Two Distinct Velocity Groups Today...?

[timberelk]

Shot today at 300 and 400 yards. Both under MOA with a 5mph or so wind so I'm pretty pleased for this being a hunting rifle.



But I got two different velocity groups today... I had 7 cases I loaded earlier today and those were around 3000 FPS +- 20 FPS. I also had 3 cases that I loaded 4 days ago that read 3073 and 3090 and error on the last one. The 3 cases from 4 days ago were loaded with the exact same powder (4831 SC), powder charge (58.3), seating depth (3.320") as the 7 I loaded today but they shot about 80 FPS faster.



I couldn't tell the difference on the target despite my zeiss hunting app saying there should be 1.1" difference at 400 yards.



The conclusion I came to was that the cases that were put together 4 days ago experienced a very mild "cold weld". I'm going to load up a bunch and then wait a few days to shoot them to see if I can replicate what I saw today.

These cases were on their second firing and were FL sized to bump the shoulder back .002-.003.



Has anyone experienced higher velocities when shooting reloaded cases that had been assembled for a while?

 

[PBramble]

I have. It's been discussed on several forums I'm on, and the general consensus says the brass in the neck "moves" and neck tension changes as they sit. I don't have a gauge to measure the tension required to pull one down to verify it, but it makes sense.

 

[timberelk]

So after the cases sit for a few days does the neck tension stop "increasing"? For example, if I was shooting cases I loaded 4 days ago along with cases I loaded 4 month ago, I should see a similar velocity?

 

[entoptics]

I'd be more inclined to check my chrony, scale, powder, etc., etc., than invoke "cold welding" or neck tension for 80 fps.

4 days of sitting around won't make rifle ammo go 80 fps faster. At least not that I've ever read or experienced.

 

[timberelk]

Good point....my chrono is a basic Caldwell deluxe model that I don't believe is 100% accurate but I believe it is consistent.

powder is measured by dumping onto a scale by hand until I hit 58.3 grains. 58.2 and 58.4 is not good enough for me. Scale is calibrated with the supplied weight for Hornady.

 

[James Pearson]

This is why loading should all be done in a single session, with the exception of load development where small batches loaded will all be shot together.

I have found that if I load 20, then load another 20 several days later, that my process, however close, can differ slightly and I get what you got.

When I complete load development, I usually load 100 or more rounds all at the same session and they shoot very consistent.
JM$.02

 

[milo-2]

I am betting on chrono placement. Do the test again, load 5 today, let sit for 4 days, load 5 more the day of the test. Now things are equal. There is no reason to speculate, or have anyone else guess as to what happened.
I mess with neck tensions a lot, I have yet to see much velocity increase or decrease doing so. Even with a hard crimp, getting 80 fps more will take some doing.

 

[timberelk]

This is why loading should all be done in a single session, with the exception of load development where small batches loaded will all be shot together.

I have found that if I load 20, then load another 20 several days later, that my process, however close, can differ slightly and I get what you got.

When I complete load development, I usually load 100 or more rounds all at the same session and they shoot very consistent.
JM$.02

Thank you for the info, I should start doing my reloading it large batches.

Just for my knowledge, how can factory ammo be consistent from year to year? For example, my rifle shoots Hornady whitetail 130 grain interlocks at 2770 +-30 FPS. I first got those results early this year (April) and I bought another 2 boxes a few weeks ago from a different retailer and the velocity was within the same extreme spread as back in April.

My reloading process is painstakingly slow and extremely detail oriented, just trying to figure out what I'm doing wrong

 

[ShtrRdy]

Another possible factor is powder temperature difference.

 

[James Pearson]

Thank you for the info, I should start doing my reloading it large batches.

Just for my knowledge, how can factory ammo be consistent from year to year? For example, my rifle shoots Hornady whitetail 130 grain interlocks at 2770 +-30 FPS. I first got those results early this year (April) and I bought another 2 boxes a few weeks ago from a different retailer and the velocity was within the same extreme spread as back in April.

Millions of $$$ spent on quality control, that's how.

 

[milo-2]

My reloading process is painstakingly slow and extremely detail oriented, just trying to figure out what I'm doing wrong

You need to re-run a test in the same controlled environment. At this point, there is no proof you have done anything wrong.
I myself am not a big fan of having loaded precision ammo sitting around, and cold weld is not the reason, that is something I have not experienced. I have 223 ammo loaded in 2000 that shoots the same today as when it was loaded.

 

[Shane Lindsey]

+1 on loading in larger batches. I too have noticed this from lot to lot.

Also noticed a velocity difference from virgin cases to 1x 2x fired. I try to batch all my cases by lot and firings for this reason. Load up a hundred and chrony first thing if changing lots.

Sounds like you essentially loaded two different lots, but 80 fps is a pretty big swing.

If using the $30 Hornady scale, I have noticed if I take the charge/pan off and shake it, it will be .1 a grain heavy when I put it back on.

If using a beam scale, I find it really hard to get it back to exactly the same for different lots.

 

[DUSTY NOGGIN]

your scale , your temps , or your chrono would be my guess ..

 

[timberelk]

+1 on loading in larger batches. I too have noticed this from lot to lot.

Also noticed a velocity difference from virgin cases to 1x 2x fired. I try to batch all my cases by lot and firings for this reason. Load up a hundred and chrony first thing if changing lots.

Sounds like you essentially loaded two different lots, but 80 fps is a pretty big swing.

If using the $30 Hornady scale, I have noticed if I take the charge/pan off and shake it, it will be .1 a grain heavy when I put it back on.

If using a beam scale, I find it really hard to get it back to exactly the same for different lots.

Thanks for the info. I use the Hornady digital gauge