What does "Precision Guarantee" mean?

[rome107]

Hi people,
Many gunbuilders and manufacturers claim a ".5 MOA guarantee for 3 shot groups with match grade ammo".
What does that mean?

That I shoot 10 groups with any "Match" ammo and one of these groups will be .5 MOA?
That I shoot 10 shots and the best 3 hits will be closer than .5 MOA?
That 9/10 3 round groups are .5 MOA?

If each 3 round group is guaranteed to be less than .5 MOA, 5 rounds should not make it bigger either as no "flyers" are allowed.

I documented a lot in during the last year, as I was facing precision issues with one of my 308. I would regularly see good 3 round groups and sometimes also 5 shots but sometimes also the first 2 rounds would be spread wide. Extending the groups to 10 rounds would never result in realy small groups. The 10 round groups stayed constant in size though and would also not differ seriously from a 20 round group (I logged and printed all shots in an excel file).
I often see people shooting 3-4 close rounds and then there is the 5th round a bit off the group and it is always "I jerked that one". I can shoot under 1 MOA (10 rounds) with my good rifle, but suddenly jerk bullets off with another rifle? Therefore I became a big fan of big groups (10 rounds) for tesing reloads to be sure I am not judging the lucky 3. 3 rounds can confirm a bad load but only 10 seem to be able to realy confirm a good load.

How do you determine the capability/precision of your rifle? What can one expect from the "guaranteed precision"?

Thanks a lot for your ideas...

 

[davsco]

you should ask the manufacturer/builder what it means and how they test it (are they in an underground tunnel with zero wind, 32x scope, pet handload with 1fps extreme spread, etc). it should mean the rifle will consistently get 1/2 moa groups with match ammo. not the best 3 out of 5 or 10 shots or not the best 3 out of 10 groups. the problem is there are a lot of variables that affect accuracy. including the shooter, ammo variability, wind and enviro, scope magnification, repeatable and firm shooting position, etc. my takeaway on an accuracy guarantee (versus no guarantee) is the manufacturer is saying they're making an accurate rifle and will stand behind it to some extent. if you are getting 3/4moa groups they'll prob just say it's you, the ammo, enviro, etc. if you're getting 2moa groups they'll prob have you send it in to check it out. but ask them what they do if you aren't shooting to their accuracy guarantee. it's a fair question.

 

[Sogan]

^^^^^ Well said

 

[J.Boyette]

Hi people,
Many gunbuilders and manufacturers claim a ".5 MOA guarantee for 3 shot groups with match grade ammo".
What does that mean?

That I shoot 10 groups with any "Match" ammo and one of these groups will be .5 MOA?
That I shoot 10 shots and the best 3 hits will be closer than .5 MOA?
That 9/10 3 round groups are .5 MOA?

If each 3 round group is guaranteed to be less than .5 MOA, 5 rounds should not make it bigger either as no "flyers" are allowed.

I documented a lot in during the last year, as I was facing precision issues with one of my 308. I would regularly see good 3 round groups and sometimes also 5 shots but sometimes also the first 2 rounds would be spread wide. Extending the groups to 10 rounds would never result in realy small groups. The 10 round groups stayed constant in size though and would also not differ seriously from a 20 round group (I logged and printed all shots in an excel file).
I often see people shooting 3-4 close rounds and then there is the 5th round a bit off the group and it is always "I jerked that one". I can shoot under 1 MOA (10 rounds) with my good rifle, but suddenly jerk bullets off with another rifle? Therefore I became a big fan of big groups (10 rounds) for tesing reloads to be sure I am not judging the lucky 3. 3 rounds can confirm a bad load but only 10 seem to be able to realy confirm a good load.

How do you determine the capability/precision of your rifle? What can one expect from the "guaranteed precision"?

Thanks a lot for your ideas...

your point is well taken and true.

Try this for your next day of testing. Do 10 single round shots on 10 dots. Measure how close to center each shot is. give your self a 30 sec window between shot. That will be a better test for precision from point of aim.

John

 

[Ankeny]

I once asked George at G&A the same question about his 3/8 MOA guarantee considering there are so many shooters who can't consistently pound out 3/8 MOA groups. I am not sure I will ever completely understand his answer, but the bottom line is if the rifle doesn't pile them all in the same spot they will stand behind their warranty.

 

[cuz]

I always thought it meant that if you locked the rifle in some sort of vise/rest where it couldn't move and fired 3 shots with the "correct" ammo you would regularly get .5 MOA groups. When talking about the accuracy of a rifle, it shouldn't have anything to do with optics, the shooter, or environment as the rifle mfg has no control over them.

 

[Graywolf.260]

your point is well taken and true.

Try this for your next day of testing. Do 10 single round shots on 10 dots. Measure how close to center each shot is. give your self a 30 sec window between shot. That will be a better test for precision from point of aim.

John

I agree that measuring distance to group center, with as many shots as is practical, is a better approach. You can then apply normal statistics. The way group accuracy has been traditionally determined (greatest distance between shots in a group) is completely flawed for the purposes it's usually used. WTF do we still not apply basic statistics to group accuracy? Everyone understands that e.g. chronograph data includes the mean, ES, and SD.