finding my best load

[iamJim]

I've just started on my handloading journey and have been doing some load development for my Sabatti STR 308...I have been using N-140 and SMK 155gr Palmas.  i started by loading in 0.5gr intervals from 40gr up to 43gr and firing 2 3 shot groups with each load.

The problem is that i haven't seen a consistent difference in group sizes.  First time through the cycle (starting at 40 and working upwards) i found my best group was at 40gr (0.330in group) and got worse from there.  Second time around though, i found my group at 43gr was the best (0.345in), although 40gr was still good (0.390).  I also found that the velocities were slightly higher second time round.  Have i done something wrong here and what should my next actions be?

 

Thanks in advance everyone!

[forbie]

Youre barrel and bullet combination will have a few "nodes" as you go up in charge weight where bullets will group better with barrel harmonies being right. You need to find the best one for your rifle.

You don't mention anything about seating depth. How far off the lands you are or how you achieve this. Consistensy here with give a better indication of group sizes with velocities. An OCW (Optimal charge weight) method will give you a structured way to test charge weight versus group size and a definite indicator as to what works best in your rifle. Search the internet for the above as to how to do it. Bullet seating depths are best done on a specific point on the ogive of the bullet. Hornady do a comparotor and the Shooting Shed does an improved version. OCW sheet will point you in the right direction as to charge weights once this is sorted then you can add subtract fractions to re check and then adjust seating depth for further possible improvements

[iamJim]

43 minutes ago, forbie said:

You don't mention anything about seating depth. How far off the lands you are or how you achieve this. 

First, thanks for your reply i appreciate the effort. 

Its funny, i almost mentioned seating depth in my op, i haven't played with seating depth, i'm setting my COL to 2.9in and i haven't fiddled with that yet.  I'm not sure how best to calculate my optimum seating depth or how to calculate distance to lands.

I will google the OCW method though...Thanks

[Richiew]

Hi there 

go to load for 155’s in 26” barrel  acc int AT 308 using N140 is round the 46 grain mark . 

42.5 grains N135 for Berger 155.5 s 

44 grains N150 for 175’s 

all at 2.9 coal  and found base to ogive length of 2.234 or 2.237 seems to be the magic length for all bullets in my barrel . I have previously put some of my loads in the hand loading section along with bullet speeds so have a look there for further info . Cheers Rich