Nosler 168gr BTHP vs 165gr AB: POI Left?

[Bullwhip]

Hi all,

I did some load development on the weekend for my .308 Win Tikka T3.
Brass, primers, powder, OAL (due to having to fit the clip), are all the same - in fact both bullets ended up liking the same powder charge range (43.6 to 43.8 IMR4895).

I used a round robin method, going from 42.0gr to 44.0 grains, 0.2gr increments for each bullet, until I had 6 targets each with three rounds in them. The gun was given 2 to 5 minutes between shots and a half an hour between 165gr and 168gr tests.

There was a slight wind from the 11 o'clock but this was present throughout both tests.

The performance was very consistent for both bullets - and printed the same 3 to 3.5 inches high at 100 yards, right where I wanted vertically.

The only thing is the 168gr BTHPs printed dead on the horizontal axis POI but the 165br Accubonds printed 3 inches right.

Why 3 inches right?

The only thing I can think of is I mis-judged the wind throughout the day and it increased, affecting the AB tests more than the BTHP. But 3 inches worth?

Just wondering if anyone had a similar experience or some suggestions.

 

[rgv]

3 inches of wind at 100 yards on a 165/168 308 bullet is a lot.

Barrels vibrate and whip when they fire. With different bullets/loads, the barrel will be at a different point of 'whip' when the bullet leaves tha muzzle. Heavier barrels are (naturally) less sensitive to this, but bullets of different construction will often group to different point of impact.

 

[RePete]

Why?

You are trying to compare 2 different bullets made in 2 different ways - apples and oranges.

The 168 is a precision made bullet whereas the 165 is a hunting bullet and not made in the same precision way.

The tolerences for the 165 are greater than the 168.

 

[Eagleye]

This phenomenon is often seen when developing loads for two different bullets. It has to do with barrel "whip" as explained by rgv. Two match grade bullets from the same manufacturer can exhibit the same POI shift. (i.e Sierra 308 168 & 175 grain HPBTMatch) There is usually little one can do except try another powder. Or perhaps a seating depth change may bring the two POI's closer, but no guarantees. Regards, Eagleye.