CP1-M pistol first impressions

[Bob Pratl]

Bob,
Jason listed them here: http://www.gatewaytoairguns.org/GTA/index.php?topic=124266.msg1214042#msg1214042
Theoringstore.com is backordered on one of these for another day or 2.

Kevin, thanks...I missed it.

[nervoustrigger]

That reminds me I should have mentioned I was unable to use the barrel O-rings I ordered.  They are the correct size but 75 durometer.  I think the originals are 50.  The barrel is a snug fit to the receiver and the harder O-rings would not compress sufficiently.  Fortunately the originals were not damaged so I was able to reuse them.  But even if they had a bite taken out of them, it's very likely the seal would be just fine given how closely the metalwork fits.  Plus they are not under constant pressure, they just need to resist a pulse of pressure for a few milliseconds each time the valve is knocked open.
 
Just saying that in case someone finds themselves staring at a gnarly looking barrel O-ring and no prospects for a replacement, I think it would be reasonable to go ahead and reassemble anyway and see how it goes.

[imadunatic]

That reminds me I should have mentioned I was unable to use the barrel O-rings I ordered.

Does anyone need 20 O-Rings 8mmx1mm 70 Duro... I hear they won't work for my application. 

I think I'm getting too far down the rabbit hole here. I built an internal SSG that works great as far as reducing the amount of cocking force, the gap isn't adjustable (I started at .025" gap, ended at .040" gap by grinding the length of the SHCS down) but the preload is fully adjustable independent of the gap.

Here's a couple pics to show my idea, also note that I cut 1.5 coils off the stock spring trying to reduce the amount of hammer force (then I chickened out that I wouldn't have enough preload to provide the "wall" needed in an SSG so I stopped tuning on that):





The issue is that even with the stock ~3.4 LB/in spring, it's still hitting too hard and blasting CO2 for the first 30 shots. I was able to get the shot count up to ~57, but it wasn't flat at all, and to be honest, I just don't like the look of the shot string:



Currently the hammer throw on this pistol is ~1.2", I started having visions of reducing the hammer throw to 1" (similar to the 22XX's) but then I started thinking that maybe I need to forget the idea of the SSG and focus more on a BStaley Oring type mod like Ribbonstone had done with his. I'm not sure what buffer material to use yet, I've read a bit about LLoyd's experimenting with that, but I don't recall seeing him mention what he's using or what worked best.

I am starting to think that limiting poppet travel might be the best way to tame this beast (or hog, as in gas hog), and I'm almost wondering if I'm not missing a travel limiter of some sort that some pistols have and that explains the major discrepancies between some pistol's efficiency and the rest of the world (Jason was missing an o-ring, mine is missing a spring guide, so it's not out of the question).

[Ribbonstone]

Other end of the stick.

If you think a co2 airgun is using more co2 per shot than is needed for the energy produced, have two choices:

1. reduce the valve dweell (through several methods) so that the valve open/closing cycle is fast enough to not squirt out "useless" gas (gas that doens't do anything towards pellet velocity,,,,just got to the party too late to increase the fun).

Or

2. Starve the valve so that it can't pass on more than a limited amount of gas.  Limit both it's volume and the ability for gas to pass though quickly.

I went with #2 today.


Pistol:





Where I left it: Shot string: using a slightly reduced striker spring and a "bstaley" pad on the front of the valve body to cusion/reduce  vlave dwell.

<a href="http://s157.photobucket.com/user/ribbonstone/media/air%20pistol/5bc683d6-1464-44b2-be17-a923a2ef774c.jpg.html" target="_blank"><img src="http://i157.photobucket.com/albums/t50/ribbonstone/air%20pistol/5bc683d6-1464-44b2-be17-a923a2ef774c.jpg" border="0" alt=" photo 5bc683d6-1464-44b2-be17-a923a2ef774c.jpg"/>[/url]



Rather than reinvent the wheel, thought I'd look around for somthing close to what I needed.


Standard tubing:





LAthe reductioin of OD of tubing:




Rechcek fit of valve stem/retrun spring befor polishing:



Cut off length/fit of tubing inside the valve:




Length:





Test shot string:





So basically, all that "work" on the valve limter was worth 1%,,I'm not "griping" about it. 50 shots inside of 3% is better than 50 shots inside of 4%, but I had hoped for a bit more.

Not that I've really unhappy with +50 shots inside of 3% vs +50 hots inside of 4%.

It really doesn't seem like much, but I'll take a gain in consistency/gas-use efficiency..may not be a bad thing for future tuning. Still looking at 50 shots before it starts dropping off,but those 50 shots are pretty close together in velocity.

[nervoustrigger]

Okay, I think I've found a satisfactory balance of shot count for the effort.

After seeing the other day it's possible to hit the spoon spinners at 25 yards with confidence and the rat spinner at 43 yards more often than not, I decided I didn't want to trade off much velocity to get the total fpe up.  So this morning I set out to try O-ring buffer combinations until the velocity dropped off to about 90% of maximum and just let the shot count fall where it may.

