Load change/new brass

[FishfinderAK]

Hi all
Quick rookie question.
I recently, after many attempts, put together a load that was shooting great in my .300 WM. 76.5 gr H1000 and 200 ELD-X.
I was shooting consistent 1” groups at 200 yards. All this development was using factory Barnes reloaded brass.

NOW, I bought some of the new Gunwerks brass and it seems my groups increased to 4-5” groups at 200 yard using the same recipe. Even on second loadings.

I did notice the new GW brass is 30 gr heavier. Assuming this is because of thicker walls.

Would these thicker walls cause higher pressure? Thus, should I down-load (reduce amount of powder) with the GW brass. If so, by roughly how much?

Thank you.

 

[N2TRKYS]

What readings did your chrono give you with the different brass?

 

[codym]

I’m not an expert but I just had a similar experience. I bought a barreled action, load work up was done with Winchester brass and the gun was shooting beautiful little groups with 110 smks and 42gns h4350 at 3080fps. I know the guy and he did meticulous load workup as I usually do. Well being in a hurry I duplicated the load with nosler brass, in short order I blew the primer out of the first piece of brass and had a 3178 FPS velocity! What a moron, I knew better. I’m at 39.6 grains to hit the 3080 node in the heavier nosler brass where he was at 42.2 in the winny brass. Yes it makes a huge difference on pressures. Always start low and work up when changing a component.

 

[Sawfish]

Very likely. Reduce your current load 10-15%, which you should do after a major component change, and work up/down from there. Does your brass show any signs of high pressure i.e, bright marks on the bolt head, sticky extraction or brass stretching?

 

[BRTreedogs]

3p grns wow
Have you reshot the old brass and verified?
Check all mounting screws?
The difference may be cbto.
Have you tried a 2nd round of the gw brass 1 fired resized?
If the headspace is different on the new brass vs your old once fired brass you have to adjust the cbto according and then back after you bump the shoulder 2 tho.

 

[BRTreedogs]

 

[Lazzwarbird]

From 1” to 4-5” seems like a huge change. Wouldn’t think overall length could make that big of a difference????