Would it cause balance issues to combine the warhammer and war pick?

Question

The vast majority of the historic warhammer heads found have a pointed and a blunt end.

The horseman's pick was a weapon of Islamic origin used by cavalry during the Middle Ages in Europe. This was a type of war hammer that had a very long spike on the reverse of the hammer head. Usually this spike was slightly curved downwards, much like a miner's pickaxe. The term is sometimes used interchangeably with war hammer.
(http://www.medievalwarfare.info/weapons.htm)

In D&D 5 however they are handled as distinct weapons. They have two lines in the Weapons table (PHB 149). This alone might not mean they are separate items, as one side is piercing, the other is bludgeoning, and the damage could differ as well. But based on the price, they are indeed separate: the War Pick costs 5 gp, the Warhammer three times as much. (This incidentally makes no sense; a point is harder to forge than a slab.)

I know D&D is not exactly medieval Europe, but I am trying to make it more logical by combining the two weapons. The user of a Warhammer could choose between bludgeoning and piercing damage as a free action on his turn.
Would this cause any balance issues?

Answer 1

It shouldn't create any imbalance issues. Which physical damage type (Bludgeoning/Slashing/Piercing) you use has very little impact in the game, with regard to enemy resistance and vulnerabilities.

Answer 2

At the bottom of this slippery slope are players who demand a weapon with a hammer head, backed by an axe blade and topped with a spike so they they can select any sort of damage at all. With enough avid searching, they'll even find historical examples. The balance issue is then between these do-it-all weapons and the does-one-job-well weapons. The weapon list in 5e is rather well-balanced such that whatever weapon you think is cool has some kind of build that makes it a viable choice. The risk is that players could feel they have to choose the "right" weapon rather than the fun one.

If you're looking for a house rule to cover this, my suggestion would be to say that the officially listed damage and type describes the most effective way to use the weapon, and to only allow alternative damage types with less than the listed damage. So for your warhammer, it's 1d8 when used to bludgeon, and perhaps 1d6 when reversed to pierce. You might similarly let someone stab with a longsword for 1d6, or slice with a rapier for 1d6. A less generous (but more RAW) suggestion would be to consider all alternative uses as improvised weapons doing only 1d4, but allowing people their proficiency bonus since the secondary use is part of weapon's design.

In practice this will preserve the usual balance, since people will almost never use a weapon in any way except the one that does the most damage. It still makes certain weapons better against creatures with particular resistances, just less noticeably so.

(Bonus: a historian's opinion on the does-it-all versus does-one-thing-well issue.)

Answer 3

Weapon stats in a game like DnD only have enough similarity to the real world to aid in suspension of disbelief, and considerations after that are for balance. Bludgeoning is a relatively valuable damage type for a lot of DnD adventuring parties (undead either don't resist it or are vulnerable to it), and so I would imagine that the price difference is based more on that consideration, and the lower damage dice of the pick, and not on actual real-world pricing.

However, like @Philipp says, once you start dealing with anything beyond third level or so, the difference is going to be spare change. If the current rules make it harder for you and your group to suspend disbelief, just give the warhammer the exact same stats as the morningstar and be done with it.

Answer 4

In previous editions, some weapons could do two types of damage (either both at once, like the Morningstar, or either-or, like the Dagger).

In 5th Edition, all weapons¹ now only do one type. Presumably, this was a balance consideration. Reversing that decision is up to you as DM, and if you allow all² weapons to choose between two types, then you're not changing the balance.

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¹ at least in the Basic rules
² except where it makes no sense - what would the second damage type be for a (non-spiked) club?