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PostPosted: Thu Feb 20, 2014 11:59 pm 
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I got my FD-PCP in the mail today, filled it to 1500 psi and shot a few strings with JSB 15.9 gr. Exacts.... 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 31 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....

Image

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 an excellent 1.28 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 27.5 FPE at an efficiency of 1.28 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

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Feb 21, 2014 12:10 am 
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Ahh here we go again with another project :)


What does the gun look like and how did they PCP it?

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PostPosted: Fri Feb 21, 2014 12:44 am 
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Photo tomorrow.... Mike Melick put a longer tube on it and a male Foster to fill it.... no onboard gauge, 1500 psi recommended pressure from Mike.... Heck of a deal for $100 US shipped within the lower 48.... or $240 with a pump.... It's not very sophisticated, more of an experimenter's special.... but I'm impressed, especially for the price.... There is a guy in the US who is converting them to use the 10-shot MRod magazine, milled right into the breech, which I plan on doing to mine....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Feb 21, 2014 2:08 pm 
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Location: Coalmont BC
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....

Image

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

Image

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

Image

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....

Image

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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Feb 21, 2014 4:57 pm 
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Location: Annapolis Valley, Nova Scotia
I have one of the XS60C, and like it, most likely going to leave it in stock form and run co2, but very interesting read, thank you for sharing.

-Matt


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PostPosted: Fri Feb 21, 2014 5:21 pm 
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Location: Toronto
A PCP for $100, damn! 8)

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PostPosted: Fri Feb 21, 2014 8:09 pm 
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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....

Image

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....

Image

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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Feb 21, 2014 10:17 pm 
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The velocity adjuster comes stock? :shock:

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PostPosted: Fri Feb 21, 2014 10:39 pm 
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Location: Coalmont BC
Yes, it's built into the gun....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Feb 22, 2014 7:53 am 
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Can you see any reason or something in the design to prevent the gun being made into a reverse tanker with a regulator Bob ( like your design)?

With the reg and a milled receiver for a mag would be great!

Nathan


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PostPosted: Sat Feb 22, 2014 12:47 pm 
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No reason at all, the tube ID will fit a QB or JDS tank block (or one of my reverse ones).... HOWEVER, make sure you have a 1.8K burst disc fitted, which will limit you to 1500 psi to stay safe.... With the velocity adjuster, you will even be able to tune it for any pressure from 850-1500 psi for the best balance of velocity/efficiency.... I see this as the perfect candidate for that conversion.... and I think the valve breathes well enough for it to work in .25 cal with a few tweeks (eg. 3/16" barrel port)....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Feb 22, 2014 4:41 pm 
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i'll be keeping a close eye on this thread and how you develop this gun to becoming a repeater


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PostPosted: Sat Feb 22, 2014 5:29 pm 
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NOTE:

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 cannot correct that post, it is too late to edit it or the title of the graph.... Since the pellets are lighter, the maximum FPE reached was 28 FPE (not 31), and the best string was at 24.7 FPE and 1.15 FPE/CI efficiency, not the higher values in the first post.... My apologies for the error....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Feb 22, 2014 6:16 pm 
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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....

Image

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....

Image

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....

Image

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....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Feb 22, 2014 7:50 pm 
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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....

Image

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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
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