I tried several of the miracle adhesives and was unhappy until I soldered.
My first soldered shim lasted about 4K rounds before coming loose. I think I feathered it to near zero thickness in a spot or two and once it began to peel it was all over. My second is well beyond 5K now.
I used 60/40 and a propane torch. As stated, the barrels need to go up and back so the shim tapers from top to bottom. It's that thin bottom edge, which is also the leading edge that feels a lot of friction when closing the barrels that caused my first to fail. I wanted 4-5 thou max so I started with a 10 thou piece of feeler gauge that I bent around a drill bit until it held a bit of curl. It's so thin that just touching it with the flame was enough to turn it cherry red and put scale on it. I suppose that softened it somewhat. My hingepin is case hardened so I've no concern. I had to have the shim stock thickly coated with flux but it was doable.
Once tinned, Nial's second post describes my approach exactly. Being as nervous as a long tailed cat in a room full of rocking chairs, I plugged the chambers with wet paper towels, though it's likely unecessary.
Once my shim was soldered in place, I had a lot of metal to move and spent hours with blue magic marker, drill bits and quality papers. I'll even confess to a few passes with a stone in a Dremel tool to get started. I've only done it twice and that probably accounts for the hours of tedium but I'm extremely pleased with the result.
