Help me understand this 300WM load

[Duh]

Hey guys can someone please help me wrap my head around this load I developed. To start, I’m shooting a Seekins havak 300WM with a banish 30 suppressor and a NF NX8.
The load is virgin Petersons long brass with 77 grains of H1000, fed 215, and a 212 eldx.

I’ve shot over two separate days at basically the same temperature and humidity and haven’t ran into pressure signs yet.

The bottom group is my first grouping for this load and ended up about 4 inches low of my previous zero, which was a significantly slower load. This was shot on 8/14/23 and the temp was 70 F.

I liked the accuracy of this new load and the numbers so I loaded up 30 more and went to zero today. As you can see, the only changes I made to the load was seating the bullet 4 thousandths longer. I did that so I would be a even 20 thou off JAM. I figured this wouldn’t cause a huge change.

I figured that I was going to be 4 inches low based on the previous group from 8/14/23 so I made a 4 MOA adjustment and hit above the cardboard target. This surprised me so I just dialed back down to my regular zero and I hit perfect vertically but a tad left. I ended up shooting a 10 shot group and made a 1/4 MOA adjustment to the right. This is the top grouping shown in the picture.

My shooting was done off a solid bipod and rear bag. I have not cleaned the barrel between these two loads. The components are all the same and the temps were pretty much the same. The only real difference between the two loads is the 4 thou longer seating depth (which I didn’t think was enough to give me that different of results). As you can see, my velocities are slightly faster in the bottom group but not by much. The Chrono was a magnetospeed v3 on a MK machine mount so I there was no barrel interference.

Why was the first group so low compared to the top group?

 

[A382DWDZQ]

What distance was this at? I would start by loading up 10 of the 2.896 rounds, then alternate every other round with a 2.900 round. See if you are able to replicate what you have on there now.

 

[ResearchinStuff]

Did you take the suppressor off and put it back on between groups? Or take it apart to clean it?

Are the action screws tight? What about the scope ring screws?

 

[Duh]

What distance was this at? I would start by loading up 10 of the 2.896 rounds, then alternate every other round with a 2.900 round. See if you are able to replicate what you have on there now.

It’s at 100 yards.

 

[Duh]

Did you take the suppressor off and put it back on between groups? Or take it apart to clean it?

Are the action screws tight? What about the scope ring screws?

I did take the suppressor off. It’s a direct thread but it has not been cleaned between groups. The van stayed tight through the groups.

Screws on the gun and scope are all tight. That was my first thought so those were double checked right after the group.

I’ll add this, on 8/14/23 I did a ladder test between different charge weights of H1000. The lowest load of 75grains hit bullseye but the other charge weights hit lower from that point on, as the velocity increased. I’ll post a picture of that ladder test when I get back to the house.

 

[ResearchinStuff]

I bet it has to do with removing and replacing the suppressor. Should be easy enough to test and see if that causes the issue or not. My 22 can that disassembles causes random poi shifts when its removed and replaced.

 

[Duh]

Ok here’s the rest of the groups from the ladder test on 8/14/23. The lower charge hit bullseye and then they groups get lower as the charge weight goes up, (Don’t pay attention to the small 22 holes at 76.5grains, that was my kid). But as you can see it’s a consistent lower impact. The suppressor was not removed during that session. I did start shooting the ladder with a cleaned barrel. I took 3 fouling shots before I started shooting groups. There was also sufficient barrel cool down between groups, regardless of the of heat desperation I’ve read about on here.

 

[Duh]

I bet it has to do with removing and replacing the suppressor. Should be easy enough to test and see if that causes the issue or not. My 22 can that disassembles causes random poi shifts when its removed and replaced.

So should I mark the suppressor in the position it’s at now and try to attach it to the exact spot every time? I’ve never had a POI shift from this gun and suppressor before.

I also haven’t taken the suppressor off since shooting my “zeroing” group.

