A friend of Gun Lab just completed an interesting project and was nice enough to write up a nice article. This is being brought to you by Orin H.

Swedish M1867 Rolling Block
12.7x44R to .50-70 Government Conversion

I have a Swedish M1867 Rolling Block that was originally in 12.7x44R and you cannot find any brass for that caliber. The rifle had been “sporterized” sometime in the late 1800’s so it wasn’t original and making a conversion really wouldn’t affect its value but to me, in my humble opinion, it would actually increase its value as well as utility.
12.7x44R Brass can be made from .50-70 Government brass but you’ll find that the rim will have to be reduced in diameter, length changed, and in some cases the cartridge base in front of the rim will need to be reduced in diameter also. I found that Bertram brass rims are too thick and you’ll have to reduce the rim thickness for both 12.7x44R and .50-70.
Apparently the 12.7x44R was a modification by Sweden, Denmark, and Norway of the .50-70 Government cartridge which had been adopted by the US Government in 1866. The cartridge went by several names; 12mm Remington, 12.17x42R, and 12.7x44R to name a few. When adopted in 1867, the case was 42mm long and then in April of 1871 it was changed to 44mm so the black powder load could be increased.
Here is a comparison of the basic dimensions and drawings of each cartridge:
12.7x44R *                                                       .50-70 Government
Case Length: 43.57mm (1.715”)                           1.75”
Rim Diameter: 16.018mm (0.631”)                    0.660”
Rim Thickness: 1.63mm (0.064”)                       0.065”
Overall Length: 57.05mm (2.25”)                       2.25”

Bullet Length 24.5mm (0.965”)                          0.965”
Bullet Diameter 13.25mm (0.522”)                    0.515”
Bullet Weight 425gr                                                450gr

Bore 13mm (0.512”) **                                           0.5”
Lands 12.42mm (0.489”) **                                 0.520”

* Approximate because at the time of adoption, 1871, Sweden and Norway used a unit of measure called “Linje” or Decimal Lines. To add to the confusion, Sweden used a different value for a “Linje” and Norway another. The conversions of dimensions shown on the drawing are as close as I have been able to determine so the numbers in red are approximated metric values.
**Actual measurements of two rifle bores
As a side note, Norway started adopting the metric system in 1875, Sweden 1876, and Denmark in 1907.
I’ve never found an original drawing of the 12.7×42 or 44R cartridge in metric units and if anyone has one then I would love to get a copy.

Above is a photo of the rifle prior to the conversion. Note that barrel has been shortened as well as the forearm. I have removed the really cheap front and rear sights that were soldered to the barrel as well as the front sling loop. I’ll be replacing them with something of a better quality but still with a “period” look. Eventually the stock and forearm will also be replaced but that’s a project for another day.

After removing the stock and forearm, remove the cross bolt locking screws.

After removing the screws, cock the hammer to full cock and press out the breech block pin from the right side of the receiver and withdraw the breech block. You may find that a tap, using a non-marring tool, may be necessary to remove the pin.

You need to keep the cross pins with the hammer or breech block so that they are retained with the original component. I wrapped the breech block with tape securing the pin so it doesn’t get exchanged with the hammer pin.
After this you should ease the hammer forward, relaxing the spring tension, and remove the cross pin and hammer.

Remove the extractor retaining screw and remove the extractor by sliding the extractor out of its recess.

Clamp the receiver in your vise with soft or padded jaws to protect the receiver’s finish and you’re now ready to start reaming the chamber.
NOTE: You should leave the trigger guard in position to prevent any possibility of distorting the receiver when clamping it in your vise.

