Tuning your open gun for the new 165 power factor

© Bob Londrigan - Brazos Custom Gunworks 2000

 

If you have not developed a load yet for your open gun for the new lower power factor you are missing out on an advantage to be gained. The lower power factor loads will let you shoot follow up shots faster and control your gun easier. I have heard many people say that they are staying at the old power factor and "my comp works better at the old power factor" or "my gun won't run at the lower power factor." You may be able to solve either of these problems with a little experimentation.

Let's address the first problem - "my comp works better at the old power factor." The reason your comp works better at the old power factor is because you had more pressure and more gas to work with. You can solve the problem in two ways install a more efficient comp and develop a different load. A more efficient comp works better at the lower pressures and will get you back on target quicker. You also need to develop a load using a slower powder than you were using before. For instance I was using 10.0 gr of powder at 179 power factor under the old system when I tried to download this powder to 169 power factor I was using 9.0 gr. It shot softer but I was not completely happy with it. I then went to a slower powder and loaded 10.0 gr. the gun shot much softer and was just as flat as at the higher power factor. The reason for this is that I had the same volume of gas to work the comp. The only difference was that I was not pushing the bullet as fast so I got less perceived recoil.

One of the driving concepts behind the Pro Sx was the lower power factor.  At the lower power factor I could develop a shorter gun (shorter barrel =  more powder for same speed)  that would  use higher charges of slower powders and produce about the same amount of gas that we had under the 175 power factor. This allowed development of a lighter faster gun that still shoots flat.

How about "my gun won't run at the lower power factor" - First try it again with the load you developed with the slower powder that might work. If that doesn't work you may have to do a little bit of experimentation with your gun. The problem you are having with the lower power factor is caused by the reduced recoil impulse available to cycle the slide. Let's look at what you can do to increase the energy available to cycle the slide.

1) Your compensator - A comp works as a result of the gasses hitting the baffles and pushing the entire barrel forward in addition to the downward vector you get from the gasses vented out the top. Pushing forward reduces the recoil impulse available to cycle the slide. The more efficient you comp the less recoil impulse available. You don't want to make you comp less efficient so let's leave this factor alone. However, you should keep in mind that if you switch to a more efficient comp you may have to make other changes to your gun. If you can accept a little more recoil with a trade off for more speed target to target you may want to go with a shorter comp.

 

2) Weight - The slide, barrel, and comp all move as one unit in response to recoil, therefore you must consider the weight of this unit when trying to tune your gun. If you have a full profile slide, bull barrel, and big long heavy efficient comp you are going to need a lot of recoil energy to cycle the gun. This combo will not work at the lower power factor. What you can do:

a) Reduce weight in the comp - cut more ports, flatten the bottom and top, cut holes in side. If you weigh the Thundercomps and compare them against other comps of similar length you will find they weight significantly less. This is on purpose to cycle the gun better.

b) Reduce weight in the barrel - a cone comp and regular profile barrel weighs 1 1/2 oz. less than a bull barrel and comp.

c) Reduce weight in the slide - this can be done in a number of ways. You can take out up to 3 ozs. out of the slide.

d) Shorten the slide/barrel/comp as in the Pro Sx

 

3) Springs - You can reduce you recoil spring and your mainspring. Don't go under 10 lbs on the recoil spring or 19 lbs on the mainspring.

 

4) General - You need to be sure that nothing is dragging on the slide. The barrel unlocks smoothly and everything operates as it should. Any drag on the slide as it opens will cause you problems.

 

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