Sabots

[Dictator]

Guys,
What do you think of sabots for a 3" 6lb smooth bore? I've made these as a prototype because our gun's barrel is a little loose. The object is to keep the ball centered in the bore instead of rattling down the barrel. Our battery is going to try them to see if they improve accuracy. I'll let you know if it works better or worse.

Joe

[GGaskill]

How much does the sabot weigh compared to the shot?  It will lower the shot velocity and increase chamber pressure because of the greater inertia.  Also it looks like the windage will be reduced which will also increase pressure.

Make a few test firings from cover before surrounding the gun with crew members or reduce the charge weight.

[Cat Whisperer]

Questions and thoughts?

Material?

How did you make the sabot?

Great Concern (worrysome if not addressed by experience) - if the material acts like a plastic, you could get great pressure to the sides from the hydraulic principle of equal pressure applied in all directions.  Sabots of CW time were often wood and were secured by metal banding - no expansion effect.

[guardsgunner]

There are allot of guys using hard foam sabot with good results. The back of the foam is coated with a resin of some sort to act as a shield.

[Dictator]

These are good questions and concerns. The material is CNC lathe turned UHMW. It will obturate from gas pressure i'm sure. We will greatly reduce the powder charge for this. Guys shooting rifled guns use a much smaller powder charge than we do with a smooth bore. The ball weighs 6 lbs. I estimate the sabot to be 1/4 lb. UHMW is softer than, say, a nylon plastic. This, in my estimation, will allow it to expand to bore diameter. I'm hoping this will center the ball in the bore for more consistence. A concern is pressures, and if the rear of the sabot will shred exiting the muzzle in an uneven manner causing a loss in accuracy. If I change the design, I might reduce the rear radius so the edges aren't so thin and thus, hopefully, they might not shred at the rear and could be reused. Another concern is keeping the ball in the cup before firing. I'm going to try vaseline or STP for a mechanical bond. I want the ball to stay seated in the barrel and release immediately after clearing the muzzle. We'll see

[GGaskill]

I would reduce the depth of the front cavity if I wanted them to separate in flight.  But I would also try keeping them together as the sabot will act somewhat like a tail and may improve accuracy by preventing random rotation of the shot.

[Cat Whisperer]

UHMW is solid enough and slick enough that you shouldn't have to worry much (assuming a flat base).  

When I first started I filled the cans with water and increased the charge until the sides would scrape the inside of the bore lightly.  Tried one or two with heavier charges and would split the seam down the sides.

So if you're concerned about UHMW, consider starting light and work up observing the recovered sabot and inspect the sides for bore scraping scratches.

I would think that if doing a radius on the bottom a very small radius (1/4 to 1/2" would do well.  Pure conjecture.

If you want it to release it just has to catch the wind and it WILL come off, as do the modern ultra-thin beercans from the concrete.

[Double D]

I see a very great danger of that UHMW in your sabot expanding and sealing the bore and driving pressures sky and  worse. Pressure is going to force that UHMW forward and get between bore and around that ball and it is going make a seal and seriously increase friction or even make a blockage.  Pressure from Black powder is a Genie that will not stay in the bottle.   I would not use that design.

Take a look at the what a real sabot is suppose to look like.



If you made your UHMW sabot closer to this shape, size and dimensions it would probably work.  The one you show is scarey!

[Dictator]

All good point. That's why our team is studying all the points. G, I'm thinking like you, that if the sabot travels with the ball to the target, it may have a stabilizing effect. I'm thinking of running a bolt right through the ball into the sabot to lock them together in flight. Sealing the bore and increased pressure from it is one of my concerns also. I'm thinking of reducing the rear radius as well. I have several other thoughts on material. UH is a softer plastic, nylon would not abturate as much as UHMW. This might be an option??

The Breneke shotgun slugs have the wadding attached to the base & do not separate.  So do some other brands.

Sealing the bore is a sensitive issue.  Most cannon are built (strength wise) with windage in the calculations.  If you seal it tight you will get a little more veloicty and a lot more pressure.

UHMW is slick.  So you're ballancing the pressure applied pushing it to the outside against it's lubricity going down the bore to not raise the pressure too much.  I think with a flat base you wouldn't have trouble, but wouldn't venture a guess with a cupped base.

[GGaskill]

I see no problem with obturation if the charge is adjusted to compensate for the changes.

[Double D]

I'm thinking like you, that if the sabot travels with the ball to the target, it may have a stabilizing effect. I'm thinking of running a bolt right through the ball into the sabot to lock them together in flight.

If the ball has windage and the sabot is properly constructed you want the sabot to discard. If attached it must be precisely mounted and if not it will impart pitch and yaw into your projectile.  

You only want your sabot to help your ball get down the bore square. If done right the sabot will center the ball in the bore, impart velocity to the ball and  and fall away as the ball goes down range.  

I am thinking about picking up some delrin, chucking it up in the lathe an cutting a cone in the face.  The idea of a cone and not a form fitting ball is so the cone will center the ball on firing, but not full diameter.  When the air flow contacts the outer portion of the cone in will push the sabot away.  That's my theory any way.

By the way here is a guy listed on Steen's website listed as a maker of Sabots.
 
WOOD SABOTS FOR SMOOTH BORE CANNONS:
Steve Cameron FHD
292 West Old Andrew Johnson Hwy.
Jefferson City, TN 37760
(865) 471-6640

Something else you might check. Are sabots allowed in the matches you will be shooting?  Some do not allow the use of Sabots.

[Cat Whisperer]

Durlin is wonderfull stuff - hard, extremely abrasion resistant!



A number of years ago I dropped into a Petersburg, VA store (15 minutes before the torando too) where the fellow in the gun shop showed me the winning 200 yard cannon target and one of the bullets he used (N-SSA).

It was cast of lead (or lead alloy) about 3" in diameter and 3" long.  It had a hollow base about 2" deep.  Flat nose.  The pocket had a flat bottom in the hole.  

We left just in time.  An  hour later I saw the pictures on TV (from Richmond) - where we were parked was a 4' deep pile of bricks from a collapsed wall.

[Dictator]

Double D,
 The cone idea is interesting. One of the problems we encounter is that when firing on some ranges, we have to position the barrel pointing slightly downward. To keep the ball from rolling out of the barrel, we coat it with STP and then wrap a piece of fiberglass cloth around it. This give just a slight grab to the bore, keeping the ball against the powder bag. I do like that cone sabot idea. Let me know if you try it and how it works. One question, why delrin, UHMW is much cheaper? You could also try nylon or PVC rod materials. These are all harder and more crystalline than UHMW. This might be good or bad. Aside from cost, the harder material may be more prone to cracking or breaking under firing. Our team tried bondo in the past for a sabot material. It shattered upon firing.
 On your range question. Some ranges do allow anything as long as it's safe, some don't allow anything not period-accurate.

Let me know---Joe