I'm not entirely clear on the logic/lore being able to explain how you can swap what kind of ammo is in the gun without reloading it.
That said, however, the idea does seem like it has merit, and I can see simple solutions to a couple of the other objections here:
hard to keep track of in a HUD.
The HUD only has to show the current ammo count for the ammo type you're using. If the gun is at 50% ammo and you have an ammo type with 6 shots per reload, it will display 3 shots. If you switch that to a different ammo type with 10 shots per reload, the HUD will show 5 because it's still at 50% capacity.
Lochnagar might screw it though, since the gun will have 1 shot, which could be interpreted as 100% so within maybe 3 seconds you could have a fully reloaded burst hwacha, but that depends on how good the code is written, I suppose.
If the Lochnagar round can't be loaded into a less-than-full gun without a full reload, this would negate the problem entirely. Switching to Loch after firing even a single round with some other ammo type would automatically force a reload.
It could be a special feature of Lochnagar rounds, OR it could be a function which kicks in any time the ammo count on a gun would drop below 1 on a reload. If we use the reverse of the example from above, If you're using an ammo type with 10 shots per reload, then unload until there's only one left, maybe you wouldn't be able to switch to an ammo type that only gets 6 shots per reload. Or doing so will force a reload because you don't have a full unit of ammo in the chamber. It could just "discard" any amount of ammo below a full round. So while 5/10 -> 3/6 is a simple whole-number conversion, 6/10 -> 3.6/10 =
. Which do you think? If it's above 0.5 do we "round up" and give them the bullet unless it's the last round in the clip? Or round down so ammo swapping with less than full ammo could be costing some of the clip as well as time?
Personally, I'd rather see forced rounding down on the ammo count (truncation is the mathematical term, but it's likely nobody cares). But hey, discussion point! Anyone else got ideas?
Also, another point of interest... if you decide to switch ammo types, but select the wrong type in the first instance, does the ammo-swap timer work like a reload timer where it's only locked in at the last second? Or would you reset the timer every time you switch ammo types?
Again, I have my own opinion, and that is that, for simplicity's sake with the current controls (I sometimes use the scroll wheel for ammo swapping), they should apply the current reload mechanics here as well. Switch ammo type to begin the timer, but until it ends, you can freely swap. This would also mean that cancelling a quick-swap and reverting to your already-used ammo type wouldn't cost extra time, just the 1.5s *IF* you notice before the swap completes.
When looking at the idea from a "realistic" perspective,
my own suggestion for solving this issue would make a little more sense. Unlike this proposal, it explains how new ammo types make it into the gun, which this idea doesn't. That said, looking at things in relation to fun, game balance and user-friendliness, I think this suggestion is probably the better option. (Yes, I like someone else's idea more than my own. Problem?)
Also, because I can't remain 100% on-topic without saying SOMETHING to spoil it...
It's "amount" not "ammount" and "flare" not "flair". Although at least "flair" is a real word, just not the one you were looking for.