Some of you might know me from my instagram account called longrange_airgunning and know that every now and then I like to turn an airgun into a project, just for fun and for the challenge of tuning it. This time it was a FX Impact MKII and I wanted to turn it into the ultimate compact setup with a fairly large shotcount without sacrificing power. I still had a 40cm stainless steel barrel from a previous project (the Dreamline Compact with pistol length barrel build):
The 40cm long barrel on the floor is the barrel that is the centerpiece of this Impact Compact build. The two barrels (20cm and 40cm long) on the photo were actually one piece before the Dreamline build. Specifications of the barrel: Lothar Walther stainless steel .22 barrel without choke with a 1:17.7 twist. It used to be a 18mm thick barrel but to fit in the impact it had to be turned down to 14mm thick. While fitting it in the impact we saw that barrel was just a tad bit too short to fit a moderator to it. The thread came past the scope rail but the end stop of the thread was 2 or 3 mm behind the end of this rail so it couldn't bottom out. Since the thread length was long enough we decided to make an extension piece to move the end stop of the thread 5mm forward so a 30mm moderator could be fitted.
So now that the barrel is chosen the rest of the setup had to be chosen. SInce I bought an Impact M3 one of my MKII impacts 'lost' it's purpose so that was going to be the base. Other items and specs I wanted to include are the following:
First things first to get started:
Stripped the Impact MKII of it's accessories and started collecting the 300cc bottle and extended rail. The extended rail was easily taken care of by a trade with a friend, the 300cc bottle was a different story. Couldn't really find one in europe (out of stock) so Johan Axelsson was kind enough to send one over. Why the Ergo Deluxe Tactical grip? Just because I love to use that for shooting standing and some quick bench work. Since I also wanted to be able to shoot from any underground I decided it needed a bag rider but it needed to be lightweight. I really like my buttstocks with bagrider from PrecisionRifleSystems (from the UK) but they are just too heavy for a build like this so I decided to go with the Saber Tactical lightweight bag rider. To hush the sound a Huma Air moderator was chosen since it gave me the capability to test different setups due to it's modular design. Putting these parts together gives the following result:
Since this is a relatively small and compact build with the appearance/style of a french bulldog shotcount becomes a thing. So the first thing to do when it was put together was to determine how to achieve maximum shotcount. I already decided the muzzle velocity had to be close to 275 m/s so I measured the air consumption per shot at different pressures with this fixed muzzle velocity. If you listen to the well known tuning videos on youtube and a lot of comments on forums the lowest air consumption is achieved at approximately the lowest pressure you can reach your velocity. Well sorry guys but this is just not true.... Let me show it to you:
I've set up the french bulldog on the testbench with a Magnetospeed V3 at the muzzle to accurately measure the velocity. Short recap: fixed muzzle velocity was set at 275 m/s, which means I had to tune it again to the right velocity (including minimizing muzzle velocity spread to below 2 m/s) with each increase in regulator pressure. The result:
How to do this test you may ask: Fill the gun to a fixed pressure (I used 200 bar) and leave the hose attached without depressurizing it, shoot a magazine (28 shots in this case) and see how far the pressure has dropped. Divide that pressure drop by the amount of shots and you know how much bar / shot is used. Multiply that number by the metric volume of the reservoir (0,3 liter in this case) and you know how much liters of air are consumed per shot. To calculate how many shots you have you take the fill pressure, substract the regulator pressure from the fill pressure and multiply it by the reservoir volume -> this gives you the available amount of liters of air to shoot with. Divide the amount of available liters of air by the consumption of liters per shot and you know the amount of shots you will have. In formulas:
(200 bar - end pressure) / magazine size = bar per shot
bar per shot x volume of reservoir in liters = liters per shot
(fill pressure - reg pressure) x volume of reservoir in liters = available liters of air
available liters of air / liters per shot = amount of shots
So, looking at the bottom line of the graph you can see the air consumption (liters of air per shot) is maximum at the lowest pressure and minimum at the highest pressure -> read: airguns are more efficient with air consumption per shot at higher reg pressures!!