First thing I noticed was the stepped-down nose of the hammer is a diameter that would want to catch on the -113 size O-rings I planned to use for the buffer.  So I improvised an arbor to let me chuck up the hammer in my drill press and grind down the diameter with an emery wheel.


It's hardened steel so taking off 25 thousandths took a bit of time but it turned out nicely:


The first two O-ring combinations I tried dropped the velocity too much.  The third try was a simple pair of 50 durometer silicone O-rings and that gave me the ~450fps velocity I was looking for. 

Then over to the chronograph with a fresh CO2 cartridge and it produced 84 shots inside of an 8% ES with an average velocity of 459fps (3.7fpe) using 7.9gr CPHP.  Total energy was 311fpe.  Nothing special but more than a 50% improvement over stock.  I can live with that

As an aside, if I hadn't managed to find an O-ring combination that worked, the next step would have been to take an arrangement that was somewhat close to my goal and then either shim up the O-ring stack height or sand down the O-rings to reduce it.   Very small differences of just a few thousandths can have a big effect so that's why it's nice if you happen to be working with a hammer that has an adjustable striker...can fine tune things that way rather than fussing about with the height of the O-ring stack).

[Ribbonstone]

Think I'll stop now and wait for warmer/hot weather.

Have been caught in the past with co2 tuned up in mild weather, only to find that it shot SLOW in warm/hot weather (although if I shot at a fast enough pace for the gun to self-cool, it got back up to "normal" speeds).



Higher temps =  higher gas pressure =  higher valve closing force. So a co2 rifle tuned for opitimal gas use at room temp (say 74F)will sometimes be kind of strangled off/slow at 88fF.


I'll wait a month or two before seeking out the last 8-9  shots in that string.

[cobalt327]

Okay, I think I've found a satisfactory balance of shot count for the effort.

After seeing the other day it's possible to hit the spoon spinners at 25 yards with confidence and the rat spinner at 43 yards more often than not, I decided I didn't want to trade off much velocity to get the total fpe up.  So this morning I set out to try O-ring buffer combinations until the velocity dropped off to about 90% of maximum and just let the shot count fall where it may.

First thing I noticed was the stepped-down nose of the hammer is a diameter that would want to catch on the -113 size O-rings I planned to use for the buffer.  So I improvised an arbor to let me chuck up the hammer in my drill press and grind down the diameter with an emery wheel.


It's hardened steel so taking off 25 thousandths took a bit of time but it turned out nicely:


The first two O-ring combinations I tried dropped the velocity too much.  The third try was a simple pair of 50 durometer silicone O-rings and that gave me the ~450fps velocity I was looking for. 

Then over to the chronograph with a fresh CO2 cartridge and it produced 84 shots inside of an 8% ES with an average velocity of 459fps (3.7fpe) using 7.9gr CPHP.  Total energy was 311fpe.  Nothing special but more than a 50% improvement over stock.  I can live with that

As an aside, if I hadn't managed to find an O-ring combination that worked, the next step would have been to take an arrangement that was somewhat close to my goal and then either shim up the O-ring stack height or sand down the O-rings to reduce it.   Very small differences of just a few thousandths can have a big effect so that's why it's nice if you happen to be working with a hammer that has an adjustable striker...can fine tune things that way rather than fussing about with the height of the O-ring stack).

Not following you on the part about the nose needing to pass through the -113 0-rings- my problem, nothing to do w/the explanation. I've not had the valve out of mine to know what relationship your pair of O-rings has to the face of the striker.

Anyway, will my crude rendering below work to reduce the travel of the valve? The O-rings would act as a bumper, and the nose would hold them in place by stretching them over the nose so no need to reduce the OD. I'm sure there's a good reason this will not work but I had to ask, I don't have access to my gun to see for myself. In practice I would probably opt for a solid spacer against the 'flange' then a single O-ring for the bumper, instead of 2 O-rings.

Thanks for this thread- best I've seen.

[nervoustrigger]

I'll see if I can explain.  For the O-ring buffer to do its thing, the O-rings need to remain against the valve.  As it was, the nose of the striker was a diameter that a -113 size O-ring will stretch over when the striker comes flying forward.  That would cause the O-ring to compress radially between the striker and the tube, thus when you go to pull the hammer back for the next shot, it would tend to pull the O-ring back with it. 

What happens next becomes unpredictable.  I suspect more often than not, the O-ring would roll off the end of the striker somewhere along the way.  Then when you fire and the hammer flings forward, it picks up the O-ring and it acts as a friction brake for an unpredictable portion of the hammer's travel.  The result is an inconsistent hammer strike from shot to shot.



Or worse, the O-ring rolls off and tumbles over inside the tube.  Once that happens, pretty much have to take the gun apart to deal with it.  So long as the O-ring stays butted against the valve, it can't tumble over like that, and making sure the striker's nose doesn't contact its inside diameter will keep that from happening.

