We all know the caliber debate about for instance, 38 vs 9mm. The 9mm has more velocity, blah blah. But how can this be? Visually a 38 looks like a way longer 9mm, no? So if they use the same powder, shouldn't 38 be more impressive? Or is 38 not loaded all the way? I've heard that revolvers are slow burn, so this must mean a different powder right?

Thanks!

9MM cartridges are loaded to a much higher pressure than 38 Specials. The case length doesn't figure into the equation.

And yes, many powders can be used for both cartridges. Again, that doesn't matter....

Also, with equal barrel length and equal weight bullets, the velocity difference may be less than you think....

IMHO, a lot depends on application. In semi and full auto applications I have always tended to the faster burn rate to ensure 100% functioning of the mechanism. There is a difference in the function of a blow-back operated Sten and a retarded ejection in an H&K P7. To make a long story short if you want one powder for both semi and revolver applications, pick the one that runs your semi/full best (most reliable) and let the revo's fend for themselves. My son and I both frequently shoot our S&W 625 (45acp) and our Colt 1911's on reloads made to run a full-auto, blow back MAC 10. It may not the the optimum load for the 625 but it does pretty good.

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Randy
Provenance nerd

I use the same load in my .45 ACP revolver and my .45 ACP auto loader. Same .22 LR in revolver and auto loader. I don't have a .357M or .44M auto loader but I use the same load in all barrel lengths. Larry

There are hundreds of different powders with different burn rates and most smokeless powder loads only partially fill the case.Blackpowder loads do ( for the most part) fill the case.

Case length doesn't matter.

The 9mm has more velocity because it is generally loaded with a lighter weight bullet. The lighter the bullet, the lower the pressures, therefore the more powder you can use. Velocity isn't the do all and end all of stopping power, but does have its place. Actually the .38 Special can be a very impressive round with medium weight bullets, i.e. 135 grain Speer Gold Dot bonded jacketed hollow point and even with 158 gr. lead semi-wadcutter hollow points. The attraction with the 9mm is that one can carry more ammo in a semi-auto pistol, than in a revolver.

Actually, all else being equal case volume is king.

In a given gun(again, the "all else being equal part") velocity is proportional to the integral of the pressure-time curve. Velocity is also roughly proportional to the volume of gas generated by the burning powder, which is again roughly proportional to the mass of powder.

If case volume is increased while maintaining the same peak pressure and using the same powder, bullet, and gun(again, all else being equal) a greater mass of powder can be used. More powder means more gas, which means higher velocity.

I think a good example of this is to compare standard pressure 9mm Luger vs. 38 Super. Both can be loaded with the same bullets, and have roughly the same maximum pressure. The Super case is longer, and therefore has more volume.

Looking at reloading data for both-just as an example-Hodgdon specifies a max 9mm load of 4.8gr CFE Pistol Powder under a 125gr Hornady HAP. The stated pressure for this load is 33,400 psi and gives 1096fps out of a 4" barrel. The same bullet in 38 Super over 6.2gr CFE Pistol generates 32,300 PSI and 1259fps out of a 5" barrel. Admittedly the differences in barrel length do have some impact, although Ballistics by the Inch(link) shows a drop of somewhere around 50-75 fps for most factory 9mm ammo when going from a 5" barrel to a 4".

Of course, this is just one example-and I used it because the cartridges are fairly similar other than length.

I'm pretty sure that someone who really knows this stuff(which I don't) could make a college course or two out of internal ballistics. I know enough about them to realize how little I know!

Yes but it doesn't work how the OP is thinking. You can't just look at the case and assume it's more or less powder/pressure/velocity based on the length of the case. Both 40 and 9 are higher pressure then 38spl but are shorter

The 38 special case was designed when black powder was king. The large case capacity is for the amount of black powder needed to propel a lead slug to suitable velocities.

A 9mm case, for example, was designed later; after the advent of smokeless powder. This required less case volume than blackpowder, thus the smaller case.

Most non magnum handgun rounds use a fairly fast powder. As a reloader, I use the same powders in both revolver and semi auto loads.

I cannot attest to what commercial ammunition manufacturers do. If the don't use the same powders, I at least expect they use very similar powders in both.

As others have stated, the 9mm is designed to be loaded fir higher pressures than the 38 special; thus the faster projectile of similar weight.

