Slavia 631 tune up... (practical demo of why huge transfer ports are bad)

[Shed tuner]

I know these are not they are common, but they are decent and cheap, so figured I'd stick this up for info...

Got a 631 lux the other day... decent enough gun.

Chrono'd as follows
8.4 gr JSB - 510 fps
7.9 gr JSB - 520 fps
8.3 gr Superdome - 530 fps

Google tells me this is pretty close to expected performance for these. The JSBs were a bit loose in the lead in, hence the lower power.

The gun felt OK to fire, but maybe a fraction slammy with the JSBs. Figured I may as well strip it down and give it a basic tune...

I found the piston washer in poor condition. Weird looking fitment, so I just machined the piston nose flat and converted it to take an HW seal - the cylinder is 25mm, so seemed an easy solution. This effectively added 4mm to the stroke, so I had to lengthen the cocking lever slot in the piston by the same amount.

Second significant thing was the huge transfer port - 3.8mm x 21mm Now this is a low powered, short stroke gun, so that port is way oversize. Sleeved it down to 3mm with a bit of brass tube glued in. Could easily have gone smaller (say 2.7), but this size was to hand.

Finally I did what I originally intended to do - fitted a beer-can piston sleave, and a small steel top hat, lubed it all up and put it back together.

I gave it a couple of dozen shots to settle down and stuck it on the chrono. Now bearing in mind I kept the original (quite weedy) spring, and slightly reduced the preload (stroke increase 4mm - top hat thickness 2mm = -2mm preload).

Superdomes were now just a fraction shy of 700 fps

Shot cycle was noticeably snappier and smoother, and the reaction at the target end having gained 3 FPE was fairly clear. Accuracy a bit early to say, but certainly sub 1" at 30 yards.

HTH - JB

[markmac]

Sounds very interesting Jon.I really admire you clever folk who can work magic with springers.Just goes to show that you don't need an expensive rifle to have fun with.

[Shed tuner]

The other advantage of working with cheap guns is that if it all goes horribly wrong....

[bigtoe01]

Jon

HW55 has 25mm bore, piston is a mix of alu and steel around 170g weight, skirt is not hardened, stroke is around 67mm (from memory) maybe 68mm, TP is 4mm x 26mm long.

So now:

Bespoke piston, all steel, 72mm stroke, trigger block machined back to give more spring room, spring is near stock 6fpe one...TP reduced to 2.7mm x 26mm..result 10.5fpe with ease using superdomes. The piston is O ringed, im going to alter this to an LGV seal. Making new pistons for 3 HW55's this month, the pistons are to be made from 25mm tube 3mm wall, only the nose and 8mm of the skirt at the end will be just 24.5mm, the centre section of the piston tubes will be 22mm or so, the cocking arm will push back on the skirt like on an LGV etc. Pistons will rotate, goal weight is 210g maybe 220g, springs will be close to stock hw55 stiffness etc but smaller od to fit the 19mm id of the tube im using, all will have LGV seals...im hoping to see 11fpe from all 3. All 3 will have 2.6mm TP's...the last one i mention is already at 2.7 so im leaving it there...this too eventually will get a another new piston and the old one will go up for sale.

The old one is seriously accurate but a little hard on shot feel, very very consistent however...im thinking converting to LGV seal will soften it up and just maybe release 0.5fpe more power. I have seen an old HW50 make 11.5+ with 72mm stroke 25mm bore etc....remembering the old 50 is a cheaper version of the 55 so there is hope.

All these guns are .177...

If the 55 had a 10mm long TP it would have been easy to get 11+ fpe from them, little harder with the long TP. Also seen an old Venom tuned one...they left the TP at 4mm dia, never going to be nice to shoot left like that.

T 20 found some 4mm OD tube with a 2.5mm ID, wish i could find the same tube online...any idea's?

[HW777]

Has Ringwood precision engineering not got any 4mm tube with 2.5mm ID in stock, If not, I would have thought solid 4mm bar could be drilled out to 2.5mm ID easy enough.

www.ringwoodprecision.com

[joffy]

Jon




T 20 found some 4mm OD tube with a 2.5mm ID, wish i could find the same tube online...any idea's?

tony have you tried drilling a bit of 4mm rod

[Shed tuner]

Good info Tony

I think these are even shorter stroke (mine is now around 65) and defo lighter piston though !
Next job for this one isn't more power, it's getter the trigger to perform better...

I use bits of old telescopic antenna for sleeving ports, but nothing as thick as you are looking for - for those oversize ports I just turn down a bit of brass, tap/glue into place, and then drill to suit. Tube would be easier though.

Your 55 plans sounds good, but with the LGV seal's lost vol might you need to go even smaller with that port ?

ATB - JB

[T 20]

T 20 found some 4mm OD tube with a 2.5mm ID, wish i could find the same tube online...any idea's?

I didn't find it Tony, I machined it.



