CP2 HPA conversion

[Fatbob 59]

Now it’s exactly 15mm the whole way along.

Better with the band here?

View attachment 854793

It looks better but something must be under stress , what does it look like without a barrel band fitted ? Maybe print a two piece band so the barrel and bottle are both relaxed but still joined together ?

 

[Easton81]

It looks better but something must be under stress , what does it look like without a barrel band fitted ? Maybe print a two piece band so the barrel and bottle are both relaxed but still joined together ?

Not under stress at all, without the band the gap is between 14-15mm all the way.

 

[Easton81]

I’ve now fitted a 3.5mm transfer port, up from the original 2mm, and also fitted a 4mm power spring guide, but I’m a bit disappointed by the results.

Max ft/lbs with .22 JSB Heavy pellets has gone up 1ft/lbs to 8.5ft/lbs, and max fps with JSB RS has gone up by 30 to 504fps, is this as much as is to be expected from these mods?

 

[Hermitage10]

I’ve now fitted a 3.5mm transfer port, up from the original 2mm, and also fitted a 4mm power spring guide, but I’m a bit disappointed by the results.

Max ft/lbs with .22 JSB Heavy pellets has gone up 1ft/lbs to 8.5ft/lbs, and max fps with JSB RS has gone up by 30 to 504fps, is this as much as is to be expected from these mods?

Is it .177 or .22

 

[Easton81]

Is it .177 or .22

.22

 

[Fatbob 59]

Maybe I'm barking up the wrong tree but the gun has miniscule plenum volume and a Norris conversion feeds air through the tiny hole in the CO2 piercer so surely that's the restriction ?

 

[Shadowryder]

@Easton81
If you remove the piercer shown in above picture and replace the seal and brass locking ring this will give better air flow,
I also seem to remember shortening the threads on the valve head so as to create a larger plenum.
See pic.

 

[ninja9]

Maybe I'm barking up the wrong tree but the gun has miniscule plenum volume and a Norris conversion feeds air through the tiny hole in the CO2 piercer so surely that's the restriction ?View attachment 856094

What barrel are you using, iget 8.5flb in 177 with the short barrel with a 1200psi reg. Great for rats outto 20-25 yards, with the longer barrel it's close to the limit. 3.5 tp

 

[Hermitage10]

Maybe I'm barking up the wrong tree but the gun has miniscule plenum volume and a Norris conversion feeds air through the tiny hole in the CO2 piercer so surely that's the restriction ?View attachment 856094

You can do away with the piercer cap and replace it with a larger holed…. None piercing end cap … sure available on flea bay

 

[Easton81]

@Easton81
If you remove the piercer shown in above picture and replace the seal and brass locking ring this will give better air flow,
I also seem to remember shortening the threads on the valve head so as to create a larger plenum.
See pic.
View attachment 856155

Thanks I’ll give that a try!

I wouldn’t have thought the piercer hole would restrict power, as the plenum has all the time between reloads to get up to full pressure, but it’s worth a try.

I’ve also ordered a 1000psi reg from aliexpress to tryout.

 

[Shadowryder]

Way I figure it is similar to enlarging the TP in that it improves Airflow.
I may be wrong but it all seemed to help with mine.

 

[Easton81]

Well, what can I say, those two mods make a massive difference!!

I need to put a smaller TP in now!

 

[Easton81]

So, my gun is legal now, phew!

First I tried removing the weighted hammer spring spacer, which made zero difference to the power. So basically all it does is introduce hammer bounce and slightly stiffer cocking. Avoid this mod imo.

I have now put the 2mm TP back in and I’m at 10.5ft/lbs with JSB Heavy at 510fps, and 9.3ft/lbs with JSB RS at 560fps.

I could tinker with opening up the TP a bit, but tbh this is probably a good mixture of power level and shot count, and no legality worries, so might just leave it like this.

 

[Shadowryder]

So, my gun is legal now, phew!

First I tried removing the weighted hammer spring spacer, which made zero difference to the power. So basically all it does is introduce hammer bounce and slightly stiffer cocking. Avoid this mod imo.

I have now put the 2mm TP back in and I’m at 10.5ft/lbs with JSB Heavy at 510fps, and 9.3ft/lbs with JSB RS at 560fps.

I could tinker with opening up the TP a bit, but tbh this is probably a good mixture of power level and shot count, and no legality worries, so might just leave it like this.

Sounds like a nice balance and should give loads of shots.

 

[Vorlund]

@Fatbob 59 Hi can you provide dimensions for the extension tube please? Length and thread length and sizes?

 

[Fatbob 59]

@Fatbob 59 Hi can you provide dimensions for the extension tube please? Length and thread length and sizes?

I no longer have a drawing but I do have an extension tube at home I can measure , length and threads at the front end will depend on what you want to fit on it and whether you are keeping the tube at full length or shortening it

 

[Vorlund]

Hi Bob, It's to go in a CP2 so needs to clear the front end of the caplet holder to take a drop block.
I haven't decided on which drop block just now. Are the Shan Bao units any good?

 

[Fatbob 59]

The Shan Bao blocks are fine , my personal preference is to use the basic unregulated block and a regulated bottle rather than the block with a built in reg , they're available with M16 or M18 threads so you need to specify which thread you want on the adapter , I've got one here that I could modify to do what you want but I can't help you until you have sales access to post a wanted ad

 

[peter9]

can u still buy a froggy drop block that just screws in and a reg bottle or is that wrong,it seems a easy way

 

[Michaelmilneminster]

can u still buy a froggy drop block that just screws in and a reg bottle or is that wrong,it seems a easy way

I believe you can as last time I looked on his website they were still listed . Very easy to install and I like the fact they don't choke down the air flow like the co2 plug and play ones do .