Peter J. Dickinson wrote in rec.guns:
The M1A does great at the 600 yd range but starts to get somewhat iffy at the 1000 yd range. The bullet I'm using is the Sierra 168 hpbt MatchKing at 2800 fps muzzle velocity from a Fulton Armory Peerless grade M1A. Apparently the bullet starts to yaw as it goes subsonic which has a negative effect on accuracy. I've heard the Berger 168 gr LBT has better performance than the Sierra 168 gr MatchKing but is it going to have the same trouble at 1000 yds? Or possibly the Sierra 175 gr MatchKing. I'm told the Sierra 175 gr. MatchKing has a better BC and can be driven almost as fast, reaching the target without going subsonic.
Does anyone have any info they can share concerning bullet selection and long range shooting with the M1A?
For years the "standard" match load for the M1A/M14 class of rifles has been what the military calls "M852." Normal velocity for M852 is 2600 to 2650 feet per second. Attempts to push it much further will soon show up as blown primers. The next symptom is a cracked receiver from the force of the bolt slamming against the back of the receiver. It would be a shame to do that to that fine piece of equipment from Clint.
Some shooters (usually military teams with access to unlimited replacement parts) install barrels with reduced-diameter gas ports on their 1000-yard rifles. This reduces the force of the bolt coming back. But, it doesn't reduce the chamber pressure. The M14 is designed to withstand obscenely over-pressure loads without blowing up in your face. That is not to say that you won't damage the gun by repeated firing of over-pressure loads.
For any long range shooting, one should obtain bullets with the highest Ballistic Coefficient (BC). The reality of shooting a service rifle at 1000 yards is that you are going to have trouble, even with the best rifle and loads, when the wind picks up. For most .308 loads, the subsonic threshold is between 900 and 1100 yards when fired from a gas gun. Bolt guns can reliably maintain supersonic velocities at 1000 yards.
There is a certain amount of coffee-table validity to the notion that yaw increases when the bullet goes subsonic. The theory is that a shock wave just precedes a supersonic bullet. So long as the bullet is supersonic, the relationship between the bullet and the shock wave is constant. When the bullet goes subsonic, the relationship between the bullet and the shock wave changes. The shock wave backs up to the midsection of the bullet, effective ly whacking it in the ass, creating unstable flight. Maybe so. In my experience, subsonic loads have produced respectable accuracy so long as winds are minimal. I've shot some decent scores with subsonic ammo from a service rifle on calm days. But, let the wind pick up, and things go to hell. The empirical reality is that subsonic bullets are MUCH more affected by wind than supersonic bullets - for whatever reason. If you are begin experiencing inaccuracy with extra-hot loads irrespective of wind conditions, I would suggest that it may be due to the fact that you are on the ragged edge in terms of extreme velocity. Rarely are such loads the most accurate choice for a given rifle.
Most 1000 yard highpower matches have few service rifle entries. Of the ones that do show up in that class, a high percentage are military. A bunch more are novices who are learning a hard lesson at the expense of a match entry fee. The rest (few) of us are the die-hards who remember that 190 they shot one day from the 1000 yard line. Realistically, those 190 days are few and far between for civilian shooters.
Stick with the high BC bullets. Be sensible in your pressure limits. And pray for dead calm.
--Gary M. Jeter
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