I’m curious what would be the hottest load you would run over a prolonged period through a new model 66-8? I have a large amount of 125gr jacketed soft points. My current load for them is 18.9gr of w296 with cci magnum primers. The velocity is running right at 1400fps which is what the handbook has listed for that load but with a 6” barrel (mine is 4”). 20.3 grains is the max listed in the handbook. I’m just curious if prolonged firing of these will be detrimental to my firearm, or am I just overthinking it.

Why would you want to "Hot Rod" a K-frame?

Problems with that is what inspired the L-frame (which I have a 4") But my beast loads always went in the 4" 28-2.

I had companion loads for the M-92 & Marlin 1894 and the 686 and 28-2. I often prefered them in the handguns to the carbines.

Ivan

Hot 125's are thought to be responsible for cracked forcing cones on K frames, I sure wouldn't shoot it in any of mine.

Your Model 66-8 is the modern incarnation of the original Military & Police revolver of late 1890s vintage. Steel alloys have improved somewhat and modern manufacturing methods have evolved to a higher state, but essentially you are dealing with a platform originally designed and intended for much lower pressure loads (.38 S&W, .32-20, and black powder level loadings in the original .38 Special).

.357 magnum chambering in the medium frame S&W (now known as the K-frame) was added much later, adapting a cartridge originally designed for the large-frame (N-frame) magnum revolvers to a more compact piece.

Since its introduction as the Combat Magnum (later known as the Model 19) there have been many commentaries about the wisdom of regular use of magnum ammunition in the K-frame revolvers. 60-plus years of experience have led to a general consensus that occasional use of .357 magnum ammunition is probably acceptable, but regular use of such high pressure ammunition should be avoided.

I have owned and used Model 19 and Model 66 revolvers for about 50 years. I consider them to be very well suited for regular use with .38 Special and +P level ammunition, but not sufficient for a steady diet of factory-level pressures of .357 magnum. In my opinion, subjecting a K-frame revolver to magnum ammunition on a regular basis is an invitation to premature wear, at best, or catastrophic failure at worst.

__________________
Life of the party until 8:00PM

There is no SAAMI spec load that is unsafe in your Model 66. Certainly none that that should lead you to worry about catastrophic failure of your 357 Magnum firearm.

I would not recommend that you exceed (Hot Rod) SAAMI specifications for any firearm's cartridge

The -8 engineering revision of the Model 66 brings new metallurgy and manufacturing techniques to the K-frame that are significant improvements over what could be manufactured over 60 years ago when the K-Magnums first came on the scene

As you are already aware, your hand load is on the low side for that powder/projectile combination

Over the last 40+ years I have hand loaded and fired just in excess of 8000 of the Winchester 125 JHPs with a somewhat larger charge of H110 for my snub nosed Model 19/66 revolvers and the rest of my 357 Magnum family with all of those loads within SAAMI spec. Heck my 125JHP load gets 1243 FPS out of the 2 1/8" Model 640s. Many tens of thousands of rounds of various other hand loads and Factory ammunition has additionally gone through my firearms over the decades. I still have a large amount of the Winchester 125s on hand to load and I plan on enjoying them

It is a shame when we let the shortcomings of 1970s manufacturing hold us back from what is achievable half a century later in the 2020s

It is kind of like driving our modern cars at under 30 miles per hour because that was what the tires that came out 100 years ago were designed for

Every time that metallurgy, manufacturing or design improved . . . . Smith & Wesson incorporated those improvements into their products. How else could we have gotten to J-Magnums in 1996 ?

__________________
"Acta non verba"

The new S&W 66-8 is a great weapon but with the heavy 15 pound trigger
it is 10 seconds slower in shooting all rounds vs the lighter trigger on the M66-6.

However the new design has not removed any metal from the bottom of the barrel,
like they did with the M19's, which makes this revolver a lot safer
with the use of full load 125 gr JHP.

