How semi auto function is achieved in an airgun

[Pale_Rider]

To the best of my knowledge, there are five different semi auto platforms:

1) Recylcled Air Piston 

This is the same concept seen in many semi auto PBs. For the first shot the bolt must be cycled manually. After the first shot, there are holes in the barrel that capture the air behind the projectile. This captured air pushes a piston back to cycle the bolt for the subsequent shots. AEA, hatsan, and other companies implement this system to achieve semi auto. It’s my least favorite because lead will eventually build up inside of the piston mechanism. Just one extra thing to maintain. 


2) Hammerless

Contrary to the name there actually is a hammer with a spring that is used to expel the air that will push the projectile. Only difference is the hammer is not cocked manually with a bolt; it is cocked from air pressure. It really should be called a boltless system. Many have voiced their opinions about this potential safety hazard. Being that the gun is cocked and ready to shoot as soon as you fill it with air. I’ve never had an issue with it and the safety has proven reliable in both my hubens that have this hammerless system. This system is extremely efficient and capable of producing power that would require HEAVY modification in a platform with conventional valve. 
Huben invented this system and LCS used the same system in their sk19. I assume the Leshiy 2 functions similarly. Also curious how steyr makes their guns semi auto.

3) Electronic valve

In this system an electronic valve and solenoid are controlled by an electronic control unit. The solenoid, acting as the hammer, knocks open the valve to expel air. This system allows for very fine tuning and the ability to select a different tune in a matter of seconds via a display screen. Daystate utilizes this electronic technology without the semi auto feature. It’s the reason why the bolt is so smooth and easy to cycle, there’s no hammer spring that needs to be compressed. Currently, there are no electronic semi auto airguns being made. At one point evanix made them, also drozd.


4) Balanced Valve

Here the energy from a balanced valve is used to cock the hammer. The bolt is manually cocked for the first shot. When the hammer hits the balanced valve, air is released and the valve stem is powerfully sent back to seal the valve. The energy from the valve stem resetting is enough to push the hammer back for another shot. There’s a fellow on GTA, goes by jackssmirkingrevenge, who developed this system. Although, his airguns was only full auto. To make it semi auto a sear would need to be added to catch the hammer. I was really impressed how he was able to get the valve to seal using very low pressure, 400-600 psi. It’s an intriguing and simple system that deserves more R&D. 


5) Diverted Air System

Air is used from the reservoir to cock the hammer. The bolt and hammer are connected so that each time the hammer is cocked the bolt moves back to allow a spring loaded mag to rotate for another shot. This system is used in mechanical semi autos manufactured by Evanix




To those who have owned one or more of these platforms, what are your thoughts on them? 

 

[dizzums]

not a fan of relying on electric power in a gun .. ive had a couple of hatsans and i think the design concept is superb ... its the execution of the concept that leaves much to be desired, it would take alot more precision machining and quality materials to make a hatsan an excellent gun and im sure cost and profit is why they butchered the original design .. im sure the actual guy that designed the system hates what they did to his concept lol ..

 

[bamavet55]

Does the Daystate Red Wolf count?

I owned one in .22 caliber HP. The rifle has beautiful gray/red, laminate stock. No pcp I've ever owned was more accurate. Of the ammo I fed it, this gun shot the pellets and slugs alike with great accuracy. The cocking cycle is the smoothest of any rifle I've shot. It is as quiet as the Taipan Veteran of the same caliber.

A few weeks ago, I traded this gem for a Daystate Revere .22 cal (reg). I don't regret the decision. 

Why? 

The Red Wolf measures 50 inches with the 0db moderator.

The Revere measures less-than 40 inches -- if memory serves...

 

[john8]

Go hammerless, I've 3 Hubens and a LCS, ease of dialing in wanted performance, barn safe to a firebreathing monster. The safety issue has been a nonissue for me, always treat your gun as it's cocked and locked. There is a learning curve for operating parameters, quickly learned.

 

[Long_Gun_Dallas]

not a fan of relying on electric power in a gun .. ive had a couple of hatsans and i think the design concept is superb ... its the execution of the concept that leaves much to be desired, it would take alot more precision machining and quality materials to make a hatsan an excellent gun and im sure cost and profit is why they butchered the original design .. im sure the actual guy that designed the system hates what they did to his concept lol ..

Indeed. The semi auto hatsan I had worked well, but it was a two parter. 

