Help me figure out what Im overlooking

[CRNA]

Ok, been loading for a couple of years. Loaded many rounds for my 7mmRM that I use in competition as well as hunting. Never had this problem before:

I loaded 60 rounds two nights ago for a competition that's coming up next month. All was well.

I start loading tonight and I am having a big variation in my OAL (measured from the ogive with my bullet comparator in calipers.)
I loaded 30 rounds that had a spread of 0.0010" between that lot. I quit loading until I figure out the problem.
They are Bergers, from a 500ct box that I have used probably 2/3 of. Never had an issue.

I thought it may be dirt on the shellholder. Nope.

I thought it may be dirt in the comparator. Nope.

Thought it may be batteries in the calipers. Nope.

I rechecked the lengths of the rounds loaded two night ago and they are dead-nuts on the money (maybe .0001" variation).

What gives? The die has not been touched in two days. Nothing has changed.

Any help that anyone may think of that I haven't yet would be greatly appreciated.

Steve

 

[Mikecr]

I'm pretty picky, but wouldn't call 1thou of total spread in seating 'extreme'.

Were these cases(including the 60 perfect) neck sized at the same time?
If so, that sizing keeps creeping with time, and could change seating forces a bit.

 

[green 788]

If you're shooting compressed loads and using minimal neck tension... that could do it... bullet pushed back out by powder compression.

 

[41mag]

I'm reading your post, and what I am seeing is you might have added an extra "0" in your measurements. Maybe you meant .010" spread instead of .001"?

Heck I wouldn't sweat a .001" spread in any of my ammo, but yes a .010" in match ammo might ruin groups for sure.

That said, I have had some cases where the head might not have been exactly square that drove me nuts till I found it. I don't know why it was that they were way as they were new cases, but it sure gave me some weird readings. I used a Wilson trimmer to square them up and it only took a turn or two to do so. After that everything was back to normal. More or less it simply shined up the high spot and nothing more.

 

[CRNA]

I'm reading your post, and what I am seeing is you might have added an extra "0" in your measurements. Maybe you meant .010" spread instead of .001"?

Heck I wouldn't sweat a .001" spread in any of my ammo, but yes a .010" in match ammo might ruin groups for sure.

That said, I have had some cases where the head might not have been exactly square that drove me nuts till I found it. I don't know why it was that they were way as they were new cases, but it sure gave me some weird readings. I used a Wilson trimmer to square them up and it only took a turn or two to do so. After that everything was back to normal. More or less it simply shined up the high spot and nothing more.

Yes, I got zero happy.
The good ammo varied by about one thousandth.
The stuff I did last night varied by ten thousandths.

 

[Joe King]

What bullets are you using? You may want to sort through them could be something with the bullets, something loose on your press? Assuming nobody was messing with your die when your weren't looking. with my Redding die I have the micrometer reading written down makes it nice to be able to confirm it's where it should be.

 

[green 788]

maybe bullet tips of the longer bullets are touching inside the seater button...

Pull a couple of the bullets which seemed to seat too deep, and measure their length compared to some bullets which seated properly...

 

[CRNA]

Ok, so I think I have it sorted out. I took the die apart and it was pretty dirty. Sprayed the die with some carburetor cleaner and put things back together and the readings tightened up considerably.

Thanks for all of the good ideas. There were a few suggestions that people made that I would have never thought of for sure. Thanks again guys.

 

[farout]

I have had this happen after the brass has been shot 3 or 4 times. Especially if I am loading brass that has mixed shot counts. For example some have two shots and some have 4. Seems the necks are worked harder on the ones with more shots and it takes a little more pressure from the seating die to get to the right seating depth.

Annealing the brass has helped before.

 

[CRNA]

Well, they are mixed. Some once fired. Some several firings. There was a difference that I noticed in the amount of seating force needed.
I can't wrap my head around why that would make a difference though.
If I'm using a press, the die doesn't change, why would that make a difference in length?
I can understand why it would make a difference in neck tension.

 

[Joe King]

It would depend on the press you have and how much use it's seen, say it's a good press but generations and 10's of thousands of rounds old it could have wear in some areas, or if it's weaker press type (C frame, cast aluminum) those can flex also. But Presses like Lee's classic cast, RCBS Rockchucker, ect are built very solid I can't see them flexing under normal use in good condition.

 

[green 788]

Well, they are mixed. Some once fired. Some several firings. There was a difference that I noticed in the amount of seating force needed.
I can't wrap my head around why that would make a difference though.
If I'm using a press, the die doesn't change, why would that make a difference in length?
I can understand why it would make a difference in neck tension.

If there's more force needed to seat some bullets, and other go easier... and you said the cases were fired different numbers of times... it's time to anneal the cases with the larger number of firings. Some of the brass is more work hardened than other pieces, and that's the reason for the variation in seating depth resistance. And likely the reason for your varied OAL numbers, as cases may not be springing back to the same shoulder position when they come out of the sizing die.

Anneal all of the cases... then you should find that the bullets seat with the same pressure on the handle...

Dan

 

[CRNA]

If there's more force needed to seat some bullets, and other go easier... and you said the cases were fired different numbers of times... it's time to anneal the cases with the larger number of firings. Some of the brass is more work hardened than other pieces, and that's the reason for the variation in seating depth resistance. And likely the reason for your varied OAL numbers, as cases may not be springing back to the same shoulder position when they come out of the sizing die.

Anneal all of the cases... then you should find that the bullets seat with the same pressure on the handle...

Dan

Thanks Dan.
I have never annealed before, but I have been c