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1st time exp. w/ shooting custom load development. Got some questions…


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Hello, I shot today my 1st load development at the range and I have some questions. I just start reloading so I am a beginner.

I shoot a Mossberg ATR 100 30.06 w/ Vortex Crossfire II 4x12 44mm. Leupold good quality rings w/ Loctite. 18lbs of torque value on the scope rings much higher on the base (don’t remember the value). I am young I have good eyes. I shot from Caldwell “the rock“ front rest + protector rear bag (=not professional but very stable setup in my opinion). I shot in sitting position on a very stable wooden table (public range so build to last). Minimal to no wind. Typical Arkansas weather in May. I shot at 100 yards in public range. I know by experience that my gun is capable of 0.9 MOA w/ military surplus Ball FMJ ammo. I am comfortable to say that my shooting skills allowed me to take human factor to the strict minimum thanks to very stable shooting setup. I have a Timney 2lbs trigger. I reloaded these rounds the best I could to ensure repeatability in the process. I took my time. All parameters are very consistent within +/-0.005”. I used same powder, bullets from same lot, cases are from 2 different batches thought. I used Hornady GMX 165grain, “Varget” powder and rem. # 9 ½ large rifle primers and a mixed of once fired cases. I full size all the cases but the shoulder height to base value correspond to the max value my gun will accept before I can’t shut the bolt (I have Hornady headspace kit). I set the bullet 0.010” away from the land. I measure COAL w/ Hornady bullet comparator (from the ogive and not the tip). I always clean by gun after ea. trip to the range so there is no excessive waste buildup that could affect accuracy. I shot 15 rounds of regular hunting ammo (Rem. PSP CoreLockt) before shooting my loads to set my scope and warm the barrel (and the shooter lol). I let the rifle cooled 10 minutes (bolt open, rifle muzzle up) before start shooting my load. For my load, I shot 10 groups of 3 rounds ea. I let at least 2 min between groups to cool barrel off. I let about 45 sec between ea round within ea. group. Sometimes I let the gun cool off more (so not always consistent). I took a 10 min break between group 5 and 6 (to change target when the range officer call). There is 0.2 grain powder increment between ea groups except the 3 first group are 0.8 grain increments.

I measured my groups and I can see a pattern showing where it shows the good nodes from the harmonic effect. Those 2 nodes give me about 1.3” MOA and 1.6” MOA. The others group are crappy, they go from 1.8” MOA up to 3.2” MOA. What interesting is that I loaded these results into an excel chart in the order of shots and you see visually 2 waves of harmonic accuracy. The bottom of the 2 waves are my 2 best nodes that give me the best groups (1.3”). The top of the waste are the worse groups obviously (3.2”).

But my problem is the following:

I understand that I should have shot 4 or 5 rounds for ea group in order to get a real statistic instead of only 3 but it is too late, I have to deal with what I did. What I don’t understand is that for 5 of the 10 groups, I have 2 bullet holes out of the 3 that are real close to each other’s below 1” but the 3rd bullet hole is away (=which drives my group performance to the roof as I measure the 2 farest holes distance to determine the grouping value).

I wouldn’t be worry if it was very few groups due to typical math’s statistic but half of the groups seems too many for bad luck. It seems a lot. I didn’t pay attention to see if it is always the 1st or 2nd or 3rd bullets that I shoot that do that so I can’t tell you.

So can barrel temperature real affect the accuracy at this distance (since I wasn’t perfectly consistent in my cooling time)??? Can the different sources of brass I used affect accuracy that much at that distance? Can it be simply that my $350 Mossberg can’t do more w/ this load for some reasons? Can my reloading process affect accuracy that much (maybe I wasn’t very consistent after all and I don’t know it). For some of the cartridges I had to push a little the bolt to shut as I may have set the shoulder to the limit. In others words WHAT COULD be THE ROOT CAUSE OF THIS strange PATTERN? I am wondering if I should measure my group on the 2 bullets close to ea others instead? What do you think please?

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Sounds like your rifle can shoot 0.9" groups, but your reloads are 1.3 - 3.2",

so you should be able to improve your reloads.

I favor shooting larger groups - at least five shot groups, maybe larger.

I'd definitely stay with a single case headstamp (and number of times fired)

for the cases, and see where it goes from there.

Might do better with a different weight bullet or different powder.

Isn't load development GREAT!!! My favorite part of shooting. :cheers:

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Some guns just dont like some powder bullet combinations. If you have a lot of these bullets & this powder, work around your best node. Check slightly shorter. Load .1 gr more & less. Try them at 200yds. Make the most with what you have.

I have a load for 1 of my ars that shoots same actual measured group at 200 as it does at 100.

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