NathanielF said...

the biggest factor here is additional magazine weight

Would poly mags change the argument a bit?

I mean, where would be the sweet spot for case dimensions x loaded magazine weight, keeping projo weight the same? And how much case volume would this solution squeeze out?

It would take a bit more dedication from me to solve that problem; however my current preferences are for cartridges that have about a 1.75-1.85 caliber case base and maybe 6-7.5 calibers of case length. That should give the best all-around performance, based on what I know about interior ballistics. The cartridges 6mm PPC, 5.45x39, 6.5x47 Lapua, and .284 Winchester all fall within or very near this range.

In general, while the case head of a round is one of the biggest contributors to weight, in the end I think the squatter cartridges (see the above set) win out anyway, as they improve things in so many other ways (lighter magazines due to more favorable dimensions, better, more consistent propellant burn, etc) that they're worth their disadvantages (greater bolt thrust, greater cartridge weight).

But there's really too many 6.something rounds in this thread, so I'd better balance it out with some SCHV, hadn't I? ;)

Stays above 2,000 ft/s out to over 500m, and punches with 91% more energy than M855 at that range... Not bad for a .22 cal "mousegun" round, eh? ;)

It certainly looks a lot better than the 5.56mm, Nathaniel, but I have a reservation about the dual loading approach - it never seems to work. 

In the interwar period the French introduced heavy (MG) and light (IW) loadings of the 7.5x54. Postwar they dropped the heavy load and concentrated on the light for everything. Germany was in a similar situation with the 7.92x57 during WW2 but decided to drop the light loading and use only the heavy. More recently, the Chinese introduced the 5.8x42 in light and heavy loadings, but dropped both after a few years in favour of one universal loading. In practice, two different loadings just seem to be too much trouble to bother with.

So if your round were ever introduced in that form, I suspect that the light and heavy loadings would soon be replaced by one compromise loading - something rather close to a GPC!

On the subject of the SCHV - Badcow54 has been doing a very interesting analysis of suppression, taking into account previous experimentation and working out aural and physical impact factors to calculate an overall suppression index (which varies with range). This makes it very clear why 7.62mm MG fire is perceived by its users to be far more effective than 5.56mm fire. This will be included in the revised version of his article which should be up on my website in the next week or so.

autogun said...

 

On the subject of the SCHV - Badcow54 has been doing a very interesting analysis of suppression, taking into account previous experimentation and working out aural and physical impact factors to calculate an overall suppression index (which varies with range). This makes it very clear why 7.62mm MG fire is perceived by its users to be far more effective than 5.56mm fire. This will be included in the revised version of his article which should be up on my website in the next week or so.

 

 

That would be pretty interesting to see. I always enjoy reading Emeric's work, even if we don't always see eye-to-eye.

NathanielF said...

...the light 85gr bullet satisfies the Army's requirement for a round that can be used in training ranges. The Army has shown that they will accept combat rounds with lead cores (e.g., Mk. 262 being used outside of SOCOM) as long as those rounds are not being used for training. Great, so here's where you cheat. If more range is desired, additional loads can be introduced or brought out from stores that have heavy, lead-cored bullets in either OTM (for DMRs) or steel-jacketed FMJ (for SAWs/MGs) bullets to meet those additional requirements...

The problem with the above idea is that the Army has shown they want only one round for both training and combat.

NathanielF said...

This does mean there would need to be additional suites of tracers, etc...

Same problem as above.  The Army wants only one standard tracer, etc, round.

renatohm said...

NathanielF said...

the biggest factor here is additional magazine weight

Would poly mags change the argument a bit?

There's a good chance that a future rifle would use polymer magazines.  If so, then I don't see magazine weight being a significant issue.

More important, IMO, is magazine size.  The longer (front to rear) the magazine is, the worse the ergonomics, especially for soldiers with smaller hands.  The length is also critical in determining how many mags can be worn in chest pouches.

autogun said...

stancrist said...

autogun said...

...bearing in mind that MGs are always likely to have longer barrels than IWs...

Two words that should never be used -- "never" and "always"   ;^)

Basic English comprehension: "always likely to have" does not mean the same as "always have" - it's describing a probability.

Yup.  But is "always likely to have" even an accurate statement?

  M1 rifle, 24" bbl; M1919 machine gun, 24" bbl

  M14 rifle, 22" bbl; M60 machine gun, 22" bbl

  M16 rifle, 20" bbl; M249 machine gun, 18" barrel

  M4 carbine, 14.5" bbl; M249 machine gun, 14.5" bbl

Thanks for the detailed answer.

In short: life is compromise, and one has to make the optimal choices based on one's needs.

And as Stan points out, mag lenght is important in ergonomics, especially for warfighters with smaller hands, and for storing, for all warfighters.

Being a little pickier: do you have any idea how much volume is lost when using poly cases?