New Old Project - .25 Disco Revisited

[rsterne]

The transfer port is 0.219" (7/32").... The barrel port is oval, 3/16" x 1/4" (same area).... The exhaust port in the valve is also 7/32".... The valve throat was 1/4" and the stem is 1/8", so teh resulting area was the equivalent of a 0.217" hole.... Now that the throat is drilled to 17/64' (0.266"), the equivalent would be 0.234".... The fact that I didn't gain any performance at any given pressure leads me to believe that the smallest area (ie everything except the valve throat area) is the limiting factor.... However, I did gain some efficiency, which makes me think that the larger throat allows less dwell to do the same job, which is a good thing.... The negative is that you then need a stronger hammer strike because of the increased seat area....

The Mr. Hollowpoint pellets look very nice, and are very consistent in size.... One weight didn't appear to shoot well, the others will have to wait until I get outside.... They are VERY expensive, however.... I am running a QB 7X hammer spring, a hammer (with guide) that weighs about 70 gr., and has about 0.85" of stroke before it hits the stem the way it is adjusted.... and the maximum valve lift possible at this adjustment is 0.2" (but in practice is much less)....

Bob

[SeanMP]

Hmmmm

I was afraid of that. The strongest spring I have here is a QB Spring. The .049 size.

I assumed that I was going to need a stronger spring but as you saw Trakar is a bust. The only thing they had was the light spring I wanted for a bolt assist spring.

So I'm shopping around for a spring supplier...any suggestions?

[rsterne]

Two QB springs end to end on a guide, and a much longer hammer travel?.... You may be able to find something at a hardware store, automotive supply (Lordco?), etc.... Go up in diameter, wire size, and length?.... My DAQ uses a 4.5" long spring, 1/2" OD, made of 0.063" wire, and about 1 5/8" travel (I don't know the hammer weight)....

Bob

[rsterne]

Sean.... I dug around looking at hammer springs today, and I also rebuilt the hammer on my Hayabusa to get a full 1.0" of travel.... I'm using a QB spring, and at 1900 psi, the last 4 turns of preload do nothing to the velocity.... I'm guessing it might be close to working properly at 3000 psi.... My .25 cal Disco would when the valve throat was 0.250" (the Hayabusa is the same), but didn't have enough hammer strike at 3000 psi with the QB spring with the throat drilled to 0.266".... The Hayabusa has a heavier hammer and more stroke, so it just might do it with a QB spring....

Anyway, I have two Trakar springs that are 0.360" OD (fit a 3/8" hole) x 2.5" long.... one is 0.051" wire, and acts identically to the QB (0.330" OD, 0.047" wire) rate is 17.9 lb./in..... The other is 0.059" wire, and it's a BEAST, 32.2 lb./in (#C0914-150-0635).... That spring has a whisker over a 1" maximum travel to coil bind.... I just noticed you can buy it in a 3".... I also have a 0.375" OD Trakar, 2.25" long, 0.062" wire (#C0953-157-0572) with a rate of 40.7 lb.in., about the same force to collapse to CB as the 0.059" x 0.360" one (but less total travel)....

I also have some 0.50" OD springs, 2.5" long, and they have more travel, but a lower spring rate.... The 0.062" wire (#C1270-160-0635) has a rate of 21 lb.in. but nearly 1.5" of travel, so at CB it has about the same force as the 0.059" x 0.360" as well.... Trakar also make 0.42" OD (fit a 7/16" hole) x 2.5" long x 0.063" wire (28.5 lb./in.) and 0.48" OD (fit a 1/2" hole) x 2.5 - 3.0" long and 0.063" - 0.072", many of which should be OK as well.... Hope that helps....

Bob

[SeanMP]

Hi Bob

Thanks for all the info. On my Trakar order I think I had selected every spring they made that was between 19 and 30 lb/in, and from 2 to 3" in length. I am going to go back through the entire thing or possibly contact them with my parameters and see if I missed something.

My hammer is 72g and has a total travel of 1"

The pocket in the hammer is large enough to accept a spring up to .450"

Of course you know the other parameters. The throat is .302" and there should be about 215 lbs of load on the valve....Lloyds handy dandy hammer energy calculator would take a lot of pain out of recalculating for every change. I was expecting to require something in the 25lb/in range in order to have any useful range of adjustment.

[rsterne]

Sean.... I ran your numbers, and with a QB spring you're probably OK at 3000 psi but you may not have much adjustment.... it will probably be close to maxed out at 3000 psi....

Bob

[SeanMP]

Thanks Bob

Right on the edge of disaster...my favorite place