Hacking the CP-2

[George Schmermund]

The carbine barrel, when mounted, is 17". The diameter is .473" (nominal).

I'm thinking about some trick things that can be done to improve the hammer operation. Hammer bounce in the Vigilante was a none issue as far as I could tell, but these CP2 hammers are probably pretty bad in the bounce department. Dry firing the gun without a powerlet gives a suggestion of a problem and firing a pellet with a full powerlet can mask the bounce ringing.

Here's a test that I thought was instructional. If you loosen the barrel set screws and rotate the barrel 180º and then re-tighten the screws you can fire the gun without moving any gas into the barrel. There's basically no noise from the muzzle or any movement except the hammer hitting the valve stem and rebounding several times. The muted sound and feel of the vibration give a good impression of what must be happening when the gun is fired normally. The accelerometer will tell all when I get there, but this is a simple test that any CP(1-2) owner can do.

[George Schmermund]

After cleaning and deburring, the moving parts were greased and then reassembled. There is a small elastomeric ball That sits under a set screw and presses against the bolt. The pressure is adjusted with the screw and definitely effects the smoothness of the cocking action. I had to take the gun apart a couple of times to make the adjustment. No big deal.

The trigger action is simplicity itself. I reassembled it without polishing anything and the feel was in need of improvement. The empty trigger set screw hole was left empty because I didn't have a screw that would fit. There were some discussions about the screw in other threads that referenced the CP1 trigger and a set screw provided by Mrodair as an after sale item. Considering what was said about the process of adjustment I wasn't keen on following that procedure.

The decision was made to improve upon the factory approach with something that might be better. Looking around the shop I found a sheet of .030" thick Teflon. I cut a small strip of the material and shaped it as shown in the photos. The shape made the Teflon easy to install and hold in place. The .030" thickness took up most of the first stage motion and really smoothed out the trigger/sear engagement. The overall effect was very pleasing, but there was still a bit of grittiness. Poking around some it seems that the culprit was the spring that loads the sear. There actually was a small amount of factory grease on the ends of the spring. Even so, when the spring is compressed it scraps along the edges of the holes.

The spring is stiffer than I thought was necessary. Modifying it or replacing it with another spring could lighten the trigger pull, but not necessarily reduce the roughness during compression. My solution will be to fashion a leaf spring. The spacing between the top surface of the sear and the trigger frame looks perfect to accommodate the leaf. An assortment of different springs can be fashioned easily and tested without having to do more than remove the plastic grip. I'll report back when I've done some testing.

[Rob M]

theres actually an aftermarket supersear that brings the trigger to mere ounces. I just received mine , yet to install. I'm sure the trigger can be vastly impoved with the method you have outlined also. looking forward to before and after impressions

[WhatUPSbox?]

Thank you for the clear photo of the new 2 stage trigger blade. I had not seen that. If you chose to put the second set screw in, I would be interested in how easy it is to dial in the 1st/2nd stages.

[George Schmermund]

I'm starting to see that the CP2 is a different gun than the CP1 in some ways. As far as the second screw in the trigger, I don't see any reason to install it compared to the sheet of Teflon. The .030" thickness actually adds .060" to the sear displacement because the sheet wraps around the on both sides of the trigger to also displaces it from the stop pin. I doubt that anything is going to make the sear/trigger interface any silkier that the Teflon. The 2 stages are very smooth and distinct for what I'm after at the moment. The sear spring needs to be attended to as described in a previous post.

Does the CP1 have the bolt drag adjustment? I haven't read about that yet in other threads. It really improves the feel of cocking and loading. It's important to thoroughly debur the bolt tunnel first to get the best effects of smooth cocking.

[George Schmermund]

The .177 version of the CP2 arrived from Mrodair. The moving parts seem a little better out of the box compared to the .22 gun when it arrived, but will still need attention. Most of the shooting that I've done with the .22 was with it clamped in a vise. After each lathe treatment it went back into the vise to compare the results. When I finally did some shooting with it myself it was with the carbine setup.

After spending some time with both guns last night while sitting in a comfortable chair I got some new impressions. On the positive side I can report(?) that the thing on the end of the .177 barrel is even more effective than the .22 version, though they seem to be the same devices. I guess that result could be expected.

On the down side I have to confess that the grip and trigger guard are small and awkward for my hand. With the narrow grip area the weight distribution feels unbalanced when trying to aim in a freehand hold. This would be a problem if I wasn't planning to use them both in the carbine setup. The balance and overall comfort is remarkably different and better for me in that mode. I'll have to figure out how to improve these issues.

Another thing that I should mention is that right out of the box the piercing pin would not puncture the powerlet. I turned the locking sleeve in until it was out of threads and still nothing. The powerlet was then removed and examined. There was only a dimple in the end of the powerlet seal. The remedy was to put a washer between the end of the powerlet and the inside of the locking sleeve. This was inconvenient, but it worked. I'll have to turn a couple of threads off of the end of the main tube, but I going to put the tube in the lathe for deburring anyhow. It's just another factory oversight.  It's early and much can be done to make things better. I'm still impressed with what wonderful project guns these have turned out to be.

