It uses co2 and is designed to shoot projectiles.. so.. I started investigating an idea i had to convert the .68 semi-auto marker to .22 single shot pellet. 

Basic idea is disable the blowback, and create a slot for bolt action like a Crosman 2250.

Below is the basic function of the paintball gun:

Then below the idea of the conversion:

First was solving blowback, this system uses a hammer to strike the valve pin, and a flat section on the pin allowing gas to flow through and reset the hammer. 

I filed the flat section rough and filled with JB Weld. When dry file and sand to fit the valve hole, and hope the gas is redirected to the pellet. 

This didnt work 100% as there was hammer bounce leading to a nice farting and wasted gas. enough to open the valve but not reset the hammer. I found there was around 5mm preload on the hammer spring.

Next step was a firmer but shorter spring, coupled with 10-15mm free flight for the hammer. This meant the hammer hit the valve pin then hit the firm spring to absorb the energy rather than throw it back at the pin. 

 

This worked just enough. Resulted in a hammer that flops around freely, but I can live with that.. 

Next was the breech, this was cut out with a half-buggered drill press, and a $4 Aliexpress end mill bit then filed / sanded to acceptable finish.

Next up is the Bolt; this will use the existing alloy bolt which is attached to the hammer. It was cut in two sections so pulling back cocks the hammer, then push forward to close breach. Filed, sanded and fitted with a neo magnet so the bolt can stay open when loading. 

Simple bolt handle made by a double end thread rod (Aliexpress), and cheap metal guitar knob (Aliexpress).

Cocking slot was precision cut on this same milling rig (cringe now):

But cut ok.. 

Filing will smooth the edges for smooth cocking. This is by no means planned as an exhibition or match grade rifle 

But, this is a bit of fun, and hopefully something functional at the end. Below is where I am at; a functioning bolt action single shot .68 paintball gun. 

(Also shows the 'fuel filter' planned for a suppressor. From.... Aliexpress)

Oh.. the barrel. It is now cut to 19", Crosman 2260 barrel. Good enough for this project. It will be mounted using .68 paintball barrel as a shroud.

NEXT steps involve a little more accurate machining than my hand tools can allow:

- bushes to centre the .22 barrel inside the .68 barrel

- an insert in the current bolt that will be a flow through probe to seal the barrel (like a 2250)

- muzzle end bush will need to be an adapter for the 'fuel filter' supp. 

The above will prove if it will function and to test the power. Updates coming soon. 

 cheers mike

Yeah its a bit of fun. problem is I have to get it all functioning good to go, before I can see if it has enough power to be useful!

 cheers mike

Update: I trialled shooting loading a pellet into the barrel, then orings on the breech end of the barrel securing into the paintball bolt. This gave me a huge 1.8fpe!! and 180-230fps

So i did a trial with spring replacements based on assumption the valve is not being opened fully.

1) the short firm spring was replaced with a long firm spring - no free flight and minimal pre-load to try and avoid bounce

2) Conical soft valve pin spring was replace with a bodge job made from the firm spring - idea is the strong hammer spring opens it up fully, and a strong valve pin spring returns closed and resists bounce. 

It worked! not fully where i want it but it is now 7.8fpe, and much louder so a good amount of gas used.

The valve pin spring bent the last couple of coils where it was heated and widened to fit the seat to keep it centre - I have ordered more springs  (to try in a month when they arrive in a month from AliExpress) and will make a spring guide of sorts, to keep the spring seated centre without needing to be conical shape.

(Silver Springs are the standard paintball jobbies)

 cheers mike

Cheers! Nicely explained indeed. 

I think another issue with the test is that the paintball bolt is a 14mm cavity, so i guess once the valve shuts the gas is expanding in there as well as down the barrel?? 

Plan is the probe insert which will act as a narrow transfer port on 3-4mm, blasting directly behind the pellet... parts request is in the queue for lathe time with a certain tuner.

Once complete I can play with increasing valve volume, more springs etc etc.. 

