First bullet fires fine but then gun fails with bullets falling out of the end of the barrel. Tried bullets and cartridge on another gun and works ok.

Make sure you know your terminology.
The bullet is what comes out of the business end of the barrel.
There is no powder in the bullet (guessing you are not using a tracer bullet which does have chemicals in it to make it glow.)
The firing pin is in the bolt of the rifle and not part of the bullet.
The case is what holds the powder and the bullet. The primer in the end of the case is what the firing pin strikes in order to ignite the powder and fire the bullet.
You can drill a hole anywhere in a bullet (as defined above) and not have any problems.

Head to Walmart and buy whatever's cheapest. Just because some other "expert" tells you something there's no reason you should fall for that dreg and there's no reason to pass it on. Your gun will fire *any* common 5.56 ammo. Buy whatever's cheapest and that will run reliably in your gun. You aren't sniping terrorists at 1,000 yards.

is this a gas cartridge type of nailer? It could be the effects of gravity on the spray nozzle. try pushing down in normal position but dont fire it. quickly move to ceiling then try firing. I am not a fan of this type of nailer as they are problematic and finicky.

Shoot it with .38 special cartridges to practice trigger control and function drills (less recoil). Save your .357 for hunting, self protection, and familiarization fire. The weight of the bullet is not overly important, construction is. hollow points for self defense and hunting medium game. Rule of thumb? Light weight and fast for humans, heavy weight and slower for medium game.

Bullet proof vests normally provide very little to no protection at all against bullets fired from rifles (like the M4 carbine 5.56mm or AK-47 7.62mm). They only provide protection against bullets fired from all hand guns.

Not sure what your asking, but I will try to explain what I think is going on. If you fire the gun cold (one or two shots) and you are on target or zeroed in. Then the more you shot, the point of impact wanders off center or gets worse. This can be caused by the receiver getting hot (warm) from firing, and tweaking the scope in the rings enough to move it. Another reason can be the bullets you are using Then also through a hot (warm) barrel. Bullets stringing or shot placement going up / down can be attributed to the hot (warm) barrel. As the barrel gets warm the diameter increases and gas from the powder will escape around the bullet in the bore and cause flame cutting. Flame cutting can/ will cause a decrease in muzzle velocity, which will string the bullets in a vertical line out at target range. Horizontal bullet placement is caused by sight errors (scope moving) or movement of the gun in the shooters rest, called flinching, or "pulling" as the shooter expects the gun to go off. One way to find out if this is what is happing, is to have a friend load the gun or not load the gun (single rounds) and hand it to you to fire. if your friend does not load it and you flinch thinking shes about to go off you have to work on that aspect of your control. Once you have that control issue out of the way you will see a huge improvement in your shot placement.Hope this helps Fix Ya up.

Sound like your ball detent is gone or broken.

The detent is a tiny piece of rubber that keeps the paintballs in the chamber and from rolling out the barrel. It's a cheap part, but you will need basic knowledge of disassembling a Tippmann 98 to replace it.

You can find ball detents here!

firing pin broke.

This happens will all firearms. what happens when the bullet leaves the bullet is a decieving "rise" of the bullet. The reason for this is the Line of Sight (Scope View), angles down and away from the Line of Departure (Barrel). The bullet actually never rises and is in fact continally falling away from your rifles Line of Departure but because this is higher than the Line of Sight the bullet seems to Rise than fall to the set distance in the scope (i mention set distance and not zero because you can change your Minutes of Angle on your scope to increase and decrease range)

http://www.rifleshootermag.com/shooting_tips/ballistics_0303/

this is a chart that illustrates what i just said.

now that you understand that you should take a good read into Exterior Ballistics. this is the Mathematics of your fireamrs trajectory ( I say your firearms because your bullet's flight depends on the length of the barel which will vary from gun to gun) this science of shooting will teach you how to understand bullet Grain and Volume relations. understanding the Feet per second of your rounds and how the affects you. teach you about shooting in high pressure and low pressure environments and extremly windy environment.

now there is alot of math to all of this and its hard to find it all on the net and if your not that great at math you can do what i do bc im lazy and im not a sniper im just a hobby kinda guy. '

Sierra Infinity V 6 Ballistics Software. I dl'd mine off the net you might have to buy it depending on how resourceful you are. it is well worth the buy. You can punch in the daily variables (Barometric Pressure, Temp, Humidity, and Altitude) (of couse with your bullet as well) and it will give you a "Cheat Sheet" for those conditions stating Windage and Elevation adjustments per decided incriment (50 yrds is standard) then you take that to the range and (bring a laptop if you got it and arent embarrased (som1 might even help you tune in the variables) hope this helps if not ill check back in a bit to see how you did

We have same problem too!