Hmm... strange chrono numbers from 223

[Kraze]

First a little background info. This is the first time I've worked up a load for a semi-auto and the first time for .223/5.56. The rifle is just a generic S&W M&P 15 chambered in 5.56 with a 16" barrel. I loaded up 20 rounds, going up in .1 increments just to get an idea of velocity/pressure, hoping to maybe find a flat spot in the velocities to try loading for. I'm certainly not looking for precision from this rifle or ammo, just want to find something that will shoot minute of coyote consistently.

Everything was loaded on a Co-ax, charges were thrown on a CM Lite (and it certainly seemed to be throwing accurate charges).

The load:
New Sig 223 brass, fl resized
CCI 450s
53 gr Vmax
Benchmark
Loaded to mag length

Velocities:
23.5 - 2533
23.6 - 2509
23.7 - Error
23.8 - 2664
23.9 - 2571
24.0 - Error (at this point I switched to the thinner MS spacer)
24.1 - 2773
24.2 - 2678
24.3 - 2718
24.4 - 2681
24.5 - 2797
24.6 - 2820
24.7 - 2865
24.8 - 2787
24.9 - 2840
25.0 - 2849
25.1 - 2886
25.2 - 2879
25.3 - 2972
25.4 - 2918

So the question is, is it normal for a 223/AR to jump +- 100 fps in a .1 gr charge weight increase sometimes? I've done the same sort of velocity work up with .3 and .5 grain increments in 6.5 CM and 300 WM and didn't have near such erratic results. Or should I quit worrying about all this and just load some up at 24.9 and 25 to see what kind of groups and SD/ES I can get?

 

[ShtrRdy]

Those numbers look erratic to me. I've never tried doing this in 0.1 gr steps. It sounds like you're using a Magnetospeed?

Try something like this again but do the follwing:
Use the once fired brass.
Use non-magnum primers
Use 0.2 gr increment
After the Charge Master delivers a charge, re-weigh it on a separate scale

 

[Kraze]

Those numbers look erratic to me. I've never tried doing this in 0.1 gr steps. It sounds like you're using a Magnetospeed?

Try something like this again but do the follwing:
Use the once fired brass.
Use non-magnum primers
Use 0.2 gr increment
After the Charge Master delivers a charge, re-weigh it on a separate scale

Yep, Magnetospeed Sporter. I didn't use it on any other rifles this trip, but it's been reliable in the past. I think the 2 errors were from using the thicker spacer.

I was going back and forth on whether to do .1 or .2 gr increments. I'll try .2 next time, and see if I can find some 205s or maybe some BR-4 primers locally. And my only other scale is a cheap Frankford Arsenal digital scale, but I guess it's better than nothing for double checking the CM.

Thanks for the suggestions.

 

[black5.3]

I have seen crazy swings in neck tension cause wild jumps in muzzle velocity. When you are seating bullets you can feel the difference in neck tension... just one if the many variables that could cause what you saw.

 

[Kraze]

I have seen crazy swings in neck tension cause wild jumps in muzzle velocity. When you are seating bullets you can feel the difference in neck tension... just one if the many variables that could cause what you saw.

I don't remember feeling anything out of the ordinary when I was seating these, but I'll definitely be paying closer attention to that (along with everything else) on the next batch I load up.

Keeping in mind that the goal here is just to load ammo cheaply and without too much effort (doubtful this rifle/shooter combo would be capable of consistent sub MOA with any ammo, so not exactly looking to reload match grade ammo), is there anything you would do to reduce possible wide swings in neck tension? Current die set is the Hornady Custom Grade 223 dies.

 

[black5.3]

If your just loading plinking ammo then the main things i would do pick a safe/functional powder charge, keep brass trimmed to required length, and seating depth. I dont know if you anneal but thats never a bad thing to do. How i control neck tension is anneal after every firing, size with decapping rod removed and then expand with a 21st century TiNi mandrel. Keeps necks pretty consistent. THIS IS IN A BOLT GUN SO I RUN LOGHT NECK TENSION. You need adequate neck tension/crimping for your autoloader.

 

[Kraze]

Thanks for the suggestions. I'm sure I'll end up with an annealer, some bushing dies, and the 21st Century mandrel setup someday soon, but I'll probably only bother with that for the bolt guns lol. Hoping to keep things a bit simpler/cheaper for this one. I'll definitely pay more attention to how this next batch feels when I'm seating the bullets though.

 

[black5.3]

If its plinking ammo then in my opinion there is no need to be real strict with it. Just cover the safety/function aspect of it and shoot it. Save the minute details for guns that your trying to shoot with precision.

 

[10ring1]

Yes. Same. If blasting ammo, find a good, functional, safe load and skip the Chrono for now. Look for 1moa or better. Once you've found your load then test your velocity a few times for documentation sake.

I know it may not be cool with some but I work loads without Chrono. But I am typically looking for accuracy over speed. I built an AR15 with a WOA barrel that shoots a shade over 0.5" on a 6x5 with Sierra 77SMK that when I shoot over the Chrono, i almost threw up. Sd was all over the place, just like yours. But it shoots lights out

 

[Kraze]

Thanks for the input everyone, I appreciate it. The main goal for this rifle was always safety/function first, accuracy second, speed third, but the crazy velocity swings with less than .5% charge weight increase threw me for a loop.

I'll load some up to shoot for groups next time without the MS on to see how they do. And if I can find a pack of 100 of something like CCI 41s or Fed 205s locally, I'll also give those a shot with a 10 round, .2 gr workup over the MS just to see if maybe the 450s were the cause of the crazy swings.

 

[RackOpsTactical]

The only time I've seen this exact thing - MS, AR, crazy MV - was when my brass was past its prime or was not the same head stamp / sorted lot.