It's often possible to convert an older gun from rimfire to centerfire, let me show you
one way to do that. Here's an old Winchester Low Wall 1885 that I've had rebored and then
chambered it to 357 Magnum. This gun was made in 1891 and the original 32 caliber bore was
badly pitted. The breech block is still in the original 32 rimfire configuration with
the firing pin designed to hit the edge of the case. Since the barrel is now chambered
for a centerfire cartridge the 357 Magnum, I'll need to move the firing pin to hit the center
of the primer. I'm going to plug the original firing pin hole before drilling the new one.
We start by clamping the breech block in the milling vise then drilling out the old firing
pin hole with the #28 drill, being careful not to drill too deep. Then tapping it for an 8x40 screw.
I'll chamfer the mouth of the hole then degrease both the screw and the threads.
Using green Loctite on the threads I'll turn in the screw till the tip is flush with the
backside of the firing pin channel. Once the Loctite is cured I'll cut off the excess screw
and peen the outer edge of the screw into the chamfer. The vice is padded with tape to keep
from marring the breech block. Any remaining material is dressed off until it's flush.
Next, I'll locate the new firing pin hole. I could convert the rimfire pin to centerfire,
however, I've got an original centerfire pin with a broken tip. To locate the new firing
pin hole I've made up a bushing to position it in the center of the firing pin channel.
I'll drill all the way through with a 5/64" bit. To prepare the broken firing pin for a
new tip I'll chuck it in the lathe and face off the broken part of the pin. After center
drilling the face of the firing pin, I'll drill the new hole about 3/8" deep with a
5/64 drill. The new tip is made from a piece of #49 drill rod, I'll check to make sure it
doesn't bind. Old-timers would have used soft solder but modern chemistry has given
us green Loctite which will hold it securely. I'll shorten and around the tip till I have
about 50 thousandths of protrusion I'm using a washer to prevent cutting the tip too short.
The last step on the breech-block is to drill a 5/64" vent hole. I'll locate it in the same
position as on the factory centerfire gun. This is really important for centerfire cartridges
as it will help vent off the gas if a primer is pierced. The hole extends all the way into
the firing pin channel. All that remains is to reshape the extractor for the larger cartridge.
I'll install the extractor and scribe a mark to note how much material to remove.
Then carefully grind off the excess.
I'll reinstall the extractor and very carefully use the 357 chamber
reamer to cut it to final size. Once everything is back together
I'll function test it with a dummy round, then I'm off to the range.
When test-firing with some 38 special ammo it's obvious the firing pin is hitting too
low on the primer. A firing pin that doesn't hit the center won't always fire the round.
To demonstrate I've got the parts assembled on the outside of the action the three key
parts are the breech block, finger lever, and the link which holds them together.
Since the breech block is a little low in the receiver, raising it to align the firing pin
with the center of the primer requires a new link with the hole slightly farther apart.
Looking at the old case it appears I have to raise the breech block about 40 thousandths to
center the firing pin on the primer. Because the link is at an angle I'll have to increase the
length by a little more than 40 thousandths to raise the block the correct amount.
The whole spacing on the original length is 428 thousandths.
I'll make a pattern link out of quarter-inch brass since it's quicker to shape than steel.
The holes are drilled with the #9 drill, I'll trace around the original link to mark the shape.
I've applied dicom to make the scribe lines more visible the
bottom hole is extended about fifty thousandths
and the outside edge is blended around the new hole. Then the pattern link is cut out and shaped.
Obtaining the original shape of the link is very important as this bump retracts the firing pin
when the lever is opened. Once the brass link is finished we can reassemble the gun for a simple
test. You may get it right the first time or maybe not. Now I'll make the real one out of
steel. Notice this little curve in the link it's needed for the longer link to clear the inside
of the action. All this left is to harden it using Kasenit. First the link is heated red hot,
then dipped in the Kasenit powder
and heated red-hot again, before quenching in water. Now the surface is hard and will
resist wear as the gun is used. Once everything is
together it's back to the range. Wow and this is what we're looking for.