I have 2 WWII vintage rifles that hit way, WAY low, and they don't have an adjustable front sight, so I'm stuck to either:
a) grinding down the front sight
b) moving the rear sight to 300m in one case, 400 on the other.
I have several other WWII vintage rifles that are bang on for elevation at 100M, point of aim is point of impact.
My personal theory?
1) One was arsenal refurbed. When it was refurbed, it might have gotten a new front sight post, and then might very well have not gotten sighted after the refurb, on the assumption that if it was brought out of storage, the regimental armourer would have had to give it a once over anyway, and sighted and adjusted it then.
2) The other is, well, pretty thoroughly used. And it looks like it was just stored after the war without being refurbed. Who the heck knows what it went through before being stored, and eventually bought by an importer and shipped to Canada.
3) The stocks. They're wood. They can either dry out (fairly common), or absorb grease (a LOT of grease) if they were given the dip before storage. Either way, both are full stock rifles, and the shrinkage or expansion of the wood due to drying out or absorbing a lot of grease, can put a lot of pressure on the barrel, and really move the point of aim around.
To fix it, you can either grind down the front post or push the rear elevation/distance adjustment up to the point where it's close to point of aim. Personally, I just moved the rear adjustment, because they're just range blaster/fun guns/long term collectibles. I'd rather not risk messing up the front sight by taking a file to it, and I only need it to be so-so accurate for fun at the range.
If you decide to grind down the front post, pause and think about it first. Make sure that you've tried a number of different types of ammo for it - maybe the ammo you have is light loaded, or the powder has degraded if it's REALLY old surplus.
Also, get someone else to shoot it and do a sanity check that you're not doing anything silly with how you're sighting - it can happen, especially with a rifle that you're not used to.
Hope this helps. If anyone else chimes in, as always, I'm willing to be proven wrong, so long as I get to learn something in the process.