[TargetTerror]

I'm well aware that lighter bullets in front of a full charge of slow burning, magnum powder can lead to flame cutting of the top strap, but why? How are the pressures, temperature, and/or gas volumes any different with a heavier-for-caliber bullet? (or is something else the culprit?)

[Sport45]

For one thing lighter bullets have more powder under them. This might mean more gas escaping from the cylinder gap.

I don't know that you really get more flame cutting with the lighter bullets. I though the problem there was cracking the forcing cone on K-frame S&W's due to the higher impact velocity.

[zt77]

H110 should not be run in .357 mags in k frame magnums as it could result in flame cutting.
Then again neither should 125 grain bullets.
Heck it seems as if k frame magnums all of a sudden became .38 +p's.

I've seen a few shot out and shot loose m19/66's, never have I seen one with a cracked forcing cone.

As for the OP, couldn't say. I don't mess with light bullets in .357 much.

[Sport45]

There's a picture of a cracked Mod-19 forcing cone in this thread at TheHighRoad.us (http://www.thehighroad.us/showthread.php?p=5058326). They admit not knowing the history that resulted in the failure.

Results of a Google image search on the subject. (http://images.google.com/images?hl=en&source=hp&q=k-frame+forcing+cone+crack&btnG=Search+Images&gbv=2&aq=f&oq=&aqi=)

[Oro]

It's the powder and burn characteristics that determine if you get cutting, not just bullet weight. It can happen with any bullet type. Lighter ones can do it more easily, and there is a reason.

But correct there is a counter-intuitive relationship with charge and weight at similar power levels. The reason is the inertia of the bullet as it sits there in the case at ignition. At first, it's straight-forward: heavier bullets are harder to get moving - they require more force. But then why are the powder charges smaller? Because the gas expands and pressure spikes much faster than the bullet gets moving. You have to back the powder off compared to a light bullet so as not to overpressure the case and chamber.

Once the bullet is out of the case and into the bore, the bore becomes additional chamber volume. The powder continues to burn and the gas continues to expand and effectively use the bore as additional chamber volume to accelerate the bullet. But you have to get the bullet out of the case before you exceed the limits of the case or chamber. Because the heavier bullet stays in the case just that much longer, you need to have less powder behind it so you don't spike the pressure over safe limits while it's still in the case.

Sooo - lighter bullets, with more charge, will still be burning and expanding more aggressively than a similar full-power load with a heavy bullet. The added gas volume will result in more escaping out the b/c gap, and more chance of cutting, but no guarantee it's going to happen.

Hope that wasn't too wordy or muddled. Lighter bullets don't cause flame cutting - powder characteristics do. But full-pressure, slow burning powders behind light bullets can make it more possible.

[Steve C]

Flame cutting of the top strap results from slow powders and is not necessarily restricted to light bullets though as mentioned you use more powder with light bullets than with heavier. 2400, H110, W296 are the common slow powders you will see flame cutting from. Its the same idea as running a blow torch on metal, run enough hot bunning gas on metal and it will begin to cut. Usually flame cutting will run its course and stop progressany any further. Usually its not considered a major problem, at least it doesn't disable the gun and you won't see a frame cut through or come apart due to flame cutting. Its presence is an indicator of how many heavy loads a pistols has shot though.

[1911Tuner]

Oro...Excellent post and a very good explanation.

About all I can add is that the slow powders typically used for extreme velocities not only produce a higher voulme of gas...but peak pressure is maintained for a longer peroid of time...which go hand in hand with Steve C's blow torch description. Quicker powders peak early and abruptly...often before the bullet has even left the case. The effect is more like a flash instead of a steady flame.

Liken it to quickly passing your finger over a lighted candle...and letting it dwell for a few seconds.

Another factor that adds to the flame cutting effect is the lighter bullets are shorter, and exit the case earlier...thus exposing the barrel/cylinder gap to the pressurized gasses for an even longer period of time.

Of course, the barrel/cylinder gap itself plays a role. The wider the gap, the larger the gas volume that escapes, and although a larger gap tends to reduce pressures a little...the difference between a .003 inch gap and a .006 inch gap isn't all that signifigant, pressure-wise...and it doesn't affect the final bullet velocity very much. .003 inch of extra gap might cause a drop in velocity of 12-15 fps with a given cartridge. The variation between rounds within the same lot is more than that...so it's mostly theoretical.

