Flying Dragons PCP - XS60C based

[rsterne]

I got my FD-PCP in the mail today, filled it to 1500 psi and shot a few strings with JSB 14.3 gr. Express.... I had a few teething troubles, the first of which I never did fully figure out.... The first string was great, high 800s, about 9 shots within 4% ES ending at 1500 psi.... I tried another string, didn't change anything, and the string started in the high 700s, with the first 6 shots way to slow to include in the string.... The next string was even slower, so I figured something had to be changing.... I knew the trigger could alter the velocity and when I checked it, it wasn't fully back (and the screws not that tight, it may have slipped forward), so I reset it fully aft, and while I had it off did a quick trigger tune, as the stock setting was horrible, the sear engagement was wayyyyyyyyyy too long and therefore creepy.... I shortened up the sear engagement to about 1/16", clipped 2 coils off the trigger spring (the adjusting screw was nearly falling out), and it was much improved.... With a bit of polishing it should be every bit as good as the QB trigger it is based on.... Incidently, this trigger uses the spring-loaded 2-piece blade like the ARs, so it has a 2-stage feel to it....

Anyway, with the trigger fully back, the gun wouldn't cock, the bolt slot wasn't quite long enough, so I had to move the trigger ahead about 0.020" and then it was fine.... The next string duplicated the first, so I thought I had found the problem, but the next string was once again slow.... and now I knew nothing was moving.... I found that the set screw in the bottom of the striker was loose, as was the slotted screw under it, and I tightened those and proceeded to find out what changing the preload would do.... I was curious if there was enough adjustment to get to coil bind, so I removed the lock nut and washer from the preload adjusting screw and wound the screw in until it was flush with the threaded plate, and the gun would still cock, no coil bind.... I filled to 1500 and shot a couple of shots, just over 940 fps which is 28 FPE.... Pretty impressive performance, I have to say, this thing must breathe pretty well.... I then started backing out the preload and recording the velocity, filling to 1500 each time, and the gun was solidly on a plateau, I had to back the preload out 5 turns before it even started to loose velocity.... I can only imaging what an air hog it would have been with the screw cranked in flush.... Anyway, at 6 turns from flush with the plate (which I took to be the maximum usable preload), I reinstalled the washer and lock nut, and the screw was flush with the surface of the nut when the slot was vertical, and the velocity was just beginning to drop, so I used that as a starting point for further preload testing.... As I backed off the adjusting screw so that it protruded from the lock nut, the velocity dropped rapidly, and at 3 turns out it was under 500 fps.... This is with the trigger as far back as I could get it and still cock the gun.... I graphed the results, and then proceeded to shoot some strings.... Here are the graphs.... NOTE: PELLET WAS 14.3 GRAIN, NOT 15.9 GRAIN !



With the screw flush with the surface of the lock nut the gun was shooting right at the top of the sweet spot, but only got 6 shots before the velocity dropped more than 4% below the peak.... So, for my gun at least, there is no point in going for any more preload at 1500 psi.... At 1 turn out, I got a beautiful string of 9 shots, starting right at 1500 psi and ending at about 1100.... The efficiency was very good at 1.15 FPE/CI, and the string started out fairly quiet and by the end it was really loud.... At 2 turns out from flush with the locknut, the first shot was only 646 fps and really quiet, and the velocity gradually built until I could start counting shots at about 1350 psi, and the string ended at 1000 psi.... In other words, if you are using the recommended 1500 psi fill, all the usuable adjustment range (at least on my gun), with the trigger set back as far as you can and have the gun cock, occurs from where the adjusting screws is flush with the lock nut to about 2 turns out from there.... Since the adjustment is so sensitive, and I'm sure there are differences between hammer springs and other parts (not to mention trigger position, which makes a huge difference) the only way to determine this for your gun is to basically duplicate my testing method.... Keep cranking in the preload until the velocity plateaus, and then you know how far is too far, back it off until the velocity starts to drop, and then a bit further until you find your best tune....

