SpudFiles

So I read that the minimum regulation ball size is 1.68 for golf balls. What size bore is favored? Are there a lot of variance between brands, batches?

One that barely fits.

For me, I've been working on using large bore with a sabot to up the precision as well as the power. Haven't had a chance yet to test a long BG barrel against a sabot in the Tennis Ball barrel. Been too busy building the 2.5 inch cannon to drive it hard. I plan on driving a few with the 7 foot 2.5 inch barrel to compare it against a standard golf ball barrel. With a big valve, GGDT says nice things at 200 PSI. Hearing protection is recommended.

Golf Ball - Spud Wiki

Spud Wiki wrote:Golf balls fit perfectly in 1.5" SDR 21 PVC pipe, but because of its thin walls, it should be sleeved inside 2" SCH 80 PVC pipe.

Another barrel is Sch 10 1.5" aluminum or stainless steel pipe.

The 1.5" SDR-21, more commonly called class 200, has an ID of 1.7" (SDR series dimensions). Also the extrusion tolerances, surface variation/ minimum ID, change noticeably. So best bet is bring a golf ball to the store.

Now something your more apt to use, 1.5" sch 10 metal tubing, has an ID of 1.682". Any problems as far as tight spots could be taken out with a sanding drum on a metal rod.

Solar wrote:Are there a lot of variance between brands, batches?

Good thing you bring this up. I definitely have to say batch. As well I don't think ID variances are prioritized, just not important for boring old piping. I have bought 1.5" class 200 pipe that did not fit golf balls, so again test it at the store.

Haha, I was referring to variances in the batches of Golf balls. I am very aware that the ID is not a priority for extruded tube. SCH10 sounds like the way to go. What type of accuracy is to be expected from a golf ball?

I'd say 4' groupings at 50'. At farther ranges, hooking is inevitable.

Smooth-bore is out of simplicity, but a hop-up or rifled barrel would surely get your better accuracy.

I read on the wiki about lead balls being shot at 1:60" twist rates. I think ultimately a rifled barrel may get the most accuracy.

Golf balls seem much like a tumbling projectile that "catches" an angular hook. (this from the rotational circulation of faces) The golf ball having a back spin in this direction. If it were spun with rifling the golf ball would be gyroscopically stabilized. Uggh hard to explain, but it would seem having the golf ball stabilized in the most perpendicular fashion possible, would attain the most accuracy. Also the shell of a GB would take up metal rifling quite well.

I want to try the Polara golf balls. They have shallower dimples at the poles to auto spin stabilize. The tippman flatline barrel uses a curved barrel and texture to put backspin on paintballs but if you turn the velocity up too much they will climb, or if the gun is tipped, they will curve. I have also seen airsoft guns that have an adjustment to catch the top of the bb to induce backspin. I can hit a chest sized target from 100', at most about 120ft consistently with 4" finned rounds made of dense foam. (35grams). The solid center mini tennis balls were good for about 80 feet before they would curve. I ordered some trick golf balls like the exploding one that I am guessing is compressed talc or corn starch. The phantom golf ball apparently vanishes into cloud of vapor mist. I am hoping to make these OC tainted if they can handle the initial shot. I have the task of coming up with a super short barrel and ammo that can be used on ships and tight quarters. The 1:48 twist on the M32 with a short barrel is not doing the trick. We are making our own round rounds out of foam (varying durometer) and I was considering adding the dimples. Basically 40mm rubber golf balls. I will start with the real thing first though.

To impart backspin in perpendicular manner, maybe a strip of the barrel has a ridge of some nature.

and was that four INCH groupings at 50' or really 4'?

Well looked it up, probably more like 80' on those shots, and I was shooting a small car hood. But come on, my style of shooting potato guns is nothing like benchrest shooting. No sights, this was an un-sleeved barrel, hip-fired, etc... Basically I'm sure you could do better.




As I proposed earlier, if the ball surface is rotating, then the boundary layer also rotates (Picture 2). When this happens lift is generated, the ball will arc from your desired trajectory.

The magnus effect most importantly generates the lift, and most difficult part of it all is generating that backspin square on so you'll also get some horizontal accuracy.

But if the ball were spun with rifling it would be stabilized, but not generate lift.

pimpmann22 wrote:But if the ball were spun with rifling it would be stabilized, but not generate lift.

Not entirely true. Sidewinds can cause a rifled projectile to generate lift... still, the effect is minimal relative to the actual side drift caused by wind.

Solar wrote:To impart backspin in perpendicular manner, maybe a strip of the barrel has a ridge of some nature.

I would strongly advise fitting it with some sort of adjustable hop-up. Fixed hop-ups always demand a specific relationship of projectile mass to velocity (else the trajectory can hook sharply skywards*), leaving you without potential to adjust velocity or projectile.

*Alternatively, lift can be too low to have a particular benefit on the trajectory, but at least it would then be spin stabilized to some extent.

pimpmann22 wrote:I read on the wiki about lead balls being shot at 1:60" twist rates. I think ultimately a rifled barrel may get the most accuracy.

Yes, but less dense (and lower velocity) projectiles demand faster twist rates (countered to some extent by the fact that larger bores need slower twists)
Punching some numbers into a modern version of the Greenhill equation suggests that a golf ball at likely velocities would need rates of about 20" or steeper.

... anyway, I could ramble on trajectory and ballistics for hours, but as the LRC is down (because of my sick laptop) I can't run (m)any numbers, so I'll leave my musings there.

Was 20" or steeper meaning 1:20 for the rate? I know the M203 is 1:48, but is using nearly 1 pound 40mm rounds.

Solar wrote:Was 20" or steeper meaning 1:20 for the rate?

Sorry, I totally cocked up earlier.

I put a factor into the equation which I'd forgotten wasn't used with the metric version of the equation (It's used in the imperial version, but I built it into the overall coefficient when I converted it to metric)

With that error corrected, depending on exact velocity, for a golf-ball, you're likely to be looking at a twist of between 1 turn in 36" and 1 turn in 48". (500 fps correlates roughly to 1 in 42 inches calculated rate.)

That said, the calculated twist is not the twist you necessarily need. It's just a rough number which may vary depending on the exact nuances of the projectile.
The other thing to consider is the projectile's actual strength - spinning a weak projectile too fast will simply cause it to fly apart.

That said, golf-balls are pretty tough, so that's unlikely to be a problem. They're also unlikely to be too picky about the exact twist rate... you can probably shift it a foot per turn either way quite comfortably.