Issues with offset rifle scopes?

[meles meles]

We have a scope (6x42 Pecar) mounted on a Swiss K31. As the rifle loads from a clip, the scope mount is offset to the side, about 1.5" from the bore axis. We set it up for the sight axis to remain parallel to the bore axis rather than seeking a convergence at some set distance. As Pops said above, being 1.5 " to one side from the point of aim may seem a lot at 100 yards but as the range increases it starts to disappear into the general noise. If you wish, you can always aim off by the horizontal separation, in our case 1.5". We frequently use the K31 for 300 and 600 yards shoots and have no problems keeping all shots within the bull. Well, the rifle doesn't anyway...

[Popsbengo]

5 minutes ago, meles meles said:

We have a scope (6x42 Pecar) mounted on a Swiss K31. As the rifle loads from a clip, the scope mount is offset to the side, about 1.5" from the bore axis. We set it up for the sight axis to remain parallel to the bore axis rather than seeking a convergence at some set distance. As Pops said above, being 1.5 " to one side from the point of aim may seem a lot at 100 yards but as the range increases it starts to disappear into the general noise. If you wish, you can always aim off by the horizontal separation, in our case 1.5". We frequently use the K31 for 300 and 600 yards shoots and have no problems keeping all shots within the bull. Well, the rifle doesn't anyway...

Have I seen this rifle?  Do you shoot left eyed or do you can't your head over and use your right eye? 

[Popsbengo]

It's also important to ensure that an offset scope is accurately measured for hight above the barrel centre line too so as to not introduce a zero angle error.

By the way, I noticed that "Shooter" app allows the user to enter scope horizontal offset as well as height.  Potentially useful for @That bald headed Geordie

[Webley]

https://www.guntrader.uk/guns/rifles/bsa/bolt-action/303/smle-mk-iii-191021114617487

A reproduction of an smle sniper with offset scope. Just for general interest.

Matt

[That bald headed Geordie]

3 hours ago, Popsbengo said:

It's also important to ensure that an offset scope is accurately measured for hight above the barrel centre line too so as to not introduce a zero angle error.

By the way, I noticed that "Shooter" app allows the user to enter scope horizontal offset as well as height.  Potentially useful for @That bald headed Geordie

Hi,  just checked Shooter app on my phone and yes it gives me the option to enter my zero height and zero offset,  so will do some checks once I get my offset mounts and get some zeroing done.

Cheers

BHG.

Edited May 17, 2020 by That bald headed Geordie
sentence correction.

[Popsbengo]

28 minutes ago, That bald headed Geordie said:

Hi,  just checked Shooter app on my phone and yes it gives me the option to enter my zero height and zero offset,  so will do some checks once I get my offset mounts and get some zeroing done.

Cheers

BHG.

that's grand.  The app will give you proper calculations taking into account other factors - my bit of a table is too simplistic.  Don't know whether you need a 'minus' sign for left offset in Shooter??

[KABOOM]

16 hours ago, Popsbengo said:

I be interested to understand how the M1C/D was zeroed due to the issue of introducing a "windage angle" correct only at the zero distance.  Did the military issue a standard drop chart that included instructions for dialing out the horizontal error at differing distances or did they adopt the more obvious practice (to me) of setting the scope parallel to the barrel and just allowing for a fixed offset at all ranges?  Obviously at more distant ranges the parallel error becomes largely irrelevant ( 2" at 100yds is a 'large' error where as, 2" at 600yds is irrelevant as it's lost in the general variability in the system)

if I knew I would tell you, Never have seen the tech manuals or instructed on that system, Time to ponder just where that info exists. Im curious too and possibly the NRA has info in the USA, they may have published some in our monthly magazine in the last year.Back to work Monday and if nothing else time to think about where I may have stashed that months American Rifleman. Best Wishes for good shooting.

[meles meles]

On 5/17/2020 at 10:58 AM, Popsbengo said:

Have I seen this rifle?  Do you shoot left eyed or do you can't your head over and use your right eye? 

The K31 sight mount is offset to starboard so using it with your left eye would be awkward. It has the benefit that iron sights can be used too, so we tend to have the irons zeroed for 300 yards and the scope for 600. Another mount exists that puts the scope over the rifle centreline but that is quite high to allow cases to eject well and obscures the iron sights. 

The fiendishly cunning Swiss developed another system for their sniper version of the K31, the  Zielfernrohr Karabiner 55 (ZfK55). In this, the action was canted 15 degrees within a slightly widened stock to allow the cases to be ejected cleanly whilst placing the scope on the rifle centreline using a mount offset to port. It had an integral bipod too, along with a muzzle brake and a dinky little case to carry the scope in.

 

[KABOOM]

On 5/17/2020 at 5:31 AM, Popsbengo said:

I be interested to understand how the M1C/D was zeroed due to the issue of introducing a "windage angle" correct only at the zero distance.  Did the military issue a standard drop chart that included instructions for dialing out the horizontal error at differing distances or did they adopt the more obvious practice (to me) of setting the scope parallel to the barrel and just allowing for a fixed offset at all ranges?  Obviously at more distant ranges the parallel error becomes largely irrelevant ( 2" at 100yds is a 'large' error where as, 2" at 600yds is irrelevant as it's lost in the general variability in the system)

I found reference in a magazine article the m1C/D was zeroed at between 200-300 yds to help with ever problematic windage nothing more precise noted. 

[Popsbengo]

37 minutes ago, KABOOM said:

I found reference in a magazine article the m1C/D was zeroed at between 200-300 yds to help with ever problematic windage nothing more precise noted. 

That's very interesting, kudos for digging that info out.  I understand that most sniper 'action' took place at moderate distances so that would make good sense.  The offset at >200 would be of little worry, dead is dead.

[KABOOM]

2 hours ago, Popsbengo said:

That's very interesting, kudos for digging that info out.  I understand that most sniper 'action' took place at moderate distances so that would make good sense.  The offset at >200 would be of little worry, dead is dead.

Correct, I have never been a sniper however I have read accounts of those who where and the question of " what is the preferred range to engage" the reply I agree with is the closer the better. Another way to express I read from one the Lords of The Admiralty  gunnery gunnery gunnery HIT the target all else is twaddle. I may have some error in the quote and do not recall which Lord. Best wishes for good shooting.

[That bald headed Geordie]

The Chinese offset mounts arrived this morning and put them on my rifle.

Will try them out sometime but could have done with them being a little longer and further out to the left as I still have to tilt my head to the right which is not perfect.

I did give them a dip in Domestos as they came from China with a Wuhan stamp on them.

Quality seems pretty good and better than expected.

 

 

 

 

[Dellboy]

keep us imformed please   couple of our club members have similar problems

[That bald headed Geordie]

5 minutes ago, Dellboy said:

keep us imformed please   couple of our club members have similar problems

Even if it works for me using my non dominant left eye,  it doesn't mean it will work for everyone,  but it will give me/them a better sight picture. 

I guess the more I use my left eye I should get used to it eventually.

All I can suggest is that they get the correct type of offset mount (mine is good for Picatinny and Weaver rail) to suit whatever is on their rifle and try it.

If I need to move the scope over to the left a little then a local gunsmith to me has offered a possible solution that might make it easier.