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PostPosted: Mon Feb 22, 2016 8:23 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
I've been having some fun last evening and today tinkering with my QB78, thanks to an article I found by 'Steve in NC' on a Network54 forum:
http://www.network54.com/Forum/79537/me ... Hammer+Mod

The idea was to come up with an adaptation similar to the SSG to let the striker/hammer fly free before impact with the valve stem, reducing potential for air wasting hammer bounce. Though Steve's clever idea doesn't quite deliver the stopped spring guide (SSG - initially developed by Bob Sterne at the beginning of this year) properties it does an impressive job of eliminating secondary valve openings when set up carefully. I was finding yesterday while plinking a bit with the QB78 in Mission that the hammer debounce device (HDD - a thing I made last fall based on another of Steve's ideas) was not really working very effectively any more. Seemed to have worn a bit and was allowing some secondary burps of air after the shot, especially as pressure dropped towards the end of the fill. So I went Googling for an SSG for the QB78 and immediately came up with the above thread showing how to make something similar with minimal intervention, very little machining and certainly something easily put into place with modest machine tools. A drill will do, though a lathe might help.

I won't repeat everything I wrote in my contributions to that discussion but just wanted to point it out for other QB owners who happen to like keeping the 'cock on close' function but want a more efficient shooter, with more shots per fill and less noise at the same power level. In my case it's still shooting slightly faster than my target velocity but I'm trusting that the spring breaking in over some hundreds of shots will mellow it slightly to bring me below the HFT 20fpe limit. It's fussier to adjust compared to the externally adjustable SSG, obviously, but taking the QB apart isn't very challenging and once set up it can just be left alone.

My efficiency prior to this modification was about 1.74fpe/ci, which is pretty darn good. But hey, some guys with SSG tuning are managing in excess of 2.0fpe/ci - foot pounds per cubic inch of air used, derived by plugging one's various stats into Loyd Sikes' calculator - http://www.calc.sikes.us/1/index.php - so why not push for better use of air? After several disassembly/reassembly cycles to adjust spring length and preload I've managed to improve this to 1.87fpe/ci while getting a nice peak in my shot string velocity, highest power right in the middle. Once I get the QB hooked up with its regulated Ninja bottle set to about 950psi I'll have over 2,000psi worth of shots to play with at just the right power for FT, and thanks to the improved efficiency that means even more pellets downrange before hitting the FX pump for a refill.


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PostPosted: Wed Feb 24, 2016 4:08 pm 
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Joined: Tue Feb 18, 2014 7:24 pm
Posts: 667
Location: Dowling ,ontario
Nice job by Steve. Although not sure why he's calling it a ffh instead of an SSG . Let's give credit where credit is due .JMo

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PostPosted: Wed Feb 24, 2016 4:22 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
There seems to be a bit of either ego involved or some sort of marketing strategy with Steve. He's not always the easiest guy to get along with in discussion forums. But I like his eagerness to get solutions found and some of his ideas, or interpretations of Bob's (in this case) or other folks' ideas can be very helpful in moving our airguns towards perfection.

In this case though the 'FFH' is in a way significantly different from many implementations of the SSG, in that it does not provide a solid stop for the hammer on rebound. Instead, with the FFH the hammer comes back and hits a free-floated stopped spring, dumping a bit of energy into that rod as it starts it moving backward then continuing onward as far as momentum and room to move backward will allow, perhaps hitting a stop at the end of travel if there's still energy to be dissipated. It's not quite the same dynamic but the effect is similar. Neither system allows the hammer to bounce back and re-strike the valve stem if properly made and adjusted.


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