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Air Gun Home Forum Index » Antique, Collector and Novelty Airguns » Crosman 140 Results
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Crosman 140 Results 
PostPosted: Mon Dec 13, 2010 6:19 pm Reply with quote
rsterne
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I've been working on the first of the three Crosman 140s I purchased.... I started on the one that basically didn't work.... I tracked that down to a bad O-ring inside the valve.... Replacing that got the gun holding air but the velocity was quite a bit below what I expected.... I decided that the pump cup was probably too hard so I built a new top end for the pump rod from aluminum and fitted an O-ring like on the FTPs for a 2289.... I had done this before on my .22 Uber-Pumper which used a 1400 pump tube and linkage.... but in this case instead of making everything all I did was cut off the pump rod just below the piston, threaded it, and made a new piston which I screwed on with loctite.... The other (fork) end is still adjustable for length....

I put everything back together and it was a bit better, but not a lot.... I pulled it apart and drilled out the transfer port (I'm using one from a 2289, with the barrel and breech drilled to accept it) to 0.161" and the barrel port to the same size.... I initially picked up about 20 fps, but during this session I discovered that if you wait 2-3 seconds at the top of each pump stroke (ie when the pump is open) that I started moving a LOT more air.... What was happening was that the O-ring is coming far enough to reach the small recessed groove in the bottom of the pump tube near the slot.... but it takes a few seconds to fill the pump tube with the air required.... That discovery made a HUGE difference to the velocity numbers (~100 fps).... and also to how hard it was to pump.... I tried pumping up the other two 140s that I have, waiting in a similar fashion.... and it didn't make near the difference.... although they were a bit better when pumped slowly....

I pulled the gun apart once more and drilled the end of the valve out to 0.157" (from 0.125").... The port in the valve sleeve was already 0.157".... I also drilled the ports in the bolt out to 0.157".... This meant that all the ports were 0.157" or larger.... I put the gun back together, and did some testing at different pump numbers and pellet weights.... The results are below:



Note that with 14.3 gr. JSB Express pellets, the gun is shooting 520 fps in four pumps, 606 fps in 6 pumps, 725 fps (16.7 FPE) in 10 pumps, 790 fps in 14 pumps, and 857 fps (23.3 FPE) at 20 pumps.... and still climbing.... The valve design in the 140 doesn't rely on a hammer spring to open it.... so it shows no sign of peaking, even at 20 pumps.... The gun is INCREDIBLY hard to pump at that level.... and the trigger pull is ATROCIOUS.... The sear is holding back the shuttle against the air pressure in the valve.... so the more you pump, the heavier the trigger pull gets.... I can see now why 10 pumps is the practical limit with this gun....



Using 10 pumps, I got the following results with different pellets:

RWS Hobby 11.9 gr. 785 fps - 16.3 FPE
JSB Express 14.3 gr. 725 fps - 16.7 FPE
JSB Exact 15.9 gr. 695 fps - 17.1 FPE
JSB Heavy 18.1 gr. 661 fps - 17.6 FPE
H&N Baracuda 21.0 gr. 622 fps - 18.0 FPE
JSB Monster 25.2 gr. 572 fps - 18.3 FPE
EunJin Domed 28.4 gr. 532 fps - 17.9 FPE

You can see that just like a PCP, the Crosman 140 produces more energy as the pellet weight increases up to a point.... A 25 gr. pellet produces the most energy at 10 pumps in this particular gun.... I'm extremely pleased with the results.... They are actually better than the original version of my .22 Uber-Pumper which used a 2289 valve (and a 24" barrel, the 140 barrel is only 19.6").... I did eventually get better numbers from that gun (750 @ 10 pumps, 900 @ 20 pumps), but only after I increased the volume of the valve by nearly 80% by adding a center section....

