The Crosman 2100 is scopeable. You will need a scope mount that is 11 mm not a weaver mount. 11 MM or 3/8" is common on air rifles and is narrower than weaver mounts. The scope rings are 1 inch as most all scopes are 1 inch tubes. I suggest a simple 4X10 scope would be sufficient for this rifle. It's inexpensive and won't break your wallet to buy one. You could go crazy and purchase an expensive scope that would cost you 10 times the price of the rifle but that is not necessary. see the link below for a suggestion. This one has a slightly smaller tube but is communally used with this rifle.
The gun is not really designed to hold a scope. The barrel has no way of holding a scope rail. You would have to drill holes in the barrel to mount one. a pistol scope would also be required and it would out cost the price of the gun many times over. a regular rifle scope would not work. So I suggest that this not be attempted. But it's your pistol.
How many times larger the image in the scope appears. A 4 power scope makes the image 4 times larger.
The magnification of the scope can be varied between 3 and 9 times.
The Benjamin or Sheridan pump rifle should never be pumped more than 8 times. See the link below for the owners manual (Crosman owns Benjamin and Sheridan air rifles)
It means that it has variable magnifcation, from 3 to 9 times larger, and has a front lens that is 40mm in diameter.
It is expressed as how many times larger the scope makes something appear to be. It can be determined mathmatically if the curve of the lenses are known.
It magnifies 4 times, and the objective (front lens) is 40 mm in diameter. A 3x9-40 would be a 3 to 9 power variable magnification scope, with a 40mm objective lens.
At least 2 times but NEVER more that 10 times, or you may damage the seals. Also you can find the owners manual on the crosman home page, see the related link.
These are exceptional rifles but are one of the most confusing to identify by age. I almost hate to try to identify these but I'm going to try. Here is some history: Sheridan first made this rifle. Benjamin air rifle bought them out and continued to make the rifle. Later still, Crosman bought out Benjamin and continued to produce the C series rifle. Some times it was marketed as a Benjamin/Sheridan later Crosman separated the rifles into two categories, .177 and .22 caliber rifles. These were marketed as "Benjamin rifles" and the .20 (5.0) were marketed as a "Sheridan rifles." (Same rifle, just different calibers.) Crosman also produced the C9, CB, CBW, CW, CB9, C9BP. Some were called "Blue streak" and some were called "Silver streak" depending on Color. In some places you can find Sheridan and in other placed you can find Crosman in the instructions. I believe yours was made sometime between 1998 to 2000. (Best Guess) Foot Note: at one point Benjamin marketed rifles under the "Benjamin Franklin" name as a marketing ploy. Benjamin Franklin had nothing to do with the rifles it just sounded good for sales.
The Daisy model 880 and the Crosman 760 are both Variable pump rifles. To charge the rifle you must pump the forearm from 1 to 10 times to store enough air to fire the pellet or BB. With each pump you store a little more air in the air cylinder and increase the power of the rifle when it is fired. It takes a minimum of 2 pumps to store enough energy/air to make the BB or Pellet fire. Never pump the rifle more than 10 times or it may rupture the seals.
The 1400 like its predecessor 140 are both .22 caliber pellet rifles. The 1400 was made from 1968 to 1978. If you want the owners manual it is still available from Crosman as a download. ( see link below ) on the Crosman web page click on "Download a Manual" and locate your owners manual. You can purchase pellets at any large sporting-goods stores like Big 5, Walmart, Cabelas, Basspro or Dick's.Remember don't pump the rifle more than 10 times or it will damage the seals.