If the bullet wasn't stabilized, it would keyhole at 300 and 400. it's hard to keyhole a sub-MOA group. OP stated that he noticed the keyhole issue at farther distances.
I'm betting that the bullet is hitting trans-sonic about the 830 yard mark and is just having hard time STAYING stabilized.
My recommendation stands: Try a slower powder. I'll add that you should give the powder a chance by loading the bullet out a bit. get back some more room in that case if you can.
175 SMK's dont do this. They were SPECIFICALLY designed to NOT do this because thats the issue the 168's have. 168's will reach out to whatever you can push them to, thats not the issue with them, its the transonic tumble that kills them. I know a guy that burns 168's out of a 300win mag out to 1500+. He loves em, I think its a barrel burner. Ive shot 175's in 308 out to 1200, where they were FAR below subsonic and all they did was stick in the plywood we shot them at.
To the OP: you sure you are shooting 175's? Not saying you arent loading from a box that says "175g MATCH", but that the bullets are in fact, 175g SMK's and not a factory **** up of 168's?
The other thing to check for as has been mentioned, pull a round and inspect the bullet. Do you chamfer the case mouth at all? If you shave copper you will have accuracy and possibly stability issue. 308 has fairly thick case mouth walls and without a healthy chamfer will shave a noticeable amount of copper from the jacket.
Well guys, thanks to suggestions to pull the bullet and see what is going on I have found the problem. I stopped after work and bought a bullet puller and started disassembly as soon as I got home. Weights were consistently off by around TEN FULL GRAINS on each and every round. It's time to get a new scale.
I appreciate all your help guys. Sorry it took so long for such a simple answer, but I wouldn't have even pulled the bullets unless I posted.
Glad you got it worked out. See I told you it was something simple!
that is why I have 2 scales on my bench and I still don't trust either one.
never hurts to have one of those old timey beam scales handy. May not be as accurate as a new digital but it sure wouldn't be 10 grs off
im still skeptical of the claim of a 175g SMK tumbling when going transonic/subsonic as they are not known to do that(168g SMK's on the other hand ARE known for doing that). They are known to transition through that range very well. Ive shot out to distance where I knew they were subsonic upon impact and never once saw a tumble. Im shooting out of a 10 twist gun as well.
I would lean more towards an impact well short of the target and them ricochet/skipping into the target.
rjacobs is dead nuts on. Given the significant reduction in velocity, there is no way that: A) They even made it to the target in the air and B) As he stated - the 175s are not known to tumble, and C) Given the fact that 15 rds were fired and only 2 made it on paper - smart money are rounds impacting well short of the target and having a wee bit of luck in that 2 of them skipped / riccocheted on paper.
I also think that the extrapolation of an aproximate MV of 2025 is being very kind. I would not be surprised if the MV was well short of 2K.
Last edited by opsoff1; 07-31-15 at 12:49.
opsoff
"I'd rather go down the river with seven studs than with a hundred shitheads"- Colonel Charlie Beckwith
Bookmarks