HW55 power spring

Beeman suggested an R8 spring for the HW55's. I don't want a kit. Just a spring. The leather seal in it is probably fine. I can make my own fitted guide if necessary. Should I add a steel top hat to increase the piston weight a little bit? I probably wouldn't be using light wadcutters in it.

I have three 55's. One came to me (1976-77 model SM) without sights so I mounted a scope and like the way it handles. The stock fits my big ape hands well. I'm planning to add a steel muzzle weight like the one shown. Maybe a little longer but only a few ounces. Not a bench or 10m rifle. I want to carry it comfortably.

LOL! I'm not trying to turn it into an R9. 

Thank you in advance for any useful advise. AND

Have a blessed Easter weekend

Air rifle Headquarters.

https://www.airrifleheadquarters.com/catalog/item/251488/925874.htm

JM is the guy for springs.

Okay,,,,, which spring? 

The link should be everything you need. 
I believe Jim will do custom work if you call him. I’ve had no problems with his springs.

@kwk

Send him an email telling him exactly what you have, he will recommend the correct spring for your application. 

I wouldn't add weight to the piston end unless you put it together, shoot it, and it's bouncy. I predict it won't be. 

These have large 4mm transfer ports, and are setup to basically partially slam at the end of the stroke to prevent bounce that hurts accuracy and lengthens lock time. Adding weight would likely make it slam worse with a leather seal and a hotter spring. 

A parachute seal may pick up some braking action with a hotter spring, and may benefit from piston weight. 

But just a drop in with the leather seal, I wouldn't add weight right out of the gate. 

One thing you can do to get more spring room, is face off the threaded end of the receiver plug almost to the stock screw hole. This will allow you to get another coil or two of spring into it. 

Mine has a longer spring and a flat faced synthetic seal with the above modification. It shoots about 670fps with a 7.9gr pellet. I'd tell you the spring dimensions, but I have no idea, I just dug it out of the drawer and tossed it in spaced to coil bind. I do know it's almost certainly .120" wire. 

The original factory spring for the OLD HW 50 (this is much different from the current gun of that name) works very well in the HW 55 - no surprise as the two were basically the same gun. As you mentioned, this was a pretty common upgrade back in Beeman's heyday. I have a 55 set up that way and actually like it a little better than the OEM target spring, it feels a little crisper and less buzzy to me. 

The Maccari HW 55 springs that I've put in my guns shoot significantly hotter than the factory target spring, so you may find that one suits you as is, especially if spaced up a bit. His "old HW 50/R8" spring, in my experience, gets about 20 or 30 FPS more speed than his 55 spring when pushing the leather piston seal, but is noticeably stiffer to cock. I use Jim's kits with spring guide BTW, have not tried a spring alone as a drop-in on factory parts.

All that being said, the JM springs I've used were purchased several years ago, and I am far from a pro tuner! All I do is clean, lube, and install his goodies. Jim is always tweaking and improving things, so they could be different today. I second Mr. Bentley's note to chat first.

Thank you gentlemen .