by John St.Clair
|In an effort to squeeze a bit more
accuracy out an AR, shooters will mount a variety of sighting devices on
the rifle. While the "flat top" AR is more suitable for the variety
of optics and sights on the market, one sometimes finds themselves owning
the more traditional version with a permanently attached carry handle.
You can mount a scope, holographic sight, or some other aiming device on the carry handle by affixing one of the many aftermarket rails to it. But despite the claims of precision by the manufacturer, machining tolerances are different between manufacturers. Unless the mounting rail is perfectly fitted and properly secured to the groove in your carry handle you will often get a point of impact change caused by the rail shifting in the groove of the carry handle.
Regardless the price you paid for it, the carry-handle mount may not be as stable as you think. I found that even tightened down, mine could be flexed in the rail, changing point of impact by several inches. The solution was to glass bed the mount into the rail. Not permanently mind you. It is still removable.
The process is simple, will provide the best possible fit for the rail, and minimizes the possibility of the rail shifting. It may or may not eliminate the problem, but it removes one more potential element for error.
There are several very good materials available on the market to perform this operation. However, I would recommend either "Marine Tex" or a good glass bedding kit. Both of which are available from Brownells.
Just be sure to apply release agent to the handle so it doesn't end up a permanent fixture. This operation can be performed on an assembled rifle or with the lower unit removed.
all mounts, rings etc. from the accessory rail. Remove the accessory
rail from the carry handle and clean it with a solvent that won't leave
a residue such as Gun Scrubber or carburetor cleaner. This will ensure
the resin achieves positive adhesion to the metal.
Coat the threads of the stud(s) and nuts that attach the rail to the carry handle with gun grease to ensure resin doesn't get into the threads and permanently freeze the nut in place.
Release agent is NOT recommended for the threads. When you screw the nut onto the threads, the release agent will be stripped out of the threads. Don't forget to coat the nut itself in grease or release agent as well.
Carefully mask off the sides, front, and rear of the carry handle. A bit of artistry is involved here. You'll want to put tape over all areas except the inside of the carry handle's groove. Bring the tape up to the top outside edge of the carry handle but not over the edge. Make sure you do not put tape anywhere the accessory rail will contact as this will keep it from forming a good tight fit once the tape is removed.
Use modeling clay, putty or even playdough to block the groove at the rear to keep resin from migrating into the sight mechanism.
|Apply masking tape or some kind of
covering to the rifles upper, especially in the area under and around the
carry handle and anywhere resin might drip or get smeared. I would
also recommend covering the rest of the upper with a towel or cloth to
ensure nothing inadvertently drips or smears on the rest of the rifle.
Resin has a bad habit of getting on your fingers and can easily transfer
to the rifle if you touch it.
Apply a layer of release agent to the groove in the carry handle of the rifle. The Brownells glass bed kit comes with release agent.
When the release agent has dried, thoroughly mix the bedding material per the manufacturers instructions. Spread the resin evenly in the carry handle groove. Not to much but you'll want to get enough resin in it to squeeze out a little bit all around the accessory rail.
Place the rail in the groove and gently help it settle into place. Using a small flat object, (a popsicle stick works pretty well), remove any excess resin as it squeezes out.
Once the rail is settled in place thread the nut(s) onto the stud, but do NOT tighten it. Thread it in until it just contacts the carry handle and snug enough to keep the rail from moving around. Again, check for, and remove any excess resin.
Allow the resin to harden per the manufacturers instructions. After the resin has completely cured, you may remove all the masking tape and coverings from the rifle. Remove the accessory rail from the carry handle, trim off any excess resin, and remove the release agent as well.
Your accessory rail should now be secure and less likely to shift your point of impact. Reattach your rings, bases, optics etc. and you're ready to go. You will of course, have to re-zero your rifle.
Article by John St.Clair