The Ultimate Combat Round

[GunTech]

Anything with a 473 case head is going to be big, defeating the requirement for a light round.

The issue with the grendel as a fighting round is the sharp shoulder and the almost non-existant body taper. It's really a target round - basically an opened up 6mm PPC.

The problem with a lot of these rounds is if you restrict yourself to an M16 magazine, you are basically limited in performance. You can increase persormance marginally by going to a fatter case (and reducing mag capacity) but you cannot duplicate the performance of a full power cartridge in an assault rifle sized case.

Further, recoil is a huge factor in auto weapons. You need to keep recoil at or below that of the 7.62x39 AK. Other wise, you might as well go semi-automatic and use a full power case.

The current 5.56 fires a 62 bullet with a spec'd 3000fps in a 20" barrel. That can be beat, although when limited to ball ammo, lethality with a larger cartridge is an issue. The 223, at optimal ranges, tumbles and breaks up, giving it a huge advantage in wounding over other cartridges such as the various 7.62.

Here's what I would look for in a combat cartridge.

A bullet in the 80-110gn range with a velocity between 2500-2800 and a high BC. This will equal or better the energy of the 5.56. High BC, allowing the round to retain high energy at long range, making it suitabel for DMR and GPMG

Shoulder angle of between 20 and 25 degrees. Body taper of not less than 30 minutes of angle, and ideally about 1 degree.

Case head of 0.452 or less, otherwise just use a full power case.

Lose the requirement of M16 magazine size, but keep the overall length to less tha 2.600 inches and case length of less than 50mm.

The best bullet possibilities look to be 6mm, 6.5mm and 7mm as these have a number of suitible High BC bullets in the right weight range. A BC of over 0.400 is highly desireable. Over 0.500 is outstanding.

For developmental purposes, it is probably easiest to stick with standard case head size: 0.387, 0.422, 0.453.

Tod

 

[dodging230grainers]

I don't think there can be an "ultimate" combat round because it depends on what kind of people you're fighting.

If you're on the U.S. military side fighting completely unarmored insurgents with ****ty medical care, the 5.56mm NATO cartridge fits the bill perfectly. However, if we were fighting a modern army in WW2 style fighting, we might find the 5.56mm becomes much less effective due to increased ranges and the fact our enemy would have body armor similar to ours. Don't forget they'd have vehicles too.

From the insurgent point of view, the 5.56mm NATO might not be as effective against their enemies- U.S. soldiers. Our troops wear some of the most modern body armor to date, and we have some of the best medical care in the world.
Our troops are often behind cover, or inside a vehicle, meaning the insurgents are going to need a more powerful rifle cartridge to do the job.

So in short, the ultimate rifle combat round is the one that fits the job at the time. For us, right now, with the people we're currently fighting, I think the 5.56mm NATO does fine.

 

[Nolo]

In my first post I stated that there was really no such think as an "ultimate combat round", but I went ahead anyway. I think that, for an assault rifle, 6mm bullets are the best. They have extremely high ballistic coefficients (sometimes as high as .55) and have decent weight to them (80-120 grains). If you fitted that bullet with a case that had it doing around 3000 f/s and still was under 70mm (total cartridge length), you'd be golden. I think that could be accomplished by opening up the 5.45x39mm case (to 6mm) and lengthening it until you got acceptable pressures.

 

[Nolo]

Hey GunTech, could you run what velocities you'd get out of a 5.45x39mm case necked up to 6mm (100 grain bullet) through your doohickey?

 

[GunTech]

Here's you 5.45x39mm necked up to 0.243 with no other changes. BL-C(2) looks like one of the better powders.

