Daystate Slingshot anti bounce hammer

[eeler1]

For you guys that like to tinker with pcp hammers and get them to not bounce.  I hadn't seen this discussed before, though maybe I missed it.  I noticed this in their catalog, and it looks like a spring loaded follower to dampen the hammer bounce back off a valve stem, so it doesn't have enough energy to pop the valve open a 2nd time.

[rsterne]

Yes, the Daystate hammer is a 2-piece design, where the main spring launches the outer part, and then the inner part, that is just going along for the ride, is what opens the valve (through it's own energy/momentum) after the outer part comes to a halt.... It is then sent back by the valve stem to hit a spring/cushion in the outer part, robbing it of enough energy to prevent it from opening the valve a second time, as the outer part never rebounds to load the main spring....

It's a clever design, protected by copyright and patents, so although it is possible to make one for yourself, commercial production would not be kosher.... We have been experimenting with a vastly simplfied version with some success, using a regular 1-piece hammer, but a short stiff hammer spring with NO preload so that the hammer coasts the last part of it's travel to the valve stem and has a more difficult time storing rebound energy in the (much stiffer) spring.... It seems to provide added efficiency, which most of us attribute to reduced air-wasting hammer bounce....

Bob

[csdilligaf]

  The sling shot design sure sounded like it should work but I watched the video of it in action and maybe someone else should watch it and give their opinion but I did not think it to be that effective.  I have seen others that hit once and have one dribble.  Dan Brown on the east coast had some slow mo video of his FX that he tuned and it did one dribble.  I will take some slow mo of mine soon and see how it does.  I just took it apart and milled in a window so my Casio EX FC150 can see it at 1000 fps. 

[rsterne]

I'm not surprised that it bounces, the key is, does it release air on the 2nd hit of the valve?.... I have a Hatsan AT44-Long that has a (factory) device that prevents the hammer from rebounding and loading the spring.... Most of my PCPs don't have any such device, and yet the Hatsan is no more efficient than any properly tuned PCP.... I am in the camp that believes most hammers bounce, but most PCPs can be tuned so that the amount of air wasted (if any) by a second hammer hit is minimal.... However, should you choose to tune a PCP so that the hammer is bouncing like mad and wasting air, you can prove that on that gun an HDD does wonders.... *grin*....

Bob

[rkr]

There's also John Bowkett's blast tamer design as used in BSAs. There's an additional "hammer" situated behind the main hammer and when the main hammer is released it follows it and hits it with much lesser force in rebound. In practice it kills the bounce completely. I've built and measured two DIY versions and on both cases the valve opened just one time while previously it opened two to three times. I got about 30% more shots in both cases. I actually have some plans to build a different version for my Blizzard to see how it works on bigbores.

[csdilligaf]

  here is the link to daystates video.   Its the second one on this page.  Actually after watching again it is not to bad.

http://www.daystate.com/huntsman.htm

[rsterne]

Very poor quality video, not fast enough frame rate so the images are blurry.... However, what I find interesting is that the outside hammer still has one very large bounce and then a smaller one.... I suspect the key to this working (or not) is the relative masses and spring rates of the inner and outer hammers so that when the outer hammer is travelling forward (which would cause the valve to open), the inner hammer is (because of a higher frequency of vibration) travelling backwards, tending to cancel out the 2nd impact.... Third and subsequent impacts would therefore be at such a low level as to be insignificant....

The problem I see is that the mass of the inner hammer, which is the only one that can open the valve, is MUCH less than the total mass.... which means you need a lot more total energy provided by the spring since most of it (certainly over 50%) is lost to the buffer when the outer hammer hits the back of the valve....

Bob