Page 25 of Arms Law (RMC2) table 03-01 provides a +15 initiative for longer weapon when charging.
Page 28 of Arms Law states:
1) the person charging must be moving at a pase of "run" or better.
2) The bonus to OB is the number of feet the person charging moves in a straight line. So in the example of a dwarf moving 100 feet, it would be +100, except the bonus is capped at +50. So it would be +50.
3) The penalty to DB is the same, so in this case, the penalty would be -50DB.
I am not aware that RMC had any penalties to combat for moving. We usually played that it was a moving manuever, and the resulting value was the penalty to OB with a corresponding bonus to DB. So if you charged at a foe (as in the example above), you would get +50 OB, -50 DB for the charge. You would then make a moving manuever (we used a terrain-base, so a nice floor was easy, but rocky ground was hard.) If your manuever resulted in a penalty (any number lower than 100), your OB suffered that penalty, but you gained that in DB. (Erratic movement.) So, assuming you made a successful moving manuever, you would have a net +50OB.
And, if you had the longer weapon, you would likely win initiative, as +15 is significant in a 2d10 environment. If you had a shorter weapon, that -50DB would likely send you to the grave.
Some of the companions changed the charging rules, and moved the damage up instead of OB. I liked that batter, and we switched to using that once we understood the rules. But they are more complex, because you have more to calculate.