Quoted:
Actually the supplied instructions specify using JB weld.
braindoc

Quoted:
The tricks to getting a good bond are:

REALLY clean surfaces.
Use Acetone or another really good solvent to degrease and clean everything.  The less grease on the parts the better adhesion.
Use the solvent and a solvent-proof toothbrush to clean, flush with fresh solvent, allow to mostly dry, then use a hair drier to warm the parts up.  Note I said WARM, not real hot.
The warmth will bring any remaining lube out of the metal so you can see if you need more solvent cleaning.
Don't touch the areas the epoxy will contact with your fingers.

For areas you DON'T want epoxy sticking, apply some sort of release agent.  If you don't over warm the parts, you can use a paste wax.  Just apply a thin coat and DON'T wipe off.  This will prevent the epoxy from sticking and any excess can be cut and peeled off later.
Brownell's epoxy kits come with a liquid release agent, and you can buy it separately.
You'll want a release agent on the front 1/4 of the barrel everywhere except right were the epoxy needs to be.
If you can, put release agent all over the sight base except where the epoxy will go.
Make sure no release agent gets where the parts will fit together.

A good mix of the epoxy.
The mix needs to be very exact for the best bond.  Many epoxies are 50-50 so it's easier.
If you have a small scale, you can actually weigh the components to get them right.
After dispensing, you want to get the components WELL mixed.
If the instructions call for mixing one minute, do 1 1/2 minutes or more, as long as the epoxy doesn't start "kicking over" and begin curing.
Try to keep air bubbles out by not "whipping" the mix.  Just stir well.

Have the barrel and parts ready to go, clean, and test fitted to insure everything is going to fit.
Have the parts pre-warmed slightly.  You can have a hair drier on them or other method of just slightly warming them.  Again NOT HOT, just warm.  Epoxies cure by internally generated heat, and the warmth will help give a faster, better bond.

Apply the epoxy and put the base on, you want to use no more epoxy then necessary so there won't be a huge glop of excess running everywhere.
Have some method of pressing the base in place and holding ready to go.
You can use rubber bands, weights, a clamp of some sort, etc.  It doesn't have to be a lot of pressure, just enough to hold it down.

Put the assembly in a warm place and allow to cure until the epoxy is in a rubbery state.
Keep an eye on the excess you mixed up so the epoxy won't get too hard.
With the epoxy in a rubbery state, use a plastic or brass "knife" to cut the excess epoxy away, then allow to fully cure at least 24 hours.

As with all these sort of things, the fine details of prep are where how good the bond is will be determined.