Regarding the possibility of using hard spacer and a single O-ring, I don't think the proportions of the actual parts will allow that to work very well.  It's kinda hard to explain but the nose is just long enough that it would fully accommodate one -113 O-ring in whole and half of another.  That is to say your spacer would have to be thicker than a single O-ring--any thinner and the nose will reach in and grab the single O-ring--and at that point there isn't a sufficient blend of travel and compliance to give you the right mix of valve lift and dwell.  If instead you have the thickness of 2 or 3 O-rings to play with, you can mix and match O-ring durometers and thin spacers to get the results you want.

[cobalt327]

Got it. I'll give this more consideration once I get a chance to put hands on mine.

In my idea, the O-ring(s)/spacer were not to contact the tube in any way. In other words I had envisioned the O-ring to be proud of the end of the striker nose, but not in contact w/the tube the striker moves in. Seeing as how limited the space is for that to happen, a round cross section O-ring ain't gonna work. But it'll take me seeing what I'm dealing with to make any useful contributions, though (if then, even). Thanks for the input.

[rrdstarr]

Hmm?
Why not turn a piece of delrin the same thickness as the two O-rings? 
Is the hammer to hard to turn to carve an O-ring groove to hold the O-ring?
Is there room on the valve body to cut an O-ring groove so the O-ring isn't traveling, hence coming off the striker?

I haven't tore down my two CP-1M's yet, so just flipping out some ideas....

[nervoustrigger]

In my idea, the O-ring(s)/spacer were not to contact the tube in any way.

Oh okay, I was basing my modified sketch on the -113 size O-rings as described in my writeup. 

In other words I had envisioned the O-ring to be proud of the end of the striker nose, but not in contact w/the tube the striker moves in.

How do you plan to support the O-ring, keeping it proud of the end of the striker and simultaneously keeping it concentric to both the hammer and tube?  By gluing it to a spacer behind it which is closely fitted to the nose of the hammer?

Whatever the method, I think a single O-ring will not have sufficient compliance (squish) to work well.  Not impossible, just unlikely.

I suppose an alternative could be to find a piece of rubber tubing whose ID is a snug fit to the nose of the hammer, but whose OD is small enough to not drag the inside the tube.  Then cut a piece long enough that it just barely allows the hammer to contact the valve stem, and gradually sand down its length by way of trial and error until you get the velocity tradeoff you're looking for.

[Bob Pratl]

Why does it have to be an o ring? Can't it be a small spring with an ID slightly larger than the hammers adjustable striker OD?
The spring could be captured in the face of the hammer and the adjustable striker could be set for the proper preload. Or maybe the spring could cause more bounce than a o ring, Just my 2 cents.  Bob

[nervoustrigger]

Why not turn a piece of delrin the same thickness as the two O-rings?

...And then place a single O-ring against the valve?  You could but the result would be insufficient valve lift to do anything useful.

Is the hammer to hard to turn to carve an O-ring groove to hold the O-ring?

Very hard, indeed.  It's do-able but it seems like a lot of trouble compared to simply reducing the diameter of the nose which allows the use of a more conventional and versatile O-ring stack.

Is there room on the valve body to cut an O-ring groove so the O-ring isn't traveling, hence coming off the striker?

I don't remember for certain but I think there's enough meat on the valve to do that (at least it's true of the vast majority of valves I've dealt with).  The issue just comes back to having only a single O-ring for tuning.

[nervoustrigger]

Bob, I think it's fair to say a couple of O-rings acts like a very short, stiff spring with a highly progressive spring rate.  I'm having a hard time wrapping my head around the practicality of making a compression spring that would fit into this type of space that has the right characteristics.

[cobalt327]

Jason, what holds the 2, -113 O-rings in place- are they just pushed inside the tube, against the face of the valve?

[nervoustrigger]

Right, just placed against the valve.  Some like to use a heavy grease to help keep them in place, just be sure to remove any remnants that could slow down the hammer.

[cobalt327]

Okay, I'm sure that's a better setup. Just so I don't repeat your too-slow combinations, do you remember what durometer/material the first two were? Because for my money, this looks to be better than anything else so far, and the low cost and simplicity ices the cake for me!

[nervoustrigger]

Yeah, the first was a 70 and a 90, and the second was a 70 and a 50.  Those combinations were slow...something like 200fps and 330fps, respectively...ridiculously quiet too.  If I were going to use it exclusively for 10m duty, one of those might have been fun to try.

The winning configuration of two 50 durometer gave almost twice as many shots with very little change in velocity, but I have no idea how similar others will be.  For example, just the slightest variation in valve stem projection would have a profound effect so be prepared to experiment.  Just a reminder that you can also sand down your O-rings or use spacers to tweak the results.

[cobalt327]

Got it, thanks again- good stuff.

[rrdstarr]

Almost where I want it.  There is plenty of wood to carve off to get a good match style grip.