If you are new to tuning regulated PCPs, then the basic 95% tune is a good place to start. This tune process applies to any regulated PCP with an adjustable regulator and hammer spring. It is a reliable point to tune at, and if you just want to shoot and not mess with your gun a lot, you will likely be able to stop here. I am also going to briefly outline how to simplify tuning the Impact M3 since a lot of people are intimidated by it.
What is happening when you tune a regulated PCP
At a set reg pressure, if you were to run through the hammer spring tension from min to max, you would get a graph of the velocity. At minimum hammer spring, velocity is low, noise is low due to valve closing very early, and velocity spread is higher due to light hammer strike. At the top of this graph as you increase hammer spring, there is a velocity plateau. Above a certain hammer spring tension, velocity does not increase even if you increase hammer spring. At this plateau level, velocity is at max, noise is at max due to valve being open when projectile leaves barrel (also a waste of air), and velocity spread is low due to heavy hammer strike. There is a sweet spot on this graph at the point where velocity is around 95% of max. This point often referred to as the 'knee', and is an intersection of positive characteristics of noise, velocity spread, and air efficiency/shot count. Airgun technical guru Bob Sterne explains this in detail here: https://hardairmagazine.com/ham-columns/tuning-regulated-pcp-airguns
Quick Impact M3 simplification (Just because it has options doesn't mean you necessarily have to or need to use them all)
Valve Adjuster - set it to 'full out' per your manual and leave it alone
Macro Wheel - set it to 16 and leave it alone. The macro wheel is irrelevant for tuning and is a distraction. The indicator on the micro adjuster is the only indicator of hammer spring power.
First/Front reg - It is not critical and only needs to be around 50bar (or more) above your second/back reg for good performance. Factory setting is ~150bar, so if you are tuning pellets you won't have to touch it. If you are tuning slugs, your second reg pressure is going to be higher than 100bar and you'll want to make a one time adjustment to raise the first reg ~50bar above your second reg's final pressure. More than 50 bar difference is ok.
With the above adjustments excluded, you are left with hammer spring (via micro adjuster), and second reg pressure. This is the same as most regulated PCPs and all you need to get a decent tune.
Example: Regulated PCP 95% tune process
You will need to select a target tune velocity for your projectile, and this may require some research. Standard weight pellets are easy since they are the most well understood. They perform well in the 850-900fps range. Slugs have a lot more variation, but 950fps probably a good starting point.
I am going to choose 890fps for a standard weight pellet
890fps = 95%
Max(100%)fps = 890fps / 0.95 = 937fps
The goal now is to find the reg pressure where 937fps is the max and then dial back the hammer spring to get 890fps
You start by setting hammer spring tension to a high level where you are confident that you are getting max fps. You can find this by working up through hammer spring tension until velocity stops increasing, or you could shortcut the process by setting your hammer spring to max if that is safe on your airgun. Difference in access to regulator and hammer spring adjustment is going to dictate strategy here depending on the gun. It is best to start at a reg pressure that is below where you think you'll end up, and then work up from there.
Shoot a few shots over the chronograph and note the velocity. If it is still below 937fps, increase reg pressure and try again. If velocity is too high, lower the reg pressure.
Once you've found the reg pressure where max velocity is 937fps, dial back the hammer spring tension until velocity drops to 890fps.
You are now at a 95% tune. If you want to tune for higher or lower velocity in the future, repeat the process.
Some final notes
What is happening when you tune a regulated PCP
At a set reg pressure, if you were to run through the hammer spring tension from min to max, you would get a graph of the velocity. At minimum hammer spring, velocity is low, noise is low due to valve closing very early, and velocity spread is higher due to light hammer strike. At the top of this graph as you increase hammer spring, there is a velocity plateau. Above a certain hammer spring tension, velocity does not increase even if you increase hammer spring. At this plateau level, velocity is at max, noise is at max due to valve being open when projectile leaves barrel (also a waste of air), and velocity spread is low due to heavy hammer strike. There is a sweet spot on this graph at the point where velocity is around 95% of max. This point often referred to as the 'knee', and is an intersection of positive characteristics of noise, velocity spread, and air efficiency/shot count. Airgun technical guru Bob Sterne explains this in detail here: https://hardairmagazine.com/ham-columns/tuning-regulated-pcp-airguns
Quick Impact M3 simplification (Just because it has options doesn't mean you necessarily have to or need to use them all)
Valve Adjuster - set it to 'full out' per your manual and leave it alone
Macro Wheel - set it to 16 and leave it alone. The macro wheel is irrelevant for tuning and is a distraction. The indicator on the micro adjuster is the only indicator of hammer spring power.
First/Front reg - It is not critical and only needs to be around 50bar (or more) above your second/back reg for good performance. Factory setting is ~150bar, so if you are tuning pellets you won't have to touch it. If you are tuning slugs, your second reg pressure is going to be higher than 100bar and you'll want to make a one time adjustment to raise the first reg ~50bar above your second reg's final pressure. More than 50 bar difference is ok.
With the above adjustments excluded, you are left with hammer spring (via micro adjuster), and second reg pressure. This is the same as most regulated PCPs and all you need to get a decent tune.
Example: Regulated PCP 95% tune process
You will need to select a target tune velocity for your projectile, and this may require some research. Standard weight pellets are easy since they are the most well understood. They perform well in the 850-900fps range. Slugs have a lot more variation, but 950fps probably a good starting point.
I am going to choose 890fps for a standard weight pellet
890fps = 95%
Max(100%)fps = 890fps / 0.95 = 937fps
The goal now is to find the reg pressure where 937fps is the max and then dial back the hammer spring to get 890fps
You start by setting hammer spring tension to a high level where you are confident that you are getting max fps. You can find this by working up through hammer spring tension until velocity stops increasing, or you could shortcut the process by setting your hammer spring to max if that is safe on your airgun. Difference in access to regulator and hammer spring adjustment is going to dictate strategy here depending on the gun. It is best to start at a reg pressure that is below where you think you'll end up, and then work up from there.
Shoot a few shots over the chronograph and note the velocity. If it is still below 937fps, increase reg pressure and try again. If velocity is too high, lower the reg pressure.
Once you've found the reg pressure where max velocity is 937fps, dial back the hammer spring tension until velocity drops to 890fps.
You are now at a 95% tune. If you want to tune for higher or lower velocity in the future, repeat the process.
Some final notes
- My .22 M3 factory tune was well above 95%. In about 5 mins using the above tune method, I set it to 95% and cut perceived noise in half.
- Once you've done a tune like this, you can see the problem with trying to tune an M3 solely off someone else's shared tune settings. It will not be accurate, with a key culprit being reg gauge differences. If the FX factory is tuning via settings only, then this is exactly how I got a loud tune.
- If you want to explore outside of the 95% point, I personally haven't noticed anything good happen above 96% tune level. Going in the other direction below 95%, your main concern will be increased velocity spread, but depending on your gun can still be good. This is how you would get a really quiet tune.
️You should repost this in the RESOURCES subforum... — this is an "essential guide". 
