DIY Built airgun power??

[djmoe95]

Hi everyone!!
I'm new here and would like to put up a discussion on DIY airguns built with some AliExpress parts.
For now, I don't own any big branded airguns. Neither PCP nor break barrel as the place I live in doesn't have much suppliers. So, my only option (sort of) is to buy locally made action blocks and put together with some AliExpress parts. The things I outsource mainly are action block, AliExpress Z valve with regulator (sometimes that comes with paintball regulator), and high pressure air aluminium bottles (from AliExpress or some online shops in SEA). Barrels, I made myself with some 5.5mm bore carbon steel hydraulic pipes with AliExpress rifling button pushed through with an hydraulic jack. No choke, no tapered bore what so ever. Stress released with a propane torch and polished the rifled barrel with metal polish. Crown made with a countersunk bit and used multiple grades of sandpapers to get it smooth. Checked crown using cotton swab method. It shoots great with 0.5-1 inch groups at 50 meters. My set up is a 13 inch barrel with regulator pressure set at 2000 psi which I really don't wanna crank up anymore because with 3500 psi in reservoir, I'm only left with 1500 psi head room which I get around 45 good shots. The AliExpress regulator have sort of like a small plenum area built into their Z valve although I don't know how much cc I get from that. Shooting 22 cal 18 grain pellets, I get only 750-765 fps (22-23.4 ft-lb of energy) which I feels too weak for my liking. I tried to tweak with regulator set point and hammer spring tension. Installed multiple thickness sizes of HDPE spacer on the valve stem to get consistent valve stem travel distance to get consistent airflow. The transfer port on the valve is around 3.5-4mm. hammer spring is a spring that I got from my lil brother's cheap Chinese airsoft gun which I can adjust using a screw in the middle of spring stop in the back. With everything explained as far as I can, my question is how do I get more velocity/power without changing barrel length and is the power I got is maximum that I can get with current set up which I feels not really because according to the equation I've read somewhere, the maximum power = bore volume x pressure / 12. According to that equation, my maximum power should be around 80ft-lb which is nearly 4 times what I'm getting right now. So, my target power is around 45-50 ft-lb.
As a side note, I got velocities using cheap Chinese AliExpress Chrono which I find a bit not trust worthy. I also tried calculate (or estimate) the velocity using strelok app using POI drop which gave me nearly 1025-1040 fps.

Attached file descriptions.

1. AliExpress valve and regulator with small plenum area with red arrow.

2. My shooter with a shroud and regulator on.

3. My DIY barrel bore

 

[Long_Gun_Dallas]

Power is largely determined by the valve and porting. A lot of our guns nowadays employ semi balanced valves that are relatively easy to open. These have the rear of the valve stem exposed to atmospheric pressure so the force required to open is greatly reduced. Compared to a completely internal valve that is subject to the full operating pressure of the regulator. This pressure hinders opening. Ideally on a .22 the valve seat would be 5.5mm, ports the same. Though they would need to be elongated or bridged to avoid having the projectile fall into the port. I'm sure the valve and barrel could stand to have some port work done and this will help some. But I imagine it may be difficult to get much over 30fpe. And with rough operation of the gun with stiffer spring/heavier hammer, it may be entirely undesirable.

 

[djmoe95]

Power is largely determined by the valve and porting. A lot of our guns nowadays employ semi balanced valves that are relatively easy to open. These have the rear of the valve stem exposed to atmospheric pressure so the force required to open is greatly reduced. Compared to a completely internal valve that is subject to the full operating pressure of the regulator. This pressure hinders opening. Ideally on a .22 the valve seat would be 5.5mm, ports the same. Though they would need to be elongated or bridged to avoid having the projectile fall into the port. I'm sure the valve and barrel could stand to have some port work done and this will help some. But I imagine it may be difficult to get much over 30fpe. And with rough operation of the gun with stiffer spring/heavier hammer, it may be entirely undesirable.

