Author Topic: My .257 Condor Build  (Read 248 times)

rsterne

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My .257 Condor Build
« on: December 04, 2019, 03:12:27 PM »
I got a screaming deal on a good used .22 cal Condor a month ago, c/w a Hawke 6-24 x 50 SF Scope and BiPod…. I have never had one before, so it will be a bit of a learning experience.... As it turns out, I also bought a .257 cal 14" twist TJ's barrel that was 1/2" diameter and 26" long, which I didn't really have a home for, and it hadn't even arrived when I bought the gun.... It was deserving of a good home, so I decided to convert the Condor to .257 cal, it just seems a better fit than a .22 cal in such a powerful platform....

Lloyd Sikes offered me a piece of 14mm ID x 23mm OD carbon fibre tubing for a barrel sleeve, so all I had to do was shim the barrel up to 14mm.... I had a piece of 1/2" ID x 9/16" OD carbon tubing here left over from my Model Yachting days, so I glued that to the barrel and then sanded it down to fit inside the large 14mm ID tube.... I also got a short piece of .45 cal barrel that was 5/8" OD from Lloyd to use as a shim for the part behind the collars that the hammer slides on, and drilled it out to 1/2" ID to slide over the barrel, and Loctite'd it in place.... I made two new collars from 6061-T6 aluminum, turned to fit inside the Condor tube (1.010" OD)…. The front one was drilled out 7/8" ID and the rear one was 1" long, with the rear half drilled to 5/8" like the Condor collar.... but a recess in the front drilled 7/8" ID by 1/2" deep.... I then turned the rear part of the 23mm OD carbon tubing to fit inside the collars, and ended up with these parts....



The back inch of the 23mm CF tube is drilled to 5/8" to slide over the CrMoly tube made from the .45 cal barrel.... In this way, the end of that 5/8" steel tube stops inside the CF tube, and the OD of the tube fits inside the rear collar.... so nothing ends at the same point to spread out any possible bending loads in that area.... The thin front collar is just glued to the CF tube, but it will be screwed to it after the final barrel assembly and all the glue dries.... All gluing is done with Loctite 638, and after it dries overnight, it will get a 3 hour post-cure in my wife's over at 175*F.... I'll have a photo of the assembled .257 cal barrel tomorrow....

Bob
« Last Edit: December 04, 2019, 03:16:58 PM by rsterne »


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steveoh

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Re: My .257 Condor Build
« Reply #1 on: December 04, 2019, 05:42:40 PM »
Now this is exciting! Love hearing about .257’s and wrapping the barrels in carbon fiber.

I saw that Travis is finally working on .257 Raptor builds. Will be interesting to see how they go.
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sixshootertexan

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Re: My .257 Condor Build
« Reply #2 on: December 04, 2019, 09:01:24 PM »
Awesome Bob. I been wanting to build a AF .257 but I have other things going right now.
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rsterne

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Re: My .257 Condor Build
« Reply #3 on: December 05, 2019, 06:22:29 PM »
Here is the completed .257 barrel, along with the stock .22 cal Condor barrel....



The collars are glued on with Loctite 638, along with the CF sleeve and 5/8" CrMoly sleeve in the hammer/spring portion.... The muzzle is threaded 1/2"-20NF to accept a Hatsan Air Stripper or a shot-filled damper.... There is an O-ring on the barrel that pushes into the gap at the front of the Condor main tube.... basically just to keep any dirt out.... The barrel, sleeved with a 23mm OD carbon fibre tube, is about 4 times as stiff as the stock 5/8" barrel.... and yet the assembly is 1 oz. lighter, even though the new barrel is 2" longer....  8)

As in the stock barrel, the four 10-32 set screws that locate the barrel inside the Condor tube tighten against the barrel.... The assembly should be VERY rigid....   ;) …. Here is the barrel installed in the frame....



