.25 Disco fever.... add another project to the pile

[rsterne]

On my .25 cal Disco I have seen 58 FPE with an 0.040" wire x 1.75" long hammer spring just shy of coil bind and a 2400 psi fill.... The peak velocity was 919 fps with 30.9 gr. Baracudas and occurred at 2000 psi.... The barrel port was 0.169", the TP was 0.166" and the valve exhaust port was 0.161" at a 20* angle and then streamlined by hand with a dremel.... The valve throat was drilled out but was not a full 1/4" (IIRC it was 15/64").... but the valve stem was slimmed to 0.115" and it was shortened 0.060" to increase the hammer stroke.... The valve was also bored out to 0.60" ID and the threads shortened to 0.30" long on the male (front) and tapered from that depth into the 0.60" ID on the back half.... The valve inlet was tapered and streamlined and the gauge port was 5/16" ID (offset) and tapered both ends for better flow into the valve....

Bob

[lloyd-ss]

Bob,
Thanks for those details. It looks I have a couple more "opportunities for improvement" (that's what they call it at work, LOL) between the valve head and the pellet. I've got the rest of it pretty well covered.
Lloyd

[workinmanVA]

Hi guys,
I've been following this post. I also like to build a lot of custom guns. Mostly Crosman. Any way I recently built a 32 cal. disco  and came to a dead end with the power. I'd say right around the same 55 FPE with .310 RND ball. I did all the normal valve porting, transfer ports, .046 x 1.75 heavy hammer spring etc. I came to the conclusion that I was never going to get any were unless 1 had more hammer weight and 2 major valve mods. Any way I saw Don Cothran had made a rear cocker for some ones custom build. Don't know if he was trying to achieve the same thing as me but was the prefect way of adding more hammer weight. This is what I came up with. 4 oz hammer rear cocker. By doing this I gained about 10 FPE which put me up to 64/65 FPE. Still have some fine toning with the power adjuster.

Any way food for thought. Keep them coming.

[rsterne]

Nice setup.... That looks like a Crosman hammer.... how did you install the cocking rod?.... Press fit?.... I don't imagine you drilled and tapped it and put in a setscrew because they are (case?) hardened.... My RVA is almost identical I could easily adapt it if desired....

Incidently, I have a 9mm 2260 Carbine running only a 16.5" barrel.... I got it to over 63 FPE (606 fps with 77.8 gr. EunJins) with a modded Disco valve and a stock hammer.... So you CAN get over 60 FPE if you go to a big enough caliber....  

Bob

[lloyd-ss]

Workingman,
Mine is in pieces on the bench right now and ready to go back together.  I like that hammer cocker.  I am headed to the lathe right now!
Thanks,
Lloyd
P.S.  I'll be back

[workinmanVA]

I had to machine a completely new hammer. Its made out of stainless steel. The rod is threaded on both ends and screws in to hammer and then into weight.

Those are really good # s on the 9mm.especially with such a short barrel. I think I ported the valve out to the max with out re designing the valve stem. Cut threads, stream line inlets, bored to .250, TP .190, angled exhaust port and that using stock valve spring. I had a light valve spring and was getting higher # s but was all over the place.

I don't want to high jack lloyds thread. But would like to talk more about some of your mods. I do have a 9mm 16.5 L barrel Hi pac carbine I built and currently building two more 32 cals 14.5L barrel  and another Disco.
TO BE CONTINUED

[lloyd-ss]

Workingman,
Sounds like you have some neat projects going, I hope we get to see some pics and such.

--------------
It's late, and I refined several of my mods this evening, and added the heavier hammer and cocker.  Great timing.
Only took a handful of shots, but ....
.25 cal RWS superdome weighed 31.4 and I got 962 fps = 64.5 fpe
.25 cal EunJin weighed 42.7 , 855 fps = 69.3 fpe

Details tomorrow night.
Lloyd

[0351_Vet]

What an amazingly informative and interesting thread. Thanks Lloyd (& Bob, & WMinVA)

Totally in awe, at the knowledge you guys posses. Thanks for such a great posting.

[rsterne]

Incidently, Lloyd and workinmanVA.... you don't need the recessed "waist" in the Disco hammer.... and in fact if you make the hammer a simple cylinder it will not only be heavier but it will work better if you should decide to use an MRod trigger group.... The shoulder on the original style hammer crashes into the sear and can break it.... I had it happen on my Hayabusa.... The shoulder provides a "half cock" position which I have never seen the use of.... except maybe for filling from zero pressure if your hammer spring is holding the valve open....

Great numbers on the .25, Lloyd.... can't wait for the details....