Air was taken from the transfer port and diverted to a gas piston (in between bolt and hammer, normally airguns have two holes bored for hammer and bolt, this had a third in the middle)... that would reset the hammer. 

While there was a cup on a connecting rod I side the shroud that would capture spent muzzle pressure and actuate a gear and rack system to operate the bolt and feed the next round. 

Overly complicated and clunky in my opinion. And LOUD. But very reliable. Until you throw a moderator at it and alter the back pressure. This disturbed the dynamic of the cup that cycles the bolt. I made some workarounds, but it ended up being very hard on the gun, and even damaged the trigger mechanism from getting very hard lockup from the increased forces needed to overcome the back pressure. I broke some other parts as well. 

 

[Pale_Rider]

dizzums

not a fan of relying on electric power in a gun .. ive had a couple of hatsans and i think the design concept is superb ... its the execution of the concept that leaves much to be desired, it would take alot more precision machining and quality materials to make a hatsan an excellent gun and im sure cost and profit is why they butchered the original design .. im sure the actual guy that designed the system hates what they did to his concept lol ..

Lol would be interesting to see this design with better machining and quality material

Does the Daystate Red Wolf count?

I owned one in .22 caliber HP. The rifle has beautiful gray/red, laminate stock. No pcp I've ever owned was more accurate. Of the ammo I fed it, this gun shot the pellets and slugs alike with great accuracy. The cocking cycle is the smoothest of any rifle I've shot. It is as quiet as the Taipan Veteran of the same caliber.

A few weeks ago, I traded this gem for a Daystate Revere .22 cal (reg). I don't regret the decision. 

Why? 

The Red Wolf measures 50 inches with the 0db moderator.

The Revere measures less-than 40 inches -- if memory serves...

The red wolf doesn’t count because it’s not a semi auto. It does have most of the parts to make it a semi auto. The bolt would need to be automated and the programming to make it semi auto would be relatively easy.

Go hammerless, I've 3 Hubens and a LCS, ease of dialing in wanted performance, barn safe to a firebreathing monster. The safety issue has been a nonissue for me, always treat your gun as it's cocked and locked. There is a learning curve for operating parameters, quickly learned.

I have 2 hubens, an sk19 and an AEA terminator. Contemplating on selling the sk19 and terminator. Might convert one of my hubens to a .177 like you did. Would be nice to be able to sling slugs without having to crank up the power like the .25. And retaining a high shot count

 

[Guest]

Evanix has a different System,

a portion of the air goes directly to reset the hammer, clean air system but you lose a bit of power like that.

 

[napairgunner]

I's an interesting discussion but I've never seen the point of semi auto it's an interesting engineering feat but that's about it as far as I am concerned.

 

[theLBC]

i have a leshiy 2, which might not fit exactly into one of the categories,

immediate follow up shots aren't a requirement for everyone, but can be of use for some kinds of hunting, and is enormously fun if you enjoy steel arcade type shooting or plinking and want something less expensive to shoot than conventional firearms (particularly with ammo prices right now).

my intention was to only buy/own one air rifle, so i wanted something that would to everything, as long as reasonable accuracy wasn't sacrificed.

because of the way the trigger actuates the valve more or less directly (via a lever) on the edgun, some people aren't going to like it (compared to a typical target trigger), but i have used many terrible triggers over the last 40 years, so this wasn't so hard for me to get used to (i shoot da/sa handguns with 10lb triggers).

it may not be for everyone, but being able to dump the magazine in less than a couple seconds is pretty impressive, even with that trigger and it being my first hour behind the gun. you have to slow it down to even see all 8 shots. i am probably faster now.



https://youtu.be/Od8kOn29J1c

 

[Pale_Rider]

Evanix has a different System,

a portion of the air goes directly to reset the hammer, clean air system but you lose a bit of power like that.

I vaguely remember reading about the air speed using that diverted air to reset the hammer. How does it cycle the bolt or rotate the mag?

I's an interesting discussion but I've never seen the point of semi auto it's an interesting engineering feat but that's about it as far as I am concerned.

