by B.B. Pelletier

Part 1
Part 2

If you can remember back to the .177 Diana 27 I started testing in December, you’ll remember that the breech seal was destroyed and needed replacing. Several readers suggested I use a modern synthetic breech seal, but I wanted to keep the look as original as possible, so I opted to try a leather breech seal first.


This is the old breech seal. Bits of leather have torn out and an oil spray comes out of the breech with every shot.


You can see the groove the new seal must fit. This photo is like an Escher print until you decode it in your mind. We’re looking at a breech that’s pointing up–away from us. The groove for the seal is wide and flat and there’s a stub of the barrel in the middle. This is where the new leather seal has to fit.

I was going to cut out the new seal with a razor knife, but someone pointed me to a set of nine punches that Harbor Freight sells for $5, and I could hardly argue with that price. Of course, shipping more than doubled the cost, but it was still a no-brainer. What I wasn’t prepared for was how nice the punches would be. They are well beyond my expectations and went a long way toward making this job an easy one. They took a couple weeks to arrive; and when they did, I went straight to work.


Nine good punches for five dollars is too good to pass up.

I knew the leather belt I used would work for this job because I’ve used it for similar projects in the past. But for those who wonder, I measured it with a dial caliper and found it was thicker than the depth of the breech groove.


I measured the leather belt to make sure it was thick enough to make a good breech seal.

I foolishly thought this job was going to be straightforward and quick. Boy, was I in for a learning curve! The hard leather belt chosen for the seal material resisted the punch, making it impossible to cut. However, I’ve worked leather before and know wet leather works better than dry, so the belt went into the drink for several days. After that, the punches cut it like warm butter. I backed it with a 4×4 timber when punching, and that soaked up the force of the blow so the punches didn’t dull.

The outside diameter of the seal was easy to cut, and there’gs a punch in the set that is within a few thousandths of being the exact size. When I tell you how I work the seal into the groove, you’ll appreciate that a few thousandths is immaterial–it’s an exact fit. So, the outside was easy to punch out. It was the inside hole that fought me.

There’s an inside punch that’s also very close to the outside diameter of the breech stub. That one will cut the inner hole–making a leather doughnut to fit into the groove at the breech. But this time there was a real problem. The outside of the punch is tapered. When it cuts the hole, it also squeezes the leather away from the hole it has just cut. That makes the hole too large. It took several attempts to discover this.


The taper on the outside of the punch spread the inner hole too much when cutting the leather. I had to use a smaller punch to get the hole the right size.


Once I discovered how the job was done–a thoroughly wet leather and cutting the inner hole first–the job went fast. Notice that the bottom three seals are torn. That’s because I cut the inner hole last and used too large a punch. The top three seals don’t look nice, but any of them will work well, because they will be mashed into the seal groove.

Also, no matter how carefully I worked, I could never get the center hole in the exact center of the outer hole. It just didn’t want to cooperate. So I sat there wondering what to do next, and that’s when it hit me. I was working with leather! Good old pliable, malleable leather. It didn’t HAVE to be centered! The way to finish this job is to pound the leather seal into the groove and trim it to the right height. The wet leather will flow into every crevice that way, and when itll be the perfect shape when it dries.

To get the best possible shape from my work, I cut the inside hole first. If it looked good, I then cut the outside. Doing it the other way ruined every seal I made.

I selected a seal that was close to the fit I wanted and pressed it into the open breech seal groove of the gun, with the finished side of the leather down toward the bottom of the groove. I used a plastic mallet to hammer the seal into place until it seemed to go in no farther. The hammering spread the leather in all directions, so I know it fits the groove perfectly. At that point, I had a mass of leather spread out all over the breech, but you would have thought from a glance that it would never fit properly. The final step was to trim the leather flush with the breech face, giving me the fit you see here. For this trimming, you need a razor-sharp knife, and maybe some of you will remember that we had a lively discussion on this blog about sharpening knives. I used an Opinel kitchen paring knife, sharpened on my Warthog sharpener that I reported on at the end of this report.


This is what is in the gun now. It’s flush with the breech and looks good.

After trimming, I oiled the seal heavily over the next several days. The oil soaked into the new seal, giving me what you see in the photo.

And how does it work? Well, you’ll just have to wait for the next report to find out!