High Group Variance within a Ladder Test

[PrairieHunter]

Hello resident experts!
While testing a batch of handloads yesterday, I experienced an interesting variance in my ladder test. Attached is an image of my groups for reference.

My test was run with a 7mm-08 Savage Axis II to find a good load for a surplus of 154gr. Hornady spire point bullets using H4350. Group A was a powder charge of 42.5 grains, Group B = 43, Group C = 43.5, and Group D = 44 grains.

Groups A, B, and D all shot within 1.1 inches, while Group C was a massive outlier at over 3 inches. I was shooting from my standard solid platform and felt steady on all shots. My question is why would there be a sudden spread in Group C when all other groups seemed to be pretty tight? I have heard of this phenomenon of a "mini spread" right before the tightest node is found in ladder testing, but have never before seen it this evident in the dozens of loads I have developed for 4 rifles.

Where do I go from here? I did not see any pressure signs at my highest powder charge, so I can keep increasing by .3 grains or so to see what those groups look like (max is around 46gr in most manuals). Or I could be perfectly happy to stick with one of the sub-MOA groups within this ladder. My concern is that a change of only +- 0.5 grains of powder can show that huge of a group blowout. I feel like I need to get at least 1.0 +- grains away from Group C to feel like I can maintain a nice tight group.

Any wisdom or opinions are welcome. Thanks in advance!

 

[sveltri]

I would load at 44.5, 45, 45.5, 46, 46.5. D shows the least vertical, but I'd want to know what I'm leaving on the table. Do you have any velocity data?

 

[ShtrRdy]

What was your aiming point for each group?

 

[PrairieHunter]

I do not have a chrono, so velocity is estimated in the neighborhood of 2,500 fps and likely a tad higher (according to published data). I agree with another ladder increasing as you suggest.

My point of aim is about 3-4 inches high and right of each group. The rifle is currently zeroed for Nosler Custom ammo with 140gr accubonds, so I knew I would be impacting fairly low of that point of aim. Sorry I didn't keep my paper on the cardboard backer. It got wet in the rain shortly after shooting and the cardboard actually showed my groups better.

Thanks guys.

 

[PddPdd]

In theory, your nodes should be about 3% apart with regard to powder charge. So your groups for A & D seem to reflect that. If you move to the next node up ~45.3 plus or minus, you should see another tighter group and perhaps your bullet/barrel prefers to be run faster. You will need to do smaller powder increments to find the sweet spot for powder charge imo. Have you done any seating depth testing?

 

[birddog 68]

I would load at 44.5, 45, 45.5, 46, 46.5

This is what I would do. You can always come back down to the lesser charge if there's no improvement.

 

[FireFlyFishing]

Chrono would assist you greatly.

Half grain increments are a bit coarse for my taste. Max 0.3 grain increments are the norm for me.

 

[Phil Rizzo]

.5 gr steps are pretty large, especially for that volume case.
Go smaller than that around the interesting groups, and I'm talking down to .1 in the end.
If you find that 2 or more different charge weights print similar groups, it indicates a stable "zone" or node.

 

[PrairieHunter]

In theory, your nodes should be about 3% apart with regard to powder charge. So your groups for A & D seem to reflect that. If you move to the next node up ~45.3 plus or minus, you should see another tighter group and perhaps your bullet/barrel prefers to be run faster. You will need to do smaller powder increments to find the sweet spot for powder charge imo. Have you done any seating depth testing?

Thank you. I have tested the seating depth and have been seating to 2.84" OAL which is about as close to the lands as I can get (according to my tests). Is there any chance that deeper seating might improve groups versus being as close to the lands as I can get?

Regardless, once I find my best group, I can then play with seating depth some more to refine the group.

 

[VinceMule]

In my rifle, the 154's like to be seated very close to the lands. Sort bullets by ogive length and try them .003 off the lands, and 7/08s are not hard to tune. Winchester 760 is my favorite powder with the 154.

With your best load, try a different primer, and I hope you are using the same brand of brass, Lapua if you can find it, which is extremely tough.

Those 154's, shoot holes through both shoulders on large hogs, great short range bullet.

Your barrel will DEMAND a cleaning frequency to keep the copper fouling to a minimum. This is a huge issue. Some barrels will go 9 rounds, while others may go 30 rounds as these barrels can have quite a rough bore. Good Dewey or Pro Shot brushes and Montana Extreme Copper Killer Keeps you shooting small groups.

My last Savage 116 in 7 Mag would go 9 rounds, shooting 1/4" groups, then go to 3/4" groups by the 15th round. A cousin owns that rifle today, still shooting tiny groups, beautiful walnut stock, bedded and trigger reworked by Sharpshooter supply, and a Gentry muzzle break.

 

[PrairieHunter]

In my rifle, the 154's like to be seated very close to the lands. Sort bullets by ogive length and try them .003 off the lands, and 7/08s are not hard to tune. Winchester 760 is my favorite powder with the 154.

With your best load, try a different primer, and I hope you are using the same brand of brass, Lapua if you can find it, which is extremely tough.

Those 154's, shoot holes through both shoulders on large hogs, great short range bullet.

Your barrel will DEMAND a cleaning frequency to keep the copper fouling to a minimum. This is a huge issue. Some barrels will go 9 rounds, while others may go 30 rounds as these barrels can have quite a rough bore. Good Dewey or Pro Shot brushes and Montana Extreme Copper Killer Keeps you shooting small groups.

My last Savage 116 in 7 Mag would go 9 rounds, shooting 1/4" groups, then go to 3/4" groups by the 15th round. A cousin owns that rifle today, still shooting tiny groups, beautiful walnut stock, bedded and trigger reworked by Sharpshooter supply, and a Gentry muzzle break.

Thank you. I have been very consistent with my brass and primers for this rifle. Federal brass feeds the best and that is what I have been using exclusively. Since I have a decent stock of Rem primers, that's what I've been using. I have not yet acquired any Lapua brass, but if I can find it, I'll try that once I have hit the sweet spot of this load.

Good point about barrel cleaning too. I don't exceed 24 shots when testing loads (usually 4 loads with 3 shot groups = 12 shots x 2 different ladders), but I could be cleaning after each 12-shot ladder.

My purpose for the 154's is smallish Oklahoma whitetails inside of 300 yards. And a few wild pigs when the chance presents itself.

 

[willfrye027]

Nodes are a fairy tale. If you shot a 20 shot group or some other large number that is statistically meaningful, it will probably fill in and look like group C, just with more holes.

 

[PrairieHunter]

Nodes are a fairy tale. If you shot a 20 shot group or some other large number that is statistically meaningful, it will probably fill in and look like group C, just with more holes.

That is exactly where my brain wanders most days. I work in the wildlife science field and have a decent amount of education and experience with statistics and data. I keep thinking that if I shot the exact ladder from yesterday 10 times, would group C always look like that?

The tightness of the other 3 groups has me thinking I'm in the ballpark. The nice thing about this game of load development is that shooting more always seems to be the best answer! I won't ever complain about more bench time.

 

[Phil Rizzo]

Will Frye, how many different 20 shot groups should he shoot, and specifically, at what charge weights to determine the best charge weight?

And for a hunting gun only, at 300yds or less, could he shoot less than 20?
say 5 shots or 10 or ?