Case weight variation powder capacity and significants on the target

Many factors could come into the variation in case weight before an observable difference in case volume becomes obvious - as I mentioned earlier the average plant producing cases will have a lot more than one machine producing a type of case to get the volume they need to fill orders. Mil brass especially (going back to my Lake City milsurp experience).

It would not take much of a difference in punch and die set ups to create a minute difference in case head thickness, each machine would have a different roll of feedstock metal that is being made into the cases (slight difference in metal composition will give you a different density of metal), and the extractor groove cut and rim chamfer would all play a part in this. The main thing here is one grain of metal is a hell of a lot less than one grain of powder so you might be able to see a big difference in batch weight of cases without seeing a large difference in internal volume.

What that could do is give you cases which resize and age differently than others as the factors that can change if cases are coming off different machines include things like different annealing cycles so you are starting with different hardness and ductility in amongst your batch of cases giving you different neck tension and different obturation and springback amounts potentially.

We can't really control this though, and most people I think would not be using big enough sample sizes to get a handle on if there are weight groups in the batch of cases - about 500 of the LC milsurp cases showed 5 distinct groups where the case weight was within 2gr in the batch, but there were if I remember right something like 4 or 5 grains at least between batches. It was noticeable at any rate (all cases cleaned, trimmed and resized with the primer pocket uniformed/decrimped prior to weighing).

My main point is internal volume is only one thing that might affect case performance.

"What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?"

To clarify out to 200 yards.

I had a load using winchester brass that would shoot .4 of an inch at 100 meters, I have duplicated this load in about 4 different types of brass and they all shoot fine. I don't notice any difference.

Quote:

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Originally Posted by Oldbloke

"What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?"

To clarify out to 200 yards.

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If by "significantly", you mean "to a point where it would be meaningfully detrimental to hit probability for hunting purposes out to 200 metres"

The answer is that I'm highly confident that it absolutely would not matter in the slightest.

E: I might test this though as I've got a dozen different types of .223 brass, maybe I'll load a 10rd group with 1 type, then a 10rd group with 10 different types - and see what it looks like on paper.

E2: It may present a risk of exceeding maximum SAAMI (or CIP) pressures in some of the cases, in some circumstances. The real safety risk of this is highly variable.

The obvious advance to this line of thought, is to actually go and do some shooting and test it.

edit: As Gimp has suggested. The obvious comparison would be between commercial and military.

Quote:

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Originally Posted by Oldbloke

"What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?"

To clarify out to 200 yards.

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Greetings,
Yes some of us had abandoned the original question and headed down into the rabbit warren. To address your questions and from my experience with the .223 the difference is unlikely to be significant out to 200 yards. The difference between the 55 grain Hornady in my .223 fired at 110 metres at velocities of around 2,700 fps and 3,150 fps was only 30mm. Velocity differences due to case make would be significantly less than that.
Regards Grandpamac.

Quote:

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Originally Posted by gimp

If by "significantly", you mean "to a point where it would be meaningfully detrimental to hit probability for hunting purposes out to 200 metres"

The answer is that I'm highly confident that it absolutely would not matter in the slightest.

E: I might test this though as I've got a dozen different types of .223 brass, maybe I'll load a 10rd group with 1 type, then a 10rd group with 10 different types - and see what it looks like on paper.

E2: It may present a risk of exceeding maximum SAAMI (or CIP) pressures in some of the cases, in some circumstances. The real safety risk of this is highly variable.

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Yep. most of my experience with mixed brass has been little effect. But I had one memorable occasion where a mate changed brass brands without checking load and ended up with blown primers and a popped mag floor plate.
Though to be fair we were young and he might have been pushing pressures with his original load.
it did lead me to never mix brass too this day however.

So again using the milsurp brass example, there's over 20 grains of weight difference between the lightest batch of cases and heaviest batch of cases. Comparing to the sporting cases I have on hand, they all fall into a similar range there's maybe a few lighter than the lightest of the milsurp and a few in the middle but I was comparing a small sample size of one of each case on the digital scale.