The fact that it is an interesting engineering feat is one of the reasons I buy them. The other is I find it redundant and boring to manually cycle a bolt every shot. The only guns I enjoy manually charging are cowboy lever action rifles like the Sumatra’s and Careers. 

i have a leshiy 2, which might not fit exactly into one of the categories,

immediate follow up shots aren't a requirement for everyone, but can be of use for some kinds of hunting, and is enormously fun if you enjoy steel arcade type shooting or plinking and want something less expensive to shoot than conventional firearms (particularly with ammo prices right now).

my intention was to only buy/own one air rifle, so i wanted something that would to everything, as long as reasonable accuracy wasn't sacrificed.

because of the way the trigger actuates the valve more or less directly (via a lever) on the edgun, some people aren't going to like it (compared to a typical target trigger), but i have used many terrible triggers over the last 40 years, so this wasn't so hard for me to get used to (i shoot da/sa handguns with 10lb triggers).

it may not be for everyone, but being able to dump the magazine in less than a couple seconds is pretty impressive, even with that trigger and it being my first hour behind the gun. you have to slow it down to even see all 8 shots. i am probably faster now.







https://youtu.be/Od8kOn29J1c

The L2 fits somewhere in there, I’m just not sure what system they use to make it semi auto. 


Yea I’m not much of a precise target shooter or need the best trigger. The accuracy that I get from the semis I own is not too far off what the best bolt action guns can achieve. And it’s a lot more fun 

 

[Guest]

As the hammer is pushed back by the air it carries the bolt too ( bolt and hammer are basically one unit connected by a rod ), the bolt then once retrieved from the mag frees it to rotate since it's spring loaded.

 

[DaystateRebel]

My L2 is a lot of fun, as theLBC said you can empty the magazine in 2-3 seconds. It's awesome to be able to stay on target for follow up shots if/when the first one doesn't kill a bunny outright

 

[Pale_Rider]

As the hammer is pushed back by the air it carries the bolt too ( bolt and hammer are basically one unit connected by a rod ), the bolt then once retrieved from the mag frees it to rotate since it's spring loaded.

Seems like a simple design, I like it. There were issues with the mechanical evanix semis, did you experience any?

My L2 is a lot of fun, as theLBC said you can empty the magazine in 2-3 seconds. It's awesome to be able to stay on target for follow up shots if/when the first one doesn't kill a bunny outright

If you enjoy mag dumps in 2-3 seconds, try a huben; dumps a 17-19 round mag as fast as you can squeeze the trigger. And it can be adjusted unlike the leshiy. Only downside is the mag is not removable. 

 

[Guest]

Very early there was an issue with the magazines that only took 18gr + .22 rounds,...Exanix quickly came out with Magazines that would take the 14.3gr too after that my Airspeed was flawless, I hear that the latest models are even more refined and work great.

 

[Pale_Rider]

Good to know. Have been thinking about picking one up for a while but hesitated because of those first issues and the lack of info thereafter. Think I’ll be grabbing one now

 

[Cruisers]

"Also curious how steyr makes their guns semi auto". Does this statement mean you're not sure how the Hunting 5 Automatic works? Got one and have wondered many times just how it does what it does.

 

[thammer]

Kral for sure uses a variation of the recycled air piston and I believe AEA does it this way too. Kral has a piston cylinder that rides the barrel inside the shroud with a push rod connected to the rear of it and a cocking lug in the breech. When you fire the gun and the air exits the barrel it goes through an airstripper forcing the volume of air backwards driving the piston to the rear thus cocking the gun for an additional shot. It does require manual cocking for the first shot though. The benefits I see are simplicity and its using air that was already used to power the projectile after its finished so it is truly recycled vs having to share a portion of the released air between the shot and cocking of the gun. Seems more efficient this way on the simple side of a semi auto. But no where near the adjustability of a Huben/leishy style gun. If not regulated the simple style will not work on a high fill or once it's dropped to low pressure since there's not enough air to cycle the hammer. If you really tune it for efficient air use its the same way with not having enough air volume after the shot to cycle. 

 

[Pale_Rider]

"Also curious how steyr makes their guns semi auto". Does this statement mean you're not sure how the Hunting 5 Automatic works? Got one and have wondered many times just how it does what it does.

Yes I’m not sure how it works. I assume they divert air from the reservoir since the steyr is a relatively low power semi auto like the mechanical evanix rifles. 

