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Magnification And Group Size

by Hugh Birnbaum   |  January 3rd, 2011 1

Hugh shoots groups with scopes set on 1.5X, 6X, and 35X to demonstrate the relationship between magnification and group size. Does it make a difference?

Like many shooters, I have always accepted uncritically the notion that, all other factors being equal, increasing scope magnification decreases group size. That’s the conventional wisdom, and I never really questioned it.

The bottom line, for me, is that scope magnification within very broad limits is probably less determinative of group size than is generally believed. As long as the optical sight permits you to place the reticle precisely and repeatably where it needs to be, you should have no problem producing groups as good as your rifle/ammo/skill will allow under prevailing shooting conditions. For those who are not benchrest or extreme-precision shooters, that’s about as good as it gets.


A Remington Model 700 Varmint Special in .223 Rem. with a compact Bausch & Lomb 1.5-6X 20mm riflescope was used to shoot groups at 1.5X and 6X (T). The same rifle with a Leupold 35X Competition scope (B) was used to shoot groups at 35X. Group sizes were more similar than gross differences in magnification would suggest.

I began to have doubts recently while leafing through notebooks of shooting data I have logged over several decades. I was searching for the optimum handload I had worked up for a .223 Rem. varmint rifle that I used primarily as a test bed for evaluating riflescopes. I found the data, and I also found that the 100-yard group sizes the load yielded in years of field testing a wide variety of scopes were strikingly uniform.

With scopes ranging in power from about 4X to 36X, five-shot groups nearly always stayed between 0.625 and 1.00 inch under favorable shooting conditions. In normally careful shooting, as opposed to supermeticulous benchrest competition, for example, there didn’t seem to be any significant group-size penalty associated with the lower-powered scopes. That appeared to contradict the conventional wisdom.

I decided to put the theory to the test. I still have the Remington Model 700 Varmint Special used in compiling the load data and in field testing the scopes. Components for loading its favored ammunition are still readily available.


MAGNIFICATION & GROUP SIZE
SCOPE MAGNIFICATION 100-Yard Accuracy
Group 1 Group 2 Group 3 Group 4
1.5X 0.75 1.0 1.125 0.96
6X 0.625 0.625 1.0 0.75
35X 0.625 0.625 0.875 0.708
A Remington Model 700 Varmint Special chambered in .223 Rem. was used to obtain the accuracy data. Groups were fired from a concrete benchrest using a Sinclair pedestal front rest and a bunny-ear rear sandbag. Three, five-shot groups were fired at each magnification setting.

And I had two riflescopes that would let me hit three significant magnification milestones with just one scope change–an old but sweet Bausch & Lomb 1.5-6X 20mm and a new Leupold 35X Competition model. I loaded a sufficient batch of .223 Rem. cartridges to fire three, five-shot test groups at 1.5X, 6X, and 35X, respectively, with ample rounds left over for sighting-in and fouling shots.

Shooting was done with a Sinclair front rest and a bunny-ear rear sandbag on a concrete shooting bench. The first test series was with the 35X Leupold to be certain the rifle and load were still compatible. Results matched the historical record. I removed the 35X scope and installed the 1.5-6X model and zeroed it. At that point, a wretched, gusting wind developed, and it ended the day’s festivities. I returned to the range a few days later in more stable conditions to complete the test runs at 1.5X and 6X. The groups are detailed in the accompanying chart.

Average group size at 1.5X was 0.96 inch. At 6X it was 0.75 inch. And at 35X it was 0.708 inch. Although it’s undeniable that the 1.5X groups ran about 1/4 inch larger than the others, the difference in group size between the 6X and the 35X series is, in my opinion, insignificant.

  • Doctor Fine

    When I feel anal retentive I never trust three or four groups. My gold standard is ten five shot groups with no excuses or "gimmes." Consecutive. On a dead calm day. To me that is a fair test with pretty tustworthy results.

    My own results with a gun I tried this method with showed that using a 36X target scope tightened up my 100 yard results by a not insignificant 1/4 inch. The gun in question was a Savage 10FP LE2B which is on average a hair under one MOA with Federal GMM. The 36X was a Weaver T36 and the hunting scope was a Bushnell. 1/4 inch isn't the end of the world but sometimes it is all about that Holy MOA, don'cha know?

    On the other hand maybe you are much better at testing than I am. I have to say it really matters which targets I use once the magnification drops down. It is harder to find POA within a 1/4 inch at 100 yds. unless the target is super helpfull. In conclusion, I don't have any reason to doubt your particular results but whenever I try this stuff three or four groups doesn't prove diddly.

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