Speargun designs I can't stand

You get more power with a roller gun because the bands are pulling the shaft for a longer distance. With standard band configurations after you pull the trigger the bands lose contact with the shaft sooner because the shaft is traveling faster than the bands. As Don sd the band with a roller gun is in contact with the shaft until the last few inches of the gun making it more than 1 roller gun band equals 2 conventional bands. Phil Herran had some numbers up on other boards about how quickly the shaft is moving faster than the bands on a standard configuration.

From my understanding the reason the 1 roller band is similar to 2.5 bands, which is a very rough approximation, has to do with how long the band is applying force. In a conventional gun with a 20 in band there is a section at the front of the gun, roughly the last 12", where the band is no longer applying force. Once the rubber has reached its natural length it is no longer propelling the shaft. Thats why you often hear people describe a 100cm wood gun shooting like a 120 or some longer length. From what I read Bill was saying that if you kept gun length, shaft size, etc the same a roller gun 1.25 times more power than a 2 band gun. Obviously this would depend on how each gun is rigged how right the bands are to begin and other factors but it is a simple way to avoid comparing lengths which as most of us know has its own issues.

Personally I dont like feel of a roller gun. Ive never shot one but intuitively they seem bulky and difficult to maneuver. I havent had an issue with recoil in the past and dont mind a little punch, like Dan said it lets me know the gun is shooting hard. That being said I appreciate the thought and ingenuity of roller guns and I like to see the technological advance of the gear in the industry.

Dan, I have had guys tell me that their skinny 6mil shaft is hitting as hard as my 5/16, because of increased speed of the light shaft with the same power.

Aviation people distinguish air resistance as parasitic and induced drag, but the importent thing to understand is that drag increases as the square of speed. While power increases in a linear fashion, drag increases exponentially with speed, in a parabolic function. Lets think of a car for example but leave out rolling resistance. If 100 horsepower would push a certain vehicle 100 miles per hour through the air, doubling the speed to 200 would require two-squared or 400 horsepower to overcome air resistance, while 300 miles per hour would require 900 horsepower.

High shaft speed (7-8 meters per second) from a light/thin shaft has it's limitations when we want 2O foot shots to penetrate.

Shite:@ what am I doing here.......I have a kitten to play with.;):D

Cheers, Don

Quote from John Hanson

Thanks for the explanation and your perspective. Most everything said is all stuff I have already heard. I guess my real problem is understanding how one long band equates to 2.5 short bands. I didn't do a very good job of asking the question in my post. It may sound silly, I know I should "get it", but there is something in my mind that just doesn't seem to agree.

Like most things for me, the best way to gain any real perspective on something is to experience it. I would like the opportunity to shoot a roller gun someday.

"After all is said and done, it's about like 2.5 bands on a comparable conventional gun. so, you could take the same gun, put 3 bands on it, and the main differences would be a "better" sight picture due to 1 band instead of 3 (some would argue they actually prefer 3), and a softer recoil. For a shooter who practiced with both, there probably wouldn't be a noticeable difference in loading time. The time it takes me to load my 48" lever action rg is so close to what it takes to load a 2 banded conventional gun that it's academic if there at all."

I'm referring specifically to my 48" lever action roller here, that's why I said "it depends". For a conventional gun in that configuration the energy developed at 250% elongation with a single 5/8" band is 1664 inch Lbs. (This comes from the spreadsheet Tin Man and Jim Cuda developed from the Primeline tables and charts on the Primeline website). For the roller version of that gun, the cocked power is 3400 inch Lbs, 4100 inch Lbs, and 4900 inch Lbs. for a 5/8, 11/16, and 3/4" band, respectively. This is equivalent to 3400 / 1663 = 2 bands for a 5/8" band, 4100 / 1663 = 2.5 bands for an 11/16" band, and 4900 / 1663 = 3.0 bands for a 3/4" band. I mentioned earlier that the max power is determined by the shooter's ability to cock the top band. If he's already doing that, he can't just go to a bigger band to get more power. But with the lever he can go to a bigger band, make it the length he can just load on top, and still load the bottom because the lever gives him a mechanical advantage (in this case 2:1) to cock the bottom, which he would otherwise be unable to cock.

Like I said in an earlier post, you can put 3 bands on a conventional gun the same length and get the same power. It's not faster to load 3 bands than it is a one band roller, and the roller will shoot with less recoil if that's important to you. They can be sleek and streamlined, just as conventional guns can be, so if they aren't, it's because the builder built them that way, not something that's inherent in the concept. If shooting 3 - 5/8 bands on a conventional guns is something a builder prefers, then that's what he should do. Rollers are no more "one gun for all situations" than a pipe gun, hybrid, or pneumatic. It just comes down to what you want to shoot.

Don you are absolutely right about the lighter, faster shaft not hitting as hard as your 5/16 shaft. It works the same with bullets, as a bullet weighing 77 grains traveling at 2500 fps is going to penetrate deeper than say a 55 grain bullet traveling at 3000 fps.

I incorporated this into my spearguns, as I was not getting quite as much penetration as I needed with the factory shaft. While it was fast, it didn't have the kinetic energy and weight to penetrate a big catfish's hard skull at much beyond 5'. When I installed a heavier shaft, immediately the penetration went way up, despite losing a little velocity, and had no problem piercing skulls after that.

