Benjamin 342 Steroid project

[Tack Driver 10]

I've worked on a few of these Benjamins so this will be a similar mod.
Steroid pump link, replace the valve internals and upgrade the piston.

Picked up this 342 about a year ago from a member.
It needs work but was offered a good deal on it.

Serial # T 9234 so made in 1969?
It's in overall good condition but the main pump bushing is toast.
No problem, MAC1 billet pump link to the rescue.
The stock is average with a good amount of battle scars typical of a 50 YO gun.

Stripped the stock and steamed out the majority of the little dings.
Made a manly (super size me) walnut pump arm with a dark finish to replace the tootsie.
This pump arm was originally to go on a 312 but the stripes matched up on this gun nicely.

Replaced the valve internals with a lighter spring and Delrin stem.
Shorter hammer spring with a poly bumper to limit stem travel to .100".
New pump cup on the original piston for now.

I'll post baseline chrony results later.

 

[avator]

Love the pump arm handle.

[Hack21]

Ron,

What does limiting the stem travel accomplish on a dump valve? 

Any idea what the inlet check valve pressure will be?

Looks great by the way.

Thanks.

[Habanero69er]

Yeah, I like the pump arm too. Almost looks like a pump action shotgun.

[Tack Driver 10]

Ron,

What does limiting the stem travel accomplish on a dump valve? 

Any idea what the inlet check valve pressure will be?

Looks great by the way.

Thanks.

The bumper is primarily there to cushion the hammer impact.
With the light valve spring the hammer can hit the back of the valve.
Can also dry fire the gun without damage.
I leave the travel at .100" since that's all that's needed to fire the valve.

I think the pressure at the check is a lot less than 2K.
Probably closer to 1200 psi.

[Tack Driver 10]

Yeah, I like the pump arm too. Almost looks like a pump action shotgun.

Exactly my thoughts when modding the 312.

"The forearm and steroid link make the gun look like a serious pump shotgun.
Makes you want to grab it and rack that mutha!....LOL"

https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.msg155881675#msg155881675

[Tack Driver 10]

Ran the gun over the chrony with the stock piston and new seal.

05 pumps 509 FPS 08.23 FPE
08 pumps 604 FPS 11.58 FPE  some retained air

Replaced the short hammer spring with the long stock spring.
Replaced the stock piston head with a test poly piston head.

03 pumps 469 FPS 06.98 FPE
05 pumps 600 FPS 11.43 FPE
08 pumps 706 FPS 15.82 FPE  full dump

Velocity results are very close to the 312.
Next I'll make an o-ring piston head from peek and install the steroid pump link.

[Tack Driver 10]

Made the piston head.
Used peek shaped like a pellet with a duro 70 poly o-ring.

[Hack21]

Made the piston head.
Used peek shaped like a pellet with a duro 70 poly o-ring.

Ron,

Now you are just showing off!  That's awesome.

Thanks.

[Tack Driver 10]

Made the piston head.
Used peek shaped like a pellet with a duro 70 poly o-ring.

Ron,

Now you are just showing off!  That's awesome.

Thanks.

Well, maybe just a little bit.....LOL

Installed the pellet piston and steroid pump link in the gun.
Velocity was the same as with the test piston head and stock pump link/tootsie.
Has minimum cam over, not going to push this gun.

The gun is mostly done but still has the temp pivot pins in the front plug.
Here it is with a rare guest appearance from the 312.
Twins, separated at birth?....LOL

[sicumj]

Like the bumper on the pump handle.  I use cabinet bumpers on my pump handles, makes a big difference out in the field noise wise between shots.

[avator]

Ron, should I give you my home address? You know, just in case you get tired of looking at it... 

[Habanero69er]

Like the bumper on the pump handle.  I use cabinet bumpers on my pump handles, makes a big difference out in the field noise wise between shots.

A 3-4" strip of the fuzzy side of some Velcro works as a good noise dampener also.

[Tack Driver 10]

Ron, should I give you my home address? You know, just in case you get tired of looking at it... 

LOL....I still have your address unless you moved since you sent the 312.
I do have to thin the herd out some.