While working up a handload for a .300 Win Mag, I was having terrible accuracy, getting 6-7" inch groups at 100 yards. I did all the usual things, worked my way up through powder charges, tried two different bullet weights and brands with the same terrible results. I was using new PPU brass, full length resizing, chamfering, etc. After double checking my usual process and not finding any issues there, I took some measurements on the brass and found that the shoulders were 6-8 thousandths out of concentricity AFTER fire forming. Additionally, I weighed a 10 cartridge sample and found the extreme spread to be 10 grains.

I ran the same measurements on some fire formed Hornady brass and found virtually no runout on the shoulder(less than 1 thousandth), and case weight extreme spread to be 3 grains.

I have not had time to make any loads with the Hornady brass, but will be doing so this week. I have never encountered such problems developing a load for any rifle, and the rifle will shoot honest 1.5 inch groups with the little bit of factory ammo that I have run through it.

My question to the forum is would the variances in the PPU brass be causing my accuracy issues? Thoughts?

Thanks!

PPU (Prvi) brass is some of the lowest grade brass you can use. That would be a big factor, yes. But 6"-7" groups, that's another problem entirely. If I'm seeing groups that big, I'm looking for major issues with the rifle/scope.

Thank you. After going back and looking at the targets, the groups are closer to 4 inches, which is still pretty dern awful.

I ran these rounds through 2 rifles with similar results.

I reckon I’ll know more when I load up the Hornady brass and try again.

I would agree that the brass is a starting place followed by the scope. Another more unusual issue is action to barrel alignment. Take a look at the spent primers after firing. Look to see if the primer strike is centered. Any slight misalignment of bolt to centerline of barrel will cause point of impact variations and this shows as non-centered primer strikes. Also, mis-alignment cants the bolt face at battery and might cause shoulder variation after fire forming.

I would try some of the new Peterson 300 Win Brass, they have a longer length that will headspace properly on the shoulder. Eliminate poor case fitment on belted mags.

What powder and bullets are you loading? If the rifle does an inch and a half with factory ammo you should be able to improve on that with hand loads. If the PMU is that bad, I would switch to your Hornady brass.

I am running Imr 7977 and have tried 178 Amax, 178 ELDX, and 200 Sierra Gamekings. All had erratic results.

Hopefully this brass is the issue. I wiil shoot new loads with Hornday brass this weekend and reevaluate.

Thanks for all of the input!

As a follow-up, this ended up being a brass issue.

I loaded some ELDX in Hornady brass and as I worked up through powder charges the worst group was just over an inch. Everything else was sub-MOA.

That is great news. I never dreamed brass could cause that big of an issue.

I have never seen anything like it. The brass was just terrible, with inconsistencies all over. Lesson learned though!

Now you know why it's important to have quality brass. There are some brands, and even some cartridges within a brand that I will stay away from.