The one point that hasn't been addressed is that the flame cut topstrap is weakened and doesn't resist tensile stress as well as a full-thickness topstrap. The level of stretch that goes on during a "magnum" ballistic event is pretty signifigant...especially if jacketed bullets are fired. Not so much with lead. If you're a handloader and you want to extend the service life of your revolver...use lead bullets and powders in the mid-range burn rates. You'll get velocities nearly as high as you get with the slow burners...and your gun will reward you with a long, happy life.

IMO...The obsession with absolute top velocities in defensive handguns is much ado about nothing. At powder burn engagement distances, a hundred fps give or take won't make a whit of difference.

EDI TO ADD:

Cracking of the forcing cones doesn't come from impact. It starts as a result of the intense heat generated by slow powders causing the outer surface of the exposed steel to crystalize. When a layer flakes off, it exposes fresh steel, and the process repeats. When it goes deep enough...it breaks through.

[christcorp]

Part of the problem with cutting and bullet weight is that the smaller the bullet, the SHORTER it is. Obviously, the diameter is identical on all bullets of the same caliber. So, for the bullet to be lighter, it must be shorter. And because the overall length of the round is usually the same, there is LESS bullet inside of the shell. Therefor, with the amount of powder in the round, more of the powder is burning as the bullet leaves the round than with a longer bullet. Also, from the point of impact where the bullet touches the barrel and the gap between the rear of the bullet and the case, will obviously be a larger gap with a lighter bullet because it is shorter. Which means more gas around it than with a longer bullet that is closer to the case.

[TargetTerror]

Thanks interesting christcorp. Do you think that would change with a lighter bullet with the same length? (imagine a very exagerated hollow point)

[harmonic]

Dunno where I copied this, but......

The 125 grain bullets driven to maximum velocities used large charges of relatively slow-burning powders. Handloaders know the powder types as WW296 and H-110, among others. The combination of slow ball-type powders and the short bearing surface of the 125 bullets allows prolonged gas cutting of the forcing cone and top strap area, accelerating erosion and wear.

Borescope studies of rifle, machine gun, and auto cannon chamber throats shows a lizzard-skin-like texture due to this gas cutting damage, called "brinelling". The results of brinelling are fine microcracks that weaken the surface of the steel, and further promote erosion. In machine guns and auto cannons, barrel life is measured in terms of "useable accuracy", and round counts that determine this are based on group sizes at engagement ranges.

In the K-frame magnums, the forcing cone dimensions combined with the barrel shank dimensions results in a relatively thin shank at the 6 o'clock position, where a machine cut is made to clear the crane. This is usually where the forcing cone cracks. The L and N frames use much beefier barrel shanks and do not have this cut. S&W intended the K frame magnums to be "carried much and fired seldom" service arms, designed to fire .38 Specials indefinitely, with light to moderate use of .357 Magnums. You notice that S&W has discontinued production of K frame .357 magnums, no doubt due to product liability issues and a couple generations of K frame magnum experience.

[DWFan]

Scots Powder, before being taken over by Accurate Arms, used to produce powders with lower peak temperatures that eliminated frame cutting and forcing cone erosion. My only experience was with Brigadier 1680 in a .357 Maximum. There was no real difference in velocity compared to AA-1680 and W680 was slightly better than both. I didn't load the Maximum with anything under 158gr so I can't comment on lighter bullets. The big difference I found was that the barrel didn't heat up as quickly with the Scots powder.

[christcorp]

Realize that there are some people that will "DOG" the "K" frame guns and say things like: "What good is a gun that can't shoot the ammunition that it was chambered for?" Well, the truth is, when the Model 19, 13, and other "K" frames were developed, there was no 125 hyper-velocity bullets. Generally, they were 158 grain bullets. And so you know; the "K" frame guns can shoot all the 158 grain bullets you want to throw at it.

To answer your question Target-Terror; in theory, if you could make a 125 grain bullet the same length as a 158 grain bullet, then yes; it would be as safe as the 158 grain when it comes to flaming the force cone. But unfortunately, you're not going to find that weight bullet in that design. It would more than likely be so thin, that it would start mushrooming and falling apart just by the air pressure.

