How Much Does 1 Gr. Difference In Bullet Weight Make?


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parker51
February 9, 2010, 04:31 PM
I just weighed several Privi 168 gr (supposedly) bullets and found they weighed anywhere from 167.8 up to 168.8 grs. I have only found 2 out of the 20 that I have weighed so far that weighted exactly 168 grs. I don't shoot competition (other than with myself) so an inch high or low at 100 yards doesn't bother me that much but I do wonder now if bullet weight may have something to do with those occasional fliers. How much difference would 1 gr in bullet weight would make at 100 yds? Do you think it would be worthwhile to separate these bullets by weight? Seems kind of silly to make sure powder weights are exact only to find out that there is this much variance in the weight of the projectile. I guess I always assumed that what they advertised on the boxes is what these bullets actually weighed.

The load is for a Swiss K-31 (7.5 x 55) and I am using Privi 168 gr. bullets with 45 grs. of Varget powder. Thanks!

Chuck

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rcmodel
February 9, 2010, 04:38 PM
None.
Bullet balance, and/or base deformity (not square with the bullet shank) will make a huge differance in groups compared to a slight weight variance.
Bullet tip deformity or slight weight variance is not a deal breaker.

For that matter, +/- 0.1 grain variance in powder won't either.

rc

interlock
February 9, 2010, 04:43 PM
i saw a study where tips of bullets were snipped off with pliers. this was not done too precisely and bullets varied by quite an amount. it was amazing how much varience in bullet point and wieght made next to no difference in accuracy, however base deformity was suprising how little made a big difference.

moxie
February 9, 2010, 05:01 PM
Welcome to what I call the bullet bell curve. If you weigh every one of the bullets, and graph the weights, you'll see a distribution that follows a bell curve with the majority clustering fairly closely around the stated weight and a small number with the max weight variance isolated to the "tails" of the curve. You could, for the sake of perfection, throw out those that deviate the most from the stated weight, but, as stated above, it usually doesn't make much difference. You can even, if you are into self-inflicted pain, run a linear regression and figure the standard deviation, then make a judgment call on acceptability.

Canuck-IL
February 9, 2010, 05:11 PM
You certainly don't need a regression to calculate the std dev.

A lot of HP shooters sort by weight for 600 yds and beyond ... probably into cells of 2 grains or so. I don't hold well enough to begin to think that a few grains here'n'there account for my misses.

As RC noted, same thing for powder - with the preferred powders my drop keeps it to +/- .1 ... plenty good enough to not bother with trickling.
/Bryan

ReloaderFred
February 9, 2010, 05:15 PM
If you want a real eye opener, try weighing the M-72 .30-06 Match bullets the military used for years for all the big matches. I've had them weigh fromm 171 grains to 177 grains. The specs call for a 175.5 grain bullet +/- 3 grains.

Even with that big a spread, they still shoot pretty good, but not as good as the commercial bullets, but still better than ball ammunition.

Hope this helps.

Fred

parker51
February 9, 2010, 09:17 PM
Very interesting! Thanks for your help!

Chuck

GP100man
February 9, 2010, 10:53 PM
if the bullet weighs 10gr thats 10% of the total weight , if the bullet weighs 100grs. thats 1% .
So with your 167 gr. bullet your down in the .5-.6 % range & for a production bullet thats darn close!!!

with my cast I set the limit at 3% .

Smokey Joe
February 10, 2010, 11:57 AM
Parker 51--FWIW, I note that in all the reloading manuals I have, for .308 bullets in .30-'06, .308Win, and .300WSM, the given powder load for 165 grain hunting bullets, and 168 grain target bullets, is exactly the same.

So apparently for internal pressure differences, and external ballistics, THREE grains of bullet weight doesn't signify, at least in 3 common cartridges, with .308 bullets in 165/168 grain weight.

Therefore I wouldn't worry about your variation of ONE grain of bullet weight in a rather similar cartridge. Especially at a short range like 100 yd. Now, if you were competing @, say, 1000 yd, or you were a SERIOUS benchrest shooter and you had ALL other factors in yr load, and rifle, measured down to a fare-thee-well, you could get all anal about the bullet weight variance. But in either of those cases you'd be shooting a much more specialized, high-falutin' rifle than a K-31.

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