".  We clean our scale seacoast guns after every shot for both safety and so the next bolt will slide down the bore easily although we allow only .0025" between the lathe-turned 12L14 steel projectiles and the bore.  Why have excess windage when your expanding sabot will reduce it to almost ZERO WINDAGE at the instant your charge goes off?

Just seems like that would increase the pressure by quite a bit?

      DoktorD,   You are certainly correct here.  This is exactly what happens and it explains why the Confederate ordnance engineers insisted on banding hundreds of those large cannon tubes they captured at the Gosport Naval Yard in 1861 to convert them to rifles.  A large majority of rifled guns produced after 1862 by North or South had wrought iron reinforcing bands covering the breech area of the tube to contain the area subjected to the highest pressure.

Regards,

Mike and Tracy

[subdjoe]

Actually a solid lead shot the diameter of a 12 lb cast iron shot would weigh 19.6 lbs and (I think) the Napoleon powder charge was 1 1/4 lbs.  You can let your web browser calculate the shot weights by using the Spherical Shot Weight Calculator.

Sorry, I wasn't clear.  For the projectile I was thinking of one for a 3" rifle.  A standard 15 oz. vegetable can filled with lead weighs about 10 lb, and the bolts were about half again as long as that, hence the guestimate of 15 lb. 

Mike/Tracy, thanks for the confirmation, I was going from memory. 
You say you clean your gun after each shot.  Is that as in sponge, bore brush, sponge, dry sponge?  Or just wet and dry sponge?  And, do you lube your projectiles?

[seacoastartillery]

Mike/Tracy, thanks for the confirmation, I was going from memory. 
You say you clean your gun after each shot.  Is that as in sponge, bore brush, sponge, dry sponge?  Or just wet and dry sponge?  And, do you lube your projectiles?

      We wet sponge the bore, then clean the vent with a wet then a dry pipe cleaner, then we finish with a dry sponge in the bore.  This works well for us and if you do this for each shot, you can be certain that powder fouling is not affecting your accuracy. 

      We DO NOT lube our projectiles and there is a very good reason for that.  As the powder charge goes off you want your machined skirt or expanding sabot to be pressed into the rifling and to engage it WITHOUT SLIPPAGE or any ROTATIONAL SKIDDING.  Lubricant on the projectile facilitates slippage and we have empirical evidence on recovered bolts to back up this claim.  Also our 5 shot groups at 100 yards went from around 3" to almost 12" when we used oil and also high temp. grease for our lubed bolt tests.  So, there you are, a few tricks of the accuracy game from the Seacoast guys.  You can read in some historical texts about the artillerymen wiping off or oiling or greasing their projectiles, but we believe this wiping was done merely to make sure the projectile was clean and free of sand or soil.

FYI,

Mike and Tracy

[subdjoe]

      We wet sponge the bore, then clean the vent with a wet then a dry pipe cleaner, then we finish with a dry sponge in the bore.  This works well for us and if you do this for each shot, you can be certain that powder fouling is not affecting your accuracy. 

      We DO NOT lube our projectiles and there is a very good reason for that.  As the powder charge goes off you want your machined skirt or expanding sabot to be pressed into the rifling and to engage it WITHOUT SLIPPAGE or any ROTATIONAL SKIDDING.  Lubricant on the projectile facilitates slippage and we have empirical evidence on recovered bolts to back up this claim.  Also our 5 shot groups at 100 yards went from around 3" to almost 12" when we used oil and also high temp. grease for our lubed bolt tests.  So, there you are, a few tricks of the accuracy game from the Seacoast guys.  You can read in some historical texts about the artillerymen wiping off or oiling or greasing their projectiles, but we believe this wiping was done merely to make sure the projectile was clean and free of sand or soil.

FYI,

Mike and Tracy

AH!  And this is why I love this forum.  So much information to be had here, just for the asking. 

I had been going back and forth in my mind about the lube.  On the one hand, it would keep the fouling softer and make loading a bit easier (thinking lke a big muzzle loader here).  On the other hand, I had not seen anything suggesting that our ancestors lubed them for loading.  I as more thinking that the oil/grease would kind of fry as the flame came around it and could cause a momentary sticking of the projectile in the bore, and that might cause it to slip rather than spin.  Not to mention overpressure from that momentary sticking. 

