Transfer Port Screw Adjustment

[TenMetrePeter]

Just screw it right out. You might want to first screw it right in, counting the turns so you can put it back roughly as it was.

Peter, do you know the dimension or how many turns are required for the transfer port to be fully un-restricted? I wondered if there is an easy way of setting this in conjunction with backing off the pot to cap maximum power. If the screw is unwound too far it's going to increase the dead volume of the transfer port, reducing efficiency, which is what I want to avoid. Otherwise it's a matter of trial and error - simple enough provided there is minimal interdependency between valve setting and free flow through the transfer port. At the moment I have the venturi screw well back - possibly too far.

That level of tuning is for the enthusiast who is willing to decompress the rifle and strip it over and over again as a hobby in itself. My hobby is shooting and I set the muzzle energy to the design level, (for a full power rifle that would be 11.0 ftlbs) put the plug back, then leave it alone. Check every 6 months.

Put it another way, I haven’t a f**king clue

[rob2hook]

I wonder if the adjustment screw has a greater affect on the 10m variants? I was under the impression that on a 12fpe model the screw had a fairly minimal affect, though possibly enough to get you into trouble... Certainly the FAC models use a heavier striker and more powerful striker spring to get the firing valve open for longer along with a less restricted pot - all of which greatly increase air usage per shot.

Rob.

[TenMetrePeter]

Quite possibly. I only ever worked on mine. It doesnt have a sweet spot curve, just flat then drops off, the firing valve pot is different and both hammer and spring are lighter. All I know is if you dusturb it with a locking screw you can drop from 6 to 5 ft lb in one go. When I finally took the plunge and took out the A/T it had worked its way down to 2.5 ftlb. It still gave consistent clean target holes , I just ran out of elevation on the sights!

On general point. All three power regimes use the same 100-180 bar power source and going up in power loses shot count and flat curve and going down to 10m power levels gives 100 consistent shots without the need for a reg. AA describe it as “self regulating” and at low power I think it is. I am talking club shooting not World Championships!

[tonyc]

Peter, do you know the dimension or how many turns are required for the transfer port to be fully un-restricted?

That level of tuning is for the enthusiast who is willing to decompress the rifle and strip it over and over again as a hobby in itself. My hobby is shooting and I set the muzzle energy to the design level, (for a full power rifle that would be 11.0 ftlbs) put the plug back, then leave it alone. Check every 6 months.

Put it another way, I haven’t a f**king clue

I shall have a fiddle sometime... no need to strip it. I can use a depth gauge/vernier to measure the hole and screw position. I already know the screw is out far enough to cap the power. It will be interesting to see if power goes up just a little as I screw it in, which would show me I have unnecessary dead space. I doubt it'll be enough to detect and won't be enough to need adjustment to the valve pre-load as I already have some headroom at 11.3ftlb. Might give me a couple of extra shots though.

The problem is OCD!... 69 regulated shots, not 70!

[John814ce]

If you can fully remove both cover screw and adjustment grub screw from ventrui then do so and replace with 1 single stainless steel button allen head screw and taper the end like the original grub screw. You want to start with 13.75mm length from tip to the button head were the allen key hole is, then grind a bit off at a time to suit power required, and keep the taper shape. Btw grind a bit and i mean a bit at a time, once done use a little bit of ptfe around the thread not on the taper bit, once done you never have any issues every again with your ventrui screw moving. Its an absolute shocking design by aa, it was one of the first things i did with my gun. I have several lengths of the screw for different types and weights of pellets, but unless you have an fac keep it under 12ftlbs with the heaviest pellets mate.

[Torny]

Sorry to bring this up again but I'd like to know how deep the hole for the Venturi screw is as I'd like to blank it off full stop...

Mine keeps moving and no matter how many times I've re-adjusted it after a while it moves again...

The rifle in question is a 2001 S410 in .22 and runs at 11.5-7 with AADF's with the Venturi screw backed rite out...

Any advice would be most appreciated...

[tonyc]

The length of screw is going to depend on the setting of the firing valve on each individual gun so it's probably best to measure the position of the screw when the power is as you want it.
Two suggestions to lock the screw:
1. Use Loctite purple (weakest type)
2. Measure depth of hole to top of existing set screw and cut security torx screw to length. This wouldn't necessarily stop the screw from creeping in but it would stop it from creeping out.

[Torny]

Cheers for the advice buddy...