Result of the test is that the reg pressure had to become about 115 bar to maximize shotcount at a muzzle velocity of 275 m/s. I can see you wondering why I would limit myself to a fized muzzle velocity and reg pressure since you would normally tune for best accuracy (by altering barrel harmonics). For one it is that I know this barrel likes this velocity with the 18 grain JSBs and aside from that I just wanted to see if I could get it to shoot the way I want it too (which is accurately of course) -> challenge accepted
With the impact there are two ways to reduce / increase velocity to tune apart from regulator pressure; loosen/tighten hammer spring and make the valve spring stiffer or weaker. After about an hour of playing around with these settings I found a setting that worked best and continued with it. It wasn't giving me completely the results I wanted but I had a last asset for both sound and group size tuning -> the Huma modular moderator.
Moderators can make or break your group size; the weight helps in the barrel harmonics but clipping and air distribution will do more to your group size. I used the Huma Mod30 3/1 setup (3 long, filled, chambers and 1 short, empty, chamber), this gives some space to try how many modules are needed and in what configuration. the 40mm long pieces come with the cloth insert and the 20mm long chambers are empty. Huma advises that for airguns with a large blast you take out the felt and hair curler out the first chamber to give it some space to expand. So the ways to play with these moderators is as follows: chamber order can be changed, moderator length can be changed and chambers can be used both filled and empty. Unfortunately I couldn't really take pictures of the testing with the order and filled and empty chambers etc since a friend of mine poluted the whole card with his .25 . But I ended up with the following stack:
First module empty, second 40mm module filled with felt and the hair curler and the third module empty again. Moderators will not change your group size from horrible to the best you've ever seen (unless it was clipping maybe) but they can make that last bit of difference in your group size. So, what is the end result in group size:
This is including the two sighters I used:
This is without:
Recap of the whole story: I think my little project of the french bulldog build turned out quite succesful and learned some new things along the way The handling is awesome, sound is better than expected, shoots lights out with plenty of shots and is just one of the most awesome and compact builds I've seen or done!! Last thing to be done is trying to find the right scope for it.....
Some last pictures (some are already posted):
This picture was taken before I experimented with the Huma moderator.
The extended Saber tactical picatinny rail was cut down to the right length:
The 40cm long barrel on the floor is the barrel that is the centerpiece of this Impact Compact build. The two barrels (20cm and 40cm long) on the photo were actually one piece before the Dreamline build. Specifications of the barrel: Lothar Walther stainless steel .22 barrel without choke with a 1:17.7 twist. It used to be a 18mm thick barrel but to fit in the impact it had to be turned down to 14mm thick. While fitting it in the impact we saw that barrel was just a tad bit too short to fit a moderator to it. The thread came past the scope rail but the end stop of the thread was 2 or 3 mm behind the end of this rail so it couldn't bottom out. Since the thread length was long enough we decided to make an extension piece to move the end stop of the thread 5mm forward so a 30mm moderator could be fitted.
So now that the barrel is chosen the rest of the setup had to be chosen. SInce I bought an Impact M3 one of my MKII impacts 'lost' it's purpose so that was going to be the base. Other items and specs I wanted to include are the following:
- 300cc bottle
- extended rail underneath the bottle
- a foregrip
- ergo deluxe tactical grip with beavertail
- lightweight bag rider
- JSB .22 18.1 grain at 275 m/s (used to be it's favorite speed before machining it down)
- maximize shotcount
- get it backyard friendly with sound
First things first to get started:
Stripped the Impact MKII of it's accessories and started collecting the 300cc bottle and extended rail. The extended rail was easily taken care of by a trade with a friend, the 300cc bottle was a different story. Couldn't really find one in europe (out of stock) so Johan Axelsson was kind enough to send one over. Why the Ergo Deluxe Tactical grip? Just because I love to use that for shooting standing and some quick bench work. Since I also wanted to be able to shoot from any underground I decided it needed a bag rider but it needed to be lightweight. I really like my buttstocks with bagrider from PrecisionRifleSystems (from the UK) but they are just too heavy for a build like this so I decided to go with the Saber Tactical lightweight bag rider. To hush the sound a Huma Air moderator was chosen since it gave me the capability to test different setups due to it's modular design. Putting these parts together gives the following result:
