When muzzle energy data is given is there a standard length test barrel used so numbers can be compared directly among brands?

E.g. I use mostly Magtech .357 FMC/FLAT (158 grains). Numbers are: 1233 FPS, 535 FTLB. It is stated that the test barrel was a 4" vented barrel.

Why a vented barrel?
Would numbers be higher from a 4" non vented barrel?
What would numbers approx. be in a 6" non vented barrel?

Is this considered to be a standard .357 mag load?

I wish it were so, but it is not, and in some cases, the barrel used is not identified. A vented barrel is sometimes used for revolver cartidges to simulate the cylinder-barrel gap, but even then may give higher numbers than a real gun.

You see, particularly in the USA, the prime reason for the testing is to simulate the highest possible pressure by using a minimum dimensioned chamber and barrel, which may give higher performance than a typical revolver, but will certainly be safe in a looser chamber. We have more lawyers than engineers here, and the company is concerned about being sued if a gun blows up.

I have a chronograph, and it was a real revelation to find that the numbers I get with my guns sometimes are very close to published data--like with Speer's Gold Dot .38 +P 135gr shot through a S&W 442- and sometimes very different, such as certain .357 magnum data taken in 10" test barrels, compared to my 4" Model 686.

I don't really know what I am going to get in my guns until I chronograph them myself. I handload, and adjust as needed for the desired power and accuracy, which is often better about 5% below max.

Since muzzle energy is proportional to mass times speed squared, a small change in muzzle speed gives a large change in muzzle energy. Muzzle energy alone is not the most important factor in handgun ammunition performance, in my experience.

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Science plus Art

Ok.....so the numbers given which was measured on a 4" vented test barrel may correspond to my 686 with 6" barrel.

Where I live I am only allowed to use the 686 on a ranch and not for home protection or carry (not allowed......only from home to ranch and back again). Therefor I just use 158 gr. FMJ/FLAT. But if a situation should occur.....a FMJ/FLAT should be better than nothing.....or even better than a .22 LR LRN I guess.......

Actually it is one-half mass times velocity squared....

True.
My personal choice for "walkabout" .357 ammunition is 158gr jacketed soft points loaded over Win 296, which have enough penetration for our feral pigs (no season, no limits, shoot all you want) , and expand enough for our smallish 55 kilo deer (in season). I'm not a fan of FMJ, and it is not legal for deer here, anyway.

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Science plus Art

Fixed it for you:

proportional to mass times speed squared...

Actually there is also a numerical constant in addition to the 1/2, to account for shooting's odd mixed units, but I was trying to focus on the speed squared part. A BB going Mach 6 would have tremendous muzzle energy, but not much real effeciveness on an animal, zipping through and expending the energy on the landscape.

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Science plus Art

A .357 FMJ will probably do a full penetration on a deer or a human body. In many cases it will be lethal? ....but not an instant kill?

That it is why you should use a JHP? ....will a JHP in most cases be more lethan than a FMJ? .....probably?

A friend illegally and stupidly shot a deer with FMJ surplus 7.7 Japanese ammunition, and we only found it the following afternoon, 1 1/2 miles away. The coyotes enjoyed it.

Soft point or hollow point expanding bullets are much more effective on deer. Don't need anything super powered or exotic, just an expanding bullet in the heart/lung area. I find most within 100yds or less of where they were shot. A heart shot animal typically will run for about 8 seconds and then collapse. I've never seen it in people myself, but I've been told people can do the same thing, and the "instant one-shot stop" requires hitting brains, spine, or some such.

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Science plus Art

Ok.....and it is the same bullets you would use for "home protection" ? and the result on a human.....will be the same as on a deer?

Well, ANY pistol is second choice for me for home protection, if I can get to a shotgun.

Having said that, I tend to use somewhat lower-powered premium HP .38 +P ammunition in the smaller revolvers I routinely have on me when not in the field, and that's what I would use if surprised and forced to defend myself immediately around the house.
Sometimes people ask me what I would prefer if I knew in advance I was going to be in a gunfight, and I answer "lots of armed friends."

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Science plus Art

But "over there" .....if a person comes into your house.....without beeing invited...can just shoot and aks afterward? ....or do you have to prove that you where in danger and was forced to shoot?

Each of the 50 states of the United States has its own laws on the use of deadly force, and you must folow the laws of the state you are standing in. I teach a concealed carry course for the state of Oklahoma that includes 3 hours on this subject, so I can't give you a one sentence answer, other than to say only a fool would employ deadly force against someone based only on their location.
What if you left the door open, and the paperboy came in to ask for his money? That's different than someone kicking in your door at 2AM.
Gun ownership carries great responsibility, which most exercise with intelligence and restraint. In spite of the anti-gun rhetoric, there are no "shoot first and ask questions later" laws.

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Science plus Art

I like the sentence "great responsibility". It will probably be a very bad experience for most people to shoot another. So something most people only will do if more or less forced to it. Why I asked about the "shoot and ask later" was the case from Florida with a black boy killed.....without any reason....it seems. It also seems that if there had been no press on the case.....the shooter would have been a free man today. So Florida has one of the most "liberal" laws? ....how is it in Texas?

Ok.....this was be a bit "off subject" .....but it seems that even with .357 FJM/FLAT I would be able to defend myself....if needed. On a Federal ammo box....think it was a 125 gr, JHP there was written "law enforcement use only". Is this only a kind of warning?

Hello MXP, welcome to the forum.

I agree with what OKFC05 is telling you. A JSP or JHP bullet is a much better choice than a FMJ bullet most times. You want an expanding bullet because it will create a wider wound channel causing greater and faster blood loss. Also, the expansion of the bullet will cause the energy generated by the bullet to be dumped inside the body instead of a pass-through will minimal energy dump. I feel a .357 Magnum is a very good caliber for woods/range carry.

For home defense again I agree a shotgun is probably the best choice. My HD shotgun is loaded with #4 Buckshot. If you do use a revolver I would and do use a good SD .38 Special +P ammo which uses a premium hollow point bullet. The classic FBI Load is my usual choice. (158gr LSWC/HP .38 Special +P) I feel a .38 Special +P is a safer round to use indoors because it is less likely to over penetrate, the flash and report are less than the Magnum and the recoil is less allowing for a faster and more accurate followup shot if necessary. Just remember, the best ammo in the world will do you no good unless you make good hits.

As for the "Law Enforcement Only' load, that usually means it's usually over SAAMI pressure limits so the velocity is higher than most available ammo. (I said usually but not always) The 125gr JHP .357 Magnum load is probably the best man stopper available. I know the .45 Auto shooters would disagree but that's a discussion for another thread... lol

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In most areas FMJ ammo is not allowed for hunting...precisely because it doesn't always give a quick humane kill.

My old Speer book has a chart where they measured shots from all types of guns, barrel lengths and sometimes different examples of the exact same model. It was amazing how much variance there was between makes, model and even sever individual examples of the same model. The thing is that all guns are different and what works for my gun would be irrelevant for yours, even if it were 'just like mine'.