Bob
« Last Edit: December 05, 2019, 06:56:53 PM by rsterne »
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sixshootertexan

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Re: My .257 Condor Build
« Reply #4 on: December 06, 2019, 10:02:20 AM »
I'd love to see what this bullet would do.
257-112-FN 2 cavity BT
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steveoh

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Re: My .257 Condor Build
« Reply #5 on: December 06, 2019, 10:14:40 AM »
I'd love to see what this bullet would do.
257-112-FN 2 cavity BT

From my experience it looks a bit heavy.
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rsterne

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Re: My .257 Condor Build
« Reply #6 on: December 06, 2019, 03:32:01 PM »
That is certainly way too heavy for the stock valve.... It would take about 4000 psi or maybe more in the 26" barrel to hit the 900s, with a wide open valve, even in a Condor.... My Monocoque .257 can just push them at 950, running wide open on 4000 psi, with a 33" barrel.... Detuned for reasonable efficiency they shoot at 900....

Here is the assembled gun with the .257 barrel, but everything else stock....



Now bear in mind I have never shot a Condor before, so I have no idea what to expect or how to tune them.... I made a guess that with the stock valve the 63.4 gr. BBT FNs I have would be about the right weight, and it was a good guess.... Here is a chart of the velocity at all power wheel settings....



What I didn't expect, and don't understand, is why the velocity decreases, and the report is reduced, at PW 9 and above....  ??? …. Is the hammer driving the breech and top hat so hard it is bouncing off the valve and reducing the dwell?.... Most PCPs simply hit the plateau velocity and then sit there.... In any case, the gun maxed out at 915 fps (118 FPE) with the stock valve, at 3000 psi.... not too bad, I think....  I then ran some strings at various PW settings, with the following results....



At PW 9 the velocities were all over the place, so I didn't include them.... At PW 8 I got only 3 declining shots within a 4% ES, and the efficiency was about 0.86 FPE/CI.... At PW 7 that increased to 4 shots within 4% at 0.93 FPE/CI.... When I reduced the preload to PW 6, the number of shots within 4% increased to 6, at 0.95 FPE/CI, but the velocity was still declining every shot....

A bell-curve developed at PW 5, giving me 9 shots within a 4% ES at an average of 881 fps (109 FPE) and an efficiency of 1.08 FPE/CI.... At PW 4, the number of shots within 4% increased to 12 (the first shot at 3000 psi was too slow), with the average velocity down to 869 fps (106 FPE) at 1.10 FPE/CI.... It looks like a setting between PW 4 and PW 5 would give me 10 shots within a 4% ES, starting at 3000 psi and ending at about 2500 psi....

This gives me a good baseline for my .257 Condor.... As a comparison, my .257 Hayabusa, with its 460 cc reservoir filled to 3000 psi and using a 66 gr. slug, gets 11 shots within 4% averaging 938 fps (129 FPE) ending at 2340 psi, which is 1.11 FPE/CI.... However, it has a 28" barrel and the smallest port is the equivalent of 0.241".... The Hayabusa peaks at 160 FPE with an 88 gr. slug.... To get more power, the Condor will need larger ports (or increased pressure)….

Bob
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steveoh

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Re: My .257 Condor Build
« Reply #7 on: December 07, 2019, 09:29:27 AM »
My Texan with the give or take 72 grain 257420 or the Noe BT of similar weight likes the power wheel set pretty low. I can get a bell curve and about 10 shots. I do wish AirForce had put a numerical scale on the power wheel for my own reference and not for pissing contests.
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rsterne

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Re: My .257 Condor Build
« Reply #8 on: December 07, 2019, 03:28:53 PM »
I have been trying to wrap my brain around the forces on the Condor valve, in particular when the valve is open.... When the valve is closed, it has HPA inside the tank, and atmospheric pressure inside the stem, breech and barrel.... so the force holding the valve closed is the seat area of the poppet times the pressure, just like any other PCP.... However, when the valve is open, but before the slug leaves the muzzle, it is completely different than a conventional PCP....

In a conventional PCP, when the valve is open, there are three closing forces on the valve.... In order of importance:

1. The pressure in the valve throat times the area of the stem that penetrates the valve body (with atmospheric pressure outside)….

2. The drag (or pressure differential) across the head of the poppet, caused by the airflow past it.... This starts out low, and increases as the slug accelerates down the bore and the airflow through the valve increases....

