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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One issue is that polymer casings dont hold on to heat very well. A shotgun is not typically a rapid fire weapon (some can yes), where a rifle could be needed to fire quickly with multiple reloads in both semi and full auto etc. A brass cartridge fired from a rifle will carry a good amount of heat out of the weapon with it, leaving the chamber with less heat and thus able to safely fire for longer periods. I believe this is part of the reason the army gave up on the polymer belt fed expirements they were doing in an attempt to lighten the load for machine gunners.
As everyone said the pressure difference is massive. But the effective range is also extremely different. The effective range of a shotgun with buckshot (large pellets) is only 35m, birdshot (small pellets) is 45m. Where as a 62 grain 5.56 maximum effective range is 600m to 1000m. So you need a LOT more pressure to push the round at that speed.
1.) Pressure – rifle cartridges not only have have more powder charge, but also generate exponentially more pressure, more quickly and that pressure must be controlled for a longer period of time. That malleable, yet strong brass expands to seal the chamber until pressure reaches a safe level. To use a different case material, you’d have to alter the charge chemistry (altering ballistics) and/or the structure of the chamber to be stronger… possibly making the firearm heavier, need maintenance more frequently or have a shorter service life
2.) Heat – since metal conducts heat, a metal case acts as a heatsink carrying heat away from the firearm. This isn’t important in slow/low volume/infrequent firing. However, for fully automatic firearms used frequently for long periods of time this is a problem. You will either have to modify the firearm to better handle thermal energy (heavier/more complex/more expensive) or have less time between failures and maintenance (dangerous and expensive).
3.) Cost – right now, polymer case technology costs more.
4.) Market – firearm buyers are hesitant to change. The military and police market have large stockpiles of ammunition they know works in all of their firearms, something important for organizations like NATO. An American, UK, French, German and Australian army can all use the exact same ammunition in their rifles and know it will work reliably.
Civilians will take cues from the military. If something is more expensive, potentially less effective/reliable and doesn’t offer appreciable benefits, it’s not going to catch on in the civilian market. And, polymer cases aren’t reloadable like brass, so that’s a big detractor doe some of the biggest spenders in the civilian market.
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As the science behind polymers, propellants and metallurgy continue to improved, eventually performance and logistics games will allow polymer case ammunition to eclipse brass case. When that happens militaries and police forces will begin to invest in the technology im earnest and wide adoption will follow. Right now, it’s still an emerging technology.
So basically, the plastic in shotgun shells is just playing Cupid for the pellets. Keeping them all cozy and together. 🎉
I think it’s because shotgun shells are supposed to exppode and release the little pellets inside
Edit:fixed typo
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