SpudFiles

For my next project, I plan on adding new barrels for my combustion (once I finish its current upgrades). I want a golf ball barrel and a tennis ball barrel, however, I have no experience with either barrel type. Here are a few questions:

1) Golf balls - I plan on using a ball valve breech loader. What are some of the ways you guys keep the golf ball from rolling out of the barrel? I was thinking a rubber washer between the ball valve and pipe. Also, is the ball valve a 2"?

2) Tennis balls - Would I benefit any from a choke tube between the barrel and chamber? I was thinking this choke may help to accelerate the tennis ball more and help overcome that 12 lb force through the barrel friction. I was thinking half the barrel size (1.25"). Has anyone ever experimented with a choked combustion in this manner?

hubb017 wrote:2) Tennis balls - Would I benefit any from a choke tube between the barrel and chamber?

I very much doubt it. Unless I'm mistaken, all you'll do is restrict gas flow by 75%, and thus cut the all important barrel pressure if you do what you're suggesting.

Choking the flow will decrease pressure but, in turn, will increase velocity. With the tennis ball having a drag of around 12 pounds, the pressure will begin to build again once the gasses begin to push on it, making up for the pressure drop. It should also allow the gases in the chamber to have more time to complete combustion (without using a burst disk), which, in turn, should compensate for a not-so-ideal barrel length.

I should, however, consider making the choke (if I use one) with relation to the chamber instead of the barrel.

I've always considered experimenting with choked flow in this manner, but never have. I've never seen anyone else do it, either. Maybe I should make a barrel with and without choke to see the performance differences.

Regarding the tennis ball barrel, you'll increase the velocity of the gases but lose the absolute pounds (as opposed to psi) of force the large transition gives you. Imagine taking your logic to its extreme and replacing your choke point with a soda straw....amazing velocity, no power.

I would keep your breech openings as large as you can until the gas comes in contact with the projectile itself. Also the tight fit of the tennis ball allows a semi burst disk effect anyway...and the big drag on a tennis ball is really going to be your limiting factor for a distance shot. Close in target/damage shooting is a different story though...long barrel, good c:b ratios, burst disking, etc for that.

Re. the golf ball barrel. I personally use the standard SDR 21 1.5" sleeved in 2" sched 80. Tap an 8-32 threaded hole in the sched 80, but not the SDR 21, where you want the ball stop. Because the SDR 21 is somewhat pliable, you can screw a 3/8" 8-32 screw in the hole and tighten until you cause a small dimple in the barrel...just enough to catch the ball from rolling out the muzzle, but easily let go when you shoot it.

Fine tune the dimple setting with a real golf ball while you tighten or loosen the screw. Take care not to "over dimple".

Does your dimple method cause backspin? I don't necessarily need backspin, but the more accurate, the better.

What about the ball valve size for the breech loading golf balls? I wanted the ball to stop while it was inside the valve.

hubb017 wrote:Does your dimple method cause backspin? I don't necessarily need backspin, but the more accurate, the better.

What about the ball valve size for the breech loading golf balls? I wanted the ball to stop while it was inside the valve.

I can't see any back spin effect. I suspect the ball is equally pinched at the dimple and the opposite side of the barrel so the net spin is canceled out or insignificant.

I haven't worked with the ball valve breech loaders, but the one I saw some time ago here was a 2" with a 1 3/4" hole sawed into the side of it. I can't see the dimple method working with a hard walled ball valve.

hubb017 wrote:With the tennis ball having a drag of around 12 pounds

That equates to a pressure of just 2 psi. Even with a chrony, you'd seriously struggle to notice the loss in amongst shot to shot variability.
At your likely muzzle velocities, that will probably be a loss of little more than single digits.

Unless you're really fussed about that little difference, I say forget it.

Like Ragnarok said.

Besides, friction actually helps a combustion gun's performance. Well, at least up to a point. Static friction forces in the range of a few tens of pounds is beneficial.

Post a picture of your launcher, I'll make some suggestions. My last mod was a 2" breech barrel for potatoes. I had to make an adapter for it so I also made a tennis ball barrel which is more fun.

Post a picture of your launcher

http://www.spudfiles.com/forums/my-new- ... 13987.html

The ball valve is a 2in ball valve. I had done this before for pete in a thread about a year ago. It worked well but ugly(I used a dremel) I suggest a hloe saw for more pleasing results. Ill try to find the thread for you.

EDIT: found it the pics of it are at the bottom of the page.http://www.spudfiles.com/forums/ball-va ... rt,15.html

I remember that thread, Maniac. Thanks.

As far as my tennis ball situation, it seems that I have no choice but to have the choke implemented. The barrel is 2.5" Sch40. The outlet for the chamber is 2" female thread. I don't think, though, that it's going to make to much of a difference.

Alright, here is my two cents. I think your launcher will perform better than mine because you used a 2 inch fitting at the end of your chamber and not 1 1/2 like I did. You can easily adapt to 2 1/2 by going to graingers.com where you can find the fittings and your barrel. There is a graingers almost everywhere, just say your with a large company in your area and they will let you buy there and they may pass you their discount. Make sure you have their real phone number though and say that you'll pick up with cash.

Forget choke tubes unless you are hunting with a shotgun. Figure for .7 to 1, that seems to be the sweetspot although without a chrony you'll never know. My barrel was shorter(.8 to 1) but I couldn't tell. It was a hell of a lot louder than my spud barrel though. I used a coupler and extended my barrel to .8 to 1 thinking I will quiet it down but the noise level was the same as far as I can detect.

The tennis balls will seem very tight and you'll think it will never pass; don't worry but be cautious, the weakest part of your launcher will be the end cap. Tennis balls are designed to slow down, thats what the fuzzy stuff is for any why you don't see players with bruises on their bodies.

Goodluck and have fun, tennisballs are reusable, cleaner and cheaper.


Here are some links for ideas....

http://en.wikipedia.org/wiki/Tennis_balls
http://www.advancedspuds.com/tennis.htm
http://www.burntlatke.com/jpg600/25cb-graph.gif

Well, my launcher is going through a makeover. I also plan on replacing the end cap with a ball valve (sometimes, it's a pain to take it off after a shot). I may even scrap it and start over (I'm really not a fan for DWV, even in a combustion), the new version being similar but having more accessibility for upgrades (sort of like Tippmann's Model 98 compared to their Custom 98 ).

I've already rebuilt my super spark strip to make it even better and more "user friendly."

As far as ratio, the wiki puts a golf ball at about half the weight of a standard spud and a tennis ball at a little more than that. I figured a ratio of around 1.2:1 for the golf ball and around 1:1 for the tennis ball (to compensate for higher drag), unless someone has any suggestions. I'm looking for best performance.

Now, I agree that tennis balls are cheaper, but I don't know about reusable. I can easily clear 200 yards with a spud at the right angle