What lubes can I put through the air transfer port

Gas or spring makes no difference. Oil should hardly ever be put in the chamber. Why do you think you need to oil it? If the rifle rifle is an older model then tear it down and clean out all the factory oil. If it’s newer then it already has more oil in it than it needs. Dieseling from oil will damage the piston seal quicker than a lack of oil ever would.
 
When I first got my HW95 it was dieseling pretty bad but I didn’t really know any better at the time and figured it would stop after a couple hundred shots. Last week I decided it was time to learn how to tear it down and clean all the factory lube off, make a few changes and relube it sparingly. Once I got it tore down this is what I found.



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My new, 2019, HW95L .22 piston seal after about 1K shots. I cleaned, polished re-lubed with GPL-205 and installed an ARH kit & Vortek seal. Soundless cocking and very accurate with 715 FPS average using H&N FTT 14.66 gr pellets. Dieseling was caused by over oiling/greasing by the Weihrauch factory.



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Here is another example of dieseling with a HW95.

HW95 OEM seal 1500shots.1645804044.png

 
Modern guns with synthetic seals need very little oil and a couple of drops of chamber lube or silicone oil every two or three thousand rounds is usually plenty.

I have gone far longer between oiling sessions with my Diana 54.

The old leather seals on the other hand require oiling every few hundred shots. Once again apply the oil sparingly.

The guns will usually, squeak or make a honking sound, when you cock them, or loose velocity, when they need oil. 
 
Modern guns with synthetic seals need very little oil and a couple of drops of chamber lube or silicone oil every two or three thousand rounds is usually plenty.

I have gone far longer between oiling sessions with my Diana 54.

The old leather seals on the other hand require oiling every few hundred shots. Once again apply the oil sparingly.

The guns will usually, squeak or make a honking sound, when you cock them, or loose velocity, when they need oil.

What silicone oil do I use? What brand?
 
Gas or spring makes no difference. Oil should hardly ever be put in the chamber. Why do you think you need to oil it? If the rifle rifle is an older model then tear it down and clean out all the factory oil. If it’s newer then it already has more oil in it than it needs. Dieseling from oil will damage the piston seal quicker than a lack of oil ever would.

I don’t plan on doing it now. I’ll do it after around 1000 shots. The rifle is new.
 
Modern guns with synthetic seals need very little oil and a couple of drops of chamber lube or silicone oil every two or three thousand rounds is usually plenty.

I have gone far longer between oiling sessions with my Diana 54.

The old leather seals on the other hand require oiling every few hundred shots. Once again apply the oil sparingly.

The guns will usually, squeak or make a honking sound, when you cock them, or loose velocity, when they need oil.

What silicone oil do I use? What brand?

RWS and Crosman both market some silicone chamber lube but I only had some 3-in-one silicone oil. So, that is what I used on my Diana 45. It seems to quiet down the honking and squealing of the gun when being cocked. It is silent and smooth when cocking now. It did detonate for two shots before it returned to normal firing after the two drops of oil though. Probly should have left it sit overnight for the carrier to evaporate a bit more. I have never checked it with the chrony to see the results. 

Before that I used the Beeman Penta-dry, a couple of times, although I never trusted the stuff for some reason.
 
Modern guns with synthetic seals need very little oil and a couple of drops of chamber lube or chamber oil occasionally it's good.

I have gone far longer between oiling sessions with my Diana 54.

The old leather seals on the other hand require oiling every few hundred shots. Once again apply the oil sparingly.

The guns will usually, squeak or make a honking sound, when you cock them, or loose velocity, when they need oil.

He speaks with experience and wisdom. The lubricant used is only half the equation; the other other half is the materials being lubricated.

Silicone oil is a great leather-to-metal lube. It is an absolutely TERRIBLE metal-to-metal lube. Go for a high quality and fairly stiff oil, available at places that sell radio-control model car stuff: https://www.rccaraction.com/silicone-oil-explained-weight-w-wt-versus-cst/#visitor_pref_pop

For plastic seals, something like Abbey SM 50 or the old Beeman Ultra Lube is good - a fairly stiff mix of silicone, moly powder, and other selected ingredients. Use in VERY sparing amounts.


 
This subject has as many opinions as there are member's of AGN. If Beeman and RWS ( including back in the Dynamit Nobel days) recommend 1-2 drops of SILICONE chamber every 500-1000 shots then it was done for a reason ! I've done it on factory guns since the 1980's and still do today. One drop every 500-600 shots. The velocity on my FWB 124D has stayed up long after that one drop of oil has stopped producing any smoke in the barrel after firing ! When I first bought it 775 fps with 8.4gr JSB was the average. After one drop, and several hundred shots later, the velocity is still 800 fps with same pellet. Why ? Because even though the oil isn't creating combustion (smoke in barrel) the silicone molecules are still present on the cylinder compression chamber walls. Less friction translates into faster piston movement. That means greater peak pressure and more velocity. Over lubing is bad and many people make that mistake. My comments are based on stock airguns. Special lubed tuned airguns probably don't need to be lubed in the chamber but who knows ! 
 
I'm in the camp of no oil in the transfer port, silicone or otherwise. Especially in a Hw90. You'll be lucky if it doesn't burn through the factory seal without adding oil to it. Weihrauch has been over lubricating their guns the last couple of years. The Hw90 is a very high pressure gun that burns through factory seals if it just lightly overcharged when lubed correctly. It happened to my Rx1. 

In my early days of playing with springers I used the RWS silicone oil in a Hw30. After adding just three drops it clocked over 900fps and blew out the seal. So it will detonate if you use too much. I still have the bottle and you can have it for the cost of postage if you want.

Silicone oil has no place in an airgun. Even a leather sealed gun has to have better options because silicone is absolutely a terrible metal lubricant that contaminates and degrades the rest of the proper lubricants. There's always a thin layer of grease throughout the compression stroke in the best sealing airguns. Silicone oil will only wash that away. 

Do what you want, but you're a thousand times more likely to do more harm than good. I never lube my guns through the port (or cocking slot) and I get tens of thousands of shots on my guns between seals.
 
I'm in the camp of no oil in the transfer port, silicone or otherwise. Especially in a Hw90. You'll be lucky if it doesn't burn through the factory seal without adding oil to it. Weihrauch has been over lubricating their guns the last couple of years. The Hw90 is a very high pressure gun that burns through factory seals if it just lightly overcharged when lubed correctly. It happened to my Rx1. 

In my early days of playing with springers I used the RWS silicone oil in a Hw30. After adding just three drops it clocked over 900fps and blew out the seal. So it will detonate if you use too much. I still have the bottle and you can have it for the cost of postage if you want.

Silicone oil has no place in an airgun. Even a leather sealed gun has to have better options because silicone is absolutely a terrible metal lubricant that contaminates and degrades the rest of the proper lubricants. There's always a thin layer of grease throughout the compression stroke in the best sealing airguns. Silicone oil will only wash that away. 

Do what you want, but you're a thousand times more likely to do more harm than good. I never lube my guns through the port (or cocking slot) and I get tens of thousands of shots on my guns between seals.

" After adding just three drops it clocked over 900fps and blew out the seal. "

Like I said, some people over lube their airguns. As you just indicated.