GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Lostcoast on June 05, 2017, 01:12:56 PM
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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
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That's a good idea. I feel there's enough out there on Discos for it's own sticky.
Joe
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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.
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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..
:-)
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This would be cool.
I see references to a lot of new items on the market, since I've been on hiatus.
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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. ;D
I'm glad I'm not holding my breath waiting for the Gauntlet :o
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.
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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!
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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!
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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
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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?
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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!
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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
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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.
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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...
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Thanks for that input, Bob. What are the simple power mods that you make reference to?
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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....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/DiscoveryShotStrings.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/DiscoveryShotStrings.jpg.html)
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
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Great, Bob - this is exactly what I was hoping for! I look forward to your further posts!
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Here is what happened when I added a velocity adjuster, with no other changes....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/DiscoAdjuster.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/DiscoAdjuster.jpg.html)
The above was with JSB Exact Jumbo 15.9 gr. pellets.... Below are the shot strings with a 4% ES applied....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/Disco96.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/Disco96.jpg.html)
Bob
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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"....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/DiscoPorted.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/DiscoPorted.jpg.html)
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
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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....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/WebDiscoModded.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/WebDiscoModded.jpg.html)
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
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Bob do you have any photos of the port work you did? As a beginner here, I am not even sure of what the different ports are. Also, does this work need a drill press to achieve the precise measurements that you offer here (aside from the dremel work you mention)? Are there particular drill bit sizes that can accomplish these modifications?
Perhaps when I gain and know how to apply all this great information I will create some videos about it for YouTube for others to learn by. But in the meantime I am a total newbie in need of visual aids...
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You can drill the barrel port and valve exhaust port with a hand drill, if you are careful, although a drill press is better.... The transfer port you can do as well, but it is so tiny it is difficult to hold without crushing it.... If you want to try that, get a set of "numbered" drills, and drill ONE step at a time.... The same process on the barrel and exhaust ports is a good idea too, just to make sure you keep the holes straight....
The exhaust port, at 0.157", is finished with a 5/32" drill.... The largest you can go on the transfer port is a #20 drill (0.161") or you will risk collapsing the wall.... In reality, there is not any advantage to drilling one port larger than the other.... Drilling them all to 5/32" will get you most of the gains, along with streamlining the inside of the valve porting.... If you want to get the last fraction, then drill that 5/32" hole out with a #21 drill and then a #20 drill, and stop there for all the ports.... Some guys drill the barrel port out to 11/64" (0.172") which is 78% of the .22 cal bore.... Any larger and you can damage the pellets on loading.... I usually don't go that big, stopping at 0.161" for all the ports, because that is as large as you can drill a stock Crosman transfer port.... If you want to go larger, then you can use a short piece of ice-maker tubing, if you can find some of the larger diameter (but most is only 0.161" anyways).... Absolutely square ends, and the perfect length (just a slight crush for sealing) is critical.... and you have to drill out the seat in the barrel for it, another place to muck up.... I prefer using the Crosman transfer port, drilled to 5/32" or 0.161"....
Bob
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I don't have any photos of the Disco valve I did way back then.... I'm almost afraid to put them on here, because this thread is about simple mods, but here is a much later valve I did for a .25 cal conversion.... These photos show what can be done with the proper equipment.... The exhaust port is 0.219" on a 20 deg. angle.... more than double the flow....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/IMG_2799.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20PCP/IMG_2799.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/IMG_2802.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20PCP/IMG_2802.jpg.html)
There is a lot of potential in the humble Disco, but this stuff is way beyond the scope of this thread....
Bob
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Thanks very much, Bob. This is really helping. I look forward to hearing about your further evolution with the stronger hammer spring and higher pressure fill. I am about to buy another hammer spring from Hill Airguns and it would be great to know which one to get in terms of length and wire size.
Also, what do you mean by "streamlining the inside of the valve porting?
I'm going to have to find someone near me who will allow me some time on their drill press..
Is there a particular hammer you would recommend? I just ordered a Challenger hammer, having had some folks on this forum recommend it last night..
Is anyone aware of any tutorials that show how to disassemble a Discovery, get to the internals, and reassemble it?
