Author Topic: My .257 Condor Build  (Read 1770 times)

rsterne

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Re: My .257 Condor Build
« Reply #15 on: January 31, 2020, 10:49:18 AM »
While I was poking around the internet looking for information on removing the Condor valve, I ran across a YouTube video, and took this screen shot from it....



Here is the Video, in interest of full disclosure....
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This is, quite obviously, a regulated valve to fit INSIDE the Condor tank.... The regulator is at the bottom of the tube, and the tube between the regulator and the valve is the plenum....  :o

I have never seen or heard of anything like this before, but it seems a quite brilliant solution for that particular PCP, and in fact could find use in other bottle guns where there is insufficient room for a decent sized plenum.... It does give up some of the reservoir volume, of course.... but the ability to have a decent sized plenum might outweigh that in many instances....

I have a 250 bar 500 cc bottle here that is 3/4" longer than a Condor tank.... That is less length than you would add with an external regulator, which would have NO plenum.... The neck is just over 5/8" ID, and it is 12" long from the inside bottom to the top of the neck.... With care, deducting an inch each for the regulator and valve, that would leave you a maximum of 10" of length for the plenum.... If the wall thickness was 0.065" (ID of 0.495"), the plenum volume would be 32 cc.... That would probably work great for a .22 cal, and could work with a .25 cal by increasing the setpoint about 5-10%, depending on FPE level....

Calculating the external crush pressure of a tube is much more complex than the internal burst pressure, but many I checked seem to be about 40% of the burst pressure.... If we made the assumption that the minimum regulator setpoint pressure was 1600 psi, inside a 3600 psi tank, the greatest pressure differential would be 2000 psi.... Therefore a tube with a decent safety margin to burst with 5000 psi of internal pressure would probably be OK.... Since it is contained inside the bottle, the worst that would happen is that it would flatten, and be impossible to remove from the bottle....

You can get 5/8" OD 2024-T3 tubing in either 0.058" or 0.065" wall, and you can get 4130 CrMoly tubing in those, plus 0.049" wall.... The thinner the wall, the greater the plenum volume, but even going down to 0.049", the volume would only increase to 36 cc.... With the thicker wall, you could use threads to attach the plenum tube to the ends (regulator and valve), as those would provide additional crush support, so the simplest might be to use the 0.065" wall 2024 aluminum.... That should give about a 2:1 safety margin with a 2000 psi differential, so should resist collapse even if the regulator vented.... The same applies to the CrMoly tube at 0.049" wall....

I don't plan on building such a device.... but I thought it was worth posting about it, since I have never seen this idea before....

Bob
  • Coalmont, BC

rsterne

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Re: My .257 Condor Build
« Reply #16 on: January 31, 2020, 11:34:42 AM »
I had one more thing I wanted to try this morning.... I removed the O-ring from behind the Top Hat.... I was wondering if that 1 mm thick, 70D rubber ring was absorbing enough hammer energy to reduce the velocity.... I filled the gun to 3000 psi (for each shot), loaded an 82.5 gr. slug, set the PW to 8 and took a shot across the Chrony….

768 fps instead of 872 with the O-ring.... I repeated at PW = 7 (793), PW = 6 (maximum recorded at 800 fps), PW = 5 (785) and PW = 4 (733 fps)…. I then put the O-ring back on, and checked at PW = 4 and PW = 6, and those shots were 868 & 869 fps....  :o

OK, so that is quite a revelation.... The O-ring appears to be slowing the hammer gently, instead of letting it drive the top hat hard enough to bounce off the valve.... It appears that with the larger, angled ports the breech volume is filling much more rapidly, causing a faster pressure rise.... This drives the top hat back harder/faster, blowing the valve open much more quickly, which is why the valve can't be tuned for a bell-curve now.... If the hammer strike is too light, and barely cracks the valve, it slams shut and you get really low velocity.... Once the valve opens past a certain point, you get that fast pressure rise behind the slug, and the valve gets blown open and you get full power.... almost regardless of the power wheel setting after that....  8)

It appears that the O-ring, by slowing the reversal of the valve stem, increases the dwell and reduces the bouncing closed of the stem, which is limiting the velocity to 800 fps in this case, instead of 870.... This is a rather strange case of an O-ring buffer actually increasing the peak power of a PCP (by nearly 20%)....  :o

Bob

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Alan

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Re: My .257 Condor Build
« Reply #17 on: January 31, 2020, 12:23:39 PM »
Makes me wonder if the o-ring "size" is specific? As in thicker or thinner?
  • Roswell, New Mexico
Alan

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rsterne

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Re: My .257 Condor Build
« Reply #18 on: January 31, 2020, 02:36:38 PM »
It absolutely would be.... I tried a 0.070" thick one before I tried this one (0.039"), and the gun at that time lost a LOT of power.... See previous page, Reply #10....