If I had to use full loads in this revolver, I would move to the 140 gr XTP
that would be a little easier on the weapon......
and receive better accuracy, at least in my revolvers.

Load up some hot 110, 125 and 140's and see what happens.
I was a speed freak when I first started loading but learned that full loads
usually were saved for hunting loads and I backed off the powder for my target loads.

Have fun.

Thanks for your input. I ended up going alittle crazy when I first started reloading for my 66 and was able to snag about 2k 125grain bullets for a very good price. It wasn’t until afterwards looking for data I came across all the horror story’s of flame cutting the top strap and cracked forcing cones attributed to 125gr bullets. But with most online firearm lore I took it with a grain of salt. It always seems the majority of the time the input you come across are the horror stories of mishaps and such but none with first hand experience.

My biggest concern with regards to my situation was the fact I’m seeing 1400fps with 2” shorter barrel then the test gun the handbook lists. I wasn’t sure if that was cause for concern or not.

The revised M66-8 is a lot stronger than it's predecessor.

As stated, the load you mentioned is a reduced load, & while W296/H110 isn't my favorite magnum powder in my 357s, that's also a plus.

The new forcing cone design on the 66-8 is far better than the old design.

Of course, as to be expected, hot loads will be harder than mild loads on any revolver.

.



.
.



.

__________________
Waiting for the break of day

Question, why shoot max or close to max loads continuously from a K frame? Saw a M-66 at swap meet this spring that had Obviously fired way to many hot loads. Forcing cone looked like someone had used a dremel tool with cut off disk to cut slots in it. Years of experience has been posted above regarding hot loads in K frames. Obtain a N frame if you insist on shooting hot loads all the time. Sell or trade up.

The Model 66-8 is the current production version and does address the short comings of the prior versions of the K-frame when chambered in 357 Magnum. It is quite a bit stronger than the older K-frames and the barrel's forcing cone is far less likely to develop a crack. The Models 19-9 and 66-8 should be able to withstand thousands of rounds of full power 357 Magnum ammo. I certainly would not use hot-rodded reloads that exceed published data that is known to be within SAAMI safe pressure levels.

Getting the most velocity out of the 357 Magnum with any full power ammo will require a barrel longer than 4 inches. S&W developed the 357 Magnum cartridge and the Model 27 revolver with an 8 3/8 inch barrel. They did not use this length of barrel because it made the Model 27 look pretty. To see some effects of barrel length and velocity, check out a website called Ballistics by the Inch. Here is a link to their site, interesting reading.
BBTI - Ballistics by the Inch :: Home

__________________
VCDL, GOA, NRA

Any modern firearm with the .357 Magnum designation should withstand a constant diet of magnum loads.

I have a $300 plastic Taurus 605 that's never chambered a non magnum round. It seems to be just fine. The revolver has withstood the punishment better than my right hand.

__________________
GOA
USA Shooting Supporter

I think it depends on your motivation for putting (near) full power loads through it?

Yes, as noted above it will take many SAAMI spec loads before shooting loose, but if your primary purpose is shooting targets lower powered loads (with the occasional full load mixed in) will be easier on you and the gun. Kind of like not driving your powerful sports sedan at 9/10s just to get to the grocery store.

Good luck in your decision.

__________________
Alan
SWCA LM 2023, SWHF 220

Blast away with your 66-8. Even if you erode the forcing cone, swapping a barrel liner is an easy job.
As has been pointed out, the weak points of the old designs were engineered out of the new one. Smith says they are strong as the L-frames.
I shoot 125 gr bullets exclusively. I have the short barrel so I use a faster powder (AA5) at maximum loading.

__________________
To cannon, all men are equal

To be honest, I never set out to just run max loads through it. What I found all over the internet about not reducing loads with H110/W296 had me concerned because your hand will blow off and this and that. I figured running at the middle of the handbooks data would be a happy medium for my first loads. And it seemed accurate enough and isn’t miserable on your hand. I eventually got around to getting a chronograph to be on the safe side and I was surprised when my velocity was hitting right at what the handbook stated with 2” less barrel. I guess my real question should be is how much velocity is lost or gain from 2”. Or is it too little to pick up a discernible difference until you get to the 8” and up range.