My initial conclusions are that this gun is a powerhouse; my best string of 9 shots, from 1500 psi down to 1100, averaged 24.7 FPE at an efficiency of 1.15 FPE/CI.... I think the biggest challenge is going to be figuring out how to get a longer shot string within a 4% ES.... I'd like to set this gun up as a Grouse gun for my son, as a repeater using the MRod mags, and the ideal would be 20 shots (2 magazines) at 20 FPE with 18.1 gr. JSB pellets, which I know to be a deadly combination on Ditch Chickens.... I have a feeling that to accomplish that, I will have to restrict the porting somewhat to flatten out the shot string and increase the usuable pressure range beyond its current 400 psi....

Bob

[rsterne]

Here is a photo of the Flying Dragons PCP, which is based on the XS-60C.... Mike installs a longer reservoir plus a fill fitting....



Here are some photos with the stock removed....



The angle bracket at the back has the screw that holds the back of the action in the stock....



The trigger is basically a QB/AR unit with the spring-loaded trigger blade and has the same adjustments.... I shortened the trigger spring 2 coils as the adjusting screw was nearly falling out when a suitable pull was achieved.... There is a slot in the read of the trigger guard, and a movable block that the front trigger screw threads into, which allows the trigger to slide fore-and-aft.... This changes the position of the sear, and hence the hammer travel and preload, drastically changing the hammer strike.... On my gun, when I moved it back all the way, the bolt wouldn't come far enough back to cock the gun, so I ended up with it about 0.020" forward of the back position....



There is a spring inside the bolt, when you remove the screw and pull out the handle, ahead of that is the spring, don't lose it!.... The rear block that mounts the velocity adjuster has two screws one on the bottom and one on the side, and once removed and the screws are removed from the bolt and striker, everything slides out the back (so I understand).... I haven't had them or the valve out yet, I'll add pics when I do....

Bob

[rsterne]

I completely disassembled the FD-PCP today, and did some measuring.... First of all, here are the parts.... You can pretty much tell from the photo where everything goes....



Here are a few observations about the construction, and some comments about the safety of the design....

1. The fill fitting has an internal check valve, there is no check valve inside the male Foster.... The means you can't use a "T" and install a gauge where the Foster is, it won't read the gun's internal pressure once the check valve closes.... The O-ring that seals the fill fitting is located in the threaded portion of the tube, so part of the threads are pressurized....

2. The back of the tube threads into the receiver.... There are lots of threads, so the shear strength isn't an issue, even though the receiver is aluminum of unknown quality, I wouldn't worry about that.... However, the tube seals at the inner end against a square-section O-ring which sits against a shoulder flush with the front of the valve.... As such, the threaded area of the tube is pressurized....

3. I measured the threads, and they appear to be 22mm OD x 1mm pitch.... While I couldn't find a listed diameter at the bottom of the thread groove, using the standard formula for Metric threads with a 1mm pitch, the diameter should be at least 20.6 mm (0.811").... The inside diameter of the threads in the receiver is 0.827", so the OD of the structural part of the tube certainly has to be smaller than that.... The ID of the tube is 0.745".... I do not know the material the tube is made from, but using 1010 mild steel (44K yield, 53K tensile), I get a pressure to yield of 3900 psi, and 4700 psi to burst.... At the 1500 psi recommended fill pressure, that works out to a 2.6:1 safety margin to yield.... If the threads are shallower, or the material is stronger, then that increases....

4. The valve is located by two 5mm x 0.8 mm steel screws of unknown quality in shear.... Since one of the load-bearing screws is in the steel block behind the valve, is it critical that the valve bear tightly against that block, otherwise only the valve screw would be taking the shear load.... I would highly recommend that when you have your gun apart that you check that, and if they are not in firm contact, add a thin shim between them to insure both screws are doing equal load bearing.... The threaded portion of the screw is subject to the shear load, so I used the minimum listed minor diameter and calculated a total shear force of 1154 lb.f. for the two screws, assuming 1010 mild steel with a 53K tensile strength (32K in shear) .... With a 0.745" ID for the reservoir, at 1500 psi, the load on the valve is 654 lbs. which means the safety margin is 1.8:1.... If the screws were upgraded to high-tensile screws, this would increase, and I would highly recommend that anyone contemplating using more that the recommended fill pressure confirm that the screws are up to the job.... Where the valve screws penetrate the receiver, you could see faint marks from where the threads of the screws were pressing on the back of the hole.... However, the material is thick enough that I was not concerned about the bearing load at the recommended 1500 psi, but it is something to keep an eye on each time you have the gun apart....

