Of course, bullets are a tiny bit unbalanced as they go past the gas port in semiautos. They’re also unbalanced a tiny bit if they enter the rifling crooked. If the gas pushing them out doesn’t do so evenly all the way around them as they leave, that tips and may also unbalance them a tiny bit. Does it matter?
Firearm accuracy is best (bullets land on target in the smallest area) when everything that moves does so repeatable from shot to shot. That includes the barrel, bullet and whatever’s holding the firearm. If they all move the same amount and in the same direction as the arm fires and the bullet goes through the barrel until it exits, their trajectories will be repeatable. They’ll all land in the same place; environmental variables remaining constant for each shot.
Dr. F W Mann proved over a century ago that bullets unbalanced the same way (small holes drilled in their sides) took a different path to the target than balanced ones. But if the unbalance point was at the same place at the muzzle when they all left, their trajectories would be repeatable. Same thing with bullets indexed in the chamber with their high runout point at the same clock number. Same with service rifle lands and grooves at their muzzles enlarged more at one point around the bore and groove surface by cleaning rods rubbing the metal away. Accuracy was the same as unbalanced bullets with no runout, but the group center would be a fraction or two of a MOA different for the same sight settings. M118 match ammo typically had bullet runout up to .006" and those shot test groups twice the size of ones with zero runout. Indexed to the same place in the chamber of Garands I tested them in, they shot as accurate as ammo with .001" or less bullet runout. (Runout setup was the round’s pressure ring and shoulder midpoint in a V block and dial indicator tip 1/10th inch back from bullet tip; this is the only way to get runout numbers equal to what they’ll be when the rounds are chambered.)
7.62 M118 match ammo’s best lots tested about 10 inches extreme spread at 600 yards fired from bolt action test barrels in a Mann rest. Same accuracy was attained by M1 and M14/M1A rebuilt rifles with standard profile or heavy barrels equal to the quality of the test barrel shooting the same lot. And their bolts are selected so there’s .001" or less head clearance on a 7.62 NATO chamber GO headspace gauge. Good lots of commercial match ammo as well as handloads have shot the same level of accuracy in bolt action match rifles as well as service semiauto ones. Rifles were tested from accuracy cradles which eliminates all the variables us humans have and how they effect both gas operated and bolt action rifles; explained in the next paragraphs.
Semiauto service rifles such as the M14 and M1 used in military, CMP and NRA competition for them can have top quality barrels (groove diameter’s smaller than bullet diameter), any dimension rear aperture and front sight width but virtual standard stock dimensions and a 4.5 pound trigger pull. There’s’ no difference in accuracy across different barrel weights of the same length. With their rear sight all the way up for long range, the shooter’s cheek weld on the stock comb is minimal; not too steady. A post front sight is hard to be repeatable in its alignment on a black bullseye. Such sighted rifles tend to shoot into the light when sunlight shines more on one side than the other and if the zero was attained in bright light but later shot in dim light, the rear sight requires a half or more MOA down and/or side adjustment. Their op rods have to go back into battery exactly the same place for every shot else they won’t vibrate the same for each round fired while the bullets’ are in the barrel; their muzzle axis relative to the line of sight won’t be repeatable. Barely tapping the op rod handle in any way changes it’s fit parameters to the metal parts it touches and that changes how the barrel whips and wiggles before the bullet exits. With their stocks’ same size and shape for people with different shapes and sizes makes them harder to shoot precisely compared to bolt action match rifles. It’s nigh impossible to shoulder and aim a semiauto service rifle held exactly the same for each shot so they’ll shoot to point of aim for each shot. Only new cases produced best accuracy in these semiautos; resized fired ones from these rifles have their heads too much out of square with the case axis causing the head impacting the bolt face off center which forces the barreled action to flex more in that axis; mostly at right angles to the bolt lug axis from center to 1 or 7 o’clock. Nobody I know of ever squared up an M1 or M14/M1A bolt face.
Bolt action match rifles’ stocks and their shape can be tailored to the shooter making very repeatable positioning to the human shooting them for each shot. Their light triggers of a pound or less means less aiming disturbance when the sear releases the firing pin or hammer when the trigger stops against its limit. And their shaded front aperture sight is light amount/angle indifferent as well as virtually equal in repeatable alignment on the bullseye as scope sights have; evidenced by any sight scores virtually equal to metallic sight scores in long range matches. Their square bolt faces and no more than .001" head clearance on a GO gauge means minimal changes to case heads being square for every shot. Even new cases shoot virtually the same level of accuracy as proper full length sized ones; both center bullets perfectly in the bore when the round fires.
I’ve shot the same lot of M118 match ammo in two different rebuilt M1's and three Win 70 factory barreled match rifles. Accuracy at 600 yards was the same for 30-shot test groups; about 12 inches. Lake City told me the acceptance tests for accuracy with that lot of ammo in their bolt action barrel was 2.5" mean radius (about 5" average spread for 10 shot groups, extreme spread’s about 5X mean radius). The following’s a 270-shot test group Lake City arsenal shot at 600 yards for their 1965 National Match lot of M119 ammo with a 1.9" mean radius; inner circle’s 6", outer is 12":
All of Lake City’s 30 caliber match ammo (7.62 and .30-06) was loaded with bullets from 3 or 4 production lots; each lot from a different set of coin, cup, trim, core and shape dies. Each set of bullet making dies in the machine holding them made slightly different bullets. One machine and set of dies typically made more uniform bullets than the others and it’s bullets would shoot under MOA at 600 yards. The outliers in the above group come from the worst batch of bullets with the greatest runout in the lot of loaded ammo.
Actually I am not sure which rifles are taking home the matches anymore and I agree it would be interesting to see.
