My Custom .25 Caliber 16" Disco Carbine

[Norm_m]

Well my Disco Carbine is now a completed project. It was a long time coming as the LW barrel took forever to come and now to the details of the little beauty.
It started off as a factory Disco and from there the following have been done:
•   Everything was designed for it to be a .25 caliber Disco
•   Added a BNM Weaver style Multi breech with shroud
•   Cut 3” from the air tube
•   Installed a 16” LW choked barrel
•   Custom valve and transfer port
•   Hammer (striker) was modified to incorporate a means to Adjust Stroke Length for more flexibility in tuning
•   Disco Double Tube
•   Gauge was relocated to the back end of the Double Tube and utilizes the same stock hole as the factory gauge used. This permitted a big increase in air flow through the valve, seeing there were no valve block restrictions. It also added an extra 1 ½” to the normal Double Tube
•   Modified to be able to us higher fill pressures (do not try this with your Disco as it could be a safety issue)
•   Brass ends to both air tubes
•   Brass barrel band
•   Added a custom brass Power Adjuster
•   Custom brass trigger
•   Modified QB78 Target Stock
•   Three screw trigger mod with hardened pins and lubed
•   Depinger in the factory tube to reduce ping
•   Weight of the Carbine is 6lbs. 10.6 oz. with no scope

All the machining and custom parts where done by Lloyd of Airgun Lab and he worked his magic to get me the FPE I was looking for and with a great number of shots. Without his help this would never have turned out so nice. THANKS LLOYD! I was hoping for a minimum of 8 shots and kept my fingers crossed that I would get 12 - 16 and as it turned out I'm getting 24 but I have much more tuning to do. Pretty difficult to tune when no one has the Kodiak or Barracuda 31.2 grain pellets in stock, PA just got the Kodiaks in and I ordered 8 tins, still have 8 tins of Barracudas on order since April 30th. When you look at the shot strings you will need to remember that this is a .25 caliber 16” barrel Disco Carbine. I was told by a good number of AG PCP enthusiasts when I started that with a 16” barrel and being a .25 caliber it was going to be very difficult to accomplish.

Now for the shot strings: all stings were shot with Barracuda 31.02 grain pellets
1st string is for the one 3” shortened factory barrel: Fill pressure  2400 PSI  Ending Pressure  900 PSI  DO NOT USE MY STARTING PRESSURE IN YOUR DISCO AS IT IS ONLY BUILT TO HAVE A MAX OF 2000 PSI. MINE HAS BEEN MODIFIED TO ACCEPT HIGHER PRESSURES
794.81      856.32      817.51
805.22      855.11      798.32
820.56      854.14      775.41
830.87      847.14      741.86
849.29      836.73      701.81

Now for the 1st string with the Double Tube:
Fill pressure 2400 PSI Ending pressure 1100 PSI DO NOT USE MY STARTING PRESSURE IN YOUR DISCO AS IT IS ONLY BUILT TO HAVE A MAX OF 2000 PSI. MINE HAS BEEN MODIFIED TO ACCEPT HIGHER PRESSURES
798.00      858.81      836.21         
814.54      860.82      823.58      
825.37      855.17      817.29
828.42      860.40      806.13
830.41      861.68      792.41
844.02      851.98      778.10
848.87      848.57      760.88
856.08      840.15      743.27

2nd  String with Double Tube
Fill pressure 2450 PSI Ending pressure 1100 PSI DO NOT USE MY STARTING PRESSURE IN YOUR DISCO AS IT IS ONLY BUILT TO HAVE A MAX OF 2000 PSI. MINE HAS BEEN MODIFIED TO ACCEPT HIGHER PRESSURES
795.22      836.15      839.69
811.21      849.05      831.44
811.97      852.46      825.71
826.27      860.64      815.04
829.44      858.26      802.87
832.01      856.98      790.81
842.78      853.6      778.05
846.67      847.56      758.64

So as you can see the Double Tube mad a big difference in the shot string and power that this little Carbine has. I have more testing to be done when my pellet supply arrives!! If you have been thinking about adding a Double Tube Kit to your Disco just imagine what it would do to your Disco if I gained the extra shots and power with my 16” Carbine.

Norm   

[gene_sc]

Norm that is a really sweet looking double Disco there. Lloyd did a super job on the tune for shot count and fps. You to guys are a great team.. So what is next?
Gene

[ezman604]

ABSOLUTELY awesome Norm. What a Great job Lloyd & Norm!!!!
Making me want more shop time. 
Yeah, WHAT'S next from you too??? Your audience awaits.
Happy Shooting!!!!
Dave
 

[bradyman1]

That's a sweet gun. Great job guys!

[only1harry]

Wow really good looking gun!  At first glance you have no idea that is a Disco.

That's some good power it's putting out.  Almost the same as an Mrod.  The LW barrels shoot the 25.4gr JSB Kings really well.  Buy a few tins of those.  The JSB King will be the most accurate pellet in your Disco.   
What does the gun weigh now?  Is it still lighter than an Mrod?  Just curious.   

[rsterne]

HI Norm....

