Before you start tuning ...
Before you start make sure you are familiar with "Before you start tuning" page. Below you can see also link to my tuning parts shop.
Air rifle powered by external CO2 tank
Now let's consider an air rifle powered by a external CO2 tank and test it.
Test environment:
- I use PCP conversion with adjustable pressure from 650-1050 psi (using 0 - 1500 psi pressure gauge). It simulates CO2 powered rifle in temperatures from 10-30℃.
- During the test I used JSB Exact 4,50mm (0,547g).
- I used an Artemis CP2 air rifle in caliber 4,50mm with a long barrel.
- Barrel port and valve unit is not drilled yet to a bigger size (important while playing with the transfer port)!
Let's remove the piercer
Below, you can see a comparison between the factory air rifle and the air rifle without a cartridge piercer:
As you see, now we have huge power gain, just after removing the cartridge piercer. You gain 31-47% power in the 10-25℃ temperature range. In 25-30 ℃ temperature range power gain drops to 12%. Without any disadvantages in air gun handling (trigger action, air rifle reloading force, kicking during shooting).
Piercer eliminator and stronger hammer spring
I added a 4mm and 8mm spacer to the factory spring. Bigger spring preload makes the hammer strike valve harder. How about power increase? Let's see the chart:
In temperatures below 20℃ adding any spacer to hammer spring decreases the power a little. A bigger spacer limits it more than a smaller spacer. Above 20℃ you will gain some extra power. You will gain 40-46% of power while compared to a stock air rifle.
Factory spring is not bad. A stronger hammer spring makes the air rifle harder to reload, the air rifle kicks harder, and the trigger is harder to operate. So after all, there are more disadvantages than advantages. Definitely there is no need for a harder one, you can only try adding a small spacer during a hot day.
Piercer eliminator and weaker valve return spring
I've tested two new return springs instead of factory valve return spring (medium and super soft). With a weaker valve spring, it is easier to open the valve and the valve stays open for more time, because the weaker valve spring pushes the hammer back with smaller force. It sounds like a better upgrade than a harder hammer spring, because it doesn't influence trigger action, air rifle reloading force or kicking during shooting. How about power increase? Let's see the chart:
In temperature range 10-30℃: Super soft valve return spring performs the best. It gives 41-48% extra power, without any disadvantages in air gun performance (of course, there will be fewer shots per cartridge).
Good choice for tuning, gives extra power in all temperatures, no disadvantages in air rifle handling.
Piercer eliminator and transfer port size
As far as I know in a couple countries this air rifle is equipped with a 2,5mm transfer port and in fact it can restrict power a little.
Keep in mind that the transfer port is only one part, there are two more: barrel port and valve port. To achieve full power gain, you should drill the barrel port and valve port to a bigger size.
Making the barrel port hole too big may damage pellet during loading, or pellet may partially fall into the port and block there. Some people say you shouldn't drill it bigger than 3,8mm for 4,5mm caliber. During drilling, you can also damage the barrel and valve, drill press is recommended.
I plan some more tests with "factory" air rifle so my barrel and valve ports are factory size, about 3,5mm. I tested various transfer port sizes (port diameter 2,5mm; 3,0mm and 4,0mm) instead of the 3,5mm factory transfer port. A bigger transfer port restricts gas flow less, so bigger is better. How about power increase? Let's see the chart
When you change the 2,5mm transfer port to a bigger one, you will gain some power. When you already have a 3,5mm transfer port, then changing it to 4mm gives small gain during hot days and small decrease near 15℃. After drilling the barrel port and valve, it should perform better. In both cases, there are no disadvantages in air gun handling (of course there will be fewer shots per cartridge).
Good choice for tuning when your rifle uses a 2,5mm transfer port. When you already have a 3,5mm transfer port, a bigger transfer port gives no profit (without drilling barrel port and valve!). No disadvantages in air rifle handling.
Piercer eliminator and single upgrades comparison
Now you know how a single upgrade works with no piercer mod. Below you can see comparison between single upgrades to see which one gives the best results:
Again, the best single upgrade is a super soft valve return spring. The 4mm hammer spring spacer works similarly to a super soft valve spring, but it decreases performance of air rifle handling (worse trigger action, harder air rifle reloading, stronger kick during shoot). Changing the transfer port from 3,5mm to 4mm (without drilling barrel/valve!) makes minimal impact to air rifle power.
Piercer eliminator and multi upgrades comparison
Below you can see comparison between multi upgrades to see which combination gives the best results:
As you see, you can't add two upgrades together and expect double power gain from those upgrades. While upgrading air gun powered by CO2 external tank you achieve the best result while replacing valve return spring and adding piercer eliminator mod only. Replacing more parts like: transfer port (without drilling barrel/valve), adding stronger hammer spring or adding spacer to the factory spring, gives nothing more after replacing valve return spring and adding piercer eliminator mod.
Do you need instruction to make external CO2 tank build?
Instruction and parts list needed for external CO2 tank build are available here:
Do you need more power?
You can't do more with an air rifle powered by CO2. To make it more powerful, you need to power it by an external tank with air under high pressure, so you need to go for PCP mod.
