.25 CO2 beast
Printed From: Kiwi Airgunners
Category: Technical
Forum Name: Pauly's Technical Area
Forum Description: Technical information, Modifications and DIY projects are all in here
URL: www.kiwiairgunners.co.nz/forum_posts.asp?TID=1341
Printed Date: 27 Jul 2026 at 10:21am
Software Version: Web Wiz Forums 10.14 - http://www.webwizforums.com
Topic: .25 CO2 beast
Posted By: nunga
Subject: .25 CO2 beast
Date Posted: 20 Apr 2026 at 6:35pm
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Just want to say a big thanks to http://kiwiairgunners.co.nz/member_profile.asp?PF=622" rel="nofollow - jwabfrog for sending me the .25 barrel. I will be starting my new project over the weekend. This will be a 30PFE .25 CO2 bolt action rifle Powered by a standard Sodastream 60L bottle. This will take a while as everything will be made by me (apart form the barrel) I have been planing and researching this for the last year and i am finally ready to start. So watch this space! ------------- 2nd place HP springer - WFTF World Championships 2014 |
Replies:
Posted By: -Ec
Date Posted: 20 Apr 2026 at 7:43pm
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30FPE - that'll hit HARD. Any guestimate on how many shots you might get from a soda stream bottle? Going to take some careful engineering to put it together. Looking forward to seeing this project unfold. Good luck with it all. ------------- Regards, -Ec |
Posted By: nunga
Date Posted: 17 May 2026 at 7:39pm
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So ive been super busy lately but i managed to get into the garage today to make a start on this project. I have done the research but now i will test this research to make sue i am on the right track before i even start making the parts for the gun. So i am making an adapter to screw onto the end of the Sodastream bottle. It will have a thread on both ends. One to fit the Sodastream bottle and the other to have a threaded rod that will screw into the valve of the bottle to open it. Then i will tap a thread in the side to install a pressure gauge to make sure the bottle will give me the 800PSI needed for these calculations to get the 30PFE target output.   I will drill and tap the rest tomorrow with a bit of luck and test.
------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: Ashman
Date Posted: 17 May 2026 at 10:16pm
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Holy sh*te there's mad ass engineers on here. When you've finished that, any chance of building me a time machine? Just a basic one. Nothing fancy. Will need a dunny though.
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Posted By: nunga
Date Posted: 17 May 2026 at 10:42pm
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Ha ha, sure thing! ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: nunga
Date Posted: 23 May 2026 at 3:27pm
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So just a quick update. I have made everything and test fitted to make sure all the orings seal and so forth. Went to the shop and swapped the empty bottle that i used as a template to cut the threads in my adapter, Screwed the new full bottle in and the threads bound up halfway screwing it on. I have 3 bottles here as i have a sodestream machine here to make my cola for my whiskey I make. All 3 bottles have slightly different threads by the looks. one screws in just fine, the other is a little tight and the last one only gets half way. This is going to be a problem. Their quality control on their bottles is not the best. Probably because its designed to screw onto a lose fitting plastic nut in the machine with very back low pressure. I need my threads perfect if they are going to hold the full pressure of the CO2. So i will have a little think about who to safely overcome this problem. ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: kruzaroad
Date Posted: 23 May 2026 at 8:27pm
| Could you make a new adaptor that takes a sleeve you can screw in and out and have slightly differnt threads for the bottles. Can you make a adaptor for filling the bottle and get co2 in a bulk bottle and fill the canastas that work yourself? |
Posted By: nunga
Date Posted: 23 May 2026 at 9:04pm
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I do not have the technology to full the bottles myself as they are liquid CO2 when full. I would need some way of freezing the gas then full the bottles in liquid state. (i think) Making a sleeve might work but then the wall thickness of the adapter will need to be bigger to take the different inserts. this might not be practical. ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: kruzaroad
Date Posted: 23 May 2026 at 9:31pm
| Other option might be to get a die and just tidy up threads on the bottles that don't fit when you get them. Assuming they must be pretty close. Would still work in a soda stream when connected and wouldn't be noticed when swapping bottles |
Posted By: nunga
Date Posted: 23 May 2026 at 9:58pm
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Yeah thats probably the best option. For now ill just try to find a full bottle to test that has a good thread. If it all works out ill look at what a die is worth ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: kruzaroad
Date Posted: 23 May 2026 at 10:08pm
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Cut one on the lathe. If your just tiding up thread basically a harden nut would do the job. |
Posted By: nunga
Date Posted: 25 May 2026 at 5:38pm
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So I solved the thread problem. I made a homemade die nut to clean up the threads.
I had to use another pressure gauge because the nice new one had a nipple on the bottom which got in the way of the shaft so I installed my old flat bottom gauge.
900 PSI is more than expected and it is winter as well
with 19 degrees so that’s good pressure.
So now i can move on with the build since the tests have proven very successful. ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: Pauly5
Date Posted: 25 May 2026 at 6:44pm
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That's looking great Nunga. I can't believe I had missed the earlier posts. I was thinking of doing a CO2 bulk fill carbine with a 30 cal barrel I have, so I will enjoy watching this.
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Posted By: kruzaroad
Date Posted: 25 May 2026 at 7:14pm
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What sort of pressure increase would say a 20° day give it. Pish it to a 950psi? How consistent are you expecting the refills to be? I'm guessing that they should be pretty well pressure regulated at refill place. Whats the next step? |
Posted By: nunga
Date Posted: 25 May 2026 at 7:36pm
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Next step is to make the 120cc tank, Hammer and ports on a hot summers day 30.0 °C it would push it up to around 1200 ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: nunga
Date Posted: 25 May 2026 at 8:44pm
To get 30FPE it will take approximately 2.2 grams of CO2 per shot with the 120cc tank i will have screwed to the Sodastream bottle, so the math says 182 of usable shots. So i can safely say 150 shots per tank.