Your groups went from 3" to 12", would I be correct in assuming that is center to center?  Or is that outside edge to outside edge? Either way, good shooting.

[Double D]

It's a mind set thing.  Most new comers to black powder artillery just think of them as bigger muzzleloaders.  Well they are, but because they are you have to do things different.  Like bore cleaning between shots, leaving some windage, no patches, if you could even seat one with a patch, etc.

[BoomLover]

That is what I have found to be the most difficult part of explaining the difference between traditional muzzleloading rifle shooters vs cannon shooting...with the windage factor which is necessary in smooth bore cannon shooting, and NOT needing a patch! A concept they don't seem to grasp...main question is, "But, won't you lose so much of your power if you don't have a patch for a tight fit? Windage is a hard thing to teach muzzleloaders! (At least the one's I talk to!) BoomLover

[Double D]

They can be taught, but it's not easy....

[Artilleryman]

Since this thread started as windage and rifling I thought I would add my two cents.  For rifled barrels the windage only has to be large enough to safely seat the projectile without it hanging up in the bore.  Reducing the windage will increase the accuracy, just don't reduce it to the point that it gets stuck in the bore.  This is the main reason for bore gages, usually a section of the rifling.  Do not worry about increasing pressures.  Think about the Parrott round that has a cup that seals the bore as it expands into the rifling, or the Hotchkiss round that has a lead band that seals the bore as it is forced into the rifling, or the Schenkle round that has paper mache forced into the rifling, and I am sure that there are others.

Having said that, the testing that I helped Matt Switlik and Don Lutz with showed that lugged rounds got a higher velocity with lower pressures than the same weight projectile with a saboted (cupped) base.  So if you are interested in lower pressures develop a lugged round.

I guess this was more than two cents.

[Cat Whisperer]

...
I guess this was more than two cents.

Two cents (1964 dollars).   

[BoomLover]

That Shot Calculator is a handy tool! Thanks for posting it, I put in into my Bookmarks....BoomLover

[Double D]

Jim,

That is a handy little tool isn't.  It's in CW's reference sticky.  There is a lot of other neat stuff in there that Tim rounded up for us.  The round ball Calculator was made by GGaskill, thanks George!

[GGaskill]

I'm estimating his miniball weighs roughly 0.42 lbs (6.67 ounces) in lead and 0.25 lbs (3.93 ounces) in zinc?

GGaskill can you verify your weight?--I will weigh one tonight.  For the moment, I think a lead hollow base one weighs about 10 ounces and a solid base one weights about a pound.

If this is true, its not too much more than the cannon ball which according to the shot calculator would be 0.329 lbs lead and 0.194 lbs zinc.

HOWEVER, one question I have after reading the responses in this thread is: what kind of windage should I be giving it to allow for the expansion of the rear into the rifling, but yet not accumulate too much additional pressure behind the projectile?--Don't worry about accumulating pressure.  You need some pressure for the process to work.  The way to not have too much is to not use too much powder.  You need only enough clearance to be able to easily load the shot with no chance of it sticking part way down the bore.  If you thoroughly clean the bore after each shot, you don't need much.

GGaskill -- does your miniball mould still use the 1/40th rule?--My cast Minie ball is a little too large, so you could say it has no windage (although the grooves are open at least at the beginning.  I hope the skirt expands and completely seals the bore but I have not confirmed that.

[DoktorD]

Whoops!

Faulty integration 

I got 9.8 ounces for lead and 5.78 ounces in zinc hollow bottom

12.58 ounces lead and 7.41 zinc solid bottom...

would have been more impressive if I would have gotten my integration right the first time 

[GGaskill]

The curves are parabolas?

[DoktorD]

Parabolas, no... Ellipses yes! At least in my design they were... haha. Treating the nose ans rear void as part of ellipses, you can get an some equations to work a little calculus on 

[GGaskill]

My Minie style shot are not as cast but have been machined to get them to a size that will muzzle load, so they are a little less in weight than as cast.  The one I weighed was 8.5 oz; it is 2.1" long and 1.177" in diameter.  The ogive is about 7/8" long and the skirt is about .54" deep and .045" thick.