5. I noticed that the valve stem only protrudes 0.100" from the back of the steel supporting block.... That limits the valve lift to that distance, although the poppet itself is capable of much more.... I have not measured the actual lift in the FD-PCP, but it would not surprise me that the striker is hitting the block at the low pressure end of the shot string.... This is not likely the case in a properly adjusted shot string at the high pressure end, because the valve is achieving self-regulation.... but it could result in the right hand (low pressure) side of the shot string dropping off quicker than it should if there was more lift available.... This may be the reason for the very limited (approx. 400 psi) pressure range I was seeing between fill and refill when restricting the string to a 4% ES.... I am going to machine 0.050" off the back of that block to allow more lift before I reassemble my gun to confirm this theory.... I have already determined that it is possible to take off 0.080" and still have the striker hit the block without the pin hitting the end of the cocking slot in my gun....

6. I measured the porting on this gun, and to be frank, IT'S HUGE !!! .... The valve throat is 0.205" and the stem is 0.118" giving an equivalvent diameter for the throat of 0.168".... The exhaust port on the valve is 0.195", and the port through the receiver is the same.... The barrel port is 0.162", which is right at the recommended maximum for a .22 cal bore.... About the only thing I can see where you could possibly improve the flow would be to drill out the throat slightly to 7/32" (0.219") and round off the transition between the throat and the bottom of the exhaust port.... No other changes would be necessary for .22 cal, IMO, and in fact the valve is capable of being enlarged to flow well for a .25 cal by increasing the throat to 15/64" and angling the port with a 3/16" mill.... A 3/16" barrel port for the .25 cal barrel would complete the changes.... I did notice that the barrel port was slightly forward of the hole in the receiver, although not enough to shroud it, but if you were building a .25 cal you would want to make sure they lined up better....

In conclusion, the gun is pretty well made, especially considering the price point.... Like most guns, it can benefit from disassembly and cleaning, checking for burrs, and polishing up the hammer, sear, and trigger contact points.... and making sure that bolt functions smoothly, then reassembling with the proper lubes.... With the size of the ports, it is not surprising to see the power the gun puts out, but also not surprising to see the rather "peaky" power curve, which leads to a shorter shot count within a decent ES.... I have made a new fill fitting with integral gauge mount as shown below....



The O-ring is moved inboard of the threads, and it takes up less volume in the reservoir.... I added a check valve to the male Foster fitting....

Bob

[rsterne]

I just realized I made an error in the first post, the pellets I have been using for testing are 14.3 gr. JSB Express, not the 15.9 gr. Exacts.... I have corrected that post but the title on the graph is misleading.... my apologies for the error....

Bob

[Doc Sharptail]

Wonder if the porting is factory? Or is this something flying dragons would do?

Breeching system appears to be well thought-out. Do you think it's more stable than the QB/AR series?

Looks like an interesting gun. Looking forward to seeing a few targets...

Regards,

Doc Sharptail

[rsterne]

Today I did some mods to the valve, just to see what would happen, and where there might be some remaining restrictions.... I did this in two stages, first by increasing the flow OUT of the valve, and then by increasing the potential flow INTO it.... In the first stage I made the following changes:

1. I drilled the throat to 7/32"....
2. I used a 5/32" spherical burr in a Dremil to smooth the transition between the throat and the bottom of the exhaust port, where there was a sharp 90* corner.... I smoothed that out to ease the flow....
3. I tapered the sides of the brass poppet from the OD of the spring at the front to the stock OD (OK, I filed it down a bit!) at the back....
4. I bored out the inside of the back of the valve to 0.475" to increase the gap between that and the OD of the poppet from 0.035" to 0.050"....

