In my book, Acraglas gel is the one I have settled on for customer jobs / recommendations. Get the GlasBed version if you are a beginner because it comes with everything and doesn't require measuring out. I use it a lot too because it is so handy. make sure you prep the surfaces to get a mechanical lock (undercutting the recoil lug region, for example) in addition to the normal 'stickiness' (a.k.a. keying).
I have been doing some research into the various properties and this is what I have found ... As a rule of thumb the thinner the epoxy the better the 'keying' into the stock material so I personally stay away from putties. If using a putty engineering a mechanical lock of some sort would be very important. Also, the slower the cure the better the keying because it has more time to soak in. I thought the slower cures were also harder but reviewing specs on about 100 different epoxies this past weekend shows that not to be true, or even a rule of thumb. Some of the faster ones are very hard.
Here's an interesting fact: Simply stated, keying is the ability of the epoxy to microscopically penetrate into the pores of the material being bonded and harden like that, locked or 'keyed' in place. That is how epoxies operate. The resulting curing process converts them to an inert material which chemically sticks to nothing so keying is very important. That's why, when attempting to bed many 'tupperware' stocks, it stays put for a period of time but eventually falls right out. Oops. Also, epoxy will only chemically bond with itself while it is still tacky. (don't feel bad, I didn't know that either) If fully cured one must do the mechanical lock thing to be sucessful.
I realize other epoxies are good also, and use about 10 different types for other purposes (including 10 feet tall, 6 inch diameter high-powered rockets that break the sound barrier) but for bedding purposes I have found nothing better.
On the subject of marine epoxy, just got me a jug of West Systems 105 with some various filler agents for the rockets, but I may try a rifle with one. Specs say 0% shrinkage with an 83 hardness so it should be great when thickened. Aeropoxy 6029 would be a good candidate also. Both are formulated to take a pounding, one for waves and the other for light aircraft.
After doing one rifle way back when with Pam as a release agent I'll not do that again because it left ripples & waves in the epoxy. Guess you have to keep it on thin which makes me nervous. Use it all the time on screws and small stuff however.
I don't use any waxes either as it is difficult to remove completely from the metal and also hard to see gaps where it may not have been applied. Also seems to change the color of the steel also, perhaps this is because of residual wax remaining.
Acraglas release agent rinses off completely with warm water and is relatively easy to see on the steel in good light.
If you haven't tried it out yet I have been using the new Brownells Acra-20 in the dispenser gun with great results. Bit pricey to get set up but really easy and very accurate to use if you are doing a bunch of pillars or something. Self mixes in the tip and you can put it right where you need it.
Whatever you do don't get the stainless gel, it's soft and it smells like steel to high heaven even after it cures. I put like 1CC of it on a block over a month ago and it still stinks, it'd spook game for miles.