Cartridge          : 6 mm x 39 Nolo
Bullet             : .243, 100, Sierra SPBT 1560
Cartridge O.A.L. L6: 2.244 inch or 57.00 mm
Barrel Length      : 18.0 inch or 457.2 mm
Powder             : Hodgdon BL-C2

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.735% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-07.4   90    22.24   2190    1065   37271   7804     91.5    1.187
-06.6   91    22.41   2209    1083   38189   7879     91.9    1.173
-05.9   92    22.59   2227    1102   39138   7952     92.3    1.160
-05.1   93    22.76   2246    1120   40110   8025     92.7    1.147
-04.4   93    22.94   2265    1139   41108   8097     93.1    1.134
-03.7   94    23.12   2283    1158   42135   8167     93.5    1.121
-02.9   95    23.29   2302    1177   43191   8236     93.9    1.109
-02.2   95    23.47   2321    1196   44276   8304     94.2    1.096
-01.5   96    23.65   2340    1216   45392   8370     94.6    1.084
-00.7   97    23.82   2358    1235   46540   8435     94.9    1.072
+00.0   98    24.00   2377    1255   47722   8499     95.2    1.060  ! Near Maximum !
+00.7   98    24.18   2396    1275   48939   8561     95.5    1.048  ! Near Maximum !
+01.5   99    24.35   2415    1295   50188   8622     95.8    1.037  ! Near Maximum !
+02.2  100    24.53   2434    1315   51477   8681     96.1    1.025  ! Near Maximum !
+02.9  100    24.71   2453    1336   52804   8738     96.4    1.014  ! Near Maximum !
+03.7  101    24.88   2472    1356   54169   8794     96.7    1.003  ! Near Maximum !

 

[Nolo]

That's all I get, huh? 1300 ft-lbs? Hmmm... How much longer would I have to make the case to get 2000 ft-lbs?

 

[GunTech]

My cartridge isn't doing much better:

At least it has a 40 minute of angle body taper and 23 degree shoulder

Cartridge          : 6.5 combat
Bullet             : .264, 108, Lapua Scenar GB464
Cartridge O.A.L. L6: 2.571 inch or 65.30 mm
Barrel Length      : 20.0 inch or 508.0 mm
Powder             : Winchester 760

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.735% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-07.4   91    34.28   2419    1403   35453   8526     84.8    1.239
-06.6   92    34.55   2440    1428   36302   8621     85.3    1.227
-05.9   93    34.82   2461    1453   37173   8716     85.8    1.215
-05.1   93    35.10   2483    1478   38067   8810     86.3    1.200
-04.4   94    35.37   2504    1504   38983   8903     86.8    1.187
-03.7   95    35.64   2525    1529   39924   8995     87.3    1.174
-02.9   95    35.91   2547    1555   40890   9086     87.7    1.161
-02.2   96    36.18   2568    1582   41883   9176     88.2    1.148
-01.5   97    36.46   2590    1608   42903   9265     88.7    1.135
-00.7   98    36.73   2612    1635   43948   9354     89.1    1.122  ! Near Maximum !
+00.0   98    37.00   2633    1663   45024   9440     89.6    1.110  ! Near Maximum !
+00.7   99    37.27   2655    1690   46126   9526     90.0    1.098  ! Near Maximum !
+01.5  100    37.54   2677    1718   47264   9610     90.5    1.085  ! Near Maximum !
+02.2  100    37.82   2698    1746   48431   9693     90.9    1.073  ! Near Maximum !
+02.9  101    38.09   2720    1774   49631   9774     91.3    1.062  ! Near Maximum !
+03.7  102    38.36   2742    1803   50864   9855     91.7    1.050  !DANGEROUS LOAD-DO NOT USE!

 

[Nolo]

I should be getting better performance out of this.
How long of a case do you need to propel the 6mm 100 grain bullet to 3000 f/s using a 5.45 case (lengthened, of course)?

 

[timmyb21]

6.8 spc, good comprimise between 5.56 and 7.62, already commercially available. (disclaimer: this is just my opinion, I have no professional experience with the round, but it would be cheap to convert the current issued 5.56 weapons to 6.8)

 

[Nolo]

That's not exactly the point of this, thread, however.
I know 6.8 is a good round, what I'm looking for is a round that doesn't have stupid constraints put on it by 30-year-old pieces of weaponry. I want the best.

