Discovery valve porting questions

[Rivers3Plinker]

I've begun a two phase project with the goal of increasing FPE as well as shot count on my Discovery.
The shot count will be helped by a SSG which I'll be working on later.

I have a BNM breach on this gun along with a 2260 barrel and a couple barrel bands from BNM.

I drilled the exhaust port in the valve body to 5/32 at 20 degree angle using my drill press and a simple DIY angle gauge block in my drill press vice. That seemed to work out fine, but of course the resulting hole is oval or ellipse shaped and not round. I measured my transfer port bushing from BNM and it was under 5/32 so I carefully drilled that out as well. No pics but I'm satisfied with the concentric results considering the limited tools I have to do it.

When I mock up the valve in the tube with screws and install the crosman seal over the port, I note some overhang of the seal at the back side of the port. This is due to the 20 degree angle drilling. I am debating filling this area with some JB weld and blending it into the exhaust port to eliminate this ridge. I would say it's maybe .015 or so. Does anyone think this would hold or will it simply be blasted out of the port and fired down my barrel eventually? Not sure if anyone has tried this.

Second question is I opened the throat to 15/64 again with satisfactory results as far as staying centered in the bore. However that also changes the profile of the throat edge where the poppet seals to it. The air now has to make a sharper turn into the throat because making throat larger makes it thinner and the new bore is straight out into the valve. I wanted to blend this turn. I tried to work this area with an abrasive rubber dremel bit I shaped for this purpose on my sander. Seemed to work OK. I then lapped the sealing surface using the poppet and some polishing compound with my cordless drill so it won't leak after assembly here. I think this will be ok and only other aspect I don't like is a ridge inside the chamber left by the end of the drill bit. I tried to blend that too but I'm not overly pleased with the results. It's just too difficult to access it with anything. There's also sharp ridges in the chamber from the retaining screw holes which I took to 10-32. I have no easy way to work those and clean it up.

What are others using to do this kind of work? It's so small and in such a tight area it's hard to see what you're doing and easy to make mistakes that render the valve body junk. I have another valve body on the way from Crosman so I can take another poke at this.

Thanks for replies

[nervoustrigger]

I use a small set of diamond burrs for fine shaping operations, forming radii to ease airflow, etc.  1/8" shanks can be used in a Dremel or handheld drill.  Even a cheap $10 set from Amazon or Harbor Freight will give a lot of mileage on soft materials like brass and aluminum, even occasional unhardened steel like a barrel or bolt probe. 

[Iamscotticus]

@ Steve:
With 600 posts you probably already know about ice machine tubing,  but FWIW,
Ice machine water tubing is .25 dia. and fits in the transfer port.
It is a popular TP alternative.
You can cut and shape it easily.
And its cheap.
I found the top of my Disco TP seal meets with the curvature of the outer bottom of the barrel.
So using a flat face seal is not going to give the best seal.
I can wrap a piece of fine sand paper around the barrel and use that to shape the top sealing face of the tubing,
then cut the bottom to length, which is square, I believe.
This and a thin layer of liquid thread sealant around the TP should work.

[Rivers3Plinker]

Thanks Guys,
I have diamond coated burrs for my rotary tool but the short shanks make it tough to get in there and still see what you're doing. Really what I've been wanting is a set with 2 inch shanks. I also need some speed control. I suppose a high-end rotary tool with foot controls, drive cable, and a smaller, hand held tool piece would be the best solution.

Yes I have the poly tubing on my 2289G with ported valve and it's a pain in the posterior to get that right. Once you do, it works though. I've made a number of them. I'm not sure it will work with BNM breach however because of the design for the bushing and the way it mounts up into the breach.

[MichaelM]

Out of curiosity...  What for levels are you shooting for. imho the disco valve already flows pretty massively because it's set to be used with co2 as well....  I actually have a smaller then stock port in mine .136 and making an easy 26.5 fpe with 14.3 grain cphp....

