New project. 9mm 2260

[Rescue35]

Ok, so my 2260 has seen a lot of modifications. A new breech with weaver rails. I removed the CO2 and made it PCP. However I haven't shot it any since I received my Marauder. I have been wanting a nice carbine for hunting coyote in the thick brush and something lighter for my sun to use.

The concept is a 9mm with very few of the original 2260 left. Here are the parts as they sit now.



The barrel was a 17.5"x1.25" 9mm blank from Green Mountain that I have had for about 18 months. Major diameter now is .65 and I have plans for a shroud in the long term.

The air tube and fill cap are aluminum. As is the valve body that will thread into the air tube. The transfer port will not go through the air tube. The back of the valve body still needs to be machined to thread into the hammer tube which still needs to be made also.

Of course I still need to make a breech for it.

[rsterne]

KEWL project.... What size tubing (diameter and wall thickness) are you using for the air reservoir?.... Any idea what the volume of the reservoir will be?.... What pressure are you going to run?.... FPE expectations?....

Bob

[Rescue35]

The air tube is .875 OD x .062 wall. It is 18" long now but once I get everything sized it might be shortened another inch or so. It will have roughly 12-14" internal capacity. That will give me roughly 5.75 cubic inches.

Operating pressure will start at 2000psi and I will work my way up to 3000psi (I still have to do the stress calculations for 2200 PSI+). If necessary I will make a steel air tube. The thread in valve negates the concern over the valve retention screw safety concern of the disco.

I have no clue what kind of power to expect out of it. I will start by using the 2260 hammer and spring.

[rsterne]

Using 6061-T6 aluminum (40K yield, 45K tensile) I get 3.3:1 safety margin at 2000 psi.... 2.2:1 at 3000 psi.... It's certainly not as strong as the steel tubing used in the Disco as an example.... If you use 4130 CrMoly (63K yield, 97K tensile) you would get 3.5:1 at 3000 psi....

I would recommend you start with a Disco hammer spring, that will work well up to about 1800-2000 psi.... A 2260 hammer spring will not be strong enough, IMO.... The 2260 hammer is OK for a starting point.... Here is a shot string from my 9mm 2260 based Carbine....

544
553
562
570
573 - 56.7 FPE
567
545

I was running a 22XX hammer, Disco spring, and an 1800 psi fill (shot down to 600 psi!).... seven shots averaging 54 FPE.... I used a slightly modded Disco valve (3/16" port) and stock 0.140" transfer port.... 16" TOW barrel, and 77.8 gr. EunJin pellets.... Using the same gun with a larger 0.218" transfer port and a much heavier hammer spring (0.045" wire).... filling to 2400 psi and shooting down to 1200.... I got the following string....

639
655
664 - 76.2 FPE
658
642

That works out to 5 shots at 74 FPE average.... Here is a photo of the completed carbine....



It was a great project, I'm sure you'll enjoy yourself....

Bob

[MustangMike]

bob i wonder what that thing could do with a double tube on it ? more power a few extra shots.

[rsterne]

I later built a Disco Double 9mm Rifle.... http://www.gatewaytoairguns.org/GTA/index.php/topic,28070.0.html

More shots, more power (with rear cocking hammer).... but it's not a carbine any more.... Of course you could use a shortened Disco Double kit and end up in between.... or more shots at the Carbine power level I had above....

Bob

[Bryan Heimann]

7 shots at 55 fpe with only 1800 psi of pressure is outrageous!  Bet it's nice and light, too.   I cant wait to see how yours turns out, rescue!

[Rescue35]

Thanks, for the reply's everyone.

Bob, your 2260 inspired me. I can't wait to see what she can do.

I managed to get some more work done today. The breech is 30% done. It's amazing how much more work you get done when there is AC in the shop when it is over 100 degrees outside. Unfortunately I will not have a chance to work on it again until after the holiday.