If I had my choice I'd have to admit that I wouldn't buy a CP1 over a CP2. The CP2 package is too good of a deal. Also, the CP1 is an unfinished design that finally blossomed into the CP2 and there's no turning back for my money.

[WhatUPSbox?]

I'm glad that just the teflon set the two stages at good points. The second screw would be just for additional tuning. I'm wondering if the longer lever arm approach could be applied to the CP1 with a custom trigger blade.

No bolt drag adjustment on cp1

Yes, CP2 looks like a good evolutionary step and a great deal for the money

[George Schmermund]

I may be behind the curve on this, but I just looked at the Mrodair site and saw that they now show an exploded view of the CP2. The CP1 can now be compared with the CP2 for design differences and parts count. Hopefully there will be replacement parts available for both airguns soon. I'd like to get an extra 1 or 2 of those things that screw onto the end of the CP2 barrel (I don't mean the thread protector).

[George Schmermund]

To distract myself from other projects that have been started I decided to do some experiments with one of the accelerometers. The easiest place to attach the device is onto the bolt holding in the valve. This gets me very close to where the hammer will be striking the valve stem. The instrument will be fixed in the direction that will be most sensitive to forward and back motion parallel to the barrel's axis.

Hammer and valve stem interaction as well as transit time markers will be recorded. The transit time will be measured at the muzzle with the same force transducer that was used in the timing experiments that were done on the Vigilante.

The photos show the grip being milled out to accommodate the accelerometer and the basic arrangement for mounting. The wires can be easily routed along the inside of the grip along the action and will exit out the back.

I've returned to my usual inability to march a straight course while doing experiments.

[George Schmermund]

While I was setting up the accelerometer arrangement I got to looking at the main tube section and and decided to try a fit test with one of the heater experiments from the Vigilante days. It turns out that the heater is a perfect fit for the CP2 and a second pair of heaters will also fit. The extended grip in the front will cover the heaters and offer a good insulator so that the heat will conduct through the tube into the powerlet and the valve with little loss. This will be an interesting new project for these airguns.

The photo shows one of the powerlets and a pair of heater strips from the earlier Vigilante project.

[George Schmermund]

The sear spring project reemerged this morning. I was thinking about the roll that the spring played in the overall trigger's pressure response. I needed a ground zero place to start measurements. The obvious starting point would be to measure the trigger pressure without the spring involved. The results were enlightening, so I thought it was best to share what was found.

To start with I can report that the trigger is no trigger at all when the spring is removed and the gun is cocked in the normal upright orientation. The sear can't engage the hammer sans spring. The next thing was to remove the grip and install the gun upside down in the vise. Now the springless sear can be engaged when the bolt is pulled back and the hammer allows the sear to drop in. It's like setting a spring mouse trap.

The force gage was then setup to push on the trigger from a low friction surface as shown in the photos. A piece of paper was placed between the trigger and sear surfaces and could act as a feeler gage to detect when the the surfaces met. What surprised me was that the first stage trigger pull was reinstated without the agency of the missing sear spring. This was interesting. On further investigation it was revealed that the first stage is basically generated by the resistance of the surface of the sear sliding along the face of hammer's catch with a total force of .68 lbs. When the sear reaches the wall of the second stage the force increased to 1.58 lbs when the gun fires. This would indicate that the sear spring is only needed to return the trigger and sear to their original positions. Any trigger force above 1.58 lbs (in this case) is just extra baggage from the sear spring. It's the hammer spring and hammer/sear surface friction that runs the show.

My conclusion is that the real trigger 1st and 2nd stage force requirements are determined, for the most part, by friction of all the moving parts' surfaces. Now that I've got my baseline numbers I can do surface polishing (including the pivots) and see what happens. If These experimental results are true, then changing the hammer spring will also effect the trigger force.

As an aside I'll add that a good vise soft jaw solution for holding barrels is to cut a piece of PVC pipe and slot it as shown.

[George Schmermund]

The .177 CP2 was dismantled today and I was able to inspect the trigger parts for comparison to the .22 version. There was actually some lube on some of the parts. This seems To be as hit and miss as lube in the Vigilantes. There was a set screw (missing in the .22) installed in the extra trigger hole that can be used to adjust the first stage travel. The first stage force needed to get to the second stage wall was 1.22 lbs, the second stage break was in excess of 3 lbs. These CP2 triggers are very tunable with little work required to make big improvements. Replacing the sear return spring and polishing the contact surface are all that are needed.

A trigger shoe could also be fashioned to reduce the perceived trigger pressure. I'm giving that some thought because I've been spoiled by the generous blade width on the Vigilantes.