3. The valve spring....

In the Condor (and Texan) valve, however, the end of the stem is not exposed to atmospheric pressure as long as the slug/pellet is in the barrel.... Inside the sliding breech, the pressure is very nearly the same as inside the tank.... This means that there is a force on the top hat (which seals the back of the breech) acting to hold the valve OPEN....  :o …. Here is a sketch I made to show what I mean....



The Breech and Valve Body are in blue, and the Poppet Head, Valve Stem and Top Hat are in black.... The valve is shown open, and I am assuming that the pressure inside the tank, valve stem, and breech is the same everywhere.... This means that the head of the poppet is surrounded by HPA, and there is no force on it in any direction (neglecting airflow for the moment)…. The forces, represented by the teal coloured lines, cancel out.... The valve stem is sealed in the valve body with an O-ring, through which it slides.... If the OD of the stem is a constant, it doesn't matter how big the hole through it is, because the exposed area on both ends (represented by the green lines) also cancels out... This leaves the Top Hat.... The front end of it, which seals in the breech, is larger than the valve stem, where it seals inside the valve body.... This means that a force is generated, represented by the red lines, trying to push the valve OPEN....  :o

If the OD of the stem where it slides through the O-ring in the valve body is "d" and the OD of the top hat is "D", we can calculate that force as follows:

[ (D x D) - (d x d) ] x PI/4 x (Pressure inside the Breech)

For my stock Condor valve, at 3000 psi, I get.... [ (0.309 x 0.309) - (0.246 x 0.246) ] x PI/4 = 0.0274 x 3000 = 82 lbs....  :o

That seems like a very high number, when you consider that the valve spring is only a few lbs. force.... so the fact that the valve closes at all must be due to the drag of the air moving past the poppet and through the valve stem, and the pressure differential that causes between the tank and inside the breech.... That not only reduces the opening force on the top hat area, but adds a closing force as well.... Obviously, this must work, or the valve would always stay open until the slug exits the muzzle and the pressure in the breech drops drastically....

This force, which for a given valve stem OD is dependent on the ID of the breech and the pressure inside it, explains some things about the infamous Condor "tank dump".... For the tank to dump, it seems reasonable to me that this opening force on the top hat must still be large enough to hold the valve open even after the slug has left the muzzle.... That means that the pressure inside the breech cannot escape fast enough through the open bore.... The larger the OD of the top hat (which must be the same as the OD of the barrel stub), the greater the opening force.... Since that OD is the same as the OD of the barrel stub that slides inside the breech, a thicker wall in that area will trap more pressure and increase the likelihood of a dump.... This is because the air cannot escape out of the muzzle fast enough to drop the pressure in the breech, and that increases the force on the top hat, and that overcomes the closing forces on the valve....

Additionally, the opening force on the top hat assists the hammer in getting enough dwell to produce the desired power.... For a given top hat (and barrel) OD, the larger the caliber, the more work the hammer must do to create the shot, because the barrel volume is larger, and as the slug moves down the bore, the greater the pressure drop in the breech, and the less assist to the hammer from the opening force on the top hat.... The opposite occurs with a heavy slug.... It moves slower down the barrel, increasing the pressure inside the breech, which increases the force on the top hat, and increasing the chance of a tank dump....

Assuming my thoughts are correct (and this is only my first kick at the can)…. I think a lot of the variables in tuning a Condor have to do with the relationship between the caliber and the OD of the barrel stub.... and how freely the air can flow through the valve stem.... The bigger and less restrictive the ports in the stem, the less the pressure differential should be (particularly near the end of the shot) and the higher the breech pressure.... This reduces the closing force on the poppet, and should increase the chance of a tank dump....

