I have my new socom, and since marty had to run for cover, I am looking for an accurate (non-firebreathing) load for the remmington 300 grainers.  I have 296 and reloader 7 on hand.  Looking for what has worked well for others with the normal disclaimers.

For RL7 and the Remmy 300gn, I start with 42gn, seat to 2.020 and crimp .010.  Work up from there...(insert the usual caveats here).

Tom  

Quoted: For RL7 and the Remmy 300gn, I start with 42gn, seat to 2.020 and crimp .010.  Work up from there...(insert the usual caveats here). Tom

I really like this load too.

I however am getting a slight bolt impression on my brass and wonder if working up to much more will start wasting cases.

Any thoughts Banzai?

Blueblood, not to hijack the thread, but this load has proven to be a pretty much universal starter load for the most recent group buy uppers with the LW barrel.  What upper do you have?

I'm by no means an authority on loading or the 458, but here is my experience:

I, too, am getting slight bolt impressions on my brass, but since it's pretty much happening with ALL of my virgin Starline 458 SOCOM brass, regardless of load, I quickly chalked it up to the brass, as the impression on the head of the case is not changing on subsequent firings.  This also happens for my CorBon loads.  What I think I (and possibly you) are seeing is a swipe of the ejector across the brass as the bolt rotates and unlocks as opposed to a real bolt impression pressure indicator.  Near as I can tell, the marks that I'm seeing pretty much line up and suport this conclusion as there are no other pressure indicators on my primers (rounded edges, working pressure, but by no means flat).

With this RL7 load and 300gn Remmy bulk bullets, I've put no less than 12 firings on my first lot of 500 cases with no problems related to the brass.  I have this lot set aside for further evaluation (I plan to section a few sample cases and compare them to new ones to judge suitability of further loading).

I usually judge suitability of a load in terms of pressure/brass condition based on all the "usual" indicators like soot ring, primer indication, case head appearance, but mostly I correlate this with case head expansion numbers and chrony data (OK, I'm anal, give me a break).  I fire a select lot of commercial loads (with the same brass/bullet where possible as what I'm going to load) to determine case head expansion.  For 458, this means CorBon.  I got a case head expansion normalization number for my gun (either through averageing or selecting a spread, depending on the load/gun).  Upon firing of my loads, I compare case head expansion numbers.  Once I've reached my normalization number, I know that I'm at or near max pressure, in combination with all the other indicators.  A chrony helps with this, too.

My notes indicate, in my gun, that this is a safe load for my gun.  I suggest that you perform the same procedure to get a number for your gun, and compare accordingly to help guide you.  A "C" style .0001 indicating micrometer is required, as a standard reloading caliper won't read with this degree of accuracy.  I have set a max case head expansion number for gun of .5425.  Your number will almost definately be different.  I post my number here for illustration purposes only.

Sorry if this was a little wordy, but it's the path I went down with this particular cartridge, and it has served me well, as I have several different tweaked MOA loads with the Remmy 300 and 405gn loads, as well as the Speer 400gn and the Hornady 500gn TMJs.  Mostly it's related to just tinkering with the right powder charge and crimp (I crimp all my 458 loads with RL7 about .010.  My chrony sheets indicate that, for me at least, it improves my SD numbers).

Tom  

Quoted: Blueblood, not to hijack the thread, but this load has proven to be a pretty much universal starter load for the most recent group buy uppers with the LW barrel.  What upper do you have? I'm by no means an authority on loading or the 458, but here is my experience: I, too, am getting slight bolt impressions on my brass, but since it's pretty much happening with ALL of my virgin Starline 458 SOCOM brass, regardless of load, I quickly chalked it up to the brass, as the impression on the head of the case is not changing on subsequent firings.  This also happens for my CorBon loads.  What I think I (and possibly you) are seeing is a swipe of the ejector across the brass as the bolt rotates and unlocks as opposed to a real bolt impression pressure indicator.  Near as I can tell, the marks that I'm seeing pretty much line up and suport this conclusion as there are no other pressure indicators on my primers (rounded edges, working pressure, but by no means flat). With this RL7 load and 300gn Remmy bulk bullets, I've put no less than 12 firings on my first lot of 500 cases with no problems related to the brass.  I have this lot set aside for further evaluation (I plan to section a few sample cases and compare them to new ones to judge suitability of further loading). I usually judge suitability of a load in terms of pressure/brass condition based on all the "usual" indicators like soot ring, primer indication, case head appearance, but mostly I correlate this with case head expansion numbers and chrony data (OK, I'm anal, give me a break).  I fire a select lot of commercial loads (with the same brass/bullet where possible as what I'm going to load) to determine case head expansion.  For 458, this means CorBon.  I got a case head expansion normalization number for my gun (either through averageing or selecting a spread, depending on the load/gun).  Upon firing of my loads, I compare case head expansion numbers.  Once I've reached my normalization number, I know that I'm at or near max pressure, in combination with all the other indicators.  A chrony helps with this, too. My notes indicate, in my gun, that this is a safe load for my gun.  I suggest that you perform the same procedure to get a number for your gun, and compare accordingly to help guide you.  A "C" style .0001 indicating micrometer is required, as a standard reloading caliper won't read with this degree of accuracy.  I have set a max case head expansion number for gun of .5425.  Your number will almost definately be different.  I post my number here for illustration purposes only. Sorry if this was a little wordy, but it's the path I went down with this particular cartridge, and it has served me well, as I have several different tweaked MOA loads with the Remmy 300 and 405gn loads, as well as the Speer 400gn and the Hornady 500gn TMJs.  Mostly it's related to just tinkering with the right powder charge and crimp (I crimp all my 458 loads with RL7 about .010.  My chrony sheets indicate that, for me at least, it improves my SD numbers). Tom

This is some great info, thank you.  
Dont get me wrong I love this load and  load all my rounds to this.  I am probably mistaking the bolt  impression for the swipe and ejection like you stated. More time and great info like this makes it a lot easier to develop loads and learn.
My upper was a custom build by Master Marty and I believe it was a LW barrle. You can see picks of it here.
http://208.16.99.27/cmmg_images/tbl_images/MODCC10Sept/MODCC8.jpg
I'm getting .5405 on my cases with this load.  What kind of fps are you seeing with this load? If my memory searves me right I think last time I had a chance to use a crony they were right at 1689 to 1710 fps.

Once again thank you for all the great info. This will help a lot of people including myself.

Doug