Okay, so I'm pretty new to reloading (and to the forum) so this might be kind of a noob question, but I noticed something pretty weird the other day at the range. I normally reload with lapua brass and am getting velocities right around 2750. I wanted to load some more but all the lapua brass was already loaded, so I figured I'd just load up some Hornady brass I had lying around from when I had shot some of their factory match stuff. Went to the range and the velocities were consistently a full 350 FPS slower. I couldn't believe it. Everything was done the exact same: fire formed, neck sized, same charge, bullet etc. So my questions is if this is normal and why this would happen? I mean I know that different brass can get different velocities with the same charges, but 350 FPS seems like a lot... And I feel like jacking up the charge in the Hornady brass to get the same velocities as the Lapua would be sketchy as all hell.
-
Having trouble using the site?
Contact support
.308 velocity question w/ different brass
- Thread starter Calihunter33
- Start date
What chronograph are you using, if it is one with sky screens I would blame lighting conditions. Take a magic marker and color the bullet tips tips black and try again. Also double check all of your work before you go adjusting charges. Also did you shoot this load on paper, was the POI the same?
Yes, it can happen. Different brand brass can have a different case capacity. The volume of the case is different and therefore the pressure will be different. The result is different velocity.
It is the Prochrono from Competition Electronics. I hadn't even considered the lighting conditions to be a factor, so Ill try painting the tips and see if the readings change at all. It has happened on 2 different range trips and both times I shot the stuff with lapua brass and then the stuff with Hornady right after, so conditions were the same. And POI shifted slightly under and to the left. ShtrRdy, I guess I just didn't realize it could make that drastic of a difference. Lesson learned I guess. Thanks for the input guys.
If you shot them both on the same range trip lighting is probably not the culprit unless the lighting conditions changed fairly drastically. weigh the empty cases, write the numbers down, then fill them with water then weigh them again and subtract the original case weight and you will be left the weight of water in grains which will translate into case volume. 350fps seems to be quite the variance from one case brand to another. Double and triple check your work, I have been reloading for 12 or so years and still can make mistakes if im not paying close attention.
Different case volumes, different neck tensions, and perhaps operator error are the most likely causes.
I think this is how it would work . . . the Hornady case is likely lighter, so at the same outside dimensions has more internal volume (measure using water). The neck at the same outside diameter would have a larger inside diameter and less neck tension. Both would contribute to less pressure and less velocity. (A shorter neck - if present - might also contribute due to less bearing surface on the bullet.)
I think this is how it would work . . . the Hornady case is likely lighter, so at the same outside dimensions has more internal volume (measure using water). The neck at the same outside diameter would have a larger inside diameter and less neck tension. Both would contribute to less pressure and less velocity. (A shorter neck - if present - might also contribute due to less bearing surface on the bullet.)
Awesome, thanks for the replies, that all makes sense. I'm unfortunately not going to be home until tomorrow but as soon as I'm home I'm going to check on the case weight and internal volume. Also, I'm going to take some once fired lapua and hornady and reload them side by side, just to make sure that I don't botch anything and screw up the charges or something. Like you said, double check your work. I have the feeling it was probably me, but we'll find out tomorrow. I'll let you guys know when I get back from the range.
No way in hell switching to Hornady brass from Lapua caused 350 fps slower velocities. I can accept maybe 50-100 fps, but 350 fps ... no way.
OP, check your drops at 300 yards or further. Do they jive with a 350 fps difference? I highly doubt it.
Probably a chrono malfunction. I have seen it plenty of times. Sun and light conditions can make those things do wacky things.
OP, check your drops at 300 yards or further. Do they jive with a 350 fps difference? I highly doubt it.
Probably a chrono malfunction. I have seen it plenty of times. Sun and light conditions can make those things do wacky things.
Determine the case volume of fired Lapua and Hornady cases (water fill and weigh method is pretty easy). That will tell you the difference in case volume. Sounds to me like 350 fps is much more variance than you'd expect simply from different case volumes.
Okay, so I measured their case volumes and they were within .2 grains of each other and the lapua only weighed 4 grains more than the hornady, so I'm assuming I just blew it somewhere along the line and dicked up the chargers or something, which is frustrating because I'm normally super careful so I have no idea what I did wrong. But thanks for all your help, much obliged.