------------- 2nd place HP springer - WFTF World Championships 2014 |
-Ec wrote:Posted By: kruzaroad
Date Posted: 25 May 2026 at 9:52pm
| Plenty for a evenings hunting. Goat/wallaby hunting at that. |
Posted By: BC_Clark
Date Posted: 29 May 2026 at 10:07pm
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I love seeing custom builds. Following this build with interest. CO2 is well capable of 30 ft-lbs in .25 and it may use less gas than expected. e.g. I got 26 ft-lbs in .35 from a 6" barrel and it used 1.1 grams per shot. |
Posted By: nunga
Date Posted: 10 Jun 2026 at 8:58pm
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So it has been a little while since ive done anything. I have made the trigger now and will start on the rest of the trigger over the next couple of weeks.     ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: Pauly5
Date Posted: 11 Jun 2026 at 8:13am
| A true custom trigger. Good stuff! |
Posted By: Myson
Date Posted: 11 Jun 2026 at 11:20am
You guys continually amaze me!!!  I wish I had your skills, knowledge and creativity.... sheer brilliance before me and other readers here!!! Well done! In my next life I'm going to study engineering!!!!!!  ------------- https://www.youtube.com/watch?v=eq7jVyBfFqE" rel="nofollow - https://www.youtube.com/watch?v=eq7jVyBfFqE Air Arms S510 US .22 Air Arms S410 .22 Weihrauch HW97KT .177 Weihrauch HW95 .177 |
Posted By: Pauly5
Date Posted: 11 Jun 2026 at 11:22am
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You could buy yourself a benchtop lathe. That'd open up another slippery slide to fall into. :)
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Posted By: jwabfrog
Date Posted: 11 Jun 2026 at 1:31pm
| Lost wax cast? Very cool! What metal for the trigger? |
Posted By: nunga
Date Posted: 11 Jun 2026 at 2:46pm
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Trigger is made from recycled beer cans. I melt them down in my big furnace into ingots. That is a leftover bit from my melt. So the trigger is made of beer!  ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: metallicsting
Date Posted: 12 Jun 2026 at 7:27am
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Speaking of mods. Has anyone ever tried one of these in a co2 gun? Just wondering if it would actually work if I was to buy a co2 gun and use this instead of buying the disposable ones. I just found this on AliExpress: | Outdoor Inflation Reusable gas Tank Tire Inflator Stainless Steel Mini Pump 8/12/16g Co2 Cartridge MTB Bicycle Bike Accessories https://a.aliexpress.com/_mtqUWl9 ------------- FX Impact M4 .22 Cal Ruger 22LR |
Posted By: J-S
Date Posted: 12 Jun 2026 at 10:14am
You should share some of your builds here! ------------- https://www.instagram.com/js_airguns/" rel="nofollow - J S Airguns Air Arms TX200('s) Theoben Sirocco HW77 FWB 300s Webley Patriot One or two others... Current projects: Too many.. |
Posted By: RangerPete
Date Posted: 14 Jun 2026 at 2:44pm
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Nunga, the big question is does your new trigger SMELL like beer??? ------------- Walk quietly, but carry a big stick. |
Posted By: Mintie
Date Posted: 14 Jun 2026 at 3:17pm
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Keen to see how this turns out, ive done a few .25 CO2 builds over the years but only with standard sized valves that I have hogged out for more volume, will be interesting to see what sort of power you can get out of a full custom valve! From memory one of the Crosman builds I called the 2540 got about 16 fpe from a 10" barrel, and the 25cal CR600 i built for Zooboy got about 22fpe from a 20" barrel. Both of those just ran on 12gr cartridges. |
Posted By: vault
Date Posted: 15 Jun 2026 at 8:49pm
| amazing engineering skills but not a fan of c02 in otago, gets to cold and then it's useless |
Posted By: BC_Clark
Date Posted: 17 Jun 2026 at 10:09pm
I can't show this one due to NDA. That's the annoying thing, can't show the most interesting ones.
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Posted By: nunga
Date Posted: 21 Jun 2026 at 4:55pm
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So i had some time today to get some more machining done. I made the adjustable hammer. Everything is 316 Stainless. My setup is going to be a threaded shaft which screws into the back of the value body which will stick out the back of the gun. the piston (hammer) has a hole in it to slide along the shaft to guide to to the valve. I made a custom threaded adjustment knob.. i just wind the knob in for more power of back it off for less. this will be sticking out the back of the gun as well.         ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: kruzaroad
Date Posted: 21 Jun 2026 at 6:47pm
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How does actuate the valve? Being that shaft is screwed into the valve and im assuming doesn't move, and hammer is hollow in the middle to slide down the shaft, im at a bit of loss as to where the hammer contacts on the valve set up to cause the pushing motion to open the valve. Im looking at it from limited understanding and basing it off a 1322 valve which strikes a central pin pushing the valve open. What am missing/ not seeing in your design? Love the pics with lathe in motion. Brings back memories from yesteryear. Very envious of you guys who set up a permanent base and set up with the tools to make use metal.👍 |
Posted By: nunga
Date Posted: 21 Jun 2026 at 7:40pm
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So the shaft screws into the housing just above the valve. the hammer slides down the shaft and hits the Valve  ------------- 2nd place HP springer - WFTF World Championships 2014 |
Posted By: kruzaroad
Date Posted: 21 Jun 2026 at 8:01pm
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Gotcha. The valve is off set from the center. Which i assume is part of the reason it has a central guide. To stop the hammer tilting as it hits. Cheers |