I’ve never fired/handled guns but have some knowledge of guns and their basic mechanisms, and this thought just came across. If you could make cartridges out of polymer/plastic, and they are significantly lighter, wouldn’t you want to switch to them asap? yet there is no adoption. On the other hand shotgun shells have always been plastic but it’s not problematic in any way? why is this the case?
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A 12 gauge shells operate at about 11-14 thousand psi. The 5.56mm NATO operate at 62 thousand PSI.
But your assumption is partially wrong to begin with. See the part of the shotgun shell where the power explode is actually made of brass, the same material as a rifle casing. Different shotgun shells will have a different length of brass (low vs high brass) that depend on how much powder the shell will be loaded with.
The plastic part of the shell is not where the powder is, but where the pellets are. The equivalent in a rifle cartridge would be where the bullet is, which have nothing around it. The plastic is only there to keep the pellets together.
It has to do with where the explosion occurs.
In a rifle shell, the explosion happens in the brass casing itself which then forces the bullet down the rifle barrel and out to the target. Basically the entire brass casing holds the powder charge to propel the bullet.
Shotgun shells work similarly, the plastic casing holds the buckshot or lead slug, while the little brass bit on the bottom holds the powered charge where the explosion occurs. Incidentally the smaller powder charge is one of the reasons why shotguns are considered “close range weapons”
While yes it is possible to design polymer casings to handles the explosive material and the heat generated, it can cause a whole lot more problems for the weapon itself.
Essentially; if it ain’t broke, don’t fix it.
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It has to do with the amount of propellant used and the resulting chamber pressure. Rifle cartridges can see 50,000 psi chamber pressure, which necessitates a metallic case. Shotguns use much less propellant, so the chamber pressures are 10-15,000 psi, so a plastic case can be used. Note that the head of the shotgun shell is still made of metal
Thank you for the explanations
The bullet of a rifle create a very tight pressure fit against the barrel. The shotgun pellets do not fit into the barrel in the same way and any wadding is also a relatively lose fit. So the pressure inside a rifle tends to be at least five times higher then inside a shotgun. At the rear of the chamber it is actually the brass casing which seals the pressure inside. The brass expands to make a very tight fit to the chamber walls and the bolt face preventing any gasses from escaping. Shotgun shells do also have brass on the base to do this. But the relatively short brass base of the shotgun shell is able to contain the lower pressures of the shotgun compared to the pressures inside a rifle.
This does not mean that polymer cartridges does not work in rifles. They are in commercial production. However they have to be thicker leaving less room for propellant. And the tolerances are tighter. So to get the reliability to an acceptable standard there needs to be more quality control to find out which combination of ammunition works in which guns and to check that the ammunition maintain quality through their production and in storage. This is therefore mostly done by militaries who go through lots of ammunition and use identical guns. For private users this is very hard to do and results in ammunition which might have been tested in a different gun with slightly different chamber size, feed ramps and chamber pressure being unreliable in this other gun.
Rifles wants to be able to fly on a long flat trajectory as much as possible while keeping penetrating power
Shotgun shells want to shred at short range so their internal pellets can be de facto shrapnel
Remember tho a shotgun shells contact surface is still
Metal though, not plastic all the way through
I think some people here have no idea what they’re talking about.
The reason is hasn’t been adopted across the board is the same reason a lot of things don’t get adopted immediately. Momentum. Most bullet manufacturers are set up to make bullets the same way they’ve been making bullets for a hundred years. With a brass cartridge.
In regards to case pressure, there is something to be said about that, but most of the pressure in the bullet is contained *by the barrel of the gun*. There’s a reason you can throw a grenade down a tank barrel without a problem. The tank barrel is made for something exploding with 1000 times the pressure. Some people won’t load a bullet into their gun if there is a dent in the case. I’ve done it a few times with no problem, *because the bullet case just expands to fit the chamber*. Load it with a dent, it comes out without a dent. The pressure is contained in the chamber and barrel of the gun.
Something to be noted, before I continue. Polymer cases aren’t entirely polymer. They still have a steel or brass base. There are a couple reasons for that, not important for this discussion.
Do a search for “polymer ammo casing”. I found an article on gunsandammo.com that features a picture of a man catching the polymer case of a 50 caliber rifle, something that you shouldn’t do with brass because it would burn you. Polymer doesn’t absorb heat as quickly as brass, it’s an insulator rather than a conductor, so most of the heat goes down the barrel. You can find more results with the same search terms on youtube of people firing the rounds.
The company spearheading polymer ammo is called True Velocity. They’ve made ammo in many different calibers and tested it with zero issues.
The one downside that I know of, that can legitimately be argued in civilian use, is that brass ammo can be reloaded. Polymer ammo can’t be. Neither can steel case, but people buy a lot of that. And .22 ammo is brass, but nobody reloads that because it’s so cheap.
For the shotgun question, if you search on youtube for Taofledermaus, those guys load shotgun rounds and you should figure out why certain statements here are wrong.
edit: I didn’t discuss cost. Yes, they are more expensive now. As with all other new technologies, price will go down over time. Look at how much a computer hard drive or a flat screen tv used to cost when they were first introduced. They were unobtainable for the common consumer.
One of the issues is that the gun will get hot when you repeatedly fire the weapon. Some of the heat will be absorbed by the brass shell and will leave the weapon contained in the shell.
Shell will get so hot that they will burn if they come into contact with skin.
Polymer shell will not have the same heat absorbing properties and if the gun gets to hot the cartridge may “cook” off when loaded.
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