Here's how to determine your rifle & load's TBR/W "Group Number" to make the RX2800's ballistic solution as accurate as possible. You can also figure out a correction when using a 100 yard zero versus a 200 or 300 yard zero from the RX2800 group charts.
The Leupold RX2800 uses "Group Numbers" to categorize rifle ballistics. Use your favorite ballistic calculator to work up three range tables:
1. Use a 200 or 300 yard zero, zero wind and 600 yards as max range. Write down the
600 yard trajectory in inches.
2. Add a 10mph crosswind from 3 o'clock or 90 degrees and write down the
600 yard wind drift in inches. We do a separate chart to keep vertical wind jump out of our elevation number.
3. If you don't zero your rifle at 200 or 300 yards then do another range table using your actual zero range (I use 100 yards) and no crosswind. Write down the
600 yard trajectory in inches. Since the RX2800 Load Group Selection Table uses 200 or 300 yard zeros we'll use this number to calculate an elevation correction to make the RX2800's ballistic solution more accurate.
These numbers must be in inches to use the RX2800 Group Selection Table. I use the free online
Hornady 4DOF calculator. Be sure and select the units as inches, not MOA or Mils.
With value #1 and #2 go into the RX2800 TBR/W LOAD GROUP SELECTION TABLE: FOR BEST FIT UP TO 600 YARDS (page 25 of the
owner's manual) and find where your numbers fit in. You have to match the zero range (200 or 300 yards), value #1 and value #2 in the chart. When you match all that you get the "Group Number" you will enter into the RX2800's setup menu. Turn the RX2800 on then hold the Mode button for more than 2 seconds to enter the setup menu. Press the Mode button to move between fields and press the Power button to select values. "Function 2" is where you set your Group Number. You only have to set the Group Number once unless you change rifles or loads.
If you don't use a 200 or 300 yard zero that the Group Selection chart uses we can calculate a correction to compensate. For example, I zero my rifle at 100 yards so I subtract value #3 from value #1 to get my correction. For my Tikka T3x TAC A1 in 6.5 Creedmoor with Hornady 147 ELDM factory ammo gives me a 2665fps muzzle velocity and I zero my rifle at 100 yards. This load puts me into Group 10 with a zero elevation correction of 0.4mil. I add 0.4 to the RX2800's elevation mil display. The wind solution does not need to be corrected. The elevation correction is the same at all ranges.
P.S. I freakin' love this range finder.