So, that means I need a bigger port? I do have a valve with bigger hole on it around 5mm. And I could just change the transfer piece behind the barrel. I know most airguns you guys have had transfer port made into barrel itself but mine had two pieces. One solid barrel with it's bore as it's only hole and a small piece of brass that act as a transfer port to barrel. I do have a transfer piece which I made just for slugs although I never had any luck with being able to shoot slugs accurately. That piece has a bigger port with a bridge at the center of the transfer hole. The valve has a stiff spring behind the valve stem. But I never tried using it thinking the efficiency would be terrible. Gonna try out your advice tomorrow. Currently, out in the field shooting doves with longer 18 inch barrel to see if I can get any noticable difference.
A friend of mine have a Benjamin marauder .22cal and it is fun to shoot but not fun for tinkering. His shoots around the same fpe as mine did. But the difference is that the efficiency and the sound is better on his. His Benjamin has a short snap sound while mine has sort of like a whoosh sound like a blowgun. I think I accidentally made a pcp blowgun. LOL

 

[Long_Gun_Dallas]

I'd try maybe a weaker valve return spring as well. And you might consider making a SSG like so. It will keep the hammer from hitting the valve multiple times. (this will help efficiency a lot, will also make the gun sound snappier like the marauder) If you can, try and tune the gun for around 125 bar as well. In addition to the port work I mentioned. Of course you can try higher or lower reg pressure. But jsut an educated guess 125 bar should work pretty good.

 

[sb327]

Can you share a picture of the assemble gun? Would be interesting to see how everything is laid out.

Dave

 

[djmoe95]

I'd try maybe a weaker valve return spring as well. And you might consider making a SSG like so. It will keep the hammer from hitting the valve multiple times. (this will help efficiency a lot, will also make the gun sound snappier like the marauder) If you can, try and tune the gun for around 125 bar as well. In addition to the port work I mentioned. Of course you can try higher or lower reg pressure. But jsut an educated guess 125 bar should work pretty good.

Thanks for the Advice, Long_Gun_Dallas.
Tomorrow, I'll try that or some kind of other SSG with the same principle as there are some limitations because of the design of my gun. The principle behind is to stop the hammer spring before the hammer has touched the valve stem. That might definitely prevent or reduce hammer bounce. Actually my gun design would go well with a zero bounce hammer design from the guy named Face Off. But that's only for efficiency and the snappy sound that I likes. On the power part, in addition to the transfer port and valve tweaking, the barrel length really makes a difference as I found out today. the FPS went up to 850 which is nearly a 100 fps increase with just changing the barrel from 13 inches to 18 inches with other things untouched. Although I likes an increase in power with 18 inches barrel, I'd like to use the 13 inches barrel as going hunting/pesting with long guns is not a good thing for me because a bump on the barrel on the way could make a shift in POI. I don't know why my gun suffers from POI shifts a lot but I got used to the way it is and had a habit of being careful on where the barrel will be at all time. I found all over the internet about using a barrel band but the result I get from using barrel band is a 2-3 inches group compared to a free floating barrel with 0.5-1 inch. The band mess up the harmonic somehow as I've read on some forum posts. Anyhow, just gonna try out a few things tomorrow and see if there is any changes.

Can you share a picture of the assemble gun? Would be interesting to see how everything is laid out.

Dave

I'll take a picture tomorrow when I disassemble the gun to try out Long_Gun_Dallas's advices. You'll see a frankenstein of a gun for sure. LOL

 

[Long_Gun_Dallas]

15" is a very ideal length for comprimise between length and power for .22 caliber. I've tested a lot of barrel lengths. I have a .22 pistol with a standard valve like yours that will do 27fpe, but it is unregulated. It is easier to make more power without a regulator. That gun has a 7.6" barrel, but I do not normally shoot it at this power level. Normally is tuned way down to 15fpe for shot count, and less noise.

POI shift can occur for many reasons. Sometimes I simply find that the sight is faulty. Making small adjustments to your tune as well as trying different weight moderators (if you have any) can change harmonics and accuracy. Some people put thick rubber devices on their barrel to dampen vibrations. But I personally prefer to jsut tune the gun. And use ammo it likes at a power level it likes.

