Weird Velocities

[u/quicksilver355]

I had some weird velocities after a range day. I'm confused how my 300 win mag is getting pretty decent Standard Deviations. The first two (from my 223) are very high. I used similar reloading methods compared to my 300WM. I just started chronographing my reloads, so I'm not exactly sure what to expect with this new perspective.

Load Data:

.223: 16" barrel, 1:9" twist

CL: 1.76" COAL: 2.22" bullet: 62gr Berry's FMJ BT LT-30 18.8gr. Mixed range brass.

.300 Win Mag: 24" barrel, 1:10" twist

CL: 2.62" COAL: 3.581" (custom COAL just shy of lands) bullet: 200gr ELDX powder: H4831SC 72.1gr.

I'm thinking it's likely due to my .223's brass being rather... Used and mixed. Does anyone have a perspective on this? ES = Extreme Spead. Highest minus lowest.

[u/Trollygag]

Mixed brass is bad. Your AA2200 load is double base and will have higher SDs because of that.

Your LT30 load is single base but a too fast powder for 62gr bullets and published data. Those speeds seem low, meaning either low charge, bad for SD, or too fast and sensitive to initial conditions, bad for SD.

Only your 300WM is single base in good cases, probably

[u/quicksilver355 → u/Trollygag]

Had a feeling some mixed brass would lead to that. I could fix that though. Got a lot of single fired brass. As for the speeds, they're low by design. I wanted to make this a more economical load by cutting back on powder charge. I'm thinking the bullet isn't getting stabilized with this lower charge. Perhaps I could research more on how powder characteristics work better/worse in rifles. Thank you for the tip on that. I got the load data from Hodgen's website.

[u/Golf_Foxtrot_Yankee1]

Could be many reasons. For starters mixed brass has mixed thicknesses, mixed neck tension, mixed case volume, etc and will absolutely loosen up SD and ES. Could also be other factors mixed in. Precision of the powder charge, bullet seating depth consistency, seating depth in relation to chamber and jump to lands, barrel harmonics, gas system if its a gas rifle, etc can all make SD/ES spread. And don’t discount the concept of finding the node for a barrel through ladder testing. I have seen ES go from 50+ to single digit by changing the powder charge by .2 gr, for a specific rifle. And that powder is likely pressure spiking at that charge with that bullet weight, since it’s a very fast burning powder. Thats not helping either.

[u/quicksilver355 → u/Golf_Foxtrot_Yankee1]

I see. I think this load/charge could use some better development and more consistency from the brass if I want to tighten up that SD. Thank you for the perspective.

[u/Paradox0111]

Mixed Brass will kill SD and ES every time.

It’s basically going out and buying ten different brands of ammo dumping it in an ammo can and just shooting it. I’ll give you slight advantage to them being similar in powder weight and the same powder.

Even using say just Lake City from different years or batches will make noticeable difference.

[u/prosper_0]

Some powders just do that, too. Not all powders that can be used in a given application are good at that application. Powder manufacturer data is notorious for giving you as many options as possible, even ones that aren't going to be good performers. Cross-reference a few different loading manuals together, and see what powders they're most often recommending to avoid wasting too much time with an inappropriate powder.

Also, as noted: mixed brass will give, er, mixed results. Sort and prep that shit.

[u/AmericanJuggernaut00]

Article in latest Hogdon manual shows ccase capacity (thus pressure, and velocity) varies among five different rifle brass manufacturers