please review my homebrew for guns

[King of Nowhere]

I'm planning a setting where technology moved on, more or less to an industrial level. This means guns. I read the pathfinder rules for guns, and I am quite unhappy with them. Furthermore, I already introduced some early experimental guns in my previous campaign (set in the same world a century earlier) and I want to keep consistent with what I did earlier. So I devised some homebrew rules for guns. I would appreciate some constructive reviews on them
Do notice, this is work in progress. I tried to outline the rules and effects, not to be pedantic with the exact terminology.

Spoiler: New game concepts

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Armor Penetration (AP): firearms ignore part of the armor, natural armor and shield bonus to AC (those factors not contributing to touch AC). In most practical cases, AP can be considered a straight to-hit boost. AP decreases by 1 for every range increment.
Armor Penetration Resistance (APR): some advanced armor specifically made to resist bullets may have an APR factor, that is subtracted from AP before that takes effect. In those cases, AP applies first to the armor bonuses lacking APR.

Example of functioning: dude has a bullet-resistant breastplate (+5 AC, 5 APR), and he got a barkskin for a +4 to AC. He is shot with a heavy sniper rifle (AP 10). The rifle first ignores the barkskin entirely (using up 4 points of AP) and then interacts with the breastplate with its 6 remaining points of AP. 5 of those are nullified by the breastplate APR, 1 is left, decreasing the armor value of the breastplate to 4. So dude has effectively a 14 AC against this rifle.
Now dude also straps on a heavy shield (+2 AC), so the bullet AP interacts with the barkskin and the shield first, ignoring all 6 points of AC provided by those. At this point it has 4 AP left, and it faces a breastplate with APR 5, so it cannot ignore further AC. Dude has now an effective AC 15.

Fluff-wise, the high-caliber rifle is powerful enough that a magically hardened skin does not offer a significant resistance to it, and it will even systematically punch through the thick breastplate designed to repel small-caliber guns. However, after penetrating the breastplate the bullet has slowed down enough that the magically hardened skin can probably stop it.

Spoiler: weapons table

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Simple firearms		Revolver, light	Revolver, medium	Rifle, medium°	bayonet*	Martial firearms	Revolver, heavy	rifle, heavy°	rifle, revolver, medium°	rifle, revolver, heavy°	Shotgun, small°	Shotgun°	Exotic firearms	Sniper rifle, medium*	Sniper rifle, heavy*
	Damage	1d4	1d6	1d8	1d6		1d10	2d6	1d6	1d10	2d6	3d6		2d6	3d6
	Critical	x2	x3	x3	x2		x3	x4	x3	x3	x2	x2		x4	x4
	AP	3	4	5	/		6	7	5	6	3	4		8	10
	Range (m)	6	9	30	/		9	42	21	24	9	9		90	120
	Capacity	5	6	1	/		5	1	6	5	2	2		1	1
	Size#	Tiny	S	M	Tiny		S	L	M	L	M	L		M	L
	Weight (kg)	0.5	1	4	0.5		2	5	4.5	5.5	5	6		6	8

# i am using the 3.0 rules for weapon size because the 3.5 treatment of weapon size does not work well here. A revolver handled by an halfling will deal as much damage as the same weapon used by a human, or a giant. And if i make a smaller rifle for a halfling, armor penetration and range are going to be also affected.
* see special rules for this weapon
° see rifle general rules

Reloading a revolver takes two full-round actions, reduced to 1 with the rapid reload feat.
Reloading a rifle takes a full-round action, reduced to a move action with the rapid reload feat.

Rifle special rules: rifles are unwieldy in close range. Using one in melee has a -4 penalty to hit. However, in melee they can be effectively used as clubs or greatclubs. Regardless of size, rifles need two hands to use properly, and they take a -4 penalty to hit for one-handed use.
Sniper rifle special rules: sniper rifle are big, heavy and very hard to point at close targets. Their recoil also make it near impossible to achieve a quick rate of fire, even with magic-assisted reloading. Their scopes can be used as spyglasses.
Using a sniper rifle at less than 30 meters of range against a moving target (one that is not flat-footed or immobilized somehow) entails a -4 penalty to hit. Using it in melee entails a further, cumulative -4. The recoil from using a sniper rifle entails a -4 penalty to all eventual subsequent attacks made in the same round. Using a sniper rifle to its full range incremement requires taking a full-round action to make an attack; otherwise, use the range increment of a regular rifle of the same size.
If a character who is proficient with the sniper rifle takes a full round action to make a single attack, she can apply any source of precision-based damage (including, but not limited to, sneak attack and death attack) regardless of distance, if the other conditions for applying that effect are met. In addition to that, if the the result of the hit roll beats the target AC by more than 20, the hit is authomatically a critical.
bayonet: a knife made to be fitted under a rifle barrel. Attaching or detaching a bayonet is a full-round action (reduced to move action with the rapid reload feat). With the bayonet, the weapon can be used as a short spear or long spear, depending on the rifle size. However, the extra weight on the tip imparts a -2 penalty to hit when using the rifle to shoot.