Quote from Dan

Using roller gun logic: 1 band roller = 2 band conventional = 4 band tie in/ferrules which brings us back full circle

The only scientific way to prove this is to have someone from spearbored fire both guns straight up in the air and see which shaft goes higher...

this sounds a lot like the barrel and caliber size argument in riffles .

I am not sure if this is pertinent but my father did say that he had both the Nimrod [ pneumatic ] and a Champion 3 5/8 band gun at the same time and same length . when he judged both , the Champion had more power but was loud [ metal wishbones ] but the Nimrod was far more quite and accurate with less recoil .He ended up using only the Nimrod because he did not like buying bands . Take into consideration that at this time he was squatting 500lbs [ 7 yrs bodybuilding ] and both guns power were completely maxed out . [ he bent the Nimrods pump ]
from pumping it to hard. they also both used 5/16 shafts

For what it's worth, when I first tested my "Dirty Water Rollergun" in my test tank I took a 9/32" and a 5/16" shaft and shot them into a block archery target that was 12" thick. With the same gun, same band setup, same target I got roughly twice the penetration with the 5/16" shaft, with both one and 2 bands. Not very scientific, but it definitely supports what Don is saying. Target was at about 12' so distances were pretty close. I got the same result at 16'.

Quote from ladvr

The only scientific way to prove this is to have someone from spearbored fire both guns straight up in the air and see which shaft goes higher...

:laughing3::laughing3:.

D

Quote from Wood Guy

For what it's worth, when I first tested my "Dirty Water Rollergun" in my test tank I took a 9/32" and a 5/16" shaft and shot them into a block archery target that was 12" thick. With the same gun, same band setup, same target I got roughly twice the penetration with the 5/16" shaft, with both one and 2 bands. Not very scientific, but it definitely supports what Don is saying. Target was at about 12' so distances were pretty close. I got the same result at 16'.

I would like to see the results of a similar test done with a roller gun and a "standard" 2 band gun of the same length shooting the same shaft.

Part of the problem of my understanding the roller concept is that half of the band is under the gun with tension opposing the travel direction of the shaft. I appreciate the further explanations. It definitely helps.

Quote from Dan

You're not missing anything John, it's just smoke and mirrors. A one band roller is the same as two band conventional gun, the bands are just positioned in a different place, running along each side of the gun instead of both running along the top. If you measure each band section and the band stretch on a roller, you'll see that even at best (loaded as close to the trigger guard on the bottom as possible) it doesn't reach the minimum %300 stretch we require on conventional guns. And it's more difficult to load.

Using roller gun logic: 1 band roller = 2 band conventional = 4 band tie in/ferrules which brings us back full circle

Like most other things, it's not necessarily about convincing me that it's something that is better than what I currently use. It's simply a matter of having the actual experience to develop an informed opinion on the matter;)

Quote from Wishihadgills

From my understanding the reason the 1 roller band is similar to 2.5 bands, which is a very rough approximation, has to do with how long the band is applying force. In a conventional gun with a 20 in band there is a section at the front of the gun, roughly the last 12", where the band is no longer applying force.

That is the clearest explanation I have ever heard about the subject. Thank you

In further detail, I will explain my confusion.

I have never seen or handled a roller gun in person. My only experience with them is through photos. I have only ever seen a photo of a roller gun with the bands loaded on the tabs of the shaft or with no bands on the gun at all. I now understand, that in the contracted state of the band, the wishbone would actually rest at or near the muzzle.

Again, it may sound silly but I had never really put any thought into it before. But, I had this vision that the band would lie as a circular would in the contracted state. I never had any interest in the guns to begin with just because of of the complexity of the build.

I appreciate all those that that took the time to explain the concept. I learned a lot

I've spent quite a bit of time thinking about rollerguns. The idea intrigues me because I want to know where the "future" of spearguns lay. The current designs have pretty much maxed out the range. The only way I think we can get more would be some variation of the rollergun. The only way the standard gun design gets better range is by getting better rubber and stiffer shafts.

Rollers are an interesting problem to solve, but they're a pain in the butt. The lines get tangled on the rollers and the muzzle gets too bulky, so it's hard to swing. One way they get more range is that they deliver the same amount of power more gradually, so shaft whip becomes less of an issue. This gives a lighter shaft more range because you can put more total force on it.

I'm sorta done with rollers, for now anyway. I realize that I like a soft shooting gun; so that I'm done remodeling the hose, I'll get back to my 110cm euro project. Ballasted, wood, 1-16mm + 1-14mm band (a la GR Tarr), 6.75mm -7mm shafts.

Side question:
Why are we pretty much stuck at 250% (3.5x) stretch? Is it because of the rubber's ability to retain power?

Quote from JimCuda

Side question:
Why are we pretty much stuck at 250% (3.5x) stretch? Is it because of the rubber's ability to retain power?

From what Ive researched, stretching the bands beyond 250% results in a decrease in band life. You can pull them tighter and get more power but youll have to change your bands more often. Also a lot of people have trouble pulling back really tight bands which prevents commercial gun makers from making bands too "tight".

Im sure Don can explain better as he is an expert when it comes to speargun rubber.