The butt caps are for a pair of Swedish officer pistols I am building by blueprints by Runastav.
https://americanlongrifles.org/forum/index.php?topic=22826.0I could not find anything written on the subject. This is how I solved it. It is labor intensive and if anyone has simpler solutions, I hope they will share it with us.
One piece blank or three pieces?I had originally hoped to swage the butt cap out of a single piece of brass looking something like the picture below. The idea being this would avoid solder seams.
This proved too difficult for two reasons. As the metal is forced down into the swage block, the rim of the blank has to contract. The spurs hamper this. Uneven contraction of the cup makes it impossible to get the spurs to line up with each other. In theory, you could make the spur blanks oversized and cut out the spurs afterwards. However, making them that large would make swaging the cup impossible. The best solution is to use three pieces. One for the cup and two for the spurs and join them with brass color silver solder.
Making the pattern for the cup.Using measurements from the pistol drawing, carve a model of the cup.
Measure the length of the outside curves of the model and use them to draw an ellipse. This is the pattern for the cup blank. Remember to score the short and long axis lines on the brass blank. These are used to line up the blank in the swaging blocks.
Making the swagging blocks.Lay the cup pattern on top of the blank pattern. This shows how much the rim has to contract to go down into the swage. It also shows you are going to need a series of swage blocks with increasing depths to avoid stretching and thinning the metal out of proportions.
Draw a series of ellipses that divide the distance between the rim of the blank and the rim of the cup model at 50% and 75%.
Based on these patterns carve models of the cup at 75% and 50% of the full depth of the cup. These models are inlet into a piece of hard wood to make the swage block. The models are made of hard maple and are used as punches to drive the metal into the swage. It is surprising how much abuse they could stand without breaking.
Before hogging out the swaging blocks, remember to mark the long and short axis with a chisel.
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Adjusting the cup patternCut the blank out of 2mm (0.08”) brass. Brass wants to stretch, not thicken. As the rim contacts, excess material is forced out of the swage block. After swaging to 50% depth it became clear, the blank had to be reduced with about a 1/8” around the edge.
Swaging the cup.This cup is much deeper and narrower than a regular Kentucky style butt cap and required a lot more work. When making a Kentucky style cap with the same brass, I had to anneal 12 times.
http://americanlongrifles.org/forum/index.php?topic=6615.0When making this one, I lost count after annealing 60 times. The deeper you go, the less movement you get before the brass work hardens. Took about 10 hours of pounding to make one cup.
When swaging the cup, you want to avoid stretching and thinning the metal. Avoid using ballpoint hammers and metal punches as much as possible. I only used a ballpoint hammer in the very beginning when starting the flat blank into the first swage. I shifted over to wooden punches as soon as possible.
There is a tendency for the blank to warp and twist during the swaging. Regulate the blank by placing on a block of hard wood and hitting the edge with a plastic mallet.
In the last swag block, it proved impossible to force the blank the last 1/8” down into the block using a punch. Even with a punch made specifically for this.
I had to place a block of hard wood on top of the blank and beat the $#@* out of it.
This worked nicely, and I got a perfect cup but cracked my swag block.
I had to make a new one that I reinforced with oak staffs bolted on and clamps. This one has three holes, 100%, 90% and 80%. I still used the 50% and 75% in the old block.
Since was impossible to get the two blocks identical, I banged out two new cups.
Since them come out of the same block, they are identical.
Put the cups back in the swage block and transfer the marks for the long and short axis onto the rim of the cup. Take a caliper and mark the rings on the cup. Saw these rings to the depth of a number 6 jeweler saw blade. This way the markings do not disappear later during soldering. It also helps you get a consistent depth when filing.
Making the spur blanks.Cut out two square blanks out of 3mm (1/8”) brass sheet. Make sure this is the same alloy as used for the cups or you will get a color mismatch when the parts are joined. Epoxy the two blanks together. Drill and tap four holes in the bottom half.
Burn away the epoxy and bolt together the blanks. True up one top corner and two sides.
Glue on the paper patterns, lining them up with the trued corner (marked X) and sides. Take a knife and score the spur pattern into the blanks. Score the vertical line. This line marks the middle of the spur base. Saw out the top corners on the blanks.
Place the cup on top of two blocks of hard wood so that one-half of the cup rest on each block. Draw around with a pencil and cut out with a band saw.
This is the swaging blocks for the spurs. Remember to anneal often.
Joining the parts.Make four spacers out round stock. Center drill and tap.
Remember the cup is made of 2mm brass sheet and the spurs from 3mm brass sheet.
Adjust the length of the spacers so the rim of cup fits in the middle of the rim of the spurs.
This will give you a ledge to place small pieces of silver solder when joining the two parts.
It also gives you the broadest joint possible for maximum strength. Tape a piece of sandpaper to a tile and sand the rims flat.
Line up the marks on the cup rim with the center lines scored on the spur blanks.
Solder together with brass colored silver solder.
Final shapingFile out the moldings on the cup before cutting out the spurs. It is easier to clamp the butt cap in a vice using spacers.
Remove the spacers. Attach the butt cap to a piece of wood that fits tightly between the spurs. Drill out the spurs following the lines scored on the blanks and file to the lines
To clamp the butt cap while filing the rest of the moldings:
• Cut a stave that fits tight between the spurs
• Put a large blob of epoxy and sawdust on one end and put a plastic bag over it.
• Press the butt cap down on it and let it cure.
• Wind masking tape around the spurs and finish the filing.
The moldings were cut out with a triangular needle file. Background removed with barrette needle file. Shaping done with first a round needle file and even out with a chainsaw file. All needle files second cut.
Finished butt caps.
Final thoughts.A typical brass supplier will tell his brass contains:
Copper 59.50 -61.50
Tin 0.5-1.00
Lead 0.20 -0.60
Zinc- the balance.
As result, different batches of the same brass alloy can have a slightly different color. The 2mm and 3mm brass sheet came from the same supplier and were supposed to be the same alloy. However, they came from different batches. The 3mm was slightly redder. This annoying color difference would have been avoided if both sheets had come from the same batch.
Another solution would be to make one butt cap and use it as a master to cast a pair. It would also have saved a lot of work and insured two identical butt caps. But I have not been able find anywhere I can get that done.
Best gards
Rolf
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