NOTE: Keith does not have a web site or use emails so you’ll have to write or phone him to see if he has the reamer you need.
Here is the reamer I rented from Keith Rice, White Rock Tool & Die, 6400 N. Brighton Avenue, Kansas City, MO 64119 Phone (816) 454-0478 mounted in a 10” reamer T-Handle I bought off eBay. You’ll need the longer handle to give clearance for the cross bar of the T-Handle. I also use CRC HD Cutting Fluid because it has the consistency of honey and will adhere to the reamer and it’s a really slick, high pressure cutting fluid. White rock will rent you a reamer for 30 days for the same price that others charge and they only allow you to keep it 3 – 5 days. Keith is a very nice guy to deal with and his reamers are sharp so be careful.

You will need to slug your barrel so you can let Keith know the diameter of rotating pilot he needs to supply. In my case the barrel measured .489” across the lands and the pilot Keith supplied was an exact fit. The bullet I chose is cast using a Lee 515-450 mold and my bullets are casting at 0.515” + 0.0005 to 0.001 and 418gr +0.0005 to 1.5gr using pure lead.

Here is the reamer starting into the chamber with a good coating of cutting fluid.

Guide the reamer into the chamber and the rotating pilot should be a snug fit into the bore. Don’t put any side to side or up and down pressure on the reamer handle. Let the reamers pilot guide the reamer so the reamer/chamber will be aligned with the bore.

Start turning the reamer clockwise but don’t put a great deal of pressure on the handle forcing it into the chamber. Light cuts are the key and if you feel the reamer starting to stick, don’t force it. Reverse the rotation and pull the reamer out, clean it and the chamber, reapply cutting fluid and start again.

You’ll have to repeat this process a number of times. It’s a slow process – it took me about an hour to cut mine. Notice how dark the patch is in this photo. This is the reamer cleaning out 150 years of black powder corrosion from the 12.7x44R chamber and some metal. Rechambering will also correct, unless it’s really bad, any out of round chamber which isn’t uncommon for these rifles.

Continue the cutting process until the rim cutter part of the reamer just “kisses” the existing cartridge rim seating surface. This will give you a depth of .065” +/- 0.001” or so. Ideally you should end up with a rim depth of 0.065”. I have found that Starline brass has the most consistent and accurate dimensions and Bertram the worse.

Insert a cartridge case and check headspace. The easiest way to do this on a rolling block is to take a straight edge and place it on the cartridge base and make sure that it is flush or slightly below the surface of the barrels Breech Face.
Once you have the rim seating depth right it’s time to modify the extractor. If you’re lucky, your extractor will be in good shape and you will be able to modify the extractor that came with the gun. In my case, the actuating “tit” on the extractor was broken off so I had to come up with a replacement. The only reasonable priced extractors (there are no originals available) I could find were .45-70 extractors sold by Numrich. I ordered two of them in case I made a mistake modifying the first one.

The upper extractor is the one that came with the rifle and as you can see the breech block extractor cam slot engagement “tit” is broken off. The lower replacement is a .45-70 extractor that I obtained from Numrich.

Here is a photo (right to left) of the original broken extractor, the modified .45-70 extractor, and an unmodified .45-70 extractor.
You’ll have to file or use a Drimel tool to get the shape of the new extractor close to the dimensions of the original. You should first get the extractor to be a snug, but free, fit into the barrel’s extractor slot then remove the excess metal from the extractor rim. I used a Drimel tool with a small grinding wheel to get it as close as I could.

Re-insert the reamer – using a lot of cutting fluid – and SLOWLY cut the rim recess in the extractor. Use LIGHT pressure on the reamer and you’ll find that it wants to catch on the edge of the uncut portion of the extractor. Making very light cuts will finally get you the results shown in the photo.

Here are the final results. As you can see, the fit is perfect.
The next step is to mark the barrel with the new 50-70 Government caliber marking.

Here is the barrel after having the new chambering engraved by a local engraving shop. I chose this marking to avoid any confusion because there were several different .50 caliber cartridges produced during the time period when the rifle was made.
After test firing, the next step will be to mount new sights, sling swivels, and refinish the metal and stock.

Thank you very much Orin.

If anyone else has a project they would like to share please drop me a line. I would be happy to post it.