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By streamlining the porting what I mean is rounding the front end of the exhaust port, where it meets the valve throat, to minimize that sharp corner, and it's associated turbulence.... Ideally (as shown in the photo above), you would angle the entire exhaust port about 20 deg., but this requires a milling maching to do accurately.... With hand tools, all you can do is use a 1/8" spherical burr in a Dremel, and working carefully, through the exhaust port, round the front lower corner of the port, and smooth the sides, to blend into the throat in the valve....
All the above was done with the stock Disco hammer.... There is no advantage to using a Challenger hammer, IMO, unless it is required because you are using a PRod trigger group.... I have used them, but the first thing I did was take out the adjustable striker and replace it with a flush screw, so that the stroke returned to that of a Disco hammer.... If you use the Challenger hammer, you will lose hammer stroke, which will require a stronger hammer spring (to get the same FPE), hence making the gun harder to cock.... The only reason to use a Challenger hammer is to set the screw BELOW flush, to increase hammer stroke.... but it is easier to simply remove 1/16" from the end of the valve stem to do that.... If you try and get more than about 1/16" increase in hammer stroke, the hammer pin ends up hitting either the end of the bolt (which can cause the handle to pop up on firing)... or the front end of the cocking slot.... Either one is hard on the hammer pin, and unless you modify things, limits your gains....
When you start modding a gun, there is a rule of thumb you must accept.... Each mod often creates two more, and each of those two more each.... Pretty soon, you run into problems you never even thought about when you started.... If you are unable to diagnose and correct these compounding errors, you are doomed to failure and disappointment.... "Nothing is as simple as it seems"....
Bob
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I have the Gen 1 Marauder trigger in my Discovery - is the Challenger hammer recommended for that? Otherwise I will cancel my order for the hammer..
What are the dimensions of the hammer spring that you recommend?
Great knowledge here - thanks for your continued sharing..
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The next step in the evolution of my original Disco was to fit a heavier (stiffer) hammer spring to allow using a higher fill pressure (2400 psi).... Here is the graph with those results, with the spring adjusted just shy of coil bind (ie maximum power).... The gun was now capable of 36.6 FPE average over 12 shots within 4%, using 18 gr pellets.... and over 40 FPE with 28.7 gr EunJins....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/WebDiscoTrakarMax.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/WebDiscoTrakarMax.jpg.html)
NOTE: TO SAFELY FILL ABOVE 2000 PSI, YOU SHOULD REPLACE THE THREE VALVE SCREWS WITH HIGHER QUALITY SCREWS....
The hammer spring I used was the stock 2" long, but made from 0.040" wire instead of the stock 0.035".... I have no experience with the new stiffer hammer spring supplied stock on the new Discos, but from what I have read, by using a velocity adjuster, you can make use of higher fill pressures without having to change the spring.... You may, or may not, get similar results to the above.... Remember, these mods are progressive (additive), each one adding to the performance of the previous one.... If you didn't do the port mods above, don't expect just installing a heavier spring and filling to 2400 psi to duplicate these results....
Bob
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The next stage in my modifications was to bore the inside of the valve out, to create more flow past the OD of the head of the poppet, and to thin the valve stem from 5/32" down to 1/8".... I didn't know it at the time, but almost all of the increase came from thinning out the valve stem to increase the flow through the valve throat.... Here are the results at that stage.... This gained about 1 FPE across the board.... Gains are getting harder to achieve....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/WebDiscoBoredValve.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/WebDiscoBoredValve.jpg.html)
Bob
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The next thing I did was to shorten the valve stem 1/16" to increase the hammer stroke.... I also used a slightly shorter, 1.75" long spring, also with 0.040" wire.... In addition, I hogged out the gauge port and the front of the valve for increased flow into the valve, which made a significant difference.... The combination of these mods added FPE, increased the efficiency slightly, and gave a couple more shots.... This concluded my development at that time.... At 2500 psi, I had achieved over 50 FPE, but at the expense of shot count....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/Disco1050FPE.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/Disco1050FPE.jpg.html)
The best, most usuable string above was with the 18 gr. JSB Heavies, with the preload backed out 2 turns from coil bind (labelled "Heavy-2T").... It gave me 14 shots within a 4% ES, averaging 40 FPE (1000 fps) at an efficiency of 1.14 FPE/CI.... Detuning it slightly to 37 FPE (960 fps), using a 2200-2300 psi fill, has become my standard tune for a .22 cal Disco.... giving about 14-15 shots at that power within a 4% ES.... It is not shown on the graph above, but would lie between the "Heavy-2T" and "Heavy-4T" curves....
