So the 77 TMK is probably the best bullet to use for mag length out to 600 then? Better than the 73g ELDM even?
Just a suggestion, not a guarantee that any given bullet is "best" for you. You should try them all before you bulk up on anything.
However, the 77 weight bullets are popular in the XTC competition crowds where magazine length is required, and for a good reason. Along comes the TMK version, and they managed to raise the BC. Nothing wrong with the other choices either, but some are just too long for the magazine and we single load those for the 600 yard stage.
To get one of the ones that is too long to run from the magazine, may or may not be worth your efforts. The only thing I am trying to do, is put some perspective in front of you.
Here is the view from 100,000 feet that will put a perspective on what I mean.
Some folks will do better than these speeds, some will do worse. Here they are just to give an energy based perspective. I am not trying to start a pissing contest on who can push faster or slower, but trying to show the perspective of these different bullets and their value.
In terms of external ballistics, we will assume we have roughly 1700 Joules or 1300 ft*lbs worth of energy to keep things similar. That pushes a 77 at roughly 2750 fps, and an 80 at 2700 and the 73 ELDM at 2831.
Berger says that the Berger 80.5 Fullbore has a G1 BC of 0.441
Sierra says that the Sierra 80 SMK has a BC of 0.461 @ 2100 fps and above .453 between 1750 and 2100 fps .420 @ 1750 fps and below.
Sierra says that the Sierra 77 SMK which is popular from the magazine, is .372 @ 3000 fps and above .362 between 2500 and 3000 fps .362 between 1700 and 2500 fps .343 @ 1700 fps and below
However, later on they came out with the 77 TMK version, which splits the difference with .420 @ 2400 fps and above .415 between 2400 and 2000 fps .395 between 2000 and 1750 fps .380 @ 1750 fps and below.
If there were a 200 yard zero on these rounds, their 1000 yard drops, and 10 MPH full value wind would be as follows.
I'll pick an altitude of 2650 feet MSL and 50 F.
77 SMK, 39.7" (goes subsonic before the 900 yard line) windage 130.9"
77 TMK, 36.7" (goes subsonic just past the 1000 yard line) windage 116.1"
80 SMK, 36.3" (goes subsonic just past the 1000 yard line) windage 110.2"
80.5 Berg, 34.1" (goes subsonic just past the 1100 yard line) windage 98.8"
The 73 ELDM 35.5" (goes subsonic at 975 yards) windage 118.7"
(Staying sonic is important where matches use eTargets since they won't mark a subsonic bullet.)
So the TMK is pretty good for a magazine length bullet, and helps split the difference to the bullets like the Berger 80.5 and the SMK 80, which are both traditionally loaded long for the 600 yard XTC stages or Midrange matches where Service Rifle competitors run their AR for practice.
Nothing wrong with trying the 73 ELDM either. For games where score is kept on standard targets as in highpower-sling, you will want to pay attention to the accuracy and precision of these loads. It is one thing to shoot rapids at 300 yards, and other to shoot slow fire at 600 or 1000.
There is some force and violence in the AR when the round goes from the mag to the chamber. The longer the round gets, the more leverage there is between the nose and the shoulder. The magazine fed rounds must be sturdy.
In any case, good luck with your AR journey and have fun.