I haven't done any accuracy testing yet.... That will wait until I fit the gun with a dovetailed breech and a scope.... I'm thinking that JSB 15.9 gr. Exacts at nearly 700 fps and 17+ FPE is looking like a great combination if they are accurate.... Pretty decent numbers for a 50 year old airgun.... Mr. Green

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Mon Dec 13, 2010 9:33 pm Reply with quote
AirGunEric
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How about some pictures of that pump cup repair? Mr. Green
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PostPosted: Tue Dec 14, 2010 12:17 am Reply with quote
rsterne
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Next time I have the gun apart.... It's exactly like the top half of a 2289 F-T-P....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Thu Dec 16, 2010 6:58 pm Reply with quote
rsterne
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I stripped the gun down again today and lengthened the slot to allow air to enter the tube without having to wait at the top end of each pump stroke.... While I was at it, I took a couple of photos of the tube and the new piston with the O-ring:





The mark on the piston shows where the end of the original slot was.... Note that even with the lengthened slot, the original groove is still further forward.... The photo of the tube shows where the piston stops at full open.... I used a 1/4" mill to lengthen the slot (nearly 1/2") until it just cleared the O-ring.... and then used a Dremel with a 1/4" ball to deburr and round the inside end of the slot so that the O-ring had a nice smooth surface to slide over.... then polished it with 320 grit....

I lost about 10 fps but I don't have to wait 3+ seconds at the top of each stroke for the tube to fill with air.... plus the velocity is more consistent.... With the original setup, if you didn't wait long enough on every stroke you lost velocity (up to ~100 fps if you pumped fast).... That no longer occurs, leading to more consistent velocity, shot to shot.... just 2-3 fps variation is typical over 5 shots and you can pump as fast as you want....

I also polished the sear on the trigger to 2000 grit and lubricated it with a dab of Moly grease.... At 10 pumps the trigger pull is about 4 lbs.... I had previously polished the edge on the hammer that contacts the sear.... I'm really impressed with this half-century old airgun....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Thu Dec 16, 2010 7:00 pm Reply with quote
rsterne
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Tried the last mod I can think of this afternoon.... I bored out the valve.... I shortened the threads to 0.25", and bored the inside of the back half to 0.53" ID for a depth of 0.57" with a 45* taper about 0.1" wide leading down into the smaller back section.... I didn't measure the increase in volume, but it calculates out to about 0.35cc which should be about 20%....

When the gun was reassembled and chrony tested I got just about what I figured.... The velocity at 10 pumps stayed the same.... at lower pump numbers it lost a bit.... and at higher pump numbers it gained a bit.... The biggest difference was that it was noticeably easier to pump, and the trigger pull was lighter.... It dropped about a half pound, to 3.5 lbs at 10 pumps.... where I'm getting 710 fps with 14.3 gr. pellets... Cool

The Crosman 140 is a true "pump and dump" rifle.... The valve is held closed by the sear, and when you pull the trigger, a cup slides back and uncovers both the end of the valve and the transfer port.... Once the air has all escaped, a spring behind the "hammer" pushes the cup and "hammer" forward again and recocks the gun.... Boring out the valve increases the volume.... so at any given number of pumps, the pressure inside the valve is less.... Since the sear, which is a part of the trigger, is holding the valve shut.... the load on the trigger, and hence it's pull weight.... increases with pressure.... As you add more pumps, the trigger pull increases.... Boring out the valve has the opposite effect, it reduces the trigger pull for a given number of pumps.... while still having the same amount of air in the valve.... and hence the same "potential" performance....

As with most pneumatics, at low velocities, the gun is more efficient with a short, sharp, high pressure pulse to accelerate the pellet.... That is why boring out the valve loses performance at the bottom end.... eg. 4 pumps is now 500 fps instead of 520.... At the top end, the pump is more efficient at the lowered pressures, and packs a bit more air into the valve (with less heating and effort), which gains a bit of performance.... In the 140, 10 pumps (the normal number) is in between and the performance isn't changed with the bigger volume.... just the trigger pull....

Would I bore out the valve again on a 140?.... Probably not worth the effort.... certainly in terms of performance gain.... It did improve the trigger and ease of pumping, though.... Mr. Green

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Mon Jan 12, 2015 8:48 pm Reply with quote
DavidSaunders
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That is one nice set of simple mods.

Why is it that all of your Crosman 140 mods are listed in antique, or vintage sections of forums?

The Crosman 140 is barely 62 years old, it has another 48 years before it is an antique, or vintage Smile .
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PostPosted: Mon Jan 12, 2015 10:29 pm Reply with quote
Slavia
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I'm 61, out of production, with parts that don't work like they used to, and repair parts are expensive. Yes, the 140 is vintage.

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PostPosted: Mon Jan 12, 2015 11:06 pm Reply with quote
rsterne
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^X2....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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Crosman 140 Results 
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