Case Weight

452 Views
Last Post 2 weeks ago

CBA Board

Glenn R. Latham posted this 17 January 2025

Jeff in NZ started a thread about 3 weeks ago discussing case weight variation (see "case head stamps"). This got me to thinking about the batch of cases I've been using for my CB loads in the 270. I acquired the cases from a friend that worked public sight-in at his club. He saved a large box full of mostly 30-06 and 270 brass since he knew I shot them a lot. 99.9% of the cases were once-fired. When I got serious about shooting CBs in the 270 I went thru all the cases and separated them by head stamp. I had close to 250 R-P cases so chose them for my CB loads. I FL sized, trimmed, and annealed the necks and started working up loads, and shot the rifle at the 2024 CBA National Tournament.

Jeff's post encouraged me to go thru all those cases and weigh them. I thought they were pretty consistent, ranging from 193.8 grs. to 200.4 grs. I selected the 10 lightest and 10 heaviest cases. The light cases ranged from 193.8 to 194.1, and the heavy cases ran from 198.7 to 200.4 grs. I loaded them with a powder charge I have found to shoot well, 19 grain of Accurate LT-30. I always throw my powder charges, but weighed them for this test. Had to wipe the dust off the powder trickler - it's been years since I used it last.

Yesterday was forecast to be in the 50's so I headed out to the range. It was 40° when I got there but quickly warmed up to 50°.

The light cases chronographed 1653 f.p.s. with a standard deviation of 20 f.p.s. The heavy cases ran 1675 f.p.s. with an SD of 22. With only one SD between them, that's statistically insignificant. The groups weren't anything to get excited about:

I don't think I'm going to worry about segregating these cases.

Glenn

Attached Files

Liked by
and 3 others

16 Comments

Order By: Standard | Newest | Votes

Standard Member

OU812 posted this 17 January 2025

I think there is a noticeable difference. Especially at longer ranges. I would continue to segregate for best accuracy.

Attached Files

Liked by

CBA Member

RicinYakima posted this 17 January 2025

I agree with OU812. One 10 shot group isn't enough data points.

Attached Files

Liked by

CBA Board

Paul Pollard posted this 17 January 2025

How do you like the shooting bench? Do you lose brass off the edge? Eliminates the right hand - left hand bench assignments.

Attached Files

CBA Board

Glenn R. Latham posted this 18 January 2025

Paul,

Some don't like this "U" style. I've had problems with the "T" style that was more like a "V". You see I like to set up at the back of the bench, and with the "V" style it's sometimes not wide enough yet where the front rest goes.

Glenn

Attached Files

Liked by

Online CBA Member

Premod70 posted this 18 January 2025

Definitely like the round PVC uprights, more space than with blocks and a lot less abrasive to the knees.

Forrest Gump is my smarter brother.

Attached Files

Liked by

CBA Board

mhice posted this 18 January 2025

I noticed a difference in weight sorting cases even from the same lot in jacketed bullets. It's a stage in the first-round brass prep for brass that is going to stay with the rifle, does not matter if its range pick up or new Lapua/Peterson/Alpha. After that, I only weight if there is a reason too like a flier on a good wind call. Thou, I stay away from R-P brass in general as I have experienced less than desirable ROI.

Michael

-Michael

Attached Files

CBA Member

Ed Harris posted this 18 January 2025

Cartridge brass has an average density of about 8.5 grams per cc. Common flake and extruded smokeless powders average about 0.85 grams per cc. So if you compare the weight of sized, trimmed, prepped and uniformed cases, adjust the powder charge by 0.1 grain to compensate for each full grain difference in the case weight.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

Attached Files

Liked by

CBA Board

John Alexander posted this 5 weeks ago

In my study of case volumes (TFS 276) I found a very poor correlation between case weight and the actual volume of the case. This implied that a lot of the variation in case weight is in the base where it has nothing to do with volume.

In a bunch of cases with gross variation in weight (as in Jeff Brown's post in "Case Head Stamps" where cases varied 8 grains (16%), or with range pick ups of mixed origin) weighing to sort makes sense as shown by Jeff's results.

