Tuning a NEW Disco

[Tommy]

The newer Discos have a stronger hammer spring. I got my .22 Disco in June from Norm. The string he shot started at 909fps and ended at 789fps for 13 shots. After doing a lot of reading I new what was going on. Too much preload on the hammer spring. Before i made the power adjuster I knew I had to reduce the tension on the hammer spring. I started with cutting off one coil and that gave me a few more shots. I knew it could do better. I then cut off two more coils and voila 30 shots. I then bought a chrony and found i was getting 30 shots at 775fps average within 4%.cool. Now I put in my power adjuster. I screwed it in to max {coil bind can,t cock then 1/2 turn out]I shot it over the chrony and got 20 shots at 850fps at less than 4%
Now I can adjust from all the way in to all the way out depending on what power i want.
Hope this helps some of the new Disco owners
Good luck
Tom

[Arkyarcher]

Thanks Tom ,I have been breaking in to pcp's and just got a disco and I was looking for a simple solution to the short shot count.

[mooseslayer]

Tommy...do you know how long your spring+ guide  is now? I made own pa and therefore modded a screw to be a spring guide. I will measure tonight but I think my cut spring with spring guide is under 2 inches now. I would love to know exactly what yours is as I have disco apart now and will be reassembling tonight.

[Ribbonstone]

Thanks for posting that, I like simple direct solutions.

[UCChris]

Good to know. I have a Disco coming Friday. I wonder why a short spring turned in with a PA shoots the same velocity as the stock spring, but for more shots? I guess I don't fully understand the relationship between hammer spring and valve dwell.

[Ed38574]

What grain pellet are you shooting Tom? As high as the numbers were I'm assuming 14 grain?

[Tommy]

I use 14.3 cphp
Tom

[Ed38574]

Good to know. I have a Disco coming Friday. I wonder why a short spring turned in with a PA shoots the same velocity as the stock spring, but for more shots? I guess I don't fully understand the relationship between hammer spring and valve dwell.

Keep in mind the numbers he ended up with with the power adjuster are not nearly as high as what it started out at with the stock spring. His string started just over 900 but finished in the 700's. With the PA he started, and finished in the 700's.

[UCChris]

Good to know. I have a Disco coming Friday. I wonder why a short spring turned in with a PA shoots the same velocity as the stock spring, but for more shots? I guess I don't fully understand the relationship between hammer spring and valve dwell.

Keep in mind the numbers he ended up with with the power adjuster are not nearly as high as what it started out at with the stock spring. His string started just over 900 but finished in the 700's. With the PA he started, and finished in the 700's.

Good point.

So his string started at 900 without the modifications.

Let's say he turns the PA in until his string starts at 900 again. Will it be more consistent, or will it have the same decreasing string? Will it have a few more shots?

[rsterne]

Generally if you return to the previous high starting velocity the string should look the same (decreasing) with the same number of shots.... The fly in the ointment would be if the original setup was getting more air-wasting hammer bounce compared to the shortened spring (quite possible), in which case you might gain a few shots with the shortened spring.... However, tuning for a falling shot string is not, IMO, the way to go.... you want at the minimum a plateau to start, and preferably dial the power back a bit until the first shot is 3-4% below the peak and then stop shooting at 3-4% below the peak as well.... That is how the original Disco was tuned....

I haven't seen the "new" Disco hammer spring, but I wonder if Crosman used the one from a 2200?.... It is both stiffer and longer than the original Disco spring....

Bob

[Tommy]

yep What Bob said
Tom

[Benjamin disco]

I consider my rifle to be one of the new ones with the stiffer spring everyone was talking about. This one is 2 inches long with 16 coils. I believe the spring is music wire and Is .039" wire diameter

[tjcib]

Thanks for the post. Just ordered a Disco (my first pcp) today. I've been compiling a list of things to look into and tweak after cleaning the barrel and getting it quiet.

[rsterne]

The original Disco springs were 0.035" wire.... so if yours is 0.039" they are not the same wire diam....

Bob

[Benjamin disco]

II understand this and I wasn't disagreeing or stating otherwise. I was just simply stating the diameter and specs of my spring. so other people with similar issues or questions / concerns can read and see my comment

[UCChris]

II understand this and I wasn't disagreeing or stating otherwise. I was just simply stating the diameter and specs of my spring. so other people with similar issues or questions / concerns can read and see my comment
[/quote

I don't think Bob was saying you are wrong, just confirming that they are, in fact, different.

I wonder if one could find the part number for the old Disco spring, or if Crosman has completely phased that spring out.

[rsterne]

more likely they are still using the same part number.... even though they changed the spring....

Bob

[Benjamin disco]

I apologize for the misunderstanding. And if they changed the part without changing the part number then I would check ebay or amazone for .22 disco hammer springs. Most of them do not have the specs of the springs but occasionally you'll run across one with the specs of the old spring. The old lighter spring came in today and this allows me to shoot at a wider variety of velocities.  It FIXED my sudden velocity drop after 1400 psi. Bob suggested I replace my hammer spring and what do ya know. Smother closer groups. I believe the (bell curve) is fixed now. Once again thanks bob.

[UCChris]

Good thought Jeremy. But keep in mind that a seller might be selling new springs and has not updated the specs.

[Benjamin disco]

True, for more variety in fps in go with the old springs, and a adjuster allow trait shot strings. Just go my orders in I'm happy.