The 9mm Disco Double

[Monkeydad1969]

Hey Bob, is that a stock Disco valve that you ported out for this project?  If so, how big are the openings now?

[rsterne]

The gun had 7/32" porting, and a 90 gr. rear-cocking hammer with increased travel.... It used a spring similar to a QB, but slightly longer, the valve was mounted with 10-32 screws, and ran on 3000 psi.... It got 8 shots at 117 FPE with the EunJins and 9 shots at 127 FPE with 132 gr. bullets within a 5% ES.... using the Disco Double kit....

Bob

[Monkeydad1969]

The gun had 7/32" porting, and a 90 gr. rear-cocking hammer with increased travel.... It used a spring similar to a QB, but slightly longer, the valve was mounted with 10-32 screws, and ran on 3000 psi.... It got 8 shots at 117 FPE with the EunJins and 9 shots at 127 FPE with 132 gr. bullets within a 5% ES.... using the Disco Double kit....

Bob

Wow, that's crazy.  Thanks.

[rsterne]

It's about as large as you can make a Disco valve.... the throat was 1/4" with a thinned stem, so the same area.... Going larger requires a PEEK poppet and you start running out of room in the 3/4" OD valve with the mounting screws in the way anyway.... Besides, more power would need more air, or get fewer shots.... I think the .30 cal is a better conversion for a maxed out Disco.... as those size ports are about perfect for it....

Bob

[Monkeydad1969]

It's about as large as you can make a Disco valve.... the throat was 1/4" with a thinned stem, so the same area.... Going larger requires a PEEK poppet and you start running out of room in the 3/4" OD valve with the mounting screws in the way anyway.... Besides, more power would need more air, or get fewer shots.... I think the .30 cal is a better conversion for a maxed out Disco.... as those size ports are about perfect for it....

Bob

Still a beast of a Disco.

[pebkac]

Some day I will build one of those

[Monkeydad1969]

If I can get my Career 707 9mm barrel to work, then I will have my 9mm beast of a carbine.  My breech is 3 1/4" x .500 ID, the barrel is .470 OD.

Any takers on how to get that to work?

[rsterne]

Yep, that is VERY close to 15/32" OD, and you can buy brass tubing at a hobby shop that is 1/2" OD x 15/32" ID.... Make a sleeve for the barrel (filing it down if necessary) and glue the tubing on with green Loctite (stud and bearing mount).... Drill through the tubing for the barrel set-screws so that they bite into the steel.... Machine the transfer port through both....

Bob

[Monkeydad1969]

Yep, that is VERY close to 15/32" OD, and you can buy brass tubing at a hobby shop that is 1/2" OD x 15/32" ID.... Make a sleeve for the barrel (filing it down if necessary) and glue the tubing on with green Loctite (stud and bearing mount).... Drill through the tubing for the barrel set-screws so that they bite into the steel.... Machine the transfer port through both....

Bob

Thanks Bob.  I will get to work this weekend.

[Monkeydad1969]

Hey Bob,

What diameter should I drill for the TP?  Using the B&A Big Bore Breech, Cothran SS 2260 pcp tube, Disco hammer and spring, and vinyl tubing for TP.

Joe

[rsterne]

If you can manage, for maximum power, I would use 75% of the bore, which is 0.267" (17/64") for the barrel port, transfer port, and exhaust port.... The throat will have to be larger to have the same area with the stem area subtracted.... I would use a 5/16" throat (have fun fitting that in a Disco valve), which with the 5/32" stem will give you an area equivalent to a 0.270" hole.... If you slim the stem to 1/8", that goes up to 0.286" and it's always a good idea to have a bit more flow through the throat than the ports.... For that large a throat, a PEEK poppet will be required....

Your biggest challenge will be getting a hammer and spring combination to open that monster valve, particularly if you start pushing the pressure towards 3000 psi.... Because of that, it might be a good idea to start smaller on the ports and throat.... more like what I did with 7/32" ports and a 1/4" throat (1/8" stem).... Even then, knocking that valve open will be a challenge....You will still need more hammer weight, travel, and spring than stock....

Bob

[Monkeydad1969]

Thanks for the info.