Spoiler: enchantments and other stuff

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Firearms-specific enchantments:
self-reloading, lesser: the reloading mechanism of this gun is animated and is able to move on its own. Those guns are generally fit with a magazine, and work basically like a modern authomated gun with a magazine would work [the technology to make fully mechanical authomated is still not available in this world]. The speed of the mechanism is such that you can fire no more than twice per round. Loading a new magazine into your gun is a full-round action, or a move action with rapid reload. Price: +4000 gp on the base price

self-reloading: as self-reloading, but the limitation on shots fired per round is now 6. Price: +10000 gp on the base price

self-reloading, greater: this gun is using a spell similar to dimension door to transport the bullets directly from your bag to the chamber. As such, there is never any need to reload or do anything with the gun besides pulling the trigger. The gun has no limitations on the number of times it can be fired in a round. However, if some effect is preventing teleportation, the gun will need to be reloaded normally.
Price: +30000 gp on the base price.
bullet-resistant: an armor or shield with this quality is particularly hard for bullets to perforate, gaining +3 APR. Price: equivalent to +1
bullet-resistant, greater: as bullet-resistant, but gains +5 APR. Price: equivalent to +2

Special materials: adamantine bullets gain +2 AP. Adamantine armor gain+1 APR if light, +2 APR if medium, +3 if heavy. Adamantine bucklers gain +1 APR, other adamantine shields gain +2 APR.

As a general concept, I want guns to be reasonably realistic, in a way consistent with the setting. Guns made armor obsolete, but they are not going to punch holes into the scales of an ancient dragon, or of a tarrasque. hence why i introduced the armor penetration.
Also, in a world where some people have the capacity to survive falling down a cliff with minor injuries and knock down a stone wall with their fists, guns are not as useful as they would be in our world. However, they do significantly reduce the gap between the common man and the high level adventurer. And they are still going to be useful in the right circumstances.
while i don't like the pathfinder rules, i am going to allow most of the related feats and special stuff; hopefully, using guns should be viable in the right build. I expect rogues will take advantage from them: sneak attack applies, and the armor penetration factor is very useful for a class whose main obstacle to dealing damage is actually managing to hit. I also think an assassin with a sniper rifle can be very annoying. But I also expect most fighter types will still keep to medieval weapons; in the hands of someone who can lift a car, they'd be more effective at killing fast a creature bigger than a building.

[Elves]

Guns made armor obsolete, but they are not going to punch holes into the scales of an ancient dragon, or of a tarrasque. hence why i introduced the armor penetration

You could make them ignore armor but not NA. It's less realistic, but it portrays the fantasy of bullets piercing armor but not the thick hide of monsters in a simplified way.

[King of Nowhere]

You could make them ignore armor but not NA. It's less realistic, but it portrays the fantasy of bullets piercing armor but not the thick hide of monsters in a simplified way.

I don't see how that would simplify anything.
In 90% of practical circumstances, AP can be easily calculated as a flat bonus to hit, which is much simpler than breaking down the AC of a foe in all its components. When it exhist, armor penetration resistance can be either subtracted from AP, or ignored entirely. Especially since humanoid opponents (with gear) are going to be prevalent.
I can see armor penetration resistance making things complex at high level; if i were to ditch something, i'd ditch that. but i like that it allows to build a realistic bulletproof vest

[BioCharge]

Coincidetally, I actually did something similar in my setting. However, I changed it to not ignore shields (assuming that shield skill usage and design would deflect rounds rather than outright stop them; I also wanted to give shields a little buff). However, I made penetration a bit more simple:

Light Weapon: Pen 2, One-handed: Pen 4, and Two-Handed: Pen 6. Some weapons used light or heavy rounds which decreased or increased penetration by 2, and the penetration increased or decreased in similar increments depending on weapon size. So far it has worked quite well.

I also made them high crit range, but low multiplier, but that's just me. I believe it'd be easier to hit something vital with a bullet, but it might just punch right through and overpenetrate, hence a lower multipler. But that is neither here nor there. I should mention my guns are also WW2 level, so we have machine guns and the likes, so that may have some relevance.

[haplot]

Have you looked at or thought about looking at D20 past at all?

And many sorrys for what might be viewed as necroing old thread