Schmidt Rubin K312 scope mounting - bewilderment !

[meles meles]

A while ago, we fitted a Pecar 6x42 scope to our K31 using a side mount from Andy Allwood. First time out, we zeroed it at 300 yards and got some nice tight groups with it. Today we tried it at 100 yards and found it was shooting way low and left - far too much to bring on target by adjusting the scope. Now, to our knowledge, only one thing has changed: today's ammo was GP11 whereas previously we had to use Privi because GP11 wasn't available.

We can understand that a change of ammo might cause the shot placement to rise or fall, but surely it shouldn't change the point of impact to move left or right?

What should we be thinking of changing to bring the GP11 on target ? We plan to stick with the GP11, and usually shoot at 300 yards. We fired a few rounds over open sights and those were pretty much spot on...

[ovenpaa]

My 7mm climbs hight right as I wind the load up.

[meles meles]

What causes that?

[kennyc]

A while ago, we fitted a Pecar 6x42 scope to our K31 using a side mount from Andy Allwood. First time out, we zeroed it at 300 yards and got some nice tight groups with it. Today we tried it at 100 yards and found it was shooting way low and left - far too much to bring on target by adjusting the scope. Now, to our knowledge, only one thing has changed: today's ammo was GP11 whereas previously we had to use Privi because GP11 wasn't available.

We can understand that a change of ammo might cause the shot placement to rise or fall, but surely it shouldn't change the point of impact to move left or right?

What should we be thinking of changing to bring the GP11 on target ? We plan to stick with the GP11, and usually shoot at 300 yards. We fired a few rounds over open sights and those were pretty much spot on...

reload the Prvi for use with the scope, save the GP11 for longer range use with the iron sights, as that is what the sights were zeroed for. I only use the scope for 1000yrds its too much fun with the irons at shorter ranges as to the sights issue, had you removed the scope? I and others have found the mount very good for return to zero on refitting, but I guess you could fit it slightly different on occasion.

[meles meles]

We don't reload...

The scope hadn't been removed between zeroing at 300 yards and shooting at 100 yards, and to our knowledge it hasn't been knocked at all. We expected the point of impact to have shifted vertically with a different ammo type but we're baffled by the lateral displacement.

[M99]

Are both rounds the same weight?

Mike

[meles meles]

Almost. The Privi is claimed to be 174 gns, the GP11 is 174.9 gns - both according to the packets they come in.

[kennyc]

thinking about it, it sounds like you are having problems with crossover, try zeroing the scope at 100 yrds 3/4" right of the POA then move out to 300yrds, the shot should fall low but still 3/4" to the right of POA as the scope is now parallel with the barrel (allowing for wind of course) you may also need to check the mounts to ensure they are true to the rail dovetail, it could be the scope but I would check the other stuff first as I have been caught out with out of line dovetail mounts before.

[meles meles]

Hmm, we're still baffled. Maybe it's because we have a small brain. Are we correct in thinking it may be because the scope isn't mounted parallel to the bore? A problem we have at the moment is that we can't zero the scope at 100 yards because we have run out of adjustment, and we can't shoot at 300 yards to check things out die to the ban on large calibres at Kingsbury.

[ovenpaa]

Badger, have you tried bore sighting it to see where it points at all four extremes of adjustment? Bolt it into a workmate or similar, sight it on a known target by squinting up the bore and then carefully move windage and elevation, what happens?

Regarding the bullets climbing high left on the 7mm it was the only rifle that really did this and at one point I thought I was going mad...