[Rivers3Plinker]

Out of curiosity...  What for levels are you shooting for. imho the disco valve already flows pretty massively because it's set to be used with co2 as well....  I actually have a smaller then stock port in mine .136 and making an easy 26.5 fpe with 14.3 grain cphp....

Good question. I don't have a number. My plan was to massage the valve for better flow, modify for stronger screws, fill it and start testing with a chrony. Compare numbers to stock and then start getting some shot strings. Try higher pressures up to maybe 2200 max and see what I get. My objective is to get the gun tuned well enough to be somewhat competitive with a .25 Mrod, or at least as good as I can get with a .22 disco without getting ridiculous. That would include converting to .25 caliber.
I'm shooting the JSB heavies 18.13 primarily but also the H&N Cuda match 21.14. I'm shooting out to 65 yards max today and would like to reach out a bit longer with these rounds assuming my mods help in that regard. More punch and less holdover.

[MichaelM]

I easily get 14.4's into the 900 fps range... currently I am getting about 1.36 fpe/ci eff in the gun but even so its still LOUD! so I would imagine 18.1's wouldn't be terribly slower to be honest and may give me even better eff... so you should be able to get those 18.1's up there where you want without to many problems...  getting my SSG built for the disco hopefully I can improve those numbers even further!!

[Rivers3Plinker]

I easily get 14.4's into the 900 fps range... currently I am getting about 1.36 fpe/ci eff in the gun but even so its still LOUD! so I would imagine 18.1's wouldn't be terribly slower to be honest and may give me even better eff... so you should be able to get those 18.1's up there where you want without to many problems...  getting my SSG built for the disco hopefully I can improve those numbers even further!!

I think those are good numbers for sure. I have seen similar with discos and CPHP on charts posted by Bob here along with what the other rounds shoot at. The 18.1 are slower but you get better efficiency and I like the added FPE down range. I have shot a wide variety through this gun and so far the 18.1 and H&N cuda group best and hit hardest at 50 to 60 yards for me.
Are you using an LDC? I agree it's LOUD - surprisingly so. I cannot shoot mine in my yard without the TKO on it. Eventually I plan to shroud it with kit from BNM and put the TKO on my 2289 instead. Yes the SSG....that is next. Should help with the noise and efficiency both.

[rsterne]

This will give you an idea of what you can do to the ports in a Disco valve....





The valve is quite capable of flowing enough air for over 100 FPE in .25 or .30 cal, providing you can get a hammer/spring combination to open it long enough at the 3000 psi pressure that requires.... You would need the 10-32 valve screws for safety, of course.... The valve in those pics is in my 2560, which produces 52 FPE in .25 cal at only 1900 psi (regulated)....

Bob

[Rivers3Plinker]

Holy Wah Bob....going big or going home there.
That's beastly sized. Is that grove in the
The added spring pressure is one of my concerns. I don't want to build it so I need to stand on the bolt to cock it just so I can hit the numbers.

So If I'm sticking to .22 and wanting to stay around 900fps with 21 grain, do you have any guidelines about how much work / what work would be necessary to hit those numbers?
I am more or less taking a stab at it and trying to keep the BNM supplied transfer port bushing, crosman OEM port seal, and round barrel port. I was thinking( hoping ) the 5/32 port size should flow enough combined with angle porting of the exhaust. I guess I don't want to get so crazy that I'm fabricating anything for a transfer port bushing for the BNM breach. It's a tall breach and the transfer port bushing is a long, custom turned and sized affair to fit snug up inside the breach.

[MichaelM]

I actually just finished my SSG setup last night for the double... Now my results my not be typical because when I first got the gun Lloyd had done extensive work on it, hogged out valve, Completely hogged out gauge block, Heavy spring and a Bstaley stack, and a .138 transferport.. he had it shooting an average of 38 shots at 26.3 fpe with 14.3gr pellets or a 1.36fpe/cuin eff on  a 2k to 1300psi fill... it took me a few days to try to get it set and tweaked with a ssg to copy as closely to his power lvls to compare apples to apples...

