How much does case weight matter? (243)

[berettaprofessor]

Boys, I took a deep step off the edge today and need your experience. As a new-to-243 loader, I tried my first 10 reloads this weekend, two different OAL's, and got just under an inch at 50 yards on the second (longer OAL) 5 shot group. That's prone off a front sandbag with the butt on my shoulder. I'm hoping to do better. I had crimped those rounds before you taught me otherwise, so that could be part of the pattern problem.

So, tonight, I loaded another 10, very carefully. 34.0 grains of 414, no variation (and no crimp). Then, as I was finishing up, I weighed the finished cartridges for yucks and was shocked to find a 5 grain variation in weight....once-fired brass, all RP stamped. I checked the bullets (Hornady 100 BTSP) and found they only varied ±0.2 grains, so that wasn't it. Then, I checked a set of tumbled but empty cases and found a wide variation of 10 grains in both RP and WIN stamped cases.

So, my question, do I need to start weighing cases before loading them and sorting them by weight to get the best groups? Will it really matter? Part of me says the case remains behind so it doesn't matter, only powder and bullet variation count. But the other part of me knows that the extra (or missing) brass has to be in the case wall thickness, and that means chamber volume differences, and that means pressure differences, right? Does it matter?

I partially blame all you guys for this new quest for perfection......

 

[1911 guy]

Your second thought was correct. Extra weight means more brass in the case. If the external dimensions are the same, the extra is in case walls thickness. And yes, this does change pressure. This is why the rule of thumb is to work up loads in NATO cases beginning at less than published minimum loads.

 

[rcmodel]

Who knows?
But 5.0 grain case variation in the same brand of sized & trimmed cases is way too much.

You sure your scales aren't fibbing to you sometimes?


I built a 22-250 98 Mauser with a medium weight Douglas barrel in 1968 that would shoot one-hole, 10-shot groups like this all day long, prone off a rolled up coat.



And that was before I even heard of.
* weighing cases.
* using match primers.
* uniforming primer pockets.
* trimming brass.
* reaming flash holes.
* neck reaming or neck turning.
* trying 15 kinds of powder, and 6 brands of primers.
* or seating to the lands using a $150 tool to find the length?

What do you suppose it would have done had I known all that stuff they say on the inter-web you have to do now, back then?

rc

 

[gamestalker]

I'm pretty anal about brass weights, so I sort my brass and work the loads up accordingly.

If your load is being run in a bunch of brass that swings by 10 grs. your going to very likely see some pressure variations across the chrony, on visual inspection, and bolt lift may be stiff if the loads are at the upper end of the table. As for accuracy, any element of the process that effects pressures, is surely going to show up on the target.

I've experienced significant pressure variations in the past, completely caused by weight variations of the brass.

GS

 

[243winxb]

http://www.thehighroad.org/archive/index.php/t-621125.html Sort by weight to get rid of flyers.

 

[berettaprofessor]

RC, I'm pretty sure the scale is accurate. Digital Lyman and it gives me repeated readings accurate to 0.1. But I'll check it against a beam scale too.

Mostly, I'll chalk it up to having to buy 2nd hand brass of unknown parentage when I started reloading 243. Due to the brass shortage, I've searched gun shops from here to Kansas City and a single $17 bag of 67 mixed cases (RP, Winchester, and 3 cases of 22-250's!) was all I could snag to start reloading. Even now, I can't find any new Winchester or Federal brass available online, so my choices would be Priv at 50 cents/case, Hornady at 80 cents, and Lapua at almost $1. I don't trust the Privi and the other seems a bit high.

 

[spitballer]

Case weight is an indicator of volume (internal dimensions), and ideally cases should be sorted before charging. Probably even more important for smaller cases.

 

[Andrew Leigh]

I doubt if you had 5gr on a batch of the same head stamp of .243, not 0.5gr?

I sort by case weight and use RP cases, culling cases to 1std deviation generally results in the loss of 15 from a batch of 50 which is rather aggressive and probably over the top. Weight and case volume do differ slightly but for all intents and purposes it does not matter. Volume is the measure that is more accurate.

Now before you get too bent out of shape about weight you must know that the specific gravity of brass is 8.5X that of water which means that when reducing brass weight to correspond to the H2O volume of the case that a 5gr. variation in case mass is 0.58gr of water volume. The average case volume of a .243 is 54gr. H2O so .58/54 = 1% volume change.

Now to put that into a loaded round. Your load, and I assume SAAMI spec's and a 24" barrel should have produced 2 446fps. The 5gr. variation in case weight would have altered the speed by +- 8fps depending on which way it goes. I doubt you will see a difference in vertical displacement +-8fps swing at 100yds.

On the side I would personally NEVER mix head stamps or batches of the same head stamp. Use your odd head stamp cases for fouling rounds and plinking. Your load is mild, as it should be for a new loader but you should be aiming for a powder / load combination that fills at least 85% of the case volume. Currently you are at 70%. Confirm that 414 is the Hodgsons brand? I am not familiar with your powders.

Hope this makes sense.

 

[ironworkerwill]

Mr Leigh, I agree.

OP: Are you using mixed brass, or are they all the same brand, lot, ect?

 

[gamestalker]

I just sorted about #160 resized and trimmed - 300 Win Mag a couple weeks ago, I still have those log notes. And considering it's 300 WM, which would have the potential to have greater weight spreads, the largest spread I came across within the same head stamp was 3.6 grs., most were within about .5 grs..

The combined spread of all head stamps, Hornady, Win, RP, and Federal was quite extreme though, 16.9 grs..