All the best Mick

[Phil Russell]

hi Jon
What a superb thread ... quite cheered me up on a dull drizzly morning. I have never tried sleeving transfer ports nor making piston heads to take, for instance, HW seals ... maybe I should experiment a bit more than making leather seals for veteran rifles.
Cheers, Phil
An afterthought: I tend to collect any bits that 'may be useful one day', including odd bits of metal tubing. A few bits I have are from electronic equipment where they were used as spacers between circuit boards etc. ... came from defunct radios etc. Always strip such things down to see if there is anything potentially useful.

[bigtoe01]

tony have you tried drilling a bit of 4mm rod

yeah i have...it would just be dead easy if i had 4mm od 2.5mm id to start with

[bigtoe01]

I didn't find it Tony, I machined it.



All the best Mick

ahh...well i have 4mm round bar already and i can get K&S 4mm od tube with a 3mm id so plenty to choose from

[bigtoe01]

Good info Tony

I think these are even shorter stroke (mine is now around 65) and defo lighter piston though !
Next job for this one isn't more power, it's getter the trigger to perform better...

I use bits of old telescopic antenna for sleeving ports, but nothing as thick as you are looking for - for those oversize ports I just turn down a bit of brass, tap/glue into place, and then drill to suit. Tube would be easier though.

Your 55 plans sounds good, but with the LGV seal's lost vol might you need to go even smaller with that port ?

ATB - JB

Jon the old 55 has a thread in collectors where me and T20 were working out how to get it to 11fpe...i did meet some resistance from the leave it alone its a lovely gone brigade along the way but we pushed on
I actually have tested it back at 6fpe and its nicer than it was at stock..so that 4mm port is to big even at the lower power level

I was thinking about the LGV seals, i may only see 70mm stroke with them BUT thats still enough the trick is no mad springs like venom used to fit, as close to stock spring rate as possible so the gun is unstressed, much like your 631

I have 4mm brass rod and drills from 2mm to 4mm in 0.1mm steps so I can just machine the tube up, im thinking of drilling to 2.3mm and sending a tapered reamer in from both ends to form a slight venturi with 2.5mm in the middle and 2.7mm at either end.

[TonyL]

I know these are not they are common, but they are decent and cheap, so figured I'd stick this up for info...

Got a 631 lux the other day... decent enough gun.

Chrono'd as follows
8.4 gr JSB - 510 fps
7.9 gr JSB - 520 fps
8.3 gr Superdome - 530 fps

Google tells me this is pretty close to expected performance for these. The JSBs were a bit loose in the lead in, hence the lower power.

The gun felt OK to fire, but maybe a fraction slammy with the JSBs. Figured I may as well strip it down and give it a basic tune...

I found the piston washer in poor condition. Weird looking fitment, so I just machined the piston nose flat and converted it to take an HW seal - the cylinder is 25mm, so seemed an easy solution. This effectively added 4mm to the stroke, so I had to lengthen the cocking lever slot in the piston by the same amount.

Second significant thing was the huge transfer port - 3.8mm x 21mm Now this is a low powered, short stroke gun, so that port is way oversize. Sleeved it down to 3mm with a bit of brass tube glued in. Could easily have gone smaller (say 2.7), but this size was to hand.

Finally I did what I originally intended to do - fitted a beer-can piston sleave, and a small steel top hat, lubed it all up and put it back together.

I gave it a couple of dozen shots to settle down and stuck it on the chrono. Now bearing in mind I kept the original (quite weedy) spring, and slightly reduced the preload (stroke increase 4mm - top hat thickness 2mm = -2mm preload).

Superdomes were now just a fraction shy of 700 fps

Shot cycle was noticeably snappier and smoother, and the reaction at the target end having gained 3 FPE was fairly clear. Accuracy a bit early to say, but certainly sub 1" at 30 yards.

HTH - JB

Excellent result, Jon.

And cheers to you and Tone for sharing all this info.

Once the trigger's to your liking, will you be bringing the little Slavia to the Bash?

[Shed tuner]

Once the trigger's to your liking, will you be bringing the little Slavia to the Bash?

I definitely will, 'cos I'd either have sorted the trigger, or got pi55ed off with it and be flogging the gun

(it's not that bad - certainly better than the meteor's; I reckon I can get it pretty usable)

[Shed tuner]

OK, got the trigger sorted... It's now pseudo 2 stage... it's still single, but after a short "first stage" movement it goes a little firm, and more pressure releases; crude, but light enough and completely predictable, so job done

Unfortunately I'm not completely convinced on accuracy - could be better. The barrel is over 20" long which is OTT at 12FP, never mind 9 !
I'm thinking of chopping it down to 16" (which is still technically too long, but will be much better and still very easy to cock) and doing a recrown.
I'd also expect to gain 10-20 fps as a result as it simply hasn't got the air volume to maintain pressure over that barrel length.

Will let you know....