by Tom Gaylord
Writing as B.B. Pelletier
The Johnson Indoor Target Gun is a catapult BB gun that was made in the late 1940s for youth target practice.
This report covers:
- Cutting trouble
- Sloppy cutting
- It worked — sort of
- What to do?
- Experiment over?
- Too much power
Today I will try a different kind of rubber in the Johnson Indoor Target Gun. Several readers who are more knowledgeable than me about slingshots recommended I try Theraband Gold. It is one of the types of elastic that’s favored by catapult users and makers around the world. I watched a You Tube video of the Slingshot Channel titled, The BIGGEST slingshot EVER. The builder uses Theraband Gold to launch a bowling ball into a Mercedes car repeatedly, destroying it.
I bought 6 feet of Thereband gold rubber on Ebay, a rotary cutter to make clean cuts and a cutting mat for this project. I used the data from Part 3 of this report as my starting point, simply because there was nothing else to use. Maybe someone has done what I am about to do before, but I have never seen it in print.
The rotary cutter is to cut the Theraband material cleanly.
Right off I noticed that the cutter had a mind of its own. I should have used a seamstress’s plastic cutting guide, but I have already spent a lot of money and I wanted to get on with this test. I needed it quick and dirty and that’s how I got it.
Here is the band I made to shoot. As you can see, I got sloppy in the cutting. I will explain why in the text.
Once I figured out that I wasn’t going to cut the band straight, I gave up and cut it freehand. I wasn’t looking for a final solution. All I wanted was to see if this was even possible. So any band I made would not be used in a final test. I just wanted to see if this worked.
It worked — sort of
Well, it worked, and then again, it didn’t, I installed the band and shot the gun but it was extremely weak. Cocking was normal and the launcher caught the band when it went forward, but I didn’t bother to chronograph the shot because it was way below what we have seen. As a guess it was in the 50-60 f.p.s. range.
The band has to fit inside the groove in the launcher (arrow) or it won’t work.
What to do?
Well one band wasn’t going to do anything, so I wondered about multiple bands. They would be more powerful, but there would be a problem. The rubber band has to fit into the groove that’s in the launcher in order for the gun to work. Surgical rubber tubing is great because it fits into the groove very well when it’s stretched, but a flat band like the Theraband has to be stretched very thin to fit in. If it’s not all the way in, it can slip out on firing or even when the gun is just cocked and left alone.
Nevertheless, I wanted to know, so I cut three bands of equal length and made a loop at each end of all three.
I cut three bands of equal length from the Theraband material.
I then made a loop at each end of the three bands.
The bands are uneven, but all I want is to see whether this approach even works. The bands went into the top cover of the gun, but they slopped over the anchors and when I cocked the gun, they didn’t all fit into the cocking groove on the launcher. It was a disaster!
Then I took the three bands apart and used the two smaller bands together in the same way. This worked — sort of. I could cock the gun, but when I shot it, the bands popped out of the launcher groove and the shot was weak. It registered 86 f.p.s. Okay, that doesn’t work.
I thought this was the end of it and I could install another surgical tube and be done with it, so I did. Since I knew the tube had to start out 7 inches long, there was no wasted time. The velocity was 127 f.p.s. which is very close to the best velocity I got in the Part 3 test.
I thought this experiment was over. But that evening I thought about it some more and I wondered whether twisting the flat Theraband might be a solution. It’s flat to begin with, and if I twist it many times would it roll into a cylinder that might work better?
I used the widest of the three bands I had cut before — the band I had removed when I tried two bands. As you can see, a wide band can be twisted thin.
After anchoring one side of the band I rolled it to one side, twisting it into a cylinder.
It worked! This time the band loaded into the launcher’s groove and also allowed the gun to be cocked. The velocity was 129 f.p.s., which is as fast as I have shot so far. That is a good place to stop. I have no doubt that a higher velocity can be reached. I think 160 f.p.s. or even a little more might be possible, though I doubt 200 f.p.s. can be broken. I even cut a wider piece of Theraband Gold to test whether a special shape of rubber might help.
I cut this band and even started installing it.
