Monday, January 21, 2008

RWS 850 AirMagnum PCP Conversion - Part 2

By A.R. Tinkerer

Part 1

Last time we looked at the performance of a .22 caliber RWS 850 AirMagnum using air (actually nitrogen) instead of CO2. It was connect to the nitrogen source using a paintball remote setup. Today we will look at a different setup. This time the tank was filled with air, but that shouldn't make much difference.

I was puzzled by the results from my first test so I began to figure out why the results weren't better. The first thing I did was to set up a pressure gauge on the paintball tank to check its output pressure. It read 800 PSI. Pressure for CO2 at room temperature is about 850 PSI, so that could explain at least part of it.

Next Step
At this point I decided that if the project was worth continuing, I might as well convert my 850 AirMagnum into a true PCP (Pre-Charged Pneumatic). I began to look for small tanks that would fit under the barrel and a paintball regulator that would put out higher pressure. I found a 13 ci (cubic inch) tank, a Smart Parts Max Flow Inline regulator, and put together the setup below. Finding the parts to connect everything was a challenge since I used only off the shelf parts. I did have to drill and tap one part.

RWS 850 AirMagnum PCP

The tank and regulator are connected to the adapter via paintball macro line. The Smart Parts Max Flow Inline regulator is great because it is adjustable and has an on/off built-in. Not only that, but it has a tank pressure gauge and an output pressure gauge!

Tank, regulator & adapter closeup

The adapter includes the Cooper-T AirSource to ASA adapter discussed last time plus a customized adapter with a burst disk, macro line connector and bleed plug. The customized part is a Palmer's Pursuit adapter that has been drilled and tapped for the burst disk and macro line fitting.


The mount is made out of a Daisy scope mount. Rubber gasket material protects the barrel and a Lucky Paintball drop forward mounts to the regulator.


Testing the new setup
I planned to test the new setup by setting the regulator to around 800 PSI, shooting a couple of shots, then increasing the pressure by 50 PSI. I would continue until I reached 1000 PSI. That would give me a nice set of results for 800, 850, 900, 950 and 1000 PSI. With that spread I should be able to see what pressure the AirMagnum liked best. Things didn't go as planned. I set everything up, turned on the regulator, and the output pressure was lower than I wanted. I tried to adjust it and found that it wasn't easy to adjust the pressure with the air on! Ok, I figured I'll go to the maximum pressure and try to adjust down. Maybe that would be easier. I turned off the air, adjusted to maximum and was pleased to find the regulator put out about 1050 PSI. I shot a couple of shots and tried to adjust the pressure down. It was just as hard to adjust down as to adjust up! So I shot the rest of the tank at 1050 PSI and did some testing with the RWS compensator I had just purchased.

This time I was shooting with a friend who owned a commercial chronograph. Unfortunately the light wasn't right or something else was wrong and we were only able to record the speed of one shot. That shot was 619 fps. At first I thought even that reading must be wrong, but after posting my comment on the Pyramyd Air blog, BB Pelletier commented that I might be experiencing valve lock at that pressure (1050 PSI).

Going futher
I didn't like the look of this new version and it was difficult to adjust, so instead of trying to test further, I decide to go back to the drawing board once more. At this point I am going to go backwards and explain the original design criteria. Then I will fast forward to the next design and the search for components to fit those criteria. Don't worry, I will post some intermediate results next time.


Shooter said...


Interesting, the unexpected problems we run into when designing something new, or modifying something that someone else hasn't worked out beforehand. Who would have thought about running into valve lock? Couldn't you re-spring the hammer a little stronger to get around this? It would undoubtedly mess with how your trigger feels, but that could be addressed as you chased the bug down the line.


A.R. Tinkerer said...


Yep, I certainly didn't expect to run into valve lock that quick! CO2 pressures can go quite high as the temperature increases so I thought I was safe. However, now I'm not sure it was valve lock. The results coming in the next post seem to indicate otherwise. It may have been flow restriction.

I definitely could change the hammer spring. People have done that now with good results. I am trying a different approach because of what I've heard the Mac1 US-FT rifle, the historic Girandoni rifle and now the Benjamin Discovery have done with lower pressures.

A.R. Tinkerer

Shooter said...


Did you read ANA's site? ( Nibecker does quite a bit with higher flow, lower pressure air. Granted, it's a totally different approach, but it does prove what can be done.


A.R. Tinkerer said...

I like what he has done - bit too expensive for me though ($2850)! As will be explained in future posts, I intend to experiment to find the maximum performance for the 850 while limiting what has to be modified.


Shooter said...


A little rich for my blood too... But it would be nice to have one!


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