Another update, I just picked up another cheap paintball marker for future project; this one has an electronic trigger that is super light compared to the current mechanical job.. 

Update.. nothing on this one..

BUT, i did get a couple more cheap paintball guns of Trademe to hatch some more evil plans. Both are electric triggers which a very light compared to the current mechanical.

Current project has a long bolt insert which acts as a transfer port of around 70mm. Is this wasted space for gas expansion, or does it aid in power?

The next project may be a pistol version; if I make the barrel transfer port directly over the valve (like a crosman 2250), should this provide better use of the gas?

(Im a springer fan at heart so this gas stuff is a bit less known).

Below is a quick preview idea of project number 2:

 cheers mike

Cheers! A lot to lear and certainly fun playing...

I did have another idea, but tollerances may be a little tight to make successfully, and dont know if it would work well anyway...

But using the semi - auto blowback system + a self indexing .22 mag and a slim probe like a crosman 2250 to feed the pellets and seal the breach to make a semi-auto .22.

Gas is wasted on the blowback, so it wouldnt be high power, but should be ok for a pistol..

Just ideas for now

 to explain a lttle clearer a dissconnector is a mechanical part of a trigger that operates independantly of the actual trigger that catchs and holds a hammer in its full cocked position after being cocked by th bolt reciplicating to the rear,and hold hammer in full cock notch until trigger is released when trigger then engages the true full cock notch,holds it there until trigger is pulled again to fire next shot,all semi autos have some form of dissconnector in the trigger,getting this right and to function correctly maybe your biggest head ache for you semi auto co2 guns,as for blow back cycling the action using unused co2,thats still in barrel ,thats another very different issue,most semi auto bb guns use some form of blow back,most semi auto pellet guns are use some form of blow back to recock the action but neither are true semi autos in the true sense as they dont chamber a bb or pellet but fire them directly from their mags,this is very different to what you are thinking about,been toying with the concept of true semi auto pcp guns for some time,just for the hell of it,it can be done as fx and others have proven,but its not quiet as simple as it may seem,there are two bassic ways to go about this,one,the most common used for rifles is to bleed co2/hpa from barrel usually at muzzle and redirect it to cycle bolt and action,the other way is to use one the various ways of delaying the breech from opening until pellet is about to leave barrel and the use this residual co2 or hpa to cycle the action and load another pellet on return stoke of the bolt,thelater system is the only practical way to doso in a pistol as it operstes essentually to a recoil operated semi auto pistol,but without using recoil as airguns have no usable recoil,second world war german belt feed machine guns work on this delayed breech opening system as do several modern machine gus,its simple and absolutly reliable,bit long winded but interesting topic for sure,nobody yet has produced a truely practical semi auto pcp pistol as those acailable are simply cut down semi auto pcp rifles minus their buttstocks,sawn off rifles essentually,too big and heavy to be practical pistols as sawn off rifles usually are,there have been several true semi auto co2 handguns the old crosman 600 being one the first and still a goody today if you can find one,the fun of messing around with different co2 projects is there lot potentual for all sorts projects,dont give up on your paintball projects if nothing else they will keep you occupied and out of the pub eh!!

 cheers mike

Cheers Mike! Yeah this was just an idea for something that 'may work'.. paintball guns have the transfer port in a large bolt, and as its joined to the hammer the hole in bolt lines up with valve hole beneath it to release gas at correct time. These models use the gas to have a small portion flow back through the valve to reset the hammer on the trigger sear. BUT, they are fairly basic and crude; i imagine these entry level guns arent designed for best use of gas and consistency. 

Perhaps the idea could be used as single shot, but using the magazine for a multishot version.. 

These are just a little bit of fun to play around with, help keep me thinking.. 

the idea of 4 weeks lockdown sounded great, heaps of time to tinker... But that didnt take into consderation having an intense 2 & 1/2 year old running around, and the wife and I trying to get in full time work! i havent been able to do a thing

 cheers mike

In 4 weeks of lockdown I have managed to shoot 3 pellets, and cut a groove in an alloy suppressor adapter so it fits firm inside a paintball marker with an o ring. Such a small achievement felt mighty, as its the only thing i have done between working from home and entertaining a 2.5 year old!  

