Posted: 03/09/2008 3:55 AM Post subject: Bofors - GB Coax - Video!
Big Daddio
Joined: 12 Dec 2007 Posts: 1370 2550.30 Spud Bux
Bofors Little Brother - GB Coax
I started on my mission to build my first pneumatic only knowing that I wanted to a) build a golfball gun, b) a coaxial model and c) somehow utilize one of those dumb 2' pieces of 3" PVC that Home Depot and Lowes love to sell these days. After considerable time and effort, I came up with "Bofors Little Brother", named after the Swedish 40mm anti-aircraft guns used on allied ships in WWII because they have similar look and share a similar caliber.
Features include:
- 48" 1.5" SDR 21 barrel
- c:b = 1:1
- overall gun length about 5'
- 3" barrel sealing piston, multiple plastic paint coatings to build out to ideal diameter
- 3/8" to 1/2" piston travel
- 3/4" Orbit Watermaster pilot valve, 3/4" brass and sched 80 piped, blowgun actuated
- schrader air fill
- screw ball stop and barrel dimple, holds ball in place reliably
- cool 2 tone flat black/glossy black paint job
- cool looking but useless barrel noozle
- deep throated, fast pulse shots, 50 - 100 psi feels about right in this gun. Laser beam GB shots...
After this project, I guess I still count myself a combustion man at heart. The whole air compressor requirement for medium and big guns makes me really enjoy the advanced combustion's always ready-to-go anywhere appeal. However, I wanted some pneumatic experience and this has been invaluable. The toughest part was getting the piston right and figuring out what order and what type adhesives to use when finally gluing the coax body and barrel together. You need a set of octupus arms to do everything you need to do almost all at once. You don't get a do over with a socket weld. Epoxy is my new best friend...
The BLB with Cool McCool. Reasonable ergonomics and power aplenty.
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Business end of the BLB
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Rear view
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Valve and piston assembly
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Sealing barrel face and airtank. Barrel standoff was made by using a tablesaw to slice the first 3/8" face off of a 3" / 1.5" reducer bushing. It is welded to the 3" only and floats around the 1.5" barrel. Screw ball-stop visable, barrel dimple on opposite side and is 7/8" in front of the stop.
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Piston cylinder and pilot valve system
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Piston, used a slice of 2.5 " PVC pipe to build out the "ring" on a 2" socket to male NPT adapter. Most of the NPT threads were sanded off. Used multiple paint passes to build out ideal ring diameter.
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Last edited by starman on 07/08/2008 9:21 AM; edited 14 times in total
Hmmm, the 2ft sections they sell at the Lowes and Home Depot near me are PVC-DWV, gotta replace one on my cannon same reason. Pass it off as pressure rated...
Aside from that, beautiful gun, Nice job with your first cannon, jumping right in on a piston. Very clean!
Very nicely made, epsecially for your first pneumatic venture some videos, perhaps?
Yes indeed there are! Just need to get them downscaled and uploaded...they are HD and way too large at the moment.
Rokmonkey wrote:
Hmmm, the 2ft sections they sell at the Lowes and Home Depot near me are PVC-DWV, gotta replace one on my cannon same reason. Pass it off as pressure rated...
Ding ding ding...You win the rubber ice-pick! First one to mention DWV. Your homework for today...trip on down to Lowe's and check again for yourself. The 2' sections of 3" and 4" are pressure rated PVC and wayyyyy over priced. Longer 5' and 10' foot sections are cell core. If they are substituting cell core for the 2' items in your area, complain to the store manager.
It truly depends on the individual store. Currently our local Lowe's only stocks 2' sections of ABS. The only NSF-PW PVC that they are stocking now is 2" and below. Their reason is, it's what they have had requests for. No need to stock what people aren't going to buy.
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