[George Schmermund]

The hammer was easy to improve upon by reshaping the slope of the sear ramp. The slope was cut to 30º and extended to within .040 of the edge of the sear latch. The ramp and latch face were then polished with the Dremel using a Scotch-Brite wheel.

I chose a small spring from a collection in the shop to replace the factory sear spring. As the photo shows, the new spring is ~ .130" shorter and ~ .004" larger in diameter. The larger dia. allows the new spring to be pushed snugly into the sear hole to keep it in place. This spring also requires less compression to do it's job. Being shorter than the original spring means that when the gun is in its normal orientation the trigger falls away from the sear if the gun is not cocked. This has the interesting effect of leaving the trigger's first stage loose with no spring preload when the gun isn't cocked. I going to consider this outcome to be a feature rather than a flaw because now I don't have to pull the cocking arm back to check it the gun is cocked and loaded. This will reduce the likelihood of jamming from double cocking when using the magazines. When the gun is cocked the first stage of the trigger reasserts itself do to the hammer and sear being engaged. 

The trigger force is now .72 lbs for the first stage and 1.52 lbs for the second stage. The new ramp on the hammer is impressive in it smoothness. The first stage pull is slicker than..... The second stage wall is distinct and the break is very clean and positive. The Sta-Lube 3161 grease that I'm using is also very effective.

[George Schmermund]

The accelerometer testing got underway today. Both the .177 as shipped and the .22 with the hammer mod and the main tube deburring were tested next to each other. The photos show the 2 pistols with the accelerometers each mounted in the same place and the scope traces of the hammer strikes. Neither gun had a powerlet installed. It's just the hammer impacting the valve stem. The top 2 photos are of the .177 results with the traces separated and then overlaid. The bottom 2 photos are of the .22 results, also separated and then overlaid. All instrument settings were identical for these tests.

The red trace on each screen is the unfiltered signal coming from the accelerometer and the yellow trace is the same signal after it's passed through a 1 octave filter centered at 10KHz to eliminate the high frequency noise. The red trace shows a lot of signal that is not directly related to the hammer/valve interaction. Both signals on each screen are triggered simultaneously.

This is the tip of the iceberg for these tests. I'm also planning to put a mini-pressure transducer through the side of the valve so that the pressure/time curves can be synchronized with this hammer/valve timing. With a force transducer at the muzzle we'll probably see some interesting stuff.

 

[George Schmermund]

Things have gotten increasingly interesting with the impact testing. Using only the improved .22 gun, the measurements can proceed on a single platform. The photos shows what the accelerometer signal looks like when a powerlet is installed and the gun is pressurized. As with the Vigilante, the CP2 is much more under control as far as having a bunch of rattling of the moving parts. The impact signals are quite distinct now in the 10KHz filtered channel (#2). Channel #1 is still noisy with the high frequency vibration of the main tube longitudinal waves. Note that the vertical signal gain has been doubled to get the signal heights to about the same level as the unpressurized tests done previously. There is significant timing information that is starting to gather. This should be tantalizing stuff for the hammer bounce sleuths out there.

The next test will be to plug the barrel hole in the breech and install a pressure gage in one of the unplugged  barrel clamping screw holes. This will correlate the hammer impact timing with the pressure/time signals. This will confirm if there is any hammer bounce to deal with.

[Rob M]

very cool , looking forward to the hammer /pressure test.

[George Schmermund]

Looking at the accelerometer signals in the previous post with the gun pressurized it is apparent that there is a low frequency signal hiding in the middle of things. After changing the octave filter from a 10KHz center frequency to one centered at 1KHz the hidden signal popped right out. As can be seen in the menu at the right of the screen the frequency is about 1.1KHz and appears to be a low Q undamped resonance. The scope ranges were changed to get better signal contrast.

After closer examination using my nifty little tapping hammer it turns out that this resonance signal is the bolt and hammer spring acting as a classic spring/mass system.

[WhatUPSbox?]

George,
Interesting data, as always.
Can you describe the filter you applied? Since you are looking for data in the 1 to 10 Khz range how does the filter affect that?

[George Schmermund]

Stan - Thanks for your interest in the instruments and methodology I'm using for these measurements. These tests are done using analog gear because I'm so enamored with the exquisiteness of Bruel & kjaer equipment of that era. The HP Digital Signal Analyzer (DSA) will be used in the next iteration of tests. The DSA can run circles around the instruments used here, but I still enjoy playing with some of my older toys.

There's no compact way to properly explain how these measurements work without shortcutting the information and causing probable confusion. Here's a link to a PDF that covers it all very well. The measuring amplifier I'm using is the 2636.

[PDF]Third-octave and Octave Band Pass Filter — Type 1617 meteosat.pessac.free.fr/IMA/ressources/tp_avio/TP.../FILTRE_1617_bp0163.pdf

I hope this link works. It comes up on the top of the page on my Google search.

[WhatUPSbox?]

Yes, thanks,
That filter spec helped quite a bit.