All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Dual Tank Benchrest Rifle

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I have come up with a crazy idea for what may be my last big (and heavy) project.... My hands are getting very arthritic, and I don't know if I will be able to complete this one, but I have decided to have a go.... The concept is to use two 700 cc Carbon Fibre 4500 psi Bottles mounted under a plenum of equal length (16") made from 4130 CrMoly tubing of the same dimensions as an MRod tube.... ie 1.25" OD x 0.95" wall.... Here are the bottles, which I have on order from Wes at ArcheryAirgunFun in Saskatchewan....

The two tanks will be mounted side by side with the plenum above, using a scaled up version of this tank block I made for two 88 gr. CO2 cylinders.... The three holes in the block will be threaded 18mm x 1.5mm, with the regulator screwing into the upper hole, and stubs made from 18mm steel bolts used to mount the tanks.... They will be sealed to the block with an O-ring at the parting face to the top of the tank....

There will be a short piece of Picatinny rail mounted on the bottom of the block to mount a BiPod, like I did on the converted QB....

Here is a sketch of how I plan to mount an adjustable Ninja Regulator, with the bonnet inside the end of the plenum tube.... The adapter is shown in red....

I will turn down the OD of the bonnet by 0.020" for a length of 1/2", and that part will fit inside the end of the tube.... The bonnet setscrews will be accessible without removing the bonnet from the tube if a regulator rebuild is necessary.... Since the adapter is mounted with four 10-32 screws into the tube, the assembly can be turned in 90 degree increments for orientation of the regulator, and then the position fine tuned by rotating it on the 1/2" NPS bonnet threads, and then the position locked into place with two setscrews.... Here is what the dual tank CO2 setup looked like to give you an idea of the plan....

I have not made a final decision yet on caliber, but if Al at NOE makes the mold I have asked for, this Lothar Walther barrel is what I would use....

I haven't decided whether to use this profile, or something a bit lighter....

Here is a drawing of the bullet I have asked Al to make a mold for.... It is a full 4 calibers long, and made for the 5.9" twist of the 4.6mm barrel from LW....

This is very much a matter of finding the fastest twist barrel I could afford in a small caliber, and building the bullet and gun around it.... It will take about 3000 psi to get into the 900's and the plenum is good for the full 4500 psi at a 3.5:1 safety margin.... There will be 1.4 litres of air (85 CI), so if I can achieve an efficiency of 1.0 FPE/CI, at 85 FPE I should get about 70 shots with a 1000 psi (70 bar) drop in tank pressure.... I hope it all comes together....  8)


bear air:
Sounds like fun Bob. I really like the double block. I have a 30 cal armada I wouldn't mind double tanking.

I think itíll come together just fine. For sure will be interesting. Look forward to progress updates.



Time to start those winter projects for folks up north.  Too cold to do anything outside.  Here in central Fl, it'll be cool enough to work in the garage for more than a couple of hours each morning. :o ;D

Pending finding a regulator that can handle outputs of 2800-3600 psi that will fit and I can afford.... and considering the costs.... this project is unfortunately on hold for now....  :(



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