Bob

[workinmanVA]

You know I wondered about making the recess. The first one I made I completely recessed the hammer and the one in the pic I made just like the stock Crosman one. I guess the reason I recessed them was that I was worried about sear drag across a larger area of the hammer. If sear drags not a deal breaker, it would defiantly be a lot easier to machine. I have two more I have to make. How did it damage the sear? That hammer must of been putting a real beating the that sear.
I've been following your Hayabusa project on here and the Canadian forum. Very impressive. Actually that thread on the Canadian forum is the reason I vented my tube close to valve to prevent hammer bounce. Some times building and tuning air gun re mines me of the guy who invented the planetary gear set used in automatic transmission (he went crazy). So many variables.

lloyd nice #s. Can't wait to see some more.

[rsterne]

The sear broke completely.... it was impacting the shoulder on the hammer, there was quite a mark there (I didn't harden the hammer)....

Bob

[lloyd-ss]

Things are still in a flux, but I managed to get a few numbers.
After thinking about what I ended up with last night, I decided to increase the hammer weight and use a larger spring to see what will happen, like was mentioned above.

Here is the setup I have:
Valve opening is drilled out to .281 (seat dia)
Valve head .390 max dia , .356 dia at seal line
Valve stem .139 for about .15 of length under the head.  Remainder is .156 dia.
Valve body exhaust .201 dia, but heavily beveled inside the valve body.
Used a very light return spring on the valve head, 1.75 lbs to open the valve. Normal spring must be at least 5 pounds.
Valve body bored out to .680 dia
Remainder of the valve body has been opened up significantly and streamlined.
Old gauge port area has been opened up to the front of the tube.
Transfer port between the lower tank and the upper tank is .156 dia.
Transfer passage from the valve, thru the tank wall and breech, and to the inside of the barrel is now .199
Barrel is 30" long.
The hammer spring I used this time is  .388 dia x .060 wire x 2.1 long, 17 coils.
Hammer now has extension attached to it with another weight of approx 50 grams.
Special cocking device like in Workingman's picture above.
Total tank volume approx 310cc.

I filled it to 2000 psi and took a few high power shots:
1) 1001 fps, 31.4 gn, 69.9 fpe  (eff .85 fpe/cuin)
2) 903 fps,  42.7 gn, 77.3 fpe (Holy &^^& !!)  (eff .94 fpe/cuin)
3) 1027 fps, 25.4 gn, 59.5 fpe  (eff .71 fpe/cuin)
4) 963 fps,  31.4 gn, 64.7 fpe  (eff .78 fpe/cuin)
pressure ended at 1800 psi

Still needs lots of fine tuning, but I should be able to make it manageable.

Best regards, Lloyd

(edit- corrected the hammer weight)

[0351_Vet]

I wish I understood all of that Lloyd....but the numbers are looking real GOOD.
You have my attention.

[rsterne]

Well, you've taken your Disco beyond what I did with my Hayabusa, congratulations.... The valve I am using is 1/4" at the throat and 3/16" ports through all the way to the barrel.... I guess size is important!....  I got the following:

1061 fps JSB King 25.3 gr - 60.5 FPE @ 2000 psi
983 fps H&N Baracuda 30.9 gr. - 66.3 FPE @ 1900 psi
867 fps EunJin Pointed 43.2 gr. - 72.1 FPE @ 1800 psi

Note that the heavier pellets were peaking at less than 2000 psi, I didn't have enough hammer strike to dump 2000 properly....

How did you bore the valve out to 0.680" when it's only 0.740" OD?.... that's only a 0.030" wall thickness, pretty thin for 2000 psi, isn't it?.... or do you figure it's just expanding out against the tube?....   

I get such a hoot out of bouncing ideas off each other and pushing each other to new levels of performance.... We are approaching Condor performance.... I wonder what we could do with some of those 60-80 gr. slugs?.... What REALLY tickles me is the level of performance we are getting at only 2000 psi.... or even less.... 

When I do my 9mm Disco I will likely be borrowing the weighted outside cocking hammer idea as well.... and it looks like I'm going to have to find some bigger hammer springs....

Bob

[0351_Vet]

All I know is I'm sending my PCP to you guys when it's tune-up time (And I haven't even got to shot it yet). Hoping for the weekend.

Man, I love this thread.....and  .25 Go big or go home.

[lloyd-ss]

Ha, ha, this really is quite a trip.  Almost an obsession.  My wife just shakes her head and calls me a sick f***.  Terms of endearment.
It certainly does make it a lot more fun and worthwhile when there are other folks to exchange ideas with.
Thanks  everyone!

Bob, I think it was the big hammer and spring, combined with the extra light return spring that gave it the final few fpe.  I don't think I can get any sort of string at that power level, but who knows?  I had to do a fast fill from my scuba tank to get the initial seal on the valve.