The other thing I didn’t realize is the complete aversion everyone apparently has to firing 357 magnum out of their 357 magnum. I’m very confused by this.

Do you trust your chronograph? If so....
Congratulations, you have a "fast" gun. Enjoy.

__________________
To cannon, all men are equal

Between the 357 yielding near perfect results and my M1 carbine slinging my loads for that right at it’s expected velocities. I would say that I trust it to be reasonably accurate.

From my own chronograph tests with 125 JHPs and 296 out of a 4” mod 28-2 if you’re actually getting 1400 FPS out of your gun and loads I’d also say you have a very fast gun.

I saw a M19-4 killed by using tons of Factory full load 110 & 125 JHP back
in the 1970's , to the late 199o's.
A crack at the bottom of the barrel finally showed up.

I would use +P 357 light bullets less than most speed freaks........
and treat my M19 as a light weight .357 Magnum revolver made for heavier &
slower bullets , that are easier on the weapon, for it to last a long time.

The 66-8 is almost a "L" frame ...........
I just don't think that todays full ammo, is any thing like the ammo made back in the 70's, with the light 110 & 125 JHP ammo.
The last 110 JHP ammo that I saw, was waterd down, a lot.

I started loading the .357 Magnum cartridge in a variety of revolvers about fifty years ago. Most loads have been with cast bullets but I tried lightweight jacketed bullets as well with heavy charges of slow burning powder. I saw no advantage to these light bullets but all our needs are different so they likely have some usefulness with some shooters.

My concern with such loads would be more rapid bore wear just ahead of the forcing cone as well as in the forcing cone itself. However, if you find light bullet high velocity loads are more accurate than other combinations, they might be good loads to stick with, particularly if you don't shoot a lot. Bore life would be worth sacrificing for excellent accuracy.

Back in my younger days, I did not have use of a chrony and just bought any ammo I could find
and send it down range at paper, jack rabbits and other things of interrest.

With a 2014 chrony I started to see what my ammo was finally doing.
Midway had some data on it's 110 & 125 JHP and that was all over the place.
They only had two 110 gr jhp loads and they both stated a watered down 1295fps.
However, the 125gr was still healty with a few at 1450 fps ..... (no barrel lengths)

In my early years I only had Blue Dot for my full loads.
About ten years ago I finally bought my first pound of 2400 powder.
I have never used the H110 type powders in my 357 revolvers, yet.

I do agree with this 1450fps out of a 6" barrel, since I did reach this high fps in one box of ammo, with my newer M686.........
but find my rem/w-w jhp bullets a lot more enjoyable at 1220fps.

PS;
a note on recoil in my 686 6" 2.5 lb revolver;
125 jhp 1448fps.................. R 7.07 ft/lbs

158 jhp 1430fps................. R 11.45 ft/lbs

Feel lucky ?

I note that the OP said something about hottest loads over a prolonged period. In other words, seeking input before a full decision.

Based on the improved engineering, design and maybe metallurgy of the modern 19, I would see no reason not to run powerful loads through it, such as you mention, if you so choose. But they sure will kick, make a lot of noise/flash, and wear out a fine revolver earlier.

That said, I had luck with Bluedot and 125s in 357 Mag. Also 2400. I felt my heavy loads of 296 or H110 were more like spraying granules out the barrel along with the 125s.

Please let us know if/what you decide - and do be safe.

I split the forcing cone on a brand new Model 19-4 by firing about 750 of my reloads with data from an old Speer book. S&W replaced the barrel for me, but it was my fault.

It has nothing to do with a "steady diet" as we so often read about, it is the total number of high pressure cartridges fired in the gun. I would like to see the term "steady diet" go away.

After that I learned that the old style K frame revolvers could indeed be damaged by shooting a fairly small number of high pressure cartridges in them.

