.300 win mag load with IMR 7828 SSC and 190gr SMK

[Cncjerry]

I'm having pretty good luck with 168 smk's load with 71 gr of IMR 7828SSC. I can't seem to find a load with 190 smk's. I tried around 70gr and they seemed hot, so I dropped to 67gr and they seem hotter. I have some flat primers with very slightly raised dimples. According to the books I have, IMR 7828 SSC with 190 gr should be between 75 and 80 but the hornady book is more like 65 and 70. I read the with slow burn powder you shouldn't load too lightly, and I assume my 67gr is too light?

I am loading for accuracy and shooting a 1:10 26" barrel. I am getting .5" groups from the 168's with 71gr and about the same with the occasional flyer with the 190's and 67gr but they are hot. I am using Winchester magnum large rifle primers.

So should I go higher on the 190s to like 70 gr or higher or lower? They shoot 4" higher than my 168's. My chrono isn't setup for testing these right now but the 190's kick like crazy and shooting so high they must be hot, no?


thanks for the help

Jerry

 

[Cncjerry]

nobody? Can a load as light as 67gr of 7828 cause over pressure with a 190gr SMK?

 

[Big Z]

What kind of brass are you using? Fireformed?
Pressure signs could go away with an extra grain or 2.. pretty unusual for a starting charge to show pressure from being too heavy.

 

[koz]

You should only be @ 51.3k psi with 70gr in the 190SMK @110F. That's pretty far under max psi (62.3k).

QL shows just under max press (62.1k psi) with 74.3gr of 7827SSC @110F. 70F drops you down to 57.5k psi.

 

[Cncjerry]

yes, fireformed brass.

I thought 67 grains would be fine for 7828SSC but I am clearly getting flat primers. Would magnum primers with a somewhat light load cause this? I am sort of stuck as moving in the wrong direction could cause a bigger problem.

 

[Big Z]

Well it certainly sounds like an undercharge is causing your pressure signs...I asked if it was fireformed as that'll increase the case volume and would make more sense that it'd show pressure with a normal starting charge. It ain't my rifle, but I'd try going up. Personally I just load a couple grains under book max when trying a new bullet or something...as I generally end up over max a couple/few grains. I peeked in a hornady book and noticed I had some loads that were several grains over their max. I like their bullets, but it looks like I'm not going to buy their book after all.

 

[Cncjerry]

Z, yes, thanks, found the same with their book as most of my loads are on their heavy side and I think my light loads are too low with the magnum primer. I am going to load a little heavier and see what happens.

 

[Aimsmall55]

A reputable guy on here gave me some advice. If your brass is fire formed , you neck size and you don't bump the shoulder back your case really has no where to expand then retract. Meaning it doesn't have any room to balloon. That would be the reason for say sticky bolt or ejector marks. I ran into the exact same thing with fire formed brass and a lighter charge. I then shot new brass with 1.5 more grains and had no issues at all. Try some virgin brass. I'll bet you the op issues will disappear.