Should I Care About Variation in Full Cartridge Weight?

S

Swifty Morgan

New member
I made a bunch of .45 ACP rounds with 6.1 grains of Unique. I used new Starline brass. I was careful about the charges, but I decided to weigh the cartridges anyway.

I found the vast majority weighed 320.0 or 320.2 grains, using a scale accurate to within 0.2 grains. A little under 10% by my guess were under or over by 0.4 grains. Some were a whole grain low or nearly a whole grain high.

My question: should I have concerns about squibs or overcharges? I think I'm fine because the brass itself, while surprisingly uniform in weight, varies within a range of about 0.8 grains.

My powder measure is very consistent, I'm very careful, and if I get interrupted, I pull cartridges that could be affected and run them through a second time.
 
Simple enough if you're worried about it. Pull a couple of the outliers and measure the powder charge to see if it's what its supposed to be.
 
You don’t know which components have how much variation to begin with. If you’re using cast bullets you’ll find more variation than you will with jacketed.You can also measure some cases to see how much they vary. Every single component you use will have some variation and that’s normal. It can all add up in one direction at times and give a more extreme plus or minus in that direction. Pull a bullet on one of the more extreme variations and you might find the powder charge is pretty close to being right on. Just the lube on a cast bullet can add a significant amount of extra weight. You may have simply just discovered what was already there. I’d only be concerned if it were a significant variation in the powder charge. Note: while loading, it’s a good idea to weigh every 5th or 10th charge to see if there are any problems in that area.
 
I suspect that most of the variability in total loaded cartridge weight you're seeing is due to the bullet, which is by far the majority of the weight (230 gr. ?) in the loaded cartridge. You already know that the variability in weight of the brass case can account for about half of the variability you've measured, so it would be easy for the bullet to account for the rest. Assuming you have some extra bullets it would be a simple matter to weigh a few of them to see. A +/- 1.0 gr variation in a nominal 230 gr bullet is only +/- 0.43%. I think it would take a very good bulletsmith indeed to hold to less than that tolerance in their finished product.
 
If you want to know what a squib would weigh -- make one. Just place a primed case and a bullet in the pan and weigh them.

To allow for variations, do this with 5 or 10 cases and bullets selected at random.
 
Final cartridge weight won't show you anything.
Unless....
You weigh & sort every casing, primer, bullet.

Personally i don't know anyone THAT anal about 45ACP cartridges.
Precision Bench Rest shooters, yeah..
But that's a whole other story! :D
 
Aguila Blanca said:
If you want to know what a squib would weigh -- make one. Just place a primed case and a bullet in the pan and weigh them.

To allow for variations, do this with 5 or 10 cases and bullets selected at random.
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I did just that. I was concerned about short loads/ no powder loads. The variance between mixed branded brass is considerable ... Often as much as 5-6 grains (about the weight of my powder charge) So, there is really no way to weigh a full cartridge for this purpose with any confidence.

Above based on my experience. Your results may vary.
 
I think I'm fine because the brass itself, while surprisingly uniform in weight, varies within a range of about 0.8 grains.
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That seems like your answer right there. Add in slight variations in charge and bullet weights and you are going to get something like a bell curve. I doubt you have anything dangerous in any direction, such as a double charge or a missed charge, based on that and on the fact that you emphasized that you were careful about your powder charges.
 
The guys are probably correct that it isn't significant, but every once in awhile you run into an anomaly. The way a statistician would answer the question is with the bell curve already mentioned by TailGator. Does a histogram of those weights form a bell curve distribution? If so, that's normal and expected. From your description, though, it doesn't sound like you have that. I can't say for sure without a list of your weights, but it sounds like you have a lot of tight weights and ten percent outliers that jump away from the weight of the 90 percent. That's not what you expect from random variation, so if I'm understanding your description correctly, the difference has a non-random cause.

Personally, I would want to know what the cause is, but I wouldn't get too excited about it. If the bullets are cast bullets, I would expect an occasional mould closing error to turn out some heavy ones, and occasional inclusions to make light ones. If the bullets are jacketed, though, I find most of those are remarkably consistent, but that depends on how they were made.

So, the first thing I would do is weigh some of the bullets you haven't loaded yet to see if their variation is like that of the loads. If so, unless you shoot beyond fifty yards, ignore the difference, as a bullet weight difference that small will not show up on standard range pistol targets without being very carefully sandbagged, and not even then if the weight error is symmetrically distributed. If the weight variation is not in the bullets, and knowing Starline brass is pretty consistent, I would pull down a few of the heaviest ones and a few of the lightest ones to see which component is responsible for the difference. If it is the powder, as long as the loads are within safe limits, I would reseat the bullets and simultaneously sandbag those rounds onto a target at my maximum range and chronograph them, so I can decide whether or not I care about the difference.
 
I've heard of people weight separating primers. :eek:
Just too over the top for me!
I think my time is better spent actually shooting. :D
 
Swifty Morgan said:
I found the vast majority weighed 320.0 or 320.2 grains, using a scale accurate to within 0.2 grains.
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Another consideration is that if the variation is plus-or-minus 0.2 grains and your scale is accurate to plus-or-minus 0.2 grains, you may not have any variation at all.

Or you may have variations of plus-or-minus 0.4 grains.

My solution to this is not not load anything to the maximum published charge.
 
std7mag said:
I've heard of people weight separating primers.
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For 45 Auto? Total waste of time for that. Someone regularly shooting rifles in the ones in benchrest matches might do it, but you'd have to have incredibly small groups to start with for that to even think of showing up on paper.
 
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