Tuning Tuning question

[bowdude]

I’ve been trying to de-tune my Caiman X with no avail. Here’s my basic run down: degas the gun, remove cylinder, remove regulator, turn reg adjuster screw CW 1/16 of a turn & reassemble. Full gun to 3000 & start shooting over chrony. Adjust hammer spring till I hit the highest fps & back off the hammer about 1/8 of a turn. Then the gun is very consistent, 3-6fps spread. But the gun still shoots around 30-31fpe, I’m looking for 18-20fpe. 
Redo the whole process over & over again till I’m roughly a half turn CW on the reg, but nothing I do changes the the fps once I get it consistent. 
Now for more power that’s no big deal. A 1/4 turn CWW will give me around 45-47fpe. But once I hit 30fpe that’s as low as I can go, with consistency & efficiency. I can adjust the hammer & get 20fpe out of it but I’ll have 12-21fpe SD. 

So any ideas that I could try to de-tune this thing to about where I want it? 

 

[Bander124]

I feel ya. I tried to detune my katran and found your experience to be mine. I’m in the process of trying to find a weaker hammer-spring but no avail. I know they make sub 12 fpe guns but can’t find a kit either.

 

[nervoustrig]

I can't quite tell for certain from your description but if you've reached the lower limit of the regulator's range, you'll need to reconfigure or replace the Belleville spring washers so you can reach lower pressures (if not Belleville washers, a weaker compression spring).

Or another option is to restrict the flow of air. There are various ways of doing it, just depends on what is easiest for the particular gun or your comfort level. For example, could be to plug the transfer port and drill it to a smaller size, or use threadlocker to bond a segment of brass tubing into the valve exhaust to reduce its flow rate, or something along those lines.

Or you can do a little of both.

Another option is to use an O-ring hammer buffer (bstaley O-ring stack). There is typically a fair amount of trial and error associated with this approach but it has the added benefit of helping prevent hammer bounce so you get better efficiency / shot count.

What you are currently seeing when backing off the hammer spring is indeed as expected...the gun is operating at a state of partial valve lock so the velocity swings up and down wildly due to little inevitable differences in friction.

 

[Vetmx]

What Nervoustrig said. I believe you are trying to tune below the regs operating range. If you want the gun to shine at the lower fpe, you’re going to have to do it right. Choking the gun to death might work, but it won’t be right.

 

[bowdude]

I can't quite tell for certain from your description but if you've reached the lower limit of the regulator's range, you'll need to reconfigure or replace the Belleville spring washers so you can reach lower pressures (if not Belleville washers, a weaker compression spring).

Or another option is to restrict the flow of air. There are various ways of doing it, just depends on what is easiest for the particular gun or your comfort level. For example, could be to plug the transfer port and drill it to a smaller size, or use threadlocker to bond a segment of brass tubing into the valve exhaust to reduce its flow rate, or something along those lines.

Or you can do a little of both.

Another option is to use an O-ring hammer buffer (bstaley O-ring stack). There is typically a fair amount of trial and error associated with this approach but it has the added benefit of helping prevent hammer bounce so you get better efficiency / shot count.

What you are currently seeing when backing off the hammer spring is indeed as expected...the gun is operating at a state of partial valve lock so the velocity swings up and down wildly due to little inevitable differences in friction.

I believe I’m at the lowest set point of the reg cause of I try to adjust it any more it doesn’t let any air into the plenum. So I think your spot on with the reg be at its operating limit. Next time I’ll take the reg apart & see if it’s bevel washers or spring. 
Also I never even thought about a transfer port. If I can’t get where I want it I may try to get ahold of Airmaks & see about a 12fpe kit for it. I went ahead & set it back as close to factory as I could. It settled in around 35fpe, that’s Jsb 15.89’s @ 1000-1004fps over a magazine. I’ll just leave it here for now I’ve got a couple over other guns I need to work on. 

 

[corny]

Couple tips, 

You can clip a couple rings of ur existing spring to weaken it.

also, you could try increasing the weight of your valve spring. 


Do you know what your plenum size is? 

 

[bowdude]

Couple tips, 

You can clip a couple rings of ur existing spring to weaken it.

also, you could try increasing the weight of your valve spring. 


Do you know what your plenum size is?

The hammer spring is ok. I can adjust the hammer spring down & get it as low as 775fps with 15.89’s. But the consistency is horrible, we’re taking 30-40fps spread over 1 mag. To get it consistent I have the hammer spring turned about 4-4.5 turns, that it where I get my smallest sd. I’m not sure on plenum size, I can measure it next I take it down. I did machine a spacer to make the plenum smaller but it did nothing. Nothing changed with the spacer, it shot the same with or without it. 

 

[nervoustrig]

Constraining the plenum volume by adding a solid mass would reduce the energy at the expense of efficiency and shot count. 

 

[bowdude]

Constraining the plenum volume by adding a solid mass would reduce the energy at the expense of efficiency and shot count.

Yeah you’ve told me that In another thread but I could never understand why. I didn’t doubt what you said in my other post but the way my mind works I needed to see it. I only ran 2 mags across the chrony, I couldn’t attest for the efficiency & didn’t pay attention to my gauge. But as for power the power was the same when I got it to the point of consistency that was the best. Which still was 10-13fps spread over the 2 mags.