Can I use my proxy or conversion?

A frequent question that crops up in wargaming forums, particularly those for Warhammer 40,000, is the request for permission to use a conversion or proxy model. It's not a question that can often be definitively answered because the details of the game you are playing aren't up to random people on the Internet.

The person who can answer that question is your opponent or, if its a game at an organised event, the tournament organiser / venue owner.

That said, here are some guidelines as to how reasonable it is for them to say "No". The more of these questions that you answer "very" then the more reasonable it is for them to not allow your conversion or proxy.

How serious is the game?

Some games are played at home on the floor. Some games are played at tournaments where people have travelled from around the world to compete for prizes. Most fall somewhere in between.

The more serious a game, the more reasonable it is to be told you have to use the official models.

Does the proxy/conversion grant a rules advantage?

Some wargames, including 40K, use true line of sight to varying degrees. If your sniper is significantly taller than the official version then it is going to be able to see over more cover and be more effective. Likewise, shrinking the silhouette of a melee unit is going to make it easier to protect until it is close enough to engage in hand-to-hand combat.

Is it confusing?

If every model is WYSIWYG then an opponent can look at them and know what they represent. If you have one or two proxies (I built my Termagants with Fleshborers, but is it OK if we say this unit actually has Spinefists?) then that's not too much to expect them to keep track of, but if half the units in your army aren't what they look like then your opponent is going to have a hard time remembering what is what.

Are you costing them sales?

Let's take a simple example. Games Workshop sell a wide range of Space Marine models. 3D modellers sell a wide range of designs with a variety of names that look a lot like 40K Space Marines. Some are straight up copies. Some try to do something cool and different.

Going to an event organised by a miniature manufacturer or a shop and taking along a competitor's models is, effectively, advertising to the other players that they should spend their money elsewhere. It's not unreasonable for the host to ban such models.

Is it uncool?

Proxies range from "I haven't spent the time and money to have the right models so I'm going to use vaguely similar models I already own" to "I've taken these Fyreslayers and Kharadron Overlords, converted each individual model to have the right kind of weapons, and am using them to represent the Leagues of Votann".

The rule of cool is worth a lot.