GUN FOR OPTIMUM CAST BULLET FIT
Optimum bullet performance, cast or
jacketed, is impossible if the gun's guiding surfaces aren’t capable of holding
and starting the bullet in perfect balance. The causes of inferior accuracy and
excessive fouling, with lead especially, are: rough internal finishes, eccentric
chambers/throats, oversize throats and, or, bores, rapid changes (roughness) in
twist rate, and constrictions or lumpy bore diameters.
Constrictions or diameter
changes are almost certain where revolver barrels thread into frames. Although
manufacturers have corrected this considerably since LBT made the public aware of
the problem. All guns can have bore diameter changes at any point along the barrel where it was
machined, stamped, or welded on the exterior, including contouring, etc.
worst possible condition is probably a bell-mouthed bore, or enlargement at the
muzzle, and, unfortunately, it’s not uncommon. For your personal information, jacketed bullet
fouling only causes inaccuracy when it builds up enough down close to the throat
that the muzzle becomes bell-mouthed. This will make it more bell-mouthed and less accurate
with jacketed. With cast, the increasing bore diameter as the bullet travels down the
bore, causes the rifling to lose its grip on the bullet, and worst of all releases
hydraulic lube pressure which is essential for obtaining high velocities. Lapping cures the problem.
If you haven’t read that elsewhere, it
is because people have not been able to feel out and measure bores. Push through
slugs measure it exactly, and are how I learned it!
The following list of items will help you
turn most production class barrels into premium performers, and in fact improve
most premium barrels, for use with jacketed or lead. Our push through slugs will
let you feel the problems and our lap kit will fix them.
The rifle throat slugs
are primarily for fitting cast bullets, and will find rifle throat sizes EXACTLY,
and show whether they are out of concentric or off center with the bore and all
other bad throat conditions.
With the bore lapping instructions provided
in the lap kit, we show you how to make the
best of the worst and get good performance. To put it in a nutshell: shooters
commonly believe that if a rifle will not shoot jacketed accurately it will not
shoot lead accurately either.
However, if a rifle won’t shoot jacketed well
because of internal problems, our goodies will tell you why, no matter what the
cause, and normally can make it a stellar performer with lead or jacketed.
SLUGS – Package of 2.
Price $4.00 Ship weight ¼ pound
These are a smooth cylinder of soft lead
for taking an EXACT impression of rifle type throats. LBT developed Rifle Throat Slugs
because no chamber cast is accurate enough to be useful for cast bullet fitting.
First you need to obtain all of the items you need to slug your barrel.
1. A Rifle Throat Slug Kit from LBT.
2. A 3 foot section of cold rolled steel rod which fits your bore as closely as
possible. This is available from most hardware stores.
A fired case of your rifle's caliber, filled to the top of the case with lead.
4. A large hammer.
Insert the lead filled case into the chamber and close
the action. Rest the butt of the rifle on the floor and insert the Rifle Throat
Slug into the muzzle end of the barrel. You may need to use a piece of wood or
similar hard non-marring material to start the slug. Carefully set the steel rod against the end
of the slug and tap lightly with the large hammer. Your intent is to swage the
slug over the end of the lead-filled rifle case and fill the throat portion of
One should use Rifle Throat Slugs as a reference when loading jacketed, but we
consider them mandatory for fitting cast, to determine the most suitable bullet
to fit the throat. The round cold rolled steel rod is softer than the barrel, so it will not damage
your bore in any way if the instructions which come with the slugs are followed.
These slugs are available for all calibers. Be sure to specify your caliber when
ordering. Only one per gun is needed, if done right. We send two in case of a
To select one of our straight bullets,
measure your throat slug to find the full diameter bearing length which will
fill the cartridge neck, yet contain the bullet base or gas check, with the
forward driving band in contact with the throat taper or rifling. Our spitzer
chart shows a bearing length, and the LFN’s overall length and ogive length,
which, when deducted, gives the bearing length.
If your rifle has a
very large throat and chamber, send the throat slug with the cartridge it was slugged
on with your order. Also send a dummy round loaded with a jacketed bullet so I can determine
how much larger the cast bullet can be over the jacketed sample. I'll cut a mold with a
body that fills the case neck and start of the throat with a large diameter, and reduce the
nose to whatever groove diameter is at the point where rifling begins. Sizing in a
standard sizing die will provide a close chamber fit and a quick grab on the throat
as the bullet starts forward, while the groove diameter nose will be engaged and
centered in the rifling before takeoff. I know of no better way to build a bullet for
large throats and chambers than this.