Like said above, the .38 Special case is so large because it was originally designed as a black powder cartridge. The 9mm was always loaded with smokeless powder.

The type of powder used in a cartridge has nothing to do with which platform it's shot from. The cartridge itself dictates which powder is best for reloading.

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Freedom is never free!!
SWCA #3437

Just to add to the commentary......the pressure rating of the cartridge dictates many attributes of how it can be loaded.

For instance, the .38spl is a low pressure cartridge at 17,000psi. This means that it is designed to fire it's projectile before pressures reach the critical level of 17k psi. In order to do this, you must balance several factors that effect pressure levels during the loading. The harder it is to push the bullet through the barrel, the more pressures are generated(.38spl likes soft bullets). The smaller the space for the powder explosion to occur(case capacity), the greater the pressures generated. The deeper a bullet is seated, the higher the pressures(reduces case capacity). The longer the bullet(more resistance to push it out), the higher the pressures generated. There are more factors, but those are the basic ones.

Generally, any powder that is good for .38spl is also good for 9mm.....you just have to set up the load correctly. However, even at +P levels it is very difficult for the .38spl to match 9mm standard pressure performance levels. Once the 9mm gets into +P and +P+ levels, it has left the .38spl in the dust so to speak. However, the .38spl can be loaded with much heavier bullets due to its much larger case capacity and it can launch them and pretty good velocities. Combine that with the much wider meplat on the .38spl bullet, I think both cartridges are about equal when it comes to shooting soft targets.

Also, don't forget that loads for the 38 are tested in vented test barrels to mimic the barrel cylinder gap of a revolver. The 9mm is tested in a regular, closed system. This has a big effect on velocity.

Older cartridges like the .38 or .44 special, that were based on or evolved from black powder loadings generally have a LOT more space than is needed for good combustion of smokeless powder. I use the same powders reloading .38 and 9mm but there are powders that are more suitable for each, because they are different animals due to powder volume vs. available volume. You can use Titegroup powder in 9mm and .38 and the whole charge barely covers the primer hole in the case. Manufacturers most likely use blends of powders that are optimum for each caliber/cartridge. I can use a powder like Unique for mild to heavy loads in several cartridges. Sorry if this is incoherent, but powders can be versatile or very specialized. If I confused you or you need clarification, let me know.

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"He was kinda funny lookin'"

Black Powder loads *always* fill the case. Air space in a BP load is a no-no.

For reduced BP loads, fillers are used to take up the extra air space.

Genuine Black Powder loads should be at least somewhat compressed (not talking subs like 777, that's a different deal)

There are a few rules for BP loads that are a bit different than Smokeless.

To answer simply, yes. Shotguns also use the same powders.

Yes and no. Depends.

Reloading handbook is your friend. There's about 20 of them to choose from. Find one and use it.

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M&P's and K Frames Pleeze!

Thank you for all this information. I think I still need explaining on how the pressures are different in 9mm and .38 and why/how this is done. I've never loaded my own ammo before, so to my ignorance what I am envisioning is just an empty cartridge filled with powder and a bullet placed on top. So how does one change the pressure?

Or is it that let's say 38 generically uses X amount of powder in it's longer cart, but 9mm uses the exact X amount also, but since the cart is smaller its compacted more and thus more pressure? meaning 38 the powder would be "looser" so to speak?

I guess I need this explained in laymans term to really wrap my head around it.

it is the pressure the gases create when burned that causes the pressure we are talking about - not the pressure used to put the powder in the case.. the powder is dumped in the case. Each caliber has a max pressure that can be safely reached & that is determined by two "standards" group - SAAMI in the US, & CIP in most of Europe.

when you pull the trigger the primer ignites the powder & very rapidly burns turning into high temperature gas that rapidly expands - that is the pressure we are talking about - so the 9mm operates safely at higher pressures so more pressure & gas is available to propel the bullet

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Steve

As I mentioned above, internal ballistics(what you're asking about) is an enormously complicated field, and one that I know just enough about to realize that I really don't know anything about it

With that said, if we take two samples of the same powder and confine them in spaces of two different sizes(a 9mm case and a 38 special case, for example) the one in the smaller case will generate higher pressures. How much of a difference is really difficult to say, as different powders behave differently as compacted more. There are programs like Quickload that aproximate this, but there's enough complicated physics going on that calculations really can only be used as a guide and not as an absolute.

