SmallCaliberCentral

I just discovered that my newly developed 39 gr SBK load is leaving jagged holes in the paper and inaccurate groups. The weather when I shot was calm and about 15-20 degrees F.

This summer I finally got the 39SBKs to work after working up some hot loads. I believe my 1:12 twist Remington was on the cusp of stabilizing the bullets because the hotter loads shot better, and finally this summer i bought some Re-10x and loaded just over max to push the bullets fast enough to stabilize. They worked GREAT! 5 shot group .4 MOA accuracy. I shot balloons at 500 yards and all was well with the world and my beloved .204. Then the other day a friend and I went to the range to sight in before our coyote hunt. I shot my favorite load of 26.1 grains of Re-10x, WW brass, Federal 205M primers seated at 2.34" OAL and... Jagged holes with the group size almost 1.5 inches!

Is it possible the cold weather slowed them down just enough to keep them from stabilizing? Sorry I don't have a chrono to know how much its slowed down.

Does anyone have any suggestions? Are there faster, hotter powders to try? I don't think I should go any hotter with the Re-10x

One of the reasons why I switched to IMR8208...
So far I have great velocity and accuracy in different weather conditions. Reloder 10x is accurate in my 204
(Savage 10 max-1) but the carbon fouling was too much.
I use 26.8 grains of 8208 with rem 7 1/2's. I seat em' out to 2.35+... Sends my arrows(39 SBK's) fast and accurate in almost
any condition....

are there any pressure signs ? how much temperature difference between both days ? maybe it was not that it was a hotter load but that it was closer to the sweet spot ?

No doubt it was in a sweet spot this summer when I was shooting anywhere from 60-80 degrees F. I first found the load using an Audette's Ladder with .1 gr increments shooting at 200 yards. No real pressure signs. I think the bottom line is that using the same gun, same exact load, and it worked then and doesn't now. Its great that it works in the warmer months as a target round but I'm sad it isn't also my predator round. I'll have to give 8208XBR a try i think.

IMR8208XBR works very well for me, but it didn't using the 39gr.BK's. H4895 worked better with those and its not temp. sensitive either. Just a thought for you.

just a quick koo-koo test: Keep the rifle and ammo warm, and try it again...

I had the same problem with my Remington 700 when my son and I went to the range recently on a day when it was 18 degrees. My 204 is most accurate when the barrel is almost too hot to touch and that day it never got more than luke warm. Even with keeping the bullets in our pockets to keep them warm we couldn't get my best loads to group under an inch, when they usually group .5 to sub .25 inches.

Had the same problem with my Rem had egg shapped holes and fliers on a still cold morning. Shot it on a warmer day and it was laying them in there when I done my part. Was shooting the 40 gr. vmaxes. Going to try a different rifle in the morning.