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case weighing

 
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  #1  
Old 07-03-2005, 01:08 AM
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Join Date: Mar 2005
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case weighing

Hello, I'm currently weighing my 22-250 cases to within .3 grains...ex. 160.0 to 160.2, then 160.3 to 160.6 etc. I currently have enough brass to load 50 to 60 to use in coyote class benchrest...my question is, am I being picky enough or should I buy even more brass in order to narrow this .3 spread? Thanks...
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  #2  
Old 07-03-2005, 07:15 AM
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Re: case weighing

Nelsonic,

I am not a BR shooter but I am a long range varmint, predator and big game shooter and an accruacy minded gunsmith.

I personally feel case weight is an important issue with accuracy but for anything short of a full bench rifle designed for competition, it is not quite as critical as some other aspects of a handloaded round, namely, neck and bullet run outs and neck thickness uniformity.

That said, the smaller a case is in volume the more critical case weight can be to getting consistant velocities.

A 2 gr difference in case weight in a case the size of a RUM is really not extremely detrimental to consistancy, this same variation in a 223 Rem and you can go from comfortable top loads to loosening the primer pocket in pressures.

When I am sorting brass for extreme accuracy, I generally set my range specs for .5 grains of variation for every 40 gr case capacity.

For example, for a 223 Rem class round(17 Rem, 204, 222, 223, etc...) I will set a weight range limit of roughly .3 gr variation and sort brass into these ranges.

For the 22-250 class which I include in the 220, and 243 as well, I will look to hold a .5 gr range.

For the standard magnum rounds, 7mm Rem Mag, 300 Win Mag, 338 Win Mag, etc... I will use 1 grain for a standard varaiton.

And finally the RUM class cases and larger I try to keep them at 1.5 gr variation.

Now if I am loading for extreme accuracy or for extreme range shooting I will look to get these big cases grouped into 1 grain lots or less but for everything else it is not this critical.

Again, I would say the single most critical dimension to accuracy loads in neck and bullet run outs and keeping them as low as possible. True BR quality is 0.001" of run out or less.

Good Shooting!!

Kirby Allen(50)
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  #3  
Old 07-03-2005, 07:24 AM
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Join Date: Oct 2004
Location: Northamptonshire England
Posts: 676
Re: case weighing

Hi Nelsonic,
Im not familiar with "Coyote Class" or the course of fire involved but when i shoot HV benchrest i would grade my 220 Russian cases to 1/10th of a grain, putting them in a column according to their weight. Eventually a pattern of cases at the same weight will appear and i ended up with 66 cases of the same weight out of a lot of 300 tested.
These became my match cases which i fireformed and loaded for competion.
This is a very simple operation and especially quick with a good set of digital scales but of course the quality of your brass has a lot to do with the consistancy, you did not mention which make of brass you are using.
With this amount of match cases i have been able to shoot a number of competitions with out having to re-load between relays.

Ian.

"I mean't to shoot the pike but the duck got in the way"
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  #4  
Old 07-03-2005, 09:31 AM
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Join Date: Jan 2004
Location: Blackfoot, Idaho
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Re: case weighing

Howdy Nelsonic,

Just wanted to add a little personal experience that surpised me quite a bit.

Been a BR shooter where my anal habits helped quite a bit when shooting the 222. And let me say that I'm addicted to accuracy. Small consistent groups are a "rush"...

Shooting a 375 H&H in Ruger #1. It shoots well for what it is. Generally around 2" @ 200 yds. But plenty of times there are fliers. Experiment.

Group 1 - 3 cases @ 251 grains, 77.5 gr W-760, Speer 270 gr spbt.

Group 2 - 3 cases @ 255 grains (the only difference between the loads)

Velocity was about 30 fps SDs were <12 in for both groups.

However the groups were not within two inches of each other.

Who woulda thunk it with a case that big - and only 4 grains variation??
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  #5  
Old 07-03-2005, 10:37 AM
LB LB is offline
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Join Date: Jul 2004
Location: Upland, CA
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Re: case weighing

I'd work with what you have. Buying more cases is meaningless, unless by some miracle, you got the same lot number.

Assuming that you have a marked board laid out, and you can view the results of your bell curve.... as the cases are arranged, select whatever group you want; heavy, light, or right in the middle of the range.

I divide my brass into three groups, after discarding the 5% HIGH AND LOW. So, if I start with 200, there will be 20 discards. From that point on, I divide the groups as best I can, using no specific formula. It might be 50- and 50+ and 80 in the center of the range? Or it may be more equal.

I have not determined that any of the three groups are the more accurate, and consider them all to be useful, as long as they are kept separated.

Okay, that's my method, as far as it goes, as to weighing cases. I do other things in my selection and culling process, but even the discards can be useful for some purposes.

So, my question would be, are you sizing your brass before weighing. Are you removing the flash from the flash hole and uniforming the primer pockets before, or after weighing?

Are you weighing before triming and chamfering the necks, or just weighing raw cases? Whatever you do, develop a system that makes sense to you, and stick to it.

Good luck, LB
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  #6  
Old 07-04-2005, 12:07 AM
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Join Date: Mar 2005
Posts: 13
Re: case weighing

thank you for your comments! Yes, I chamfer the mouth inside and out...I also deburr the primer hole, all at the same depth...these are the only things I do to a raw case before weighing...I started w/ 500 cases of all the same lot number and unfortunatly I only ended up w/ approx. 50-60 max within .3 grains of each other...of course in seperate groupings...the coyote class is for varment rifles etc. not strict br rifles...so us new to br can get into the sport...sometimes I actually get some groups that give the 6br a run for the money! It feels good when I do...my rifle is a Kimber longmaster VT in 22-250...w/ a Burris scope 8x32...I have yet to check runout because I dont have the equip. but I think I soon will as suggested by these posts and other articles...Thanks again
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