Pressure in longer case(.38 Spec./.357)

[Frank D]

A question for you guys more advanced than I am in reloading pressures(Handgun)
How will pressure be affected if IDENTICAL loads are loaded into longer cases?
(Such as .38 Special loads in .357 brass or .44 Special loads in .44 Mag. brass.) Will the Pressure/Velocity increase or decrease in the longer cases ?
I am aware that the longer cases would need to be utilized in the correct cylinder length (.357 or.44 Mag.) to avoid the shoulder. I plan to use standard primers in all loads (Not Magnum)

[Scorch]

Rule of thumb:
If all components are the same, a larger case with the same bullet, powder charge, and primer will give you lower pressures and velocity.

[saands]

The relationship is more pronounced that you'd think ... with the pressure dropping a lot when you add that much to the case volume.

The one caution is not to use powders that have MINIMUM loads defined for them in this application. There aren't very many, but H110 is one and one of the Winchester magnum powders is as well. I don't recall if the Alliant 2400 is in that family, but it might be. As long as you are using a reasonable full load of any of the other powders you should be fine. the one thing that I try to do is use a recipe that more than half fills my case ... that way if I double-charge it, the mistake is obvious long before I touch off the bomb that would certainly be the result This might be an issue if you are using 38 spcl loads in a 357 ...

Saands

[Shootest]

If you load light 38 SPL loads in 357 MAG brass the pressure will be lower so low in fact that you might get squibs (where the bullet does not leave the barrel). And if you were to fire the next round you may have a KB. It is NOT worth the risk, why not just use 38 brass for 38 loads and 357 loads for 357 brass?
JMHO

[Lost Sheep]

While Shootest's advice is wise, I believe it goes too far.

Originally Posted by Shootest

If you load light 38 SPL loads in 357 MAG brass the pressure will be lower so low in fact that you might get squibs (where the bullet does not leave the barrel). And if you were to fire the next round you may have a KB. It is NOT worth the risk, why not just use 38 brass for 38 loads and 357 loads for 357 brass?
JMHO

Caution IS the watchword. This is where we agree.

Since the first year I started shooting and loading, I have never fired a single 38 special case out of any my guns. But around 85% of my shooting is 38 special power levels.

Where we disagree is the amount of difference between Magnum cases and Special cases. I don't think is it all that great. 1.290 vs 1.156 overall length. If you give .1" to the web and base of the case, that is 1.190 vs 1.056 (about 13%). So, for example, if I have a light 38 special load and boost it 13% to use it in a .357 magnum case, I believe I am safe.

For example; 158 gr jacketed bullet out of a 38 Spec case over a starting load of 6.8 grains of 2400 reportedly delivers 850 fps in one manual. In the same manual, the same bullet out of a .357 Mag case, the starting load reports 1620 fps from 13.8 grains of 2400. How do your figure to get 850 fps from the magnum case and 2400? Experimentally, I would start with 13.8 grains and work DOWN to 850 fps or until the velocity became erratic. Theoretically, I would start at 7.7 grains of 2400.

Alternatively, I observe that there are three powders that deliver lower velocities out of the .357 case. IMR700X, IMR PB or SR7625, which the same manual reports 885 fps, 875 fps and 855 fps at 4.7, 5.1 and 5.6 grains at 35000 cup. However, pressures with those same powders in 38 special cases at near 3.5 to 4 grains are around 15,000 cup and deliver 600 fps leads me to believe they could safely produce 700 fps from a .357 mag case if you used 5 to 5.5 grains and would probably be around the same 15000 to 16000 cup in the magnum case. The burn pressure is the key, I think.

Try reading your loading manuals and thinking about the interior ballistics. Smokeless powder burns slowly at low pressures (light 10 grains of Unique in a metal ashtray or a flat rock and see). Smokeless requires pressure to burn at the design burn rate and to be stable when it does. Figure out what you think would be enough powder to get the pressure into the range that the manual reports and see how much sense you make of it.

I haven't gone too deeply into it myself. Just enough to be comfortable with the powders I use.

