My disco's a gas hog.

[Martis 1]

I think...
I've been fiddling with the barrel bands, shims, scope mounting, etc.  Finally got it fairly dialed in and went to the range this evening after the wind died down.  Before I left the house I pumped the gun up to 2,000 psi.  (I think.  I didn't have my glasses on when I read the gauge.)
Anyway, I ranged my target at 46 yards.  Couldn't go to 50.  Too much junk in the way.  First 5 shot group measured under 9/10" outside edge to outside edge, which I'm pleased with.  I don't know which shots landed where, but I had three shots in a nearly touching horizontal string, with two more shots touching and 1/2" below the other three.
On my second 5 shot group, (without pumping the gun back up), shots 6-9 measured less than 1/2", and had the same drop as the lowest two shots in the first group.  Surprisingly, shots 10 and 11 were close together, but over an inch below the rest. 

Looks like with my Crosman domes, I'm only getting about 9 good shots per fill.  Oh, and per the gauge, I've still got at least 1100 psi left.

Granted I need to spend some time with the chrony, but it looks like if I want a decent number of shots, I'm gonna need a power doo dad and a lighter spring.

At least the gun's shooting accurately though!

Ron.

[redlined_b16a]

The newer discos are said in .22 cal to get about 12 good shots,The older reported about 20.
From my research the springs were different.
Im sure someone with hands on experience will chime in.My brothers diso got about 20 strong shots using about 1000 psi.That was about 5 years ago.

[bulldog50]

My sons disco was the same way . Norm threw a  power adjuster in it with a lighter spring now we are 24 shots start in in the low 800's climbing to mid 8's then back to low 8's at the end of the string. Clip a few coils off ur hammer spring and pick up a power adjuster . Then u have the flexibility to go back to the high end of the fps if u want.

[Martis 1]

I'll certanly install a power adjuster and probably a lighter spring, but what surprised me was that my POI started dropping after only 3-4 shots.  Not a lot, but more than I'd like. 
Ron.

[Gerard]

Well I don't have a Disco, but from my experiences tinkering with a couple of PCPs I'd suggest lightening your hammer might go a long way towards flattening out the velocity curve. By reducing the impact on the valve stem you reduce the initial air dump significantly, wasting a lot less pressure on those first few shots as the reduced mass can't force the valve quite so far open at full pressure. As pressure drops the lighter hammer is better able to open the valve so even though the pressure is dropping, the longer open time on the poppet keeps the velocity from dropping - in fact if adjusted well, in balance with the right spring length, strength and preload, the velocity should climb a bit in the middle of the string. This continues until at the end you're finally losing velocity, but the bulk of the shots in the longer shot string will be closer to the average than with a wasteful setup which starts high and just keeps dropping velocity.

Just guessing, but you might be able to tune it such that 15 to 20 shots are possible at a slight loss of average power (say 10% or so) but with a much more even string so your shots land where they're supposed to land. In one example of my fiddling I managed to take a Brocock Atomic from the stock 35 shots averaging around 480fps with RWS Hobby 11.9gr pellets up to 70 shots at the same average velocity, same pellets. Eliminating the first few and last few from each string as being too slow to be very useful in terms of pellet drop, my usable shot count went from about 28 to 55 through a lot of hammer mass reduction, porting changes, spring length and preload adjustment. Same fill pressure, just using the air a lot more efficiently now. Another nice benefit of using a Chrony and doing a lot of spreadsheet work to keep track of mods is that the blast noise quiets down as efficiency improves. Factory setups are often very poorly balanced, not really well suited to consistent shot placement.

[Martis 1]

Pardon my ignorance, as I'm still real new to this, but how do you lighten the hammer?  I was planning a lighter spring and power adjuster, but don't know anything about lightening the hammer itself.  Sounds like some machining???
Ron.

[Gerard]

Steven in NC does a good job explaining one example with an HPA Discovery in this thread:
network54 (dot) com/Forum/275684/thread/1242905996/Any+tips+on+reducing+hammer+weight-
And further down in that thread Mike T. shows one way of doing it. The hammers on these airguns are case hardened steel, extremely tough so a file will just get dull if you try filing away steel. Most drills will just spin and get dull. In modding my 2240 I used a Dremel with a grindstone burr and wore through that, put on another, and finally got enough weight carved off each side. I stayed clear of the top and bottom surfaces as I didn't want to interfere with smooth sliding nor with the sear engagement. Carving in from the left and right sides with a Dremel seems the simplest approach for a 22xx or Disco hammer or whatever else uses the same sort of hammer.

On my Brocock Atomic I opted to turn down the hammer on my lathe. It's similarly hard, case hardened steel, but I dug in hard with a carbide bit to get through that hard layer than went on until I was happy with the weight, then sleeved it in a tough, slippery plastic called Ertalyte - a bit harder and a bit slicker than Delrin. I carved out a groove for the hammer cocking pin - this airgun uses a groove in the hammer for this rather than a pin sticking out of the hammer as with the Crosman design. The Ertalyte sleeve reduced friction while more importantly bringing the hammer back to spec diameter, allowing the sear ball bearing to slide along it instead of catching and forcing pulling the trigger while cocking. The plastic weighs next to nothing so the hammer weight is much reduced but still the same size and shape. But that's a very different design of hammer and sear, just mentioning it to say there are different approaches to achieve the same result; a lighter hammer.

If you have a Dremel, or even just a bench grinder, you should be able to remove mass from the sides of a steel hammer. Of course if you don't like the result after trying various other tuning elements in concert with this mod, ordering a replacement hammer is pretty easy and cheap.

