Two two-shot groups

[wombat13]

I'm working on loads for my .300WM and shooting four shot groups to test the loads (4 rounds is what my rifle holds). With one of my loads I got two distinct groups. Two shots were nearly touching and two shots were nearly touching but about 1.5" from the other two.

I've noticed this before with my muzzle loader. I think this indicates that the load is consistent in my rifle and the source of variation is me. What do you all think?

 

[matrem]

I'm guessing you're not that consistently inconsistent.
Sounds like a bedding/ bbl heat issue to me.

 

[JerryM]

I agree with matrem. Don't make excuses for the rifle. As the barrel heats up the POI changes slightly. It is likely that bedding is the cause.
Of course, as you shoot you should be able to call the shot each time, especially from a bench.
Are you calling the shot, and know where the cross hairs were when the gun went off?

Regards,
Jerry

 

[arizona98tj]

Start shooting some 10 shot groups and see how things look. It pretty much eliminates any coincidence that you might be seeing. I can load a magazine of Wolf ammo in my AR-15 and come up with 2 two shot groups, just like you described. Doesn't even mean those cartridges are good loads.

 

[taliv]

all speculation, but my money's on seating depth

 

[Tirod]

It's sometimes hotly debated, but statistically, ten shot groups are the answer. They are also government specified when accepting ammo from suppliers.

With small groups, all you see are two points of reference. Adding another will add incremental increases in accurate measurement of a statistical group of data points. The additional increase in measurement dwindles each time, ten seems to be about right for the diminishing return and easy math.

Small sampling shot groups will leave you chasing the zero, as was plainly illustrated on your target. It's an obvious example of just exactly the sort of variation you get, and why small samples are deceptive. You'll wind up moving your sights every two shots at this rate - shoot ten and adjust to that center, it's the point of the process.

The resulting group size of ten isn't as impressive as many shooters would like, no problem. They shoot a lot of three and five shot groups so they can post the best of what they get and claim that as what they can do. Not so much.