People say they don't want to use 158 magnums because of over penetration. That's simply Poppy-Cock. The "Average" 158 magnum round is traveling 1235 fps and producing 535 ft/lbs. The increase in fps of the 125 grain is up around 1400 fps. The actual penetration will almost be the same as the 158 grain. Yes, the higher speeds of the 125 grain make it a better expanding bullet than the 158 grain, but for self defense, you'll be probably shooting at a distance of 30 feet or less. Anything past that and you should be running the other way. If it's in your house, over penetration of a 357 magnum isn't going to be a real issue. If it does over penetrate, there won't be really enough kinetic energy left to go through another wall and hit a friendly on the other side. Now, if you miss the bad guy, that's your fault and it doesn't matter what size the bullet is; innocent people can get hurt. But don't worry about over penetration.

Me personally, I stay with federal hydra-shoks or Remington SJHP. Both are fantastic at expanding. I use 158 grain in both. But to be honest, I would have no problem using Buffalo Bore which has some kick butt 158 grain JHP that will go at 1475 fps and 760 ft/lbs. For the "K" frame type older 357 magnums, simply use the size bullets that they were originally made for (158 grains) and you'll be shooting the hell out of it and still passing it down to your kids or grandkids.

If for some reason, the 158 bullets are too powerful for you, use the fact that you have a 357 magnum revolver to your advantage. Get some 38 +p ammo. You can get buffalo bore 158 grain 38 special +P that will do about 1000 fps and 350 ft/lbs. That is a great compromise. MORE POWERFUL than a 125 38 special or +P. Less speed, energy, and kick than a NORMAL 158 357 magnum. Don't have the flaming risk of the 125 grain 357 magnum. It's a good load. If you're going for the 38 special +P, then definitely get the 158 grain. You want the heavier bullet. But in case you want to know; NONE of the 38 specials or +P are high enough velocity; even with the 125 grain bullet; to cause the flaming on the forcing cone like the 125 grain full power 357 magnum does. Which means, ANY 38 special ammo is fine. But for self defense, I WANT the most powerful and hard hitting ammo that I can shoot in the 357 magnum. If I want less, because of the way I'm carrying or such, I carry my 32acp or 9mm makarove. So, choice, for the 357 magnum, in my opinion is:

1. 158 grain Buffalo Bore JHP: Kick Butt Ammo 1475/760
2. NORMAL JHP by any reputable company 158 grain: Excellent ammo 1235/535
3, If still too powerful for you, get Buffalo Bore 38 special +P jhp 158 grain: 1000/350
4. If you can't find Buffalo Bore, get any repurtable 38 special +P 158 grain: 890/278

later.....

[1911Tuner]

Well, the truth is, when the Mo del 19, 13, and other "K" frames were developed, there was no 125 hyper-velocity bullets. Generally, they were 158 grain bullets.

Indeed sir...and they were 158 grain lead bullets. Lead is easier on the gun, and not just in the matter of bore wear.

[MCgunner]

My M10 cracked a forcing cone shooting .38 wadcutter over 2.7 grains of bullseye. :rolleyes: K frame forcing cones are weak. I think it was lead build up at the forcing cone that did that, but I sold my M19, mostly because I made some money on it, but partly because I don't care for that flat bottom forcing cone after cracking the model 10 like that. I've never had any other revolver do that, ever. I fired more lead rounds during that time out of my Ruger security six than I did that 19 with no problems at all. Heck, I owned that security six for a lot more years and put a lot more rounds through it than either my M10 or my 19. You couldn't break that thing with a 10 lb sledge.

Anyway, K frames are great shootin', great carrying guns, just have an achillies heal that L frames done, way I look at it. I still shoot my M10, put another 4" barrel on it and have had no problems to date with it. I scrub the bore and watch the forcing cone for lead build up diligently, lesson learned. I have NOT stopped, nor will I stop, shooting lead bullets through it. I note that you all say the K frame wasn't designed for the 125 grain bullets, quite right. Also, I will say that the K frame wasn't designed for the .357 magnum! It was a .38 design adapted to the .357. I'd rather carry a gun DESIGNED FOR the .357 in most cases. That's why I'm a bit skeptical of J frame .357s. I had a SP101 and it was BEEFY in a .357 kinda way. That gun was strong, but the little Taurus and Smith J frame .357s just kinda don't do much for me. I'd have another K frame .357, but even K frame .357s are a bit light for the caliber IMHO. I don't read anything about J frames failing, but if I had one, I wouldn't shoot much magnum in it, especially heavy magnum loads.

