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rsterne · Moderator

Besides the work I have been doing to get more performance from the Discovery, I have also been working on the trigger.... Below is a photo of the best mods I have come up with for the Disco:

Hammer Spring

Shown below the trigger group on the left are a stock Disco hammer spring (bottom) and the best heavy hammer spring I have come up with above it.... The Disco spring is just under 2" long and made from 0.035" wire.... The heavier spring is 0.300" OD, 1.75" long and made from 0.040" wire.... Both springs have about the same compressed length....

In a stock .22 cal Disco (stock valve, ports, end plug).... using JSB 15.9 gr. Exacts.... the heavier spring allowed pumping to 2400 psi, and added about 100 fps in my gun (910 fps peak instead of 810) .... The useable number of shots (to 96% of those peaks) only fell from 25 to 22 (YMMV).... The same held true using an RVA (hammer spring tensioner) cranked to the maximum in a fully modded Disco.... Again, it allowed 2400 psi to be used instead of 2000.... which adds significantly to the maximum velocity and energy attained (at the expense of fewer shots per fill).... As an added benefit, you could actually adjust the lower end to a lesser velocity as well.... With both springs 1/2" out from coil bind, the Disco spring could bring the velocity down to about 650 fps.... while the heavier spring (because it is shorter) could get down to under 500 fps (both numbers at ~1400 psi).... So with or without an RVA, this spring gives the ability to utilize 2400 psi fills and that gains you about 100 fps.... plus it has a larger range of adjustment if you do fit an RVA.... Cool

Trigger Springs

The Discovery trigger group is exactly the same as in a 2260.... It has two springs, one coil spring behind the trigger blade, and another hairpin style spring that holds the sear and also acts as the detent for the safety (which fits in the hole behind the trigger).... In order to remove the action from the stock, you have to reach in with a small screwdriver or paper clip and pry the end of that spring forward in a small slot in the trigger guard in front of the safety.... Once the safety is removed, the action will slide from the stock (assuming you removed the large phillips head screw on the bottom of the stock in front of the trigger).... One work of caution, don't try and use the gun with the safety removed, there isn't enough spring tension to latch the sear safely, and the gun may fire on it's own.... Rolling Eyes

The stock trigger is very stiff, on the order of 4.5 to 5 lbs.... mostly because of the very heavy coil spring Crosman use behind the trigger blade.... It's made of 0.028" wire (bottom one in the pic), and because it's very short, gets harder to pull the more the trigger travels.... to the point it's almost impossible to feel where the sear spring starts working.... I replaced it with a 0.180" diameter spring made from 0.020" wire that is 0.625" long (above).... Since the spring is slightly longer, it's a bit of a fiddle to assemble the trigger.... but for a drop-in change the difference is astounding.... The result is that the pre-travel now only requires 3/4 lb. until you start to feel the sear spring.... This makes the trigger feel like a 2-stage unit, but without compromising any safety since the sear has not yet started to move.... If you release the trigger at this stage, the sear is still fully engaged.... Cool

I really liked the trigger with just this modification.... the total pull was just under 3 lbs., with a nice 2-stage feel.... If you want a lighter pull yet, you have to tweak the sear spring.... but be careful, it only takes a tiny bit to change things in a hurry, and potentially make the gun unsafe.... On the two springs I had, the included angle between the legs of the spring was about 135 degrees (IIRC).... I bent in the legs carefully until the angle dropped by about 10 degrees and ended up with a trigger pull so light you could barely feel the second stage.... I ended up using an included angle of 128 degrees to get a total pull weight of just under 2 lbs (YMMV).... I found that the pull weight didn't seem to vary with different hammer springs like it does in a 22XX or 13XX.... probably because of the trigger geometry.... I got identical results in my 2260 (which had a much lighter hammer spring than a Disco) as I did with either the stock or the heavier hammer springs in the Disco.... Wink

While you have the trigger apart, polish all the contact points up to a mirror finish, including the lower front face of the hammer where it contacts the sear.... Don't change any angles, just remove any stamping ridges, and bring the parts to at least an 800 grit finish (I use 2000 grit).... This will make the trigger release crisper, with less tendency to creep.... With just a bit of time and one small spring, you won't believe the difference in the 2260 / Discovery trigger.... Twisted Evil

Bob

Mark5043 · Silver Status Member

Thanks for the info Bob...always thorough.I have my Disco apart at the moment doing a-little stock refinishing,as it came in a rather dry,and rough condition.I have my parts for a homemade power adjuster,and would like to do the spring mods as well.Question...now that I have the dimensions,where can I get the springs?Perhaps a hardware store?My goal is to hit roughly 900fps with crow mags thus breaking 30fpe without doing any valve work.Based on your expertise with Disco mods,will it put me in the ballpark?

rsterne · Moderator

You will be very close to 30 FPE with Crow Mags (870 fps) with just the spring change.... certainly should be able to get there if you crank an adjuster in just a turn or two.... Wink

If you get greedy on the power, you will pay on shot count.... fact of life with any PCP.... Another 50 fps will cut your shot count in half in a Disco at these power levels.... Rolling Eyes

Unless you are going for absolute maximum power, I would leave the valve and ports stock.... I've generally found that modifying the valve and ports actually makes the shot string more curved.... ie higher in the middle which means shorter if you only use shots within 4% of the maximum velocity like I do.... Shocked

I've given the information on the springs to AirGunEric.... I'm hoping he will carry them in stock.... Wink

Bob

Mark5043 · Silver Status Member

Okay great.I realize I would lose shot count,with the mods,but in all reality I'm just looking for a linear shot string of 12 or so at full power.This is going to be my workhorse/pest gun.

rsterne · Moderator

I still have my Disco with the stock valve in it.... so I threw the RVA on it and dialed it up to give a 900 fps peak with Crow Magnums (ie the 96%range would be 864-900).... It did this at 2 turns from coil-bind with the heavier spring with everything else stock in the gun.... Cool

No reason you shouldn't get the same results.... I didn't do a full shot string.... but I'm guessing 16-18 shots within a 4% range filling to 2400 psi and dropping down to about 1500.... If you need a tighter velocity range, I would think you would get about 12-14 shots within a 2% window from 2300 down to about 1600 psi.... Let me know what your actual results are.... Wink

Bob

Mark5043 · Silver Status Member

Awesome,thanks.. Thumb Up!

So I'm good to go once I source some springs.In the mean time my stock is basically transformed...started with 220,and worked all the way to 1000 grit."2+ hours"...The Mrs. says my OCD is kicking in again!I have the first coat of antique oil finish doing it's thing...she sure is pretty!I do need to get a chrony once I find those springs so I can see what's happening,as I play with the mods.I have no doubt I'll be able to duplicate your results.Time for me to throw some chicken on the grill,and crack a cold one... Mr. Green

Thanks again Bob,for such a thorough,in depth analysis of various mods.... Cool

I'm looking forward to getting back to you,once I find the springs,and do the install.

Jaxom · Senior Member

Bob,

I've been follow along with your discovery/2260 builds as to how that would apply to my builds. I'm glad you posted the sizes and such for what springs are most optimal.

I started search for source to order springs from, but I need to get a few more details before I give them a call.

Fisrt is what type of metal are these springs? I think this is sorta obvious, but I just want to make sure. One place I'm looking at offers springs in music wire, oil tempered chromed silicone, 302 and 316 stainless steel. I would assume from the color, the ones you are using are music wire?

Secondly, they also have a listing for rate of compression per inch. Do I really need to know this to place an order?

Jax

Mark5043 · Silver Status Member

Teryx · Veteran Member