Keep in mind that our bullet designs are
very strong, and will shoot superbly without all the traditional fitting and
fooling. After all, we have many customers who can shoot our revolver bullets
into 1 inch groups at 100 yards with revolvers, which says something for their
design strength! Rifles are far more gentle on bullets than revolvers, so you
can expect our designs to give accuracy without a bunch of traditional cast
Because it is critical that revolvers be
measured accurately before and during lapping AND when selecting a bullet mold
diameter we developed push through slugs, which are listed and explained a bit
farther along. For example, if one attempts to lap a revolver barrel while the
cylinder throats are undersized, the effort is wasted. The same thing applies if
bullets are fitted to undersized throats, or fitted undersized to oversize
throats. Don’t guess about bullet fit or a gun's internal dimensions. It’s as
erroneous as not looking at the sights when trying to print tight groups.
To measure for a mold using push through
slugs, only three are needed in most cases, and detailed instructions come with
the push through slugs. Barrel to cylinder throat relationship can be proven by
feel as explained in the slugging instructions sent with the slugs.
It is crucial to accuracy with revolvers
that barrel constrictions from barrel to frame threads and roll stamping on the
outside of the barrels be removed, and any roughness smoothed up, which can ONLY
be done by lapping. Push through slugs will make the necessary internal
measuring easy, and our lap kit will fix the barrel and cylinder problems.
Please read the following information about each carefully.
Price, $8.00 per pack of 20, ship weight ¼ pound
For optimum results with any rifled firearm
we consider it mandatory to know the critical interior dimensions which guide
the bullet. By knowing the shape and size of a gun's throat and bore, the
jacketed bullet shooter can more wisely select an appropriate bullet, while the
cast bullet shooter can both select the most suitable bullet design and fit it
to the gun properly.
Push through slugs are one of LBT’s
latest developments, which make it possible for anyone to manually feel how the
barrel grips the bullet as it travels down the bore, and especially lets you
feel whether it has a firm grip as it exits the muzzle, giving a very precise
indicator of the barrel's accuracy potential. (The first time you feel the jerks
and bumps your bullets feel you WILL be shocked! Everyone is!) They are used for
obtaining a precision impression of cylinder throat diameters of revolvers, and
groove diameter at various points inside rifled barrels. Measuring the slug with
outside measuring equipment such as a micrometer, dial caliper or electronic
caliper will then give an exact diameter of the hole through which the slug was
We recommend push through slugs for checking
lapping progress, both by feeling out the barrel and by measuring.
Push through slugs have a tail that slip
fits into standard cleaning rods to hold them firmly while reaching through
actions, throats and chambers, etc. LBT offers push through slugs for all
calibers from 22 to .50. Be sure to specify whether it's for rifle, revolver, or auto
pistol when ordering, as several calibers are different in rifles than handguns.
We can’t send the correct diameter if we don’t know what gun it is for.
LBT BORE LAP KIT
Price, $18.50 ship weight ¼ pound
The current LBT bore lap formula is a
highly concentrated abrasive compound developed and manufactured by LBT
specifically for lapping barrels by firing lead bullets which have been
impregnated with it. (Which is why some call the process fire lapping.)
aggressively yet smoothly, without excessive throat wear. It is field proven on
thousands of barrels, with no bad reports, while most get from good to dramatic
accuracy improvement and reduction of bore fouling, using either jacketed or
lead bullets. It improves bores by straightening bore diameter end to end, and
by smoothing out rough finishes and variations in twist rate, which is
accomplished primarily by straightening and smoothing the leading edges of the
rifling lands. There are few things a shooter can do as rewarding as running a
push through slug through a lapped bore that felt cobble stones before lapping, and
feel the slug slide through tight all the way as smooth as glass. Then
you see the improved groups on target, knowing you fixed it yourself.
The lap kit contains very detailed and
complete instructions and enough abrasive compound to lap anywhere from 100 to
500 guns, depending on gun type, bore condition, and how liberally it is used. The lap
compound is used with customer supplied cast bullets. (DO NOT USE WITH JACKETED, AND BY
ALL MEANS DO NOT PURCHASE ANY LAP KIT OR SUPPLIES WHICH USE JACKETED BULLETS. DOING SO WILL
ABRADE THE THROAT EXCESSIVELY AND WILL NOT DO A PROPER JOB OF LAPPING A BARREL.)
The abrasive compound doesn’t deteriorate with age. This compound and instructions are all
you need to lap 22 rimfires, including 22 magnum, by applying it to low velocity 22 ammo.
Notice that our kit has one abrasive grit
only, and is intended ONLY for use with lead bullets. Any lap kit using multiple
grits and especially jacketed bullets will shorten barrel life dramatically and
not do a proper job.
Price $10.00 shipping weight ½ pound
Precision ground cold rolled steel plates used
to impregnate bullets with lap compound to prepare for bore lapping. You can use
glass or make your own whatever size you like. We use a 1/8 x 1 x 4 bottom plate
and a 1/8 x ¾ x 6 top plate, which is an ideal size to handle and work with. If
you make some, we recommend you try this size. Lap kit instructions tell how to