variation in powder charge ?

[rebs]

when reloading 223 with 77 gr SMK's and 69 gr SMK's with reloader 15 powder how much variation is acceptable in the powder charge ?

 

[Ned Ludd]

It's not too difficult to make a crude estimate. How much average velocity variance do you get between 0.1 gr charge weight increments? Divide the velocity variance you're willing to accept by this number, halve the resulting value, and you will have a corresponding +/- charge weight spread in tenths of a grain. For example, if you see an average increase of 8 fps per 0.1 gr charge weight and you're willing to accept 48 fps extreme spread, that means you need to weigh powder to a minimum of +/- 0.3 gr. That's a little higher than I wuld consider optimal, but it could work, depending on your needs/expectations. In my hands with 80-90gr .223 bolt gun loads, it is difficult consistently to get much below ES values (5-shots) of 15-20 fps with my best handloads. Commercial .223 ammunition often will have ES values of 50-60 fps, sometimes a little better, sometimes a little higher. Generally, you're better off with the small capacity .223 case to weigh powder as precisely as you possibly can. If you can consistently keep your charge weights at +/- 0.1 gr or better, you will never have to worry much about charge weight variance affecting your velocity numbers.

 

[K22]

Standard rule of "thumb" is + or - .01 grain probably because most balances specify this as their accuracy tolerance but the type of cartridge, powder, primer, bullet and seating depth also affect ballistics. Obviously the smaller the cartridge the more sensitive it will be to these variations.

 

[1066]

Standard rule of "thumb" is + or - .01 grain probably because most balances specify this as their accuracy tolerance but the type of cartridge, powder, primer, bullet and seating depth also affect ballistics. Obviously the smaller the cartridge the more sensitive it will be to these variations.

Should that be +/- .1 grain?

 

[onelastshot]

With today's equipment such as the charge master and new digital scales I don't see any reason for a deviation of even a tenth of a grain. The systems are so exacting there's no need to accept deviations of a tenth of a grain.

 

[Milo 2.0]

With today's equipment such as the charge master and new digital scales I don't see any reason for a deviation of even a tenth of a grain. The systems are so exacting there's no need to accept deviations of a tenth of a grain.

That is not exactly true concerning the chargemaster, it is .1gr + or -
The one thing a CM cannot(not the right word) do is show a slight undercharge, and though it is not that prevalent, it still happens, esp when a clump of powder comes out at once.
I spent close to 5 hrs comparing various powder charges coming from a CM and verifying on a FX 120i, and it used all of it's .2gr variance. Given the fact that overcharges can be remedied, it is as easy as pulling some kernels.
That said, 85% of charges coming from my 3 CM's were spot on, if the fx 120i was doing it's job.

 

[chop house]

it depends in part on how wide your rifles accuracy nodes are, does it not? fwiw i don't shoot semi's.

 

[K22]

Should that be +/- .1 grain?

Yes, sorry about that.

 

[Laurie]

That said, 85% of charges coming from my 3 CM's were spot on, if the fx 120i was doing it's job.

My experience exactly. My Chargemaster will sometimes produce strings of spot-on charges as check-weighed on a set of Acculab scales, but then throw some out by anything up to 0.1gn even when the CM scale says it's a correct charge. Powder grade / characteristics and also the charge weight set also affect the device's reliability, so some combinations can be well below 80-85% correct. That's before electronic scale 'wandering' or whatever other gremlins set in after a period of time in use.

On 223 charge consistency, I went with + or - 0.02gn, my Acculab's smallest gradation / stated accuracy standard for long-range F/TR match ammunition. 0.02gn is around a single kernel of extruded powder. At the plus/minus 0.1gn level (ie 0.2gn range) ES values will invariably exceed 20 fps and more usually run on the wrong side of 30 fps with 90gn VLDs. However, this is a very demanding application and more common usage doesn't need that standard of consistency.