No on .276 pederson. Covered that before -- basically, it's .308 equivalent not an intermediate:
I agree that .276 P would have been a superior choice to .30-06 for the M1 Garand. However, .276 P is effectively a flatter shooting, higher velocity .308 -- and it actually has a longer overall cartridge length as well. So it's still a full caliber high velocity battle rifle cartridge... Primary benefits of .276 P or .280 B vs .308 are higher velocity, flatter shooting, and reduced recoil... Primary drawbacks of these higher velocity, necked down rounds is reduced barrel life due to increase throat erosion, which is of concern in a MG role...
http://wintersoldier2008.typepad.com/summer_patriot_winter_sol/2011/12/for-those-who-think-that-the-280-british-and-the-276-pedersen-were-pipsqueak-cartridges-in-compariso.html
In regards to 7.62x45 Czech, it would really need to be necked down to 6.5-7mm to perform ideally. Vs 7.62x39, it delivers around 15% more energy at the muzzle with an 8 gr heavier bullet and an extra 100 fps or so.
6.5 Grendel, it's main limitation is case capacity. It really needs a larger, preferably longer case for optimal performance.
And short squat case, necked down like it is, throat erosion on the barrel is a serious concern, especially it talking military rates of fire. 6.5 Grendel also requires an 18"+ barrel for ideal performance...
More here:
http://www.gdiengineering.com/wordpress/2012/07/14/why-most-6-5mm-cartridges-are-great-but-6-5-grendel-is-just-okay/And discussion on the 6.8 SPC vs 6.5 Grendel, primarily in regards to barrel length, here:
http://abesguncave.com/6-5-grendel-vs-6-8-spc-a-different-perspective/5.56 vs 6.5 Grendel, velocity is particularly important as is bullet performance (heavier bullets tend to tumble later than lighter bullets):
http://abesguncave.com/6-5-grendel-vs-223-556-ballistics-hunting-combat/About how 6.5 Grendel is enough better:
http://weaponsman.com/?p=5798Again, not advocating either as I think an ideal intermediate cartridge needs a case bigger than can fit in a 5.56 designed rifle -- also to allow parts to be designed around cartridge as well which should substantially reduce drawbacks discussed in last links.
Notably, both 6.8 SPC and 6.5 G, both have about ~50% more bullet drop at 250 yards (3-4 inches more drop) and 500 yards (~25 inches more drop). And both have ~1/3rd more drop at 750 yards. All of these vs 55 and 62gr 5.56 rounds... At 1000 yards, 5.56 has dropped ~40 inches less than 6.5 G and ~80 inches less than 6.8 spc. 5.56 drops about 465 inches at 100 yards.
I think that the bullet drop/trajectory is very important, which is why more velocity and greater case capacity is needed. Without a flat shooting bullet, hits at range become much more dependent on proper range estimations than does 5.56... On a static range, heavier bullets with less wind drift are a plus as you can walk your bullets in -- and once you know your hold, wind is much less likely to get you off target. On 2 way ranges, wind drift is less of a concern when considering movement of targets, limited time of exposure, cone of fire, multiple targets in same general area, rapidly changing target distance, etc...
I understand that CZ USA is selling the Bren as a "carbine." But carbines are intended to be light and handy... From all I've seen and the one I briefly handled at the gun store, the Bren is too heavy and blocky to excel as a carbine. And the CZUB marketing I've seen identifies it as a "rifle."
IMO, the weapon system is a rifle that they're they're trying fit into the carbine niche rather than vice versa with the VZ58... I also think AKs are better as rifles than carbines... AR15s I look at as best as carbines, if in 5.56 caliber, all things considered. For me, it's a factor of both handling and weight (barrel length, compactness, etc also matter), but weight I use ~7lbs unloaded and no mag as the dividing line between a modern military rifle and a carbine. Weight is a biggie for me. Overall form factor for storage/carry on person probably 2nd, and handling/handiness 3rd... YMMV.
To be clear, I don't think it's bad that it's a rifle and not a carbine, it's just different. And throwing the BATF, etc, definitions out the window.
For instance, I think Galil's are exceptional rifles, but even the Galil SAR w/ 13" barrel weighs over 8lbs. While a carbine-length barrel with according drawbacks, it's weight definitely puts it into a rifle zone for me, a compact rifle but a rifle nonetheless. If you have to carry it, you'll know it's there and it will likely become more of a burden.
In use, I see a carbine is something you can carry or sling up and go about daily activities with minimal limitations or discomfort from having it there. It's a reduced form and weight rifle designed for convenience of carry and use, importantly primarily designed to be fired w/ a stock as accuracy is important (if wanting to fire from the hip and have even more compactness w/ no stock, I'd personally go w/ pistol caliber subguns over rifles). I see rifles as being designed to be optimal at a specific purpose, including fighting, where weight and form factor are a concern but not the primary one -- the primary goal being an optimized durability, reliability, caliber, ballistics, etc, for the intended use of that weapon in concert with other military arms, tactics, etc... Generally, I see rifles as running 7-10 lbs. Though this weight is a penalty when carrying it about, it is a bonus when firing for reducing recoil among other factors. I suppose think back to the thought process dividing the M1 Carbine and M1 Garand for use among WW2 troops.
Anything above 10lbs I see as more of a special purpose weapon like heavy barreled sniper rifle, etc.
And note that optics and other attached accessories are not included in the above weights (all furniture should be included however), so often carbines with optics will fall into rifle weights, and rifles will fall into special purpose weights, etc...
What I like about the VZ58 is that it seems to be a pretty ideal carbine for me in all factors but ammo weight and tinker toy build-ability vs the AR15 in 5.56. 7.62x39 excels in the sub 300 yards/meters envelope, the weapon and mags are very lightweight, and the weapon design is truly robust and proven to take rifle-like levels of abuse. That increased durability is often one reason for the increased weight of rifles, but the VZ58 design just doesn't need the weight...
Now the VZ58 could be modernized and improved but that's a separate discussion.