That is also why I don't use mixed head stamps for bottle neck load development, ever. I perform a separate load development for each head stamp. And not just because of the weight issue, though that is a significant concern, but also because different brass has different metallurgic properties, which creates variations during combustion, and throughout the pressure curve.

GS

 

[murf]

have you checked the sized case length? i'd make sure they are in spec.

if those used cases have been trimmed prior to you getting them, they will have different weights (cases never stretch the same).

what primer are you using? i believe h414 likes a mag primer.

you may want to switch powders. different guns like different powders (and different coals).

luck,

murf

 

[berettaprofessor]

OP: Are you using mixed brass, or are they all the same brand, lot, ect?

Oh yeah, that original case group was definitely mixed brass; Winchester and RP, and I have no idea if they belonged to the same lot and I'm just taking the seller's word that it was "once-fired"....well, that and the fact that the spent primers looked original. But the seller also had three cases of 22-250 mixed in with that 243 brass.

Murf, the sized case length was ok and yes I checked. And I am using a large rifle primer, not magnum. I may switch powder later, but for right now, HP414 was the only thing available to me that I could find a printed "recipe" for.

Andrew: I am using Hodgson 414. And I know I'm loading really light; I see no need to burn out the barrel to gain speed until I start shooting farther than I'm doing now.

I'm springing for some new Hornady brass soon. I've learned a lot here. Thanks everyone.

 

[steve4102]

Case weight is an indicator of volume (internal dimensions),

If we are talking same headstamp and same lot #, yes. If we are talking different headstamp and/or different lot #, no.

 

[pseudonymity]

Mostly, I'll chalk it up to having to buy 2nd hand brass of unknown parentage when I started reloading 243. Due to the brass shortage, I've searched gun shops from here to Kansas City and a single $17 bag of 67 mixed cases (RP, Winchester, and 3 cases of 22-250's!) was all I could snag to start reloading. Even now, I can't find any new Winchester or Federal brass available online, so my choices would be Priv at 50 cents/case, Hornady at 80 cents, and Lapua at almost $1. I don't trust the Privi and the other seems a bit high.

I load mixed brass in 308, not 243 but I suspect that the brass from manufacturers may just be necked up and down since they are otherwise the same. 308 loads can really vary widely in pressure with some brass, although I have had good luck with RP, Win, Hornady Match and PPU brass. Mild loads for each of those are more or less interchangeable in terms of pressure signs. If Federal brass in 243 is anything like 308, I would advise staying away. Not only is the case volume less than most others, the brass alloy seems to be softer as well. Loads that barely flatten a primer in Win brass will leave an ejector imprint on the head in Federal brass.

You may want to consider the Lapua brass, even for the price. It has an excellent reputation for both consistency and durability.

 

[gamestalker]

Pseudonymity, now that's just seems odd to me, regarding ejector button transfer marks on Federal case heads. I get that with RP brass at the lower end of the table, but if any brass resists imprinting of the extractor button, it has been Federal, which I've always found to be very hard and brittle, compared to RP and Win..

GS

 

[ironworkerwill]

Quote:
Case weight is an indicator of volume (internal dimensions),

If we are talking same headstamp and same lot #, yes. If we are talking different headstamp and/or different lot #, no.

Exactly. Weight dictates volume among the same brand and lot. It will likely be irrelevant among mixed brass. The specific gravity of brass can fluctuate among brass manufacturers.


I suppose everyone has a preferred brand. I would choose the PPU over the Win brass any day.

 

[spitballer]

If we are talking same headstamp and same lot #, yes. If we are talking different headstamp and/or different lot #, no.

Gee I hadn't thought of that. I've got a bunch oif Hornady brass laying around with same headstamp but no lot number. Won't help to sort these by weight? Even after neck turning?

 

[ironworkerwill]

Won't help to sort these by weight? Even after neck turning?

Thats not a huge deal. You may not see much difference if you where to spot check them by weight and volume. Or just get really OCD and check them all.

 

[Andrew Leigh]

I need to say this, and it is advice that I have unwillingly had to take myself.

The greatest improvement in accuracy come from practice and not from reloading technique. When you can REALLY shoot great reloading technique comes into play, and then only at extended ranges..

 

[mkl]

If you can get your hands on a can of either IMR4831 or H4831, you may want to give it a try. My Win. Model 70 in .243 seems to like that powder better than any of the other eight I tried.

Fill the case up to the point that the base of the bullet is just touching the top of the powder charge (no compression). That will be somewhere around 47 grains for your 100 grain bullet (I use 47.5 for a 75 grain Sierra HP).

In my gun that loading will shoot one-inch groups at 100 yards off a bench.

If you need to shrink your groups below one-inch, then you can start worrying about case weight differences, and it will make a difference for sub-one-inch groups. Just stay with the same brand of cases while you are trying different loads; after you hit one-inch, then start worrying about case weight.

4831 is not the "go to" powder in most reloading books, but if your gun's barrel harmonics insist on 100 percent loading density, it may work for you as well as it did for me.

 

[gamestalker]

My primary concern is based on pressure spikes. I run my loads at full throttle, not hot or excessive, just full velocity. So when dealing with brass that varies significantly in weight, and, or mixed head stamps, uncomfortably high pressure spikes are a certain risk without eliminating these variables. If I were loading down at the bottom of the table, I probably wouldn't give it much thought.

I like IMR-4350, IMR-4831, and H4831. Those 3 powders have all produced excellent accuracy, and good typical .243 win velocities for me with the bullet weights I hunt with. 90 gr. - 105 gr. bullets drop deer very well for me at 3000+ fps..

GS