Anyone know how these work?
pictures of the internals?

http://www.enidine-defense.com/PDFS/Recoil_Products.pdf

http://www.enidine-defense.com/Recoilmain.html

Remember, hydraulic systems perform differently based on ambient temperature.  You will notice a *significant* difference in a hydraulic operating system at -40F and at 110F.  There have been reports of hydraulic buffer systems causing issues in extreme cold.  Google-fu will help you in your research.

Yes there will be a small amount of change from the fluid being cold.

Now, you can mitigate that with a full synthetic oil...if the mfg hasn't already done this...

Synthetic oil costs about 4 times the money...so I'm sure the cheaper units will be using a natural or cheaper oil...

Just like a 100% synthetic oil pours the same at -20 at it does at 120 for engine oils...ask someone about it running in diesel engines once...

These days there is a synthetic oil that will do what you need...

Just my take on it...and yes I use lots of synthetic oils in the super cold...it -15 today down to -18 or so tomorrow...and that isn't a wind chill...

Bret

Royal Purple Hydraulic Oil, its the best stuff on the market and it has many different ranges, additives for longevity and leaks. Its the only thing I put in the rear end of my truck, and it has many uses. Marine, gears, automotive, etc.. you name it. You can't miss it when you walk into autozone or whatever part's store you have its the only purple bottle.

Yep,

Royal purple I've used it too...

But my friend stock Amsoil and it's fairly local...so I goto Amsoil...

But either is good, I think the only diff if the label and maybe a slight different additives...

They are bot good to go...

I use only synthetic oils...brwt