Power Mods for the Discovery Air Rifle? Let's Create a Sticky!

[Lostcoast]

As I have mentioned in another thread that will chronicle the overall journey of modding my Discovery .22, I am hoping to gain more power and shot-to-shot consistency over the stock configuration. My goal is to achieve at least 20 shots of 825 - 850+ fps using 18 gr pellets with no change in POI and excellent accuracy.

Towards this end I have read a great deal and learned of bits and pieces on this and other forums regarding heavier hammer springs, lighter valve springs, wider valve ports etc and my head is spinning a bit from it all. My hope is that we can create in this thread a single place where future Disco power modders can find most or all of the mods available and how to do them. Ideally a thread that can become a sticky to help our fellow airgun brethren.

As of now, I have a power adjuster and a "magnum" power spring sold by Magnum Airpower that is rated at 26lbs/inch but which the seller says only generates 14lbs of force for the length it is compressed. I'm still trying to figure out if this is an overpowered spring or not and need some guidance on that.

I also have a valve port sleeve that is .150 in diameter, also sold by Magnum Airpower. Everything else is stock in terms of power mods.

So where should I go from here to reach my stated goal? What are the options, ranging from simple inexpensive things that can be done without a lathe to more involved and / or expensive options? If you suggest particular parts, please include where to find them. If processes, please describe them (visually if possible) or link to other threads where they have been described and illustrated. As I said before, my hope is for us to all create a thread that can benefit other future Discovery modders.

Many thanks!
Kevin

[Monkeydad1969]

That's a good idea.  I feel there's enough out there on Discos for it's own sticky.

Joe

[Lostcoast]

Glad you think so, Joe. I think a good sticky documenting an array of effective power mods for the Discovery could save future modders a great deal of time and money and headache / heartache. There's so much knowledge here on this forum and so I hope we can bring it together into one place for the benefit of all.

[.]

Oh, yay! A sticky would be awesome!!

I have a new .22 Discovery w/TKO that I want to play with also. Having a one-stop thread to find all the freshest info would be such a great timesaver. Thank you for thinking of it, I have been researching this topic for a few weeks, the data is scattered far and wide, lol..

:-)

[RatRacer]

This would be cool.
I see references to a lot of new items on the market, since I've been on hiatus.

[USAFANG6799]

I thought about doing all these mods to my new Disco but think I'll just wait until the UMAREX GAUNTLET hits the market.
I'm sure I could easily spend another $100 in my Disco. That puts me over the $300 mark I've already invested in my Disco.

I do think that's a great idea though to consolidate all these mods with a Sticky. Who knows I just might find a couple to do while I wait for the GAUNLET to hit the streets.

I'm glad I'm not holding my breath waiting for the Gauntlet 

In the mean time I've replaced all the orings, installed a power adjuster, three screw valve replacement. I now fill it up to 2500 psi and very happy with how powerful it is in taking tree rats out to 35-40 yds.

[Lostcoast]

The thing that keeps me interested in modding the Discovery it the stock weight of 5.2 lbs - there's nothing like that weight out there in the $200 price range besides the Maximus. Perfect for a field gun. The Gauntlet looks interesting, but its 8.5 lbs by itself!

Okay ladies and gentlemen, hope we get some power mod suggestions here soon!

[.]

The thing that keeps me interested in modding the Discovery it the stock weight of 5.2 lbs - there's nothing like that weight out there in the $200 price range besides the Maximus. Perfect for a field gun. The Gauntlet looks interesting, but its 8.5 lbs by itself!

Okay ladies and gentlemen, hope we get some power mod suggestions here soon!

I love that the rifle is very light, but I think it is a bit top-heavy, so for now, no scopes. Maybe this build will please me enough to warrant a lam stock heavy enough to balance a scope nicely someday, but for now I'm going to enjoy using the open sights while I tinker with it and use it as a close range pest remedy. Anything too close for the scoped HW 110 will be Disco'd down, lol. The fiber optics are very usable at close ranges and they make night use pretty simple. I would love to find a higher power/shot count/noise balance. I don't need many shots, just as much tamable power as I can get, I am TKO'd, but even these have limits, ha!

[rsterne]

There are about a zillion directions this thread could take, some anybody could do, others you need a machine shop and the corresponding skills to achieve.... As an example, I have hit 223 FPE in .357 cal. using a Cothran valve at 2900 psi.... with all the appropriate safety modifications, of course.... I would suggest you restrict yourself to simple changes, using bolt-on parts, or things that can be done with a drill or Dremel.... and with the stock .177 or .22 cal barrels.... If you decide to use more than 2000 psi, then specify exactly the valve screws, etc. that you use, so that there is no doubt about the safety of your modifications.... As soon as you get into caliber changes, there is usually custom machining to be done, unless you purchase, for example, a commercially available .25 cal conversion kit....

There is a BIG difference between "mods" and "conversions", IMO....

Bob

[USAFANG6799]

Oh, yay! A sticky would be awesome!!

