Inconsistent groups

[WKR]

I've got a really picky rifle that I can't figure out, my groups from the same load on different days are sometimes sub moa and other days around 2 moa. The SD and ES is always really good though. Like 6 fps sd and under 15 extreme spread. Its not shooter error because I am shooting another rifle and printing sub .5 moa groups on the same session.

Its making me think there is something wrong in my handloading process. And I dont understand how the numbers are so good but the groups open up

 

[nobody]

How many shots per group? Rifle make and model? Cartridge? Scope type and mounting system?

Not trying to sling mud, trying to narrow down potential explanations and culprits!

 

[TxLite]

I’ve had this happen from inconsistency between reloading sessions. The biggest issue for my situation was due to measuring based off COAL instead of CBTO

 

[PineBrook413]

how many shots in each group? If you are shooting 3 or 5 shot groups you may just not realize that that the particular load is only 2 moa capable. A 2 moa gun will shoot a sub moa group here and there with only 3 shot groups. If you are shooting 10 shot groups and they are varying that much you've got something else going on.

I've found my 10 shot groups to be very consistent. They typically only vary by .1-.2" between days, or range trips. Plenty of times the first 3 shot of a 10 shot group are .5" and the by the time i get through all ten shot its 1.4".

If you have confirmed all the normal stuff is ok like scope base, rings, scope itself, action screws etc. Shoot a few 10 shot groups, I bet its pretty consistent.

 

[WKR]

I measure to the ogive and its consistent. Also I should mention the cold bore shot prints in the same place every time on any given day

I'm shooting 4 or 5 round groups typically

All the usual culprits have been double checked and torqued

 

[PineBrook413]

I'd shoot 2 ten shot groups. That will confirm what level of precision that particular load in that gun is actually producing.

 

[NW Hunt€r]

Throw another scope on it. You need to find out if the scope is going bad on you.

 

[Harvey_NW]

Small sample size variability in a nutshell.

 

[Cahunter805]

What scope and base/ring setup? I’d look at those before the load especially with an ES and SD like that.
Just curious what cartridge/powder and bullet?

 

[WKR]

What scope and base/ring setup? I’d look at those before the load especially with an ES and SD like that.
Just curious what cartridge/powder and bullet?

Zeiss v4 in talley's
7mm rem mag
168gr lrx
67.5 gr h1000
Hornady brass
Win lrmp

Barrel is a 1 in 8 twist so no stability issues

 

[RuggedYogi]

I’ve had this happen from inconsistency between reloading sessions. The biggest issue for my situation was due to measuring based off COAL instead of CBTO

I’m pretty new to reloading. Curious why measuring CBTO is superior to measuring COAL?

 

[nobody]

I’m pretty new to reloading. Curious why measuring CBTO is superior to measuring COAL?

The argument is that the ogive of the bullet is what makes contact with the rifling first, so the critical dimension (assuming the round easily fits in and feeds from your magazine) is from the base of the cartridge to the first point of contact with the rifle's barrel, which is the ogive of the bullet. The same thing happens with your die, the bullet is seated by the die contacting the ogive, not the tip of the bullet.

Variances in manufacturing mean that the lengths of the bullet can vary slightly, so the ogive is the most consistent surface to measure to arguably.

 

[madcalfe]

The argument is that the ogive of the bullet is what makes contact with the rifling first, so the critical dimension (assuming the round easily fits in and feeds from your magazine) is from the base of the cartridge to the first point of contact with the rifle's barrel, which is the ogive of the bullet. The same thing happens with your die, the bullet is seated by the die contacting the ogive, not the tip of the bullet.

Variances in manufacturing mean that the lengths of the bullet can vary slightly, so the ogive is the most consistent surface to measure to arguably.

not to mention the polymer tips on bullets can have inconsistencies

 

[DiabeticKripple]

I’m pretty new to reloading. Curious why measuring CBTO is superior to measuring COAL?

The ogive on the bullet is a lot better spot to measure cause bullet length can vary, especially with a polymer tip.

I have had bullets measure up to 0.003" different where the ogive is more consistent.

 

[LaHunter]

Zeiss v4 in talley's
7mm rem mag
168gr lrx
67.5 gr h1000
Hornady brass
Win lrmp

Barrel is a 1 in 8 twist so no stability issues

Zeiss v4 is a suspect
Talleys are a suspect. Lots of threads discussing Talley issues.

 

[TxLite]

I’m pretty new to reloading. Curious why measuring CBTO is superior to measuring COAL?

As has been well said by others, overall CBTO is a much more consistent way to measure. As long as it fits in the magazine the COAL is completely irrelevant to me

I have found inconsistencies across the board though, not just polymer tips. Lead tipped Gamekings were where I first noticed the issue. Bergers also had overall length incosistencies (at least the ones I've used). However, the ogive measurements had very little if any deviation

 

[RuggedYogi]

Thanks for the replies, sorry to hijack your thread, OP.

 

[EdP]

I think the key here is to shoot the sub moa group of 4 or 5 shots that you described, then shoot 5 or 6 more to take you to a 10 shot group and see what happens. If the group opens up to 2 moa you have your answer. It is the statistical probability of getting a sub moa group from a 2 moa rifle/load that several others described. If your group stays sub moa or very close, it's something else. Given the good sd and es you described, it doesn't sound like something with your reloading process unless your velocity is significantly different for the different group sizes.

5 shots groups have been adequate for my purposes based on often getting sequential 5 shot groups of essentially the same size in the same location when shooting groups to evaluate loads. Overlaying the 5 shot groups would not significantly change the group size. I would not say the same for 3 shot groups. This isn't much different from the 10 shot group argument because I really don't draw a conclusion based on a single 5 shot group.

 

[49ereric]

How hot does the barrel get after 2 shots?
not sure how fast you are shooting or barrel diameter.
heat will throw off groups as quick as anything.
I’d try 2 shots and let barrel cool off and repeat then check groups if you haven’t done this already.

 

[WKR]

Its not heat. The rifle has a heavy barrel contour and I let the barrel cool between shot strings.

I dont think its the scope or rings. I have the same set up on a different rifle and its shooting half moa groups consistently.

Is it possible to have that good of numbers but just have bad results on paper?

This same rifle and scope set up has shot sub moa groups with a different load. But I changed bullets because I didn't like the terminal performance. Now I thought I had a great load because it was grouping good at first and the numbers are awesome but the inconsistencies are killing me. At the same time it might be fine because the cold bore shots are in the same place everyday and within 5 fps of each other. On a hunting rifle thats really what matters.