This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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Not as much as you'd likely want/need.
There's potential workarounds but they definitely aren't risk free and would require some level of development.
The much better option is something like shellshock nas3 cases which can be ran up to pretty hefty pressures safely and reliably. I think you might get a slight bit of extra case capacity over brass even.
Being able to run 70k psi Though should do you well.
Oh, did I mention that they're also cheaper than brass cases?
Since it's a pdw you're probably gonna go through a bunch of rounds so that's not a bad thing.
been wondering that - how much liberty is there in the proportions?
Case proportions vary with projectile length and diameter, and propellant charge.
Presumably what you actually mean is, how small can the case diameter be made?
With the Textron design, case diameter is ~0.195" greater than the bullet diameter.
Caliber ---- Bullet --- Case
5.56mm --- 0.224" --- 0.419"
7.62mm --- 0.308" --- 0.504"
that's actually fine. I had reckoned on ~12mm base diametre and for 6.35mm this gives me 11.3mm (.445"). And one can profit from the higher pressures.
Looking that old 6.5 CT cutaway, I had a simple and possibly stupid idea: since bullet tip is totally surrounded by plastic case... why don't make it as pointy as possible, in order to improve slightly aerodinamics and armor penetration?
It's not a stupid idea. The 6.8mm projectile developed for NGSW is about as pointy as possible.
I meant pointy as a needle, not only a nice BC. Like, reducing impact surface as much as possible, less than 1 mm^2
You mean like an APFSDS? I guess that it has been debated here that such formats aren't really useful below some 25 mm, and APDS not good below 12.7.
For rifles and LMG, the 6.5 pictured above is basically as good as it gets.
No, I mean the same specifications as XM1186 but with a pointier point, so to speak. With the least possible point surface
You quickly run into issues with both length to diameter ratio and aerodynamic issues.
Bullets are like aircraft In that their exact shaping determines how much drag they will experience across the various velocity regimes.
What's ideal at 3300 feet per second isn't the same as what's ideal at 1500 feet per second, so you wind up making compromises to get acceptable and stable flight characteristics across the entire range of velocities your projectile could be traveling at when it impacts the target.
As you've pointed out though, you also have to consider it's impact characteristics too.
This puts you in a position where you need to have acceptable terminal performance and flight characteristics throughout a pretty large velocity window.
Because of this, no matter what you're doing it will be a compromise.
In the case of making the bullet tip needle fine, this can create drag and or stability issues that you don't want.
This is why bullet tips are shapes as they are. Unfortunately I can't remember the name of the term specifically for the bullet tip shape and fineness ratio at this time though.
I'm sure someone else will come in and expand on what I've said though.
This is my current bullet shape. full spitzer, no meplat.
And yes, I agree that CTA would make it possible to have the spitzer actually be 'spitz' (pointy in German).
Hardened Steel penetrator with polymer rest of bullet. My current v0 is 4100 fps, Which I am sure could even be improved upon with CTA and higher pressures. Mind you, I am at ca 560 MPa.