powder charge weights ?

[rebs]

How much difference in charge weight does it take to affect accuracy? is 1 or 2 tenths enough to make a difference?
This is in 223 bolt gun

 

[Doom]

The 223 is very sensitive to charge weights, accuracy will fall off at +/- .2 gr in my experience.

 

[Coyotefurharvester]

I load in a .4(+ when I can find it) gr charge weight vertical dispersion node, no matter the cartridge. Minimal dispersion is one bullet diameter or less.

 

[Metal God]

1% of max charge is my rule . So in a 223 cartridge that would be .2 to .3gr - 30-06 .5gr - 50BMG several gains . FWIW I start at .5gr increments then fine tune in smaller increments once I find a charge the gun likes inside those .5gr increment charges .

An important thing to consider is the accuracy of your scale . If it’s only a +/- .1gr scale . Trying to weigh charges in the .1 to .2 increment range is not going to give you those differences consistently .

 

[Cfshooter]

I see POI change in .2 increments during OCW tests, hence why I like to use that method for load development. I try to fine the biggest window and load in the middle of it.

 

[jelenko]

The 223 is very sensitive to charge weights, accuracy will fall off at +/- .2 gr in my experience.

This is my experience also.
Looking at barrel times vs the optimum barrel times in GRT indicates the nodes are about +/- 0.2 grains wide.

 

[dmoran]

The smaller the cartridge (less case capacity), the more charge increments will effect accuracy.

A rule of thumb for any cartridge is: the 3% rule ,,. which is: accuracy nodes tend to show up every 3% in charge weights incrementally (up or down). And "scatter nodes" tend to show up half way between, at 1.5%

That rule of thumb has proven out well to hold true, across a wide range of cartridges, calibers, and rifles. Not always spot on 3% but very close give or take a tenth or two... sort to speak.

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[Scrumbag]

This is my experience also.
Looking at barrel times vs the optimum barrel times in GRT indicates the nodes are about +/- 0.2 grains wide.

I came to a similar conclusion and my rather limited testing seems to agree

 

[Tesoro]

I just got back from range this afternoon with my 223 and 22.0 was good, 22.2 not so good and 22.4 like a laser. If this tells ya anything. In my 06 .2 gr makes no diff. All about % ( volume ) as mentioned.

 

[RegionRat]

Just an opinion, but 223 is sensitive to brass prep and charge weights once you go out to mid range or beyond.

The ability to stay in tune depends on the composite of many variables that all have dispersion and in addition, the tuning concept isn't linear.

Teasing out the amount due to one thing like charge weight isn't easy, but to get a perspective without doing a bunch of statistics means you have to just look at the slope of the charge versus velocity plot.

Once you are willing to say we all know the point of impact and the tune are not perfectly linear with speed, then we can go forward with a simple look at the vertical change due to velocity at some distance.

Say for example a 80.5 grain Berger bullet with a typical average speed of 2750.

It will have a drop of about 15 MOA at 600 yards.

Now if you assume something like Varget gives roughly 100 fps per grain, and it takes about a change from 2750 to 2675 to cause the drop to go to 16 MOA, then the math is roughly 0.75 grains to cause the shift.

So, if everything else was held to zero, the assumption implies the charge would be able to have a +/- 0.375 grain tolerance to hold 1 MOA at 600 yards.

However, since everything else is not held to the assumption and the reality is that tuning is non-linear, the typical charge tolerance is much smaller than +/- 0.375 grains, just to hold 1 MOA.

Also, since many folks here are expecting performance much better than 1 MOA, and in many instances much smaller than 1/2 MOA, then we must also assume that the powder charge and velocity changes must be held to less than half the above in our thought experiment.

This means an ES of less than 75 fps/2 = 37.5 fps for a linear assumption, which we would all agree isn't good enough when we have to give some room for other errors.

That just cut the +/- 0.375 grains in less than half, so +/- 0.1875 if everything else was perfect and tuning was linear, and much less than that for the real world since tuning isn't linear and everything else isn't perfect either.

So to estimate a charge tolerance, just look at the slope of the powder charge versus velocity change for a given example, and then plug the velocity change into a ballistic program for the amount of drop change you would accept. The reality is usually much smaller than this assumption. YMMV

 

[CharlieNC]

You can add powder and experience an increase in velocity and a drop for poi. The Audette Ladder due to harmonics can provide a node due to positive compensation and follows the approximate 3% pattern as noted by Donovan. So your impact depends on where you are on that curve, map it to find out.

 

[Doom]

The 3%/1.5% @dmoran mentioned is also what Dan Newberry references in his OCW method (which @dmoran has used) and I can confirm that it shows up repeatedly in load workups for 223 and 308. That puts nodes at ~.7 grans apart and what shows up at ~.3 to .4 grains is a scatter node. In 223 I do not see consistent POI with 0.2gr increments. At +/-0.1 gr I will generally see a slight shift in POI.

 

[Metal God]

The 3% method is for the beginning of loaded development. OP asked what’s the minimum charge that will effect accuracy. Those are two different things . Like I pointed out 1% is my rule of effecting accuracy but I do my initial load development at .5gr with 223 which would be 2%+

 

[Doom]

The 3% method is for the beginning of loaded development. OP asked what’s the minimum charge that will effect accuracy. Those are two different things . Like I pointed out 1% is my rule of effecting accuracy but I do my initial load development at .5gr with 223 which would be 2%+

I believe we have collectively concluded that +/-0.1 to +/-0.2 gr in 233 is enough to affect accuracy. The 3% is actually the approximate charge weight difference been accuracy nodes.

 

[Warz]

Been reloading 40+ years.
When looking for my best load for a particular using a particular bullet/powder I've always did this.
Took the mid-range load from the reloading data for that bullet and powder...
let's use 5.5 grains as an example.
Load 10 rounds at 5.5 gr
Load 10 rounds at 5.4 gr
Load 10 rounds at 5.3 gr
Load 10 rounds at 5.2 gr
Load 10 rounds at 5.1 gr
Load 10 rounds at 5.5 gr
Load 10 rounds at 5.6 gr
Load 10 rounds at 5.7 gr
Load 10 rounds at 5.8 gr
Load 10 rounds at 5.9 gr
Load 10 rounds at 6.0 gr

Shoot each 5 using a rest
One of the loads will pull together a better group than the rest.
My scoped Ruger Red Hawk rested found a load at 25 YARDS that put 5 into the ACE on an Ace of Spades playing card.

Thats the fun about reloading.

Good luck and good shooting.