A simple Disco Build

[Darth]

Well, a few years a go I built a 1377 and a 2240. In the quest for more power, I purchased a complete Disco tube with the intent to build a PCP air pistol. Since then I have changed (what’s left) of my mind. I’ve decided to go with a long gun platform. Mostly because of the accuracy that a long gun might lend.

Right now I’m working on the tube. Just getting everything cleaned up and ready to go. Tonight I turned two new locators for the side registers that fit the holes within .002” and used button heads to attach them to the valve. I also shimmed the valve body in the tube with .004” aluminum shim stock (pop can) to keep the valve body stable. I figure the more things that “fit well” the more “repeatable” things get.

The next thing I’ll do is start to modify the valve body itself … much like I did with my 2240, just to pick up a few extra FPE.

I did valve stem work, opened up the body itself, opened and angled the exhaust port, fabricated and installed a brass transfer tube between the main tube and breech … stuff like that.

After that is all completed, I’ll need a trigger assembly. Are the stock ones plentiful as used units ? I mean, do guys replace the stock ones with some better units and have old ones laying about ?

At some point I’ll also need a stock … or convert one I have here at the house.

Anyway, I hope to have a decent shooter when it’s all said and done ... 

Any advice ... tricks ... help ... whatever ... is appreciated 

[Darth]

Just thought I would show y'all what I was talking about ... (yes ... I'm half WVa    )

The brass pieces are also threaded 8-32

[smg id=1886 width=600 ]

[ibgp3]

The PRod trigger group (2220-103)
is sweet, and less than $40

My Disco is wearing one.

[venxxxxx]

Nice start. Which caliber are you going with? I got a bmn breech and love how easy it is to swap out barrels.

[ibgp3]

I have the .177 and .22 setups for the BNM. I ordered a .25 barrel turned down for Crosman, but it didn't fit the BNM breech, so now I have a 2540.

[NitroBobby]

The PRod trigger group (2220-103)
is sweet, and less than $40

My Disco is wearing one.

is the PROD trigger group a "drop in" replacement on the Disco or does it require modification?

kgb

[Cathartes]

It requires the P-Rod hammer, which you then have to modify to clear the breech screw.

I did it with a dremel, so it's not that hard:


I used a P-Rod trigger group for my Disco project, and I really like it. However, it can be a challenge to find a forearm that fits on with the gauge. I am having one made for my gun.

[Darth]

Nice start. Which caliber are you going with?

I'm going to use .22 for this. Both guns I've built have 22 on them ... my 1377 (PC77) has a 22 on it as well as the 2240, it has a 13.75" barrel.

I started working on the valve last night. I tapered and polished the inlet to the valve and also tapered and polished where the valve spring resides. This weekend I'll relief grind the valve stem and open up/angle the exhaust port. When I did the 2240 I did it "incrementally" so I could see what mods gave me the most FPE increase. For me ... it was the valve stem relief grind, opening up the valve body a wee bit and (of course) a longer barrel.

[Darth]

NitroBobby ... what length barrel do you have on this ??

[Darth]

OK … I’m going to open up the “hornets nest”  …

My 2240 does 595 – 597 FPS 10 shot average @ 70 deg F with the “standard” 14.3 CPHP. It has a 13.75” barrel, heavily modded valve, .220” exhaust port and transfer tube. The barrel transfer port is opened up to the same dimensions and I use a brass tube that fits into a .250” counter bore in both pieces. Mellon flow through bolt opened up and polished as well.

No matter what I seem to do, I can’t get over that “600 FPS” barrier with the above stated setup. The gun is REALLY loud as well … which I expected.

Sooo … I read on the Pyramid site that a fellow did some testing with barrel length and he shows the following data. This was for a 22 cal gun.

              11.9 ?     21.1 ?
Barrel- Hobby- Kodiak
20" -------- 645 -------- 548
19" -------- 689 -------- 564
18"-------- 680 --------- 562
17"--------- 681 --------- 555
16"-------- 671--------- 547
15"-------- 641--------- 541
14"-------- 639--------- 518
13"-------- 637--------- 512

Here is the question … since I know I can get 600 FPS with a 13.75” barrel with a 14.3 gr. Pellet (which seems to be in-line with what this guy gets) Should I expect to get about 650+  FPS  using (bulk fill) CO2 with the same 14.3 pellet using a 18-19" barrel ??

I'm trying to carefully PLAN my build ... and I want to start out using CO2 because I don't have any HPA equipment ... yet