What could cause group outliers?

[Rob L.]

In a hunting gun.... don't let barrel get warm.....
I shoot the same target 2-5 days in a row.
1 shot... only
With dirty barrel.....

I do the same except that I run a Bore Snake 2 or 3 times through the barrel after the shot. The next morning I will shoot again and do the same Bore snake routine. That would simulate how my barrel is going to be after verifying zero at hunting camp, and before my shot at game. I am lucky to have a hayfield where I can shoot anytime I want without disturbing far away neighbors.

 

[Idaho Lefty]

There's a well known Rule, in Reloading,..
IF, IF, IF,.. your Rifle,.. DOESN'T "Shoot" Sierra's,..
WRAP it,.. around, a Tree !
Or , in YOUR Case, re-barrel it to,.. a 22 -24 Incher

 

[300 Weatherby Mag]

Here's one other thing you might try to eliminate a possible odd brass case that's giving you flier. Identify and set that case from your next batch of reloads.

Keep us informed of what you discover as I am interested in your findings.

 

[Shane Lindsey]

Try loading to the slower node with those 178s. That is definitely up there for a 18" barrel and that bullet weight. I have found the heavier bullets don't do well at top end in my 308 win with a 20" barrel. Some powders do better with the heavies, but mid weight, just north of mid charge scale and they do a little better. Of course, lighter can go faster, but I cannot ever top out on the charge weights with this short barrel.

 

[Josh06]

Use your comparator and check base of the just the bullet's base to the ogive. I had a recent couple boxes of hornady bullets 162 eld-x that fell into two distinct BTO groups of just the bullet, variance was about .015 and they were in the same box.

 

[GrayCreed]

I have what seems like a good load developed using 178 ELDM bullets with TS 15.5 in Lapua brass but I'm experiencing odd fliers. SD is ~10 fps over a large number of loads and velocity is averaging 2590 fps. On average, out of 4 shot groups (odd number but it's how many my internal mag holds so thats usually what I do with this rifle) I'll have 3 making up a 2/3 MOA (or less) group and the other shot is 1.5 to 2 inches away. Sometimes this is 2 of 4 touching, sometimes is just a good group for all 4 shots. This rifle will generally shoot just under 1 MOA groups with a good load: no match rifle but fliers are not the norm. However, it is a bit picky of a barrel: not all projectiles shoot well in it.

I'm inclined to chock it up to one (or more) of a the following causes:

1. These are pandemic projectiles so perhaps I may have a not-so-good batch.
2. My jump maybe in a sensitive spot (only tried one jump so far), although I do check the CBTO on all rounds and they're quite consistant showing a variance of about 1 to 1.5 thousandths.
3. These are just not a good bullet for this picky barrel.

I'm interested to know what more experienced people think. Thanks in advance.

#2 Jump

 

[SuperBruce]

There's a well known Rule, in Reloading,..
IF, IF, IF,.. your Rifle,.. DOESN'T "Shoot" Sierra's,..
WRAP it,.. around, a Tree !
Or , in YOUR Case, re-barrel it to,.. a 22 -24 Incher

Unfortunately that's not it: this rifle likes 175 SMK's. I'm sure a better barrel would do it though: it's amazing how much difference a premium barrel can make.

Use your comparator and check base of the just the bullet's base to the ogive. I had a recent couple boxes of hornady bullets 162 eld-x that fell into two distinct BTO groups of just the bullet, variance was about .015 and they were in the same box.

I do check each cartridges CBTO and they're all very close, within 1 thousandth of one another. The one or two that end up a little shorter (typically not more than 3 thousands shorter) get segregated, but don't seem to behave any different regardless.

 

[Idaho Lefty]

Unfortunately that's not it: this rifle likes 175 SMK's. I'm sure a better barrel would do it though: it's amazing how much difference a premium barrel can make.


I do check each cartridges CBTO and they're all very close, within 1 thousandth of one another. The one or two that end up a little shorter (typically not more than 3 thousands shorter) get segregated, but don't seem to behave any different regardless.

It LIKES,.. 175 grain, Sierra's ???,..
It's most PROBABLY, the Bullet or, the "Tune" then,.. IF, it, "shoots",.. Sierra's
Why the Short, 18" Barrel ??
Try at least, a 22" next Time ( they will Burn, almost ALL of, the Powder, in the Bigger Calibers ! ).
My son, is getting 2,765 FPS out of, a 22 inch Tikka, 7MM-08 with, 168 Bergers and StaBall 65

 

[VinceMule]

It LIKES,.. 175 grain, Sierra's ???,..
It's most PROBABLY, the Bullet or, the "Tune" then,.. IF, it, "shoots",.. Sierra's

AMEN to that!

175, 168 g match kings are very very easy to tune!

169 MK likes to be just barely off to kissing the lands

168 and 175g TMK like to be off the lands just a tad. My Krieger 4G, 10T, which is a MHV with a short palma freebore chamber loves 42g of IMR XBR 8208, and it will shoot below 1/4" at 200 with about .300 or a tad less at 200. With XBR 8208, you have to stay ahead of the carbon build up in the barrel and very small groups will abound.

 

[SuperBruce]

Why the Short, 18" Barrel ??

To make it easier to pack around with a suppressor.

 

[Idaho Lefty]

@ SuperBruce,..
Might want to, think about, a 20-22 inch Bbl, "next time" to, get more, "Barrel Time" ( for Stability ) on, the Bullet and, a better / fuller, Powder "Burn",..
Something, "Fishy", is going, on for, sure ! Is it possible that Internally, the Rifling or, Bore size is,.. "Off" a Bit ??? ( is Barrel Quality, suspect ? ).
I have, 60 years of, Reloading Experience ( since Mid, 1950's) and did Gunsmithing for, 30 years and, I DON'T have, the Answer that, your looking for,.. Sorry

 

[Idaho Lefty]

Good luck !

 

[Jeremy Henderson]

Here's one other thing you might try to eliminate a possible odd brass case that's giving you flier. Identify and set that case from your next batch of reloads.

Keep us informed of what you discover as I am interested in your findings.

I had this happen to a 6BR . Checked all of the cases and 3 out of 50 were a little longer trimmed to all the same length and the flyer went away.

 

[TopPin]

Ohh there is a long list of possible reasons. I would personally look into your initial group of 3 shots. If it's consistent in a triangle formation, that in my opinion means it likes the powder. If it's a 3/4 in group, I would adjust the powder charge .3 grains on either side, your group will either shrink or grow. It will lead you into a more stable node. If it gets smaller as you increase powder charge increase another .3 gr until you either hit pressure or your group opens. (I find in a bigger triangle group your rifle typically wants more powder) Flat or Vertical groups are the worst thing you can see on paper. Adjusting seating depth is another avenue, I've found Berger and ELD bullets to have their best performance close to the lands inside of .030 even as close as .002 if you can load that close in your rifle? Brass prep, overall case length being the same or within a couple thousands in brass, neck tension, primer pockets, ext. The more meticulous you are in your brass prep the more consistency you will have in your groups. Change of primer, different brand, or large magnum makes a huge difference. Also proper bedding, checking to make sure you don't have contact on the barrel from the for-end of the stock, cleaning your barrel to illuminate cooper build up in the rifling. the list goes on…. Then test your 4 or 5 grouping. Good luck sorry for the rambling hope it helps..