Do you know your bifurcated lumps from your dovetails? Your sidelock from your boxlock? If not then read on...


Well, the title may be a trifle ambitious but there are many terms used in gun reports and bandied around in gun-making circles which confuse the average shooter. Even the sizing of shotguns is a little odd. A 12-bore is so-called because the bore diameter is that of a ball of pure lead, 12 of which would add up to one pound. Clearly, if you made twenty balls from that pound of lead, each ball would be smaller, so a 20 bore is smaller than a 12-bore.


So, this issue we decided to shine a light on some of the terminology and explain exactly what it means. If you don't know your bifurcated lumps from your cocking dogs, read on.


Let's start with gun actions. There are three main types: boxlocks, trigger plate actions and sidelocks. Sounds straightforward? It isn't!


Boxlocks are generally considered to be guns with a machined-out metal action body, into which the lock work is inserted and mounted on pins which go through the sides of the action. The first and most successful is the Anson & Deeley patent of 1875. However, lots of guns which look like boxlocks are not A&D actions. Greener's ‘Facile Princeps' of 1880 for example, or his later ‘Sovereign' and ‘Empire' models externally resemble the A&D but work on different designs, as indeed does Beesley's self-opening boxlock and Ward's ‘Target Gun' with coil springs. Perhaps a more accurate name for these guns is ‘body action', as that term covers all these types.


Trigger Plate Actions are guns in which the lockwork is mounted on the trigger plate and inserted from below. Dickson's round action of 1880 is a good and successful example, though not the first. The Murcott ‘Mousetrap' patent of 1871, considered to be the first hammerless gun of the modern era, covered sidelock and trigger plate variants. In point of fact, nearly all ‘boxlock' over/under guns are trigger plate actions.


Sidelocks are, simply put, hammer guns with the hammers on the inside of the lock instead of on the outside. Like hammer guns, the locks are mounted on either side of the action. There are two types, named according to where the mainspring is located: Bar action (in which the mainspring is in front of the tumbler (hammer) and back action, where the mainspring is behind the tumbler, closer to the hand of the shooter. A good example of a simple bar action sidelock is Holland & Holland's ‘Royal', while a back action is well represented by Scott & Baker's 1879 patent, retailed as the ‘Climax' by Holland & Holland in the 1880s. Modern ‘sidelock' over & unders all use back action locks.


Some guns are described as ‘self openers'. This means they use the mainspring to force the barrels open (like the Purdey) rather than rely on gravity (like the Anson & Deeley). Some even have separate springs to do the work of opening the gun (like the 1922 Holland & Holland patent).


Today, we don't hear too much about cocking systems, but most guns are barrel cocking designs. Earlier hammerless guns, and some cheap single barrel guns today, are cocked by the operation of the lever and are therefore lever cocking actions. The 1879 MacNaughton trigger plate gun, now made by Dickson & MacNaughton, started as a lever-cocker but was altered to become a barrel cocker in the 1880s, which it still is.


Now we get to the bifurcated lumps you will often read about when Mike Yardley does his excellent gun tests. The lumps on a shotgun are the metal protrusions under the breech end of the barrel. They fit into slots in the action bar and the front lump usually bears on the hinge pin when the gun is opened and closed. Early attempts at over & under guns had a problem with the depth of the action. The height of the top barrel, the bottom barrel and the lump beneath it made the guns look ugly. To reduce the height to solely that of the two barrels, some designers took the lumps from the bottom, split them in half (bifurcated them) and mounted them either side of the bottom barrel. A good example is the 1909 Boss patent. It has since been copied by many others.


So much for the action, what of the barrels? Modern gunmakers boast that their best guns have chopper lump barrels; is that good? Well, in the days of damascus, dovetail lumps were the norm. Damascus steel was too soft for making good bearing surfaces for hinging the barrels on the cross pin. So, harder steel lumps were dovetailed in between the tubes and brazed in place. (Dovetail lump barrels are still made and have been used on the best London guns at various times).


This is also how steel barrels were made when they were introduced to British gunmakers and gained popularity in the 1890s. Then it was found that you could deliver the steel tubes with the forging for the lump integral with the tube. This was worked-up and the two fitted together, so the lump and the barrel were part of the same piece of steel, thereby eliminating one joint.


Modern over/under guns and many side-by-side guns have mono-block barrels, this is where the breech block and lumps are made and fitted to the action in the factory and then tubes are fitted into the breech block, ribs attached and, typically, a line left showing where the two metal parts join, this is often engraved. Sleeving is essentially applying this procedure to an old gun to replace worn barrels, by cutting off the old ones about 3" from the breech and fitting new tubes.


Gun buyers are often told to make sure the gun is in proof. To ascertain whether it is or not, first reference must be made to the original bore size, which will be stamped in the barrel. You then need to measure the bore at 9" from the breech and compare those figures. You will need a conversion chart to decode the stamps (you will find one on so that you can see that a gun stamped 12 was proofed at .729. The gun remains ‘in proof' as long as it is no larger than .739 and otherwise free from defects like bulges, cracks and deep pits.


So there we have it, a whole host of commonly discussed, but often misunderstood, issues relating to the guns we know and use. I'm sure plenty remains to be written on the subject but I hope every single reader has learned at least one new fact.