I don't know or care about the new guns, but they certainly do appear to be more robust than the old models.

That’s no good! I have a Speer manual and the load data in it seems a little less informative then others. I don’t care for the fact that some of the 38 spl loads just list one load at max and have an asterisk stating “do not reduce”.

Those are usually only for slow burning powders or powders that don't burn efficiently with reduced loads. Consider reading up on more information regarding the "do not reduce" warning or substitute another powder. Nothing wrong with the Speer manual; that's good information based on their results even if it varies from what's in other manuals, but multiple manuals are always handy for comparison purposes. Good luck-

I’ve only been reloading for going on 4 years and I’ve only scratched the surface. 38/357 are the only pistol rounds I load for and it seems quite different from rifle. As you pointed out I do have tons more to learn and research to better understand all the information available.

The old Speer loads were not pressure tested, and some were dangerous. I think it was in about the mid-80s when Speer began to use pressure testing equipment. The loads since then have been reduced, and are safe to use.

Not only Speer, but other data in other manuals were not pressure tested either. Data that was tested was done so with equipment that was likely not as accurate as that currently available and probably required more in the way of operator interpretation than current pressure measuring equipment. Still, the old manuals are invaluable for comparison purposes even if some of the loads might be questionable from a safety perspective.

You're on the right track using handloading manuals.

The loads in even the very old Lyman manuals (and maybe others) were pressure tested using the copper crusher method. This did not provide pressure in actual P.S.I., but in Copper Units of Pressure (C.U.P.), which kind of, more less, in a way, sorta was probably close to actual P.S.I.

The method of testing used between copper crusher and modern transducer is different, so there is no real correlation of pressure indications between the two. Pressure readings in CUP for a given cartridge and load might be lower than the transducer method, or it might be the other way around. Sometimes they can be nearly the same.

The European C.I.P.method is yet another way to measure. None are either right or wrong, just different, depending on many variables.

I don't know how durable the new 66-8 or 19-9s are, but I tend to run mine a bit below max (13.0gr 2400, 165gr SWCGC) for most of my shooting. I would consider myself lucky to shoot enough to wear one out.

Some of the newer guns seem to run on the "fast side" so to speak. Here are some chrono results:

NOTE: No published load data avail for the below listed 200gr loads - for information purposes only.

Labradar Muzzle Velocity (familiarization run)
60 Deg F
S&W M66-8 2.75" .357 Mag

130gr Fed Hydra-Shok JHP "Personal Defense" PD357HS2 H …….. 1,416 fps avg (84 fps ES) -- two rounds
140gr Underwood Xtreme Penetrator (Philips head mono metal).. 1,422 fps avg ( 5 fps ES) -- two rounds
158gr Horn Xtp - 15.0gr A2400 Std small pistol, new Starline...… 1,316 fps avg (49 fps ES) -- six rounds
165gr CSWCGC (358156) - 13.0gr A2400 New Starline         ...… 1,180 fps avg (49 fps ES) -- six rounds
180gr Buff Bore …………………………………………………………………………….. 1,312 fps avg ( 6 fps ES) -- two rounds
185gr LFNGC (Beartooth), 15.0gr Lil'Gun, CCI 400 New Starline.. 1,228 fps avg (14 fps ES) – two rounds
200gr WLNGC (leadheads), 13.4gr H110, Fed 205, New Starline.. 1,102 fps avg ( 4 fps ES) – two rounds
200gr WLNGC (leadheads), 14.4gr H110, Fed 205, New Starline.. 1,155 fps avg ( 2 fps ES) – two rounds
(purported to be the “Doubletap” load info)
200gr WLNGC (leadheads) handload with Lil Gun ………………………. 1,266 fps avg ( 2 fps ES) -- two rounds
Load data not given -- maybe too much of a good thing. Spent cases fell from chambers, and no obvious signs of over pressure. Recoil was heavy. Don't even know if this stabilizes.


