Mildly contoversial and factually important for a shooter going beyond 300 yards, and this is the longer, more detailed look into what LebbenB just said.
So your barrel is free-floated with a top of the line bipod at the front of the handguard? It's assumed that there will be no POI change? Maybe. Maybe not. Lets use the M1 Garand as a point of reference.
The hold on an M1 for any real range shooting is critical. With all that wood, you might not think so, but the gents who specialize in that kind of shooting would disagree. Besides the use of the sling, a sandbaged M1 Must be pulled into the shoulder with some authority. Any rifle with a sensitive trigger must also be pulled tightly to the shoulder to prevent trigger milking. An example:
My own prize Garand is a one of three Don McCoy Garand. First time prone in the ShootShed with this incredible rifle was a surprising revelation of the word "milking". Long story short, the rifle was designed and built as a single shot High Masters rifle. One cartridge at a time, hand fed into the chamber with the bolt released and following behind. I didn't understand this at the time, so I loaded up all eight rounds, avoided the traditional thumb-slam and settled in for an eight round session. Sandbagged, solid hold on the forgrip, not too much pull into my shoulder, gentle squeeze on the trigger and........ all eight rounds went downrange in a single burst. Amazingly, they all stayed on the 4'x8' target. The rifle is a nominal 14 pounds, so that shouldn't be much of a surprise, but was I surprised! I actually thought I had a selective mode rifle! I didn't. Had I followed correct shooting procedure I'd have had the rifle pulled in tight against my shoulder and followed trigger procedure of pull, hold back and then release. More about that and the rifle later.
So, what does that have to do with anything about Ar10s? A lot! A rifle with a standard stock has far fewer gripping options than the AR10. Straight back into the shoulder is natural and assumed with a stock sans pistol grip. The pistol grip itself has a multitude of directions it can be leveraged, with the most common one being down. So when you pull that rifle back into your shoulder you're not changing POI? Wrong. That pistol grip acts as a counter-lever to the axis of the straight in line bore-stock setup and flexes the entire rifle right in the center. Pulling back on a pistol grip also pulls down at the same time. Simple physics. That free floating barrel means little when the pressure is applied. Don't believe it?
Do an exaggerated test. Fire from a sandbag first allowing the rifle to be fired without any undue pressure from the fore or pistol grip. Fire one shot. Now move to another target. Deploy your bipod, pull the rifle back into your shoudler tightly using the pistol grip as a lever. Fire another round. What happned?
Back in the 80's my Dad was a distributor in Montana for a number of manufacturers and importers, and one of them was Stoeger. He handled both Valmets and IMI Galils. He bought some 12 or so of the first .223's with bipods and sold them all, reordered and sales were good. Then........ IMI offered the .308 with the same setup. The first thing the noticed was the barrel diameter. It was identical to the .223! With the bipod deployed those rifles were extremely suceptible to flex, and at 100 yards he was intentionally able to make the POI change by an easy 6"! So what does all that mean?
Any rifle using a bipod is susceptible to POI change from very minor to very major. Ever wonder why the Swiss bipods on the AMTs and PE57s can be moved from the front of the barrel all the way back to just ahead of the receiver? On the zfk55 Sniper rifle the bipod is actually attatched to the receiver itself, not touching the barrel at all. On the semi-autos and autos... Bipod forward is for field-of-fire, all the way to the rear is accuracy shooting. The best of the military semi-auto application rifles have this feature.
So........... Data gathering, load proofing, bench/recreational shooting, the sandbag is the logical choice. In the field its the bipod, a log, a fence, a rock etc. Simply keep in mind that any pressure from any direction whatsoever on your rifle from any source is a potential POI changer. Use it all with logic and, most importantly....... once your hold is developed and proven to yourself, never, ever change the way you hold your rifle, bipod or not.
Latigo
*I was just asked how to pull an AR10 hard into the shoulder without pulling down and back on the pistolgrip. Do you know? If so, post the answer.