However, with cases of a single, recently manufactured lot, where the actual volumes seldom vary much more than about 1%, weighing in hope of getting more uniform volumes is useless. The good news is that strings of shots where one string had 1% more actual measured volume produced identical velocities so even sorting cases by volume instead of weight won't improve your groups anyway.

The contentions above that case weight correlates weakly with case volume and that recently manufactured cases vary only about 1% within a lot, is based on measuring the weights and volumes of cases from 12 different lots with 9 different headstamps and in 7 different calibers from 223 to 338.

John

Attached Files

Liked by

CBA Member

pat i posted this 5 weeks ago

I don't think I shoot well enough or have production guns accurate enough with cast bullets capable of showing me that 5 or so grains difference in case weight would make a difference on the target. But that's just me maybe other people experiences are different.

Attached Files

Liked by

CBA Board

Glenn R. Latham posted this 5 weeks ago

Mike,

I wasn't too impressed with R-P brass in 30-06. I used Federal until they wore out, then Winchester. I have a fair number of Winchester 270 cases from the public sight-in, so I'll have to check them out. After it warms up. Sub-zero and 5" of snow right now.

Glenn

Attached Files

Liked by

CBA Board

Glenn R. Latham posted this 2 weeks ago

Well it did warm up this week. When I got to the range it was only 30° but was up to 40° by the time I was set up. Wind was practically nothing, 0 to 3.5 mph. This was a pleasant surprise as the prediction was 15 to 25 mph! I almost didn't go, but remembered a friend told me the wind picked up just as I got there a few months ago so I got out there earlier than usual. It paid off, as the wind picked up as I was packing up.

Today I compared the RP light and heavy cases as well as Winchester light and heavy cases. Thanks Mike for the suggestion of the Win. cases, they looked a lot better than the RP. I also moved the targets out to 200 yards, figuring the greater distance would show differences better.

I didn't mention before that I segregate my match cases by measuring the case wall run-out about 9/16" ahead of the case head. Generally I keep cases that run-out no more than .005", and mark the thick side, putting it at 12:00 in the chamber. Bullets are also indexed to this mark. No John, I haven't tested to see if it really makes a difference, like I haven't tested inside deburring of flash holes. Indexing the case only takes a few seconds and I've been doing it for so long it's second nature.

The previous test was done with weighed powder charges. The standard deviations weren't any better than my thrown charges so I dispensed with the weighing. I also used a heavier charge that has shot well, 23 grains of LT-30, and is the one I used at the CBA NT.

RP light cases 1937 fps 20 SD

RP heavy cases 1962 16

Win light cases 1966 26

Win heavy cases 1975 29

The Winchester cases were actually a little lighter than the RP, which I have found before, although the velocities were higher. Could have been because I shot them second, and it was slowly warming up. Could have been because they weren't annealed, as the RP were. Who knows.

The real surprise was on the targets:

RP light

RP heavy

Win light

Win heavy

The breeze started picking up on that last target. The wide right shots were the last ones.

Still not much if any of difference in POI. But I'm definitely going to have to dig up more of those Winchester cases!

Glenn

Attached Files

Liked by

CBA Member

RicinYakima posted this 2 weeks ago

Keeping all this for an article, I hope.

Attached Files

Liked by

Standard Member

mm93 posted this 2 weeks ago

I spend my time weighing and sorting bullets instead of worrying about brass. weighing. I find my bullet sorting makes more difference than brass. I do keep brass sorted by headstamps though.

Attached Files

Liked by

CBA Board

John Alexander posted this 2 weeks ago

Ah!. A post with real shooting results -- excellent.

John

Attached Files

Standard Member

shootcast posted this 2 weeks ago

When I shot the 308 with cast I experimented with reduced volume cases. I read about it and decided to give it try. Simply expanding the 308 case mouth enough to drop a 223 case down and then full length resizing. The 223 cases were shortened some so the shoulder area of one touched in the other. I also drilled the primer pockets out on the 223. This greatly reduced case capacity but I didn’t see any noticeable benefit in accuracy or SD. If a particular load gives consistent SD regardless case capacity it must not be a big deal for cast Bullet shooting.