Big Bore Disco?

[Norm_m]

For you Disco owners check this out http://www.airguns.net/classifieds/show_ad.php?adNum=31482&adSort=&StartingAd=50&NumberOfPages=6 I think if I had a disco I would be trying this as it sounds very very interesting.

[lloyd-ss]

That looks pretty darn slick, but can the Disco valve and transfer tube be modified enough to get adequate FPE to push a .32 cal projectile?  I'd guess 50 FPE minimum?
A .312 ball is 46 gn, and 700 fps is 50 fpe.  600fps would be 37 fpe.
Lloyd

[Norm_m]

Lloyd from what I have been reading I think if anyone could do it you could. I've read many fine things about you and the Roque.
Norm

[bluzjamer]

Doesn't Big Bore Bob Dean make some 458 discos?
Ok wrong AG....he was using a QB 78 or 79 and modding it with the bigger barrel and whatever else he does. He had one up for sale on the other forums.

[rsterne]

I have a 9mm Carbine that uses a Disco valve.... I get 11 shots at 495 fps (41 FPE) detuned for the Canadian laws.... Wide open I got 9 shots at 580 fps average (58 FPE).... My answer, therefore is yes, a Disco valve can be made to handle a big bore, certainly in .30-.35 cal....

Bob

[Dead nuts dog]

Where do you get .32 pellet
--BOB where do you get a 9 mm?

[rsterne]

AFAIK, there are no "pellets" made between .25 cal and 9mm.... and only the 78 gr. EunJin in 9mm which is what I use.... One of the problems with "big bores" is the lack of proper ammo with a thin skirt to seal in the bore at airgun pressures, IMO....

Bob

[lloyd-ss]

Norm-m,
I'm deferring to one of the experts, rsterne, regarding big bore Discos and making major power.

Bob,
I was checking over some of your previous posts to try and reconstruct the many different mods you've been successful with on the Disco.  58fpe is is pretty outrageously good.  You pretty much modified everything that was there to max out the power. Job well done and impeccable record keeping.  Please tell me that your workshop is always messy or some sort of organizational fault you have so that I am not so envious.     

I have a couple of questions.
1) Regarding the little transfer port/tube between the valve and the barrel: is .166 or .171 the max you've drilled it out to? What about for the 9mm, still just a .171 drill?
2) You mentioned the restriction of the pressure gauge fitting/plug.  Might it help to just put a straight piece of metal tubing with o-rings in place of the fitting and give the PCP a real opportunity to flow?
3) have you ever modified the tip of the bolt for improved airflow?
Thanks,
Lloyd

 

[rsterne]

I have to shovel out the lathe on occassion, so what my shop looks like depends on what day you arrive.... 

The Crosman transfer port can only be drilled out to 0.166".... I tried one at 0.169" and the wall was so thin it buckled.... The riser breech I have on my 9mm uses a 1/4" OD transfer port and I had one that was 3/16" which matched the valve and the barrel ports when I got the 58 FPE (and BTW, I never bored out the valve either!).... Mind you, the gun only has a 16" barrel.... My "non-PAL" 9mm runs a 0.136" TP.... yeah that's right, SMALLER than a stock Disco.... 

I don't think you would gain much with a large bore tube replacing the gauge port.... but who knows?.... The 5/16" hole can already flow about 3-4 times what the valve outlet can....

I have an extended probe on my bolt to seat the pellet beyond the transfer port.... It is 3/32" OD in my .22 cal.... and again, the annular area (bore minus probe) is larger than any of the ports.... so I didn't think a gain was likely.... Never tried, though....

When I get my 24" .357 barrel I'll be moving the parts over and using a Disco tube and will bore the valve to see just what I can get.... 

Bob

[lloyd-ss]

Where do you get .32 pellet
--BOB where do you get a 9 mm?

Mellowroadman aka Marvin, over on the big bore gate  was shooting some .32 with nice results.
Lloyd