What Happens….

[Bonz]

What happens if you use a smokeless powder to reload a lighter bullet than recommended ???

Some smokeless powders are formulated for the heavier bullets of a specific caliber. In example, VihtaVuori N-105 is not recommended for reloading less than 130gr bullets for a 9mm Luger. I just happen to have a couple of pounds of N-105 and love it in .357 and .500 loads. I am very tempted to reload some 124gr 9mm Luger with the VV recipe for 130gr 9mm Luger. Does anyone know what the outcome would be ?

[Doc_Stihl]

I'm not familiar with the VV powder but I believe you'll get less efficient powder burn. The weights builds pressure. If there's not enough pressure the powder won't burn completely or efficiently.

That's my understanding. Someone with more knowledge will likely chime in.

[btroj]

Depends on the powder. Some, like h110 do better with heavier bullets. A heavy bullet builds pressure better which gives a better burn. Using a lighter bullet can, in some cases, lead to a larger muzzle blast and fireball at the muzzle.
Using a 124 gr bullet instead of a 130 isn't likely to cause much trouble with that powder. I would start at a mid to upper level load however.