Here are two loads shown above chronoed from a 4 1/4" M66-8 at 5 long paces from the muzzle using a Competition Electronics (before I got the Labradar).

158gr Horn JHP over 15.0gr A2400 -- 1,294 fps (5 ea at 40 deg f)
185gr LFNGC over 15.0gr Lil'gun ----- 1,295 fps (5ea at 55 deg f)

FWIW,

Paul

I am really impressed with the 2.75" barrel fps with A2400 powder that I have never used.
Those figures are matching my 686 6" with a lot of old powders that I use,
SR4756, 2400 and HS-6.

Thanks for the post, to let us know that the new stuff works !

I have a 66-8 and a 19-4 with a 6" barrel. The first thing you notice when firing full power loads of H110 powder from the 66-8 is a massive flame ball coming out of the barrel. While impressive and kind of fun, it's wasted powder still igniting long after the projectile is gone. You're just adding recoil, without much benefit in terms of projectile velocity.

In the 6" model 19, H110 has more time to burn before the projectile leaves the barrel, so much less of a flame ball. Where H110 really shines is in my Henry rifle with a 20" barrel.

IMHO your 66-8 would be better served by a faster burning powder for hot rod loads.

From a strictly utilitarian viewpoint, why punish your hand and weapon with a steady diet of hot rod loads? I don't find shooting those from either gun particularly enjoyable.

__________________
What could possibly go wrong?

I could never understand why one needed to put 14.4 gr of H110 into a .357 case to get a 158 lead bullet up to 1216 fps........

when 7.5 grs of Green Dot will get 1281fps in a 686 6" revolver.
Some times you just need to use the right powders....

if you have them.

I would caution against it. 30+ years ago, the combination of 125gr bullets, loaded with 296/H110, was said to be the culprit of the dreaded top strap flame cutting and (as others have said) cracking of the forcing cones on many K frame and later J frame 357 magnums. Much ink was put to paper by gun writers back in the day warning handloaders to avoid this combo.

IMO, the current 66-9 has greatly reduced the chance of the forcing cone cracking but theirs still the issue with the flame cutting on the top strap.

Personally, I don't load 296/H110 with anything lighter than 140 gr bullets. With the 125's, I much prefer BE-86, Power Pistol, Blue Dot, Accurate #9 or 2400.

Jeff

No aversion to shooting 357 Mag loads whether factory or hand loads, just no souped up hot loads all the time. Sure the revolver may handle it but why? Cause one can? Shooting moderate loads that are accurate (regardless of calibre )is way more enjoyable and less wear and tear on revolver. Also try and buy several loading manuals, be careful of “ the internet” unless a mfg’ers web site or check out castboolits.gunloads.com.

I took a look at my Speer manual to find out what they use to test loads and it turns out it was a 6” model 19. Their load has a much small margin then the Hornady manual at 18.3-20.3gr. So with that my load falls right in the middle and I feel pretty good with that. I never plan on taking any loads for anything close too or above max loads detailed in a handbook. I don’t see any sense in that. And when I refer to my loads as hot I suppose really they are just full blown magnum rounds that aren’t downloaded from what the handbook says. So with all that I believe I’ll carry on with what I’m doing. I don’t shoot my revolver as much as a lot of the guys on here so even if it were an issue I don’t think it would be an issue for my situation.

The biggest reason I went with H110/296 was the fact I already had it for loading for my 30carbine. I prefer to have less cans of powder laying around to reduce the chances of a mix up as well as it’s nice to buy one that can do a variety of loadings. Although I do like the idea of a smaller charge to squeeze more rounds out per pound. But for now and especially in these wild times I’ll use what I have and what I can get my hands on. I miss the days of walking past a full shelf of powder and primers and my heart not skipping a beat.

If you want the maximum velocity, irregardless of barrel length, you use a max charge of slow powder.

It's an established fact that a max load of slow magnum powder will net you a higher muzzle velocity, albeit with more flash, than a max load with a faster powder.

