Air Gun Home :: View topic - My BAM B26-2

eddie1976 · Member

I bought this gun a few weeks ago after going back and forth between this and RWS 34. I settled on this after talking with CW. I recently sent it to him for tune and stock reshaping.

There was little to like about the gun before the tune, the vibration rattle things lose and I actually spend 30 minutes looking for a screw that fell off. Anyway, CW tells me it is shooting great now. I should get it in a week or so.

Here are a few pictures...before and after.

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I will let CW tell you about the tune and the condition of the gun pre tune.

Thanks CW....can't wait to get it home and play

cw · Banned

Well, the first thing that I noticed after post delivery inspection
was that the front stock screws were loose and looked like they
had been for quite a while. The mounting bracket threads were
so worn that the screws felt like they would strip if tightened
at all ( I TIGed them shut, redrilled and retapped them and now
they are better than factory (I know, that's not saying much).

The muzzle brake was very loose, and upon removal, exposed
witness marks that showed that it had been so for a while.

I use an easily removable thermoset two part epoxy to fasten them on.
after that I could finally chrony the gun. Which yielded mid 9 fpe.
Not good.

More on this latter, duty calls. A friend stuck in the mud.

cw · Banned

...rust on the spring and in the compression tube...

...and some nicks in the piston seal.

The big one.

cw · Banned

...I polished the inside of the compression tube and piston skirt.
Then I hand fitted a Tesla piston seal. It's a little slower, but I like
to size them by hand for a more exact fit.

Basically this invoves fitting the seal into the compression chamber
and if it is too tight you remove material from the seal untill it feels right.
You then assemble the gun, run 10 rounds through it to set the seal, then
chrony five shots.
If it's where it should be, power wise, you're done. If not, then you disassemble the gun again and take the seal down a little more, untill
you get the gun where it is supposed to be. Some times it takes five
or six times to achieve top results. You just don't want to take it down too
far or you'll wreck a $20 seal and have to start all over again.

A tiny dab of Molygraph lube is painted only on the back of the seal and then the piston is slid in the compression tube.

AirGunEric · Site Admin

That factory seal looks like the same one from the B18/B19 series. Which means if you're ever in a pinch- try a Crosman Quest/G1/Phantom seal!

Where have you been getting your Tesla seals, CW? Jim Maccari or such?

cw · Banned

The new spring assembly...

... consisting of a new slightly longer spring wound from larger diameter wire.

Controlled at each end with thrust bearings. One on the stationary
end...

...and a 5.7 gram one...

...in the piston...

...

...for a combined stack height of between 0.34 and 0.35" to preload
the longer spring and allow each end to turn independently from
the rest of the mechanism.

cw · Banned

Yeah Eric, Macarri. He's out sometimes, so I need to get a lathe so that I
can fabricate my own out of raw stock instead of having to rely on
someone else.

cw · Banned

What is the size of the B18/B20 seals?

These usually run around just shy of an inch.

AirGunEric · Site Admin

I can't read the digital display on your calipers, but the seal for the Quest/Phantom reads at .9975" on mine at the widest, forward part of the umbrella.

cw · Banned

0.9915". They vary about a tenth of an inch. Anything
the same (or bigger that can be sized down) would work.

The thing with the Macarri seals is that they are so tough.
They are harder and take longer to size and to break in.

AirGunEric · Site Admin

A tenth of an inch- you mean the Tesla seals vary 1/10th compared to one another? The Crosman piece is .0060 in size difference which is less than a hundredth of an inch!

cw · Banned

No, there is not very much variation with the Teslas. I ment
that the OEM seals vary that much.

dummyracer36 · Senior Member

i have honestly never made this connection before, but the main spring looks remarkably similar to a fork spring on a motorcycle. any idea of spring rates? have progressively wound springs been tried before?

progressively wound spring on top, the idea is that the spring rate changes as the spring goes thru its stroke.

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AirGunEric · Site Admin

"Progressive weight" or "variable weight" springs could be used I would think- but I'm not sure what, in respect to the positive, they would accomplish. In a road application (i.e. on bikes or cars) they are designed so that little dips in the road become relatively unnoticeable when the spring is compressed only slightly, but can still support the suspension when a larger "hit" or a load is put upon it. What would this do for an airgun powerplant? I don't know.

The problems with using variable-rate springs in an airgun could get a bit funky I would think- the tighter wound ends would compress quickly and bind while there is still travel in the rest of the coils- but, if you look at your picture as an example, there is a lot more steel in the variable rate spring, meaning that when compared to a constant rate spring, a larger chamber or shorter cocking stroke would be required for it to operate to it's full potential when compared the the constant-rate unit. It might work for a smoother-shooting powerplant, but all else being equal I might suggest the power would be noticeably lower.

Also- ever have variable-rate springs in the rear end of a car? When they are still solid, they work great- but after a couple years in my experience- when they've been used/abused- the spacing in the shorter-coils goes away/collapses- leaving all the load to be carried by the wider-spaced coils, and leaving the a$$-end of the vehicle almost touching the ground. Put in a new set of springs, wait a couple years, same thing. Switch to constant-rate coil springs and car will stay flat/even for alot longer, albeit with a "firmer" ride to it as well.

dummyracer36 · Senior Member

just a slight correction for ya eric, the wider spaced coils are the ones to compress first as the wider spacing dictates the "softer" part of the spring. this can be demonstrated on any bench.
that being said,i only brought up that type of spring for conversation sake as i couldnt think of any advantage to using one in an air gun.