Enchanting ammunition?

[Roger Anderson 874]

Does anyone happen to know what formula is intended to be used for the cost of ammunition with spell effects? I have found only a few examples of costs for such items in the PRD and cannot make them work with any formula I have been able to think of. Basic magical enhancements are simple enough, and very straightforward, however if you add a spell effect, like you have on the sleep arrow, dustburst bullet, screaming bolt, or sizzling arrow, pricing is unfathomable.

Specifically, the sleep arrow is a +1 arrow, at a cost of 132gp(6600 for 50). A +1 arrow without any other enhancement is approximately 46gp each(2000gp for +1 on 50 arrows + 300gp for MW on 50 arrows(or 6gp each if you prefer) + 2.5gp for 50 arrows(basic cost) and then divide the total by 50 to get the cost of each). That leaves 86gp to cover the cost of the spell effect. The price for a spell effect is given as SL x CL x (an amount based on the type of activation and number of uses for the effect). Using the value for "single use spell completion" or "single use use activated" as a price for enchanting all 50 results in a price far lower than the cost given. Using the same for a per arrow cost results in a cost far exceeding the cost given, as does using any of the other spell effect activation/trigger methods. The variance of calculated cost to cost given varies with the other spell effect projectiles above but the problem is the same.

If anyone can point out something that I missed, and make the math work please let me know. If not i guess I will have to scrap the prices listed and go with a house rule of price for 50= enhancement bonus + MW + base cost + (SL x CL x 50(single use, use activated)) or something along those lines.

[Carbon D. Metric]

Firearm bullets are priced individually and sold the same way. This means each bullet (Right now at least) has to be enchanted individually. This is very likely going to change but is a good FAQ candidate.

[bdk86]

Bumping this to see if, in 4 years, anyone has figured this out. I can't seem to find any formula that makes sense for creating items akin to sleep arrow. I've even tried it by counting the lesser component of the two costs (either as the functional +1 arrow or the single charge sleep effect) and always come up short when trying to reverse engineer the math.

[Azouth]

Don't forget that

" If it strikes a foe so that it would normally deal damage, it instead bursts into magical energy that deals nonlethal damage (the same amount as it would deal lethal damage)"

So it is more like a +1 Merciful (less the extra +1d6) with a spell ability.

It is priced a little less the a +2 arrow.

[bdk86]

Sadly, that doesn't help me figure out how to make a similar item that encapsulates an ammo-centric use of a spell. Dust Bolt has the same math problem when I try to reverse engineer it.

[tonyz]

Pick a number that feels about right -- is the thing in between a +1 and a +2 arrow in effectiveness? Price it halfway between. (First rule of magic item creation: price it according to effectiveness, formulae are only a rough number to start with.)