I was FINALLY able to get close to his results by using a lighter spring in the SSG (I think its the .039 spring that bob recommended for 2200 fills in the disco..) and changing to a tiny .120 transfer port.... lol I was only able to gain 2 shots over that range with more or less the same fpe lol think it came out to 1.42fpe/cuin eff...

guess what I am trying to get at... unless your wanting to make significant more power then 30 fpe or so... you really dont need to do a lot of valve work and the stock valve and transfer port should be plenty unless your wanting to go monster power lvls ... and smaller might actually be a bit more efficient

[rsterne]

When you are modding a Disco, one thing to address is the tiny hole in the gauge port.... If you can't get air into the valve faster than it can get out, FPE suffers.... I use the PRod gauge port....

Bob

[Iamscotticus]

When you are modding a Disco, one thing to address is the tiny hole in the gauge port.... If you can't get air into the valve faster than it can get out, FPE suffers.... I use the PRod gauge port....

Bob

Prod and Disco tubes are same internal diameter?
Do the valves interchange?

[David Mccann]

id works... valves dont swap due to hole positions

[David Mccann]

also center hole thru gauge block is smaller in a disco vs prod

[rsterne]

Yep, that's why using the PRod gauge block in a Disco will give you more power in a modded gun.... tho' not much difference in a stocker.... NOTE, you cannot use the Disco gauge adapter in a PRod gauge block because it is intended to seal against an O-ring and the threads are 3/8"-24 NF, while the PRod gauge block is 1/8" NPT.... You can, however, screw the Disco gauge directly into the PRod gauge block, or use a HP rated 1/8" NPT male to female extension....

Bob

[Rivers3Plinker]

When you are modding a Disco, one thing to address is the tiny hole in the gauge port.... If you can't get air into the valve faster than it can get out, FPE suffers.... I use the PRod gauge port....

Bob

Thanks Bob - I followed your advice already and have the Prod gauge port , a new 1/8" NPT 4k psi gauge from McMaster and a high pressure extension for it too.

[Rivers3Plinker]

I actually just finished my SSG setup last night for the double... Now my results my not be typical because when I first got the gun Lloyd had done extensive work on it, hogged out valve, Completely hogged out gauge block, Heavy spring and a Bstaley stack, and a .138 transferport.. he had it shooting an average of 38 shots at 26.3 fpe with 14.3gr pellets or a 1.36fpe/cuin eff on  a 2k to 1300psi fill... it took me a few days to try to get it set and tweaked with a ssg to copy as closely to his power lvls to compare apples to apples...

I was FINALLY able to get close to his results by using a lighter spring in the SSG (I think its the .039 spring that bob recommended for 2200 fills in the disco..) and changing to a tiny .120 transfer port.... lol I was only able to gain 2 shots over that range with more or less the same fpe lol think it came out to 1.42fpe/cuin eff...

guess what I am trying to get at... unless your wanting to make significant more power then 30 fpe or so... you really dont need to do a lot of valve work and the stock valve and transfer port should be plenty unless your wanting to go monster power lvls ... and smaller might actually be a bit more efficient

Interesting....Thanks Mike. So your combo is a heavily modded valve but then a reduced transfer port to improve efficiency. The transfer port is the restriction, not the valve. BUT... you are shooting a 14.3 grain round and I'm looking to go with 18 or 21.

I think I'm going to start by modifying another valve body and go with mild mods to the exhaust port. Mod for the screws for safety, stick with stock port size but angle drill the port. Leave the throat alone and poppet too. Get some shot strings and experiment with fill pressures.

[ChrisR10]

When you are modding a Disco, one thing to address is the tiny hole in the gauge port.... If you can't get air into the valve faster than it can get out, FPE suffers.... I use the PRod gauge port....

Bob

Thanks Bob - I followed your advice already and have the Prod gauge port , a new 1/8" NPT 4k psi gauge from McMaster and a high pressure extension for it too.

Steve, was this the fitting you ordered?

[rsterne]

Yes, that is a good extension for the valve if you use a PRod gauge block....

Bob