I felt that these were the only places that the valve, with it's already generous exhaust port, needed any attention for a .22 cal gun.... When I tested the gun with the hammer spring preload maxed, I picked up 40 fps, which is not huge, but not insignificant either.... As expected, however I lost a shot or two in the shot string.... I then modded the front portion of the valve to make sure that wayyyyyyyy more air could get into the valve than it needed.... I was pretty sure this was a waste of time, as the valve already has slots to open up the flow, but I did the folowing:

1. I increased the slots from 5/32" wide to 1/4" and doubled their length....
2. I removed the washer that acts as a spring seat, and drilled a new 5/16" pocket in the end of the valve to hold the longer valve spring.... The spring is a shortened hammer spring from a Crosman 2200, but a shortened Disco hammer spring would work as well.... It is 1.5" long and 0.035" wire and has about the same seat pressure as the stock spring....
3. I drilled the hole in the end out to 15/64" (the ID of the spring)....
4. I used the Dremel to taper and round the edges left by the milling to ease the flow and reduce turbulencs....

Here is a photo of the modded valve....



As I expected, opening up the inlet side of the valve did almost nothing, it added 10 fps.... I tested the valve after the first (flow) changes and again after the second (inlet) changes, and plotted the velocity against preload with the following results....



I have a suspicion that the hammer spring is taking a "set" or that something else is changing, as the gun required more preload today before I started modding the valve.... Increasing the throat diameter of the valve may have required more hammer strike to reach the plateau, but I can't see how increasing the flow into the valve did that, unless it is "blowing" the poppet shut faster.... The important data is that there was a bit of a gain by improving the flow out of the valve, but very little to be gained by increasing the inlet area....

After these mods I played around to find the new optimum hammer preload with the 14.3 gr. JSB Express pellets used in the testing of the stock gun.... Here is the resulting string, from 1500 psi down to 1150....

942
975
976
962
953
934

Yes, only 6 shots within a 4% ES, that's what happens when you hog out the ports in a valve, you gain power but loose shots.... The efficiency was still decent, at 1.03 FPE/CI, but I had to refill at 1150 psi.... The average over the 6 shots was 957 fpe (29.1 FPE), a gain of 18% but a loss of 3 shots.... I then tested the gun with JSB 18.1 gr Heavies, with the following results....

879
890
910
915
909
895
880

I picked up one shot with the heavier pellets, plus a nice gain in power as well.... The average over the 7 shots was 897 fps (32.3 FPE) at an efficiency of 1.17 FPE/CI, filling to 1500 and refilling at 1100 psi.... This is a whack of power for a $100 gun with only a few minor changes.... especially considering the low fill pressure.... I am running out of adjustment on the preload, however, the screw is now halfway through the locknut, with no washer behind it....

Now that I have pushed the power about as far as I think it can go with a 1500 psi fill, I need to back off the power and start working on shot count.... This is where my previous experience with the Disco will hopefully come to the rescue.... This graph is my starting point....



That graph was done with a stock Disco barrel with a port of only 0.134".... That choked up the flow for the largest transfer port sizes, preventing it from continuing on up to the 30 FPE region we are getting with the FD-PCP with it's 0.161" barrel port.... If you look at where that would be on the Disco graph, it would pretty much mean a linear trend of FPE with transfer port diameter.... Since I want about 20 FPE, it looks to me I should be looking at a transfer port (or barrel port) diameter of about 7/64" (0.109").... I think that's as good a place as any to start....

Doc, I think all the porting is factory, but I'm not sure about the slots in the front end of the valve.... There is no transfer port, just a hole between the valve and barrel chambers in the receiver.... The barrel engages the receiver over a much longer length than on a QB and is therefore much more stable, IMO....

Bob

[rsterne]

Here is the first attempt at restricting the porting.... I found a small rivet that had a 0.104" hole in it and shortened it and glued it into the barrel port.... It turns out I still have a bit more power than I want.... I am looking for 20 FPE and got 23.3 FPE.... Here is the shot string, starting from 1500 psi, compared to without the port restrictor....



I'm back up to 9 shots, the same as I had at this power level when the gun was stock.... The efficiency has climbed to 1.25 FPE/CI, but to keep a 4% ES I can only use 350 psi, refilling at 1150 psi.... There has to be some way to flatten the shot string to be able to utilize a wider pressure range....

