Case weight variations and accuracy


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Durby
March 1, 2010, 01:18 AM
How much does case weight variation actually affect accuracy? I've been searching, but haven't seen any real examples.
I'm loading for a 338 Win Mag, using 250 grain Sierra Matchkings for target shooting. The gun is a Rem 700 with a Shilen barrel.
I weighed 100 sized and trimmed cases, Remingtons, all from the same lot, and came up with 5 grains variation. Most fall within 2 or 3 grains of each other, but there is no number that is found way more often than another.
Any advice or experience with case weight variations is greatly appreciated

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ReloaderFred
March 1, 2010, 02:06 AM
I personally don't pay any attention to case weights, since there's really no way to tell where the extra weight is. First of all, are they all trimmed to the same exact length? Are the primer pockets uniformed? Are the flash holes uniformed? These all have a bearing on both the weight and accuracy potential.

The reason I don't pay any attention to total weight is it's hard to tell if the small amount of weight is in the case walls, base, rim, etc. I just uniform the brass and make sure the bullets and powder charges are uniform.

Some will disagree, but that's what I've found to work for me.

Hope this helps.

Fred

USSR
March 1, 2010, 08:09 AM
For 1,000 yard shooting, I segregate cases by weight; other than that, like Fred said, just do the standard match prepping of the cases.

Don

Walkalong
March 1, 2010, 08:52 AM
Double tap.

Walkalong
March 1, 2010, 08:54 AM
Yep. For all but the most demanding work, I don't worry about it. Never hurts to sort rifle brass by weight, just don't expect groups to miraculously shrink in half.

I have never worked with cases of that size, but 2 or 3 Grs sounds fine.

Maybe someone like slamfire1 will come along and enlighten us.

243winxb
March 1, 2010, 10:28 AM
A chamber has a volume. This volume runs from the bolt face to where the bullet seals the bore. Any time a different weight is put in the volume, pressure changes. I did a simple 1 time test using 100 win new brass , 243 win caliber in my Rem 40x. Brass seperated by 1/10 gr. I took 5 heavest, and 5 lightest. Shot groups with each. Then took 3 heavy & 2 light shot group. Then took 3 light & 2 heavy shot group. You could see the difference. It pays to weigh brass for an accurate rifle IMO.

Durby
March 2, 2010, 02:03 AM
Question for those who don't weigh brass: If you don't weigh it, what kind of accuracy do you expect? This is a blueprinted 700 with a Shilen barrel, bedded in a High Tech Specialties stock, with a Leupold 4.5-14 Mark 4 scope, and I am hoping to shoot 600 yards with MOA accuracy. If you don't weigh your brass, how accurate of a load have you created?
The very first load I tried in this rifle was with cheap Hornaday 225gr hunting bullets and it shot around an inch with no experimenting, so I think this rifle will be capable of good accuracy.
To 243winxb, I'm intrigued by your test, but can't afford to try it on my own right now. How much difference was the lightest to heaviest? Did the group get bigger by .25 inches, by .5? (at 100 yards)
thanks

1858
March 2, 2010, 03:31 AM
Durby,
I tried sorting .300 Win Mag cases by weight and didn't see a significant difference. I was using Winchester W-W Super cases and after weighing all 100, the range from lightest to heaviest was 4.2gr. I picked five cases including the lightest and the heaviest and then three more all about 1.0gr apart (see actual weights in figure below). All five were loaded the same way so that the only difference was the case weight. Here's the group. With shots 1, 3 and 5 in one group and 2 and 4 in the other group, you could argue that there's an harmonic there but it's a stretch with such a small sample.

http://128.171.62.162/hawthorn-engineering/thr/rem700_300wm/range_targets/case_wt_comparison.jpg

I don't sort any other rifle cases by weight since 100 Norma .300 Win Mag cases only vary by 2.4gr. 100 Norma .300 WSM cases only vary by 2.4gr and 400 Lapua .308 cases only vary by 1.8gr. The Winchester W-W Super cases have by far the greatest weight range and the results above could just as well be from my error rather than any differences in case weight.

Bear in mind that when Ken Brucklacher set his 1000 yard benchrest world record last year, he didn't do anything to the new Norma brass, let alone sort it by weight.

http://accurateshooter.wordpress.com/2009/05/05/ken-brucklacher-sets-1000-yard-score-record-100-8x/

:)

243winxb
March 2, 2010, 10:58 AM
To 243winxb, I'm intrigued by your test, but can't afford to try it on my own right now. How much difference was the lightest to heaviest? Did the group get bigger by .25 inches, by .5? (at 100 yards)
thanks My log shows the test was done in 1998. Targets had group data, but trashed them last year. Did find the brass weight, Winchester high 170.9 gr-166.5gr low. Currently using some Remington high 166.6gr- 161.0gr low. Any variable you can control is worth doing if you want to shoot smaller groups. High power scopes help, along with Redding FLRS Type S Bushing Dies.

helg
March 2, 2010, 11:11 AM
Better sort the cases by water capacity in grains H2O.

Variations, say, in extractor groove thickness do not change shot dynamics, but do contribute to variation in shell weight. The inner size of brass, its volume, for the shells, which are trimmed to the same length, is the best factor of the shot that depends on the brass.

ranger335v
March 2, 2010, 04:05 PM
"How much does case weight variation actually affect accuracy? I've been searching, but haven't seen any real examples."

You won't find any such examples except in limited personal runs. Certainly it "affects" accuracy but, as a percentage of group size, both the rilfle and shooter will have to be better than most to ever see the differences.

1858
March 2, 2010, 08:25 PM
Better sort the cases by water capacity in grains H2O.

I have a Redding Case Neck Gauge (http://www.redding-reloading.com/index.php?option=com_content&view=article&id=46%3Acase-neck-gauge) which I've used to sort cases based on the uniformity of case wall thickness inferred by irregularities in case neck thickness. My big test for some .300 Win Mag cases went to hell in a handbasket at the 600 yard line for reasons completely unrelated to the ammunition. I'd like to try that test again someday. :(

:)

Durby
March 3, 2010, 01:07 AM
Well thank you all for the replies. Someday I will have to splurge and buy some more components to work with. These bigger cartridges aren't cheap. Maybe I will just have to build another gun that is cheaper to shoot!

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