I have looked around the internet for info on 220gr .308 SMK for long range target shooting but mostly it says it uses too much case capacity and lowers muzzle velocity too much.
I generated QuickLOAD propellant tables for the 175 and 220gr SMK from a .308 Win using 62,000psi as max pressure (.308 SAAMI), 2.8" COL from a 24" 1:10 twist barrel and used the highest velocity from the tables for each bullet.
I realize QuickLOAD data isn't gospel but it should do a pretty good job to compare these two loads. One load is "Dangerous" and the other is "Near Maximum" so I know these aren't loads we'd actually use but I'm using the data as an equalizer between the two loads so we can compare exterior ballistics. The key is both loads are QuickLOAD max velocity loads.
175gr SMK Max Muzzle Velocity 2800fps
220gr SMK Max Muzzle Velocity 2503fps
I then used the fastest muzzle velocity from the two propellant tables to generate range cards using Hornady's very accurate 4DOF ballistic calculator & G7 BCs to compare long range performance.
1000 yards
175gr SMK at 2800 fps MV
1236 fps @ 1000 yards (104 fps slower)
593.5 ft-lbs retained energy
9.67 milliradian (33.24 moa) come up
2.99 milliradian (10.28 moa) 10 mph cross-wind (24% more drift)
220gr SMK at 2503 fps MV
1340 fps at 1000 yards (8% faster)
877.0 ft-lb retained energy
10.46 milliradian (35.96 moa) come up
2.42 milliradian (8.32 moa) 10 mph cross-wind
At 1000 yards the 220gr SMK is 8% faster and the 175gr SMK gives us 24% more wind drift and spin drift.
The 220gr MatchKing is stable from a 1:10 twist barrel with a gyroscopic stability (Sg) of 1.64 at the muzzle (1.5 is minimum for stable long range flight). If the barrel twist rate was 1:12 the Sg would be unstable at 1.14 so at least a 1:10 twist barrel is needed for .308 220gr bullets at long range.
The 220gr SMK was 297 fps slower than the 175 at the muzzle.
For target shooting we know range so bullet drop isn't as critical as wind drift. The range cards show the big 220gr stays supersonic about 100 yards farther down range. The 175gr give us 24% more wind drift and spin drift at 1000 yards and beyond.
Has anyone tried a hot Reloader 17 load with 220gr SMK for 1000 yards or longer?
Photo by robrob. All rights reserved
I generated QuickLOAD propellant tables for the 175 and 220gr SMK from a .308 Win using 62,000psi as max pressure (.308 SAAMI), 2.8" COL from a 24" 1:10 twist barrel and used the highest velocity from the tables for each bullet.
I realize QuickLOAD data isn't gospel but it should do a pretty good job to compare these two loads. One load is "Dangerous" and the other is "Near Maximum" so I know these aren't loads we'd actually use but I'm using the data as an equalizer between the two loads so we can compare exterior ballistics. The key is both loads are QuickLOAD max velocity loads.
175gr SMK Max Muzzle Velocity 2800fps
220gr SMK Max Muzzle Velocity 2503fps
I then used the fastest muzzle velocity from the two propellant tables to generate range cards using Hornady's very accurate 4DOF ballistic calculator & G7 BCs to compare long range performance.
1000 yards
175gr SMK at 2800 fps MV
1236 fps @ 1000 yards (104 fps slower)
593.5 ft-lbs retained energy
9.67 milliradian (33.24 moa) come up
2.99 milliradian (10.28 moa) 10 mph cross-wind (24% more drift)
220gr SMK at 2503 fps MV
1340 fps at 1000 yards (8% faster)
877.0 ft-lb retained energy
10.46 milliradian (35.96 moa) come up
2.42 milliradian (8.32 moa) 10 mph cross-wind
At 1000 yards the 220gr SMK is 8% faster and the 175gr SMK gives us 24% more wind drift and spin drift.
The 220gr MatchKing is stable from a 1:10 twist barrel with a gyroscopic stability (Sg) of 1.64 at the muzzle (1.5 is minimum for stable long range flight). If the barrel twist rate was 1:12 the Sg would be unstable at 1.14 so at least a 1:10 twist barrel is needed for .308 220gr bullets at long range.
The 220gr SMK was 297 fps slower than the 175 at the muzzle.
For target shooting we know range so bullet drop isn't as critical as wind drift. The range cards show the big 220gr stays supersonic about 100 yards farther down range. The 175gr give us 24% more wind drift and spin drift at 1000 yards and beyond.
Has anyone tried a hot Reloader 17 load with 220gr SMK for 1000 yards or longer?
Photo by robrob. All rights reserved
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