The other day we were discussing the different types of zeroes and no, it was not their location; i.e. the 200 yard line for example. It was the “how” you shot it we were talking about. As we see it there are six different types of zeros. The are broken down into two groups; supported and unsupported, but each has it’s own subtlety.
For the average shooter they may never see the difference, for the average M4 it may be incapable of delivery the difference, but there is a difference between each of them non the less. When we initially zero we try to eliminate as many shooter related errors as possible so resting the rifle on sandbags or more likely in classes rucksacks helps us to achieve that goal. With the rifle properly rested the shooter is not responsible for “holding” the rifle and as long as the natural point of aim is lined up this method can deliver not just accurate groups, but true groups.
If the purpose of zeroing is to develop the truest zero possible and not to gauge the shooter’s ability or inability then this supported method does a great job. There are other forms of supported that we can employ, such as using a bipod or monopod, but the sandbag/rucksack method seems to deliver the best results. Each of the supporting positions will start to bring in slight variances as a result of the shooter and therefore produce what appears to be less accurate groups. In truth, your margin of error is increasing and that is what is decreasing your accuracy, assuming the shooter’s skills are solid and applied consistently.
At some point the shooter needs to move from supported to unsupported. The main reason has to do with reality. In most flash events the shooter is not able to achieve the optimal supported position or their gear interferes with their ability to achieve the best position. In these cases we have to achieve the best groups possible, but we start with the truest zero. When the shooter has trust in his zero it goes a long way, it at the very least puts to rest those nagging questions.
At this point, it is not so much about whether your rifle is zeroed. That should have been completed with the supported evolutions. Now, it is a matter of learning where it hits in these various conditions. So, we start out using an unsupported slick position, basically no gear. Now, the shooter is responsible for holding the rifle steady during the firing sequence. Through proper technique this can be developed to a pretty high level, but will it be as good as supported, probably not or you are doing something wrong supported.
From there, you start to add gear. Gear that interferes or makes it difficult to achieve the marksmanship points of performance. We recommend light weight scenarios such as chest rigs or plate carrier, then the final zero would be in fully jocked up with everything and the kitchen sink to include a helmet. Now, things are getting serious.
Some opine you should adjust your true zero to these various unsupported positions. That is very possible, but before you make the decision to adjust you first need to see the difference to know whether you should adjust.