Semi Auto …..how hard can it be ?

Well how hard can it be to make a semi auto 😯 ….let me give you a clue …….”F****n hard” 😯 . Ive been reading lots again , going deep under cover on the Russian sites to gain info ( at much risk to myself and my pet cat “Millie”) . Apart from FX airguns Monsoon ( and Daystate,s never to be released electronic controled full auto ) the Russians seam to be the only ones who have managed to make a semi auto work!. Ive only seen two manage it Dudis and Victor620 , with both looking to market their guns .
. If im going to have a blow back operation of the hammer , there needs to be an understanding of spring rates and timing of the components (which i dont have yet lol). From what ive read , to get blow back im only going need to use about 1 % – 3 % of the air used to fire the pellet ( info supplied by Bricks20 ) to push back the hammer , so thats the easy part done ………….hehe if only.
So heres my idea ( nothing radical here! ) following the idea of the monsoon with a spring loaded magazine.

Hammer would be released by the trigger , the black spring wire forcing the probe forward and the pellet into the bore. The wire spring would then need to have enough force to keep the probe held in the bore when the valve releases air or id need a locking mechanism to hold the probe shut .The hammer would continue on past the probe onto the valve releasing air.

As the pellet exits the barrel ,air is forced into the blow back valve , driving the hammer back ,which collects the probe , the mag would index and the hammer would lock on the trigger group 😯
Now dont jump on me just yet ,i freely admit its early days and ive got BIG HOLES in my understanding. Im just throwing stuff into the void to see what washes up !!!!!
This post is one thats going to run for a while , i think ! 😀


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Thanks for the pics Cygnus X and your mate 😀 , could make one of them ,if my dam lathe worked lol. Like to make it to the Monsoon size to avoid having to make them :D. Not looking to go full auto like in the vid as that would get me jailed !, im just arfter a fun gun. Im just designing at the mo and reading the law lots . Im trying to make the breach as small as possiable but having problems fitting the springs in Shadoh,s idea , early days thou.
The law over here is abit fuzzy , theres abit of a grey area which is not always good to mess with 😕 ,the fact that the manufactures have been told if they import or sell a auto ,then the goverment will put in place a law against them !. To me this means its not illegal ,i can make one but not sell it which i dont want to anyways and also its got to be below FAC levels (12lb) . Once over it would be classed as a auto fire arm which only drugs dealers are allowed to have over here!.
Crossmans Night hawk is sold here but got under the law by being at 6lb and infact its realy a revolver , indexing on each trigger pull , maybe this is the way to go!. Ive got drawings of the Colt 45 naval revolver but that mech looks a nightmear to make !.
No idea what the diff is but between the Mons and Revo but i like the Revo more ! 😀

pretty simple huh….gotta love the look of that spring FX uses ….Theoben uses same principles…but just have a slightly larger wheel, so it has room for 12 rounds in .25 and .22

whel is as long as a kodiac pellet, and complete lenght is about 15mm if i remember correctly….the “pockets” for the pellet is 6mm

dont have the measurements yet, but heres some pictures to keep you entertained 🙂 my buddy who took the pictures didnt have a caliper on him at the time..

take a look at this guy’s full auto monsoon…i’m sure he can give you some insight into this gun:

also, what’s the difference between the Revo and the Monsoon? i ant to buy one of them but I dont know which one I should get.

Anybody out there who can measure the Monsoon mag for me ,need to know how wide it is , so i can find out the stroke of the probe. Having another go at this as my lathes motor give up the fight !. Only lasted 14 months 😯 so im gona moan about it on the suppliers forum!. 😀

Thats another reson for the wire spring on my drawings , because as the probe moves forward the force of the wire would act downwards to lock the probe in the “L ” shaped slot. You can see the monsoons probe is divided in two where the end rotates. Think its all about balance of the cocking spring against the hammer spring against the pressure of the blowback valve ……i think!. Im going to make a blowback valve that i can screw onto my Stealth LDC adapter to see how much force is generated but ive got to find the time for a new valve first. Its getting warmer so it wont be long before il want to go shooting 😀 The 1% to 3% needed to have blowback dont seam alot but Bricks 20 knows what hes talking about .The Monsoon,s springs are quite small diameter and long in length. This is the one time i wish i was better at maths but thats not my strong suit. I dont want to copy another gun this time but there all worth studying before i start on CAD. 😀

Naked Monsoon……ohhhh!! 😯

The tricky part of a semi auto is being able to adust the cocking force of the bolt and hammer so it is not to strong. How will you adjust the cocking force?

So the rotational spring would just add a bit more tension on the probe? Then when rear pressure is high enough it totally lets go? I get it.

