.308 with 175gr SMK powder choice
- Thread starter Shooter83
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Shooter83
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What speeds are you getting?
Viht N150 is the obvious, and very good, choice. You will struggle with the 175gn SMK and a 24-inch barrel at 1,000 yards though. (Been there and got that very frustrating T-shirt many years ago!) You can just get away with it ballistically, if your rifle allows really heavy loads. (Note though, that really heavy loads quickly kill standard large primer brass, and if loaded up high enough, N150 kills barrels very quickly too.) The average G7 BC for the 0.308 175gn SMK is 0.243 (Litz: Performance of Rifle Bullets). Under standard ballistics conditions (59-deg F / 29.9 inches mercury pressure) 2,650 fps MV which is respectable for this combination, sees 1,117fps retained velocity at 1,000 yards - ie below the speed of sound. In practice, you want to be comfortably above the speed of sound and the worst of the turbulent transsonic speed zone at the target - the US Army identified 1,225 fps retained velocity as key a long time ago with 30-cal tangent ogive bullets and that measure is still an excellent one today. The 175 SMK needs an MV of just over 2,820 fps to achieve that. It's an excellent bullet, but high-drag / low-BC by today's standards.
The problem you face with a 2,600 odd fps MV and this bullet is that with MV variations, some bullets are barely supersonic at 1,000 and others have just dropped through the barrier into subsonic flight. This variability usually sees poor results. In my rifle's case, 800 yard results were excellent, 900 saw a large performance drop, and 1,000 was very poor. This is in line with what US military users say of the M118LR sniper round that uses this bullet. The US Army says its rifle and this cartridge are great at 1,000; the US Marines - who take rifle marksmanship very seriously indeed - report more honestly that performance falls off a cliff beyond 800 metres. The M118LR has a nominal MV of 2,580 fps and that needs a stiff load in the standard M24 barrel.
In my case, the proper answer was to spend the money on a proper long-range 308 rifle; the short-term solution was to fire the affordable and old-fashioned, but very effective, 190gn SMK over a stiff load of Viht N550. (You can also use N150 with this bullet, but as I said, very heavy N150 loads are not nearly as easy on barrels as most people believe.) The 190 SMK is a superb performer in transsonic and trans sound barrier conditions and was a favourite of Match Rifle shooters (1,000, 1,100, and 1,200 yard stages with 308 Win rifles) before today's heavy VLD and Hybrid form bullets appeared.
The problem you face with a 2,600 odd fps MV and this bullet is that with MV variations, some bullets are barely supersonic at 1,000 and others have just dropped through the barrier into subsonic flight. This variability usually sees poor results. In my rifle's case, 800 yard results were excellent, 900 saw a large performance drop, and 1,000 was very poor. This is in line with what US military users say of the M118LR sniper round that uses this bullet. The US Army says its rifle and this cartridge are great at 1,000; the US Marines - who take rifle marksmanship very seriously indeed - report more honestly that performance falls off a cliff beyond 800 metres. The M118LR has a nominal MV of 2,580 fps and that needs a stiff load in the standard M24 barrel.
In my case, the proper answer was to spend the money on a proper long-range 308 rifle; the short-term solution was to fire the affordable and old-fashioned, but very effective, 190gn SMK over a stiff load of Viht N550. (You can also use N150 with this bullet, but as I said, very heavy N150 loads are not nearly as easy on barrels as most people believe.) The 190 SMK is a superb performer in transsonic and trans sound barrier conditions and was a favourite of Match Rifle shooters (1,000, 1,100, and 1,200 yard stages with 308 Win rifles) before today's heavy VLD and Hybrid form bullets appeared.
I have been working with (the dreaded, double based) LOVEX D073.6 for 175 grain 308 loads. They seem to work well to 1000 at my altitude when fired in the 2700-ish range. Alternatively, I use the US military load of 41.745 grains of IMR 4064 for about 2600 fps.
What works and doesn't work at 1000 in a 308 largely depends on the conditions. The last time my girl friend shot steel at our range she was spanking a 12" plate at 1100 yards with 168 grain Hornady Match at 2640 fps. It was the perfect day, weather wise, to accommodate that load. Another day, different weather, and she might have been struggling to make a hit. ~Muir
What works and doesn't work at 1000 in a 308 largely depends on the conditions. The last time my girl friend shot steel at our range she was spanking a 12" plate at 1100 yards with 168 grain Hornady Match at 2640 fps. It was the perfect day, weather wise, to accommodate that load. Another day, different weather, and she might have been struggling to make a hit. ~Muir
Many people here in the UK don't understand this issue and tell you that such & such is possible because they saw Americans doing it on YouTube videos (and an Australian couple who do remarkable things with a standard 243 Win Howa M1500 Varmint rifle and its 10-inch rifling twist at beyond 1,000 yards amongst other feats). What isn't made clear in most such videos is the range's elevation above sea level and ambient temperatures, most (all?) of which are very high.
When I shot in the F-Class Worlds at Raton, New Mexico in August 2013, c. 7,500 ft ASL and over 90-deg F, my elevation rise over a 100 yard zero was reduced by more than 6-MOA at 1,000 yards - a huge difference same as aiming more than 5ft lower - than I would have used at Diggle. That was 308 Win and the 155.5gn Berger BT Fullbore at 3,100 fps. Even back in the UK, my Diggle (987 ft ASL) 1,000 yard elevation setting was 1-MOA lower than for rather lower lying Bisley with this combination, despite Diggle's well known propensity for low temperatures. AFAIK, we have no shooting in the British Isles at any real elevations. Blair Atholl's Glen Tilt range is the highest I know of and most field shooting even in Wales and Scotland won't exceed that by much if at all even on the higher slopes. WMS Firearms Training's Welsh field ranges may be higher than Glen Tilt, but neither comes anywhere near those of the upland desert ranges you see in the American videos.
Sadly, I've seen too many people, usually as visitors, turn up at Diggle 1,000 yard matches in years past with off the shelf 308 varminters and similar who had a frustrating time and went home without ever getting on the target frame. Nowadays we don't allow it. Apart from the disruption to other competitors, the range now uses Shot Marker electronic targets that use the supersonic 'crack' to place the shot, so subsonic shots aren't read even if 'on target'. (Every competitor also has to demonstrate their zero and ballistic competence by shooting at things on the backstop before being allowed onto the targets - it's too easy to damage the target microphones and wiring at this distance.)
I shot in the lever gun championships at Raton in the mid eighties. Even the 2500 ft elevation difference I experienced had me frantically filing on my sights after sight in.
Yes. If you haven't experienced the effect of elevation it's hard to relate too. I have lived and done load development in elevations ranging from 70 ft below sea level too 5500 ft above. You notice things...~Muir
Yes. If you haven't experienced the effect of elevation it's hard to relate too. I have lived and done load development in elevations ranging from 70 ft below sea level too 5500 ft above. You notice things...~Muir
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