Since this is a relatively small and compact build with the appearance/style of a french bulldog shotcount becomes a thing. So the first thing to do when it was put together was to determine how to achieve maximum shotcount. I already decided the muzzle velocity had to be close to 275 m/s so I measured the air consumption per shot at different pressures with this fixed muzzle velocity. If you listen to the well known tuning videos on youtube and a lot of comments on forums the lowest air consumption is achieved at approximately the lowest pressure you can reach your velocity. Well sorry guys but this is just not true.... Let me show it to you:
I've set up the french bulldog on the testbench with a Magnetospeed V3 at the muzzle to accurately measure the velocity. Short recap: fixed muzzle velocity was set at 275 m/s, which means I had to tune it again to the right velocity (including minimizing muzzle velocity spread to below 2 m/s) with each increase in regulator pressure. The result:
How to do this test you may ask: Fill the gun to a fixed pressure (I used 200 bar) and leave the hose attached without depressurizing it, shoot a magazine (28 shots in this case) and see how far the pressure has dropped. Divide that pressure drop by the amount of shots and you know how much bar / shot is used. Multiply that number by the metric volume of the reservoir (0,3 liter in this case) and you know how much liters of air are consumed per shot. To calculate how many shots you have you take the fill pressure, substract the regulator pressure from the fill pressure and multiply it by the reservoir volume -> this gives you the available amount of liters of air to shoot with. Divide the amount of available liters of air by the consumption of liters per shot and you know the amount of shots you will have. In formulas:
(200 bar - end pressure) / magazine size = bar per shot
bar per shot x volume of reservoir in liters = liters per shot
(fill pressure - reg pressure) x volume of reservoir in liters = available liters of air
available liters of air / liters per shot = amount of shots
So, looking at the bottom line of the graph you can see the air consumption (liters of air per shot) is maximum at the lowest pressure and minimum at the highest pressure -> read: airguns are more efficient with air consumption per shot at higher reg pressures!!
Result of the test is that the reg pressure had to become about 115 bar to maximize shotcount at a muzzle velocity of 275 m/s. I can see you wondering why I would limit myself to a fized muzzle velocity and reg pressure since you would normally tune for best accuracy (by altering barrel harmonics). For one it is that I know this barrel likes this velocity with the 18 grain JSBs and aside from that I just wanted to see if I could get it to shoot the way I want it too (which is accurately of course) -> challenge accepted
With the impact there are two ways to reduce / increase velocity to tune apart from regulator pressure; loosen/tighten hammer spring and make the valve spring stiffer or weaker. After about an hour of playing around with these settings I found a setting that worked best and continued with it. It wasn't giving me completely the results I wanted but I had a last asset for both sound and group size tuning -> the Huma modular moderator.
Moderators can make or break your group size; the weight helps in the barrel harmonics but clipping and air distribution will do more to your group size. I used the Huma Mod30 3/1 setup (3 long, filled, chambers and 1 short, empty, chamber), this gives some space to try how many modules are needed and in what configuration. the 40mm long pieces come with the cloth insert and the 20mm long chambers are empty. Huma advises that for airguns with a large blast you take out the felt and hair curler out the first chamber to give it some space to expand. So the ways to play with these moderators is as follows: chamber order can be changed, moderator length can be changed and chambers can be used both filled and empty. Unfortunately I couldn't really take pictures of the testing with the order and filled and empty chambers etc since a friend of mine poluted the whole card with his .25
. But I ended up with the following stack:First module empty, second 40mm module filled with felt and the hair curler and the third module empty again. Moderators will not change your group size from horrible to the best you've ever seen (unless it was clipping maybe) but they can make that last bit of difference in your group size. So, what is the end result in group size:
This is including the two sighters I used:
This is without:
Recap of the whole story: I think my little project of the french bulldog build turned out quite succesful and learned some new things along the way
The handling is awesome, sound is better than expected, shoots lights out with plenty of shots and is just one of the most awesome and compact builds I've seen or done!! Last thing to be done is trying to find the right scope for it.....Some last pictures (some are already posted):
This picture was taken before I experimented with the Huma moderator.
The extended Saber tactical picatinny rail was cut down to the right length:
