Smith & Wesson J, K, L and N-Frame Comparisons

Size differences between medium (K) and small (J) frame sizes are frequent topics of discussion. It is only natural for people interested in these guns’ respective attributes to be interested in how one compares to the other. 

The top revolver is the discontinued S&W Model 19 with a 2 ½” barrel.  Shown with this K-frame is a Model 642-1, one of the most popular J’s ever manufactured. Size difference from the side is readily apparent.

In this picture, we see a Model 10 with 2” barrel (top) next to a Model 442.  K-frame cylinder diameter measures 1.446” compared to the J’s 1.306”.  Though it doesn’t sound like much size difference, it can be important if contemplating IWB carry.  The lighter, readily-available J-frames can tip the scale in their favor if ankle-carry is a possibility. On the other hand, the larger, heavier K-frame is a natural for OWB carry and usually offers a longer sight radius, smoother double-action and better recoil-dampening.

J-frame 38/357 revolvers hold 5 shots while K-frames in hold six.  Some people find this reason enough to go with the larger (and heavier) medium-frame revolver.  Whether to go with the K or J-frame can depend not only on personal preferences but carry requirements or perceived concealment difficulties.

The K-frame’s (top) hammer is powered by a flat mainspring that is tensioned by a screw as are those on both L and N-frame revolvers.  The J-frame (bottom has a coiled mainspring. The K’s flat mainspring is considered a major factor in their usually very smooth double-actions.

Measured at the threads, the J-frame measures 0.500” compared to the K-frame’s 0.540”.  Shown is a 2” Model 10 barrel.  (The slight detent at the top rear of the threads at shows that this was an earlier gun with the barrel pinned in place after being screwed into the frame.)

Barrel Outer Diameters at Threads

(Thread pitch is 36 TPI for all of these barrels.)

Some K-frame fans wish for a K-frame revolver in .44 Special, .45 ACP or .45 Colt.  Sadly, this remains an area in which the K-frame just cannot provide a platform; its dimensions are just too petite to allow it.

In my opinion, K-frame S&W revolvers have another enduring attribute if compared to their larger L and N-frame brothers; I find that if barrels are no longer than 4”, they are just not very hard to conceal. Though I find them too large for effective pant pocket carry, they have proven easy to hide under outer garments from a loose-fitting t-shirt to a sports jacket or suit coat.

As this is written, it would appear that the J-frame will continue on forever!  However, the K-frame is offered in fewer models than in decades past. The K-frame is larger than the J and slightly smaller than the L-frame but it is not offered in .357 Magnum, though both the other frame sizes are! The most potent caliber currently offered for the K-frame is .38 Special.  How can frame sizes both smaller and larger than it be offered in 357, but not the K-frame?

Some recall that when the K-frame Model 19 “Combat Magnum” was introduced to the American law enforcement market, Border Patrolman and pistolero, Bill Jordan, declared it “the peace officer’s dream sidearm” and it was produced from 1957 to 1999.  Its stainless counterpart, the Model 66, was manufactured from 1970 until 2005.  It wasn’t long before the “Combat Magnum” became a major player in US law enforcement handgun selection.  Circa the ‘70’s, law enforcement agencies found themselves being sued for “negligent training” for routinely using light .38 Special target loads for firearm qualification but permitting full-power magnums for duty ammunition. This lead to using at least some full-power 357’s in the qualification process.

During this same general time-frame, gun scribes were declaring the .357 Magnum 125-gr. JHP “top dog” in the “stopping power department”.  This load was thought to be the ne plus ultra load that would both instantly deck an opponent but not over-penetrate as might traditional, heavier 158-gr. loads.  In short, the gun intended for a steady diet of .38 Specials with but occasional magnum use began being fed full-power .357’s exclusively.

Reports of heavy magnum use damaging the K-frame “dream sidearms” began.  Often, the load was reported to be the 125-gr. JHP.  Rightly or wrongly, these loads became associated with cracked forcing cones.

K-frame (top) size requires that the bottom of the forcing cone have a flat milled on it to allow clearance for the frame yoke.  Cracks usually occurred at the forcing cone’s 6 o’clock position. On the bottom is the J-frame’s forcing cone.  It has thinner walls but no flat and it doesn’t extend out from the frame as much, but does it appear somehow stronger to you and capable of handling as many magnum rounds as the K-frame forcing cone next to it?  I think that there are more factors at play than just metallurgy or design.

On the top is the forcing cone on a very frequently- fired L-frame Model 696. Note that it has no flat milled at the bottom.  Neither does the massive N-frame forcing cone on the bottom. The .357 Magnum was originally housed in revolvers on the N-frame “chassis”.

When the K-frame was replaced with the slightly larger L’s, their forcing cones did not have the milled flat; their more generous size permitted yoke clearance without it.  But does that mean that every K-frame .357 Magnum is destined to suffer a cracked forcing cone?  I believe not, but I do believe that it happens; I’ve personally seen two 4” Model 19’s with them.  Fortunately for the owners, S&W still had spare barrels and these old pinned barrel revolvers were soon good as new.  Sadly, this is no longer the case as S&W no longer has replacement barrels.  Breakage does seem less frequent when using heavier bullets such as the 140 to 158’s in the K-frames.

Similar problems were reported with other K-frame 357’s such as the Model 13 and 65 and the “prime suspect” remained the 125-gr. magnum load.

Problems with .357’s damaging S&W revolvers evaporated as the L-frames made steady inroads into the police market. Until police transitioned to the autoloader, the beefed up L-frame Model 686 and its kin led the market in law enforcement sidearm sales. They could handle an exclusive magnum diet and their increased weight, slightly larger frame-size coupled with S&W’s wise retention of the K’s grip dimensions made them quite recoil-manageable.

