Interpreting Groups

[mec1]

Hi All,

I just finished putting together my AR in .204 and I'm ready to start load development. In the past I've shot 5 different charge weights and taken the best group and used it since I'm happy with 3/4" groups for a big game rifle. But for a prairie dog rifle, I'd like to get more precise, so I would like your expertise. Here is my question:

When you are shooting groups, how do you interpret the results? I've read that for vertical strings, increase charge weight or COAL and for horizontal strings do the opposite. Are they any other rules of thumb that you guys use? What about groups that aren’t clearly stringing? How about groups that form two very tiny clusters, but each cluster is about 1" apart? I'm just trying to learn more about how to take a decent group and make it much smaller, so any advise you guys can give would be great.

[Vartarg]

I'm going to wait for some our more learned members to chime in to respond to your question, so I'll simply say WELCOME to the forum....you've come to the right place!

[fishy]

I'm interested as well in the answer. Thats a good question. Also welcome to the forum.

[Hotshot]

I read somewhere not too long ago, if your group is Vertical that's bedding and if it's Horizontal that's the shooter. Thinking back over the years there just might be something to that. Or was it the other way around?
Rule of thumb for a 204Ruger: If it won't shoot 39gr Sierras with a close to max charge of R10X, Benchmark, 4895, or 8208--Trade it off for another one, because most will shoot that load real well.

[7mag]

So far WN Mag and I have been lucky, All 3 of the 204's we shoot are sub moa with all the loads we try. Some being one hole loads. The wife loves the fact that she's taking "Tack Drivers-ed" in a Ferrari. Ya' gotta love the violent little 204! If anyone knows for sure how to interpret groups I would love to know more. I will do some testing on the theories here and see if I can figure anything out. Really great question!!

[Rick in Oregon]

In the recent past, Precision Shooting had an entire article on that very subject. I also remember seeing a piece in Varmint Hunter Magazine a while back. There's been more than one article in VHM over the years about this, and more than one method of measurement.

[Vartarg]

What Hotshot said!

[Glen]

My interpretation.

Vertical-- Shots fired too quickly & the next round lays in a hotter chamber than the previous & cooks. More pressure = higher velocity can raise POI. Poor front rest technique can also be a culprit. The rifle needs to rest the same way every time.

Horizontal-- Wind drift. Hard trigger pull. Shooter not lining up the same way every time. Again poor front rest technique & the rifle is moving on recoil.

Scattered-- A combination of the above plus parallax issue. Seating depth,charge weight,primers, & a whole host of things can cause scatter. Change 1 thing only at a time & keep strict records.

Merely my thoughts on the subject.

[mec1]

Thanks Guys, there is some excellent advise there! I was so focused on charge weight and bullet depth that I wasnt even thinking about front rest or parallax issues.

Nobody happens to remember the conclusions from the article in Varmint Hunter Mag do they? Maybe I need to get a subscription...

Does anybody else have any good ideas?

[oldguy]

So many answers to this question not sure anyone can give a direct answer most of my bench shooting is with bolt rifles with heavy barrel, various patterns are the result of scope,front rest, stock bedding, trigger, bullet weight, powder charge, etc. All this with bolt action but even more variables with auto's. Barrel harmonics with a slim barrel can also be an issue. Also have a friend try the gun with same loads to get their results.

Fun is in the process.

[Lenard]

A goodly amount of the variations are shooter error. If I am not patient in my setup, I can get either horizontals and/or verticals. Seems like after I have been getting quite a bit of trigger time, my techniques get better and then the groups shrink.

I think if you nose around on SniperHide(just google) there are posts that address the issues of horizontal and vertical groups. Some are also loads that cause vertical stringing. I can't speak for anyone else, but having the crosshairs on the target without my holding the gun is an excellent starting point.