Pick a powder, bullet, primer and case and make your best guess. Then email the powder manufacturer. They will probably have some insight and/or advice. Undoubtedly it will be educational.

I believe in finding published load data where possible (I hold the opinion that it is pretty much impossible to own too many load manuals) and staying within that range, but if I am searching for 650 fps from magnum cases, I will try to find a powder that gives that velocity, vetted by somebody's ballistics lab. If not, I will use a voluminous powder (like Trail Boss) or a fast powder (like Bullseye or Unique, maybe with a filler to keep the powder near the primer) and do some testing over a chronograph to ensure that I am guaranteed each bullet will clear the barrel.

Pressure is the key. Powder burns erratically outside the pressures for which it was designed. It may get spikey, leading to over pressure and kabooms, or it may not develop enough pressure to make the bullet clear the barrel, leading to a kaboom with the next cartridge fired.

Caution IS the watchword.

Lost Sheep

[Unclenick]

The correct answer is, it depends…

The factor you are interested in is the powder space under the bullet. This is determined by how deeply you seat the bullet into the case. For a given powder charge, less space equals more confinement, so the peak pressure tends to be higher. If you want the peak pressure to be unchanged, you then have to reduce the powder charge for that tighter confinement.

How much deeper you can seat the bullet before seeing the effect depends on the amount of space you start with. Seating a .224" bullet 0.1" deeper into a .220 Swift case reduces the volume by a much smaller percentage than seating a 9 mm bullet 0.1" deeper into the short 9 mm Luger case will do, so the effect of the latter is much more dramatic. One of the load manuals (I forget which; maybe one of the Speer manuals) reported the 9 mm pressure almost doubling as a result of seating a short distance deeper like that.

The above leads to a funny result. For a given parent case shape, if you keep the COL the same the pressure stays about the same. For example, the .44 Magnum was developed by Elmer Keith using heavy frame .44 Special guns and .44 Special brass. The reason for the longer magnum case is just to prevent the higher pressure magnum loads being accidentally chambered in a .44 Special revolver that might not withstand them. Thus, even though the .44 Magnum case is longer than a .44 Special case, the SAAMI maximum COL's are the same (within 0.005"), so the loads work interchangeably as long as you use the same COL for both. The location of crimp grooves in some cast bullets makes that constant COL difficult to hit, though a few have more than one crimp groove. You can usually take a Lee Tumble Lube design, for example, and keep the COL constant by using one of the Micro Band lube grooves as the crimp groove with the shorter .44 Special case.

For .357 Mag. and .38 Special, you'll find the SAAMI COL's are not the same, so the .357 tends to have more powder space and needs to be loaded with larger charges to reach a given pressure with a given powder. However, when you get to really fast burning powders, they tend to burn well at any pressure, so the amount of gas made before the bullet leaves the larger case is about the same. Thus, if it then goes down the same length barrel, the velocity may be about the same even though the peak pressure is reduced. (It is average pressure behind the bullet and not the peak pressure that determines velocity.)

[Sevens]

Since the first year I started shooting and loading, I have never fired a single 38 special case out of any my guns. But around 85% of my shooting is 38 special power levels.

You aren't the only one doing this, but I've always found it much ado about nothing.

I've definitely put a lot more .38 Special through my 686 since I bought it and began handloading for it in 1989. These days, I tend to run .357 Magnum through it mostly.

I've never had any sort of problem with carbon rings or chambering issues in my cylinders.

Perhaps some other revolvers give grief, but mine hasn't ever?

I can understand someone going the long route to use only magnum brass if their revolver seems to demand it... but to do it proactively, I just don't understand. I have a ton of .38 Special brass... I can't imagine never using it and putting my smaller supply of .357 Mag brass through the wear & tear of sizing/flaring/seating/crimping and firing when I've got plenty of .38 brass to handle it.

[Unclenick]

As you say, it depends on the gun. I've seen plenty of lead build-up in my Dan Wesson revolver's chambers. I suspect it mainly has to do with how snug the chamber throats are around the bullet. If there is extra room, gas bypass tends to blow metal off the base and into the chamber. Another argument favoring sizing bullets to the throat within half a thousandth or so.