I thought this was looooong archived.  Lots of good info in here as usual, but it is a Molon thread.

It is reasonable to expect your next group to be “more centered”.  Your idea is the basis for zeroing iron sights or optics.

Unfortunately, you’ll always have some variation of that group center.  Environmental issues, shooter issues (fatigue is a big one) and even trivial variations in powder weight will keep you from having a “perfect” group all the time.

But yes, adjusting your sights to your POI is a good practice.  Just remember that you’re adjusting for THAT load…

I'm not certain what it is that you're asking, but making adjustment to your sights is not going to change the average mean radius of a load.

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Sorry I was not clear. I was not asking about changing the average mean radius. I was asking about taking your average mean radius, whatever it calculated to be, and using the calculated center of the group the average mean radius was derived from to adjust your ZERO to coincide the center of that group so that the Zero predicts the best POA vs POI relationship given your round, barrel, ability, etc.

I was asking about a shooting 10-round group and then calculating the center of that 10-round group to determining how far that group center is from my POA. Then, armed with the x and y differential, adjust my optic to move my zero such that it matches the center of my group, i.e., if the group center is calculated to be 1" left and 2" low relative to the 100yd bullseye I was aiming at, is it reasonable to adjust the zero by 1moa and 2moa respectively?  

If the concept is good, is a 10-round group the right size to use to calculate and shift my zero? If YES, how many iterations do you think it would take? Alternatively, would you suggest shooting 3 10-round groups, overlaying them and use the 30-round group-center to adjust my Zero? If NO, why?

I just want to add that your contributions to this forum are fantastic and much appreciated.

I would get a better barrel before adjusting for heat deflection if your barrel warps as it heats up.

Barrels should only open up groups as they heat up, but not deflect.

If that's what you're talking about.

Sorry, I edited my post to add, I hope, some clarification. Basically, just asking if using the calculated center of a 10-round group or 30-round composite group (whatever that group pattern is) to adjust my optic's zero, would be an efficient way to get the best average POA vs POI results for a given rifle, load, optic, etc.

I can't really see why not.

Of course.  For expediency when zeroing with an optic I fire a single round, then adjust the windage and elevation to move the reticle from the point of aim to that single shot and then fire 10-shot groups to refine.





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It seemed to make sense to me. My groups to not look like yours. I'm talking about 10.5" and 12.5" carbines, both suppressed and with 1x (1 moa clicks) prisms with 3x multipliers. The round is Federal Fusion MSR 62gr. My groups are bigger but pretty consistent. When I read this thread, it made me wonder if calculating the center of 10-round groups then re-zeroing to that position using the difference between the POA and calculated center of the POI (in MOA) would give me the optimum, minimum POI spread around my POA. It seemed zeroing to the calculated center would yield the minimum deviation from POA that my particular carbine, load, POI pattern and I can typically obtain. Maybe with these combinations there would be little benefit, but it might be fun (I love the physics behind it) and good practice as I would do a 14" BRT barreled, suppressed carbine next with a 1-8 x 24 LPVO (1/4 moa adjustments) shooting 77gr OTM LR Mod 1.

This thread doesn’t make me care about three-shot groups any more or less than I already did it.

But it does make me miss Stick.

I always thought that 3 and 5 shot groups were born out of hunting rifles with blind magazines and skinny barrel profiles that might not have been stress relieved properly.

This is a testament to how far barrel making has come.

I went to the range yesterday and sighted in my suppressed 10.5", 1:7, BA barreled SBR and my suppressed 12.5", 1:7, BRT barreled SBR with Federal Fusion 62 gr MSR. Both were equipped with PA 1x Micro Prism scopes and Vortex Micro 3x multipliers. I sighted in at 100 yard. After finding this post, I shot 10-round groups and found I did not chase the zero like I have done with 3-round groups.

After sighting in, using the Federal MSR zero, I shot addition 10-round groups with both SBRs using Australian Outback, .223 REM, 69gr Sierra Matchking HPBT and PPU .223 Remington Match 75gr HPBT ammo.

When I got home, I read in one of these posts about someone using Ballistic-X. I checked it out and put it on my iPhone. Luckily, I had saved the 4 targets shot with the AO and PPU ammo and made them my first Ballistic-X projects. It was great and educational. I can't do the 30-round overlays, yet, but even my 10-round groups were beneficial.

I am so grateful Molon wrote this and that I found it. I learned a lot and hope to put it to good use. I also appreciate the other posts contributed by fellow ARFCOMMERS.
Thank you all.

My next adventure will be to sight in my suppressed, 14.0", pinned &welded, BRT barreled mini-recce with Vortex 1-8x24, BDC3, Strike Eagle and see how a 10-round group and the ATZ features work.

Here are the photos of my first four 10-round efforts with the SBRs. If anybody sees anything amiss, please let me know. By the time I got around to shooting these, my 71-year-old eyes were getting tired and it was getting hard to put the Chevron tip on the bull as well as I would have liked. The rifles were supported with a bipod on a concrete shooting bench.