Today, I would drill out the valve throat a bit, and bush the valve stem hole down to 1/8" and fit an MRod poppet, along with a PRod gauge port.... but I don't have the documentation so nicely presented to show how that would tie in with the original mods I did.... That is simply one more way to achieve similar results.... In practical terms, for a .22 cal Disco, I'm pretty happy with it tuned to shoot 18 gr. JSBs at 960 fps....
Bob
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Fascinating! Thanks very much. I think my initial aim is going to be for about 30FPE using the JSB 18.13 pellets for 20+ shots at 96%.
Time to get ahold of a drill press..
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For folks without access to the needed tools or who don't want to try their own valve mods, is this a viable option for getting good performance increases? https://www.bakerairguns.com/product/max-flow-valve-for-benjamin-discovery/ (https://www.bakerairguns.com/product/max-flow-valve-for-benjamin-discovery/)
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For those needing audiovisual aids that might help augment Bob's great instruction, I found these two videos by Airgun Labs:
https://www.youtube.com/watch?v=nPM2hapJ4xM (https://www.youtube.com/watch?v=nPM2hapJ4xM)
https://www.youtube.com/watch?v=gWLiLxLQmMM (https://www.youtube.com/watch?v=gWLiLxLQmMM)
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It's the same idea as porting an engine. Make the passages bigger, and change the shape of the port to flow more air. Eliminate or reduce sharp turns. But like an engine, if you make the ports too big, you actually lose power.
The first machine I ever bought was a small, cheap, drill press. I think it was like $40. Still works fine and I could sell it if I wanted to.
Steve
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This would be cool.
I see references to a lot of new items on the market, since I've been on hiatus.
Where ya been Rat? Glad to have you back.
Joe
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So I now have access to a drill press and I am trying to settle on what to do. I reckon my goal is to get JSB 18.13 pellets moving at 875-900 fps for 20 consistent and accurate shots, if that is possible.
Which of the valve modifications would you most recommend and for my stated goal of 875-900 fps, should I still increase port sizes to 5/32 or go with a slightly smaller diameter?
I already have the high strength valve screws so I can go above 2000psi. I am also going to order a wide bore gauge port today from Magnum Airpower.
I am admittedly a bit concerned about messing things up so any instruction and images to help me know what to do would be most appreciated..
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Today, I would drill out the valve throat a bit, and bush the valve stem hole down to 1/8" and fit an MRod poppet, along with a PRod gauge port.... but I don't have the documentation so nicely presented to show how that would tie in with the original mods I did.... That is simply one more way to achieve similar results.... In practical terms, for a .22 cal Disco, I'm pretty happy with it tuned to shoot 18 gr. JSBs at 960 fps....
Bob
I am thinking of trying this. How do I drill out the valve throat, and how much? What do I need in order to "bush the valve stem hole" to 1/8"?
Thanks..
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My results were good after following Bob's advice but I am averaging 832 fps with JSB 18.13 jumbo exact heavy for right at 28 fpe over a 20 shot string. I have a stock spring with a power adjuster, stainless steel fluted hammer and stainless steel hammer pin. Where I made the most gains was the transfer port. The stock port that comes with the BNM multi shot breech is already large enough in diameter to increase the airflow. I fill to 2300 psi (I have the upgraded valve screws) and shoot down to 1500 psi.
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My results were good after following Bob's advice but I am averaging 832 fps with JSB 18.13 jumbo exact heavy for right at 28 fpe over a 20 shot string. I have a stock spring with a power adjuster, stainless steel fluted hammer and stainless steel hammer pin. Where I made the most gains was the transfer port. The stock port that comes with the BNM multi shot breech is already large enough in diameter to increase the airflow. I fill to 2300 psi (I have the upgraded valve screws) and shoot down to 1500 psi.
Hey Phil,
That's looking good indeed - and simple! Such a great way to start.. Do you know that the diameter of your transfer port is?
