Howard NZ.
tell me and anyone else who wishes to , which do you do first during testing?
We are talking about the Handi rifle in 243. Lets say you want a light big game load and chose from various different 100 gr bullets I would start with a 100gr Hornady Interlock or the 100gr Hornady Interbond two most excellent bullets and very accurate in most 243 rifles.
I guess you would use the the Aussie (Hodgdon powders). If you use other powders start with the slowest burner minus 10%. The load listed in the Hodgdon manual is 47gr @ 49800 CUP with H1000 at 3000ft this way too hot for the Handi, me thinks? But with a bit of oversize chamber, throat and free bore this could be ok. For the Handi I always use the slowest powders.
Another reason for H1000 is, the pressure curve is longer and places the max pressure nearly outside the case mouth. This also creates lower chamber pressure and burns more powder in the barrel for higher velocities.
Lower chamber pressure also reduces the barrel vibration which theoretically increases accuracy. The Handi lock-up is very susceptical to excessive barrel vibrations. OAL comes after you get some decent groups with the bullets as far out as practical 10 thou into the lands if possible.
Tweaking a Handi for accuracy can be taxing, Handies have button rifled barrels, shallow grooves and what I have seen have pretty smooth finishes. It should not take more than 40 rounds to break in the barrel. For the first 20 rounds clean the barrel with J-B paste frequently.
If the rifle does not shoot good groups after that, start looking for loose spots, gaps and latch engagement, a light trigger helps too.
Try to make your rifle shoot with somewhat reduced pressure.
Look at my web page for some ideas of tweaking the H&R Ultra.