Venturi bolts…

[Bubkat]

90s marketing or was there something there?

[Self Medicated]

I'm curious about this too. TechT still has Hush bolts with a venturi face for sale and I'd like to know if they're all hype.

[DocsMachine]

90% hype. The only real benefit is the area of the "venturi*" holes is less than that of the usual single super-cavernous hole most "high flow" bolts have today. And one of the biggest tricks you can to for a 'Cocker (and to a lesser extent others, like a Spyder) is to let the gas expand as little as possible between the valve and the ball.

The big, open "high flow" bolts don't do anything but let the gas column expand unnecessarily- wasting some of the energy stored in the compressed gas- before it hits the ball.

Here's an example: The bolt on the left came in a customer's P&P Supercocker. He wanted "more flow" so he had me make the bolt on the right.



And even today, almost everyone would pick the right-hand bolt- it's more open, therefore it flows better, therefore it's better, right?

Nope. The left-hand "venturi" bolt was worth 35-40 FPS, no other changes. Regular as clockwork; Venturi, 285-290 FPS, all day long. Swap in the open bolt, with no other changes- same gun, same paint, same setup, same pressure, etc.- 245-250 FPS, all day long. Swap the venturi back in, 285-290.

Had nothing to do with the "venturi" part- it was simply the fact the inner volume of the venturi didn't let the gas needlessly expand.

Doc.

[scottieb]

Venturi has always been a huge hype and used for marketing purposes.

I won't speak for other marker types but as a career low pressure Spyder builder and user, I see this differently than Doc. An open face, higher flowing bolt design is what I will use 100% of the time.

[DocsMachine]

Have you tried a truly small-bore bolt? In my experience you'd practically have to make one, as save for a few Venturi styles, most are pretty cavernous- including the stock bolt.

Ideally what you want- in a 'Cocker at least- is the entire gas passage should be the same size from the valve to the face of the ball. I'd be very surprised if you didn't see more or less the same effects on a Spyder- other than the fact no one makes such a bolt, because thanks to marketing, no one would buy one.

It's worth noting that when I was initially testing my Evil Twin (an over-under double-barrel 'Cocker) I needed to 'choke off' one barrel to help divert air to the other. I made a test bolt, meaning to start with a weeny bore- 3/16", or .187"- and expecting to bore it larger in stages 'til the velocities were about the same.

I got something like 260-270 out of that barrel. On a double-barrel. With a 3/16" bore on the bolt.

"Flow" isn't the issue. The pressure and impulse time is too short for that to be a factor- yes, even on a "low pressure" marker. Maintaining the energy of the gas charge is the key.

Doc.