reg/hst tuning question

[peaceful_ruler]

In my lowly understanding of tuning a PCP I've been informed that you want to have the HST at roughly 95%-97% of the plateau or max velocity that you can get at that reg setting. Start slow and keep turning up the HST until velocities stop climbing and then back it off 3%-5%, easy peasy.

My question is this...once that harmonious balance is achieved between reg pressure and HST it doesn't matter what projectile I shoot that balance will always remain, yes? For example, my 22 grain slugs were peaking at 1050 fps so I backed the HS down until I was achieving 1000 fps, 96%; balance achieved.

Then, I decide to shoot some 26 grain slugs at this same tune and they only hit 945 fps...however, am I correct that my tune is still in balance?

 

[nervoustrig]

My question is this...once that harmonious balance is achieved between reg pressure and HST it doesn't matter what projectile I shoot that balance will always remain, yes?

If you're dealing with a wide range of projectile weights, and/or switching between pellets and slugs, you'll need to adjust hammer spring tension if you want it running optimally.

Heavier projectiles take longer to accelerate, and will therefore benefit from more hammer spring tension to produce more valve dwell to keep pushing for longer. The same is true for slugs over pellets...the vastly higher bore friction means they need a longer push to get them up to speed.

With that said, your example of 22 grains versus 26 grains represents a weight difference of just ~17%, and with them both being slugs, there's a decent chance a single state of tune can work reasonably well for shooting them both. And if they both group exceedingly well, you are hereby obligated to immediately go out and buy a lottery ticket

 

[elh0102]

I expect that you're close enough with the heavier slug to preclude the need for further HST adjustment. Will it be perfect for both? Probably not, but sometimes we forget that the magic "balance" is a tool, not necessarily the end goal, which the target will indicate. If the sound is weird, or the on-reg shot count seems off, then maybe tinker some more. I've found that it's easy to spend too much time tinkering, without getting enough shooting done. If you're a bit OCD, you've found the hobby to push you over the edge!