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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons, particularly in larger calibres (12.7+mm).

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Exploring The Design Space   Ammunition <20mm

Started 25/7/15 by NathanielF; 91658 views.
QuintusO

From: QuintusO

1-Aug

A group of a few of us have been tossing around a few cartridge ideas, and one we consistently come back to is a 7mm derived from the old .30 T65E1 case. The scholars among us may recognize this as essentially identical to the T65/7mm experimental round from the early 1950s. 

The interest in a round like this is that it exists on the junction where the maximum power and performance is achieved within the envelope of the existing 7.62x51mm round. 7mm is barely big enough to accommodate a large, general purpose steel penetrator (.277 is not too small, but a bit smaller than is desirable, and unlike the jump from .284 to .308, the ballistic performance difference is not substantial), and if you have an API requirement as well it becomes very close to the minimum practical size. All of this "depends" of course, if you sufficiently reduced requirements you could go much smaller, say to 6mm, but what you find when you play around in the space long enough is that the jump from 6.5mm to 7mm does not cost you very much in terms of trajectory and drift, but it gives you a considerable boost to bullet volume. The jump from .284 to .308, on the other hand, has you sacrificing velocity to get enough sectional density, and making other tradeoffs you'd rather not have to do. Any of these rounds from 6-7.62mm would be suitable of course, but 7mm looks like the best brokered compromise, given the constraints that you use the 7.62mm parent case or similar, that you have a steel-cored API bullet requirement, and that you are trying to achieve the highest overall performance within that footprint. A different compromise becomes desirable if those constraints change (for example, the 7.62x57 Blasphemy is better if you are not constrained by the 7.62x51 footprint, a 6.5 or 6.8mm like 6.8mm GP is better if you are not planning to use steel-cored AP or API at all, and other rounds are obviously lighter than 7mm while approaching its performance in many respects).

If you've been following my journey through the small arms ammunition sandbox, then you'll know that I've been playing around a lot recently with dedicated "Hi" calibers intended to be paired with a "Lo" caliber. Where I see the T65/7mm fitting in is as a "reach-down" Hi caliber intended to be used in lower echelons as well as higher ones. It's small enough to be used comfortably in DMRs within fireteam level units, without being excessively large or too different than a regular squad rifle caliber. This takes the pressure off the "Lo" caliber to fill that role, allowing it to be more well optimized for the close fight role.

This raises interesting questions about what kind of platoon organizations would be best suited to a combination like this (say, T65/7mm or similar, plus something like 5.56 Super). To me, the most obvious is the heterogeneous squad, with 9-12 members and three or four fireteams, one of which is a support fireteam with LMG, DMR, and ammo bearer/AG. This is sort of like the US Army platoon organization writ small onto the squad, and to be honest I am not sure what I think about it. It doesn't seem obviously poor to me, but I wonder if a homogeneous squad would simply outperform it in most relevant environs.

You could make a case for this round combination in a homogeneous squad organization as well. Assuming you could accept DMR capability out to only a few hundred meters, and emphasized mobility instead, the T65/7mm could be used in Weapons Squads with a combination of GPMGs and "heavy" DMRs providing a longer-legged and more capable overwatch if needed.

The most obvious application to me, however, is the idea of the "arms room" concept, where squad organization remains the same, but weapons are traded out as environments change. The idea here being that squads are "reconfigurable" and potentially any of the above systems could be emulated. Based on their press releases, this appears to be close to the model being pursued by the US Army with the 6.8mm GP, and I suppose that makes it no surprise that the two calibers are fairly similar. However, the Army seems more interested in delineating use of these weapons by personnel role, rather than according to the tactical environment. This, to me, feels like a mistake, as it invites all the complexity of the "arms room" system without the flexibility of allowing small unit commanders to make their own decisions about what weapons will be used where.

The worst application for the T65/7mm, I think, is the USMC's homogeneous platoon model, where the "Hi" caliber is only used at the company level with "attachable" MG teams, and the DMR capability is provided by "Lo" caliber weapons (the M38, in their case). 7mm provides only a weight benefit here, and while that may be appealing, there's a case to be made that the superior performance of rounds like the 7.62x57 Blasphemy would be a better fit.

autogun

From: autogun

2-Aug

A couple of thoughts: your 7 mm/T65 sounds rather a lot like the 7 x 49 FN offshoot of the 1950+ NATO trials which actually saw service in Venezuela, until they presumably decided that being the only country in the world to use it, wasn't very practical. (see page 22 of this for a group photo).

In terms of squad makeup I am way out of my zone, but I've tended to think that "fire and movement" called for two "weapon teams" based around an AR or LMG, so that "half-squads" can cover each other as they leapfrog forwards.