Bob
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rsterne

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Re: My .257 Condor Build
« Reply #19 on: March 06, 2020, 12:56:23 PM »
I have spent the last month nursing my dog Molly back to health after her knee surgery.... I am happy to report she is recovering well.... During that time I received a .25 cal Condor valve from Doug Noble (dyotat100) and installed it in a 250 bar (3625 psi) 500 cc bottle that I had lying around.... I did not take it apart, but I did notice that the valve spring is just enough to hold the poppet closed for filling, compared to a very stiff spring in a stock Condor valve.... The strong spring is not required because Doug's valve has a larger stem, but the same size top hat OD (necessary to fit the .25 cal breech)…. so it doesn't have any tendency to "blow open" like a stock valve does.... This means that a heavier hammer and stronger hammer spring are required to allow even the 3000 psi fill of a stock Condor, let alone more pressure for increased performance....

I wanted to find out what Doug's valve could do without upgrading the hammer and spring, and I finally got some time today to do some testing.... After a few shots to find the appropriate fill pressures, I shot two strings, one from a 2400 psi fill with some 59.6 gr. slugs, and the other from 2700 psi with slugs that weighed 82.5 gr.... Here are the results....



The FPE levels were significantly greater than stock, and slightly higher than my modified Condor valve with the angled ports in the stem.... but occurred at MUCH lower pressures, showing just how much better Doug's valve breathes.... It does, however, require a lot higher power wheel setting to reach those power levels, even at the reduced pressure.... in fact to get a string starting at 2700 psi required the PW to be maxed out.... There is no doubt that once I fit a heavier hammer and the stronger spring that Doug sent there is much greater FPE lurking inside....

The valve delivers a very nice bell-curve, with 9 shots within a 4% ES for both strings.... The average was 115 FPE with the light slugs and 135 FPE with the heavy ones, but the peak power was delivered at only 2200 psi with the 59.6 gr. and a peak of 140 FPE at just 2400 psi with the 82.5 gr.... My modified Condor valve peaked at 138 FPE at 3000 psi with the 82.5 gr. (and no bell-curve)...  :o

After a few years watching Doug's expertise with the Air Force guns, I didn't see any sense in trying to reinvent the wheel.... I am delighted with the performance of his valve, and have no doubt that with just a hammer and spring change you could tether a .257 Condor at 3000 psi or less and shoot 70-85 gr. slugs as fast as necessary.... Using the extra power available with the change to a 3600 psi bottle will just be the icing on the cake, allowing even heavier slugs to be used, up to the limit of what will work in this 14" twist barrel....

Bob
« Last Edit: March 06, 2020, 01:03:47 PM by rsterne »
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Alan

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Re: My .257 Condor Build
« Reply #20 on: March 06, 2020, 01:37:01 PM »
Summed up?  Innovation!
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: My .257 Condor Build
« Reply #21 on: March 07, 2020, 03:55:29 PM »
I installed Doug's hammer spring today, with the stock hammer.... I know Doug recommends a heavier hammer, but I wanted to see what would happen, and what fill pressure was possible with just the spring change.... The spring is about 10 lbs/in instead of about 4 lbs/in for the stock spring, but it is more than 1/4" shorter....

I started with the power wheel at the minimum setting (1), and filled to 2700 psi and tried the 82.5 gr. bullets I used for yesterday's test.... The velocity jumped to 891 fps, with the second shot slower.... Filled to 2820 psi (what my SCBA tank had in it) I got a 7 shot string, starting at 911, a second shot of 914, and then a decline down to 868 fps at 2400 psi, giving 7 shots averaging 147 FPE.... This compared to the stock spring at PW = 14 (maximum) yesterday, which gave me 9 shots from 2660 psi down to 2120 averaging 135 FPE.... So, Doug's spring at the lowest power wheel setting would allow a higher fill pressure than the stock spring at the highest PW setting.... It was, of course, harder to cock.... I tried various PW settings with the 82.5 gr. bullet at 2820 psi, and the velocity peaked at 931 fps (159 FPE) at PW=4, and then declined after that.... I assume the hammer was bouncing off the Delrin spacer under the top hat on Doug's valve when I cranked the PW over 4 at 2800 psi....

I then got out some 92.6 gr. Lyman 257464 RN bullets, to see what would happen with a heavier weight and more pressure (my other SCBA tank was full)…. The gun was even harder to cock at PW=6 (although certainly OK), so I started there at 3100 psi, and got a first shot of 922 fps (174 FPE), and then 910 for the second shot.... This means that even with the stock hammer, Doug's spring will allow a higher fill than that.... I tried PW=4 at 3000 psi (910 fps, followed by 898), and then dialed the PW back to 2, refilled to 3000 psi, and shot an 8 shot string which started at 858 fps, peaked at 880, and then fell back to 845 fps (a 4% ES), leaving 2420 psi in the 500 cc bottle.... That 8 shots averaged 154 FPE from a 3000 psi fill, with an efficiency of 1.01 FPE/CI....

