More work on my .25 disco... UPDATE now at 60 FPE

[Matt15]

Awhile back, I posted my .25 disco here:  http://www.gatewaytoairguns.org/GTA/index.php?topic=117753.0

It shot 8 shots 849-864-828 for a 16 fps spread

I just recently drilled the barrel port out to .180" from the stock .140".

I ran it over the chronograph this afternoon and after I messed with the velocity adjuster I settled on this string:

2600 psi fill

1) 834
2) 839
3) 855
4) 862
5)868
6)870
7) 868
8( 866
9) 859
10) 850
11) 840
12) 834

End pressure was 1700 psi.


I then shot a 12 shot group at 25 yards and ended up with 1 large hole the could be covered by a dime.

I am looking forward to shooting this gun at 50 yards and hopefully shoot for the NUAH club. 

[Machinist]

The Squirrels are gonna hate this gun!  Nice job.

Steve

[rsterne]

25 gr. Kings?....

Bob

[Matt15]

The Squirrels are gonna hate this gun!  Nice job.

Steve

Thanks! My first shot at a squirrel sitting on a tree 30 yards away was a head shot.

25 gr. Kings?....

Bob

Yes, I used Kings.  The max shots at coil bind was 912, 913, 905.

I will be adding an SSG soon to hopefully gain another shot or two and to get a tighter spread. I am hoping for 830-845-830 over 15 shots with the SSG instead of 830-870-830 over 12 shots.

Inside the valve, I have the stock disco valve spring. Is it possible that is choking the air off? It is a thick wire so when it opens, it may close the gaps fast and cut off the air supply. I may remove that spring and run it without it.

[mobilemail]

Good work on the .25 Disco!

[Matt15]

Thanks!

[Bicycleman]

The squirrels are going to loose their minds!   
Nice string, Matthew.

[Matt15]

The squirrels are going to loose their minds!   
Nice string, Matthew.

Thanks Mike!! This is my first pcp and I love how easy it is to load and shoot in the woods. 

[rsterne]

I seriously doubt you are opening the valve enough to cause the valve spring to choke the flow.... That occurs at 1/4" of lift, and at those velocities you are probably only at about 1/16".... Even your maxed out shots will be under 1/8" lift, IMO....

Bob

[Matt15]

Thanks Bob! Right now my throat is .25" and my t-port/barrel port are 3/16" ID. I am thinking about putting in a 5/16 OD transfer port like you use. I will then drill the t-port to 7/32" and make the barrel port 1/4" long by 3/16" wide.

[Matt15]

Today, I installed a 5/16" OD t-port so that I could increase the port sizes to 7/32". I drilled the tube and breach to 5/16" and filed a 5/16" flat on the valve and barrel.

The barrel port, I drilled to 3/16" and then lengthened it to 1/4" long. This made it oval and the pellets load with out catching on the hole.


Before I did this the max velocity was 913 fps with 25.4 gr JSB pellets with a 2600 psi fill.

With the bigger ports, at 2600 psi it shot a JSB 25.4 gr. pellet over the chrony at 985 FPS which is 54 FPE. When I shot I could feel a puff of air from the t-port so I will get that fixed. 

[mobilemail]

Hey Matt,
You're pretty close to me. When it warms up we will have to get together and shoot something. :-)

[rsterne]

Sounds about right, Matt.... My regulated 2560 shoots 52 FPE with Kings at 1900 psi with 7/32" ports....

Bob

[Matt15]

So I got the t-port sealed and I shot it over the chrony. I got 1031 FPS or 60 FPE with a 25.4 gr pellet and 2600 psi fill.  I did a three shot string: 1031, 1022, and 1004 fps.

I think that is pretty good considering I have a 20" barrel.

[Dairyboy]

You should get the Magnum airpower 3000psi screws and then fill to 3000psi and use the 34gr JSB and have one heck of a disco

[Matt15]

You should get the Magnum airpower 3000psi screws and then fill to 3000psi and use the 34gr JSB and have one heck of a disco

I bought the 2600 psi screws before he came out with the 3000 psi screws. I plan on getting some 3000 psi screws and shooting 34 gr JSB and some of Nick's swagged ammo.

[rsterne]

Sounds like you need to back off the hammer spring a little, unless you can safely use a higher fill pressure.... You should be able to get a nice, tight 3 shot bell-curve if you do one or the other.... You're pushing those Kings pretty fast, backing down the hammer a bit might be the better choice....

3000 psi fill and 34 gr. could also work out....

Bob

[Matt15]

Sounds like you need to back off the hammer spring a little, unless you can safely use a higher fill pressure.... You should be able to get a nice, tight 3 shot bell-curve if you do one or the other.... You're pushing those Kings pretty fast, backing down the hammer a bit might be the better choice....

Bob

I will be backing it down to around 950 fps for 25.4 gr Kings. That was just a 3 shot string at max power mostly to see how fast power dropped.