I've seen the future....

[bigtoe01]

I have two Diana 440's here, both .177, one sleeved down to 25mm, the other still at 28mm, today i decided the 25mm one was going down to 22mm.

Still have not messed with the transfer port, its around 6mm long with the delrin seal and 4mm dia. Piston is based on a D52 latch rod, stroke is 84mm.

I have to work out the efficiency, preload is under 9mm, shot cycle....well WOW comes to mind.

spring is 200mm long, power = 11.2 with superdomes and superfield 4.52, exacts, and anything else jsb forget it, 10fpe at best. No worried its accurate with both domes and superfields.

[slugger]

how about sleeving the port down to 3.2 ish.. adding a little preload to get back whats lost.. then try the jsb's again........ i bet the fps comes up and makes a similar ft/lbs

[bigtoe01]

how about sleeving the port down to 3.2 ish.. adding a little preload to get back whats lost.. then try the jsb's again........ i bet the fps comes up and makes a similar ft/lbs

tried that on a 77...its not a rosey outcome.

FTT do start to come good as do the 4.51 version as they are a tighter fit.

I wil no doubt look for one of the port restrictors off the 440's or the 52's I own and try a smaller TP just to see...but the rules do change when you run the smaller dia pistons a little.

The Diana barrels work well with RWS pellets though, my 54 stacks superfields at 50 yards and the 440's are just as accurate...so im not worrying to much if i can not get things to balance up.

I will also try 4.53 exacts just to be sure

[slugger]

deffo worth looking into if only for comparison purposes ...... my old 54 loved jsb's .. laser-accuracy at silly ranges,

[Shed tuner]

Been doing a bit more testing, now my 23mm has settled....

Firstly, 83mm is actually too much stroke, even in .177, for 12 FP. 80mm should be plenty, but at least 83 gives you the option of tightening the port, although the piston's second fwd stroke landing is much reduced over a 25mm, so this is less of an issue.

Secondly, it's nice, really nice.

[Shed tuner]

Thirdly....

It shoots medium and lighter pellets to exactly the same POI, presumably because the timing of the surge forces ??? Still thinking about it....

Superdomes, Express, PowaPell, larger H&Ns all shoot with 3mm of the same POI as one another, which is amazing really.

And the fact that this thing shoots 30 yards groups with all of them around 3-4mm c-c, makes it easy to notice

[TonyL]

Sounding very promising then, young JB.

[Black Beard]

I think that there is going to be a stroke length problem with small diameter pistons and the77/97/TX/LGU guns.

To get down to ¾” you are probably going to need about 100mm of stroke length or there won’t be enough air. The TX 200 Mk3 might be able to do 11.5 ftlb at a push* but the rest won’t**.

BB.

*Model says HW25 spring, ~30mm preload, ¾” piston weighing 80-120g with lighter recoiling less if you can stop it crashing, 3mm TP… but it could all be lies and nonsense;-)
**Famous last words. Someone will say they did it back in 1988