So, Doug's spring, installed with the stock hammer, can easily allow a 3000 psi fill at near minimum spring preload.... In fact, with a lighter bullet, like the 257420, even with the PW set to minimum you may not be able fill to 3000 if you want a bell-curve, although I didn't try that.... If you want to shoot 70-75 gr. bullets, you may not need to change the hammer, and just use Doug's .25 cal valve and his hammer spring.... It may even be possible to shoot 80-90 gr. bullets with a 3600 psi fill with the stock hammer, but you will have to crank up the power wheel, and the gun will be getting hard to cock.... In that case, a heavier hammer will allow you to reduce the PW setting, which is the route Doug recommends.... Again, I never tried over 3100 psi today....

I'm very pleased with Doug's valve and hammer spring.... I have already seen 170 FPE at 3000 psi, even without a hammer change....

Bob
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rsterne

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Re: My .257 Condor Build
« Reply #22 on: March 08, 2020, 01:54:08 PM »
Today I increased the pressure to 3600 psi to see how Doug's Valve and Spring worked with the stock hammer.... I did the testing with the 92.6 gr. Lyman 257464 RN bullet, which is about as heavy as you can go with the 14" twist barrel.... First I tried numerous power wheel settings, with the following results....



As you can see, the results show a similar pattern to a stock Condor.... Once you get to maximum power, increasing the PW setting causes the top hat to bounce off the Delrin stop on the valve stem, and that bounce reduces the dwell and therefore the FPE.... The velocity peaked at PW = 10 at 969 fps (193 FPE)…. My "lofty goal" calculation for 3600 psi in a .257 with a 26" barrel is 202 FPE, so that gets to within 4.5%, which is pretty good.... I backed off the PW to 8, and started a string from 3600 psi.... It was 950, 958, 946, 938 and 920 before it dropped more than 4% from the peak, so I reduced the PW setting to 7 and shot two strings, both from a 3600 psi fill.... They are shown below in red.... all strings with a 92.6 gr. bullet....



You will note that the velocity of the first shot varied, and they were either side of the 925 fps I got when I tested the velocity a PW = 7 above.... This means that I need just a whisker more hammer spring preload ( PW = 7.3? ) for a 3600 psi fill, to avoid those large swings on the first shot.... I ran out of bullets, but it is pretty obvious from the 2 strings that with a little fine tuning I can get 7 solid shots within an ES of less than 3%.... The average over the 15 shots of those two strings was 938 fpe (181 FPE) at 1.15 FPE/CI.... I am very pleased with that efficiency at this power level.... especially considering the Condor does not have a stellar reputation for efficiency....

Although Doug told me that I should make a heavier hammer, I seriously doubt that would actually give an increase in power, because the hammer is already bouncing off the valve, and more than likely it would drop the efficiency.... It certainly would reduce the cocking effort by allowing me to use a lower PW setting, but on the other hand it would likely mean that I would not be able to reduce the PW far enough to shoot a lighter bullet, such as the 257420, without having the velocity pushing over 1000 fps (or having a declining shot string)…. If you look at the black line on the chart above, you can see what happens with an 82.5 gr. bullet with a 3000 psi fill at PW = 2.... That setting would push the 257420 into the mid 900s, so Doug's spring, with the stock hammer, gives me a nice adjustment range between the minimum PW setting and PW = 8 to handle all weights of bullets and pressures up to 3600 psi.... I think I'll stay right where I am for now, as I don't think a heavy hammer would buy me any more FPE with this 26" barrel....

Bob
« Last Edit: March 08, 2020, 01:59:28 PM by rsterne »
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Alan

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Re: My .257 Condor Build
« Reply #23 on: March 08, 2020, 02:51:55 PM »
This raises a question. The most important adjustment on several FX airguns, is the hammer stop. I wonder if you have ever tried to duplicate the hammer stop adjustment on any of your home-brew airguns??

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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: My .257 Condor Build
« Reply #24 on: March 08, 2020, 03:56:15 PM »
It can only be used successfully on a regulated PCP.... some unregulated Korean guns use it, and it is one of the primary reasons for the "Korean Cliff" tune, where every shot is lower velocity as the pressure drops.... Having said that, the bstaley O-ring buffer mod, which is intended for unregulated PCPs, "sort of" works that way, but it actually works as a progressive valve spring instead of a rigid stop....

I have never used it on a regulated gun either, although I can see it's usefulness.... It is another way to get a precise mount of lift, while allowing somewhat more hammer strike than necessary to produce that lift.... This tends to "square off" the lift to dwell curve, which is a good thing.... as in theory at least it should improve the efficiency.... However, it means that to change the tune to any significant degree, you need to adjust 2 or 3 (or 4) things, instead of just one....