 

[GunTech]

I already shoot 6.8. It is OK, as is 6.5 gredel, but you can only do so much when your constraint is that it has to fit in a M16 magazine. 6.8 is dtrictly a short range cartridge.

Whay I;d like to see is something suitable for an assault rifle, that can also function well in a DMR or GPMG. 6.5 gre.del actually has more energy at long range than 308 thanks to a high BC bullet. But the gredel has almost no body taper and a steep shoulder, making it less than ideal in auto weapons.

My own idea was to lengthen and taper the 6.5 grendel to optimize it for auto weapons. Target velocity with the 108 gn Lapua scenar is 2800 fps.

 

[Nolo]

GunTech, how long does a 5.45 case have to be to push the 6mm 100gr. bullet 3000 f/s?

Oh, and a new, improved 6x49mm round:



Base Diameter: .414 inches or 10.523mm
Length of Case Under Shoulder: 1.529 inches or 38.838mm
Length of Case Under Neck: 1.683 inches or 42.736mm
Length of Case Overall: 1.963 inches or 49.860mm
Shoulder Angle: 30 degrees
Diameter of Case Opening: .267 inches or 6.782mm
Weight of Projectile: 100 or 110 grains

 

[jerkface11]

.250 savage is big now?? Ever seen a loaded round?Hardly a large cartridge.It gets 300fps easily without high pressures. Of course it won't fit in an m16 mag but so what?The sexy military designation would be 6.65x48.

 

[GunTech]

I finally did it. I reached my goal of 2800 fps with a 108 gn 6.5 lapua scenar at about 49,000psi. Case has a 45 minute taper and a 23 degree shoulder for optimal feeding.

6.5x48

The 6.5x48 is based on a lengthed 7.62x39, and makes 2800 fps with moderate pressure - well under 6.5 Grendel. In a strong action, it could make 3000 fps at 260 Rem pressures.

Cartridge          : 6.5x48
Bullet             : .264, 108, Lapua Scenar GB464
Cartridge O.A.L. L6: 2.625 inch or 66.68 mm
Barrel Length      : 24.0 inch or 610.0 mm
Powder             : IMR 4895

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.735% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-07.4   90    30.39   2609    1632   39310   6856     96.7    1.299
-06.6   91    30.63   2628    1657   40179   6906     97.0    1.286
-05.9   92    30.87   2648    1681   41069   6955     97.2    1.273
-05.1   93    31.11   2667    1706   41978   7002     97.5    1.261
-04.4   93    31.35   2686    1730   42908   7048     97.7    1.248
-03.7   94    31.59   2705    1755   43856   7093     98.0    1.236
-02.9   95    31.84   2725    1780   44832   7136     98.2    1.224
-02.2   95    32.08   2744    1805   45826   7178     98.4    1.212
-01.5   96    32.32   2763    1830   46845   7218     98.6    1.201
-00.7   97    32.56   2782    1856   47886   7257     98.7    1.189
+00.0   98    32.80   2801    1881   48952   7294     98.9    1.178
+00.7   98    33.04   2820    1907   50041   7330     99.1    1.166  ! Near Maximum !
+01.5   99    33.28   2839    1933   51156   7364     99.2    1.155  ! Near Maximum !
+02.2  100    33.52   2858    1958   52298   7396     99.3    1.144  ! Near Maximum !
+02.9  100    33.76   2877    1984   53467   7427     99.5    1.133  ! Near Maximum !
+03.7  101    34.01   2895    2010   54663   7456     99.6    1.122  ! Near Maximum !

 

[GunTech]

Starting with a 7.62x39 case head (0.452 same as 5.45) you have to blow out and lengthen the case to about 51mm to make 3000 with a 90gn 243 bullet without going ionto the realm of extreme pressure.

