Ben already posted this little gem awhile back which pretty much covers it.
However, me being as long-winded as I am, I thought I would delve a little further into the world of bipods and why I don't like 'em on an infantry/battle/utility rifle. First of all, it's more weight and my FALs and Garands are heavy enough as-is. Balance and handling can be affected, too. Despite hunting every game animal I can get a tag for, and doing a lot of that hunting in the seemingly wide-open endless high sagebrush country of Montana, one thing or another, usually vegetation, prevents me from ever being able to take a prone shot the vast majority of the time. Between the sagebrush and the steep slopes, I find the sitting shooting position, properly looped up with a shooting sling, to be useful most often and pretty darn steady to boot. If I do shoot prone, that ol' strap of leather hanging from the bottom of the rifle can get me pretty darn solid there too. Lastly, I've seen too many people come to use bipods or sticks or supports as a shooting crutch rather than a shooting aid. Without 'em, they're afraid to take the shot and all too often botch it if they do try to take it.
The biggest thing about military-style rifles is that when a bipod is used, its often attached directly to the rifle barrel metal-on-metal. Via conventional wisdom "they" know that this affects barrel harmonics and accuracy. Well, via conventional wisdom "they" also told me, "Just save up your money for a DSA/Springfield Armory/(Insert Cool Name De Jour Here) brand-name and you'll be sure to get a really fine rifle." That turned out to be a crock of shit, so I thought I had better test the bipod thing firsthand myself too.
For my little experiments, I used my Century Arms Franken-FAL "Gertie" which was originally an StG-58 kit. The Sturmgewehr StG-58 was the Austrian version of the FN FAL, a very good quality rifle manufactured under license by Steyr. The hammer-forged barrels in particular are noted for quality and accuracy.
As an aside, you'd think that in running about the Alps the Austrians would have wanted a lightweight rifle, but the StG-58 is actually the heaviest of the standard FAL infantry rifles. The Swiss out-did even that with their SIG Stgw 57, a beautifully over-engineered pig that weighs over 12-1/2 pounds empty.
At any rate, the Austrian StG-58 came with a folding aluminum bipod as standard equipment. It is kind of a cool little unit which folds neatly flush into grooves on the bottom of the handguards when not in use. The bipod feet have both spikes for traction as well as wider, flared feet for soft ground/snow. Total weight, including all the mounting hardware, is just a tish over 12 ounces. Actually sounds kinda nice. What does Bawb have to bitch about?
Austrian StG-58 type FAL with standard issue bipod extended.
When not in use, the bipod legs fold neatly into grooves in the handguards.
First off, long legs may be a desirable feature on women and horses, but not on bipods IMHO. The StG bipod legs measure 11-1/2 inches in length. When you're shooting prone off a low bipod (the 6-9" Harris comes to mind) you can get quite steady and solid by just putting the fist of your non-shooting hand under the toe of the butt stock. With legs this long, you put your fist under the toe of the stock and your bore is still pointing about 20-degrees over the top of the target. At the range, you wind up making wobbly houses of cards from sandbags and ammo cans and folded shelter halves and what not to jack the butt up enough to get the barrel on target.
Not a deal breaker, though. You can still do pretty solid shooting from this bipod just because you still have both elbows on the ground.
Now for the weenie. Does such a bipod really affect accuracy and if so, how much? Gertie and I went to the old Forest Service gravel pit one day last spring to find out for sure.
For the first test I shot two 10-round groups at two targets side by side at 100 meters. The first group was fired with the bipod folded and the forearm resting on a folded-up shelter half. The second group was fired from the bipod. It wasn't like I was putting any weight or torque on the rifle, either. There was only the weapon's own weight resting on the bipod.
10-shots, 100 meters, bipod folded, forearm rested.
10-shots, 100 meters, same rifle &ammo fired from bipod.
10-shots, 300 meters, bipod folded, forearm rested.
10-shots, 300 meters, same rifle & ammo fired from bipod.
I repeated the test with two 10-shot groups on two targets at 300 meters and got similar results. At 300 meters, the bipod-fired group was impacting approximately 12-14 inches higher. That's more than enough to completely miss a prone target.
So there you have it. A barrel-mounted bipod really can affect accuracy and zero. Your mileage, of course, may vary. There's a hundred and one little tiny factors that can influence barrel harmonics. Your personal rifle may be only slightly affected, or not at all. But then again, it could be just as bad or perhaps even worse.
It's eleven o'clock and you have a bipod. Do you know where your zero is?