Taken from FM 6-30, Observed Fire Procedures- "command used by an observer to warn the FDC that rounds will impact within 600 meters of friendly elements (for artillery) or (for naval gunfire) within 750 meters for 5-inch guns and less and within 1,000 meters for guns larger than the 5-inch". Rather arbitrary definition that doesn't account for fuze-shell combos. Given the distances involved, it shouldn't matter. I've seen FPFs plotted and adjusted(by tube)much closer. Never using actual troops, of course, as impact areas are not a recommended locale for practicing establishment of infantry NDPs (night defensive positions). We did so at Sill from a fortified concrete, hardened glass structure on the edge of the buffer zone.

It depends. DC is a procedure and the Safe Distance has to be calculated, the actual distance depends on the relationship between the line of fire and the line of own troops. Then there's a quick calc for the maximum safe correction. If the line of fire is overhead then its a PER matter, if parallel then the safe splinter distance dominates. 350 m IIRC. There may be local SOPs about how close the opening round can be aimed, this is n case of map reading or prediction errors. These days computers don't make mistakes and GPS is the idiot's friend.

So, I take it that the M777 show is using the M107 for testing. It seems bloody obvious, of course, but I always wondered why the M795 (the HE-Unitary shell with the same weight/ogive as the DPICM munitions) didn't totally supercede the M107 (although we probably have enough M107 shells sitting in ammo bunkers to last us through WW III). I just read the M107's are still being produced at Scranton Army Depot.

M107 projs. are cheap. A usefull criteria for ordinary artillery training. I probablly have the old refrence here for computing all the items Nuetralizer refered to, but it is a twelve year old doc. & likely superceded. Plus I'm crushed with work this season. For some reason memory tells me a charge error had something to do with this consideration, as well as splinter range.

The first rule for DC was to use the most consistent charge for the range (subject to crest clearance of course). The other reason for M107 is the circumstanes where a high effect HE is unacceptable. In the Balkans the Brits carried both L15 (high effect) and L17 (training, with virtually no HE), different ROE for them as well. M107 sits in the middle.

The safety consideration for charge is gun crew error, loading wrong charge. It used to be a common problem with the light & medium cannon with high ROFs and frequent changes in target. Fatigue & frequent changes in fire orders on the gun line, or a lack of attention in the FDC would lead to a round shot with the wrong charge. In my ten years on the gun line I recall seeing it happen once. But we never shot 300 or 400 rounds from the same battery in a hour at six differnt QE & def. and charge zones as happens in war.