I've read and heard that you should not use 125g bullets in K Model guns like the Model 66. Can someone please educate me on why 125g bullets could damage the gun where the 158g bullet will not?

Is this accurate or not?

S&W novice question, I know!

Thanks....

I remember reading that 125gn was causing K frames to have problems with split forcing cones. I remember advising my father not to use it in his 66. But three weeks ago I was talking to a Smith and Wesson tec and asked about light bullets in scandum revolvers and then said "there was also that issue about 125grn in K frames". He said "no there has never been a problem with light bullets in any steel revolvers". So now I am not sure what to believe.

There have been innumerable threads on this and other forums about the damage that may be caused by firing 125 gr magnums in K-frames, like the 19 and 66. The received wisdom is that the forcing cone on the Ks is flattened at the bottom as a concession to the size of the frame that this is a weak point that makes the cone vulnerable to splitting from the pressure caused by light, very fast rounds like the 125 gr magnums. The more robust L-frames like the 586 and 686 were developed to address this problem, or so the story goes.

I don't know whether the story is true or not. There have been a few examples of split forcing cones shown on this and other forums.

I think you'll notice a big difference if you fire a few 125 gr rounds followed by a few 158 gr rounds. The 125s kick a lot harder, in my opinion, and they certainly make a bigger -- even ear splitting -- boom compared to the 158s.

Personally, I don't fire 125 gr magnums from my 66 and rarely, if ever, even from my more robust .357s (686 and 27). I may come across as a wimp for saying this but these are very hot rounds and the damn things hurt my hand and wrist too much to be enjoyable. I'm very comfortable firing 158 gr magnums and that's my round of choice. If they are less destructive to the gun than the 125ers, then that's just an added reason to use the heavier round.

My theory (and it is ONLY a theory!) has always been it was a combination of a short length bullet (typically 130 grain and lighter) Made from a relatively less elastic than lead jacket material (copper). Being driven hard as all light bullets always are (look at loading info for light bullet propellant charges in any manual). The wild card is usually the individual guns timing. Leave out one or more of the variables, no problem. Bring them all together at the same time, bad things "may" happen? Again-JOMO?

Hi,
The model 19/66 was designed to shoot 158g ammo. The fps is 1100 to 1200 fps on most ammo with 158g. As history shows the ammo guys started coming out with 125g ammo. I believe law enforcement requested a hotter full power 357 magnum round. Most of this ammo is rated at 1400 to 1500 fps. The combination of the higher fps plus the 125g round was a little shorter than the 158g round. This allowed more hot gases to escape around the forcing cone and cylinder. With extended use of 125g ammo and lack of proper care to the K frame the forcing cone would wear or split. Also the top strap of the revolver work wear and stretch the frame. The combination of the wore forcing cone and top strap wear would cause the revolver to shoot loose. Here is a link explaining the problem.
Use of Magnum Loads in S&W Model 19 and Other K-Frame Magnums

Bottom line. Stay with 158g ammo or go with one of the lower recoil rounds such as Remingtons Golden Saber 125g. You want to keep the ammo in the 1100 to 1300 fps range. That way there will be less chance of damaging the K frame. Stay away from the 110g ammo.

I have a model 66-4 and I only use 158g or ammo like Remingtons Golden Saber 125g. If 357 is not availiable then use 38 special +P LSWCHP 158g ammo called the FBI load. Just about all the major Ammo brands have that availiable.

Good luck.
roaddog

Thanks folks. I very much appreciate the information.

I keep it simple:

135GR or greater in a .38SPL gun.
145GR or greater in a .357 Mag. gun.

__________________
Dick

I myself went through this whole issue regarding my 66-2. I posted here and another site and the consistent answers are this: 158 or higher is best for the longevity of the gun, but above 158 (say 180 or so) may cause over penetration in a defensive gun so I am ONLY going to use 158's hereafter in magnums or use +P in 38's.

There's a very good article over at Gunblast explaining the K frame vs 125 Magnum syndrome
Use of Magnum Loads in S&W Model 19 and Other K-Frame Magnums

125 grain .357 magnum loads caused flame cutting and other damage to the forcing cone and top strap. As I am not an engineer, I am not sure of the reason the 158 grain magnum loads did not, but I suspect it has to do with the length of the projectile (bullet).

38 special loads did not cause this problem in any weight.

The 110 grain 38 Special +P+ "Treasury Load" was hard on K frames, but not for the same reasons.

None of these loads are unsafe. They simply shorten the life of the revolver.

K frames will have a very long life with 158 grain magnums.

It is completely acceptable to carry 125 grain magnums and to shoot a box or so every now and then. Just do most practice with something else.

Did you ask the "tech" how long he has been at S&W. The issue reared its head in the 70s. The L frame was introduced in about 1981. This is a long time ago.

Keep in mind, most police out there now have never carried a revolver. I would say that there are people at S&W who have no knowledge of the issue.

NO, I didn't. It wasn't what I had called about so I didn't press the point. However I wondered the same thing, does he just not know, or are they denying it, or was there really nothing to it?