Kral for sure uses a variation of the recycled air piston and I believe AEA does it this way too. Kral has a piston cylinder that rides the barrel inside the shroud with a push rod connected to the rear of it and a cocking lug in the breech. When you fire the gun and the air exits the barrel it goes through an airstripper forcing the volume of air backwards driving the piston to the rear thus cocking the gun for an additional shot. It does require manual cocking for the first shot though. The benefits I see are simplicity and its using air that was already used to power the projectile after its finished so it is truly recycled vs having to share a portion of the released air between the shot and cocking of the gun. Seems more efficient this way on the simple side of a semi auto. But no where near the adjustability of a Huben/leishy style gun. If not regulated the simple style will not work on a high fill or once it's dropped to low pressure since there's not enough air to cycle the hammer. If you really tune it for efficient air use its the same way with not having enough air volume after the shot to cycle.

Thanks for the insight Troy. I do like the simplicity of the system but also dislike the thought of lead building up, in the piston mechanism, from the recycled air. I own an AEA terminator that uses this system and has proven reliable so far. But I haven’t shot more than 200 pellets through it to experience any lead build up in the piston mechanism. 

 

[rickpeterson]

To the best of my knowledge, there are five different semi auto platforms:

1) Recylcled Air Piston

This is the same concept seen in many semi auto PBs. For the first shot the bolt must be cycled manually. After the first shot, there are holes in the barrel that capture the air behind the projectile. This captured air pushes a piston back to cycle the bolt for the subsequent shots. AEA, hatsan, and other companies implement this system to achieve semi auto. It’s my least favorite because lead will eventually build up inside of the piston mechanism. Just one extra thing to maintain.


2) Hammerless

Contrary to the name there actually is a hammer with a spring that is used to expel the air that will push the projectile. Only difference is the hammer is not cocked manually with a bolt; it is cocked from air pressure. It really should be called a boltless system. Many have voiced their opinions about this potential safety hazard. Being that the gun is cocked and ready to shoot as soon as you fill it with air. I’ve never had an issue with it and the safety has proven reliable in both my hubens that have this hammerless system. This system is extremely efficient and capable of producing power that would require HEAVY modification in a platform with conventional valve.
Huben invented this system and LCS used the same system in their sk19. I assume the Leshiy 2 functions similarly. Also curious how steyr makes their guns semi auto.

3) Electronic valve

In this system an electronic valve and solenoid are controlled by an electronic control unit. The solenoid, acting as the hammer, knocks open the valve to expel air. This system allows for very fine tuning and the ability to select a different tune in a matter of seconds via a display screen. Daystate utilizes this electronic technology without the semi auto feature. It’s the reason why the bolt is so smooth and easy to cycle, there’s no hammer spring that needs to be compressed. Currently, there are no electronic semi auto airguns being made. At one point evanix made them, also drozd.


4) Balanced Valve

Here the energy from a balanced valve is used to cock the hammer. The bolt is manually cocked for the first shot. When the hammer hits the balanced valve, air is released and the valve stem is powerfully sent back to seal the valve. The energy from the valve stem resetting is enough to push the hammer back for another shot. There’s a fellow on GTA, goes by jackssmirkingrevenge, who developed this system. Although, his airguns was only full auto. To make it semi auto a sear would need to be added to catch the hammer. I was really impressed how he was able to get the valve to seal using very low pressure, 400-600 psi. It’s an intriguing and simple system that deserves more R&D.


5) Diverted Air System

Air is used from the reservoir to cock the hammer. The bolt and hammer are connected so that each time the hammer is cocked the bolt moves back to allow a spring loaded mag to rotate for another shot. This system is used in mechanical semi autos manufactured by Evanix




To those who have owned one or more of these platforms, what are your thoughts on them?

Not sure if this is a 6th type, or a variation of a Hammerless valve. In 2009 I built a self-cocking blow-open regulated PCP based on the Cardew GC2 valve. I put an adjustable return spring behind the plunger and used a Benjamin 422 semi-auto lower to catch it on return. The upper shown is a DAQ 308, but I planned to build an upper that held 3 bullets in-line like the Benjamin 422 and Drulov Du-10. The trigger sear released the piston which was pushed back by air in the firing chamber to expose the transfer port. When the adjustable piston rod moved back it let the regulator close preventing air from feeding from the main tube into the firing chamber When the piston returned it closed the transfer port and pushed the regulator open until the firing chamber reached 3,000 PSI. Then, assisted by Bellville washers, firing chamber pressure sealed off the 4,500 PSI in the main tube. IIRC, all of this happened as fast as I could pull the trigger.

 

[crazyaust]

Aka edgun leshiy 2