One other thing with regard to case volume-most cartridges have a maximum allowed overall length. In a revolver, the bullet nose can't stick out past the front of the cylinder or the cylinder won't be able to turn. On a semi-auto, a cartridge that's too long may not fit in the magazine, or may be too long for the gun to correctly feed it.

Bullets of a given caliber have a fixed diameter(by definition) so as a result of this a heavier bullet must be longer. Since the overall length(generally) can't get any longer, a heavier bullet extends deeper into the case and thus reduces the case volume. If you look at a reloading manual, you will see that heavier bullets tend to have lower maximum powder charges(for a given powder). One of the design goals for Keith type bullets was to place more of the bullet mass outside of the case so that one could throw more lead without decreasing case volume.

Even if you don't reload and don't plan on reloading, a good loading manual can help you out and explain a lot of these concepts. If you were inclined to buy one, I'd suggest picking up Lyman #49. It's around $20 in paperback.

Wow these last two replies really made it click for me. Thank you so much. I love learning all this!

But with regards to heavier bullets being longer because the diameter cannot increase. What about a denser bullet?

That would work theoretically, but I can't think of any inexpensive metals off the top of my head that are denser than lead. There are plenty of metals that are more dense, but a majority of them are relatively rare and/or very expensive.

There are now some solid copper(or copper alloy, most likely) bullets available. Barnes is probably the best known brand of these. Barnes bullets are available as both component bullets and in some factory loadings.

One of the things you will note about them is that they tend to be light for caliber or very long if in the "normal" weight range. The Barnes 140gr XPB 357 bullet, for example, is listed at .770". I measured some .357(or more correctly .358) lead bullets that I had lying on my desk-a 125gr LRNFP is .550", a 158gr LRNFP is .625", and a 168gr(true) Keith-type SWC is .750".

38 Special and the 9 mm can use the same powder, just not the same amount,
Faster powders work well in the two you are looking at.
You only need the slower powders in the magnum for full power loads, such as the 357, 41, and 44.

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John

You've been given some good explanations as to the "how". Let's talk about the "why".

Being an older cartridge, the 38 Special has been chambered in guns that simply can't handle the higher pressures the more modern guns chambered in 9mm can handle. I don't imagine it would take a lot to blow up and old break top Forehand Arms revolver, or an RG saturday night special. Ammunition manufacturers have to take this into consideration when selling ammunition.

With modern cases, and a strong enough gun, the 38 special can be loaded to higher pressures, but you wouldn't want to sell these to the public, many of which aren't educated on the effects of pressures in a handgun's chamber.

Smith and Wesson made a 38/44 revolver many years ago. It was built to withstand higer pressures than a standard 38. It was the forerunner to the 357 Magnum. The only difference in the two is about 1/8" in case length. This was done to prevent the higher pressure 357 rounds from being fired in 38 special chambered guns more so than for the added case capacity.

It's more the ratio between the volume of the powder and the volume in the case. Unless you are using a very bulky powder, .38 cases are over sized compared to what it needed. As noted on another thread, smokeless powder does not explode. It deflagrates, which is breaking down into ash and gases by burning. This is true when out in the open. Try lighting a little powder outdoors. It fizzles and burns. DO NOT contain the powder though, because then it will act more like it does in a gun cartridge and burn rapidly enough to almost be an explosion.

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"He was kinda funny lookin'"

Semi-auto powder can be used in revolver loads, but not all revolver powder can be used in semi-auto loads. Slow burning magnum powder is not suitable for semi-autos.

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S&WHF 366

It depends on the semi-auto cartridge.

I have a friend who bought a 45 Winchester Magnum a little while back. His is a LAR Grizzly, which is basically an oversized/overbuilt 1911. Most of the published load data uses what we'd consider traditional Magnum revolver powders like 2400 and w296.

I'd agree that for most semi auto cartridges that this is generally true.

Well sort of. AA#9 is pretty slow, so is BlueDot. Both are good magnum rev powders that also work well in high pressure/full power semi rds like 10mm & 357sig.

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NRA Cert. Inst. IDPA CSO

Only thing denser than lead would be tungsten.
There are issues with less dense bullets, all copper Barnes for example, being longer than lead core bullets even though they may be lighter. So you can't just plug those into the same powder charge w/o an over pressure event.

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NRA Cert. Inst. IDPA CSO