First off, let me say that your gun sounds like a real gem, and it looks absolutely beautiful.... You and Lloyd should both be proud.... The only thing I have I can compare it to is my .25 cal Disco with a full 24" barrel and a single tube.... With that gun I  get 11 shots within 5% at 45 FPE average (891 fps with JSB Kings) starting from 2100 psi down to 1200.... Lloyd's spreadsheet would predict that would drop to 37.5 FPE with a 16" barrel and no tuning changes.... Looking at your 2 strings using the 5% spread, I count 16 shots in the first string and also 16 in the second string.... I don't know your pressures at those points, but I'm guessing about 2200 psi down to 1300.... I'm not sure what pellet weight you are using, so I can't do an energy or efficiency calculation.... If those velocities were with 31 gr. pellets, that would be peaking at over 50 FPE which is VERY impressive....

Bob

[Norm_m]

Harry the Carbine only weighs 6 lbs. 10.6 oz. without the scope which is alot lighter than a MRod.
The MRod may get a lttle better FPE then the 2 strings it posted but you need to remember it has a much longer barrel and uses 3000 PSI of air to do so. I am sure if I adjust the hammer stoke to maximum lenght and increase the air pressure to 2600 PSI it would blow the doors off most MRods.

Everyone has to understand that my Carbine has had some mods done that will permit me to incease my PSI to those levels. ANYONE READING THIS TOPIC MUST NOT TRY TO USE THE PRESSURES I'M USING AS YOUR FACTORY DISCO IS RATED FOR 2000 PSI. AND USING HIGHER PRESSURES COULD BE HAZIDOUS! I HAVE STATED SEVERAL TIMES MY DISCO HAS HAD MODIFICATIONS TO MAKE IT SAFE FOR THE HIGHER PRESSURES!!

Bob yes to the 31.02 grain Baracudas! The stroke adjustment is pretty close to the minimum it can be and I can safely increase pressure to 2500- 2600 PSI so the little Carbine could be a big powerhouse if I wanted. I plan on playing with it to see if I can improve on those two strings. Those 16 goood shots in both strings are in the 2250 PSI down to 1450 PSI very close to what you estimated

Norm

[rsterne]

Excellent, Norm.... What is the total air capacity of the tubes?.... I'm dying to work out the efficiency.... If I understand you correct, the 16 good shots are using 800 psi, and have a total FPE of 49 FPE avg. (over the 2 strings) x 16 for a total of 784 FPE....

Bob

[Ken13]

Wow, looks awesome. Great job guys

[longislandhunter]

All I can say is that is absolutely a thing of beauty.  Congratulations on one amazing rifle.   BTW.... if you wanna sell it I'll take it

Jeff

[Archersparadox]

...WOW.....the brass accents look very NICE!!

[MustangMike]

Lookin good norm, can't wait for my carbine...

[Norm_m]

One thing that was not mentioned is even with the Double Tube it still only has an air capacity of 230 cc compared to the 315 (if I remember correctly) of a Marauder. Pretty amazing shot string numbers when all is taken into concideration.

Norm

[Devin]

HI Norm....

First off, let me say that your gun sounds like a real gem, and it looks absolutely beautiful.... You and Lloyd should both be proud.... The only thing I have I can compare it to is my .25 cal Disco with a full 24" barrel and a single tube.... With that gun I  get 11 shots within 5% at 45 FPE average (891 fps with JSB Kings) starting from 2100 psi down to 1200.... Lloyd's spreadsheet would predict that would drop to 37.5 FPE with a 16" barrel and no tuning changes.... Looking at your 2 strings using the 5% spread, I count 16 shots in the first string and also 16 in the second string.... I don't know your pressures at those points, but I'm guessing about 2200 psi down to 1300.... I'm not sure what pellet weight you are using, so I can't do an energy or efficiency calculation.... If those velocities were with 31 gr. pellets, that would be peaking at over 50 FPE which is VERY impressive....

Bob

If you want to compare efficiency to a .25 Mrod as well:

3000 to 2350psi
16 shots
41.5 Avg. FPE
ES - 17FPS
Standard 215cc capacity.

Looks like the Disco is doing pretty darn good.

[mtsheron70]

Looks great!  Absolutely AWESOME! 

[rsterne]

The air used is 800 psi / 14.5 = 55 bar.... 230 cc is 14 CI.... so the total is 771 CI.... Since the total FPE was 784, you are just over 1 FPE/CI.... 784 / 771 = 1.02 FPE/CI.... That is excellent for a carbine at that power lever.... Congratulations to you both....

The MRod is 215 cc (not 315).... For Devin's MRod, which used 650 psi the air used was 650/14.5 x 215/16.4 = 588 CI.... The total FPE was 41.5 x 16 = 664 FPE.... That works out to 664/588 = 1.13 FPE/CI.... However, that was with a lower power level, and a longer barrel.... As I said, the Carbine is doing great !!!

Bob

[BigErn]

Wow! That is some gun there. Seriously sick!

[lloyd-ss]

Norm,
You have really added the finishing touches on that carbine, and I am very glad the performance is so good!  All that brass really makes for an eye-pleaser!
I know you can really run thru lots of pellets during tuning sessions but the results keep getting better.
Looks like a real winner!
Lloyd   

[lloyd-ss]

Lookin good norm, can't wait for my carbine...

It's comin'!  Don't tell anybody how long I've had it, LOL!
Lloyd

[Nomadic Pirate]

That is one cool rifle !!!... that's what happen when people start thinking