Too much power
At this point it dawned on me that the Johnson wasn’t designed for great power. So what if I can boost the velocity by a few f.p.s.? If it breaks the gun in the process I will have lost everything. As far as I’m concerned, I have tested this as far as I plan to go. Surgical tubing is still the easiest material to use and starting with a 7-inch length gives just enough on each end to make the loops.
I will transition from velocity testing to accuracy next. The Johnson was touted as being able to hit flies at 16 feet. Let’s see about that!
23 thoughts on “Johnson Indoor Target Gun: Part 4”
I’m thinking this was designed with that velocity as a constraint. Using Theraband gold would probably allow a heavier payload but it won’t go any faster. “She’s givin’ at all she’s got Cap’n!”
Aye, an’ the warp drive’s startin’ to fuse!
She cannae take the strain too long we have to eject the core!
The Dilithuim crystals are completely fused!
Good try! Pretty innovative to try winding the rubber. Made me think of the old rubber band airplanes I used to buy at the 5 & 10 store. I would continue winding until I had double knots to make it go faster and farther. It wasn’t worth the damage to my finger.
I think the logical conclusion is just as you said: It wasn’t made for more power. You can put a supercharger on a moped but it will never be a Harley so just accept it as it is. Looking forward to the fly test.
You summed up my feelings well.
I remember those rubber band airplanes. They were a lot of fun.
B.B., I agree Johnny’s analogy is a good one. The moped will never be a Harley. Besides, you don’t want to wreck your moped, er, Johnson Indoor Target Gun.
I, for one, am curious to see just how accurate this thing is. Will any flies around your place be safe?
Flies? At my house? Not since I bought a Bug-A-Salt.
I will have to settle for inanimate targets.
You could go to a stable if there is one near you and the owners didn’t mind. They might be intrigued to see this fly-killer in action. There would also be plenty soft backstops with flies happy to sit still for your projectiles :^)
It may not be a Harley, but I’ll bet it would be a fun ride!
I hope your recovery is going well, BB.
This might interest you: Auction of of someone’s vintage airgun collection up here in Canada:
Thanks for the link. Now, who’s the Great Enabler?
I am so thankful that I do not have the money right now to participate in this auction. I saw several very nice pieces that would really like to live at RRHFWA.
Thank you for all of the effort and added expense. At least you are set up with material if you ever get into slingshots. Onwards!
Good Day to one and all,….. Chris
“…I wondered whether twisting the flat Theraband might be a solution.”
Nice work, B.B.! That was a good thought.
It will be really interesting to see if this thing can, indeed, hit a fly, or fly-sized target, at 16 feet.
Take care & God bless,
A rubber-band catapult gun is on my winter project list and I plan on powering it with a Theraband Gold bands.
Cutting the Theraband does take a bit of practice, I prefer to use a wide straight-edge (a large lexan “drafting triangle”) to stop it from moving around while cutting.
A couple of comments on the Theraband…
– The band performs best if it is stretched 4 to 5 times it’s relaxed length.
– Tapered bands work better than straight ones.
– The power is controlled by the band width and single bands are preferable to double-band sets.
– For reference, typical slingshot velocities are 175 to 225 fps using a 3/8″ steel ball
May I suggest another configuration to try? To deal with the cocking issue, try threading the Teraband through a short section of surgical tubing for the launcher to latch on to.
If you compare the resistance of the Theraband to that of the surgical tubing you will be able to tailor a band that does not exceed the strength of the Johnson gun.
The weight of the launcher is a concern but I am guessing that the Johnson could manage 150 fps with a bit of tinkering.
Happy Monday all!!!
Your Theraband in surgical tubing idea has merit, if I can figure out how to do it.
You could push a loop of string or yarn through the surgical tubing with a straw with a notch cut in the end, thread the Theraband through that loop and pull it back through the tubing.
That’s my plan, but rubber sliding against rubber isn’t smooth. I will use some Vaseline.
You should check to make sure the Vaseline won’t degrade the rubber. I’m reminded of all the warnings on condoms to only use water-based lubricants.
Water is commonly recommended for slipping surgical tubing onto the forks of slingshots but I always found rubbing alcohol worked better for me …just enough slip to get things in place but evaporates quickly so things don’t slip later
I was thinking about a dusting of talcum powder.
Larry from Algona
It is a shame that PA does not carry the Diana/Snowpeak Outlaw. It is sounding like a very serious competitor for the Marauder.