Cyg, on the drawings above the “probe” would have a cocking handle out the side of it so you could manually cock the gun or the action would do it for you after the shot. I believe what you have described with the monsoon is very similar to what we have drawn above? The only difference being where the air pressure comes from to cycle the action.

Adjusting the springs could be done by the threaded plug as you say Shadoh , its the way my Tv4 copy adjusts the main spring tention. Forgot about this damit 😀

The probe can be held in place by a rotational spring ,it would rotate a pin into a slot to lock the probe into the barrel . Believe the monsoon works by this method. Ive just found the Paint program on my PC lol so im using it at every avaliable oppertunity….hehe!

Have to get my head around the monsoon just to clarrify some isuues , always looked complicated thou 😀 .
Intresting link….. that wouldnt be Walkonking grip conversion on there!!!!!

Ooops I forgot to post the link for regualtors and rams..

Plamers Pursuit Shop

first of all i would make the piston work on the cocking handle and not the hammer, bit easier to get to work as theres plenty of designs to copy

do you know how the monsoon works ?

it has a shroud, where theres a piston…the over pressure in the shroud pushed the piston back which is connected to the cocking handle….this way power is not wasted by bleeding the barrel.

cocking handle is pushed back and takes the hammer with it….a spring in the shroud brings it piston forward, and a spring in the cocking handle bring it forward too, and slams the breech close….

you press the trigger and everything starts all over…

on the monsoon you dont want the power set too high as this will recock the gun violently leading to failures…but i bet with right spring tensions this could possibly be overcome

on the airforce rifle a cocking system could be made quite easy…by having a shroud that can mode back and fourth same distance, and link it to the breech cocking handle….when the pellet exits the barrel pressure will force shroud forward and pull the cocking handle forward as well…leaving the rifle ready for another pellet, just need to close the breech which would pull the shroud back again…optimal no…but hey its an idea

accuracy would prolly not be the best as the shroud is moving around

indexing the magazine would be easy, by using a self indexing mag like on the monsoon and rapids

You could always use a threaded plug behind the springs to adjust tension. One thing I wonder about is what keeps the bolt from blowing backwards before the pellet gets moving? Do the other guns use the spring tension to accomplish this?

Thanks for the response guys 😀
Now remember im abit of a leech for ideas , so il bleed you lot dry !!! 😀
Im not into paint ball but ive been on plenty of PB sites to gain info and as you say Adam ,auto seems run of the mill now. Im only looking for semi auto as i dont see any need for full auto.
As Jezx says blowback for round ammo is alot easier than pellet guns where the barrel bore has to seal before the pellet exits . It also needs to be more efficient in the use of energy and timing ( the hard part). I dont see the trigger group as a problem , as there are plent of designs out there for the auto powder boys which would work.
The resson i used the wire spring on my design is because its on the monsoon 😉 and being outside the breach it would be easier to adjust the tension than a coil spring! but the design is here to be ripped apart 😀
Shadoh …..if theres one guy with lots of ideas on the TAG …then your the man 😀 .Like your idea lots and im going through the thinking stage of how it could be done (pros and cons……. like life ….hehe ). Spring rates looks like the big thing.
Im going to make an adaptor for my stealth ,to fit on the 1/2 inch UnF thread to see if i can measure the amout of blowback generated……….just asoon as i make a new valve that dont leak ( ….dont ask….. 🙁 ….)
When im at my girlfriends my M/C shop is 10 miles away 🙁 so i need something to play with on the labtop , and designing the next project is it 😀 …….or i have to lisen to how the days shopping /school run went 🙁

… …. Shoot me NOW !!!!!!! PLEASE
L8r all………the sheds calling

This might simplify the assembly a bit? This was done fast so dont pick at it to much.

Rifle is ready to fire. Bolt is closed and hammer is cocked and ready.

When the gun is fired the lower spring pushes the hammer into the valve which opens and sends the pellet on its way.

Once pressure reaches the bleed line farther up the barrel it pushed the bolt assembly backward and pushes the hammer along with it. This would re cock the gun. It must be enough to compress both upper and lower springs.

When the pressure drops in front of the bolt mech the upper spring pushes the bolt assembly forward leaving the gun cocked and ready.

interesting design . the vertical spring bar (black ) throws me a bit off .? but having the ported barrel to and alternet hammer cocking looks good ,

the cr600 has a desent setup , which if a gun is made with a similar style blow back and a longer prob style bolt like your , it can acheve a good semi auto working . if the probe moves the pellet and seal in side the barrel for 1/2” you get lots of speed befor it kiks the bolt out and loses air power .
it is very hard to make a semi auto , not just the pellet load /fire but the trigger assembly to . i have made 3 with some success , but 2 use balls wich makes it way easy . i have one in the works now that seem like it will be awesome , but the springs /blowback /airpressure / porting, may be completly wrong , you’l never know till its all done .
good luck .

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