Diana The World Needs More GISS in it

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Sounds like Marflow has been around the block with these Giss guns. Just to add to what he states about rebuilding one of these, is that the timing is also critical. Both front and rear pistons must reach their end of travel at the same time or you run the risk of breaking a tooth off a cogwheel or worse, a tooth off the compression or compensation piston. I've seen both, which I believe happens when a piston seal or buffer crumble and the gun is still being fired. Basically, one piston stops while the other is still traveling; so something has to give.

If a DIY'er is feeling froggy, timing is accomplished using different thicknesses of discs in the rear end cap. If rebuilt correctly, the recoil is virtually nonexistent compared to any other springer including the famous FWB 300S.
 
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Original owner of a DIANA 75HV w/ all the tools, sight inserts & booklet. Circa 1981
Just a Very unique piece of AG history and a real pleasure to shoot ... Virtually Recoilless only making some noise when discharged.

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Wadcutter is right but there are two timing functions
one is the step spacer at the back, with the gears and caps on it should be .3mm with the step washer in place
now that you have the right step washer, you have the compress it to take the .3mm gap out and that is what then filler piece in the cap does and at the same time you have to get the cap screw back in place
with all of this done the gears have no pressure on them they are neutral
it sounds hard but it isn't
so here is the rub you will never have all the right parts if you rebuild just one
the cap spacers, i have a cheat .3mm and .5mm Teflon sheet goods cut out to the cap size with though 2 thicknesses i can make any filler size i want
one thing you might not know is once the side gears and caps are in place you can take the rear cap of and work on the spacing
 
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Big fan of the giss rifles here. The bottom finger groove one is the earliest I have seen. I rebuilt that one and it was different. It had a lacquer finish not oil finish. The gear covers had no pin holes, the gear was attached to its axel and the springs were also different.
Second from the top is a 65.


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I'm in the process of gathering what I need to re-seal my model 75 T01, and I managed to get my hands on the factory service manual. It's layed out in simple step by step form with nicely detailed illustrations. If anyone here has a 75 and wants to DIY the re-seal job, let me know and I'd be happy to PM or Email you a copy. I'm a retired gunsmith, and the Diana 75 is one of the most complex guns, firearm or air, that I've ever worked on.

Love mine-

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Northwoods22 said:
I'm in the process of gathering what I need to re-seal my model 75 T01, and I managed to get my hands on the factory service manual. It's layed out in simple step by step form with nicely detailed illustrations. If anyone here has a 75 and wants to DIY the re-seal job, let me know and I'd be happy to PM or Email you a copy. I'm a retired gunsmith, and the Diana 75 is one of the most complex guns, firearm or air, that I've ever worked on.

Love mine-

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That’s going to be so nice with a T01 trigger.
 
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but the trigger on the early version and the second version are the same
the differences are sight mount early has bevel edge, TO1 are square
front sight early is one piece with special inserts
TO1 has a simple clamp on globe sight that takes 15.9mm metal inserts or clear inserts
stock change but the rifles are the same
the barrel weights are different and could be added

https://forum.vintageairgunsgallery.com/post-war-diana-air-rifles/diana-model-75/
 
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BackStop said:
What does GISS actually stand for? I think I understand that it is recoilless springer technology...

But... what does GISS stand for?

Thanks!
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Kurt Giss was the name of the man who patented the giss system.
The story as I understand it is that the design Kurt originally patented actually had both pistons producing power pushing towards each other.
For a match rifle it actually produced too much power so they changed the design to the one we know now with one dummy piston.
The original design I think was then used as the basis by John Whiscombe for his recoilless rifles.
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Thank you vintage airgun gallery for drawings. Original GISS pattern
 
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As Air Supply so well explained, Giss is a name, not an acronym. :) A friend who is into such details pointed out to me that the Giss patent actually covered pistons moving either inward or outward. But indeed, the best-known drawings are of the inward-moving mechanism which Mr. Whiscombe so beautifully embodied.

My fave Giss Dianas are the 60-series barrel-cockers, which uniquely combine pre-war quality fit-and-finish with new-fangled (for the day) recoilless technology. These guns often have stunning wood, and some of the best oil finishes I've ever seen. The checkering makes Weihrauchs and Walthers of the day look a bit pedestrian.

The intial model 60 (introduced 1963) hung around as Diana's cheaper / Junior model for many years, out-living its top-line successors, the models 65 (1968) and 66 (1974), into the age of the fixed-barrel model 75 (1977). This RWS-marked, 1982-vintage model 60T has the OEM "Diopter 75" sight and matte-finish barrel sleeve "inherited" from those later rifles.

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Just for some giggles & being a DIANA 75 fan/owner, Sometime as much as we love the fit & feel of our vintage 10m rifles we want a little more oomph !!
Get fortunate enough to score an empty D75 stock, do some wood work & shoehorn in a PCP action. Feels & handles nearly identical ( optics difference ) shoots recoiless but reaches out further and pack a lot more punch. Likely one of very few such conversion ever done :unsure:

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The Achilles heel of any double-piston Diana is the piston seals...the originals were nylon and crumble utterly to dust over time. Modern replacement seal materials are vastly superior, but rebuilding is difficult due to having two pistons, multiple springs, timing cogs, and the need to properly shim the rear piston face.

The FWB's have been proven over time to be the most bulletproof of the classic recoilless springers, but outside of the seals I'd put the Giss Diana rifles toe-to-toe with Walther or Anschutz.

The Dianas are not truly rare - various models were manufactured for over 30 years - though I see fewer of the rifles than FWB's or Walthers. The model 6G and 6M pistols are relatively common, though, and the least expensive way to Giss bliss.
 
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Shuggoth said:
I used to have a Diana 60, fantastic guns and fortunately most people took care of them so they are still around today. The cost of manufacturing something like the Giss system vs PCP or ssp I guess doomed them to history.
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HAHAHA ," built today " just inspired a dream like thought of a guy receiving a new Gliss and thinking how can i fix this to make it better ? in the picture was various screw drivers , springs , seale's and a vice grip plyers .
 
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