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Drilling out the valve throat is better done in a lathe, to keep it centered.... Stock is 13/64" (0.203"), which with the 1/8" stem on an MRod poppet is the equivalent to a 0.160" exhaust port.... If you stay with that port size, you won't really gain much power by enlarging the throat, but you may gain a bit of efficiency.... For a .22 cal, I would only drill it to 7/32" (0.219") if using the MRod poppet....
If you stay with the Disco poppet, which has a 5/32" stem, then the stock 0.203" throat is only equal to a 0.130" exhaust port, which is why thinning the stem down to 1/8" makes such a difference in power.... I would grind down the stem to 1/8", or a few thou smaller, if you don't change over to the MRod poppet....
Installing an MRod poppet is not that difficult.... The stem is only 1/8" instead of 5/32", so you have to bush the stem hole in the valve down for the smaller size.... You can get brass tubing at Hobby Shops, made by K&S, that is 1/8" ID x 5/32" OD.... A short piece of that, glued into the back of the Disco valve, is all that is required to enable you to use an MRod poppet.... The OD of the MRod poppet head is smaller, allowing more flow past it inside the valve, so no need to bore out the valve ID like I had to in my original Disco.... In addition, the material is a bit harder, making the MRod poppet a bit easier to knock open, requiring a bit less hammer strike....
Bob
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My results were good after following Bob's advice but I am averaging 832 fps with JSB 18.13 jumbo exact heavy for right at 28 fpe over a 20 shot string. I have a stock spring with a power adjuster, stainless steel fluted hammer and stainless steel hammer pin. Where I made the most gains was the transfer port. The stock port that comes with the BNM multi shot breech is already large enough in diameter to increase the airflow. I fill to 2300 psi (I have the upgraded valve screws) and shoot down to 1500 psi.
Hey Phil,
That's looking good indeed - and simple! Such a great way to start.. Do you know that the diameter of your transfer port is?
I'm learning to document better. ran this string a couple weeks ago. just for reference the port that comes with the BNM breech is .180 I was considering drilling the valve but I think I will just leave the Disco as it is for now. I primarily use it for nutters. They hate it lol.
Bullet Weight (gr): 18.130
Altitude (FT): 200.0
Temp: 78 °F
BP: 28.78 inHG
Shots
# FPS FT-LBS PF
21 821 27.14 14.88
20 827 27.54 14.99
19 836 28.14 15.16
18 841 28.48 15.25
17 838 28.27 15.19
16 858 29.64 15.56
15 850 29.09 15.41
14 854 29.36 15.48
13 847 28.89 15.36
12 851 29.16 15.43
11 850 29.09 15.41
10 852 29.23 15.45
9 852 29.23 15.45
8 849 29.02 15.39
7 842 28.55 15.27
6 847 28.89 15.36
5 843 28.61 15.28
4 833 27.94 15.10
3 833 27.94 15.10
2 833 27.94 15.10
1 822 27.21 14.90
Average: 841.86
StdDev: 10.65
Min: 821
Max: 858
Spread: 37
True MV: 851.97
it's a bit over 4% but my POI holds for the 20 shots. it seems to build slowly then drop off quickly. I don't know the reason for that.
Is there some software for graphing? I would be interested in being able to present data in graph form.
Also everything I have learned so far about doing these mods has come from this forum and lots of time searching so I haven't innovated anything. The guys here like Bob (rsterne) and other long time members have a wealth of knowledge. the hardest part for me was getting over the "am I gonna mess this airgun up permanently" feeling. So many thanks to all for posting all the great methods and mods.
Phil
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My results were good after following Bob's advice but I am averaging 832 fps with JSB 18.13 jumbo exact heavy for right at 28 fpe over a 20 shot string. I have a stock spring with a power adjuster, stainless steel fluted hammer and stainless steel hammer pin. Where I made the most gains was the transfer port. The stock port that comes with the BNM multi shot breech is already large enough in diameter to increase the airflow. I fill to 2300 psi (I have the upgraded valve screws) and shoot down to 1500 psi.
Hey Phil,
That's looking good indeed - and simple! Such a great way to start.. Do you know that the diameter of your transfer port is?
I'm learning to document better. ran this string a couple weeks ago. just for reference the port that comes with the BNM breech is .180 I was considering drilling the valve but I think I will just leave the Disco as it is for now. I primarily use it for nutters. They hate it lol.
