At 10:17 in episode 57, Sheriff Patterson is shown checking his revolver; this was a typical police sidearm in 1966, almost always with a 4" barrel, chambered in caliber .38 special. The Sheriff's gun appears to be either a Colt Police Positive or a Smith & Wesson Model 10, both of which were very common police-issue weapons from the early part of the 20th century into the 1980's, when semi-automatic pistols became the norm. Both the Police Positive and the Model 10 went through several re-designs and changes. An early example looks very different from one built 50 years later.
The Sheriff wears an outmoded holster and bullet loops; the holster has a swivel riveted into it to allow the revolver to tilt upward for comfort and accessibility while driving a patrol car. But these holsters were often criticized for causing slow or awkward draws. When the officer pulled upward on the stocks to draw, the swivel might rotate and keep the gun from coming out smoothly in a direct line. The bullet loops provided only for one-at-a-time reloads. Various kinds of speed-loaders were made in the 1890's, but the modern revolver speed-loader did not come into general use until the early 1970's.
Starting 05:37 in episode 118, two of Roger Collins' shotguns appear several times, until the story arc ends with Matthew Morgan's death (127). The guns are of two different makes and models, but they are otherwise similar. They are typical "over and under" double-barreled shotguns, meaning that there is one upper barrel that sits vertically atop a lower one. The other type of double-barreled shotgun is the familiar "side by side" configuration (often seen in a short-barreled "sawed-off" version in cowboy films), in which the barrels are next to one another, horizontally occupying the same plane and joined by a rib that runs between them down their length. Although the precise maker is difficult to determine using only the pictures from the episode, one notes that Roger's guns are historically and culturally appropriate for this period and locale. A large estate like Collinwood would have, at the least, a wall-mounted gun rack on which the guns were displayed (this was before the modern paranoia about guns had set in with the Gun Control Act of 1968). High-end sporting guns were regarded as objects of beauty and as status symbols. On some estates, there might even be a "Gun Room," which held all the sporting rifles and shotguns owned by the family, as well as trophy heads and pelts from trips to Africa and other expensive and exotic hunting areas. Closer to home, Roger might have used the shotguns for duck or grouse hunting, and the over and under gun is the favored style for shooting games like skeet, trap, and five-stand. Judging by the rather clear picture of the ammunition box, Roger's shotguns are both chambered in 12 gauge, an old method of determining the diameter of the barrel's bore. "Twelve gauge" means that it would take 12 balls of that particular barrel's diameter to make one pound of lead. The 12 gauge shotgun is by far the most common modern bore, and most rural households had (and often still have) at least one shotgun chambered for it. With buckshot, it makes an excellent weapon for self defense, and even loaded with the smaller-sized bird shot it can cause immense damage to human tissue at close range. Thus Burke and Joe are reasonably well-armed for their mission, although most experts in combat shooting would have preferred a shotgun that loads more than two rounds at a time. Burke, Joe, and Roger are all rather casual about basic gun safety--on more than one occasion they allow the muzzles of their weapons to point at the people around them, usually by carelessly letting the barrel "sweep" across the sigthline of a bystander's body.
At 18:31 in 138, Roger is shown taking one of his two 12 ga. shotguns down from a wall rack in the drawing room. These are the same two shotguns featured in 118 et seq., but the rack, in the earlier episode, was said by Elizabeth to be down the hall in the general direction of the kitchen; it's now moved out to the drawing room. The one Roger takes to confront Burke has a gap between the barrels (not clearly visible before) that might indicate that it is a gun specially built for trap and skeet. If so, it would be culturally appropriate to the "large estate" context.