As to the 125 JHPs, I have done short barrel chronograph testing with 2, 3, 4, and 6.5" barrel guns. One thing I gleaned from that testing is that the 125 leaves the barrel of a 2" WAY before the pressure peak. It gets out of the cylinder AND barrel without efficiently capturing the pressure. Most of it, with slow powders that are appropriate for magnum calibers, burns outside a 2" barrel and the resulting flash/bang is significantly worse than even in the 3" let alone a 4" With full power 125 grain loads I was getting no more than 385 ft lbs out of the 2" SP101 where I get around 600 ft lbs from the 4" barrel. I think perhaps flame cutting and forcing cone errosion might be enhanced by the fact that less of the pressure is captured IN the cylinder and more of it is burning OUTSIDE the cylinder with such loads, thus creating more flame in the first place AT the forcing cone. I found in my testing that just stepping up to a 140 grain bullet with same 2400 powder loaded to max produced 550 ft lbs vs the 125s mas of 385 ft lbs. Just 15 grains more bullet weight made that much difference. I don't consider the 125 grain bullet for carry, myself. Suit yourself as to whether you want to carry it. It's tough on guns and won't even perform as well up to 3" barrels as does a 140 grain load. Also, the Speer 140 I shoot is a lot more accurate than the 125 grainers I've tried, which sorta seals the deal for me.

[christcorp]

I will disagree that somehow the 357 magnum "K" frames were simply a "Cheap" way to take a Model 10 38 special and make it into a 357 magnum. They tried that numerous times with the Model 10-6. Instead, they totally replaced the barrel with a heavy barrel carbon steel barrel. Thus, the model 13 (Model 65 in stainless). Prior to this, in the 50's, S&W came up with a total 357 magnum version; the model 19 (Later model 66 in stainless). The original magnum revolvers around 1935 were indeed simply variations of existing guns. Which evolved into the model 27. But when the model 19 came along around 1955, it was a new design with improved strength steel, heat treated, adjustable sights, etc... It was definitely designed for the new 357 magnum cartridge "OF THAT TIME". It was a lightweight gun. And the model 13, was basically the M&P version years later with fixed sights. And there was nothing wrong with a lightweight version of the model 27 or 357 magnum revolver. Not with the ammo of the time.

The 357 magnum definitely was based on the 38 special, because originally, the 38 special used black powder. And therefor had a very large case. With a lot of left over space once you converted to smokeless powders. But the 357 case was later intentionally increased in size so people wouldn't accidentally put 357 magnum rounds in a 38 special revolver.

So I still believe that you can take a S&W model 13, 19, 65, or 66; and using standard 357 magnum ammo, in the grain weight of the time; 145-160 grain; (Predominantly 158 grain); and shoot it as much as you want to without causing any problems. And if you wanted to keep such a gun loaded with 125 grain hard hitting modern ammo; that too would be fine for defensive purposes. Because I doubt very much that anyone is going to shoot probably more than 10 rounds in their entire lifetime in self defense. I personally prefer the 158 grain modern hollow point rounds. Matter of fact, in all the years I've had/shot the "K" frame 357 magnum, I don't know of any reputable person ever having a problem with cracked cones using 158 grain ammo.

[Radaray]

MCGunner, you been looking in my loading records?? ;) I agree with your 140grain loading. I too have done the same thing. I've always felt the 140 grain weight was ideal for defense purposes in the .357, and have worked up the following load that is used in my 2" Taurus mod.605 and my 6" mod.28.

Cases can be mixed, and I use WSP primers with 14.0 grs. 2400 powder. I use the Hornady 140grain XTP bullet (#35740), which will perform at velocities between the ranges of 800-1600fps according to Hornady.

It produces 1142fps in the mod.28 and 1145fps in the Taurus mod 605. This produces 406-408 ft/# and is very easy to control in the light weight 605. While I have not fired them into flesh or a flesh substitute, I think this velocity offers a good mix of penetration and expansion.