Average: 841.86
StdDev: 10.65
Min: 821
Max: 858
Spread: 37
True MV: 851.97
it's a bit over 4% but my POI holds for the 20 shots. it seems to build slowly then drop off quickly. I don't know the reason for that.
Phil
That looks like really good performance to me, and with a stock spring - wow. And with a .180 port - much larger than what most mods I have read talk about, which recommend .161. This is one of the areas where there seems to be a lot of disagreement. I've been having some folks tell me not to go above .156 in the transfer and barrel port or the shot count and string consistency will suffer a great deal, but that doesn't seem to have happened with your Discovery.
I'm forgetting - do you have a high flow gauge port on your rifle?
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My results were good after following Bob's advice
I'm forgetting - do you have a high flow gauge port on your rifle?
No I don't and I clipped 2 coils off the stock spring when I installed the Discosrus power adjuster.
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Using a 0.180" transfer port with a stock valve exhaust port and stock barrel port really shouldn't make much difference, compared to a 5/32" transfer port, which is already larger than the exhaust port.... In either case, the choke point then becomes the barrel port, which is the same in both .177 cal and .22 cal.... at only 0.134".... Here is a chart showing velocity and shot count in a Disco with a half size reservoir (from a 2260).... The valve and barrel ports are stock, only the transfer port size is changed.... Shot 1 was at a 2000 psi fill.... Note that the 4% ES shot strings with the larger ports started BELOW 2000 psi (ie the first 3-4 shots were more than 4% below the peak velocity)....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/2260DiscoPortStrings2_zpsc52cf166.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/2260DiscoPortStrings2_zpsc52cf166.jpg.html)
This data should apply 100% to a Disco, except the shot count would double, as the Disco reservoir is twice as large as the 2260 reservoir I tested with.... Note that as you increase the TP diameter, the shot string gets shorter and "peakier" (the ES gets worse)....
Bob
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Thanks for that great chart, Bob. Someone is recommending that I try a transfer sleeve of .150 and a transfer and barrel port of .151- .156. Looks like it will be good for velocity but pretty darn 'peaky'.
I'v decided that I am not quite ready to dive deep into valve modification work, so I am going to keep the power mods simpler for the time being:
- install a wide bore gauge port
- install .150 transfer port sleeve
- ream the transfer port and barrel port to .151?
- use stronger hammer spring (I will be trying the "43" and the "45" Hill Airgun springs;
- try higher fill pressures of 2400 - 2700 psi
How does this look?
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Certainly nothing wrong with simply matching all the ports to the size of the valve exhaust port, which is about 0.150".... I think for simplicity I would just go 5/32" (0.156") for everything, and then round off the front bottom of the exhaust port where it meets the valve throat.... Yes on the PRod gauge port, to get more air into the valve.... To get the flow through the throat to equal the 5/32" porting, you will need to either use an MRod poppet (and bush the valve stem hole).... or grind down the Disco poppet shaft to 1/8" in the exhaust port area....
You should be able to get the performance you want without going above 2400 psi.... You may need a bit stronger spring to use that pressure.... You certainly will need a much stronger spring to use 2700 psi, along with stronger valve screws.... and I don't think you will like how hard it gets to cock at those pressures.... I see no reason to do that in a .22 cal Disco.... Shooting the 18 gr. JSBs in the 900s is really all you need....
Bob
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Just picked up my first PCP, a Discovery in .22 the info here is awesome thank all of you who contribute. I work a lot on regular firearms but airguns have opened up a new ( for me) area. But then again maybe not that new my first firearm related love was a Daisey 880 that I wore out.
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Posting for future reference.
Disco mods should be a lateral "read across" to the Maximus.. no?
