Thread: Point of impact trouble shooting

G'day team,

Had an interesting issue during a short range session yesterday. Was re-testing a load that had previously performed well for me (~0.5moa). This was following a brief hiatus from reloading/range shooting so I had taken the action out of the stock to give everything a clean and check it all over. Some info:
- Caliber: 7mm Rem Mag
- Rifle: Mauser M12 Max in factory wooden stock
- Load: 162gr ELDX / AR2225 / Norma brass on 3rd firing / Federal large magnum primers
- Issue: Point of impact shifted significantly but consistently over 10 rounds

Image below shows the last 7 rounds fired in order of the horribly drawn numbers in each of the quadrants. The first three shots fired also fell in the groups shown here relative to the target but were on a different piece of paper. Strings were fired in 3, 3, 4 with ample time between each for barrel to cool. I checked the barrel after the last string (4 shots) and it wasn't hot enough for concern. A mate and I have discussed the result and we think this may be down to the stock/action being seated imperfectly after I had cleaned and checked everything; however, I'd like to crowd source all of your thoughts for anything else to consider if it happens again. Anyway, let me know your thoughts - very interested to hear.

Cheers,
Elliott

First thing to eliminate with POI shifts is scope and scope mounts. Take scope off, re tighten everything, reinstall and sight in. Until this is eliminated as a potential source of variation I wouldn't touch anything else.

What Makros said.
Just tightening the scope rings and bases onto the picatinny rail on my .22lr shifted my POI 0.3mil right last week.

Maybe take it apart again and take extra care putting it back together again,could be crumb of bedding under block etc... not familiar with your particular bedding system but a moving group or double grouping is OFTEN something sitting in place for few shots then moving somewhere else for few then moves again.

Cheers team! First thing I did was check scope rings and bases. They were all torqued up to spec. Should have said that in the post sorry.

@Micky Duck that's where we got to as well and have started with that. Couldn't find anything specific to put the blame on but may not have been careful enough first time around.

Also.did you perhaps change positions between groups???

After looking at the group, I was thinking the same as what Micky wrote, before I read it. Reading your statement about the scope being correctly torqued, it sounds like you would have also checked torque on the action screws. Other things to check is:

Are you using a suppressor and was it done up tight?
What scope are you using?, is it near limit of adjustment in either plane? could it have loose internals?
It doesn't look like inconsistent reloading, but possibly worth checking with some factory ammo to eliminate that variable.
What sort of rest were you shooting off, this can affect POI.

@Micky Duck perhaps inadvertently but but not significantly and the POI was changing within groups. Certainly something I can be more conscious of though.

@longshot suppressor was done up tight. Scope is a vx3 - I'll definitely check limits of adjustment, thanks! Not sure how to check internals? Factory ammo check is a good idea. I've got some I can use. And shooting off bipod and rear bag, which I've done for a long time without this issue.

There isn't much you can (or should) do to check internals, check scope with a boresighter between shots and listen for rattle noises is the only things I can think of. Or try a different scope.

Some scopes, usually the cheaper ones, can get a bit wobbly inside if you have to wind either adjustment all the way one way or the other.


I haven't done much range shooting with a bipod, I usually use front and rear bags, but I have heard that a bipod on a hard surface can sometimes cause issues.

Were you shooting with a head or tail wind?

@Bol Tackshin yep there was actually a reasonable tail wind. Reckon that could have affected it?

It's possible, and the shift in POI may indicate changing wind conditions which is why they are clustered. Tail wind typically pushes the group upwards. What was the speed, and what was the range? If it is 100m. Then the wind would have needed to be pretty strong.

@Bol Tackshin Yeah it was 100yd and wind was blowing but was in a relatively sheltered valley. Load is quite warm - got them going over 3000fps.

Shooting off bi pod or bags? Whats the barrel channel like?

@blip bipod with rear bag. What do you mean re barrel channel? Checked that it was free floating and clear of debris etc if that's what you mean?