Home Forums Hunting & Shooting Ask The Gunwriters 308 win loads

I'm also posting this in the reloading section. I verified two loads at 100 yards for my 308win Remington 5R yesterday at the range. First load was 43.2 grains of IMR 4064, 175 SMK, BR-2 primer in Remington cases. Seven shots 1/2 MOA, 2662 fps avg. ES 22, SD 6. Second load was 47.5 grains of CFE 223, 175 SMK, BR-2 primer in Remington cases. Five shots less than 1/2 MOA, 2774 fps avg. ES 17, SD 6. The next outing will be at 200 & 300 yards. Now for the question. I load some subsonic rounds using 10 grains of Trailboss and 165 HPBT SGK's at 50 yards. Shot (1) 1101 fps, (2) 1109 fps, (3) 1077 fps, (4) 1064 fps. First three shots straight in, fourth shot alittle side ways (not complete key hole). Could the Trailboss be fouling the barrel differently to the point of slowing down the subsonic loads. All of the loads where weighted on a GemPro 250. Thanks for some insight.

These rifles are capable of some pretty good accuracy. I can't get good groups every time like the guys with the all day long rifles, but my 700 Mil-Spec 5R .308 shoots the 168 MK very well, with many 5-shot, 100 yard groups of around one-half inch. Best group has been 1.4" for 5 shots at 300 yards on a calm day. I've found H4895 to be the best overall .308 powder for my purposes, but there are lots of good .308 powders. I don't look at SD or ES unless a load is shooting poorly, but I don't shoot at long range where SD and ES may matter.

Most people don't clock enough shots to get a good handle on SD anyway.

How many is a good number to get a fairly solid handle on it?

I was a mathematician, not a statistician, so I'll defer to Denton who deals in statistics professionally. I recall him saying something along the lines of estimates of SD derived from as many as a couple of dozen samples have a high level of uncertainty.

In statistics epidiemology lectures in veterinary school. The said sample groups of sixty or more is where you need to start.

Gotcha. No worries. I was just wondering.

I was instructed that unless there were, at a very minimum, 40 samples, you couldn't have the least bit of confidence in the Standard Deviation. More samples are always better.

tomt53,

I would guess your Trail Boss load is acting a little wonky because the muzzle velocity is around the speed of sound--not subsonic. I doubt the problem has anything to do with fouling the barrel. Instead the transonic zone often results in some bullet instability. I'd suggest using a little less Trail Boss, which should provide a true subsonic load.

Just look at ES and keep it under 20 fps. If you can keep it under 10 fps for 10 shots, you're doing very well.

It depends. Good rule of thumb is about 30.

The ammo factories I've visited have generally depended on at least 40 for hunting ammo. (Not match.) But they're loading for a "wider audience."

I have a Tikka HB that likes IMR 4064 almost as much as Varget with the MK.

IMR4064 - 0.547 inches The load is a bit lighter than yours, but I use IVI military cases. 41.5 grains manages 2565 fps. It consisteantly hovers around 0.5 an inch or a bit more. The wind always plays with them a little.

Just a quick question about your TB loads. Did you start higher and reduce to 10 grains? I know that you said you want subsonic loads, and you can reduce them, but I would only drop about half a grain to see where your velocities are. I would also load some up at 11 grains as well. The extra grain of TB might raise the velocity by 50 fps.

I think you can have some fun playing around with those loads!

Thanks everybody for the replies.
Steve, I started at 10 grains of TB based on some research. I have an Omega 300 that I will be using with the subsonic loads. I am trying to get as close but not go over the speed of sound.

I think you are just about there, Tom. My spidey sense tells me 9.5 grains should do it.