What happened to my load?!

[101stCurrahee]

I just worked up my first loads for my bergara hmr in 300 win mag a week ago. I shot 3 rounds groups going up in .5 grain increments and found a node at 77 grains that gave me <0.4moa groups at 100 yards.

So I went back and loaded up 10 more identical rounds at 77 grains, and 5 each at 77.2 and 76.8. Same exact everything. Seated .02 off the lands.

This time my 77 grain load was 2 moa, the 76.8 was 1 moa and the 77.2 was 1.5 moa.


What happened?? I was so happy. Was it just sheer accident and luck I shot <0.4 moa with a crap load?

Not only was the grouping terrible but my ES was 40-55 FPS. I'm very careful using my beam scale with a powder trickler frequently adding or removing one single granule to get exactly the same each time.


I don't even know where to go from here. Up? Back down to the next lower node that was ok? I really don't want the slower velocity several grains lower. I'd rather stay up near 2950 but now it shoots like garbage.

 

[User4302021]

3 round groups lie. What type chronograph?

 

[101stCurrahee]

Pro chrono 2

 

[L.Sherm]

3 round groups dont lie if you have a good load, perfectly fine for a hunting gun
Need more info, what brass, powder, primer, bullet?
If your 2 thou off the lands how are you measuring? CBTO?

 

[shinbone]

All else being equal, the corresponding 5-shot group will be about twice as big as the 3-shot group.

At 1 moa, your 76.8gn group is what would be expected.

 

[User4302021]

3 round groups dont lie if you have a good load, perfectly fine for a hunting gun
Need more info, what brass, powder, primer, bullet?
If your 2 thou off the lands how are you measuring? CBTO?

If you already know you have a good load then you wouldn't be shooting groups to find a good load.

How would you tell 3 rounds that just happened to group together, from 3 rounds that would regularly group together...if you only fired 3 rounds each?

 

[Canhunter35]

If you already know you have a good load then you wouldn't be shooting groups to find a good load.

How would you tell 3 rounds that just happened to group together, from 3 rounds that would regularly group together...if you only fired 3 rounds each?

Sometimes you can tell by an irregular poi. 3 that cluster together outside of you poi can be an irregular group, compared to the other groups you shot with the same bullet.

I just worked up my first loads for my bergara hmr in 300 win mag a week ago. I shot 3 rounds groups going up in .5 grain increments and found a node at 77 grains that gave me <0.4moa groups at 100 yards.

So I went back and loaded up 10 more identical rounds at 77 grains, and 5 each at 77.2 and 76.8. Same exact everything. Seated .02 off the lands.

This time my 77 grain load was 2 moa, the 76.8 was 1 moa and the 77.2 was 1.5 moa.


What happened?? I was so happy. Was it just sheer accident and luck I shot <0.4 moa with a crap load?

Not only was the grouping terrible but my ES was 40-55 FPS. I'm very careful using my beam scale with a powder trickler frequently adding or removing one single granule to get exactly the same each time.


I don't even know where to go from here. Up? Back down to the next lower node that was ok? I really don't want the slower velocity several grains lower. I'd rather stay up near 2950 but now it shoots like garbage.

Perhaps try a rough seating depth test then retry your groups?

 

[JTW24]

I mean... I'm new here, so I won't say what I'm thinking, but. That thread title makes me giggle!

 

[bigedp51]

Did you workup the first load with new brass and the second load with once fired brass.

 

[User4302021]

Sometimes you can tell by an irregular poi. 3 that cluster together outside of you poi can be an irregular group, compared to the other groups you shot with the same bullet.

If are shooting multiple groups, then you aren't just shooting 3 rounds. How would you know the POI is different if you hadn't shot previous groups with the same load?

I'm saying that shooting a charge weight progression of 3 rounds per load, and trying to read tea leaves based on group size is often misleading. Even when shooting an OCW, you have the groups on either side to consider. You are actually making a decision on 9-12 rounds.

If you have a light weight sporter barrel and don't want to shoot it hot, then shoot at least 6 rounds but do it in 2 groups of 3.

 

[Trnelson]

If you are shooting a new rifle you will want to break the barrel in before working out a load. There are several methods you can use to do that readily searchable on this site so I won't waste time explaining that.
Usually, barrels will speed up and velocity will stabilize some place between 50 and 80 rounds. Yours likely sped up as it broke in and got away from the node you thought you were exploiting. Every rifle is a bit different, I've had barrels that stabilized around 45 rounds and barrels that needed better than 85 to finally settle in.
I like to use the first 40 to 50 rounds to fire form brass, check a couple of different powders with minimum powder charges and swap a few primers as well. No reason to hot rod anything at this point. Every round goes across the chronograph and into my loading book for that barrel. That data is very valuable!! A better quality chronograph will make identifying when that barrel settles in and is ready to start identifying a load, seating depth and primer.

 

[del2les]

Are these the first loads in this rifle? If so, was the brass new then 2nd load fire-formed? Also, does the barrel need cleaning? Anything loose?

 

[emp1953]

If these are the initial shots through a new rifle then you are seeing the results of the barrel breaking in. As in Trnelson comments.

 

[Timnterra]

As stated above 3 rounds is not an adequate measure of known precision. If you said that you had fired multiple 3 round groups that measured <.4moa then you would have a question to ask here. As it stands you never found a load, all you did was have a wonderful statistical coincidence.