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Could the burn rate of N560 be a tad on the slow side, resulting in excessive muzzle blast? This could be causing the bullets to yaw (wobble) slightly on exiting the barrel, leading to the iffy groups at 100-250, improving as they re-stabilize further downrange.

Who not try a faster powder such as N160?

My initial thoughts were yaw because a 7mm Rem Mag really needs a 26" barrel to get the best performance and anything less than 24" creates problems of stability.
If it had been an Enfield action then the explanation would have been simple, because it was well known that the flexible action of a rearward locking bolt caused the bullet to be slow to stabilise, which meant that Enfields were quite often more accurate at 1000yds than they were at 600yds.
Mauser actions are the opposite though and it seems strange that the rifle is more accurate at longer ranges which would point to barrel length/rifling twist rate. But even then if the rifling was too slow why is it better with 140grn bullets than 110grn bullets.

Another thing could be barrel harmonics which could be sorted by simply tightening up the front action screw to a different torque, but even then it shouldn't be tighter at 500yds than 250yds.


Something to try Mark...... Wrap a rubber band around the barrel at the front of the for-end and see if it tightens up the groups at 250yds. If it does then move it an inch up the barrel towards you and see if it tightens up or opens out.
G.M.

Graham M,

Another thing could be barrel harmonics which could be sorted by simply tightening up the front action screw to a different torque

That is my line of thought as well, turned out it was the problem with my 270 short mag, though saying that tightening up the front action screw didn't fix the problem.

Blu

Graham M wrote:If it had been an Enfield action then the explanation would have been simple, because it was well known that the flexible action of a rearward locking bolt caused the bullet to be slow to stabilise, which meant that Enfields were quite often more accurate at 1000yds than they were at 600yds.

Can you give a source for this? I've never read anything about bolt stiffness affecting bullet stability to any great degree.

Gaz

*intrigued too*

Having trouble posting a proper reply sign85

Try this

http://staffordshirephoenixrifleandpist ... page_id=82

GazMorris wrote:

Graham M wrote:If it had been an Enfield action then the explanation would have been simple, because it was well known that the flexible action of a rearward locking bolt caused the bullet to be slow to stabilise, which meant that Enfields were quite often more accurate at 1000yds than they were at 600yds.

Can you give a source for this? I've never read anything about bolt stiffness affecting bullet stability to any great degree.

Gaz

This was the accepted "truth" with long range shooting in the past before dedicated target rifles came along. Often Bisley shooters would have 2 target rifles, a Mauser actioned rifle for up to 600 yards and a converted Enfield actioned rifle for longer ranges. This was in the days of issued ammo and when all "target" rifles were re-barrelled ex military rifles.

Chapuis wrote:This was the accepted "truth" with long range shooting in the past before dedicated target rifles came along. Often Bisley shooters would have 2 target rifles, a Mauser actioned rifle for up to 600 yards and a converted Enfield actioned rifle for longer ranges. This was in the days of issued ammo and when all "target" rifles were re-barrelled ex military rifles.

The content of Graham's link is entirely familiar to me, as are the points above regarding people having had different rifles for different ranges and I don't dispute either of these things; however the article does not mention bullet stability and the whole thrust (excuse the bad pun) of the argument has nothing to do with bullet stability but is based around the barrel pointing in slightly different directions when the thing goes bang because of the action and barrel flexing.

Can anyone provide a link or reference explaining the supposed role of bullet stability in this?

Gaz

Apologies for the delay. The local farmer decided to play destruction derby with his tractor and our bloody telephone pole.

The barrel is 24" and i'm using an Ace Ultra suppressor which i used previously with my 280. I'll check the barrel twist tomorrow, but i'm pretty sure its 1:10. Also, please note that the weird effect also happens when using the Ramshot powder.

If it were yaw, wouldn't the bullet holes be larger in the ranges less accurate (shorter ranges)? I'll pop out and try the rubber band trick this weekend.

Thanks for the advice.