Although the high L/D ratio bullet and high initial velocity can effectively improve the long-distance ballistic performance and make .243 or .260 level cartridges to reach .300 Magnum level like 6 Creedmoor made by Hornady or 6XC made by David Tubb, the barrel burning caused by it is a more serious problem, and this is totally different from long range single-shot or benchrest shooting wildcat bullets that folk shooting masters need to consider in America when they are trying to discuss 6.8 NGSW series whose design concept is based on 6.5 Creedmoor as an option of GPC cartridges( Don't forget the origin of 6.5 Creedmoor is to match the huge requirement of bolt-action precision shooting medium caliber rifle) and hardly of the previous discussions had considered this aspect. It may cause a serious decrease in the life of the barrel and accelerate the loss of the barrel and the frequency of maintenance. Although this is not annoying in a civilian competition where you can shoot leisurely, it is likely to be fatal on a battlefield where every second counts.

So in order to avoid the barrel burning in automatic mode, a meaningful diameter is .25 cal (only in my opinion). .260 cal is too big to get ideal ballistic coefficient like 6.5 Grendel (TOO slow), while .243 cal is too small to make multi-purpose bullets such as dim-tracer. What do you think?

Augmentcore said:

So in order to avoid the barrel burning in automatic mode, a meaningful diameter is .25 cal (only in my opinion). .260 cal is too big to get ideal ballistic coefficient like 6.5 Grendel (TOO slow), while .243 cal is too small to make multi-purpose bullets such as dim-tracer. What do you think?

"Optimum" bullet diameter is just a by-product of the amount of the muzzle energy you want to achieve from barrel length with an expansion ratio around 8-9.

The original idea was to duplicate the retained energy of the 7.62 x 51 mm with a smaller / lighter round, it was already demonstrated that you could achieve this goal at 600 m with a .264" bullet and ~2500 J of muzzle energy, but a .236" bullet and slightly less muzzle energy will be OK, or any diameter between (.243" and .257").

The .243" seems to be sufficient for long-range tracers and can be used in "micro action", while the .264" will eat too much internal space and will probably need a longer action.

Going back to the 5.8mm ammo, task and purpous has a new video on the chinese bullpup ...just uploaded right now

But the problem is that bullpup rifles like QBZ95 are now a marginalized part of China. The current new rifle like QBZ191 is just an imitation of the AR series and HK416, even the buttstock can only be retractable but not foldable (because the built-in reintroduction pipe has been almost reached the bottom plate of the buttstock like those old M16/M16A1), I think this can already explain the problem. So the problem of insufficient barrel length (14.5 in, the same as M4A1) will not only be faced by the American AR rifle, but the new Chinese rifle will also be troubled by this problem.