I look forward to our Condor experts reading through this post and commenting.... I may have it completely wrong.... and if so, I want to know where I made my mistakes....  8)

Bob
« Last Edit: December 07, 2019, 03:58:16 PM by rsterne »
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rsterne

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Re: My .257 Condor Build
« Reply #9 on: December 11, 2019, 01:45:31 PM »
Today I tried installing an O-ring between the Top Hat and the front of the valve.... I had a few thicknesses to choose from, and started with a standard # 010, which is 1/4" ID with a 0.070" Cross Section.... The gun had about 2700 psi in it, so I set the Power Wheel at 5, which if the O-ring was not being hit by the TH should have given me a velocity of about 880 fps, based on the tests I ran with no O-ring.... The velocity was only 760 fps, so obviously that O-ring was much too thick for my .257 Condor.... I removed that O-ring and installed the thinnest one I had instead.... This was a 6 mm ID with only a 1 mm CS.... At the same pressure, the velocity was 872 fps, very close to what I got at the same pressure without any O-ring, so I refilled the gun to 3000 psi and shot a string until the velocity fell more than 4% below the peak.... I then repeated that procedure, but with the PW set at 6 instead of 5.... The results, along with those from the initial tests with no O-ring, are below.... The black lines are at PW = 6, while the red lines are at PW = 5.... The blue line is without O-ring and PW = 4.... The solid lines are without the O-ring and the dashed lines are with the 1 mm O-ring installed.... All lines only show shots within a 4% ES....



There are three obvious differences with the O-ring installed.... Firstly, the peak velocity is about 10 fps less than the same PW setting without the O-ring.... Secondly, the shot count is significantly increased.... Thirdly, the shot strings are flatter (not as peaky), and in fact whereas at PW 6 without the O-ring I had a declining shot string, with the 1 mm O-ring installed I had a bell-curve, although barely.... What you can't see from the chart is that the efficiency also improved.... Here are the average results for the 5 shot strings above....

PW = 6.... 6 shots averaging 879 fps (108.8 FPE) at 0.95 FPE/CI
PW = 6 with O-ring.... 10 shots averaging 880 fps (109.0 FPE) at 1.02 FPE/CI
PW = 5.... 9 shots averaging 881 fps (109.2 FPE) at 1.08 FPE/CI
PW = 5 with O-ring.... 12 shots averaging 872 fps (107.2 FPE) at 1.10 FPE/CI
PW = 4.... 12 shots averaging 869 fps (106.2 FPE) at 1.10 FPE/CI

Just out of curiousity, I also shot 5 shots with an 82.5 gr. slug, with the O-ring in place, a 3000 psi fill and the PW at 6.... I got a declining shot string starting at 3000 psi, averaging 822 fps (124 FPE)…. I also wanted to see what effect the O-ring had on the Power Wheel settings, so I checked the velocity at a 3000 psi fill, with the following results....



As you can see, the O-ring started having an effect on the velocity at PW = 6, initially reducing it slightly as the PW setting was increased.... However, at PW = 9 and above, where the hammer was previously bouncing back and the velocity was reduced.... with the O-ring in place the hammer was slowed more gradually, and the velocity peaked at PW = 11 at 930 fps, instead of at PW = 8 at 915 fps.... The O-ring cushioned the contact between the TH and the front of the valve, and produced a much more normal " velocity plateau"....

In this case, the commonly available American sized O-ring, with a 0.070" CS, was much too thick for my .257 Condor.... I might work fine in a .22 cal where you wanted to detune it and extend the shot string, but all it did was lose me a lot of power.... However, the 1 mm CS O-ring was just about perfect for this gun.... It requires the PW setting to be increased by 1 to get the same velocity, but extends the shot string and increases the efficiency at the same time.... What's not to like.... !?!?!

Bob
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rsterne

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Re: My .257 Condor Build
« Reply #10 on: December 12, 2019, 10:54:25 AM »
For those of you not familiar with adding an O-ring to the valve stem on a Condor, behind the top hat, here is a photo of the tank with it installed.... You don't need to remove the top hat, just stretch the O-ring over it to install it....



Below the valve is a 6mm ID x 1mm CS O-ring (left) beside a standard 1/4" ID x 0.070" CS O-ring to show you how much thinner the 1mm is.... The 0.070" thick O-ring severely decreased the power on my .257 Condor because it limited the valve lift (and dwell) too much....

Bob
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steveoh

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Re: My .257 Condor Build
« Reply #11 on: December 12, 2019, 12:15:31 PM »
My Texan has an O-Ring there. Hmmm. I wonder if that’s stock?
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