S&W Revolver Frame Sizes Explained: J, K, L, N and X

Why the letters matter

Smith & Wesson identifies its revolvers by model number on the outside and by frame letter on the inside. According to an American Rifleman history of the J-frame, the letter designations weren't publicly disclosed for decades. Today they are how the entire accessory world is organized. Grip makers, holster makers and speedloader makers list their products by frame letter first, then by barrel length and butt shape.

The general rule, as all4shooters puts it, is that a later letter means a bigger frame. There are exceptions, which we'll get to.

The frames at a glance

Capacities vary by model and chambering. Check the specific model's spec sheet before buying loaders or moon clips.

J-frame: the pocket revolver

What it is: S&W's small frame, built for concealment.

Where it came from: In 1949, S&W's Carl Hellstrom had the older, smaller I-frame enlarged slightly and fitted with a coil mainspring to make a compact .38 Special. The first J-frame left the factory in October 1950 and was shown that year at the International Association of Chiefs of Police convention, where attendees voted to name it the Chiefs Special. When S&W adopted model numbers in 1957, it became the Model 36.

Milestones: An aluminum-frame Airweight followed in 1952 (later the Model 37). The hammerless Centennial (Models 40 and 42), with a grip safety, also debuted in 1952. The stainless Model 60 began production in 1965 as S&W's first stainless revolver. A .357 Magnum Model 60 arrived in 1996 with a slightly longer cylinder.

Dimensions: all4shooters lists the J-frame cylinder at 33.1 mm in diameter and 40.5 mm long, with the narrowest top strap of the line.

Fit notes: J-frame grips come in round-butt and square-butt versions, and Centennial-style guns sometimes take their own grips. Holsters are specific to hammer type (exposed, shrouded or concealed) and barrel length.

K-frame: the police revolver

What it is: S&W's classic medium frame, and for much of the twentieth century the shape of an American police sidearm.

Where it came from: The K-frame descends from the .38 Hand Ejector Model of 1899, the Military & Police, which adopted the then-new .38 Special cartridge. It became the Model 10 in 1957 and, with more than six million made, is often called the most popular centerfire revolver of the twentieth century.

Key models: Model 10 and its stainless twin the 64 (.38 Special), Model 13 and 65 (heavy-barrel versions), Model 19 and its stainless twin the 66 (.357 Magnum), and the 617 (.22 LR).

Dimensions: all4shooters lists a 36.8 mm cylinder diameter and a 42.4 mm cylinder length.

The K-frame magnum caveat: The slim K-frame's forcing cone was known to crack with a steady diet of high-volume .357 Magnum, which is part of why S&W created the L-frame. K-frame .357s are fine guns, but many owners practice mostly with .38 Special and save magnums for occasional use. Check the maker's guidance for your specific model.

Fit notes: K-frame grips come in round-butt and square-butt. They interchange with L-frame grips of the same butt style.

L-frame: the magnum workhorse

What it is: a medium frame between the K and the N, built to run .357 Magnum all day.

Where it came from: The L-frame line of the 1980s included the fixed-sight 581 and 681 and the adjustable-sight 586 and 686. The stainless 686 was introduced in 1981. The seven-shot 686 Plus followed in 1996.

Dimensions: all4shooters lists a 39.5 mm cylinder diameter, 2.7 mm larger than the K-frame's, and a full-length barrel underlug. It describes the L-frame as S&W's best-selling frame size.

Fit notes: L-frames share grips with K-frames. They do not reliably share holsters, because the bigger cylinder and full underlug change the profile. all4shooters notes L-frames have been made only with round-butt grip frames since 1995.

N-frame: the big one

What it is: S&W's large frame, for the heavier cartridges.

Where it came from: The N-frame carried the first .357 Magnum revolver in 1935, the gun later designated the Model 27. The .44 Special Model 24 followed on the N-frame in 1950. Production of the .44 Magnum Model 29 on the N-frame began in 1955, and the stainless 629 followed in the late 1970s.

Calibers: .357 Magnum, .44 Special, .44 Magnum, .45 Colt and .45 ACP (with moon clips) among others. The cylinder diameter stays the same across chamberings, while the cylinder length varies; all4shooters lists about 40 mm for .357 Magnum and about 44.2 mm for .44 Magnum.

Fit notes: N-frame grips come in round and square butt; current production is round butt. N-frame holsters are their own category.

Our 629 lineup guide covers the current .44 Magnum N-frames in detail.

X-frame: the hand cannon

What it is: S&W's largest frame, created for the .500 S&W Magnum.

Where it came from: The X-frame debuted in 2003 with the Model 500, designed from scratch to contain the pressures of the new cartridge. The Model 500 holds five rounds, and its variants weigh from about 56 to almost 80 ounces. The Model 460, chambered for .460 S&W Magnum, also uses the X-frame.

Dimensions: all4shooters lists a 48.7 mm cylinder diameter and a 58.4 mm cylinder length.

Fit notes: Round-butt only. Holsters are specialized, usually chest or shoulder rigs for hunting.

The exceptions: I, M and Z

• I-frame: One of the two original 1894 Hand Ejector sizes, a small .32 frame. S&W dropped it in 1961 and moved its .32s to the J-frame.
• M-frame: A phased-out frame size, rarely encountered today.
• Z-frame: Used for the Governor (.45 Colt and .410). It is a reminder that the alphabet rule isn't absolute: all4shooters lists its cylinder diameter as the same as the N-frame's, with a longer cylinder, and smaller than the X-frame in most dimensions.

How to identify your frame

1. Find the model number. On most modern S&W revolvers it is stamped inside the frame where the crane meets it; open the cylinder (after confirming the gun is unloaded) to see it.
2. Look it up in the table above or in the manufacturer's catalog.
3. Check the butt shape. Remove the grips and look at the bottom rear of the grip frame. Round butt curves; square butt has a squared heel.
4. Note the barrel length and underlug. Holsters depend on both.

Our collecting guide explains how model and dash numbers work, which will tell you more about a specific gun's era and features.

Shopping by frame

If you're choosing a revolver rather than accessories, the frame tells you much of what to expect: J for concealment, K for a slim classic, L for a durable .357, N for big bores. Ammunition Depot's revolver section carries a range of current S&W models, from J-frame Airweights to L-frame guns like the 686 Plus. Confirm the frame and caliber on Smith & Wesson's own product page, because retailer listings occasionally mislabel them, and check the barrel marking before you buy ammunition.

Store any revolver unloaded and locked when it isn't under your control, whatever the frame size.

Editorial note: This is an independent editorial overview built from manufacturer specifications, retailer listings and published sources. We have not performed hands-on testing of the products discussed, and nothing here is a performance guarantee. Verify specifications, compatibility and the law where you live.

Affiliate disclosure: Some links on this page are affiliate links to Ammunition Depot. We may earn a commission if you buy through them, at no extra cost to you. Our editorial choices are not influenced by commissions. Check current price, stock and specifications directly with the retailer.