This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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I'm not very familiar with ft-lbs,
1 ft-lb = 1.348 J.
Thanks that's great.
The round is no longer than a 17fireball / 20 vartarg. That's because it's also chambered in my handgun-sized PDW.
crucially, the case must be much wider than the fireball/556, because the long bullet is seated very very deeply. I assume there are no practical problems with seating a bullet virtually to the bottom of the case.....?
Base diameter is roughly 11. 5mm.... not far from a. 45ACP
This means it almost resembles a 'benchrest' shape like the 17PPC or the 225 JAWS pistol round.... making it feed reliably is a challenge.
A polymer coating might aid extraction (5. 7x28 uses this)...... although I wanted the entire round to be polymer/steel hybrid.
Relative capacity may be an issue - a high RC means, among other things, that the caliber is a 'barrel burner', and probably the muzzle flash / report may also be high.
Just use Actually decent non 1950's midgrade barrel steels and fun/interesting coatings for things like the barrel throat
I don't think that it's so easy like that, especially when we talk about automatic weapons.
What's relative capacity.... and can u seat a bullet right to the bottom of the case as I described... it is a fat case like the 22ppc or 220 russian
RC is case capacity divided by the cross sectional area of the bore. It's a 'rule of thumb' for thermal load estimation, that is, how much of the gunshot energy will be wasted as excess heat and muzzle report.
Broadly speaking, past a certain point (3.5, IIRC), other things being equal, RC is big enough to cause problems, chief among them an unacceptable throat erosion rate, which results in short barrel life span. This problem is even worse in weapons that fire in quick succession, like fully automatic ones.
While a short barrel life is always a problem, some folks will accept it in exchange for performance (long range civilian shooters), but the military won't.
If you read the awesome work of Emeric regarding the ideal caliber (https://quarryhs.co.uk/Emeric2019.pdf), he makes a thorough analysis on 'Thermal considerations' from page 60.
Long history short - if your pet design has too much of a thermal load, barrel life may be unacceptably short for the military, so your design is dead on arrival.