Rookie question: .308 165gr. vs. 168gr. groupings @ different ranges

[3030AT30]

Hey everyone,

I'm a rookie when it comes to shooting, so please go easy on me.

I recently purchased a Savage 10 PC in .308. It features a 20" barrel with a 1:10 twist.

I took it for the first time on Sunday to sight it in with my new scope- Vortex Diamondback Tactical 4-12x40 - and some different types of ammo to see what it likes to eat.

Weather that day was 9 degrees Celsius, pretty windy, but the lanes have good berms so I can't say how much was affecting the shots but definitely some.

The rifle quickly got on target and I was soon zero'd @ 100m with 165gr Federal Vital-Shok Bonded Trophy Tip (yes, a hunting round). With this round, I shot the best grouping I've ever shot, see below:



I then switch to 168gr. Hornady AMax Match ammo and my shots pulled left and grouped at maybe 2"? (Not well enough for me to take a pic at least).

With these results I figured, "Sweet! I found my ammo" thinking the Federal was my huckleberry, so I moved out to 200, then 300 metres shooting from a sitting position with a bipod.

Well, crap! The 165 was pretty loosey-goosey (windage was acceptable, but elevation was off) at both those longer ranges (again, not good enough to take a pic), so for fun I tried the 168's again and wow! It grouped much better but I did have to dial in 1 MOA windage (oops, bought an MOA scope for our new range which is in metres ):

200m:


300m:


So, my questions are:

• why is the 165gr tight at 100m but opens up at longer range?
  and why is the 168 a little loose at 100m but tightens up at longer range?

Could the 168's need the extra distance to stabilize given the moderately heavier bullet? And why did the 165gr have decent windage "consistency" over distance vs. the heavier bullet which should resist wind better?

The most important thing that I didn't mention: I may have been giggling like a school girl the whole time as, man, I had fun!

Any insights are appreciated.

 

[Alpheus]

So, my questions are:
why is the 165gr tight at 100m but opens up at longer range?
and why is the 168 a little loose at 100m but tightens up at longer range?

3 round groups aren't definitive enough to make comparisons with, just isn't enough data. Two 10-round groups shot from a good steady prone position with bipod and rear bag will be far more informative.
And while the stability of a bullet in flight does increase as it travels, it doesn't make the tiniest difference in grouping as long as it is stable when it leave the barrel. Bullets "going to sleep" is a myth.

 

[3030AT30]

Thanks for the input. Next time I'll take it out and try the 10 shot groups as described.

As for "bullets going to sleep", I wasn't familiar with this term so I googled it and got lost in a physics lesson about pitch, yaw, ellipses... Holy smokes! I've gone cross-eyed! lol.

I appreciate the help!

 

[LeftFootOfDoom]

from what I have read, that happens with bullets such as the 303. I thought that the modern boat tails didn't have that issue.
With the nosler custom comp. 168's, ive had great luck at 100/200.

try some federal gold medal match. 168's to see.

 

[thenerdboy]

I also have a 1in10 twist, 20" barrel .308 and no issues with 168BTHP but I'm handloading. My best 3 round group at 100m with them was 0.28MOA and I've successfully taken them out to 1000m for hits on a 2MOA sized plate. I haven't fired any five or ten round groups yet as I moved straight to long range steel from initial load development. I expect the groups will open up but hold sub-MOA.

I also worked up a load with the 165 BTSP for hunting and I would guess that the groupings varied from 2+MOA down to 0.75MOA and that's the best I can get. Really narrow accuracy node and most charges shot very poorly. Strange that you're having the opposite experience; maybe because the rifle is new? I'm curious to see what the more experienced shooters here come up with for an explanation!