[Martis 1]

Hmm, sounds interesting.  Might try that down the road.  First though, I want to go with a lighter spring and a power adjuster from a Challenger.  My goal is to be able to power down to around 650 fps for the back yard, but be able to go back up to the stock power level for hunting.
Ron.

[tjcib]

i clipped three full coils off my hammer spring, then added a power adjuster (tried homemade as well as one from Mellon Air...both same results).

I get 35 shots per fill from 1900 down to 900 PSI. Starting around 690 fps up to 710 fps...all that with JSB 18.13s, which makes for 20 FPE gun.

five shots make quarter inch groups at 30 yards.

[Martis 1]

i clipped three full coils off my hammer spring, then added a power adjuster (tried homemade as well as one from Mellon Air...both same results).

I get 35 shots per fill from 1900 down to 900 PSI. Starting around 690 fps up to 710 fps...all that with JSB 18.13s, which makes for 20 FPE gun.

five shots make quarter inch groups at 30 yards.

OK, if I could get those results, I'd be one happy camper!
Ron.

[Tommy]

I have gotten the same results. Read the link att the bottom of my gun list. It is very easy.
Tom

[Martis 1]

I have gotten the same results. Read the link att the bottom of my gun list. It is very easy.
Tom

Thanks Tommy!  I remember reading that post awhile back. 
So, am I correct that I can just order a power adjuster for a challenger from Crosman and install it in the disco?
Ron.

[tjcib]

I have gotten the same results. Read the link att the bottom of my gun list. It is very easy.
Tom

Thanks Tommy!  I remember reading that post awhile back. 
So, am I correct that I can just order a power adjuster for a challenger from Crosman and install it in the disco?
Ron.

The reason I like the power adjuster from Mellon Air is that you can change out hammer springs without taking the gun apart. Great for testing. He does take about 4 weeks on orders though...but was worth the wait for me.

You can make one at home in the meantime...

[Martis 1]

The reason I like the power adjuster from Mellon Air is that you can change out hammer springs without taking the gun apart. Great for testing. He does take about 4 weeks on orders though...but was worth the wait for me.

You can make one at home in the meantime...
[/quote]

Boy, I looked at that guy's website.  From what he writes, he seems like about the angriest "businessman" on the planet.  I'd hate to put him out by ordering anything from him and making him have to provide it. 

I'm trying to figure out if the PA from a challenger will work on my disco.  I really like dealing with the folks at Crosman, and that thing looks like it would belong on a disco, assuming it'll work.
Ron.

[Gerard]

Wow, I see what you mean! Seems to me that his fondness for ALL CAPS and frequent cautionary notices indicate a long experience of dealing with idiots. Made me feel a bit sorry for the guy. But he does seem to be a competent machinist and his hollow probe is identical to what I made and love in my 2240, bit in nicely polished stainless. Bookmarked. Some very good value there, lots of stuff cheaper and better made than a lot of other sites offer.

[Ribbonstone]

Challenger end cap/adjustor and a spare spring would work just fine.  Thing about power adjusters (at least for me) is that once I finally get the gun set up where I want it,  am likely not to touch the adjuster again for a long long time.

With just that change in parts and enough time testing/setting/chronographing, are likely to find 30-40 “good” shots in a fill.  Will be lower speed shots than before, but all within 4%.

Idea is that if shots inside 4% are acceptable, then setting the rifle up to start out at about 4% lower than the eventual max speed will give you the most shots per fill.  So (just picking numbers here) something that starts out shooting at about 770fps, climbs to about 800fps, and then falls off back to 770fps would likely manage 30-40 shots without any mods/changes to the rifle (other than the power adjuster).

[Martis 1]

I believe I'll order up the PA and spring from Crosman on Monday.  A couple of you guys have given me the very good advice to tune the gun and leave it be.  I see now that trying to adjust power up and down for different situations is probably not practical. 
The weather's warming up, so it's about time to spend a day in front of the chrony.
Thanks for the help!
Ron.

[tjcib]

I thought the same thing about the Mellon site when I first visited...seems ornery... But I did actually email him directly and he was extremely responsive and helpful. Got a bolt probe and pa from him

I, too, had delusions that I would be fiddling with my power adjuster for all my different situations. Visions of charts that tell me exactly how many turns for certain situations and needs...

Then I found out that I can plink AND kill squirrels without any changes. What a relief. I don't feel like I'm sacrificing anything for either plinking, paper, or pesting. And really, a 30 fpe disco will leave energy going out the back side of the squirrel, so while it sounded cool in my head, it just wasn't worth the hit in shot count.

[Gerard]

Yeah, anything over 20fpe on squirrels is kind of a waste of air. Unless there's a second squirrel standing just behind it, then it's perfect. With typical airgun accuracy (not counting the high end stuff like AA or FX or similar with incredible barrels) you're not looking at ethical squirrel hunting beyond maybe 40 yards anyway so no need to be concerned about longer range power retention.

[Jurai384]

 I bought a discovery as my first PCP and after watching the usual online videos etc I was expecting to get at least 20 good shots per fill. I thought something was wrong when I was only getting about 8 shots before my poi dropped about an inch at 20 yards.
 I decided to take it up to Tim at Mac1 and he explained everything to me about different hammer springs etc that crosman has used. Anyway hoping to pick it up with a better shot count and improved accuracy although it has been shooting through the same hole with 15.89 JSB's at my 20 yard range. I'd love 20 shots at double the yardage.