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For those of us who are not interested in or able to do valve modifications ourselves, Bill at Magnum Airpower just released a Magnum Valve for Discovery and 22XX conversion airguns. Prices range from $30-$53, depending on the configuration that one chooses. Bill says the valve is capable of delivering 60-70 FPE in the Discovery. Here's the link to the valve: https://onlinestore.magnumairpower.com/products/magnum-valve-discovery
My goal has not been maximum power but rather power in the range of 30-35 FPE for at least 20 shots. Tim Hill of Hill Airguns suggested to me a few months ago that I do modifications to the valve but leave the transfer port alone and even use a smaller than stock transfer port sleeve. His claim was that the valve mods will increase power while the smaller transfer port sleeve will help maintain a more consistent shot string. Since he is a respected expert I took his advice. I bought a modified valve from Magnum Airpower and then experimented with port sleeves of various diameters. I ended up settling on a .062 diameter Euro flavor Maximus port sleeve that I enlarged to approximately .088. Using the Magnum Airpower Magnum Power Spring and a fill pressure of 2350 psi I am getting a high of 904 fps and a low of 868 fps over 20 shots using the JSB 18.13 pellet. 20 shots within 3.8% of ES and an average FPE of 31.8. No doubt I could fiddle more for even better results but this is very satisfactory to me at present, especially because the accuracy is excellent.
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AWESOME results Kevin!
Naturally the Complete Valve with Marauder Stem and Bybass Cap is out of stock :( Hope he gets some soon.
Matt
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Sticky-Sticky-Sticky!!! Please ;)
Knife
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I have been looking to see it the stock barrel bands can be opened up to .5" for use if you use the Baker Big bore Breech and a .5" barrel..?
Was saving to Build a short shot count 40+ disco for the BBT 30g .22... got sidetracked by the Maximus... It's 26" barrel should be a direct fit tho...
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For those of us who are not interested in or able to do valve modifications ourselves, Bill at Magnum Airpower just released a Magnum Valve for Discovery and 22XX conversion airguns. Prices range from $30-$53, depending on the configuration that one chooses. Bill says the valve is capable of delivering 60-70 FPE in the Discovery. Here's the link to the valve: https://onlinestore.magnumairpower.com/products/magnum-valve-discovery
My goal has not been maximum power but rather power in the range of 30-35 FPE for at least 20 shots. Tim Hill of Hill Airguns suggested to me a few months ago that I do modifications to the valve but leave the transfer port alone and even use a smaller than stock transfer port sleeve. His claim was that the valve mods will increase power while the smaller transfer port sleeve will help maintain a more consistent shot string. Since he is a respected expert I took his advice. I bought a modified valve from Magnum Airpower and then experimented with port sleeves of various diameters. I ended up settling on a .062 diameter Euro flavor Maximus port sleeve that I enlarged to approximately .088. Using the Magnum Airpower Magnum Power Spring and a fill pressure of 2350 psi I am getting a high of 904 fps and a low of 868 fps over 20 shots using the JSB 18.13 pellet. 20 shots within 3.8% of ES and an average FPE of 31.8. No doubt I could fiddle more for even better results but this is very satisfactory to me at present, especially because the accuracy is excellent.
I have my disco at 28fpe and 4% for 25 shots. Fill from 2200 down to 1600 psi. at this point I think I'm done with the disco as all I use it for are nutters out to 40 yards. for close range pesting I have the P-Rod set at 22 fpe for 24 shots and long range and larger game get hit with the Hammer! which is my AT44S 10 QE .25 that is now tuned to a stunning 40 fpe for 18 shots with baracuda 31.02gr pellets. Every tool has its purpose.
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For those of us who are not interested in or able to do valve modifications ourselves, Bill at Magnum Airpower just released a Magnum Valve for Discovery and 22XX conversion airguns. Prices range from $30-$53, depending on the configuration that one chooses. Bill says the valve is capable of delivering 60-70 FPE in the Discovery. Here's the link to the valve: https://onlinestore.magnumairpower.com/products/magnum-valve-discovery
My goal has not been maximum power but rather power in the range of 30-35 FPE for at least 20 shots. Tim Hill of Hill Airguns suggested to me a few months ago that I do modifications to the valve but leave the transfer port alone and even use a smaller than stock transfer port sleeve. His claim was that the valve mods will increase power while the smaller transfer port sleeve will help maintain a more consistent shot string. Since he is a respected expert I took his advice. I bought a modified valve from Magnum Airpower and then experimented with port sleeves of various diameters. I ended up settling on a .062 diameter Euro flavor Maximus port sleeve that I enlarged to approximately .088. Using the Magnum Airpower Magnum Power Spring and a fill pressure of 2350 psi I am getting a high of 904 fps and a low of 868 fps over 20 shots using the JSB 18.13 pellet. 20 shots within 3.8% of ES and an average FPE of 31.8. No doubt I could fiddle more for even better results but this is very satisfactory to me at present, especially because the accuracy is excellent.
