windage

[Jim R. Glines]

can anyone tell me what happens if you have to much windage? a fiend of mine said he shot his mortar and the plastic bottle that was full of sand, just went about ten feet in the air, and the bottle was a mess the bottom was blown out of it and the side was split. He said he had about 2 and 1/2 to 3 oz of powder, but that the windage was about 1/8 of a inch all the way around the bottle, I think that makes it about a 1/4 in.of windage if you add the two sides. he put it away and never shot it again. It was mounted an a nice wooden box and really looked nice, but it kinda got to him.
thanks
Jim  :lol:

[Max Caliber]

Jim, I don't think that excess windage was the problem. The projectile here was something that could be compressed and or torn apart while still in the bore. Cannon/mortar projectiles should be solid objects capable of being shot from the barrel without coming apart or parts trying to pass other parts while exiting the bore. This is one of the reasons that wadding if frowned on because one never knows what the wadding will do. generally, for good accuracy, windage should be kept to a minimum as long as the projectile can be run down the bore without ANY resistance from the bore. It's always better to allow a little extra windage for safetys sake. Max

[Double D]

A review of this previous topic will provide you with the definition of windage The More Complete Cannoneer

Windage

“In preparing balls for smoothbore guns it is well to recall the standard which were once required for the difference between true bore diameter and the maximum ball diameter allowed for that caliber. The term windage is applied to this difference, and one common rule stated that windage should be one-fortieth the diameter of the bore. By this same rule, a 10 inch smooth bore would fire a ball ¼ inch smaller than the bore, and a two inch bore smooth bore would fire a ball .050 smaller than the bore.”

But I think the real problem is as Max said.

[Cat Whisperer]

I have .050" (on the diameter) clearance (windage) for my 4" pvc pipe mortar (on left) the outside diameter of 4" pipe is 4.500" and bore diameter is 4.550".

It also shoots the 46oz juice cans (of 4.237" diameter) reasonably well (even filled with sand).

Range is a little less.

When firing plastic bottles (in my 16-20-24oz soda-pop bottle caliber mortar) I fill them with concrete.  They work well for at least 2 shots, after that the plastic suffers.

Beer-can caliber mortars are funny.  The super thin aluminum is often stripped off the concrete about 20 - 30' out of the tube.

The older cans (same as modern soup cans) had the rim to the outside of the can.  They work well filled with water, sand or concrete.

I won't say anything about firing an empty propane tourch bottle.  Probably wasn't a smart idea in the first place.

So, my conclusion is that extra windage doesn't hurt, it just limits the max range a little.

[Jim R. Glines]

Thanks to all on the windage problem, I will tell my friend, or better yet I may try to buy his mortar. cat whisperer, what is this pvc mortar? is it made from pvc or does it shoot PVC?
Thanks
Jim

[Cat Whisperer]

Jim -

The 4.5" mortar of question (on the left) is 7" OD and 4.55" ID made of 4140 with 2"CRS trunion.  Bored from one piece of steel, powder chamber, shoots 4" pvc pipe (4.500" OD) filled with concrete from 4 to 7-1/2 LBS some 350 meters.  It is Armaloy industrial hard chrome plated inside and out.  Charge usually is between one and two 35mm film cans full of FFg or FFFg.  Tube and trunion weigh 103 lbs.  I consider it to be significantly overbuilt - from fear.