A few ramblings

[Shed tuner]

Hi Dave, I'm tempted to think that the reason for getting a big vac25 power increase with the weak spring variants is 'cos of the extra lost volume those seals have - without that lost vol (i.e. with the HW and to a less extend the walther seals), the weaker spring would be letting the piston bounce far more, sapping power disproportionately.

FWIW I've pretty much settled on ~78mm stroke and 210g, with an HW or walther seal, and shortened 3.5mm port.

Lots of good info on this thread

[Shed tuner]

One thing i did notice and do notice with every TX i shoot is the god awful metallic clank of the skirt of the piston hammering into the compression tube and driving the whole lot forward to muller the oring seals.

I notice it on every one i shoot and i hate it, its enough to give me a headache especially if the stock is walnut.

that should never happen.... on stock guns there is around 3mm clearance. On doing the short port mod, you may have to take 0.5 - 1mm of the front edge of the rear skirt to gain clearance.

[Two200's]

that should never happen.... on stock guns there is around 3mm clearance. On doing the short port mod, you may have to take 0.5 - 1mm of the front edge of the rear skirt to gain clearance.

I understand now.
However, i still hear and feel a metallic clank with these guns, which is absent on HW's.
What could it be?

[NickG]

The TX here has 235g piston, 82mm stroke, HW30 seal and LGV spring and rear guide, a mate cocked it last week and thought it was a .22 running 8fpe and yet its a .177 running 11.3fpe....transfer port is 3mm shorter than oem, same dia.

Not everyone likes a 235g piston, some like 190g pistons and much stiffer springs, NikG's 97 was much harder to cock but had an awesome firing cycle...a modular piston would give that capability, steel head, alu head, steel rod, steel skirt, alu skirt, all bases covered, just imagine the weights that could be hit with minimal machining. Also consider a rod 40mm longer such as what i put in my Diana's, i don't want a steel nose as that will push the piston weight to high, I want an alu nose to drop the weight I added with the longer rod.

Much bigger picture here Dave....stop thinking 97/77 and TX, add in all the Diana under lever and side lever range too along with LGV LGU range also

The 97 you tried at the bash, had a 26mm piston at around 170 grams, with a 4mm port, It was nice. Since built one with 25mm comp tube same piston weight and a 3.6 port, and its something else, really small amount of movement when shot , but I suppose I have turned it into one of my TX's Prosport ( Charlie) is building one and has been picking my brains, I wonder how that one is shooting ?

[bigtoe01]

The 97 you tried at the bash, had a 26mm piston at around 170 grams, with a 4mm port, It was nice. Since built one with 25mm comp tube same piston weight and a 3.6 port, and its something else, really small amount of movement when shot , but I suppose I have turned it into one of my TX's Prosport ( Charlie) is building one and has been picking my brains, I wonder how that one is shooting ?

It probably shoots much like my 440 did with the ubber light piston, the only issue is the fulcrum is all messed up on the under lever and i needed a hydraulic press to cock the gun...it hardly moved on the firing cycle though

The 77 and TX have a much better cocking linkage fulcrum, way easier to cock, some day I may alter the 440 and unleash the beast as i know it could be utterly superb.

[TonyL]

The one thing I won't do & I've said it before is size a seal, you take the "skin" for want of a better word off the seal, that's just plain asking for trouble imo. I've known power fall off very rapidly using sized seals so to me it's just not worth it. One other thing that can create problems is absorbtion..remember the BSA nylon/poly heads?
Put it in prospective we are talking running in seals not adding 20 more spring coils because the seals tighter than a nuns nudger!

I've never sized them, preferring to let them run in. Having said that, I've never fitted one that I deemed too tight. This suits me as (a) I'm a lazy git with so little spare time and no real workshop. When I was younger, the workshop was my dad's garage - at the moment it's the kitchen table!! . (B) I'd always be paranoid of taking too much off.

Jim Tyler pointed out in a recent article how sized seals tended to peak very quickly, which reinforced my thoughts.

And Graham Henderson (now a committed PCP man!! ), who I shot FT with many years ago, told us all about his "hydro forming method" of sizing a HW77 seal to the cylinder by boiling them in water. Apparently loads less friction, so less spring required......But he also told me that they went off quicker, too.

[bigtoe01]

which brings us full circle to needing a softish material to make a buffer from and use an o ring with set crush to form the seal...works perfect every time and cost around 3p to swap out after 15k rounds

[Jonas]

Now, I appreciate folk can get a V-Glide kit and I admit I've been a long term very satisfied user of Steve's awesomeness, but are the V-Glide kits 25 or 26mm?
If they're 25, then it's all ready done.


But if they're 26.....

Mine is 26mm, bit I think Steve Pope offers 25mm also. I fitted a new type Weihrauch seal, it shoot unbelievably well now!

[wonky donky]

Hi Dave, I'm tempted to think that the reason for getting a big vac25 power increase with the weak spring variants is 'cos of the extra lost volume those seals have - without that lost vol (i.e. with the HW and to a less extend the walther seals), the weaker spring would be letting the piston bounce far more, sapping power disproportionately.

FWIW I've pretty much settled on ~78mm stroke and 210g, with an HW or walther seal, and shortened 3.5mm port.

Lots of good info on this thread

Yes Jon I have thoughts along those lines too but it's a huge increase so I suspect something else might be going on.

It seems we are not too far away on strokes & piston weights Jon, I do like anything between 78/83mm depending on port & spring.

I had a few copies of the LGV springs made up a couple of weeks back so will repeat the tests using those when I get time........Also I should have some LGU piston seals any day now, will test them with the first spring & then with the LGU spring.

[wonky donky]

Much bigger picture here Dave....stop thinking 97/77 and TX, add in all the Diana under lever and side lever range too along with LGV LGU range also

Who's going to buy a Dodgy Diana except you & Barry? They need sorting at the factory first! I have a sorted 280 here I can't give away.

[flatrajectory]

Who's going to buy a Dodgy Diana except you & Barry? They need sorting at the factory first! I have a sorted 280 here I can't give away.

I'll take it off you Dave.....

Pete.

[wonky donky]

I don't know why I didn't think of you Pete knowing your a collector of rubbish & cheap tat.

[NickG]

which brings us full circle to needing a softish material to make a buffer from and use an o ring with set crush to form the seal...works perfect every time and cost around 3p to swap out after 15k rounds

My polyurethane heads are holding up well

[bigtoe01]

My polyurethane heads are holding up well

Yep I bet they are, however I feel something harder such as 110s is what im thinking would be better, it would machine better and hold its form better.

How did the Ertalyte TX head perform?

[NickG]

Yep I bet they are, however I feel something harder such as 110s is what im thinking would be better, it would machine better and hold its form better.

How did the Ertalyte TX head perform?

I have it on one of my skirt less pistons with a guide made from the same, Its very smooth, I like the ertalyte its easier to hold a tolerance when machining than the delrin. I find the delrin is a bit awkward to drill a good hole in. IE for spring guides.

I use the poly because I can make them with an HW fitting and it will expand to fit, do you think the 110 shore hardness would do the same?