The .680 bore inside the valve might be off a few thousandths + or -.  It's down inside the threads of the valve, so with the .280 hole at the valve seat, I laid a .201 drill blank in there to estimate the bore radius on either side.  Yes, I am relying on the tank tube as a safety back up for the valve body.  Still, with a .74 OD and .03 wall, a 28ksi yield strength wouldn't show any measurable movement until above 2500psi.  And I know the yield of the valve material is above 28ksi, and tensile is way above that.  I would not do that if it were not contained in the tank tube, though.

After the discussion of hammer design, I will probably make a new hammer to get all the weight inside the gun.  I also will try slipping an o-ring onto the pull rod for the hammer cocker to see how much the valve is opening. The o-ring will act as a tell-tale for the actual movement.  Modeling clay will do the same thing.  My valve has a short stem and the travel is limited to about .140.  I have NO idea how much it is actually opening.

This is fun!
Regards,
Lloyd 

P.S. 0351-vet, you might enjoy this video for maximum power. Its a different gun.
http://www.gatewaytoairguns.org/GTA/index.php/topic,12886.0.html

[0351_Vet]

Ha, ha, this really is quite a trip.  Almost an obsession.  My wife just shakes her head and calls me a sick f***.  Terms of endearment.
It certainly does make it a lot more fun and worthwhile when there are other folks to exchange ideas with.
Thanks  everyone!

P.S. 0351-vet, you might enjoy this video for maximum power. Its a different gun.
http://www.gatewaytoairguns.org/GTA/index.php/topic,12886.0.html

Lloyd, Thanks Bud.......Great Video (You guys kill me).

[rsterne]

I'm thinking that the hammer and spring are most of the power difference compared to my Hayabusa.... especially since my FPE with the 25 gr. is slightly higher than yours at 2000 psi.... Have you ever bothered working out all the port areas to see where the greatest restriction is?.... When I did my Hayabusa I started from 75% of the barrel (ie 0.188") and worked back from there, just making sure nothing else was more restrictive than the barrel port.... That was easy with the transfer port and valve exhaust port (also 3/16").... The valve throat is 1/4" with a stock 5/32" stem.... That works out to 0.049 - 0.019 = 0.030 sq.in. and a 3/16" hole is 0.028 so no problem there.... I use a bolt probe that is 1/8" (smaller than the valve stem).... so again, less restriction than the barrel/transfer port....

Have you noticed any tendency for the pellet to hang up on the 0.199" port?.... just curious.... I wonder where the optimum is for diameter/flow compared to TP volume losses.... I know where that is on .177, it's a stock 0.140" port.... Even angling the port / streamlining seems to decrease velocity unless you are REALLY pushing the limits.... but then that's what we are doing, right?.... If you're not having pellet loading problems perhaps I should be looking at 80% of bore for the barrel port.... or maybe an elongated hole that is only 75% of the bore wide but as much as one caliber long (ie 0.188" x 0.25")?.... That should flow about the same as a 0.216" round hole.... let's call it 7/32".... Then again, I wonder if the increased TP volume would hurt?....

BTW, I gave the Condor owners a gentle "poke" on the CAF, telling them what you were doing and that you had achieved over 77 FPE with a 43 gr. EunJin.... and asking them what a Condor can do with that same pellet.... no answer so far.... Maybe somebody here will chime in.... I'm thinking we must be getting pretty close....  

Regardless, I'm darned proud of what we are achieving on only 2000 psi.... pretty remarkable.... Really good idea using an O-ring to measure valve lift.... make SURE you tell us those results.... and you're right this is a BLAST, and it's what forums such as this are for.... sharing ideas in the best of possible ways....

Bob
 

[Norm_m]

It is most definitely interesting reading what you are working on even if it is WAY OVER MY HEAD! I kinda understand what your doing but trying to understand exactly what your saying is a bit difficult.
A dual tube Disco 25 and and a higher riser to be able to use the MRod or PRod magazine would make a great hunting rifle. look forward to more post on this subject
Norm

[lloyd-ss]

It is most definitely interesting reading what you are working on even if it is WAY OVER MY HEAD! I kinda understand what your doing but trying to understand exactly what your saying is a bit difficult.
A dual tube Disco 25 and and a higher riser to be able to use the MRod or PRod magazine would make a great hunting rifle. look forward to more post on this subject
Norm

Norm,
I hear what you are saying about a .25 MRod magazine!  Why not put the power to good use, huh? It is in the plan!

I know the explanations get a little cryptic sometimes.  It's often late at night or early int he AM and I don't take the time to explain it all.  Or I will be on a roll and won't take the time to stop and take a few good pics. But, I do hope to add some more pics that more clearly show what the mods are.  Many of them are pretty straight forward.
Glad you are enjoying it!
Lloyd