Sunday, July 26, 2015

CP1-M CO2 Pistol Disassembly

Tore down the CP1-M this evening.  Took a few pics along the way.

Make sure the gun isn't charged with CO2.

Remove the trigger guard...

then the rear grip screw.

 Grip pulls off.

Remove the single shot tray or magazine.

It's not necessary to remove the bolt handle if you're just servicing the valve, but I unscrewed it from the bolt.

 End cap retaining screw.

With the end cap off, the hammer spring guide and hammer spring can be removed.

Breech screw removed.  --It's the small screw in the middle of the shot tray/magazine slot.

 Here's the top of the transfer port.

Here's the entire transfer port.  Pulls right out.

The hammer cocking pin is a small bolt.

The hammer can be withdrawn now by pulling the trigger to get the sear out of the way. 

Here's the hammer, hammer spring, spring guide and the hammer cocking pin.  I polished the sear contact area on the hammer.  (Call it a striker if you prefer)   Shooters looking for additional power will often swap out the hammer spring with something stiffer.

Another approach is to add an additional spring inside the hammer spring.

 Like so.

 A spring within a spring.

 Inside the gun, it looks like this.

Underside of the breech shows the bolt cocking pin

The bolt withdrawn. 

With the valve screw removed...

...the valve slides out of the gas tube.

 And unscrews.

Face of the valve is similar to the Crosman 38T.  Hollow piercing pin held in place by a threaded retaining ring and a face seal.

Sometime shooters looking for additional power will substitute a weaker spring into the valve.  This also has the advantage of not increasing cocking effort --provided the original hammer spring is utilized.


OK, trigger time.  The lower stop pin practically falls out on it's own.  (That's OK, when assembled, the trigger guard keeps it in position.)


Here's that 3mm threaded hole mentioned in the first CP1-M blog post.  On the first run of pistols, this hole was threaded (thread size is M3 x .5mm), but the adjusting screw was not installed.  I've already added a sear adjusting screw.

Trigger pivot pin is pushed out and the trigger removed.

Use about a 5mm long set screw.  Round over and polish the end.

The trigger as it sits in the gun. Polish and moly all the contact points.

Only the sear is directly spring loaded.  Note that any trigger adjustment requires removing the grip and the trigger pin stop to access the 3mm screw.  This can be done with the gun charged with CO2 and dry fired until it feels right to you.  As always, err on the side of caution when working on any trigger.

The three set screws on top of the forward end of the breech are loosened to remove the barrel.


The barrel arrangement is similar to the QB series of rifles.  The transfer port is located between two o-rings on the barrel shank.


Of course, they're metric like everything else on the pistol. 

Finally, an o-ring at the breech seals around the loading bolt.

Reassembly is a simple reversal of the above.  I found the gun to be extremely easy to take apart. It was encouraging to see viton o-rings in several key spots as well as thread locking agent on all the fasteners.  Build quality was excellent.  And not just "given the price point".  I found this to be a solid attempt at making a very good pistol.  After having it a couple weeks, as a target pistol, it's easier for me to shoot offhand than my modified Crosman 22XX guns, or my Daisy 747.  It'll also outshoot my Gamo Compact, largely due to having more weight at the muzzle for stability.

Oh, that "spring within a spring" power boost took my .177 cal pistol from 365 fps to approximately 525 fps with RWS Hobby pellets.  Probably want to tweak that down a bit.  For paper punching, I'd like it to be around 410-420 fps--mostly to keep the shot count up.

More soon.


dhc8guru said...

I just got my CP1-M.

Nice pistol and it hits a sweet spot in the market. The "cheap" target pistols for us wannabe back yard 10m champions is the Daisy 747 @ $220 then it jumps to $550-$650 for a Alfa Proj or Izzy. Not exactly a lot of choices. At least we have a middle ground between inaccurate replica pellet guns and expensive guns that can out shoot 95% of us.
I also found better accuracy then my Gamo Compact and Daisy 747 with it. I suspect it is a matter of just being a better fit for me.
Sorry, but I cheated on bumping my FPS up, I just gave the hammer spring a little stretch.
I was looking for 500 fps and got 505-510 after the adjustment. 365 FPS out of the box.

Anonymous said...


Do you know the size of the additional spring you added inside the original hammer spring?


Anonymous said...

I wanted to do your mods and need to know the spring sizes you used. Yhanks for your help! This is an awesome blog!

derrick38 said...

I've no idea as to the spring sizes. Tuning is often just trial and error. I just installed something that fit and ran it over the chronograph.

Unknown said...

My CP! is just managing 4.5fpe, I had a look at the gun on take down and noticed that the transer poart was 3.5mm way bigger bore than the orifice in the breech which was 2mm. Found it rather strange that the breech was restricting Co2 rather than the transfer port, anyone else found this?

Peter Finch said...

I did the spring-in-spring mod on the single shot 177 version sold in Spain branded Artemis.
There was a noticable power increase although sadly I can't find a chrono in the toy budget just now.
Anyway it went from a big dent in a mustard tin to a much bigger one at 10M probably puncture it completely close to. This is with Webley Mosquitos.
Shot count went down from 40 to 30, adding the extra spring makes it easy to undo the mod if you don't like it. It's quite a penalty to pay.
The spring I used was out of one of those assortment boxes as follows, metric of course.
0.5 mm dia wire, 6 turns, 20 mm free length, 7 mm O/D. Spring rate 60 grams per mm

Unknown said...

I have the older model in .177 I just want to move up to a .22 barrel & redo the spring. Can I do only that for a few bucks or do I have to buy a whole new CP1-M ?

derrick38 said...

You may want to ask that question to Mrod Air. Obviously, youll need a .22 cal barrel, a couple .22 cal magazines and/or a single shot tray and possibly a new loading bolt. I don't know if the bolts are different between calibers or if its just an o-ring change.

Unknown said...

How did you remove the bolt handle without damaging it?

derrick38 said...

It's been a while since the blog was written, but I believe it just unscrewed from the bolt with a firm twist. I alsi keep a pair of rubber coated non-slip work gloves at the workbench for additional purchase. Worst case scenario would be to pad the vise with wood or rubber jaws and proceed cautiously.

Victor said...

Hi, just saw your excellent post on the CP1. Have just bought a CP2 pistol/rifle combo. Do you know the size of the O-Rings? Thank you!

jefrs said...

I have the SMK Victory CP2 which I have stripped down and rebuilt as a target pistol. The CP1 and CP2 are so similar that many components are interchangeable but not all and some spacings are different. Fitting a Zasdar CP1 limewood grip meant getting the carving chisels out. The O-rings are best replaced with genuine spare parts. O-rings are sized by o.d. x thickness. The components are all metric. To grip things without marking try a strip of bicycle inner tube. Some jewellery tools have soft jaws.
The airgun is already pretty powerful but making it completely gas tight will increase velocity and power without altering the hammer spring. On the pistol to over 500fps and shot count from spec about 45 pellets to somewhere between 50 to 70. This is about twice that of its PCP sibling the PP800, and as the vapour pressure of liquid CO2 is constant (at given temperature) it provides a degree of self-regulation, whereas unregulated PCP goes down. The CP1/2 is a relatively cheap airgun with good components but perhaps with less than meticulous factory assembly, it does benefit from some fettling.