Two Distinct Velocity Groups Today...?

[cohunt]

chrono might be the culprit--- I too have a caldwell and i notice that sometimes my velocities seem to be high or low by 100fps, if I turn off the chrono for 10 sec, then turn back on, my velocities will g back to "normal" --I sometimes see large jumps in speed at the same shooting session and once again, if I reset the chrono then my speeds will be back to "normal"--- I am now looking for a better chrono

scale might be the culprit also-- sounds like you are using the lnl powder dispenser possibly... rememebr that it is +- .1 gr so one ay it could be +.1 and the next could be -.1 so that is really a .2 difference-- but I have also noticed that my cell phone makes the hornady scale drift--I now leave it in the other room while loading and double check dropped charges on my beam scale

 

[BrentM]

It sounds like the ammo all grouped the same on the target. Since that seems to be the case I'd suspect the chrono. 80 FPS difference should be enough that your zero will change some and it should show another separate grouping on the target, even at 400.

 

[Doozy]

I was just going to recommend you keeping your cartridges covered from the sun until ready to load. Where I live in Colorado, the high altitude makes that sun intense and it can quickly heat up a cartridge and powder.

 

[skipglo]

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.

I found the Caldwell chrony throws a ton of errors.....i returned mine. If it's sunny, cloudy sunny...you get different readings all the time!

 

[Asco6]

Magnetospeed and be done

 

[timberelk]

Magnetospeed and be done

While I've seen great reviews on them, $380 seems excessive for a chrono.

 

[BrentM]

While I've seen great reviews on them, $380 seems excessive for a chrono.

#1. It might be, but there is no comparison. #2. You can get the sporter model for a lot less. #3. Labradar is way more but worth the price too.

I have used both, own the magnetospeed, but prefer the labradar.

 

[7mmTikkaShooter]

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?

Yep! That's super frustrating. I've seen it and the obvious solution is to load all of them at the same time. One reason I've read or been told that explains the phenomenon has to do with how soon after resizing you load and seat bullets. The theory goes that after a few days the brass gets a chance to "set". I'm really not sure if there's any science behind this but I will admit that loading bullets days after sizing and everything after was more consistent in velocity than those loaded immediately after sizing compared to later. Outside of some weird brass voodoo a more logical answer to me is humidity. Since water is incompressible, higher or lower air humidity when loading could create pressure differences. I have not done any kind of testing with this but since I do not have a climate controlled clinical lab area to load so I try to be conscious of those unusually high humidity days. Just some food for thought here. Would love to hear if others have any thoughts to this theory.

 

[misterc01]

Powder- I use a Lyman DPS II (digital scale) to get my powder load, then I re-measure it on an RCBS 5-0-5. I usually return the first two-three to the powder container as matter of form, then proceed. I re-check every 10 rounds. If I get a disagreement, I go back through that 10, measuring them individually to pinpoint why and resolve it. I neck size earlier in the process, so any brass changes should be stabilized, and I check concentricity as a final step. I normally shoot 600 yards, and the electronic scoring system provides my velocity at the target. They is usually no more than 20 fps difference at that range, and I consistently shoot sub-MOA. I am happy with the entire process.

 

[Pdyson]

My Caldwell chrono it was different on cloudy days from sunny, sometimes missed the shot or had bigger than expected velocity swings that led me down a rabbit hole. I bought the cheap magnetospeed sport which worked way better... at least it always gave me consistent and believable results. However it's not well shielded from muzzle blast and heat and it broke after 2yrs use. I decided to spend the cash for the pro model a little over a year ago. I wish I had bought it first, the quality shows in the pro model. IMO the only better option is labradar but it's out of my budget range right now.

 

[Bigeclipse]

+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.

depends on the beam scale. I have a 10-10 rcbs scale that is amazingly consistent. I have a gempro250 digital scale which has drifted from time to time. When I load up my stuff I weigh my stuff on my digital and then confirm with the RCBS 10-10 for every round. Since I have started this process, my loads have been much more consistent. Unless you have $1000 if not more to buy a lab grade electronic scale, I think its best to have two scales to verify each charge. Just my opinion.

 

[MNbogboy]

I'm with the others on here with concerns it may be just chrono difference due to everchanging ambient light conditions. Readings from shot to shot in steady light conditions can be very consistent and also accurate. However partly cloudy, passing clouds, full sun, low sun, falling snow or even flies & mosquitos can affect readings. Having shot literally thousands of rounds over different chronograghs has been a good teacher.
I use a magneto speed now and light condition variables have been eliminated.
(A whole new set of problems with the barrel mounted device to be discussed at a different time).
My guess is that lighting changed between your two groups. The "error" you had with one shot was my big clue.
Overcast days are the most consistent for your machine. If you have access to a mag speed or better yet labradar you can verify your findings.
My .02,
Randy

 

[planetwaves]

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....

I had a similar situation a few years ago and it turned out to be the chronograph. I became a member of a nice shooting club where the various rifle ranges are oriented north to south. I had developed an accurate load for a 270 win and a 300 wm and wanted to get final fps to order CDS dials. I had loaded 100 rounds of each and took some to the range. It was very early in the morning. The results I got were somewhat slower with wider spread than expected on both rifles. I noticed that the sun was beating down from the east, and the "shades" on the chrony were not effective at that angle. I taped a target on the side of the shades to block the direct sunlight, and tried again. The results were quite different. As I recall, about 40-50 fps higher with tighter spread. But a slight wind hit and blew the chrony over (the target I taped on acted like a sail).

Another shooter saw what happened and invited me to his bench, where he showed me his magnetospeed. He showed how easy it is to set up and explained that it isn't dependent on lighting conditions. I stopped at Cabelas on the way home and bought one. It is very consistent over batches of loads with the same components. The only time I see different fps is if I load a batch of 270 with different brass (e.g., hornady vs Nosler). Of course, I can compensate for that by having a slightly different powder charge for each brand of brass. Month to month, year to year, loads from a previous year, etc. are all consistent.

 

[dennisinaz]

LabRadar