 

[GunTech]

Oh, and a new, improved 6x49mm round:



Base Diameter: .414 inches or 10.523mm
Length of Case Under Shoulder: 1.529 inches or 38.838mm
Length of Case Under Neck: 1.683 inches or 42.736mm
Length of Case Overall: 1.963 inches or 49.860mm
Shoulder Angle: 30 degrees
Diameter of Case Opening: .267 inches or 6.782mm
Weight of Projectile: 100 or 110 grains

Cartridge          : 6x49
Bullet             : .243, 100, Lapua MEGA E457
Cartridge O.A.L. L6: 2.635 inch or 66.93 mm
Barrel Length      : 20.0 inch or 508.0 mm
Powder             : Hodgdon H4350

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.735% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-07.4   90    31.96   2462    1346   38120  10344     92.1    1.243
-06.6   91    32.22   2482    1368   39018  10445     92.6    1.230
-05.9   91    32.47   2503    1391   39928  10545     93.0    1.216
-05.1   92    32.72   2524    1414   40859  10643     93.4    1.203
-04.4   93    32.98   2544    1437   41811  10739     93.8    1.190
-03.7   93    33.23   2565    1461   42794  10834     94.2    1.177
-02.9   94    33.49   2586    1484   43795  10927     94.5    1.164
-02.2   95    33.74   2606    1508   44823  11018     94.9    1.152
-01.5   95    33.99   2627    1532   45877  11108     95.2    1.139
-00.7   96    34.25   2648    1557   46959  11195     95.6    1.127
+00.0   97    34.50   2669    1581   48066  11280     95.9    1.115
+00.7   98    34.75   2689    1606   49202  11364     96.2    1.103
+01.5   98    35.01   2710    1631   50368  11445     96.5    1.091  ! Near Maximum !
+02.2   99    35.26   2731    1656   51562  11524     96.8    1.079  ! Near Maximum !
+02.9  100    35.51   2751    1681   52789  11601     97.1    1.067  ! Near Maximum !
+03.7  100    35.77   2772    1707   54047  11676     97.3    1.056  ! Near Maximum !

 

[Tony Williams]

I posted my analysis of the assault rifle round issue here: http://www.quarry.nildram.co.uk/Assault.htm

This is an extract from it:

Such an "ideal" cartridge would need to combine a long-range effectiveness comparable with the 7.62mm, with a recoil light enough to permit controlled, full-auto fire. Is it possible to achieve this? The evidence suggests strongly that it is. The British aimed to do this with the 7x43 cartridge half a century ago, and by all accounts succeeded admirably. This gives us an upper calibre limit. I don't think that a useful increase in performance over the 5.56mm can be achieved with anything smaller than 6mm calibre, which gives us the lower limit. We need to specify a bullet sectional density ratio of about .230 in order to retain velocity better than the 7.62mm (whose 9.33g bullet has an SDR of 0.217 - the 5.56mm SS109 bullet has an SDR of 0.174,and the new 5.0g Mk 262 is 0.220) and thereby deliver the long-range performance we want. We also need a muzzle energy of no more than 2,500 joules to provide the right balance of power and recoil. Taking into account that smaller calibres need less energy to penetrate armour, this works out as the following range of choices in common calibres:

7mm/.276": bullet weight 8.4g (130 grains) at 770 m/s (2,525 fps) = 2,500j

6.85mm/.270": bullet weight 7.9g (122 grains) at 784 m/s (2,570 fps) = 2,430j

6.5mm/.258": bullet weight 6.9g (106 grains) at 820 m/s (2,690 fps) = 2,330j

6.35mm/.25": bullet weight 6.5g (100 grains) at 834 m/s (2,736 fps) = 2,260j

6mm/.24": bullet weight 5.9g (91 grains) at 854 m/s (2,800 fps) = 2,150j

Any of the above options would do, but for the sake of argument let's take the 6.5mm. A cartridge of this calibre would be smaller than the more powerful 6.5mm Arisaka. If a similar case diameter were retained then length could be reduced to about 45mm. In fact, the case diameter and length would be similar for all of the above cartridges.

These rounds - especially at the larger calibre end - are pushing the maximum recoil for controllability in auto fire, so stepping up the power by any significant amount will limit you to semi-auto only.

