Attached File


I suspect using mixed brass is my biggest problem, I didn’t sort 5.56 from .223. Will mixing brass typically have this much effect?

Powder charge, powder selection, primer brand, mixed brass and other factors contributed to good/bad ES/SD.

I use 20.7 grains of H4198 with 52 grain SMK's and they have an extreme spread of 140 fps. It shoots ten shot groups at 100 yards you can cover with a quarter.

The manual says I can go higher, but my chronograph tells me I'm within a tenth or two of maximum.

Ball powders have given me tighter ES/SD, but I won't use them because of their wild swings in pressure/velocity depending on ambient temperature.

Which propellant, and how did you measure the load?  I can't attribute that much swing to brass specs.  I might question my chronograph as well, or perhaps the lighting conditions at the time.

Mine aren't normally quite that big, but I do have huge variations in my mixed brass blasting ammo, not too far off of that.
Edit.... looking at my notes, my mixed brass blasting ammo is usually in an ES range of 150, and SD range of 50-60ish.

25.5gr TAC measured through Dillon powder measure on 550

Which bullet?
Which primer?
OAL?
Crimped?

Which chrono?
What distance?

Running 23.5 gr TAC behind a
75 gr HPBT-M
seated to 2.235",
uncrimped, in a
Winchester case and a
Winchester primer,

I got -

Average = 2827 fps (a long barrel)
ES = 77 fps
SD = 21 fps

These were just nominal, thrown charges, nothing special.  

You are doing something wrong but have given no information for us to diagnose your trouble(s).

5 shots with an extreme spread of 265 fps is way, way outside of acceptable. Even if the accuracy is good, you have something majorly wrong here. I don't deal with mixed brand 5.56 and 223, so I don't know how much variation there is possible. I know Lake city 7.62 brass compared to commercial Federal or Winchester 308 brass varies, but I've not found the same thing with Lake City 5.56 brass. It's really easy to test now that you have cases fired in your chamber. It's easiest on an electric scale, put the case on it, tare the weight, fill the case to the lip with water, and that's your case capacity in grains of water. Small differences isn't going to cause this problem. According to quickloads you would need cases that vary from 27 to 30 gr h2o capacity to get such a crazy spread. That's not impossible, but that's not something I've seen.

My gut feeling is your load is simply not working well. With that powder charge I have to assume you are using a lighter bullet like a 50 grain, 25.5 gr looks over max or right at maximum for a 55gr depending on the load data. Sometimes those light bullets and slower ball powders do not play well together. If you happen to have magnum primers, I would definitely give them a try.

If you don't trim every piece of brass to the same length, and use a crimp, the velocities will be all over the place.

I never crimp bottlenecked cases, instead I establish .003" to .0035" of neck tension by polishing the expander ball to make it happen. Simply spin polishing expander balls to achieve a little bit more neck tension, is a better option IMO than crimping. A decent hold on the bullet promotes better ignition.

What bullet are you using?

M193/M855 bullets have some of the highest inconsistencies on the market.

The secret to getting more consistent powder drops on a Dillon press is to slow down. Smooth handle operation with a pause at each end. People trying to set speed records outrun the press's ability to function properly. I average 300 to 330 rounds an hour on my Dillon 550's, that's when I'm using already primed brass. I actually look inside each case to confirm powder charge height prior to seating each bullet.

I routinely achieve SD's between 10 and 20 fps when I use ball powders loading handgun rounds.

OP, have you measured your standard deviation on your dropped powder charges?   A measurement of something like 30, 50 or even 100 dropped charges, individually weighed, can be enlightening for the reloader.  

One outcome might be you need to modify your technique.  Alternatively, it might also show the problem lies elsewhere.

I'd expect TAC to drop within 2 tenths from any powder measure so that shouldn't be the problem.  Could be neck tension differences of the various brass, but I've never had swings that wide.  I sort brass by weight to cull out the heavy cases.  Some cases have thicker walls and therefore less volume, it is possible that they also have thicker necks which might affect neck tension, which might affect bullet release, which might cause differences in velocity.  MIGHT.

Without any info from the OP, we are all just guessing about what caused his problem.

My suggestion was do something, yourself, that might help you to understand your problem.

What one "expects" and what one is actually getting are often quite different, hence real measured data is often important.  

Even if his throws are perfectly uniform, he can at least check that off as a possible cause that is not the actual problem.  Then again, he may find that his throws vary widely.

He doesn't know and will never find out without DOING something.

He hasn't presented his chronographing technique, either, and that software screen is unfamiliar to me.  It could be a speed measurement issue.