The fact that the velocities were nearly identical in both guns tell me that the combination of this bullet/powder is a good compromise for the two different barrel lengths. They group very good, and are quite pleasant to shoot. I don't think they stress either gun at all.

[MCgunner]

That's a pretty mild load. I push my Speer 140 with 17.0 grains 2400 which is a max load. 14 grains would be easy on the weapon and if it's accurate and you like it, I'm quite sure it'll do the job.

I posted on a thread in the hunting forum about shooting pigs in my trap. I shot one in the shoulder with my little M85UL with a +P 158JHP. It uses a Remington JHP bullet at around 275 ft lbs. Was a 150 lb hog shot in the shoulder with at about 10 feet and it left an impressive exit wound and broke the off side shoulder. Didn't take long for him to die, either. I was rather impressed with that, gave me more confidence in the load/caliber that it truly is enough. Any .357 load pushing a 140 even if it's a mildish load will certainly be enough for self defense IMHO.

[Prosser]

HMMM. I thought it was the unburned powder, being sandblasted into the top strap by the burned powder that caused top strap cutting?

[MCgunner]

HMMM. I thought it was the unburned powder, being sandblasted into the top strap by the burned powder that caused top strap cutting?

Possible. I can imagine there's lots more unburned powder escaping with the 125 grain bullet since I KNOW the pressure peak hasn't hit until about 3" down the barrel, at least with a powder like 2400 which is commonly loaded in hot loads.

I ain't sure what actually cuts, I just have an idea why the 125 does it worse than the heavier loads.

[1911Tuner]

I can imagine there's lots more unburned powder escaping with the 125 grain bullet since I KNOW the pressure peak hasn't hit until about 3" down the barrel, at least with a powder like 2400 which is commonly loaded in hot loads.


mmmmmmmmmm...Nah. Unique hits peak at .3 inch of bullet travel, and it's not all that much faster than 2400. Slow pistol powders will peak at about an inch, or a little less. The reason for the gigantic fireballs is that there was such a large volume of powder...and it holds peak for a longer time. So, while the bullet may exit while the pressure curve is still at or near peak in very short barrels...it still reaches peak before the bullet is gone.

Slow rifle powders will hit peak at about 3 inches...but not pistol powders. If the bullet exits before peak pressure, velocity would be extremely low. Even with huge fireballs and mucho unburned powder leaving behind the bullet...most rounds produce the highest velocities with slow powders, assuming that you don't load over safe pressures with the fast numbers.

[Blue Brick]

If you buy a Ruger, you won’t have to remember any of this information because Ruger’s don’t have any forcing cone or top strap issues and will fire any round that you can fit into the chamber.



And yes I know about the 357 Maximums-it was a gap issue. Dan Wesson eliminated the problem by changing the cylinder gap to 0.002.

[MCgunner]

mmmmmmmmmm...Nah. Unique hits peak at .3 inch of bullet travel, and it's not all that much faster than 2400. Slow pistol powders will peak at about an inch, or a little less. The reason for the gigantic fireballs is that there was such a large volume of powder...and it holds peak for a longer time. So, while the bullet may exit while the pressure curve is still at or near peak in very short barrels...it still reaches peak before the bullet is gone.

Perhaps so. However, would seem to me that a 125 grainer makes it down the bore farther than a 158 would before the pressure falls off simply from lower inertial weight. It takes less to accelerate the lower weight projectile farther. From my testing, I'm pretty sure than I can infer that the 125 grainer from a 2" barrel using 2400 is NOT capturing the whole pressure peak even if it is capturing part of it, thus the lack of efficiency, the lower energy numbers. All this is MY inference which I admit may not be right, but it makes perfect sense. And, if the bullet travels an inch down the bore before the peak even hits, it's well past the forcing cone at that point so the forcing cone is receiving the full pressure peak of the powder vs a faster powder, Unique, with which the pressure would be falling or at least well into the peak before the bullet even reaches the forcing cone.

Hell, we sound like friggin' Einsteins or something, ROFL, but it's just a theory I've had from my chronographing of various barrel lengths. I have no proof that what I've theorized is true.