If you have a hammer stop, when you increase the hammer spring preload past the point where the hammer is hitting the stop, the hammer bounces off the stop, actually decreasing the dwell.... You can see that in the upper graph in my last post on the Condor.... Without the stop, there may actually be a bit more velocity available, but you can't find it without moving the stop.... Without a stop in place, all you need to do is increase the preload until the velocity plateaus, and you then know FOR SURE what the maximum is.... Since I always tune my PCPs about 3-5% below that velocity, then the hammer would never hit the stop, if it were set with enough clearance to allow maximum FPE....

If I saw PCPs with a hammer stop greatly exceeding the efficiency I can get without one, then I might try it.... The one benefit there may be, is that you should be able to tune for a "downslope" tune without getting a large shot-to-shot variation, and that "hump" in velocity once the pressure drops below the setpoint.... You give the gun a bit more preload than necessary, and then adjust the stop to drop the velocity slightly, making the gun operate more consistently if tuned on the downslope.... I never tune my guns on the downslope (instead I reduce the setpoint pressure)…. so I don't need that feature....

Bob
« Last Edit: March 08, 2020, 04:00:05 PM by rsterne »
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rsterne

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Re: My .257 Condor Build
« Reply #25 on: March 11, 2020, 12:00:18 PM »
Today I double-checked the power wheel settting to confirm that maximum FPE occurred at PW = 10 wth a 3600 psi fill.... I tested it with bullet weights of 62 gr. and 105 gr., and that was the case with both weights.... I used that setting and tethered the gun at 3600 psi to find the velocity of every possible pellet and bullet I had in .257 cal.... The pellets I used were .25 cal, but the skirts were 0.257" or so, and I was confident that at 3600 psi they would blow out to seal just fine, and that proved correct.... Here is a chart showing the maximum velocity and FPE I am getting at 3600 psi with my .257 Condor with Doug's valve and spring....



Those below 42 gr. were pellets.... Note that this gun will push the 25.4 gr. JSB Kings at 1420 fps.... All the pellets were supersonic, I just did this out of curiousity…. Also note that the heaviest three bullets were too long to stabilize, and were tumbling by the time they hit the backstop, which was only 6 yards behind the Chrony….  :o …. This leaves a usable range of bullet weights from 58-93 gr., which produce between 160-190 FPE, with the heavier bullets having more energy, as expected.... The NOE 73.9 gr. boattail version of the 257420 shot at 1041 fps (and the HP at 1051), which may or may not be usable.... but if I have to slow it down it is a simple matter to dial back the power wheel, and/or drop the pressure a bit.... The shortened HP version, at 58.3 gr., was just supersonic (1124 fps) at PW = 10 and 3600 psi.... but if I want to use those I can easily drop the pressure down to 3000 psi and back off the power wheel accordingly....  The gun is capable of hitting the high 900s with an 85 gr. bullet, and could be backed off a bit to save air....

One other thing I determined is that PW = 8 looks like the perfect setting for tethering 80-90 gr. bullets at 3500-3600 psi, the gun shoots a 4-shot string starting from 3600 within a 2% ES, getting over 1.0 FPE/CI at that setting.... At 3500 psi and PW = 8 it is right at the top of the bell-curve.... All in all, it looks like this gun will make a very capable varmint and target rifle.... providing the accuracy matches the power....

Bob
« Last Edit: March 11, 2020, 12:05:47 PM by rsterne »
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rsterne

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Re: My .257 Condor Build
« Reply #26 on: March 12, 2020, 04:31:26 PM »
I have always been curious about how the diameter you size a bullet to effects the velocity.... so today I used the Condor and 3 different bullet weights, and tried every size from 0.251" to 0.259", shot 3 shots with each bullet and determined the average velocity.... I then plotted that vs. the diameter....



The highest velocity was at 0.257", which corresponds to the groove diameter of the barrel.... There was essentially no difference between 0.256" and 0.258", both being within 1-2 fps.... With the heaviest bullet, even sizing to 0.255" or 0.259" really didn't make more than 2-3 fps difference in the velocity, but with the lightest bullet both were down about 5-6 fps (still pretty much lost in the ES)…. Where a bit of blowby became obvious in reducing the velocity was at 0.254" and smaller.... The velocity loss was more pronounced with the lighter bullet, which likely has something to do with the relationship between mass and bore friction compared to the heavier one....

I have seen similar results to this before, but this is the first time I actually set out to find out how much blowby affected velocity.... and the answer is not much.... Basically all you need to worry about when trying different sizing is the accuracy.... Anywhere from 0.002" smaller to 0.002" larger than the bore makes virtually no difference to the velocity.... Even 0.003" under only looses 1-2%....

Bob
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