Benjamin 310 - silicone oil or 30W ND for the pump cup?

[nervoustrigger]

I am rebuilding a 1957 model 310 for a buddy.  I’ve completely stripped it down and cleaned everything.  The pump cup somehow appears to be in good shape so I’m not going to replace it unless it proves to be bad after reassembly.  I have no way of knowing if it had ever been replaced but if not, that is remarkable longevity and a real testament to their knowledge of seal material at the time. 

Anyway, on to the question.  Generally I’ve used 30W ND for my pump guns but in PCP pumps we use silicone oil on dynamic seals.  Any reason to prefer one over the other for this old 310?

BTW, the barrel is fully separated from the tube so I’ll be trying my hand at resoldering it.  I don’t expect it to be too tough with a pencil propane torch.

[RobertMcC]

I would just used the old 30W ND. They were made before a time of synthetic.

[nervoustrigger]

Okay thanks Robert, and that may be reason to recognize it’s not a natural rubber pump cup.  Petroleum products attack natural rubber pretty aggressively.  Natural rubber also has a relatively short shelf life/calendar life, and we’re confident it hasn’t been rebuilt any time in the last 20 years at least.  So my guess is it probably is a Buna-N in which case I can use 30W dino oil.  I just wasn’t sure if silicone wouldn’t be a better choice given how well it works in a high stress application like a hand pump or electric HPA pump.

[Yng@hrt]

I've had good luck with secrete sauce & pneumatic gun oil.

[RobertMcC]

Okay thanks Robert, and that may be reason to recognize it’s not a natural rubber pump cup.  Petroleum products attack natural rubber pretty aggressively.  Natural rubber also has a relatively short shelf life/calendar life, and we’re confident it hasn’t been rebuilt any time in the last 20 years at least.  So my guess is it probably is a Buna-N in which case I can use 30W dino oil.  I just wasn’t sure if silicone wouldn’t be a better choice given how well it works in a high stress application like a hand pump or electric HPA pump.

I'm no expert. Just figured it was made in a time before. It's what I would used. But that's just me.

[Habanero69er]

The difference between silicone oil & 30W ND is that both work inside the rifle, but silicone is a poor metal to metal lubricant like pump arm pivot points. So of the two choices mentioned & if you were to want to use one lube for all...30W.

I'm a Secret Sauce man myself. It's got the right lubricants for metal to metal & rubber seals.

[nervoustrigger]

Thanks, that is a good point.  Seems like it’s inevitable that the two lubes would eventually cross-contaminate so I think I’ll stick with the 30W.

[Hoosier Daddy]

Yeah... ND-30, or Crosamn pellgun oil, secret sauce, or MMO... even ATF has been used.
 So let me know how the Soldering goes. I have a buddy who has a sepperated barrel 310. I have told him to to buy another gun for parts. But I would sure like to try saving it for him.

[nervoustrigger]

Thanks, I’ll let you know about the soldering.  The black zinc coating on the tube was significantly worn so my goal is more about getting it functional again than preserving a museum-quality piece.  That lifts the anxiety of literally putting a torch to an antique. 

[ped]

silicone would be fine to lube the seal but I'd use secret sauce or the motor oil for the previous reasons

[nervoustrigger]

The soldering went fine except the barrel port got plugged and I had to carefully open it with a ball-shaped carbide burr.  That was tedious.  If I ever do another one, I'll fill it with a sacrificial plug first.

Supplies were a small propane torch, flux, solder paste, and rosin-core solder:
 

The two pieces prepped for soldering:


I used my finger to apply the tiniest film of flux to both surfaces, then painted some solder paste onto the contact surfaces under the barrel, then clamped it for soldering:
   

Fired up the torch and began soldering.  Got it hot enough that touching the wire solder to the surface would cause it to wick under the joint.  Here are a couple of closeups immediately after soldering:

      

Looks better after cleaning off the flux:
   

After that, I cleaned it up and began reassembly.  I had a few choice words for the valve but eventually got it back together.  She pumps up and fires!

[Wayne52]

Great job on the old pumper there Jason.  Back when I was a kid we built our own slot cars using copper or brass for the belly pan, we used silver solder to make them.  We (both brothers and I) had good luck using the old butane solder tips and it would flow really well.  Silver solder was the only thing that worked and didn't crack from the abuse of these cars flying 20ft at the big bank turn.

[Hoosier Daddy]

Great news!
 I was concerned the bronze would distort under the heat of the torch. You must have a delicate touch!

[ped]

great result