TX200 top hat options

[mrgeoff]

Just picked up a lovely mk2 TX200 in LH drive. 177
So after pulling out 5mm of washers, it’s down to just the 1 thin washer and still a bit close to the wind, so need to look elsewhere.

2 things I have noticed, 1 the top hat is quite long, and 2, just about every thread says replace the steel top hat with a plastic one on a 177. (Either of which I could make shorter)

So why do I need less mass if AA have designed it that way? The FAC version has a different top hat so it’s not that.

I’m specificly interested in the combined piston mass, as designed vs the tuners.
Who has the optimum solution to mass vs spring etc.


Thanks!

[JMH123]

A more simple response than you were looking for, but remove that last washer. I recently removed only the slip washer from the bottom of the spring guide and it took 3 1/2 ftlbs off a .22 TX. Surprisingly sensitive......

[jayboy]

Take a coil off the spring?
Surely removing the piston weight and putting a lower profile Delrin version will take away a fair bit of preload, however, the spring will extend quicker as the weight slows the spring, making the cycle slightly slower. I think.

[mrgeoff]

I am more looking for info around replacing the steel top hat with delrin, more the technical reason, and more so if something else needs to be done to compliment the lower mass?


Thanks!

[FPoole]

Replacing the steel tophat with a plastic one will usually help the firing cycle and should lower the power a bit. I don't know why, but it does seem better.

[Shed tuner]

the piston is just too heavy for the stroke/swept volume, for a transfer port of that size.

on the 77 they coppied, the trans post is 3.0 x 6mm. the TX is 3.8x10mm. That's well over doubel the tp volume, so less pressure build up / less bounce, so a heavier piston is the last thing you need. Remember, this was back in the day when everyone thoguht heavier pistons = better...

clearly there is a sweet spot, but a heavier piston takes more force to accelerate to the same speed; on the plus size it resists bounce better.
A light piston accelerates up to speed much faster, but is more prone to bounce earlier.

The MK2 with 230gram piston plus around 20g is just too heavy for it's stroke / TP volume combination. 200g is about perfect - some prefer a little lighter, some a little heavier, but 230 is absolutely at the top end on it's own, without the steel TH.

sleave down the TP when you are in there too.. it'll raise power a fraction and shoot softer. 3.2mm should be nice if it's still full length...

[mrgeoff]

That’s excellent, thank you.

I will have to look up sleeving of this transfer port.

Cheers!

[BTDT]

Sowhy do I need less mass if AA have designed it that way? The FAC version has adifferent top hat so it’s not that.

Since nobody appears to have addressed this question, I’ll have a go.

If an airgun manufacturer orders 2000 mainsprings, 1000 ideal for .177” rifles, and 1000 for the more energy efficient .22”, the unit cost will be higher than ordering 2000 identical mainsprings, so it makes sound financial sense to order 2000 identical mainsprings and make them work in both calibres, which can be achieved in two ways.

The manufacturer could use two different amounts of spring preload, or two different piston weights (doubling as top hats). Both methods have pros and cons.

Using preload to set muzzle energy gives fractionally less, and we are talking a fraction of a millimetre, of primary (rearward) recoil, as well as shave a fraction of a millisecond off the compression stroke, and that’s my preferred method, but it does place the mainspring under greater stress. Using piston mass to set muzzle energy fractionally increases primary recoil, but the spring is less stressed, and that is the clincher for the manufacturer, because they want the rifle to perform satisfactorily for tens if not hundreds of thousands of shots, and not be returned for a warranty repair, or get a bad reputation when the rifles are out of warranty, because over-stressed mainspring creep (shortening) has lowered the muzzle energy.

Air Arms springs are top quality, and I have yet to have one suffer creep even after tens of thousands of shots, but then, I'm not a manufacturer concerned at the prospect of thousands of rifles being returned for warranty repairs, or having my reputation trashed because of rifles failing to perform just out of warranty.