Bob

[rsterne]

I thought maybe a lighter valve spring would make a difference to the usable pressure range, so I fitted one made from a 2240 hammer spring that was less than 1.2" long, so it had very little preload.... Basically, other than requiring about a turn less hammer spring preload, the gun shot exactly the same.... About the only thing I had left to try was a bstaley O-ring buffer.... Although intended for use with an adjustable length striker, I took a chance and dropped in three #113 - 70 D O-rings and because of the 0.050" I had machined off the steel backer block for the valve they were too short, so I added a "backer ring" under them against the steel block which was 0.050" thick to make up for what I had machined off.... I figured the chances of this being the correct thickness O-ring stack to work properly was slim to none, but at this point I was getting desperate.... I still had the gun set up as per the previous string with the 0.104" barrel port, and to my surprise I got a nice flat 17 shot string from 650-680 fps (about 18 FPE).... I tried one more turn hammer spring preload and the velocity moved up to 700, but right at the beginning of the string and then a dozen shots before it dropped 4%, so I was getting very close.... At this point I had two choices, either take a bit off the O-rings to increase the valve lift, or try going larger on the barrel port.... I decided to simply remove the barrel port restrictor, and boy was THAT the right decision.... I was rewarded with an 18 shot string starting at 698 fps, peaking at 718, and ending at 692.... a 20 FPE average, just what I wanted.... Here are the results....



This was a perfect scenario for the bstaley O-ring mod.... a gun that was overpowered with big ports and tons of flow, tuned down to use tiny sips of air very efficiently.... The total pressure drop was 475 psi, for a staggering efficiency of 1.57 FPE/CI.... I'm still limited to using about 500 psi for a 4% ES string, but with the number of shots, that is no longer an issue.... I can now set the gun up as a repeater using the 8-shot PRod magazine and get 2 full magazines at the 20 FPE level I wanted.... The best 20 shots are within just 20 fps from 1500 psi down to 1050....

So far I had not mounted a scope, so I really had no idea how accurate this gun was.... I borrowed a scope from another rifle, and was rewarded with it putting the 18.1 gr. JSB Heavies into a single 1/4" hole at my 20' inside range.... When a gun shoots like that, I know it's a keeper, and I don't even have to go looking for other pellets, because I know how great these work on Grouse at this power level.... One other thing I'd like to show you is the fill system I have.... I bought the parts from China on eBay for just $16.00, it will allow me to fill the gun from any paintball tank with a 1500 psi regulated output.... It consists of a fill station valve with 3000 psi gauge, an 8" braided hose, and a slide check which came c/w a female Foster fitting.... I bought the three parts separately and the vendor combined the shipping for $9.00.... and I received it in just a week....



Using a 48 CI 3000 psi tank will give me about 20 fills, and even a tiny 13 CI tank will fill it 6 times in the field.... wayyyyyyyyy more than you need for a days hunting.... Tethered to the big tank, I would have about 360 shots available, and over 100 from a 13 CI....

For those of you who might want to try the bstaley O-ring buffer in your FD-PCP, it's as simple as just pulling out the striker and dropping them in against the back of the steel valve backer block.... Use three #113 Buna O-rings of 70 Durometer, and see what you get.... It's too bad the gun doesn't have an adjustable nose on the striker, that would make tuning it a breeze.... but the basic idea is that if you need more power you need to thin up the O-ring stack a whisker (sand the front one down).... and if you need to slow it up more, add a thin shim between the front one and the steel block.... What you are doing is limiting the amount that the striker can open the valve.... which reduces the power and lengthens the shot string.... It works best when you are reducing the power a fair amount as in this case (going from 30 FPE down to 20) where I doubled the shot count.... If the stack is thinner, at some point it does nothing and you get full power.... At the other end of the scale, if you make the stack too thick, the striker won't hit the valve at all, and the gun won't fire.... The distance between those two extremes isn't a lot, probably less than the thickness of a single O-ring....

