Sweet shooting 77k ‘recipe‘?

[lightning22]

Some time ago I bought a .177 Mk2 25mm 77k from Protek, the first 77 I’ve ever owned. It came with some Venom-ish bits on it (engraved pistol grip cap in brass and a cocking aid) and the internals had bearings fitted though it wasn’t thought to be Venom work when I put pics up on here. There’s a delrin guide and top hat fitted too.

It would have been best described as cosmetically challenged, virtually no bluing, stock varnished with a stick and a broken mainspring. Some lump has clearly had a few good swings at removing the foresight as witnessed by various dink’s in the underside of the barrel. The same lump looked to have tried to remove the end block by bashing the trigger unit, leaving creases in the casing.

I did a rust blue on it which came out pretty well, rebuilt the trigger into a new casing, fitted a new transfer port seal, an Aussie main seal and a Titan spring, I also picked up a nice CS500 stock which puts the bluing to shame.

After screwing it all together it had a pretty harsh cycle, nice and smooth to cock, but not to shoot, the grouping was correspondingly a bit rubbish and the rifle got parked in a corner mocking me whilst life turned itself upside down in more ways than one.

So, after the rambling start.. the rifle is in bits and packed up ready for Paul Chell to work his magic on the metalwork hence this post really. I get the feeling that the Titan spring is probably a bit harsh for the rifle, and has about 1 1/2” of preload. The piston slides through the compression chamber with fairly gentle finger pressure.

So, what would the HW tuners recommend for a spring, amount of preload and (looking at Shedtuner here) transfer port sizing, for a soft shooting action in one of these classics?

[Shed tuner]

how gentle is the piston pressure (ie how tight is the seal) ?
It's pretty hard to get a bad shooting 25mm 77, so I'm worried the sealing is suspect...
Also try chopping a coil off the spring (without removing the piston and disturbing as little as possible). If power goes up or stays the same, it's over sprung... find a more suitable spring. How thick is the wire ?
Finally, maybe worth checking the "lump" hasn't drilled out the Tp to something silly.. 3.5-3.8 is fine, much more will be detrimental...

You need to fix it before you tune it...

[lightning22]

how gentle is the piston pressure (ie how tight is the seal) ?
It's pretty hard to get a bad shooting 25mm 77, so I'm worried the sealing is suspect...
Also try chopping a coil off the spring (without removing the piston and disturbing as little as possible). If power goes up or stays the same, it's over sprung... find a more suitable spring. How thick is the wire ?
Finally, maybe worth checking the "lump" hasn't drilled out the Tp to something silly.. 3.5-3.8 is fine, much more will be detrimental...

You need to fix it before you tune it...

Hi Jon,

The piston won’t fall under its own weight but slides down easily when you push it. Just weighed the piston and it comes in at 228g with seal attached.

The wire on the spring measures up at 3.2mm, the compression chamber is packed up with the rest of the metalwork, but the tp didn’t look as though it had been molested when I checked the seal.

[BTDT]

It is very difficult to bog up the 25mm HW77.

I did try a Mk.3 TX200 mainspring in mine with 32mm of preload, which gave 10.9 ft. lb. and a very refined recoil cycle with 7.9gn pellets.

[Hsing-ee]

3.5-3.8 is fine, much more will be detrimental...

Can you just stick a HSS 3.7mm in your Black and Decker and run it through or do you need a drill press and several sizes of bit and a reamer and stuff? It's done from the breech side I presume, but does the piston side need finishing or something?

Basically, can this be done at home, by a monkey, using hand tools?

[Desmond.22]

I've had a couple rifles re blacked by Paul and absolutely beautiful work.

Really impressed with what he has done,

Coincidentally one he did for me is a 77k mk2 now in cs600 stock but absolutely beautiful rifle.

Looks good with comp tube blacked too.

https://youtu.be/Pa2JWg23S4g

[Shed tuner]

It's pretty hard to get a bad shooting 25mm 77, so I'm worried the sealing is suspect...
You need to fix it before you tune it...

It is very difficult to bog up the 25mm HW77.

Yup

Maybe that 3.2mm spring is too stiff - worth trying something softer, if you are sure the seal is OK.

[Shed tuner]

Can you just stick a HSS 3.7mm in your Black and Decker and run it through or do you need a drill press and several sizes of bit and a reamer and stuff? It's done from the breech side I presume, but does the piston side need finishing or something?

Basically, can this be done at home, by a monkey, using hand tools?

Al, you can use a 3.5mm drill, and then give it a finish polish with a small rat tail file, and finally some emery. You will prob end up around 3.6mm, and it should be pretty smooth. But reamers are cheap and better, and you will use them time and time again.

[lightning22]

It is very difficult to bog up the 25mm HW77.

I did try a Mk.3 TX200 mainspring in mine with 32mm of preload, which gave 10.9 ft. lb. and a very refined recoil cycle with 7.9gn pellets.

Thanks, if my description of the seal fit isn’t causing raised eyebrows I guess I’m looking at the spring again, I know Titans can be a bit on the stiff side and that shortening it will only make it comparatively stiffer, so looking for a softer spring may be at least part of the answer.

[TonyL]

It is very difficult to bog up the 25mm HW77.

I did try a Mk.3 TX200 mainspring in mine with 32mm of preload, which gave 10.9 ft. lb. and a very refined recoil cycle with 7.9gn pellets.

Excellent tips from JB, as ever.

And this is the spring that I'm most curious to try (and have big expectations of) when next fettling a suitable recipient.

[lightning22]

I've had a couple rifles re blacked by Paul and absolutely beautiful work.

Really impressed with what he has done,

Coincidentally one he did for me is a 77k mk2 now in cs600 stock but absolutely beautiful rifle.

Looks good with comp tube blacked too.

https://youtu.be/Pa2JWg23S4g

This will be the second rifle that Paul has done for me, he re-blacked my JB1 beautifully. I’ve also had rifles done by ISP and Colin Molloy, all with superb results. The only one that almost went wrong was the one I was in the process of sending to RichardH when he went incommunicado.

[Hsing-ee]

Al, you can use a 3.5mm drill, and then give it a finish polish with a small rat tail file, and finally some emery. You will prob end up around 3.6mm, and it should be pretty smooth. But reamers are cheap and better, and you will use them time and time again.

Thanks Jon. I have cleaned up the TP on an HW35 so should be easy enough. I'll look into these here reamers...

[eyebull]

Basically, can this be done at home, by a monkey, using hand tools?

It turns out that yes, it can
https://www.airgunbbs.com/showthread...39#post8109939

Followed Shedtuners advice and it was pretty straightforward. Just do it by hand, take your time and let the tool do the work, no force required. Need to back out now and again to let the swarf clear.

[deejayuu]

Have seen early 77s with, apparently, original long/soft springs 290 mm x 26 lb/inch rate.
Also later with shorter stiffer springs around 235 mm x 38 lb/inch rate.

Titan 5 looks a match for the shorter spring except diameter too small for standard guide
Titan 11 cut down will give the rate but again would need guide/sleeve.

Current HW "one size fits all" looks good from specs.

[lightning22]

Have seen early 77s with, apparently, original long/soft springs 290 mm x 26 lb/inch rate.
Also later with shorter stiffer springs around 235 mm x 38 lb/inch rate.

Titan 5 looks a match for the shorter spring except diameter too small for standard guide
Titan 11 cut down will give the rate but again would need guide/sleeve.

Current HW one size fits all looks good from specs.

Thanks, the one that is in will be a No.1 as that’s the recommended one for the 77. I can always re-deploy it into another rifle.