So about a month ago I posted on here that I was having trouble zeroing my gun, and that at 50m it was 4.8in low with the elevation adjustment maxed out. Well I kept working on it, and even did some math on it. It turns out, the barrel and receiver were both out of spec! This was on a BCM scratch and dent upper, and Spikes barrel.
The combination of the two together gave the barrel a negative angle in relationship to the optic. Normally as you'd expect, the barrel has a positive angle so that the path of the round eventually crosses the line of sight of the optic, then goes over, then comes back down and continues downward. We adjust the optic to achieve the desired zero. With this combo however, the angle was negative by 8.4MOA. This meant that with a sight height of 2.5in, the line of sight of the optic and the path of the bullet could never intersect!!!! Literally it's impossible to zero it. Your dot would always be above where your round would impact from point blank and out. Here's a table to give you an idea of what it was doing:
So I've swapped out both the barrel and upper receiver. It solved the problem and I've got it zero'd at 292m which is the max point blank range for my cartridge that I'm using (Factory Remmy 125gr OTM 300 Blackout Supersonic)
I was curious, has anyone else ever seen something like this? I'm baffled!
The combination of the two together gave the barrel a negative angle in relationship to the optic. Normally as you'd expect, the barrel has a positive angle so that the path of the round eventually crosses the line of sight of the optic, then goes over, then comes back down and continues downward. We adjust the optic to achieve the desired zero. With this combo however, the angle was negative by 8.4MOA. This meant that with a sight height of 2.5in, the line of sight of the optic and the path of the bullet could never intersect!!!! Literally it's impossible to zero it. Your dot would always be above where your round would impact from point blank and out. Here's a table to give you an idea of what it was doing:
| Range | Drop | Drop | Velocity | Mach | Energy | Time |
| (m) | (in) | (MOA) | (ft/s) | (none) | (ft•lbs) | (s) |
| 0 | -2.5 | *** | 2223 | 1.948 | 1371.4 | 0 |
| 5 | -2.6 | -45.9 | 2209.9 | 1.936 | 1355.2 | 0.007 |
| 10 | -2.8 | -24.3 | 2196.8 | 1.925 | 1339.2 | 0.015 |
| 15 | -3 | -17.2 | 2183.7 | 1.913 | 1323.3 | 0.022 |
| 20 | -3.2 | -13.8 | 2170.7 | 1.902 | 1307.6 | 0.03 |
| 25 | -3.4 | -11.8 | 2157.7 | 1.89 | 1292 | 0.037 |
| 30 | -3.6 | -10.5 | 2144.8 | 1.879 | 1276.6 | 0.045 |
| 35 | -3.9 | -9.7 | 2131.9 | 1.868 | 1261.3 | 0.053 |
| 40 | -4.2 | -9.1 | 2119.1 | 1.857 | 1246.1 | 0.06 |
| 45 | -4.5 | -8.7 | 2106.3 | 1.845 | 1231.1 | 0.068 |
| 50 | -4.8 | -8.4 | 2093.5 | 1.834 | 1216.3 | 0.076 |
| 55 | -5.2 | -8.2 | 2080.8 | 1.823 | 1201.5 | 0.084 |
| 60 | -5.5 | -8.1 | 2068.2 | 1.812 | 1187 | 0.092 |
| 65 | -5.9 | -8 | 2055.5 | 1.801 | 1172.5 | 0.1 |
| 70 | -6.4 | -7.9 | 2043 | 1.79 | 1158.2 | 0.108 |
| 75 | -6.8 | -7.9 | 2030.5 | 1.779 | 1144.1 | 0.116 |
| 80 | -7.3 | -8 | 2018 | 1.768 | 1130.1 | 0.124 |
| 85 | -7.8 | -8 | 2005.6 | 1.757 | 1116.2 | 0.132 |
| 90 | -8.3 | -8.1 | 1993 | 1.746 | 1102.3 | 0.14 |
| 95 | -8.9 | -8.2 | 1980.4 | 1.735 | 1088.4 | 0.149 |
| 100 | -9.5 | -8.3 | 1967.8 | 1.724 | 1074.6 | 0.157 |
So I've swapped out both the barrel and upper receiver. It solved the problem and I've got it zero'd at 292m which is the max point blank range for my cartridge that I'm using (Factory Remmy 125gr OTM 300 Blackout Supersonic)
I was curious, has anyone else ever seen something like this? I'm baffled!
