Load devlopment.

[martin_b]

I know I said i planned to use up all my existing ammo, but I thought Id better try a bit of load testing anyway. New barrel has had 80 rounds through it now.  Initially zeroed at 300y, then shot at 1000y and today at 200y all on Bisley electronics. 

So at 200y I shot 5 groups of 5 rounds in .2 grain increments, and the result, all groups very similar.  3 groups 4V's 1*5  2 groups 3V's and 2*5. but that difference could easily be my lack of ability/stability with the rear bag, and the breeze.

What I did find interesting is that the POI didn't seem to move much vertically between loads, again could well be down to me. 

If this an usual result, so have I just go luck and hit a 1 grain wide node.  Its not a competition rifle so will probably leave the load as it for a couple of hundred rounds and then maybe try again. 

 

[Popsbengo]

Assuming you shot your groups at a standard Bisley TR 200yd target  the 5 ring is 3.5"  and the 'V'  2.1"  (According to Bisley Handbook 2020).   The 5 ring is 3.37 moa and the V is 2.02 moa diameters.   From what you say it would seem any variance in dispersion made through load development increments may be hidden in the general dispersion due to other factors.   Load development within a maximum of 1 moa dispersion for five shot groups should begin to reveal variations due to load matching to the barrel.

[martin_b]

Thanks.  I think what Ill do is shoot my remaining made up rounds, and whilst doing that try to borrow/hire a chrono and get a real velocity reading at the moment im using a Sterlok derived result from shooting at 300 and 1000 yards and take it from there, maybe with the OBT method is save ammo!

 

cheers

[Popsbengo]

1 hour ago, martin_b said:

Thanks.  I think what Ill do is shoot my remaining made up rounds, and whilst doing that try to borrow/hire a chrono and get a real velocity reading at the moment im using a Sterlok derived result from shooting at 300 and 1000 yards and take it from there, maybe with the OBT method is save ammo!

 

cheers

Never used OBT,  I don't think it's helpful.  The only way to get statistically relevant data is to shoot a sufficient sample.  A small sample may indicate a poor performing load but the converse is not true ie a small good group is not indicative - or more precisely, not sufficient to draw a conclusion from.  The sixth shot of a five shot group may well open up that otherwise tight group...

I have read that for each load increment a 5 shot group, repeated 5 times on separate targets, and then overlaid will give the best indication of optimised loads. ( 5 targets so as to avoid rounds going unmarked through a ragged hole).

Or:  shoot some five shot groups and take the best !  It's unlikely to be the optimum load but it may well be good enough ! 

[Catch-22]

Personally, I think on a new barrel you should (step 1) load up incremental powder charges to find your max pressure.
 

After that, load development starts by (step 2) finding the optimal charge.
Make up batches of incremental powder charges (not exceeding the max pressure you found during step 1), and go shoot them over a chronograph. Ignore group size, that’s irrelevant at this point - you are purely looking to find a node of 3 or 4 charge weights in a row that give a consistently low ES & SD. As example, my .300wm load has a repeatable SD of around 7-8fps. My 6.5x47s SD is 5-7fps.

Once a suitable node is located, repeat OCW with more groups within that node window to give you some statistical significance, and get a better understanding of which place in the node is most stable. You can fine tune this with smaller increments (eg 0.1gn at a time) to find the sweet spot within the node.

Once optimum charge weight is determined, now focus on group size (step 3) by altering seating depth and/or neck tension. 
Shoot more groups, of your optimum charge but with different seating depths, starting from a touching of lands and working shorter by around 0.003” at a time. You may choose to load some longer than touching the lands, going ‘jam’ into the lands, but be aware this will raise pressure.

Once you have shrunk your group size in step 3, take your ‘final load’ out to 1,000yds and verify chosen charge and seating depth again to ensure all is well. Tweak seating and/or neck tension again if needed.