I have a new .22 Discovery w/TKO that I want to play with also. Having a one-stop thread to find all the freshest info would be such a great timesaver. Thank you for thinking of it, I have been researching this topic for a few weeks, the data is scattered far and wide, lol..

:-)

I'm waiting for my TKO to show up.
Are you happy with yours with reducing the noise report?

[Lostcoast]

Good point, Bob. I am thinking in terms of modifications that keep it the same caliber but increase the power and shot count, maximize consistency, and maintain the accuracy of the rifle.

And yes, while being safe all along with way.

I am hoping this does not become a general discussion thread about the Discovery but rather a place where generous experts can chime in with mods from simple and homemade requiring no precision tools, to those that do require say a drill press and the like, to more expensive mods in the sense of needing to purchase a regulator or different valve assembly. 

Step by step guides for the newbie modders who want their Discovery to be the best it can be in its native caliber.

So please, no general discussion and let's talk power mods for the Discovery!

[rsterne]

IMO there is no reason to purchase an aftermarket valve if you stay with .177 or .22 cal.... In fact in .177, leave the valve STOCK, the ports are already big enough.... In .22 cal, rather simple mods can increase the power to as much as is practical for a pellet shooter.... particularly if in conjunction with better valve screws and a small increase in fill pressure (to maybe 2400 psi).... Regulators are somewhat questionable in Discos, because of the small volume air tube.... unless you get the Regulated Disco Double kit from AirGunLab, which nearly doubles the air capacity.... As a bonus, it is externally adjustable with just a screwdriver.... Regulators, of course, LIMIT the power, because they reduce the operating pressure at the pellet, so perhaps that is counter to the direct the OP wants the thread to take.... The addition of the aftermarket BNM breech, which turns the Disco into a repeater using MRod magazines.... is a practical addition as well.... Of course if you add both (the DD kit and BNM) you will spend more than buying an MRod (but you will still have less weight)....

Bob

[.]

Oh, yay! A sticky would be awesome!!

I have a new .22 Discovery w/TKO that I want to play with also. Having a one-stop thread to find all the freshest info would be such a great timesaver. Thank you for thinking of it, I have been researching this topic for a few weeks, the data is scattered far and wide, lol..

:-)

I'm waiting for my TKO to show up.
Are you happy with yours with reducing the noise report?

I haven't heard the Discovery either way yet, it refuses air at the moment, ha ha. I'll get back to it later today...

But, I have two others of the same model TKO, one on a 2260 PCP conversion at 18 fpe, and the other on a .177 1300KT carbine. I wouldn't dare fire the 2260 without the TKO, but with it, it sounds like a hushed sneeze. The 1300KT I have heard both ways, and the reduction was also very satisfactory. The mechanical noise is louder on both guns, actually, than the discharge sounds.

[.]

Step by step guides for the newbie modders who want their Discovery to be the best it can be in its native caliber.

YES, this...

[Lostcoast]

Thanks for that input, Bob. What are the simple power mods that you make reference to?

[rsterne]

When I first got my Disco (it was the first PCP I bought), I did exactly what you are proposing.... I will post some of the steps I took at that time, with comments, and performance graphs.... Let's start with the way a stock .22 cal Disco shot, the way Crosman made them.... before fitting the heavier hammer spring....



As originally supplied the gun was well balanced, and IMO the strings were as close to perfect as you could get... Why Crosman changed to a heavier hammer spring and created their current declining shot string, I'll never understand....

Bob

[Lostcoast]

Great, Bob - this is exactly what I was hoping for! I look forward to your further posts!

[rsterne]

Here is what happened when I added a velocity adjuster, with no other changes....



The above was with JSB Exact Jumbo 15.9 gr. pellets.... Below are the shot strings with a 4% ES applied....



Bob

[rsterne]

The next step was to increase the port sizes.... I enlarged the barrel port to 0.166", the transfer port to 0.161", and the exhaust port to 0.157"....



Once again, the shot strings only show those shots within a 4%ES.... and starting from 2000 psi.... As an example, at 5T out on the velocity adjuster, the average FPE increased from 23.3 FPE to 25.4 FPE, but the shot count with 4% ES dropped from 21 shots to 19 shots....

Bob

[rsterne]

I then streamlined the valve exhaust port by rounding the transition between the throat and exhaust port with a small spherical burr on a Dremel.... This moved the peak velocity to a LOWER pressure, which required more hammer strike to compensate.... However, there was a power increase to 28.7 FPE average with the 15.9 gr. pellets, but now only 15 shots within a 4% ES.... The graph below compares the performance at this stage with the same hammer spring preload in a stock gun (4T out) and also with my stock Disco, pre mods....



At this power level, it made more sense to use the 18.1 gr. JSB Exact Heavy pellets, as you can see.... For one thing, that bumped the shot count within 4% ES back up to 20 shots.... The gun was now shooting them 50 fps faster than the stock gun would shoot the 15.9 gr, with the power increased from 22.4 FPE to 28.8 FPE.... That was where I stopped at that time.... My next step was to replace the valve screws with stronger ones, and to use a stiffer hammer spring and a fill pressure of 2400 psi....

Bob