I'm loading some 375 H&H using 68 grains of reloader 15, Federal Magnum primers and Hornady 300 grain RN Interlock. The COL in the Hornady manual states 3.560. When I crimp in the crimp grove I am getting like 3.573.If I adjust the seater die to seat deeper it may read 3.543 but after I use the LEE factory crimp it increases to above 3.560??? What is this newby doing wrong. Is it safe to use the over 3.560 loads? I guess I can check to see if the RN is touching the groves/lands.

Based on my recent post regarding Hornady 300gr RN you may want to take my experience with a grain of salt but...

I wouldn't worry too much about COL... seat it 2/3rds of the way up the cannelure and crimp it down. If you want to get real specific, you really need to measure the distance to the lands in your chamber and then seat based on that measurement rather than what a reloading manual would dictate. Otherwise, the cannelure is a pretty good place to start. If you get good accuracy seated at that depth, stick with it and start shootin'

Mike

As long as they fit in the magazine, cycle 100% of the time and don't hit the lands when they're in the chamber, they're fine.

Thanks for the help, my friends.I appreciate your advice.

Are all your ctg case trimmed to the same length? (I'am sure they are).

I have found that measuring COL with a caliper to be an exercise in frustration until I got the idea to measure every bullet in two boxes thats a 100 bullets.

I stood bullets on their bases, grouped in circles by their length.

The largest group that measured identical in length was the one I called the base batch and I used them to sent up by bullet seating operation.

The noses of the bullets get bashed in too much to take an accurate measurement on so I selected a bunch of bullet from this base batch that looked to have identically formed noses and use these bullets to establish my book recommended COL.

Once I loaded up a few of these "identical" bullets to the book COL I then used a bullet comparator device attached to my caliper to give me a COL measurement length number that I used to assemble all the other cartridges.

I used to the COL measured with the more accurate bullet comparator device to set up all the subsequent cartridges.

Also I keep one of these perfect "identical" cartridges (no primer or powder) as a template model so its quicker to set up the bullet seater die next time.
I squirt some glue into the primer hole so it will glue the bullet in place so their is no chance of the bullet being bumped back into the ctg case while setting up the die.

As for why your COL in growing during resizing, I don't know why this is occurring.
I just checked some 375H&H ctgs I load a few weeks ago; Rem brass and Hornady 300 gr.BTSP and crimped with my LEE Factory crimp die. I see the COL is still is within 1/2 to 1 thou of the COL I had built them to originally (3.580").
I had crimped to the maximum amount that is to say the collet fingers just closed till they touched.

Very helpful info, I appreciate it. I will check to make sure the RN don't contact the do deep and if function is ok, I will slang the lead.