Oh!, I almost forgot.... While tuning the gun today I was adjusting the preload with the velocity adjuster, and suddenly the gun wouldn't cock.... I couldn't pull the bolt back far enough for the striker to catch the sear.... If I turned the preload a half turn in either direction it was fine, so I suspected that the shoulder on the adjusting screw was off-center just enough to catch on the back of the hole in the striker.... I pulled the velocity adjuster mount off the back of the gun, and sure enough, there was a shiny mark on the shoulder where it had been rubbing on the inside of the striker.... This would not be an issue if the adjuster was backed out further, but I needed to fix it, so I chucked the adjusting screw in the lathe and remove 0.010" (on the radius) so that it was the same OD as the spring and could no longer rub on the inside of the striker.... I reassembled the gun, and not only did it cure the problem and the gun now cocked fine no matter what the rotation of the velocity adjust screw.... but the trigger pull was MUCH improved.... I guess the striker, most of the time, was being pushed offcenter by the shoulder on the screw which caused it to bind on the sear.... So, I killed two birds with the one rock.... I was wondering why the trigger on this gun was so rough, and that was the reason, it was fighting against a binding striker....

Bob

[rsterne]

Today I modified the receiver to accept the 8-shot .22 cal PRod magazines.... This was NOT my idea, I borrowed it from stalwart on the GTA who originally used a 10-shot .22 cal MRod magazine.... The basic idea is to machine a notch big enough for the PRod magazine in the receiver.... It looks like this....



You can see the back of the barrel which has been machined to 7/16" OD and protrudes 1/16" into the notch, providing a stub for the magazine to clip onto.... I used a 5/8" end mill and the notch is 1/8" deeper than the bottom of the barrel stub.... I removed a small amount of the front of the existing breech opening, and also faced a bit off the face of the bolt to get enough room for the magazine.... Here are the modified barrel and bolt....



I cut the stock bolt nose off 0.40" from the (new) bolt face, drilled and tapped it 8-32, took a piece of 1/4" drill rod 3/4" long and did the same with it and used a 1/2" long piece of an 8-32 screw as a stud to attach the new front of the bolt to the old stub using loctite.... I then turned the shaft of the bolt down to 7/32", and the probe section down to 3/32" and adjusted the lengths so that the shoulder is flush with the back of the barrel port and the probe pushes the pellet just past the port....

The mods to the barrel were tricky.... I used the old front O-ring groove for the rear O-ring and cut the barrel off about 1/8" behind that, losing about an inch of length.... The 1/2" OD portion of the barrel is a lousy fit in the receiver, so when I moved the shoulder over, I made it a better fit.... The locatons of the O-rings, barrel port (on the bottom so not visible in the photo) and the set-screw hole are all critical, as is the 7/16" shoulder.... I didn't add a groove for the third (forward) O-ring I don't see any reason for it.... Also what you can't see, there is an internal O-ring groove inside the barrel in the space between the external O-ring and the back.... That O-ring is a #009 and fits nicely on the 7/32" bolt nose to seal it.... I had to rechamber the barrel of course.... Here is the breech with the magazine in place....



It took a ton of measuring, thinking, drawing sketches, and careful fitting to accomplish this job, and my thanks to stalwart for all his help.... If you want to get your FD-PCP or XS-60C converted as a repeater, please contact him on the GTA Forum....

Bob

[rsterne]

Well I got the rifle back together today, and it works beautifully.... I get 20 shots from 1500 down to 1000 psi within 30 fps (4%), 692-720-692, which averages 705 fps (20 FPE) so that works out to 1.66 FPE/CI, which is stellar efficiency at that power level.... The bstaley O-ring buffer really works well to detune this gun for moderate power and lots of shots.... It stuck all 20 shots in the same 3/8" OD hole (at 20') while running the string through the Chrony, so the accuracy will be there I'm sure....



With a Leapers 3-9 x 32AO scope in medium rings the tube easily clears the PRod magazine, although if the turret sticks down very far below the tube on your scope, it may not fit unless, like on mine, it is either in front of or behind the magazine.... The gun as shown above weighs 6 lb. 13 oz., so it's under 6 lbs. without scope, and with the 1" shorter barrel the gun is under 39" long.... I would say that if my son can shoot, the Grouse are in for a really bad time this fall....

Bob