Lot numers are not as important as brands and types of primers. There are a lot of different manufacturers of primers and each has advantages for different applications.
As a general, blanket statement, I will agree with you on the face of what you say. However, I've got records where I had to increase/decrease certain loads significantly because the different lots from the same manufacturer altered my loads.
I hate blanket statements. They're almost always wrong and almost never right. Nevertheless, I think that 98% of the time, what you said is correct regarding primer lots. That's where the good old chronograph comes in, as well as detective work when inspecting your fired cases. I really do want to buy one of those new pressure-detecting devices from CED.
They all use a formula and construction specifications. Bench rest primers have a softer cup and usually detonate easily. This can be a problem with service rifles because the firing pins normally hit the cartridge primer during the auto loading process, a thinner cup can detonate under these conditions, so a thicker cup is recommended for this type of application. The burn rates of primers can affect accuracy.
I agree whole-heartedly about the bench-rest primers.
Years ago, I went solely with the CCI primer line because they had (and still do have) the thickest, hardest primer cup on the market. I settled on the CCI because I'd had a few pierced primers in firing my handloads. Mind you, I was still in my "let's-soup-it-up-Magnum-phase" that was really goofy on my part. I never blew up any guns, but I did wear out a perfectly good S&W 686 and a New Model Blackhawk in .41 Magnum. Oh, I forgot others, like a 1956-era Colt .357 Magnum and others I'd like to erase from my memory. (Thank God I let that "magnum phase" pass.)
I now use Winchester primers exclusively, for all my handgun loads, except those for 2400 in true magnum loads, then I still use the CCI magnum pistol primer.
The main reason I like the Winchester primers is because they're the only ones that have tapered cups, and they feed better than anything else in a progressive loading press or in the hand tool I use from RCBS.
Some magnum primers ignite really fast which can cause improper powder ingnition and lead to poor accuracy. However, with ball powders the magnum primers work fine.
I don't think its the speed -- it's the INTENSITY. I accidentally substituted magnum primers in one of my lots of .45 ACP loads using 5.0 gr. of HP-38 (thankfully, only 50 rounds). My chronograph was all over the place. Low velocities were 790 fps all the way up to 990 fps. I found two split necks (out of twice-fired brass) and had two cases that the primers simply fell out of the primer pockets -- YOWZAH!!!)
I think I'll just stay with Winchester primers if I can, but finding them can be problematic at the moment. Winchester just received at $70 million contract from the government to supply the military (the only US manufacturer -- IMI got the other $70 million -- and guess what??? We can't use the IMI ammo in Iraq or Afghanistan because it will offend the Muslims we shoot with JEWISH bullets!!!!!!!!!!!!!! Oh, please!!! I guess it will keep the towel-heads from getting into Paradise is they're shot with a Jewish-made round!!!)
Anyway, I just bought all the Winchester pistol primers I could find (10,000 small pistol, 5,000 large pistol).
Dude, the .45 ACP is BACK with the US military!!! (My son told me that he didn't see many 9mm handguns in US hands; and many soldiers were carrying either personally-owned .45 1911s or the new Kimbers being supplied to the military!!!)
When I buy a new lot of primers, I set aside up to 50 rounds of ammo to chronograph to see if I find any major variations -- and usually I don't with Winchester.
Sticking with a brand and type is far more important than lot. Use the scientific method to see if your primer is affecting accuracy; keep good written records.
This goes without saying. Primers tend to be far more uniform lot-to-lot than powders do!!!
To back up a moment, I've found it is a mistake to use magnum primers with 2400 powders in the .357 Mag., and even the .41 Mag. with certain charges. On the other hand, I would NEVER load ANYTHING with H-110 unless it has a magnum primer behind the charge.
Then again, I think I'm done with using H-110 altogether, and I have almost 4 pounds of this stuff on my hands and short on storage space. I do wish I'd bought 2400 instead!
I'd like to continue, but am afraid I'm getting too long.
Allen
Hmmm a