On the problem of piercing body armour, raised earlier by 'Don't Tread On Me', these can be addressed by improving the bullets - tungsten-cored 5.56mm and 7.62mm AP ammo is available already, and APDS could be used if required. It's worth noting that the Russians have been ramping up the AP performance of the 5.45mm with better penetrating cores, including tungsten carbide.

 

[Nolo]

Hehehe...
I read your stuff all the time.

Good stuff.
I'm still flabbergasted at why I can't get the velocities that I want out of my 6mm. I don't get it. Basically, my maximum velocity (for an assault rifle) is 2700. I want to add about 300 f/s to that, but I'm definitely hitting the ceiling of how big my cartridge can be. If I go any larger, my velocity will get higher, but my EPP will pretty much stay stagnant or, even worse, go lower. As is, I've only got an EPP of about 48000, which is lower than that of any of the other calibers that I've calculated before. :banghead: :banghead: So we might as well use .223 as my 6mm, because you get no weight benefits from it. This is what I'm trying to defeat. Let me check your cartridge, GunTech. How much does it weigh? And I like your cartridge, but the weight of the bullet seems too light (for a 6.5mm) to me, and the cartridge too big. Still good, though.
Oh, and what are you using to generate those images? I want one.

 

[Nolo]

BLARG!!!!!
Why can't I get the velocities that I want out of a 6mm cartridge of acceptable size with a 10mm (or smaller) base!?!?!?!?!?!
:banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead::banghead:

 

[glockman19]

+1 to everyting Nolo said.

 

[JWarren]

Interesting thread-- one that is a bit more technical than I can really contribute to.

I do have one question and one comment however.

Regarding "Gun hose"... Isn't this a SMG? SMG's are usually designated as a special purpose SMG or a general purpose SMG. This is mostly a funtion of their rate-of-fire respectively. SP-SMG's operate with significantly higher rates of fire than GP-SMGs. At any rate, I am just wondering why we are using the term "gun hose?"

So the Glock has seen service, it hasn't seen combat, as far as I'm aware. Plus, we haven't really seen the true test of plastics: the test of time. Will they wear out? Do they create structural problems later in life? Until I see that they are truly successful, I will stick to the good ole' mostly metal guns.

Nola, the are durable. I can understand if one doesn't LIKE Glocks, but they've proven to hold up. I've been daily carrying a Generation-II Glock 19 for literally 13 years. Same gun. It's been with me everywhere from deer hunting (as a side arm) in swamps to hanging on the beach at our condo. I won't say that I've never had a milfunction, but I honestly can't think of one. Anyway, I thought you'd like to have that in your assessment. I'm not trying to go "Fanboy" for Glocks-- but I think they've put down the concerns of holding up. That said, my 1911A1 comes in tomorrow.



--John

 

[jerkface11]

Why the desire to make the cartridge have a base diameter of 10mm or smaller? That is the ONLY criteria of yours that 6.65x48 does not meet. It even makes a 100 grain bullet go 3000 fps.

 

[GunTech]

Nolo,

The software I use for cartridge design and load analysis are called quickdesign and quickload, respectively. They are exceptionally useful to wildcatters and cartridge developers, but are really only a guide. You have to follow up with real world testing. In most cases, I find Quickload very accurate to real orld performance, but not always.

Each program costs $150, and runs on a PC running windows 98, XP or vista. I am actually running it on my mac under parallels.

Also note, I am calculating all velocities from a 20 inch barrel. Shorter or longer barrels will effect velocity. The industry standard is typically a 24 inch barrel, which can add as much as 200 fps to velocity, which may be why these numbers look low to many peopl. All of my calculations are based on conservative numbers: 20 inch barrel, low pressure, etc. You could easily get better performance using higher pressures and longer barrels, but this would not reflect current military rifles.

I'll post some more options on the 6.5x58. The cartridge came out big because I kept the shoulder angle under 25 degrees and doubles the body taper of the 5.56x45. If you adopt small body taper and sharp shoulder, you can get a shorter case, but at the expense of reliability.