Basically I haven't found anything that's a big jump of like 50gr difference anyway. Most of the cases for the dimensions that are easy to check are pretty much within cooey of each other. I don't have many other milsurp .308/7.62 NATO cases to really compare to, but I'm not seeing a massive variation in case weight or a massively obvious difference in case volume (given that not all of them a cleaned, trimmed to length so I'm not starting from a 'point' either).

Using the same powder charge in the milsurp cases, they group the same despite the batch weight variations - and any variation in speed between batches is lost in the noise (I can't pick it anyway).

I'm fairly confident to suggest that I don't think that you would see much of a variation in terms of POI changes from simply changing cases, there may be some brands out there in some calibers that have a noticeable weight difference compared to the .308 cases that I was playing with that have significant enough differences to cause issues though. I would not think that you'd want to be mixing cases for target shooting or somewhere where you need to be able to have maximum confidence in your setup, but for average hunting purposes with .308 I haven't seen anything significant in what I've checked that would cause a problem in terms of velocity variation.

I still don't think it's advisable in terms of brass life and quality control to be running mixed brass - just from what I observed with the two batched weights of milsurp brass (I keep these separate in 50-round plastic boxes - same load, same treatment just the cases aren't mixed).

Quote:

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Originally Posted by Oldbloke

"What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?"

To clarify out to 200 yards.

---

Thanks for adding the 200 yard limit to your original post @old bloke as you have already noted (and we all agree) it wont make any difference on the target. Wether you measure with biscuits or bullshit the pressure change is real though. Dont shoot the messenger, we are on a public forum where infornation dished out can be used by some that may not fully comprehend the results.

Yep, that is fair too. If you are running to the absolute limit for the safety of the components and rifle you are using, you'd be a brave operator to start swapping any components out without starting low and working back up to verify all is still OK.

I think another fair point, is that doing this exercise with something like a small .22 round would probably yield somewhat different results to a .338 barbeque-em-at-600 cannon.

Quote:

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Originally Posted by Oldbloke

"What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?"

To clarify out to 200 yards.

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Nope AS LONG as your load isn't hotrodding to begin with. It could also depends on rifle and more so on what you consider significant. I once fired 8?10? different .270 loads into same target at hundy yards...wasn't my best day of shooting and was flinching badly by day's end( before suppressors) but that multi shot,multi bullet weight group was able to be covered by a playing card.

Ummm, for further clarification.
Load is:
24.7 AR2208
55gr Sierra Superoo. 1365 game king.
It's very mild.

Sorry should have provided more info in the OP.

Quote:

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Originally Posted by grandpamac

Greetings,
Yes some of us had abandoned the original question and headed down into the rabbit warren. To address your questions and from my experience with the .223 the difference is unlikely to be significant out to 200 yards. The difference between the 55 grain Hornady in my .223 fired at 110 metres at velocities of around 2,700 fps and 3,150 fps was only 30mm. Velocity differences due to case make would be significantly less than that.
Regards Grandpamac.

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Thx. Good info.

Firstly throw those S&B cases as far away as you can. They are junk.*You would get better returns with annealing and improving neck geometry and tension for the best release. 2C.

One case (1000 rounds) of 223 I got had 4x different head stamped cases. Originally started sorting according to head stamp but the reality was they all shot to near enough same poi at 200 yards, good enough for goats, pigs, deer. Other cases of 1000 rounds have had two or three different head stamps, all close enough regarding poi to go hunting. I have a few kgs of 223 brass, about 9x different brands/head stamps. Like MD I’ve shot 10-15 rounds of mixed loads out to 300 yards at rifle range and got groups good enough for hunting with 223. Done similar at 600 yards, mixed cases and powder weights (1-1.5 grains), with 6.5 CM and ended up with groups that would have been a dead animal each shot. The only time I separate into separate lots, after checking water volume per head stamp batch, is when loading for specific long range loads or range competition. I think that sometimes we get too hung up on minor details instead of settling on a load, not hot-rodded, and getting out there shoot shit. Case weight means jack shit when it comes to comparing head stamps/ case volume. Just my observations.