Zeroing SKS scope

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e123456

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Hi,
I have NcStar 3x9-42 scope on Choate mount on my sks.
Did my best to zeroing it just shooting as usual using sand bag.
This week nice dude at my range let me use his rifle rig, where you install you rifle so it does not move, point to the middle and slowly pull the trigger.
So I zeroed it well using that thing, got a good grouping around 10, gave it back and started shooting as usual (sandbag).
To my surprise, all my holes now appear in the top left corner of the paper.
When another person shoot it, same result, so it is not me.
I re-zeroed it without that rig, by just shooting it - and everything became normal for me and for another person.
What was that and why??
 
There may be a simple reason: when held absolutely rock steady, your rifle put all its shots at one place. Once you changed the support, it changed its vibration modulus and it resulted in a change of impact point.
Maybe your stance changed and your grip too thus contributing to that group shift.
Or... your scope changed its zero, which can happen more often on low-priced optics (and sometimes on defective high-priced ones, too)...
Your Choate mount is one of the few good mounts for SKS scoping so this can be put out of the equation.
PP. :)
 
POI vs POA will be different between groups fired from a vise-type machine rest (where the rifle is gripped tightly and recoil is restrained), and groups fired hand-held on a sandbag rest. Notice that the rifle will recoil differently.

As well, a sandbag-rested rifle (even if sandbagged both front and butt) still vibrates/moves as the shooter breathes and the trigger is squeezed. Obviously a machine-rested rifle will not move when trigger is pulled, or the shooter breathes.

The reason you are shooting high, when benched, is that human hands are not as firm and solid as a machine rest, so the rifle will recoil higher when benched...so the POI is higher.

Printing left could be result of some torque as the bullet travels down the bore. Or the way we hold the rifle stock, we are allowing the rifle to recoil upwards and slightly to the left. Haven't analyzed this one yet. It doesn't take much barrel movement to throw off POI.
 
Thank you, make sense.
But then why do people use those stands to zero their rifles?
And does it mean if I install a bipod, I will have to re-zero it again as it recoils differently with the rig / sandbag / bipod? Very strange to me.

easyrider604 said:
POI vs POA will be different between groups fired from a vise-type machine rest (where the rifle is gripped tightly and recoil is restrained), and groups fired hand-held on a sandbag rest. Notice that the rifle will recoil differently.

As well, a sandbag-rested rifle (even if sandbagged both front and butt) still vibrates/moves as the shooter breathes and the trigger is squeezed. Obviously a machine-rested rifle will not move when trigger is pulled, or the shooter breathes.

The reason you are shooting high, when benched, is that human hands are not as firm and solid as a machine rest, so the rifle will recoil higher when benched...so the POI is higher.

Printing left could be result of some torque as the bullet travels down the bore. Or the way we hold the rifle stock, we are allowing the rifle to recoil upwards and slightly to the left. Haven't analyzed this one yet. It doesn't take much barrel movement to throw off POI.
Click to expand...
 
And does it mean if I install a bipod, I will have to re-zero it again as it recoils differently with the rig / sandbag / bipod? Very strange to me.
Click to expand...

In all probability, yes. But every rifle is different. Best way to zero is to use the kind of hold or rest you'l be using for your specific rifle. Like bench rest rifles should be zeroed on a similar bench rest. IPSC pistols should be zeroed for the usual weaver or isosceles stance/holds. bullseye pistols should be zeroed one hand only.

Now I do not know of any particularly useful need for a machine rest, except to determine the best possible groups obtainable from a particluar firearm, for comparison or tuning purposes, which means eliminating the human error factor.
 
ele2001 said:
Hi,
I have NcStar 3x9-42 scope on Choate mount on my sks.
Did my best to zeroing it just shooting as usual using sand bag.
This week nice dude at my range let me use his rifle rig, where you install you rifle so it does not move, point to the middle and slowly pull the trigger.
So I zeroed it well using that thing, got a good grouping around 10, gave it back and started shooting as usual (sandbag).
To my surprise, all my holes now appear in the top left corner of the paper.
When another person shoot it, same result, so it is not me.
I re-zeroed it without that rig, by just shooting it - and everything became normal for me and for another person.
What was that and why??
Click to expand...

If you've got the Mark III scope, it has a bullet drop compensator. This is the outer ring of the Elevation turret that spins freely. It's marked 1 x100 thru 5 x 100 and you can set it at the specific range you're shooting so that you can aim straight on. Trouble with these is that they spin too easily which could explain your issue with elevation. Read your manual or go to the NCStar website to get a better understanding of this feature.

You may be pulling your shots to the left which would explain the other part of your issue. The SKS trigger is heavy and not very crisp which leaves you wondering if/when it's ever going to fire. Before I had my trigger done I found it to be way too stiff and crunchy. I would regularly pull shots not from flinching, but from actually pulling the trigger, lol!

Hopefully this helps :)
 
Yes, I know about that compensator, it is and was all the time in the same position, so it is not the issue for sure.
I have to agree that trigger suks. Need to do something about it, not sure yet what can I do or shall I give it to an expert.

Can not believe I am the only one who used such a rig - nobody had a problem like mine which indicates it is really a problem for me or this is normal for everybody, which means I leave it as it is and just keep sending my bullets downrange using sandbags?

gps said:
If you've got the Mark III scope, it has a bullet drop compensator. This is the outer ring of the Elevation turret that spins freely. It's marked 1 x100 thru 5 x 100 and you can set it at the specific range you're shooting so that you can aim straight on. Trouble with these is that they spin too easily which could explain your issue with elevation. Read your manual or go to the NCStar website to get a better understanding of this feature.

You may be pulling your shots to the left which would explain the other part of your issue. The SKS trigger is heavy and not very crisp which leaves you wondering if/when it's ever going to fire. Before I had my trigger done I found it to be way too stiff and crunchy. I would regularly pull shots not from flinching, but from actually pulling the trigger, lol!

Hopefully this helps :)
Click to expand...
 
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