I won't out either company, but before I transferred to the east coast, I lived about 20 miles from one high end custom gun maker and about 50 miles from another manufacturer that made precision rifles for both civilian and law enforcement users. Both companies had a "1/2 MOA" guarantee. Both of them defined it more or less as a 1/2 MOA three shot group at 100 yards.
Both companies also used our club range when their indoor ranges were down for maintenance. They used our range as it was surrounded by high terrain on 3 sides and wind was rarely a factor at 100 yards.
What I saw when they shot was enlightening about the value of a "1/2 MOA" guarantee.
The shooter would show up with several rifles and would staple several targets on the target backer. He'd then shoot a three shot group from each rifle at its assigned target.
Out of a dozen or so rifles there would usually be 2-3 rifles that would achieve the required three shot, 1/2 MOA group on the first attempt. The shooter would box those up with the target and then shoot the other 9-10 rifles out of the initial dozen again. Most of the rifles would produce a 3 shot, 1/2 MOA group after 3 or 4 attempts. There would usually be 1 or 2 however that would not, and the shooter would then usually check the torque on the stock screws, confirm the barrel was free floated etc, and if it still would not produce a 3 shot 1/2 MOA group, he'd take it back to the factory for more in depth attention. Those would be sent out a second time for testing on the next range trip, and every range trip usually had 1-2 rifles that were back for a second attempt after some factory reworking.
There would also usually be a rifle that was a customer return due to an accuracy complaint. That returned rifle would get the same test protocol and if it managed a 3 shot 1/2 MOA group in 3 or 4 attempts, it would be sent back to the customer with a new test target. It would also have the stock screw torque checked or adjusted, and if that resulted in a suitable target it would again be sent back.
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My impressions and take-aways from observing those tests are as follows:
1) A single 3 shot 1/2 MOA group doesn't make a rifle a "1/2 MOA rifle", even if it's achieved on the first attempt. It certainly isn't a 1/2 MOA rifle if it takes several attempts to get a 1/2 MOA group.
2) Personally, I think anything less than a 5 shot group is a waste of time, and I also want to see a fairly high confidence level that it'll produce a group at any given time. I don't expect to see it every time, but 2 out of 3 is about the minimum.
3) Most of those "1/2 MOA" rifles were probably pretty solid "1 MOA rifles" based on the targets I saw and the statistical distribution of the groups on those targets.
4) Despite selling what were arguably 1 MOA rifles rather than the advertised 1/2 MOA rifles, neither company had many returns.
In the case of the high end custom gun maker, that wasn't a surprise as they were more gun art than guns intended for practical use, and I suspect most of the buyers had more money than skill and would probably blame a lack of consistent 1/2 MOA groups on their ability, not the quality of the rifle.
In the case of the precision rifle company, the return rate still appeared to be low. Again, the shooters may have regarded themselves as the limiting factor. Alternatively, since many of these went to police departments, they may have addressed any accuracy issues, with their own local armorers. Then again, solid 1 MOA accuracy may have been more than sufficient, given the average police sniper engagement is around 75 yards year in and year out and it's extremely rare to see one over 300 yards.
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My conclusion was that the 3 round, 1/2 MOA guarantee was both meaningless and just marketing hype.
To be fair however, with the rise in "long range" precision shooting and the corresponding increase in so called "long range" or "precision" shooters the accuracy claims by many of those shooters are usually just as meaningless.
I often see shooters who will show a three round group on a steel plate that was claimed to be at 1000 or so yards that may be anywhere from 3" to 6" in diameter, with the shooter claiming they can shoot 1/4 or 1/2 MOA at 1000 or so yards.
What doesn't get mentioned is the half dozen shots it may have taken the shooter to get the first round on target, or the vast majority of other groups fired that same day that were nowhere near that level of accuracy.
In other words, the bar as fallen to where many shooters seem to mistake a low frequency, third standard deviation, right hand tail group represents an average level of accuracy.