40SW weight variation

[hubcap]

I did a random weight check on my 40SW brass (assorted headstamps). It was cleaned and unprimed--just the brass. I checked the case length and they were all the same, but as much as 10.5 grains weight difference!!! Is that too much? I don't usually sort handgun brass, but should I???

I'm not as concerned about the lack of weight uniformity. I doubt there are many, if any, people who could tell the difference in accuracy with a hand-held firearm at normal pistol distances with the kinds of deviations I'm talking about here. I'm not talking about bench-rest accuracy.

My concern is not the presence of the weight/capacity deviation, but the amount of deviation-- well over 10%. I don't know how much a % of change in case capacity affects pressures, only that it most certainly does. All reputable manuals advise reloaders of semi- or full-auto firearms to make sure the ammunition does not allow for bullet setback for this very reason.

My concern is about the safety of the ammo, because the weight is a factor in determining case capacity, and therefore pressure, and therefore safety.

If you change your powder charge by that amount, you can very quickly go from safe to unsafe (or vice versa) pressures. It's also my understanding that, because of the nature of smokeless propellants, the pressure curve can rise exponentially rather than linearly at unsuitable pressure levels (high or low).

 

[ReloaderFred]

Since you don't know where the weight difference is, I believe you're overthinking this. A slightly thicker rim, or slightly thicker base, etc. will make a case a little heavier, and it doesn't take much brass to weigh 10.5 grains. That could only be 5.25 +/- grains from a median weight, too.

My guess is some of your lighter brass may have been Remington brass, which in .40 S&W tends to have thinner case walls, which can sometime result in less neck tension. That's where the danger lies, as a round with not enough neck tension is more likely to suffer bullet setback while chambering.

I've done some weighing of .40 S&W brass, but it was for bullet swaging, where I'm using the brass cases for bullet jackets. The most consistent I've found is military Federal brass in this caliber. The headstamps I weighed were FC 08 and FC 10, and they were within tenths of a grain in weight for all that I weighed. I get a lot of it, since the Coast Guard uses our range for qualifications.

For loading ammunition, I put much more emphasis on good neck tension than I do case weights.

Hope this helps.

Fred

 

[Havok7416]

You are severely over-thinking this. Case weights will be all over the place within a range. This is perfectly normal and nothing to worry about.

 

[G11354]

If the brass matches the caliber your loading and shows no defects (splits, cracks and such) then dont worry about it. Brass like all metals comes in a wide variety characteristics, some harder, some softer and so on.

 

[dgod]

Deleted...

 

[Havok7416]

I have a tricky question... I recently acquired a bunch of .40 cal brass, amoungst them are several .357Sig pieces. I noticed them after the were deprimed & Sized to .40. In retrospect, I got out my Mic, checked them against the .40's. The 357Sig Case is about .025 longer and about .002 smaller in diameter (.401 vs .398-.399).

Question: How much success could I anticipate loading the 357 Sig cases with .40 cal Data & Bullets? Is it a bad idea? Should I just put them aside until needed? I do have .357 Sig Dies, just haven't loaded any.

Thanks for your advise..

The best place for this would be a new thread so we don't derail the OP's thread.

 

[FROGO207]

Back on topic I have noticed that not all 40 S&W brass is created equal.When looking at the extraction groove they are wider on some brands than on others. Also the flash holes are different diameters on some brands. This along with some brands thinner case walls. This could be your weight difference showing up. FWIW the actual weight difference by internal volume of the brass would be accurate if you weighed the resized brass empty and then filled it with water and reweighed it. The difference would show the actual water volume by weight inside each measured case. I am betting it is much closer than you think. But FWIW I have never weighed a 40S&W brass and have been reloading mixed brass with good accuracy for four or five years now.