How much do you think a bur on a bullet affects accuracy at 200 yds?

You provided far more information than is actually needed. The correct answer is, 'a lot'. Of course you should send the remaining bullets back; AND, if the supplier is honest, he'll easily understand, 'Why'. End of story!

PROVISO: The only question I have is, 'Are you the one who's putting these, 'divots' into the bullets?'

Answer me this: Are the bullets burred or dented as they come out of the box; or are these divots suddenly appearing as part of the final reloading process?

In which situation your dies need to be completely disassembled and thoroughly cleaned in the same way you'd clean a dirty rifle barrel; or else, your seating and/or crimp die(s) are, somehow, screwed up. Are you using the correct seater plug?

200 yards with a bur that can only be barely felt, you will see no difference in POI. It's possible, assuming this is a new round, your rifle just doesn't like the combination. Auto loading rifles with soft point bullets tend to deform the tip of every round, and getting match level accuracy is no problem compared to using a FMJ that isn't deformed at all.

There's been more than enough testing to show that it won't affect anything.

Seeing a .25" increase in group even if you're shooting identical ammo is more likely to be the shooter that day than anything else. But if you're after match level precision you have to account for all kinds of things, wind conditions that day, temperature compared to the 'good' day data.

Beyond that a 3 shot group out of any rifle is statistically insignificant. I've seen a lot of "great' 3 shoot groups in a row out of 1 rifle, but when you actually overlay them to a larger group size you see that great group is actually only pretty decent. 3 shots touching is great, but when you shoot 10 and see you're actually shooting 1 -1.5, not so amazing. By the same token a 3 shot group can have a flier that makes an otherwise 1" rifle look like it's shooting 3".

What grain bullet are you using? The FGMM comes in 69 grain and 77 grain. It normally is very accurate in both weights. What type of rifle and what is the rate of twist for the barrel? If you are firing the 69 grain you will need a 1 in 9 twist rate and for the 77 grain a 1 in 7 would be recommended. This could easily have an effect on accuracy if the bullet is barely stabilizing. What kind of groups are we talking about at 200 yards and what power/type of optic are you using on it? A divet can affect accuracy, if they were all diveted, I would return them as well. That stuff is pretty pricey to get a defective lot.

I have been reloading and shooting 223/5.56 in long distance competition since 1978.

69gr Sierra MK, and the Hornady 68gr - and all others - only function in a 1:9 to 1:6.5 twist barrel. On the outside of the Sierra box in red letters it states, "1:9 twist or faster barrels only". Just because Federal loads them does not change the laws of physics and magically make them work in 1:10 barrels.

At 200 yards the 69gr projectile is only in the air for 206 milliseconds. That is not enough time for a burr on the nose to effect the trajectory.

What can effect things from one make of ammo to another is the finished OAL and coaxal concintricity. You should gauge the bullets for length and put 'em through a coax gauge.

Although Gold Medal Match is as good as it gets for civilians who do not reload - and Lake City Match is as good as it gets for military shooters - we always guage the ammo in the military. GMM is no different. In a typical box of 20 you have a few that are great, some good, some ok, and a few bad apples that need to be culled.

Not knowing what you mean by "not that great" makes it difficult to answer. If you've had good patterns with the same ammunition in the past, there are other variables (a loose screw on a scope ring, for instance) that need to be checked first. If this is your first time to use that particular ammunition, it's much more likely that you're dealing with barrel harmonics, and your rifle simply doesn't "like" that combination. The burrs may open a one-inch group to an inch and a quarter, but even that would be more than I'd be inclined to attribute to the burrs.

Likely it had a significant effect on your accuracy. You ended up firing an asymetrical projectile at incredible speed, and the "wobble" or yaw would, intuitively, have been unacceptable. Its obviously impossible to figure out how much effect in terms of MOA there was without employing a physics major, measuring the bullet, etc. You are correct to send back the entire lot.

I don't know but you have the tools to answer the question. Save three of the defective rounds. Get same ammo minus the defect. Shoot two groups off the bench for accuracy. You'll know exactly how much the burr affected it.