Velocity concerns...Retumbo powder, 300 RUM

[yoterunner]

Hey guys, recently (spring) started working up my factory Rem 700 300 RUM. I have been using Retumbo powder, and 210gr Berger VLD's. At 92grns of powder, I chrony'd the load at an average of 3040 fps during the first working up sessions. The SD was relatively low with a decent high-low range (dont have data right now). I started to work up my "dope" using this velocity. Well this past weekend I started with two shots at 100YD to confirm my zero. These two shots went 2960 & 2990 fps. I then moved back to 500YDS. I forgot to set the chrony up to "monitor" velocities. This is a Mil/Mil scope, and my adjustment through the Vortex program was to be 2.3 mils, well it actually took me 2.6 mil to get on at 500YDs. When I plugged that back into the Vortex program (far range/actual adjustment) the program states my MV would have been 2750 fps. What do you guys think, should there be that much difference (2.3mil vs 2.6mil) in adjustment (program to actual)??? This is my first work up with a tactical style scope (dialing come-ups). Also, I did a box test on the scope (covering 10mils)@ 100yds and it performed great...scope is not an issue! Please let me know your thoughts!

Additional info: first work up was at 85 degrees and this past weekend was around 60 degrees.

 

[Brain]

Re: Velocity concerns...Retumbo powder, 300 RUM

Could it be that input parameters weren't accurate?

85° to 60° shouldn't be showing a 200+fps difference.

 

[boeger42]

Re: Velocity concerns...Retumbo powder, 300 RUM

I'm going through the same issue with a 300wm. I won't continue to build a trajectory until I have the velocity somewhat under control. Here is where I'm at currently:

1. Sent 2 pieces of brass to Redding. They concluded that neither tool (rcbs precision mic nor the locknload comparator) was measuring headspace (shoulder) on the datum line. As a result I was actually pushing my headspace longer by full case sizing the brass.

2. Seated bullets (to lands) in 5 different cases and filled them with water. Subtracting the difference between wet and dry gave me case capacity, I then calculated 80%-90% of the capacity. I discovered that the manufacturers recommended loads started well below 80% and never reached 90%. (Berger Hunting vld's)

3. I've tried 2 different powders, H1000 and IMR4350. I'm going to reshoot both up to 90% to verify no pressure issues. Assuming the velocity stabilizes, I'll start shooting the ladder to find the node and finally start building a trajectory.

It's taken me 250 rounds to get this far...good luck!

 

[1shot2kill]

Re: Velocity concerns...Retumbo powder, 300 RUM

just a friendly heads up i am also loading for the 300 ultra shooting 210 hunting vld and retumbo powder nosler brass and cci magnum primers but before i loaded up the first round i emailed berger asking for load data using the components and the load info they gave me shows the max load is 92 grains of retumbo not the starting point