Speer #14:
357 Magnum, 135gr GDHP-SB, short barrel (2.5") loads:

Unique @ 8.7gr = 1109mv = 369me

AA#9 @ 15.5gr = 1258mv = 475me

.

If you want more velocity you either use a slow magnum powder or get a longer barrel.

.

__________________
Waiting for the break of day

Hello. Is the 357mag new to you? Most newbs/novices want to stoke their new mag with the hottest loads on the planet, while novel and fun, not good for steady range use. Put away your 110/296, go buy some 2400, standard LP's and you'd be better off when you do want to cap off some hot stuff. 2400 will allow you more range when loading.

I’ve had it for about 2 years now. Everyone keeps referencing 2400 everywhere I look so I may keep an eye out and pick some up to tinker with if I come across it. I definitely am not trying to load the hottest fastest rounds for it. I took the same approach as I do with all my handliading and shot for somewhere in the middle of what multiple handbooks listed for that combination of components.

The most 2400 powder I EVER stuffed in a 357mag case, was 14.0grs, after ONE cylinder of that, stuck with 13.0 & 13.5grs, Jacketed 158gr bullets ONLY, as 158gr cast/jacketed is all I load for 357mag.

AA 9 for one, is a ball powder that is nearly equivalent to 2400. Meters very precisely, but if going for midrange loads AA7 would work fine too at a lesser charge weight.

__________________
To cannon, all men are equal

or..............

be like me and load every powder that you have from bullseye,
green dot, w231, 800x, universal, trail boss etc. etc for loads that
go from 730fps up to 1,500, in my 6" barrel.

It has been probably six years since my .357 has done anything close to 1,500fps..........
since I shoot a lot of 158 gr stuff.

Hmmm , I've shot a lot of 357's using a 158 gr cast bullet using 14.7 grs of 2400 . I didn't find it too much , in fact rather enjoyable . My magnum powder of choice these days is IMR 4227 . It gives up a little velocity compared to 2400 & H110 . But it's easier on the gun and delivers fantastic accuracy . Another powder that delivers great performance and meters like water is Accurate 4100 / Ramshot Enforcer ( both the same ).

15.0 grains of 2400 under a 160 to 170 grain cast bullet (plain base, gas checked, SWC, round nosed, hollow point, etc) is a time tested maximum load from old Lyman books that has worked well for me when I want to shoot .357 Magnums, but I would not use them in a K frame S&W.

My truck has a V8 engine producing 390 HP and 394 ft. lbs. of torque. It is rated to tow over 9,000 lbs. Easily capable of exceeding 100 MPH.

I see no reason to use my truck to its ultimate performance abilities all the time, or even on a regular basis. If I were planning on towing 9,000 lbs. on a regular basis I would be looking at a 3/4 or 1-ton diesel-powered truck. If I were driving over 100 MPH regularly I would want a car with suspension and steering to deal with such uses, not a full-sized pickup.

According to HVAC guidelines my home would be well served by a 75,000 BTU forced air furnace and a 3-ton central air unit. I ordered a 100,000 BTU furnace and 4-ton AC unit. By not working them so hard I expect very good performance and a longer service life.

If I needed a revolver for regular use at the upper end of the .357 magnum performance range I would be using a .44 magnum or something else and loading it with ammunition that didn't punish me or the revolver.

I see nothing to be gained by using any tool at its absolute limits all the time.

__________________
Life of the party until 8:00PM

Good post; there's certainly nothing wrong with useful, moderate handloads.

The OP raised a lot of interest with his inquiry and much good information and many insights have been shared.

I learned to handload in the late '50s from my uncle, who had scientific laboratory background. I remember reading much of Phil Sharpe's big book and other materials on his shelves.

The first goal was ammo performance as good or better than factory.

The second goal was thrift:
(a) in loading effectively for the job at hand, whether hunting, target or just plinking (a distant lesser use) and
(b) in treating our firearms Always so that, to the extent it depended on us, they would last a lifetime.

Hard to shake that last bit. So far, so good.