Argentino M1879 Rolling Block. Is it worth restoring?

[Patrick Chadwick]

Slugging the barrel
As jmoore has kindly reminded us of the extensive thread about BP loading for the M1871 on the Mauser forum, I shall not repeat all of the considerations discussed there, but carry on with the specific actions required for your RB.

At each stage I shall require feedback from you so that I can make a good "guestimate" for the next stage. You obviously have an engineering background, so I shall assume that you have access to whatever is required for what follows and know how to use it.

Slugging the barrel is a necessary first step before ordering bullets or bullet moulds. After well over a century, BPCRs can be so variable in the actual bore and groove dimensions that to do anything else can be an expensive waste of material.

First, get a piece of 10mm or 3/8" BRASS rod. You need a length of around 3'3" or 1 meter, so that the rod can reach right through from breech to muzzle while still leaving enough for you to hold. Make sure that the ends of the rod are faced off square, with deburred or rounded. edges.

Clamp the rifle vertically in an overhanging bench vice, well padded with cloth or rubber, so that the muzzle is resting on a hard wood block on the floor. Oil the barrel liberally.
Take a well-greased .45 SOFT LEAD round ball, as used for muzzle-loading rifles and revolvers.
Tip the ball into the chamber - it will stop when it reaches the end of the neck section.
Now hold the brass rod vertically between finger and thumb above the ball.
Drop the rod onto the ball.
Repeat, using a flicking movement of the wrist to drive the rod down.
Do NOT grasp the rod and HAMMER with it, as it will not move vertically and this is not as effective as flicking it down. The impetus of the rod does the work, not your arm muscles.
The bullet will be engraved in the rifling. When it is fully engraved, you will notice that it starts to move more freely down the barrel.

If the rifling were perfect from end to end, you would expect the resistance to remain pretty much constant all the way down. In the real world you are likely to notice variations, caused by tight spots or loose spots in the barrel. In particular, watch out when the bullet is about a hand's width away from the muzzle. If the muzzle end of the rifling is loose, the rod will suddenly shoot down and hammer the ball against the wooden block, and you will have to start again.
So when you are getting close to the end, lift the rifle up in its padded clamp a couple of inches and go very carefully with the rod, until the ball pops out.
You now have a soft lead ball that has been engraved by the rifling, so you can measure the maximum diameter (matching the groove diameter) and the minimum (matching the bore of land diameter).

If the ball got noticeably lose towards the muzzle, you need to make another check.
This time, reverse the rifle so that it is muzzle up. Use a plastic hammer and the brass drift you had for the action pins as a "starter" to drive in another ball from the muzzle end until it is just fully in the muzzle (about 1/4" will do). Then use the rod from the other end to pop it out again.

You now have an engraving from the muzzle end of the rifling, which you can also measure.

Please send me both pairs of measurements, and I will advise you as to the next step.

In the meantime - get the Layman book and order a 20-pack of 43 Spanish cartridge cases and the Lee die set. I assume that you have checked the chamber as suggested. Unless you have a lot of money to spend on your hobby, do not bother getting ready-made ammo - you do not know exactly how it is loaded, so after firing it you are no wiser than before. It is just an expensive way of producing fire-formed cases.