HW 77 power issue

[Amac]

Just replaced the mainspring on my old .22 HW 77. Used a Vmach one of obvious quality. Now I appreciate that manufacturers are careful of producing springs that can send a gun over the limit, but she is still only putting out 9.3. Question is,how do I preload the spring to increase the power,and with what ?
Thanks, Andy

[ikarma70]

i'd put a few hundred pellets through the gun then retest it before adding washers.

[munchman]

Is the piston seal OK ? Also check the breech seal

[Amac]

Thanks for the feedback chaps. Will check the seals out and give it time to settle down a bit. Andy

[PeteB]

As someone already, give the spring time to settle. Stick 200 or so pellets through it and test again.

However, if the old spring was knackered, I would be suprized if the old piston washer was still serviceable.

[I. J.]

Have you been 'energetic' with the spring grease? If this gets between the piston and cylinder walls it can cause drag and power loss.

ATB
Ian

[Phil Russell]

In my (limited?) experience a new spring does not need time to 'settle' in. Providing the spring is a good quality replacement, and it appears to be so, then I would have expected a power increase if the old spring was worn out. Indeed a 'standard' replacement spring can easily put a 77K over the limit and may need trimming back a bit. Did you check that the old spring had in fact become worn ... reduced free length etc? It is possible for a too powerful spring to lead to a reduced power but I very much doubt it in this case.
So I would look at the seals. A worn breech seal is the easiest to replace but the piston seal is not difficult on a HW77. Just take care that you get the right size; 25 or 26mm. I believe BAR web site, or maybe Chambers, will tell you which you need based on the serial number of your rifle. Replace the piston seal and lube correctly. Now piston seals can take a little while to bed in ...

Cheers, Phil

[Phil Russell]

Sorry: should have added that you might like to add a polished steel washer inside the piston to act as a form of bearing for the spring, plus another over the spring guide for the other end of the spring. This smoothes out the spring action somewhat. These will, of course, act as a form of preload at the same time but I doubt if just adding these will raise your power up very much.

You did not say which pellets you were using.... which were they?
Cheers again
Phil

[Seagull]

Apologies for jumping in here but where would I find a spring for the HW77 with reduced power? One that gives a smoother and quieter action?

[Phil Russell]

About 2 years ago I replaced my .177 HW77K spring with a 'standard UK spec' spring from Chambers. There were no mods, but I had polished all internals and relubed correctly. Piston seal and breech seal were standard (and original). The new spring put the rifle a little 'over' so I had to remove about 1.5 coils to bring it to a smooth legal level.
So I suspect that you might have to be prepared to reduce spring length or get someone to do it for you. And you will need a chrono.
Cheers, Phil

[Lumberjack]

Apologies for jumping in here but where would I find a spring for the HW77 with reduced power? One that gives a smoother and quieter action?

This man sells v-mach kits and/or all the bits seperately (including springs).

http://www.air-rifle-tuning.com/

He has also been known to make alterations to springs to "fine tune" the power output. I'm sure he could alter one of his standard ones for you to make sure you got reduced power. All in all a very helpful fella. He should be able to sort you out.

That said there are others on here e.g. Bonnie & Clyde who might be able to assist.

Sorry gents - back to your original thread.

[Amac]

Blimey gents. Seems like I have loads to consider regarding this Vmach spring replacement. I am actually using Accupels. The original spring was longer than the replacement. The newly fitted spring does make the gun easier to cock and it has shot a few hundred pellets since the strip. I am actually getting used to the low power output as the gun still retains high levels of accuracy and consistency. Thanks for the feedback !
Andy

[ikarma70]

the mk1 springs were longer than the later springs,have you tried polishing the compression cylinder?

[Phil Russell]

With Accupels at, I think 14.3grain, you are doing about 543fps. To get to 11ftlbs the velocity needs to go up to about 590. I would not aim any higher as another 15 or 20fps or so would be a tad too close for comfort.
Still, I think 543 is a little low for a HW77. But have you tried other pellets? But then again, we have a .22 HW77 and it runs quite happily at just over 10.5 with what I think is a cut down spring (we had the rifle s/h).
Cheers, Phil

[Amac]

Thanks once again for the advice chaps. Guys at the club have mirrored your comments regarding the seals etc. Will check them out and try and lift that velocity a tad higher I think ! The gun is actually a pleasure to shoot and very easy to cock at present. I may just leave her as she is after all !!!