QuickLoad and QuickDesign are available here:

http://www.neconos.com/

 

[PercyShelley]

splendid thread here!

I know that we're not considering the weapons platform for these cartridges, but taking a more holistic look for just a moment, what about a short, fat cartridge with no body taper at all?

Consider the FN P90; the cases have a special polymer coating to ensure reliable feeding despite the lack of taper. Since the cases are straight, they maximise volume, although nobody would hold up the 5.7 as a ballistic majesty by any means.

Suppose that we sink the bullet fully into such a case in the manner of the Nagant gas-sealed revolver round, except with as short as possible a neck and extend the shoulder out to reclaim lost powder space. The shoulder could be made rather sharp without causing feeding difficulties, since there will be no bullet to catch on. This arrangement may necessitate the use of sabots to give the neck something to grab near the front of the bullet.

If we keep the cartridge to a reasonable OAL, we can use a P90 horizontal feed, which on an assault rifle could be quite an asset. Since the magazine could be made very long compared to the magazine on the P90; we could have potentially half a meter to work with if the assault rifle is a bullpup, the cartridges could be made as fat as we want. In addition to being ballistically vogue right now, I suspect that they will be lighter, since geometry alone would suggest that a short fat cylinder of equal volume to a long skinny one will have less surface area, and thus less brass weight.

 

[Nolo]

Thank you all.
I've really honed what I want to do with "my" assault rifle here. I want to send a 6mm (100 grain) bullet 3000 f/s with a better than 55000 EPP. Hard, but I think I can do it as long as I work long enough on it. And I realize that only the real-world test is enough, hence my assessment of "plastic guns". I have absolutely nothing against these guns, but reliability is key, and I don't want to trust the structural integrity of my weapon to plastic... yet.
As for the service that your Glock has seen, have you ever gone into combat with it (this is an actual question, it's quite possible that you have), and, if so, how has it performed? Being in a holster all day is very different from being in the sandbox. Even the most reliable shotguns (for instance) in the civilian market seem unreliable when shoved into military combat. It is truly a different world. Also, for GunTech, I would not put too much into reliability of feeding, while that is highly important to a weapon like the M16, if you mate an "unreliable" cartridge with a reliable rifle, your shouldn't have a problem.

Now, let me explain the "gun hose" concept. You may be asking, why in the world doesn't he just call it a submachine gun? Well, because it's not a submachine gun. Subbies shoot pistol ammunition, a "gun hose", as I conceive it, shoots miniature (very miniature, as small as 4mm) rifle ammunition. Also, subbies tend to (not always, look at the 10-pound Thompson) weigh less than assault rifles, whereas "gun hoses" weigh the same as assault rifles, up to 10 pounds. Also, submachine guns generally use 30- or 50- round box magazines, a "gun hose" uses 75- or 100-round magazines (drum or otherwise), and, depending on the gun, sometimes as much as 200-round magazines. Thus, for a "gun hose", weight of the ammunition is key. It must be small, or else the poor soldier carrying the weapon will be overburdened. Also, "gun hoses" must not only have high rates of fire, they must have extreme rates of fire, preferrably in the 2000 rpm range. When your round only produces 300 ft-lbs of energy or less, you'd better be dishing those puppies out at high rates of fire. Also, burst settings for "gun hoses" should be as large as 7-10 rounds per burst, or else your effectiveness is moot over an assault rifle. Also, "gun hoses" need to be accurate, so that you don't lose any of that effectiveness. So that's a "gun hose", and the differences between it and a submachine gun. Oh, and if anyone can think of a better name for the "gun hose" concept, please let me know.

Some pictures of the weapons that inspired the "gun hose" concept:

The American 180 submachine gun:

Caliber: .22 ILARCO proprietary ammunition
Magazine Capacity: Up to 275 rounds
Rate of Fire: 1500 rounds per minute

The Fabrique Nationale P90 PDW:

Caliber: 5.7x28mm proprietary ammunition
Magazine Capacity: 50 rounds
Rate of Fire: 900 rounds per minute