Powder weight variance

[Shooterken]

I'm using 4350 and I'm dropping 42.5 grains of powder in a .260. I was told that a +/- .1 grain variance is acceptable. So would a charge of 42.4- 42.6 make that big of a variance in velocity and change the POI? Any help would be greatly appreciated.

 

[sib1948]

I'm new to reloading 260, but don't think it would make a big difference, but what do I know? If you weight your brass and batch it with primer, then weight your charged brass and sort it by final weight, then load your bullets. Go shoot the 42.5gr and those found to be over and under and just see what happens!

 

[poke5353]

I recommend looking into the OCW method for developing loads. There is a lot of info on it

http://optimalchargeweight.embarqspace.com

 

[punkwood2k]

I often wonder the same thing.. Some lots, I measure to the hundreth of a grain, going so far as to clip a stick of IMR4064 in half to get it JUST right.. Others, I go +/- 0.1 grain.. Honestly, I havent seen much difference in groups, or in my velocity SD.. I'm sure some of the really good shooters can see the difference, but not at my level..

 

[jdonovan]

not the same cartridge, but I have data from yesterday from my 308 over my chrony...


vel charge
2521 41
2566 42
2666 43
2694 44

Worst jump was 100 FPS for a 1gr change in charge weight.... so if it were linear, .1gr would be 10 FPS. Probably well inside the ES of most peoples loads. Smallest jump was 28 FPS... or 2.8 FPS per 0.1gr.

unless you are hand weighing on a tuned up magnetic dampened beam scale you'll be hard pressed to get better than 0.1 accuracy anyway.

There is an interesting article over at 6mmbr that evaluated scales, and accuracy.

short version:
volumetric charge +/- 0.4 gr
RCBS 5-10 +/- 0.15 gr
beam scale +/- 0.06 gr ( custom tuned)

 

[Greg Langelius *]

I use a progressive, and I check/adjust my charges for match ammo; MOA is MOA. No good reason not to for the smaller quantities involved.

I treat my ball-equivalent handloads the same as match ammo. Probably won't, but it might happen that a life or two could depend on that ammo being dead-nuts on-target.

Heck, as long as I'm doing it for the preceding two, I might as well do the same for my hunting ammo. Ummm..., and I don't plink.

See how this stuff shakes out? Maybe a +/- .1gr variance will do for some, but as long as it's as easy to do as I find it to be, I'll weigh it, thank ya very much. It's not like I'm loading hundreds of rounds in a run.

Greg

 

[Shooterken]

So it sounds like the best practice it to drop the proper weight but the big picture is there are so many different variables that 1/10th of a grain doesn't make a significant difference.

 

[jdonovan]

So it sounds like the best practice it to drop the proper weight

if by drop you mean use a volumetric powder measure. Then I'll disagree.

From what the testing I linked to above seems to indicate is that volumetric charges have a significant enough weight variance that it does make a difference. Perhaps not for hunting ammo on big game, but if your game is paper, then +/- 0.4 matters enough to care.

 

[Shooterken]

If 1/10th of a grain reduces velocity by 10fps, when I put these numbers in my ballistic calculator the difference over 1,000 yards in my scenario is only 2.87 inch variance. I wouldn't consider that significant compared to miss judging a 90 degree cross wind by 5 mph at 1000 yards which would be a 1 mill correction difference according to Ballistic AE calculator.

I think we are saying the same thing here, I don't punch paper from a bench, I shoot steel typically from a prone position, that's anywhere from 6 inches at 100 yards to 36 inches at 1,000. So I wouldn't consider a 2.87 inch variance at 1,000 significant.

if by drop you mean use a volumetric powder measure. Then I'll disagree.

From what the testing I linked to above seems to indicate is that volumetric charges have a significant enough weight variance that it does make a difference. Perhaps not for hunting ammo on big game, but if your game is paper, then +/- 0.4 matters enough to care.

 

[bruddah]

Good thread.

 

[Pinecone]

I always wonder about those who weigh charges to the hundredth of a grain.

So they also measure the internal case volume of EVERY piece of brass? And do they adjust the charge based on internal case volume?

 

[jdonovan]

I think I've seen some tests where case weight is a very good predictor of internal volume. Hence the custom to sort brass lots by weight and cull very heavy, or light cases.

 

[J-ROD]

I weigh to the hundredth, because I can control that, so I do. 3" of vertical in addition to what I add in shooting is a big deal when shooting ftr.
I have done bunches of case weighing, and measuring water capacity. I have not found any solid correlation. Brass of different weights, once fully prepped are much closer in weight. Most of the difference I see is in outer dimension of the web where the ejector groove is. I use a Sinclair hand priming tool and this shows up clearly when the collar is snugged down on the brass.

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[mdmp5]

Variation in powder charge vs velocity is not linear. It is not possible to predict the velocity gained or lost from small increments in powder drop.

 

[MJY65]

I weigh to the hundredth, because I can control that, so I do. 3" of vertical in addition to what I add in shooting is a big deal when shooting ftr. Sent from my XT1080 using Tapatalk

That is a point I've made before. Shooters tend to focus on what they can see. As far as 3" misses at 1000 yds go, maybe someone can help me out with the math. I'm a little rusty on trigonometry, but I think that equates to moving the muzzle of a 48" rifle .004". I'm not that steady, so I don't worry about hundredths of grains.

 

[Pinecone]

But unless you are controlling the case capacity to similar tolerances, does it actually help?

 

[J-ROD]

When tolerances are stacked, reducing one of them does help. My point was I have taken fired and unfired but fl sized cases, win for example, one weighing 157gn, the other weighed 153gn. Water capacity was identical. MV was as well, within 2fps anyways.
The weight difference came from the outer dims of the case head.
To each their own, you do it your way, I'll do it mine. If we are both confident in our ammo when behind the gun, that's all that matters

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[J-ROD]

Edit, better wording would be having one variable versus two...one would be better

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[Clark]

But many tests have
shown that test groups less than 1/4th MOA can easily be produced with
powder charges varying as much as 10 to 15 percent; a 4 to 6 grain spread
with the .308 Win. for example. - Bart Bobbitt 1994

https://groups.google.com/forum/#!t...art|sort:date|spell:true/rec.guns/x6YJ1u3aR4Y

Bart is the guy in the 1997 Precision Shooting magazine ad by Krieger that showed his 3.325" 20 shot group at 800 yards with a .308.

https://groups.google.com/forum/#!topic/rec.guns/iL7zv-cktJc

 

[Twoboxer]

I'm using 4350 and I'm dropping 42.5 grains of powder in a .260. I was told that a +/- .1 grain variance is acceptable. So would a charge of 42.4- 42.6 make that big of a variance in velocity and change the POI? Any help would be greatly appreciated.

Depends .

Your scale likely has a variation of =/-0.1gr. If your PM is also (only) +/-0.1gr, you're stacking variables and the possible delta gets larger.

While there may not be much variation in fps, if you happen to be using a load that is close to the edge of an OCW node (google "OCW Dan") for that firearm, those stacked variables may well result in different barrel harmonics. That can lead to stray shots, wider groups.

Those variations are part of the reason some of us have started using Optimal Charge Weight for load development.

 

[Shooterken]

These are some great posts, I have lots of research to do over the next few weeks... Thanks for the input and keep the thoughts coming!