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.
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
deformation at the tip from bottoming out in the hole or threads not going far
enough to the bottom of the hole and
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
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.
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 "non-service re-moveable"
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
More Advanced: 6x48 taps are available from Brownell's, as are Weaver type screws
with slotted, hex socket, and Torx heads.
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
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
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 gauge 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 given
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.