Tuning Springer Bore and strokes.

Mycapt65 said:

I'm always curious about bore and strokes on my Weihrauchs. It gives me an idea of power and build potential. I recently measured a few. These statistics can be hard to find on the net, so I figured I'd post them here for orhers to reference. These are approximates. Probably within 1mm.

25mm bores
Beeman R7/Hw30 -60mm
Beeman R8 -65mm

26mm bores
Hw50/99 -70mm
Hw77/97 (IIRC) - 81mm
Hw95 85mm

30mm bore
Hw80/R1 -80mm

Feel free to correct me or add to the list. I feel this is important information and should be correct and complete.

Be well all
Ron

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What am I looking at? The bore and the stroke?
I heard that the HW35 has the bore of an R1 but is short stroked?

.20calguy said:

What am I looking at? The bore and the stroke?
I heard that the HW35 has the bore of an R1 but is short stroked?

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Correct. ~65-70mm stroke I believe

67mm is what the published lists elsewhere say. Slight variation between synthetic and leather seals. From what I recall reading there was an even shorter stroked freimark variant for the German market. I have one sitting at home that I've yet to disassemble and measure to verify though

Hw90 30x85mm

Its all about the peak pressure wave, when the pressure is at max in the compression stroke.
When the pellet break loose pressure drops fast. Then if the piston is fast and have not spend all the air the wave holds on little longer to allecerate the pellet true the bore.
Its a fine art between peak pressure, pellet fit and sweptvolume

Here you go, with a few extra details (TP volume and static compression ratio) so you can get an even better idea.

Note the HW80 and 35, it's often said the 35 is just a baby 80 but it's not just the swept volume that as reworked....

JamieUK said:

Here you go, with a few extra details (TP volume and static compression ratio) so you can get an even better idea.

Note the HW80 and 35, it's often said the 35 is just a baby 80 but it's not just the swept volume that as reworked....

View attachment 537197

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Very interesting info. I had no idea that the late model TX200 had such a long stroke.
R

EMrider said:

Very interesting info. I had no idea that the late model TX200 had such a long stroke.
R

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That's one of the big reasons why they shoot better short stroked or with a 22mm kit for 12ftlb guns. That long stroke is very unnecessary if you don't want the powa

Excellent thread - much obliged!

Thankyou for explaining all this .
Question : which is a smoother shot cycle / short or long stroke ?

Hey Ron, good information .

Given MY tuning experiences, what surprises me in tuning the (26mm) HW77 vs. HW95 with the same spring, resulted in greater power with the HW77‘s in .177 caliber. Maybe it was the (more true) compression chamber on the two HW77’s, but they both generated significantly more power vs. the HW95’s with less stroke.

I needed to remove coils off the springs of the HW77’s to calm down power/recoil.

Could there be a design difference causing this or is this just a coincidence?
Maybe a dieseling phenomenon …….. but I don’t think so .

I think theres a couple variables there. Look at the transfer port dimensions and piston weights. The 95 is squeezing the air through a teent hole, 2.5x longer with a piston 10% heavier. I'm guessing here a bit but I would imagine the longer TP allows it to build more pressure before releasing which slows the piston down some.

Yeah, I never thought about it in detail, but completely dissimilar designs create differences in air flow efficiency. The increase in efficiency completely offsets (and more) the 4mm stroke difference.

Where as the 5mm stroke difference measured between the HW90 vs. HW 80 (same air flow design) creates a huge power advantage for the HW90.

Ultimately, this just points to tuning adjustments to be made in seeking the ideal tune .
The HW90 can be adjusted via the gas ram‘s pressure setting, but coils likely need to be cut on the HW77. I don’t think I noticed this differential when I tuned my .177 HW97.

77 vs 95.....basically, a pellet gains the majority of its velocity while it and the piston are moving in the same direction.

In the 77 the pellet will let go sooner in the pistons travel, and because of the short port the energy can be 'transfered' with less resistance.

SCR is a nice figure to know (especially if your looking to improve the manners of an old rifle with a huge port for example), but in some ways is a bit meaningless as it doesn't/ cant take pellet release/ port flow into account.

Someone asked the question above about which stroke/ diameter/ port etc is best/ ideal and the truth is.....there isn't a best, its personal choice. I've lost more days/ weeks than I can remember obsessing over the perfect sub 12 set up, building/ modding/ balancing/ small bore pistons/ playing with strokes/ TP's etc etc etc, and then.....one day....you pick ya old leather sealed HW35 for a plink (which on paper has stats that would make an onion cry) and realise... its got a properly nice cycle, is easy to shoot accurately, and is bloody lovely just as it is. Whats that all about then

That’s the beauty of a properly set up spring piston airgun. Springs, pistons, levers, properly applied greases, and correctly fitting parts working in concert with each other to accurately launch a pellet towards it’s target. It’s a thing of beauty.

Sure you could just use a PCP and dispense with all of this. But what fun is that?