To get the best performance from your open pistol, you need to maximize how your compensator works. A properly designed and implemented compensator produces a system that helps control the recoil and muzzle flip of your pistol. For the purpose of this discussion, we will address the entire "system" that includes both the compensator and any barrel porting. We’re also going to assume that you will be staying with your current gun and that you will not be changing the barrel, comp, or porting configuration.
A properly designed compensator performs several functions:
Gases escaping from the barrel hit the baffles in the comp and push forward thereby reducing recoil.
Some of the gases are redirected upward which serves to push the muzzle down.
To improve tracking up and down, gases can also be redirected to the side by ports in the comp.
To some extent, the comp also functions as a barrel weight that absorbs some of the recoil.
Many guns also have ports in the barrel that vent gas and push the muzzle down. Barrel ports will vent gas until the bullet leaves the muzzle. Then the comp takes over and the pressure from the ports subsides. With this type of barrel porting, you must realize that any gas vented from the ports is not available to work the comp. Consequently, a pistol set up with barrel ports will generally shoot flatter but it also may hit your hand a little harder. How your particular gun is set up and how you want the gun to feel will determine which direction you need to go when designing a gun.
If we assume that you are not going to change the major components of your gun, you can still affect the overall feel of the gun by changing your load and your springs. Changing springs should be left until you have decided on a load - the main function of spring selection should be reliability with the load you have selected. So how do you select a load that will maximize your compensation system? Bullet and powder selection are the two variables that you have to work with.
A lighter bullet will require more powder than a heavier bullet to get to the same power factor. This is because we are working with power factor (velocity x weight) not just raw velocity. To verify this, refer to any reloading manual. Select a load using the same powder but select two different bullet weights. Then choose velocities so that the power factors are equal. You will find that the lighter bullet load always requires more powder as long as you hold the power factor the same. Lighter bullets also usually run more pressure at the same power factor (with the same powder). This is part of the reason they work the comp a little better. More powder and higher pressure will result in more work by the comp.
The type of powder selected will also have an effect on your results. Most powder companies list a burn rate chart that ranks powders based on their relative "burn rates." These charts provide rough approximations of how fast the listed powders burn. They are not exact and there are often considerable variations in rate of burn. In general, a slower powder requires more powder than a faster powder to push the same weight bullet to the same velocity. More powder works the comp better, and the slower powder usually runs less pressure. However, pressure also works the comp so sometimes it is a balancing act to get the right combination of gas volume and pressure. If you have two loads that feel like they work the comp the same and one has eight grains of faster burning powder while the other has ten grains of slower burning powder, the eight-grain load is running more pressure to get the same effect out of the comp. It gets complicated because there is no hard and fast data on what works a comp the best. You must base your decisions on what "feels" best to you and what produces the best scores for you. Your buddy may pick up the same gun and have a totally different opinion. In all cases, be very careful in working up a load. Loads for 38 Super and especially 9mm major are, at best, on the high side pressure wise. At worst, they can be downright dangerous. Higher pressure loads will wear your gun out quicker than lower pressure loads so also take that into consideration when you are evaluating what works best for you. I prefer lower pressure loads with lots of gas volume to work the comp - that means large amounts of slow powders.
When determining a load, you also need to consider the configuration of your compensation system. Do you have ports in the barrel? If so, how many and what diameter? How many ports are in your compensator? How long are the ports in your compensator? What is the total length of your compensator? How long is your barrel? How far from the muzzle are your ports in the barrel? The answers to these questions will determine how much gas you need to work your comp and/or barrel ports. You want just enough gas/pressure to work the comp/ports and have very little left over to exit the end of the comp. Any excess gas that exits out the front will produce recoil.
Once you have picked out two or three powders and decided what bullet to use (most people in open are using something between 115 gr and 125 gr.), you are ready to work up some loads. In order to compare loads, you must make them all to the same power factor. Use a chronograph to test your loads for velocity. Look for pressure signs and stick with a load that does not show pressure - it will be easier on your gun.
After you have worked up a few test loads, evaluate them to see what shoots best in your gun. Be careful here for false results. Sometimes the flattest load might not be the best. There are trade-offs - a flatter gun usually hits your hand harder. Hitting your hand harder can lead to pulling shots left and right if your grip is not set and you are not lined up solidly behind the gun. You can test your loads to see if you have excess powder creating excess gas that your comp is not using by firing into a blank target at a range of one to two inches (yes, one to two inches) and check the blast pattern. What you are looking for are nice crisp bullet holes with a very minimal blast pattern. Don't get too wrapped up in this test - a little bit of gas going out the front is not going to cause any problems. In the picture, the shot on the left is from a limited gun with 5 gr. of powder and the one on the right is from an open gun with 9 gr. of powder. I have circled the blast pattern on the left shot so you can see it easier. The blast from the limited gun was enough to rip the target. This is quite an effective reduction in the amount of gas even though the open load had almost twice the powder charge. The load in the open gun has been tuned for that specific compensator and amount of porting. If you wind up with two or more loads that all seem equivalent, I would go with the one with the least pressure.
Once you have your load you can start testing springs. Your primary goal is reliability -- then you can go for what feels the best. If you have a couple of equivalent loads test them both with different springs.
Once you have dialed in your load, make up plenty of ammo and go out and practice until the gun does the same thing every time you pull the trigger. You'll find that when you’re getting the most out of your compensator, you'll be shooting a reliable load that not only feels good but also minimizes wear and tear on your gun.