Reg Pressure Setting

[Joe.w6606]

Hello all, just looking for some tips on a good starting point for setting the reg on my project cylinder build.

It's a .177, but has a 14" barrel. I'm not sure whether the 2 inch shorter barrel would require too much of a different starting point than a full length barrel .177 in terms of reg pressure???

Current ME sits around 10.5-10.7 with 8.44 B8's, but with the block as supplied, the hammer adjuster is almost wound fully in.

The reg currently fitted is one of KevG's, but I believe it was supplied to the original owner for a .20 build. However, I cannot confirm at this point whether it has been adjusted since it was supplied. Similarly, at this point I have to assume the hammer and valve springs are original too.

I have a reg tester due to be delivered later this week, and am comfortable with the process of testing and adjustment, just after some input from any members who may have already set up a shorter barrel .177 with one of Kev's regs.

Thanks
Joe.

[Ca_Varminter]

I believe the cutoff pressure for a .177 sub 12 Fpe is about 1500 psi.
KevG should be jumping in and give you His view on this!

Good Luck,
Stuart

[Squinty]

depending on the state of tune, porting, barrel length...95 to 115 bar.
No need to worry about the hammer and valve spring, you'll be able to back off the hammer once the reg is at the right pressure.

[Joe.w6606]

Thanks both for replies.
Sure I had read somewhere that factory was 1450 psi in .20, and 1700 psi in .177, and that KevG's regs are around 150 psi lower for the respective calibre. Just not sure what difference a 14" barrel makes to these figures, I assume it'll need slightly higher.

Good to know not to bother with springs, and for the moment I have to assume all else is standard.

The barrel porting is stepped, around 4mm to 3.2 ish which I believe to be correct. So other than the reg it all seems standard.

👍

[Squinty]

 I  vauguely  remember an old thread ragarding a 177 perhaps a 20 running with a 12" barrel, 105 bar comes to mind.
Ideally you want the pressure high enough to give a sharp shot cycle without going over off reg.
Going too low with more hammer tends to be inefficient.

[KevG]

.177 and .20 calibre are basically same pressure setting 1500 psi if for a mk2/mfr.1700 psi if for the old type mk1.you hold the core with a T15 torx key and not xkey like theobens
kevG

[Joe.w6606]

.177 and .20 calibre are basically same pressure setting 1500 psi if for a mk2/mfr.1700 psi if for the old type mk1.you hold the core with a T15 torx key and not xkey like theobens
kevG

Great, thank you.
Will update once the reg tester has arrived👍

[Joe.w6606]

Thanks to everyone for the replies so far.
Tester arrived today, so have spent the last hour testing and setting, re-testing and setting......

Originally set at 1250psi, it was taken up gradually at 100 psi increments and chrono'd at all settings up to 1600 psi. With relatively zero change in output, which seemed odd.

At each chrono string the hammer was set at 2 full turns back from fully in, but testing with both JSB 10.34 and H&N B8's, the FpE did not get beyond 10.9 at any PX setting, by the time the hammer was adjusted all the way back in again.....

Can only think at this point the hammer spring is not original / trimmed down.

I added 2mm of packing between adjuster and spring guide, and the FPE shot up to 11.6 with the hammer backed out 1.5 fulls turns ish.

Does any one have the spec and a source of replacement hammer springs?

Cheers👍

[Squinty]

honestly wouldn't worry about it, 2mm is nothing  half a coil and chances are a new spring is going to be a little stiffer.
Replace the single 2mm packing with a couple of 1mm slip discs (one either end).

85 bar was a little low .22 pressure hopefully the shot cycle  sounds a bit sharper.
Even if it's 'mouse fart' quiet you can tell
No increase when you turned the pressure up sounds valve related, nothing wrong perhaps running a small-ish port.

Time for a cylinder un down/shot count to make sure it stays under when it goes off reg or if you need to tweak the pressure.

[Joe.w6606]

Having re-visited this again last night, I'm at a point where I'm happy with the set up.

I looked a bit further in to the spring and found it to be a little shorter than "the norm". 50.4mm spring length, plus around 1mm depth flange on the guide.

As advised I've replaced the 2mm packer with 2x 1mm thick M6 washers- one either side. Hammer spring OAL around 54mm with preload.

Reg has been dialled back to 1500, which is now producing a sharp shot cycle and ME @ 11.5 with JSB 10.34, and 11.1 with 8.44, which is where I wanted to be.

Just need to do a shot string from 200bar to drop off to get an idea of shot count and check there's no spike off reg.

Thanks for all the advice so far, much appreciated👍