 

[djmoe95]

I did my tests this morning and came out failed happily. Changed to bigger port, removed the spring behind valve stem, set set point around 130 bar and installed short stiff spring that would reach its uncompressed length before the hammer hitting the valve. There was no change or rather a little bit decrease in velocity. The velocity maxed out at 750 fps with hammer adjusting screw fully screwed in and at 2000 psi set point with the hammer having a free moving distance of around 5-8 mm between the spring and the valve which I assume would not be bouncing around. But the thing that made me happy is now my gun also have that snap sound that I love. A lot quieter than before. Now I tuned it according to the 95% rule like everyone did. The velocity is now at 710-715 fps at around 20 ft-lb of energy which is way higher than some countries legal limit on airgun power. But as a hobby hunter, I'm looking forward to getting able to shoot high grain slugs at a velocity of around 850-950 fps which I assume would bag me some barking deer or a medium sized hog with my gun. For dog looked like wild animal (Coyote??? But doesn't look like one) which is a problem around my area, I've got a few down with my set up before. So, I'm gonna just continue finding more ways to get more power (e.g custom power plenum with adjustable volume??) if it's needed for an 13 inches barrel. Anyhow, thanks for the advices @Long_Gun_Dallas.

I've attached some photos and videos of my gun for you, Dave.
And a group of five shots at 25 meters with the gun clamped in.

 

[sb327]

I like it. Glad the spring mod works well for you.

Does anyone make an external plenum add on? The way it is made, it appears the plug could be removed and some volume attached there.

The above with some porting would yield some increase in power.

Thanks for sharing your build.

Dave

 

[djmoe95]

Good to hear that you like it. I'm trying to improve the build so that I can make my own homemade one with a lot of customizable feature based on this build. With better hammer adjustment, port sizes, valve and adjustable regulator built into the action block, adjustable 2 stage trigger and possibly a semi-auto one. Not a lot of ppl have access to airgun in this part of the world and with internal affairs in our country right now, it's one way ticket to get questioned by the authority for owning one.
Yes. I think the plug can be replaced with some kind of small plenum there. The problem is getting the thread size and O-ring fitted nicely. And have to study more into the bore volume and plenum sizes because with the plenum volume only mainly acting as chamber for usable air before the pellet leaves the barrel, my 13 inches barrel would benefit from it or not. If not, I would be spending more air or money on a part that's not necessary.

 

[heavy-impact]

A larger plenum like this 10cc will definitely help your new FX Panthera.

Air Venturi Avenger Oversized plenum

This is an oversized plenum for the AirVenturi Avenger in all forms. Fitment is straight forward but the stock will have to be cut or clearanced in order for the plenum to fit into or through the stock. My .25 Avenger with this same 10cc plenum is currently shooting 29 grain slugs at 990 fps...

aeswede.com

 

[Long_Gun_Dallas]

For reference, my 15" 22 starts wasting a lot of air much past 32fpe with pellets. It can do more, but it gets a lot louder and becomes increasingly more difficult to get more power out of. That is 960fps with 16gr pellets. I have a 14" .22 rifle as well and have it tuned to 880 fps with 16gr, but that one is unregulated. Generally, unregulated guns make more power if you really lean on them. But the 14" one is detuned pretty significantly for consistency and shot count.

Sounds like ypur gun is at least efficient now, and likely producing a good shot count.

Definitely add more plenum if you can. But I still believe the valve is struggling to open. Either due to its design, or lack of hammer weight, or lack of hammer travel distance, or lack of hammer spring force. Problem here is if you add too much force, you may end up damaging the valve. It is better to just have a valve that is easier to open in the first place. But this is easier said than done.

 

[djmoe95]

A larger plenum like this 10cc will definitely help your new FX Panthera.

Air Venturi Avenger Oversized plenum

This is an oversized plenum for the AirVenturi Avenger in all forms. Fitment is straight forward but the stock will have to be cut or clearanced in order for the plenum to fit into or through the stock. My .25 Avenger with this same 10cc plenum is currently shooting 29 grain slugs at 990 fps...

aeswede.com

Thanks for the advice, heavy_impact. So, 10cc is as per most post I've read would be 10fpe increase theoretically. Just need to figure out a way to measure thread sizes or a visit to lathe shop. I tried CNC router threading with a CNC I assembled out of plywood but didn't worked out well. And it's not FX panthera. It's just made in Thailand FXN panthera. LOL. I don't want FX to come knocking on my door out of copyright stuffs. Gotta give it new name with a laser engraver I think.

For reference, my 15" 22 starts wasting a lot of air much past 32fpe with pellets. It can do more, but it gets a lot louder and becomes increasingly more difficult to get more power out of. That is 960fps with 16gr pellets. I have a 14" .22 rifle as well and have it tuned to 880 fps with 16gr, but that one is unregulated. Generally, unregulated guns make more power if you really lean on them. But the 14" one is detuned pretty significantly for consistency and shot count.

