Installing Weaver Scope Bases on Contender Barrels

Making a few checks along the way and taking necessary precautions
installing Weaver scope bases will help keep the base secure and also help
safeguard the screw holes from stripping out.

Normal maximum thread contact is about 4 1/2 threads in Contender barrels.
With less than 4 threads of contact, there is an increased risk of the
screws stripping out due to over tightening, high recoil, or simply bumping
or jarring the scope and mount. (Note that the TC "Duo Mount" is especially
lacking in thread contact, so use caution with this design deficiency.)

Holes should be tapped out with a "dead bottom" tap. This picks up about
1/2 turn of thread contact, but is best reserved to those experienced with
tapping small blind holes. See the "More Advanced" comments below.

The Weaver screws that come with the bases have a projection on the bottom
end of the screw that is smaller and not threaded. This limits how far the
screw can go into the hole and should be ground off. When I convert the
bases to 6-screw, I cut the countersinks deeper and use different screws
normally. I also have a special set up just for grinding screws to length
with threads all the way to the end. An individual can do this himself,
also, on a bench grinder or with a Dremel type hand grinder.

When installing a Weaver base, be sure to tighten down each screw
individually, then try to wiggle the base. If each individual screw does
not hold the base down tight, the offending screws must be shortened so they
do. Each screw tried should then be removed and examined for 1) deformation
at the tip from bottoming out in the hole or threads not going far enough to
the bottom of the hole and 2) marks on either the under side of the screw
head or on the tapered part of the countersink in the base, indicating the
screw is pulling down tight in the countersink.

If there is deformation on the tip of the screw and the hole has been tapped
all the way to the bottom, then grind some off of the tip a little at a time
until the screw does pull down tight with no deformation of the tip.

If you put a screw in the base, then hold the base up at eye level, sighting
across the underside of the base, side to side, the tip of the screw should
come just about flush with the bottom edges of the base. On barrels that
have not had the holes tapped out all the way to the bottom, the screws may
need to be very slightly above the bottom edge of the base. If you will
then sight down the underside end to end and count the number of threads
exposed on the bottom, you should come up with at least 4 threads. They are
hard to see, yes, and a magnifying glass may be a must. You can also use a
knife edge to follow the ridges of the threads down, following the crest and
counting each thread as you go.

Bolts and screws should always have a length of thread contact that is at
least equal to their diameter, and if you will do some measuring, you will
find that it takes this approx. 4 1/2 threads to achieve it on the 6x48 base
screws. If the thread contact is less than this, they will be more prone to
stripping out, and since the steel in the barrel is somewhat softer than the
screws, it will most often be the barrel's internal threads that strip out.
There are "saves" for stripped out holes using Brownell's .146x48 oversize
6x48 screws, but in these shallow holes increasing the diameter any at all
is a step backwards, and fitting these screws which only come in about a
1/2" length can be a lot of work. Plus, stripped screw holes degrade a
barrel, even when salvaged with the oversize 6x48s.

Thread Lockers. I do use and recommend them. I use the "nonservice
removeable" grade of red Loctite. But most grades are ok except the bearing
Loctite. However, with the cone shaped heads of the Weaver screws, with
proper fitting of each screw, there is little likelihood a Weaver base will
work loose.

Which brings up a side note: Especially on barrels with brakes that produce
fore and aft inertia forces on the base screws, I am totally, totally
against fillister head (flat bottom) screws in bases, any brand or type of
base. I go so far as to use Weaver screws in bases countersunk for
fillister heads in order to get the security of the cone on the underside of
the head to keep things centered and prevent movement of the base within the
limits of the clearance that is always present around every screw in every
base. I have from time to time also used fillister head screws in the
Weaver type cone shaped countersinks.... just so there is a cone somewhere
to keep things pulled to center rather than having two flat surfaces, bottom
of screw head and bottom of countersink, sliding against each other. Think
bases don't slide under recoil? Think again. In many situations they
don't, but in more extreme situations they definitely do. 4 puny screws, or
even 6, simply do not have that much clamping force available.


More Advanced:
6x48 taps are available from Brownell's, as are Weaver type screws with
slotted, hex socket, and Torx heads.

I'll not attempt to describe here how to grind a tap for dead bottom and
must caution you that there is a relatively high risk of breaking off a tap
while chasing the threads to the bottom of the hole. After many thousands
of holes, I still break off taps every couple hundred holes or so. And, of
course to save my bacon, I have pretty reliable ways of removing broken
taps, but it is still no fun and puts a barrel at risk. So do use caution
chasing threads to the bottoms of holes.

If, or once, you have a 6x48 tap, one of the best ways to hold a screw for
shortening it is to take a small strap of 1/8" thick steel and drill & tap a
hole in it. Clamp the strap in a vise or use a "C" clamp to clamp it to a
bench or other object to hold it steady, then screw each base screw into
this hole one at a time. Then file or grind the end of the screw to length.
I prefer simply filing them.

Take a few strokes with the file and try the first screw in the base screwed
down tight on the barrel. Remove the screw and make the observations above
regarding deformation at the tip and indications of a firm seat in the
countersink in the base. Once you get the right length, you can use the
first screw's protrusion through the hole in the strap to guage how much to
take off the remaining screws. But because there will often be minor
variations in the depths of the screw holes, do not assume that a give
length will be right. The right way is to check each screw. It may take a
little longer, but it will help guarantee that you are getting the maximum
holding power of each screw.

There is a right way and a wrong way to mount the Weaver bases, and
unfortunately, Weaver is somewhat lax about the importance of full thread
contact with their bases on Contender barrels. (Holes in Encore barrels are
about 50% deeper, but still should be checked as above as a precaution.)

While this article addresses Weaver bases in particular, it has of course
parallel applications with all types of bases on Contenders.

Mike Bellm