Some claim that the K-frame .357 Magnums are “fragile” while others vehemently disagree. I do not have the definitive, proven answers but will offer what I believe to be the case.

When the Combat Magnum was introduced, the 125-gr. magnum loads did not yet exist with their different pressure peak times and temperatures. Physical parameters concerning bullet impact on forcing cones was almost certainly for traditional 158-gr. loads and besides that, the guns were expected to be shot primarily with .38 Special target wadcutters.  These revolvers would handle any .38 Special loads just fine to near infinity but the move to magnum ammunition in practice coupled with the 125-gr. JHP’s popularity provided a combination right on the edge of what the K-frame could handle.  Might not a properly-timed K-frame absorb many, many, many full-power 125-gr. magnums while an out-of-time example might not due to the bullets striking the forcing cone off-center?  Add to that the normal range of differences between individual K-frame revolvers and I think we can get at least a possible idea of why some K-frames tolerated the 125-gr. magnum diet and others didn’t fare as well. For what it is worth, the only cracked K-frame forcing cones I’ve seen have been with heavily-used revolvers that fired mostly 125-gr. full-power magnums and handloaded equivalents.  That the problem exists is true but that it ran rampant in huge numbers does not appear to be in my experience.

I believe that the K-frame is best-suited for .38 Special +P or mid-power .357 Magnums such as Speer’s 135-gr. Gold Dot, Corbon 125-gr. DPX or Remington 125-gr. Golden Saber.  The K-frame still offers a potent ballistic delivery at these levels without unnecessarily risking damage to one’s handgun from frequent practice and long-term use. Though the only split forcing cones on K-frames I’ve witnessed has been from using full-power 125-gr. magnums, I’ve seen more than a few with excessive end shake and “slop” in cylinder lock-up.  All had been shot lots and almost exclusively with full-power 158-gr. handloads. Nothing had broken, but tradition-weight full-power magnums did accelerate wear-and-tear on the guns. This is only natural. Shooters intending to shoot copious amounts of full-power .357 Magnum ammunition long-term are better served with either L or N-frame S&W revolvers if staying in the S&W stable.

But how does this explain the little J-frame guns being produced in .357 Magnum if their larger K-frame cousins are not?  Doesn’t the J simply have reduced size in everything?  What’s the deal?  Surely improvements in metallurgy cannot take all the credit. I continue to believe that because felt-recoil in the J’s is significantly greater than in the larger frame wheel guns, the little shooters’ round counts are “self-limiting”.  In other words, metallurgical and maybe design improvements have “toughened” the little guns enough that they can handle more magnums than can the human hand.  It is just offered as a possibility but one I think makes at least some sense.  K-frames are indeed shootable over the long-term with full-power magnums…so some of us actually do it.  I believe this is much less-likely with the little J’s so we just don’t see as much breakage. I do not see this as any sort of condemnation of either frame size. It is my continuing belief that S&W revolvers are quite capable of “outlasting” the vast majority of their owners and have for generations and S&W’s reputation for taking care of their customers is first-rate should gun repair or replacement become necessary.

At top is the discontinued S&W Model 66, a K-frame .357 Magnum that was extremely popular for years. The one shown has a 2 1/2” barrel. Below is the Model 686 CS-1.  This 3” L-frame was a special order item for the US Customs service for a short period of time.  Many were never issued or allowed to reach any sort of market at all.  The then US Attorney-General, Janet Reno, ordered them destroyed. The L-frame does seem better-suited to digest a long-term diet of magnum ammunition.  In my opinion, we give up the superb “feel” and carry-convenience of the K for a greater durability over the long-haul with full-power loads and a little more weight.

Huge by today’s standards, the S&W Model 27 was the only platform for the .357 Magnum for years. This one sports a 3 ½” barrel to aid in concealed carry

Frame Thickness:

Cylinder Diameter:

As is the case with individual handgun designs, so do different frame-size revolvers bring their own unique advantages and problems.  With the J-frame comes extreme convenience in carry qualities but the price is harder “kick” and but a 5-shot cylinder-capacity. K-frames seem to offer a really fine blending of “shootability” without being too large for easy concealed carry or too heavy for the long hours put in by uniformed law enforcement personnel. The only downside seems to be concerns of long-term durability in those chambered for .357 Magnum, particularly using the hot 125-gr. loads.  In .38 Special, they just shoot and shoot and shoot. The L’s dissipated long-term durability issues with magnum loads but we wind up with a revolver just a little larger and a little heavier than the convenient K-frame. The big N-frame handles .357 recoil with ease and makes range sessions with full-power loads a breeze.  The problem is that they are heavy for either open or concealed carry. Some opine that for their size and heft, a shooter is better off going to a larger caliber.  In the end, the decision rests with the buyer’s perceived needs or departmental regulations.

Of the frame-sizes discussed, I find the J-frame .38 Special Airweights the most useful in my current tame lifestyle for easy concealed carry, but much prefer the K-frame Model 10 Heavy Barrel and its kin for shooting, “pride of ownership” and carrying on the waist with either IWB or OWB holsters.  My favorite K-frames are chambered in .38 Special rather than .357 Magnum, something a fair percentage of readers may disagree with. For shooting full-power .357’s, my L-frame favorites are the 581, 681 and 686 CS-1 with either the 3 or 4” barrel.  Purely subjective, the most pugnacious looking revolvers in .357 Magnum remain the 2 ½” Model 19 and 3 ½” Model 27.  If size and weight are not an issue, I have long appreciated the recoil-busting qualities of the big N’s in the Model 28 “Highway Patrolman”. 

I’ve made my choices. How about you?

Best.