What is the Difference Between a Demi-bloc Barrel and Mono-bloc Barrel?

Exploring the barrel making process for double barreled shotguns

The first time I heard the word demi-bloc, I was standing on the production floor of AYA shotguns in Spain shooting a film. I am admittedly something of an amateur when it comes to double guns. “If it hits birds, that works for me” is about as advanced as I knew growing up. Looking back, I had shot some guns with demi-bloc barrels. But past my initial curious “Did this gun hit anything?” reaction, I never investigated. So, on this day I continued my deeper dive into understanding the technology of shotguns — barrels being unquestionably one of the more important parts!

At its basic core, demi-bloc refers to a method of barrel construction and is sometimes referred to as “chopper lump.” The more popular method being called mono-bloc. What is interesting here is the etymology of the word. Demi meaning “two” (half) and mono meaning “one.” That would instantly lead one to believe (at least me) that one sounds better than two. And that is not necessarily the case, nor (as it turns out) even an accurate mental picture.

In the case of a demi-bloc barrel, it’s formed from two solid pieces of steel joined together to create a double-barrel shotgun. The continuous metal grain that occurs along the whole length of the barrel produces a stronger final product. The process of joining the two barrels is very much the handiwork of a highly skilled craftsmen. On the floors of AYA the barrels were joined with silver (although I did expect to see them melting the equivalent of my grandmother’s silverware down somewhere, it was actually long pieces of silver wire).  

If you look closely enough on a side-by-side shotgun, you can see a very thin line (up and down) between the barrels at the breach when opened. This is where the barrels were joined. Mono-bloc, which is the common way to make over and under shotguns, can be a little easier to detect. A single piece of steel is used to create the mono-bloc, essentially from the base of the chamber to the end of a shotshell. The barrel tubes are then joined into that single piece which creates a visible joint (sometimes hidden with engraving) on the outside of the barrel. Back to the deception of etymology, the demi-bloc is in fact two pieces for the whole barrel process, whereas the mono-bloc is three. Go figure. However, mono-bloc allows for the use of two different types of steel while the demi-bloc is restricted to one.

Demi-bloc has its biggest advantage in strength. The “bite” of the shotgun joins both halves of the barrels to give added support when a cartridge ignites. Add in the continuous metal grain and by definition it becomes a superior product.

Now all this makes demi-bloc seem like the coolest kid in school, and maybe back in the day, that was more accurate. The reality is that between the quality of steel and the computer automated precision of mono-bloc construction, the level of tolerances that can be perfected on a mono-bloc is truly a modern marvel. Still, the idea of the hand-constructed craftsmanship of a demi-bloc barrel has a certain level of nostalgia while still being mechanically sound.

This whole process can also apply to over-and-under shotguns by simply turning everything on its side. That, however, can call into question the significance of the strength of demi-bloc construction. The bite no longer holds both barrels, the top barrel being reliant on the braze between the barrels.

At the end of the day, it is the 21^st century. There can certainly be personal preferences from demi-bloc to mono-bloc, but to a guy like myself it’s tough to feel a real difference when shooting. In the end, the combination of both brand and quality can turn out a really good shotgun using either method.