Looking forward to getting it technically working so I can check the power and balance the springs etc to stop the hammer bouncing. 

May do a little more work on removing meat from the valve body for a touch more volume, if it is needed. 

Then may look at making a stock for it out of a chunk of rimu I have laying around.

 cheers mike

If thats the revolver project, I recall it on the other forum - VERY impressive. 

The belt fed air rifle does look interesting. looking at the diagram the cycling looks simple - if you had the machines and skill to recreate. 

The company is a Tippman company - possibly the idea brought by the paintball company or an offshoot of the paintball gun company. Either way, interesting concept. 

I dont have a lathe so I had to get some parts made for me - the bolt probe, barrel bushings, suppressor adapter etc - the things that will make the project work. 

Then Covid hit and time ran short and it has sat waiting in the list of airgun jobs he has. That didnt bother me at all as it was always for a bit of fun and covid has been a crazy time for many so the delay is perfectly understandable. (I have a FAS 604 that needs an o-ring change that has sat here for 6 months without getting time to do it!)

But looking forward to getting it back and seeing what sort of power it will be putting out. 

The transfer port is long given the nature of the valve location etc, so hopefully there is still enough expansion down the barrel to fling some lead. 

Will update once its back in hand. 

 cheers mike

Lots of projects, not a lot of time.. This one wasn't forgotten but just out of my hands at the moment for the machining parts. If it turns out to be an ok shooter ill make a stock for it

I recall a crosman 357 that had a large barrel piece for paintball version, odd looking but im sure it would be fun.

Have a look at Air Ordnance;  http://air-ordnance.com/videos/" rel="nofollow - http://air-ordnance.com/videos/

its a belt fed pellet rifle, very recognizable as a tippmann paintball marker base (they are a tippmann company i think) using the paintball style blowback with a rod that rotates a thingy to index the next shot. 

 cheers mike

Well, back into this project - I finally got the bits done to get it together and running.

An alloy insert in the paintball bolt creates a narrower transfer port (gas has a long way to travel from the valve to the seated pellet)

The barrel has orings and the bolt seals over the barrel readu for the shot.

At the moment it needs some valvbe work - it still blows back after most shots; as a paintball gun its semi auto (this would be ok if it was machined to accept a multishot mag!!) but as ainbgle shot its wasted gas.

I have another valve on its way which i will just need to fill a hole to stop the blowback, then balance the spring strength to stop any valve bounce.

The barrel is around 19" with a couple of inches protruding into the massive 'fuel filter' suppressor.

As it is now the experiment was to see if a paintball gun sould be made to shoot pellets, and it definitely can. Accuracy needs to be tested but its all firm with no flex so that should be ok.

Consistency will be improved once the valve is sorted.

In terms of power, as it is its pushing out 11.3 footpound with 18gr JSB, thats with the wasted gas blowing past the valve..

Not fully tested yet but been a fun project. Not making a match rifle so closing the group a little will be fine for me.

I need to get a stock to fit it as its a little hard to shoulder comfortably to get your eye right.

Its light weight and plenty of length to find balance - holding in front of the hose if pretty comfortable

The bug buster is a good little scope - ideal for this type of thing as well as your backpacker 1322 idea.

 cheers mike

Haha yeah, not given up yet! Its got the potential to work so no reason to stop now!

Function is there, its just fine tuning the rest - valves are designed to blow back and thats proving difficult to change as the hammer hits from behind the gas - theres a bit of gas flow past the pin. An o ring should help stop it, if not i'll deal with it blowing back the hammer ready for the next shot.

Last test was 11 footpound so its not bad in itself, i changed to a new valve that didnt have JB weld patching it and also added a small expansion chamber so will see how its power is going soon. Atleast I have a decent supply of co2 on hand!