I have a treasured M66 K frame that I want to last. I'm worried about the forcing cone issues and I've read that I should stick with 140 grain and above 357 magnum loads. The shorter 125 and 110 grain loads can cause damage because of the shorter overall round length and escaping gases/flame. My question is wouldn't the short 38 spl rounds do the same thing or are they mild enough where they don't emit super hot gases/flames? This was a police service revolver used with 125 grain loads from 1987-1991. There is some cutting on the top strap. Thanks in advance for your replys.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
K frame forcing cone question, 38spl vs 357 Mag 125 grain
- Thread starter Noreaster
- Start date
Short answer - stick to 140 gr. loads. (or heavier) It's not the bullet that damages the cone, it's the abrasive grit contained in the powder gases hitting the cone at high speed. Lighter bullets get out of the chamber faster while the powder is just getting cranked up and expose the cone to a longer duration of blast. With a .38 case there will be a little less powder but it still is harder on the cone than a heavy bullet. And IMO there is no good reason to use light bullets in a handgun. Mass is your friend. The topstrap cutting is a nonissue. It stops cutting once the groove is formed and acts as a guide to redirect the gas out the side. But the cone will keep getting blasted and carburized and hard and brittle until it eventually cracks. This has been known about for many years. Read Kuhnhausen's S&W and Ruger DA shop manuals. He has lots of photos of abused revolvers. From my experience no police dept. ever fired enough light magnum loads in their guns to do much damage. Most depts. only shoot maybe 50 rounds once or twice a year. Take good care of that M66 and it can be handed down to your grandchildren.
Last edited:
To my knowledge, there is not a problem with shooting lighter .38 specials in a K-frame .357. After all, you never hear of the forcing cone problem in K-frame .38 specials like the Model 10, 15, etc. It's not just the bullet weight but the velocity and possibly the heat of the small powder particles.
The lightweight magnums are hard on K-Frame forcing cones because they require less pressure to push them out of the case than heavier bullets, the shorter bullets do not seal the cylinder throats before leaving the case, and most .357 Magnum ammo is loaded with comparatively large charges of slow burning powder. These factors combine to allow a larger percentage of the powder to burn in the forcing cone and barrel rather than in the case and chamber.
Light bullets in a .38 Special also would not seal the cylinder throat before leaving the case, but most .38 Special loadings are loaded with smaller charges and/or faster burning powder so you still would not have nearly as much powder burning in the forcing cone and barrel as you would with a lightweight magnum. I would say that unless you're talking about a near-magnum level +P or +P+ loading, bullet weight is a non-issue with .38 Specials in a K-Frame revolver.
Light bullets in a .38 Special also would not seal the cylinder throat before leaving the case, but most .38 Special loadings are loaded with smaller charges and/or faster burning powder so you still would not have nearly as much powder burning in the forcing cone and barrel as you would with a lightweight magnum. I would say that unless you're talking about a near-magnum level +P or +P+ loading, bullet weight is a non-issue with .38 Specials in a K-Frame revolver.
FWIW - Back in the day when I carried my M66 2.5" as a duty weapon, we qualified with, and carried, Remington 110 gr. 357s. Many say that modern factory 110 gr. 357 ammo is relatively mild. So, it isn't considered unnecessarily harmful on the K-frame forcing cones. Unlike the 125 gr. ammo that is still a rather hot load and should be avoided. Plus, it seems that the VAST majority of forcing cone issues were with the M19's, not the M66's. Possibly something to do with the metalurgy?
I still shoot 110 gr. 357 through my M66 from time to time. That being said, the majority of rounds going through the gun are .38's. ...Just simply more pleasant to shoot.
Great guns! Keep 'em clean, and they'll keep shootin'!
I still shoot 110 gr. 357 through my M66 from time to time. That being said, the majority of rounds going through the gun are .38's. ...Just simply more pleasant to shoot.
Great guns! Keep 'em clean, and they'll keep shootin'!
Dfariswheel
New member
Another way to protect the forcing cone on the "K" frames is to buy and use a Lewis Lead Remover kit from Brownell's.
The kit includes a special tool head to clean the forcing cone.
You should use the Lewis cone cleaner whether you shoot lead or jacketed bullets since the cleaner head not only removes leading, it also removes copper and carbon fouling.
Most of the damaged "K" frame revolvers had badly fouled forcing cones. It's thought that the heavily fouled forcing cones contributed to cracking.
The kit includes a special tool head to clean the forcing cone.
You should use the Lewis cone cleaner whether you shoot lead or jacketed bullets since the cleaner head not only removes leading, it also removes copper and carbon fouling.
Most of the damaged "K" frame revolvers had badly fouled forcing cones. It's thought that the heavily fouled forcing cones contributed to cracking.
warningshot
New member
Bogus on the bullet weight issue. It is the CUP.
Bullet weight alone is incomplete and only half the answer at best. It's how much gun powder you put behind the bullet that creates the copper units of pressure. It is the CUP that puts the extra wear and tear on the gun. Some good reloading manuals will list the CUP, or PSI, of a particular load. Listed loadings for 38 spl. have less CUP than .357 Magnums do. Argue with the hand.
In short, your all steel K frame will shoot all the .38 specials you can buy. Keep the Magnum stuff to a couple hundred a year and the gun will outlast you.
Bullet weight alone is incomplete and only half the answer at best. It's how much gun powder you put behind the bullet that creates the copper units of pressure. It is the CUP that puts the extra wear and tear on the gun. Some good reloading manuals will list the CUP, or PSI, of a particular load. Listed loadings for 38 spl. have less CUP than .357 Magnums do. Argue with the hand.
In short, your all steel K frame will shoot all the .38 specials you can buy. Keep the Magnum stuff to a couple hundred a year and the gun will outlast you.