I have my disco at 28fpe and 4% for 25 shots. Fill from 2200 down to 1600 psi. at this point I think I'm done with the disco as all I use it for are nutters out to 40 yards. for close range pesting I have the P-Rod set at 22 fpe for 24 shots and long range and larger game get hit with the Hammer! which is my AT44S 10 QE .25 that is now tuned to a stunning 40 fpe for 18 shots with baracuda 31.02gr pellets. Every tool has its purpose.
Yea those Hatsans are nice..
I did some experimenting with other transfer port sleeves for greater power and with the stock .141 port sleeve I get 14 shots within 3% of ES and an average of 39 FPE using the JSB 18.13 pellets. I love how versatile my modified valve Disco is now through the simple changing of the transfer port sleeve - its like having multiple guns in one.
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The Magnum Valve opens a lot easier at high pressure so it doesn't require anywhere near as much striker spring tension. The new Magnum .045 spring is only 1.5" long and compresses a lot smoother and easier than the older ones. The combination of the two makes for a very powerful, efficient and easy-cocking Discovery or custom build. I have a 90 cu in tank on my Disco .22 with a 26" Maximus barrel. It produces 905 FPS with 33.95 grain pellets which is about 62 FPE. I get about 100 consistent shots per fill. It's extremely accurate with JSB Monster 25.39 grain (1000+ FPS) and JSB Beast 33.95.
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a pic of the 90 cu in disco would be cool!
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It produces 905 FPS with 33.95 grain pellets which is about 62 FPE. I get about 100 consistent shots per fill. It's extremely accurate with JSB Monster 25.39 grain (1000+ FPS) and JSB Beast 33.95.
Get the *(&^ outta here!!!
Seriously?
WOW
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Bill offers some pretty awesome custom parts and has fair pricing on Crosman factory parts. https://www.magnumairpower.com (https://www.magnumairpower.com/)/
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Bill offers some pretty awesome custom parts and has fair pricing on Crosman factory parts. https://www.magnumairpower.com (https://www.magnumairpower.com/)/
That would make me a "repeat customer" I bought one of his PA's for my 1740.
He is one "Good Joe"!
Thanks!
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I ordered one of his Magnum Valves and swapped out the top half of the frankengun in my avatar. At 1900 psi, it is launching 21.14 grain baracudas at 945 fps with a 26" barrel. That's well over 40 fpe and it didn't take a super heavy hammer spring to get there.
I really think that is where his valve will shine, is in a regulated gun. And the price is very reasonable compared to others out there. It's perfect for those of us that don't have the tools to modify a stock valve.
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I know this thread is old and yet I have a question about boring out the Discovery valve. I'm talking about the front half only.
EDIT
I'm responding to my own post. After measuring and looking at the valve I see it is not the o-ring section, it is the cutout below it that is the narrow part. I drilled the front half of the valve to 9/32 (.2812). This give enough of a lip for the poppet spring to fit and leaves about a .10 wall in the narrow part of the valve. I think I will stick with that and just quit while I'm ahead.
When I didn't have the valve in front of me I had illusions of grandeur and hollowing out the valve even more than I already had done and now I don't think it would be such a good idea.
Here is what I was originally thinking.
"I'm thinking of drilling out the front of the valve even more and wondering how thick or rather how much wall needs to be left before danger of the valve wall collapsing? I'm more concerned about the o-ring area and not wanting to get that too thin. I will be stopping about 1/4" from the bottom with a tapered reamer to leave material for poppet spring and still have a smooth sloping transition. The only reason for drilling out the hole is increase plenum space behind the de-pinger. "
By the way, this sticky is the absolute bomb for information.
Thank you,
Dave
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I got a magnum air valve and screws and it looks fantastic. I also built an internal SSG/FFH to hopefully up the shot count I have a TJ 28" .25 acp to go on to. All I have left is to decide what breach I want to put on top, or roll my own. It is a very nice valve and saves a bit of messing around. I also converted another valve to Mrod stem with brass tubing, and it really unshrouds the poppet, and was shockingly easy.