Custom PCP build on Disco or B-50 action???

[DougT]

Hello,

I've been shooting a TF-89 springer for the past year and a half and love it.  The only problem is hold sensitivity.  After reading many good things about the Disco, Katana, Marauder and B-50 rifles I think I would like to get into PCP.  The only problem is the inconsistant velocities (velocity curve) and low shot count (20-30 decent shots).  My buddy and I shoot a fair amount, typically hundreds of shots in a session (targets, birds, squirrels, cans, etc).  Springers will shoot all day so shot count is important.

I'm a tinkerer and love to fabricate, modify or custom build things that weren't ever sold.  I have  welders, a metal lathe, a milling machine as well at many other tools so fabbing isn't a problem.  I would like to custom build a rifle to meet my needs.  Here are my requirements and what I'm thinking of doing.  Input/suggestions are very welcome.

Requirements:
1.  Be very accurate (1/2" groups at 40-50 yards).
2.  Be easy to shoot from a bench or off-hand.
3.  Have a muzzle velocity of 850-900 fps using normal weight pellets (14-15g).
4.  Get at LEAST 100 consistant shots at the desired velocity.
5.  Have a pressure gauge and pressure regulator.

How I'm thinking of doing this.
1.  Start with either a Disco or B-50 barrel, action & trigger group.
2.  Fabricate a 3000# air reservoir of at least 750cc.  (the Disco is 126cc and the Marauder is 210cc?)  A piece of 2" chrome-molly steel tubing about 14" long should do this.
3.  Use a paintball regulator with a 3000# input and a 1100-1200# output.
4.  Make the reservoir endcap recessed to house the pressure gauge.
5.  Use a Marauder stock, cut off at the front of the action.  The 2" reservoir would act as the front stock (looking similar to a QB-79).
6.  Do the power adjuster mod to the Disco or B-50 action.  Port the valve.
7.  Locate the fill port on the bottom of the gun, ahead of the trigger group.

Any input on which barrel, action, trigger is better would be appreciated.  I'm no stranger to trigger work so adjusting or custom parts are not a worry.  

The larger diameter air reservoir would be about the same length at the barrel but would probably be too large a diameter to have a wood forearm surrounding it.  It could be painted or have a thin wood veneer that was stained to match the custom rear stock.  I think a laminated rear stock would be intersting.

What do you think parts (barrel, action, trigger group) would cost?  Where would be the best place to get them?

A short way around this may be to retro-fit a Disco or B-50 with a larger reservoir and regulator.  Anyone done this?

Thanks for any advice.
Doug

[lastmanout]

I am kicking around a similar idea. Your 100 shots, regulated at 900 FPS should need a lot of air. A 22CI HPA tank with regulator may do it, but is not very sleek looking. I am thinking of  modding a QB79, caliber .22, with a tank and regulator set at 1600 PSI. The B-50 looks like it has more horsepower/potential, but I am afriad it has a low build quality. Guys put lots of time into fixing Bam factory 'oversights". The Air Force Talon with a BIG air tank, 2000 PSI regulator, long barrel, might be the easiest route for me. Good luck.

[Jaymo]

The B50 is at least as well made as the QB78, if not a whole lot better. The quality of my B50 is head and shoulders above my QBs. I wouldn't worry too much about the 50. The only things that my B50 needed to have done to it are things that my 3 QBs need also. The 50, however, gives you a LOT more power potential. The majority of things I'm doing to mine are things I want to do, not need to do. My interests in the 50 are in getting as much power as is possible, without giving up  good hunting accuracy. Mine ran 867 FPS from the factory, brand new. Once I get it back together (didn't feel like going out to the shop to work on it while it was cold/rainy) It should be a monster.
It's totally worth the time and effort I'm putting into it, along with the purchase price.
My only complaint about the 50 is that it doesn't come in a left handed version. I may rectify that. If I can figure out the setup for milling the radius in the bottom of the breech, I'll make a left handed riser breech.
Considering the fact that you can get 40 fpe with very little work , I'd say it's a very worthwhile investment. A BigEd riser breech and shroud would be a great addition.
The problem I had with power output at 3,000 psi was caused by 1 tiny little thing that I overlooked. When I faced off 2mm from the nose of the hammer, I failed to also face off 2mm from the striker screw that goes in the nose of the hammer and  it was covering up the air ports in the hammer. As a result, it was slowing down the hammer speed. My fault completely. I fixed that easily enough. Most of what I'm going to do to it is also just because I can.
I can tell you one thing, even before I figured out my mistake, it was a HAMMER at 2,500-2,700 psi. It's going to be a monster once I'm done with it.

[DougT]

No need to reinvent the wheel.  It looks like the RWS/Hamerelli 850 Airmagnum is what I'm looking for.  Add a HPA conversion and I'm there.  Not much fabrication/worrying and it's already proven.  

[Phil_B]

The 850 is a good place to start.. I just got mine in .22 and did the HPA conversion .. 1800 psi regulator ,B&A short adaptor that has been flow moded, 22ci tank. A new hammer spring ,Its now doing 850 fps with 14.3 cp . There are a few more mods that can be done to boost it up more but I want it at 850 fps .And Im hoping for 80-100 shots per fill but it may go even higher. If you go over to the 850 page there is a lot of help there and the 850 store. Here are links to both.
http://www.network54.com/Index/84463
http://www.the850store.com/

[DougT]

Thanks Phil B.

I've marked those sites and scanned through them.  Lots of good stuff.  

You said your regulator is set at 1800psi.  Have you chrono'd your shots as pressure drops down below that, to say 1200psi or lower?  What sort of accuracy are you seeing?  I'm wanting to be able to accurately shoot at 50-70 yards.  Any bad traits of this gun?  How are the magazines to load?

Thanks for any info.
Doug

[Dust]

The magazines are pretty simple to load in .177, so I would say .22 would be easy.  Another thought, would be a talon with a 48 ci regged tank.  Seen a few, and the huge tank doesn't look too bad sticking out the back.  But I would say go for the 850 in .22 with mods and a 22ci tank, don't know about the regulator pressures though, I'm still on AS cartridges

[Phil_B]

DougT - 1/6/2010  1:26 AM

Thanks Phil B.

I've marked those sites and scanned through them.  Lots of good stuff.  

You said your regulator is set at 1800psi.  Have you chrono'd your shots as pressure drops down below that, to say 1200psi or lower?  What sort of accuracy are you seeing?  I'm wanting to be able to accurately shoot at 50-70 yards.  Any bad traits of this gun?  How are the magazines to load?

Thanks for any info.
Doug

With the gauge on the regulator I shot it down to 1500 psi and that's were fps started to drop. I bought a reg that was set to 1800 but I did not check that it was actually putting out 1800 psi. I got my reg from JDS Air Man so I believe it to be close to 1800. The mags are a breeze to load. And so far my accuracy is very good but my gun was bought used from someone on the yellow that said it had never been shot, and I don't know how long he had it sitting around and maybe if I cleaned the barrel it might be a great shooter but I'm happy with 1/2" at 20 yards. Others have said that the 850 is capable of one hole at 20 . If some one asked me would I buy an 850 and do the mod's again , I would tell them FOR SURE I would do it again...