QuintusO

From: QuintusO

2-Aug

autogun said:

A couple of thoughts: your 7 mm/T65 sounds rather a lot like the 7 x 49 FN offshoot of the 1950+ NATO trials which actually saw service in Venezuela, until they presumably decided that being the only country in the world to use it, wasn't very practical. (see page 22 of this for a group photo).

T65/7mm is actually a historical round itself. Yes it's somewhat similar to 7x49mm FN but a little more powerful. As you know, there were a large number of 7mm rounds during this time, including at least four basic case specs I'm aware of based on the various T65 family cases. Not to mention the commercial 7mm-08!

R1K1M

From: R1K1M

8-Aug

One advantage the heterogeneous squad has is that it takes some pressure of the weapons squad. So if you have an arms room sytsem implemented, the weapon squad may now carry HE throwers and AT weapons more often. Its also very resistant to casualties, at worst you simply fold into a two different french style 300&600m teams. However, it probably is slower than a homogeneous squad and I probably wouldt want to go in door busting with the weapons-fireteam. In a HIC against a near-peer it probably is a great layout.

R1K1M

From: R1K1M

8-Aug

Different topic: I was talking with idiot/Derpk-74 (M-100) over in the combined defense discord, and he claimed that nowadays you can design a 6mm cartridge with the same or better performance than 7.62 if you use modern high pressure technologies (poly case etc.pp.). He cited 6mm unified as an example how you could design it. However, that is fired from a 720mm barrel, which is a lot compared to the 550-650mm typical 7.62 MGs/Sniper Rifles have. When designing a modern replacement for the 7.62 round using NGSW technolgies, how would your favourite look like ? Can it really be done in 6mm without running into some weird issues ?

QuintusO

From: QuintusO

8-Aug

R1K1M said:

One advantage the heterogeneous squad has is that it takes some pressure of the weapons squad. So if you have an arms room sytsem implemented, the weapon squad may now carry HE throwers and AT weapons more often.

I get what you're saying but I don't really agree. Let's forget about the delineations of the platoon for a moment, and look at it holistically. So, in the current US Army platoon, you have two 7.62mm belt feds, which you need to be able to feed. It doesn't matter where you move those belt feds, the platoon has to carry them and all of the ammunition associated with them. As long as you have X number of belt feds and Y quantity of ammunition for them, you have to carry it. Doesn't matter if the guys carrying it are technically in the Weapons Squad or not. So that doesn't really free up any weight, in fact, it's a bit of a bait-and-switch, we're "removing" the MGs from the Weapons Squad, which sounds a lot like when you say you're going to remove a weapon from the platoon and move it up to company level, but is in fact the exact opposite. You're moving them DOWN, and you're not reducing the number carried in the TO&E at all.

There's been some argument that "oh, well if you replace the M249s with M240s or whatever that will reduce the number of belt feds and save that weight to then be used for high explosive weapons". OK, fine, but at that point you're not reducing weight, you're sort of shuffling it around. And while I support adding explosives to the platoon, the big thing that needs addressing first is the load. Another thing to consider under this scheme is that you're taking the Automatic Rifleman's (who is now perhaps better called a Machine Gunner) load up by 20 pounds or so. You're also increasing the load of the rest of the squad members (who have to carry his ammo). This reduces the mobility of the entire squad, and it also means you'll be cycling through ARs much faster as they already have one of the highest rates of injury of any member of the platoon.

QuintusO

From: QuintusO

8-Aug

R1K1M said:

Different topic: I was talking with idiot/Derpk-74 (M-100) over in the combined defense discord, and he claimed that nowadays you can design a 6mm cartridge with the same or better performance than 7.62 if you use modern high pressure technologies (poly case etc.pp.). He cited 6mm unified as an example how you could design it. However, that is fired from a 720mm barrel, which is a lot compared to the 550-650mm typical 7.62 MGs/Sniper Rifles have. When designing a modern replacement for the 7.62 round using NGSW technolgies, how would your favourite look like ? Can it really be done in 6mm without running into some weird issues ?

Depends what you mean by "7.62 performance". If, for example, what you mean is just drop and drift and energy at 1km, then you could have done this with a 6mm round in 1920.

If you check this thread you can see many of the 7.62 replacements I've worked on. Exactly what form that should take depends entirely on what combination of roles you expect it to fill.

Farmplinker

From: Farmplinker

8-Aug

Obviously, we want a 1500 meter DMR/GPMG cartridge that also works for room clearing. Out of a 10.5 barrel. That doesn't need a suppressor to be hearing safe. Needs to penetrate Level IV+ plates at a minimum of 600 meters obviously. Oh, and can be produced cheaper than M855A1 would really, really be nice. While fitting in an M4A1.

Sound about right?;-)

QuintusO

From: QuintusO

8-Aug

Picatinny: You're hired!

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