 

[ResearchinStuff]

well, if it hasn't been touched in between these groups then it is not the problem, unless it's just not tight to begin with.

 

[Duh]

well, if it hasn't been touched in between these groups then it is not the problem, unless it's just not tight to begin with.

No it hasn’t been touched between my last group (yesterday). I got the results I wanted and have left the suppressor attached. So maybe I’ll mark it and try to get it squared up every time.

The can was definitely tight for all the groups I shot.

 

[Duh]

Okay got an update, I marked the suppressor where it last was when I zeroded it and threaded it back on. Shot a quick group and did not have a POI impact at all. I’m completely lost as to what caused the significantly different groups.

 

[Sandstrom]

Is it possible your spouse or child dialed the scope between range trips?

It happened to a guy I shoot league with.
Ryan

 

[thinhorn_AK]

So should I mark the suppressor in the position it’s at now and try to attach it to the exact spot every time? I’ve never had a POI shift from this gun and suppressor before.

I also haven’t taken the suppressor off since shooting my “zeroing” group.

If it’s direct thread shouldn’t it attach to the same exact spot every time already? I’ve never had my rifle shift just from taking the silencer on and putting it back on. What sort of silencer do you have?

 

[Duh]

If it’s direct thread shouldn’t it attach to the same exact spot every time already? I’ve never had my rifle shift just from taking the silencer on and putting it back on. What sort of silencer do you have?

Yeah it does. I confirmed that yesterday by marking it and taking it off before reattaching it. Went and shot a quick group and it didn’t have poi at all.

The suppressor is a banish 30. There’s no obstructions with the baffles either.

 

[Flyjunky]

You didn’t specifically state this but I’m assuming all shots were with brand new brass?

 

[Sandstrom]

Is there any chance you are “loading” the bipod differently between groups causing the stock to contact the barrel and cause the shift? Or the rear bag catching on the sling stud causing it to recoil differently?
Ryan

 

[Duh]

You didn’t specifically state this but I’m assuming all shots were with brand new brass?

Yep the brass is brand new virgin brass. It’s Petersons long brass that has only been chamfered, debured, and the necks open up with a expander mandrel.

 

[Duh]

Is there any chance you are “loading” the bipod differently between groups causing the stock to contact the barrel and cause the shift? Or the rear bag catching on the sling stud causing it to recoil differently?
Ryan

I think there’s always a possibility of having a little variance in the shooting. However, this accutac bipod I have doesn’t have very much flex and I feel like I’ve shot all groups the same. I don’t have a rear sling stud so there’s nothing catching.

when I shot the initial ladder on 8/14/23 the groups showed a consistent downward shift in the POI as the charge weight increased. However, the screws on the rifle and scope were/remained tight throughout the shots.

Here’s a two part question, Is it possible that the 20 initial shots and the residue being relatively warm in the barrel could have caused the downward shift? Then, me leaving the barrel dirty (which this gun shoots better dirty) and that residue hardening/cooling would cause the gun to shift back to my original horizontal zero?

 

[MojaveJim]

Is the rifle new? If not what is the round count?
I've seen hotter loads group lower due to harmonics without a can hanging on the end.
Were you shooting a different brand of bullet or powder before load development ?
Seems like a stout load to be pushing a 212gn bullet @ 3000ish fps

 

[Duh]

Is the rifle new? If not what is the round count?
I've seen hotter loads group lower due to harmonics without a can hanging on the end.
Were you shooting a different brand of bullet or powder before load development ?
Seems like a stout load to be pushing a 212gn bullet @ 3000ish fps

No it’s a few years old. Has between 400-500 rounds down the tube. I was still shooting the 212 eldx but I shot that with Norma brass and H4831 SC at 2820FPS. That’s what the gun was zeroed at when starting the load development with the H1000.

The new load is at book max but I haven’t had any pressure signs and it’s shot very well so far.

I just don’t understand how it could have thrown that low group on essentially the same load then shifted back up to essentially my old zero with the same load.