Sounds like ypur gun is at least efficient now, and likely producing a good shot count.

Definitely add more plenum if you can. But I still believe the valve is struggling to open. Either due to its design, or lack of hammer weight, or lack of hammer travel distance, or lack of hammer spring force. Problem here is if you add too much force, you may end up damaging the valve. It is better to just have a valve that is easier to open in the first place. But this is easier said than done.

Long_Gun_Dallas,
I've acknowledged that every length of barrel has its limit on maximum fpe with individual set ups. So, it's on me for just loving a shorty. On efficiency part, I get surprised by the results. Filled 300cc bottle to 240 bar before heading out and after going through 2 of 15 pellets mags, the reservoir pressure is still around 200 bar. The sound of the gun is the best I've got of all time. The smacking sound of pellet hitting the bird is way louder (which results in other birds near it flying away) than the actual sound of the gun. Tried two different suppressors in combination with the different length of shroud to see if I can get James bond quiet. But there is a limit too. LOL. I'll definitely add a plenum and I have an idea in mind for a adjustable plenum using the same principal as a regulator. I think the valve opens easily but it might just be the spring still weak or because of the spacer I added on the valve stem. The hammer weight is another factor to consider too. Ah!!! Too many things to think about. Most of my friends thinks of me as a weirdo because I'm making airgun shooting like a scientific experiment while they're fine with pump air, load the gun, aim and shoot.

 

[Long_Gun_Dallas]

Haha, this is what a lot of us are here for

 

[sb327]

I applaud your determination. It seems like you have a pretty good setup.

As far as plenum size, the 1fpe/cc plenum is just a general idea to start from. The pressure used obviously changes the formula, among other factors.

Dave

 

[djmoe95]

Update if anyone interested.
Today, I tried to make sort of like a plenum using a co2 coupler with G1/2-14 thread on one size and m18 thread on the other. Used a tiny end cap thingy that came with the valve I have on the m18 side and the G1/2-14 thread on the coupler fit into the valve nice and tight. I don't know how much cc I got from that make shift plenum. But the gun now shoots 840-850 fps max with 18 grain pellets. That's 6-7 fpe increased. So, my plenum should be around 6-7 cc theoretically. Had to stop more tweaking the gun because I ran out of pellets. Have to order them 4-5 x500 pellet cans along with 22-25 grain slugs too. My wallet hurts with current prices but gotta bare with it until I could forget all about airguns.

Until I've got the cheap Chinese airforce frame and the other parts, I'll just stop tuning/ modifying the one I currently have. Then I won't have any problems like porting the current one if I just change to DIY airforce talon/condor.

 

[sb327]

That’s quite a significant jump in power. Sounds like you’re heading down the right path.

Dave

 

[djmoe95]

Update if anyone is still interested.
Got a new Z valve from Huben today. Ordered the one that came with a power plenum. Problem is that the fill probe is too close to the plenum and the coupler from my yong Heng cannot fit. But was able to find a temporary fix and now it's working great. The power didn't change significantly as I assume the plenum volume is close to my diy one. But the factory one looks nicer and smaller. The best thing about the valve is that it came with a lot of other hard to find O-rings that I'm looking for a long time.

 

[JDGriz]

A working formula for expected FPE is:

FPE=(C1*6894.76)*(C2/1000000)*LN((PI()*C4*((C3/2)/1000)^2+(C2/1000000))/(C2/1000000))*C5/1.356

where

C1 = Pressure/psi
C2 = Plenum volume/cubic centimeters
C3 = Caliber/mm
C4 = Barrel length/meters
C5 = loss factor (in .22, about 0.45 for light projectiles and 0.55 for heavy projectiles. Those numbers would be less accurate for other calibers)
LN() is natural log (base e), PI() is Pi.

Example:

Pressure/psi=3000
Plenum volume/cubic centimeters=10
Barrel caliber/mm=5.5
Barrel length/meters=0.5
loss factor=0.5
FPE=59.71509753

 

[djmoe95]

According to the equation, the calculated FPE is 124.106 ft-lb which is the FPE I shot the 123kg bear around 100 meters on a cliff around 39.99 degree incline which then fell into a bottomless pit in the dream last night (joking). I don't know where did I go wrong in solving the equation.