Military round comparisons

[Trooper]

You don't need a 140gr 6.5mm to have a .500 G1 BC. You should also be aware that G1 BC's are meant for flat-based bullets, not boat tails, and 5.56 and 7.62 have been using FMJ Boat Tails for a long, long time. The weight-to-BC ratio for a 7mm makes it too heavy, generating too much recoil, and too much cartridge space/bulk for a viable system that will be lightweight enough for riflemen.

There is some interesting work on a 7mm Grendel for hunting, but it is optimum with 120gr bullets. Those are much lower than a 6.5mm 123gr .510 BC projectile. If you're relying on just BC and trajectory comparisons, the 16" Grendel currently beats a 16" 7.62 NATO L129A1 or SCAR-17 for wind drift when pushing the 147gr M80, assuming a 2450fps speed for the Grendel, and a 2620fps speed for the 16" 7.62 carbine (7.62 NATO M80 varies in 16" guns from 2550-2620fps).

The 7.62 NATO at such low speeds for the bullet will not fragment at CQB (bad), and has the following drop/drift at 4400ft ASL (thinner air like A-Stan)...
Drop at 600yds: 4.6 Mils
Drift at 600yds: 1.4 Mils (10mph full value wind)

At 2550fps mv, it is:
600yds: 4.9 Mils
Drift: 1.5 Mils

The 16" 6.5 Grendel with current civilian factory 123gr at 2450fps:
Drop at 600yds: 4.9 Mils
Drift at 600yds: 1.2 Mils

The Grendel does that with 50% less recoil, much less ammo weight, less ammo footprint on the soldier's load-meaning more capacity to space. The energy difference at 600yds is 847ft-lbs for the 2550fps M80, and 763ft-lbs for the 2450fps 123gr 6.5mm.

Build a bolt based off of the .30 RAR, and you can push the pressure up to generate 2650fps in the 16" Grendel easily, as I have factory 123gr Lapua Scenar loads that have clocked over 2580fps in my 16" gun for some reason. Being moly-coated was one, and the temps on the range might have been another. You see the diminishing returns when you crank up to 2650fps:

600yds Drop: 4.0 Mils
600yds Drift: 1.1 Mils
Energy: 912ft-lbs (that's quite a difference actually)

Most of the data that I have refers to the 6.5mm bullet at 140 gr. When looking at a potential GPC, 6.5mm is considered to be the bottom of the range and 7mm at the upper. The 6.5x55 is seen as the gold standard by which everything else is compared. It pushes a 140 gr. bullet at 2500 fps which does more damage down range than does a faster bullet. With a BC of .500 or better, the bullet retains more velocity, thus energy, longer.

Frankly I am not seeing much gain (over the 6.5 Grendel) with the 260 Rem (.308 case) or the 6.5mm BRM (based on the .30-30 case) let alone many of the other rounds. If we come up with a General Purpose rifle in 6.5mm, it should be able to use a bullet from 120 gr. to 140 gr. if needed. From what I have seen, the Grendel does as well as the 7.62x51. I would think that the G7 bullets would be better than a G1.

The three things that a GPC would need is a BC over .500, muzzle speed of 2500 fps and potential to be used in the M16/M4 platform. But my question would be whether there is ANY advantage of going to a larger caliber (ie 7mm), of using a longer case than what we have in the 6.5 Grendel. How close is the Grendel in potential to becoming the GPC?

[cory]

More importantly, the requirement for lead free construction makes it unlikely that a general issue ball projectile would be that heavy.

Even that may be heavier than is practical. The FMJBT bullet developed for Wolf's steel case ammo is only 100 grains.

Why does it have to be lead free other than European regulations?

[stanc]

Why does it have to be lead free other than European regulations?

The US Army is going lead free, too. Hence 5.56 M855A1 and 7.62 M80A1.

[cory]

The US Army is going lead free, too. Hence 5.56 M855A1 and 7.62 M80A1.

Of course they are. :/ Thanks for the info Stanc I was unaware of that. Is there some advantage I don't know about or is it purely the tree huggers bull s***t.

[Bill Alexander]

While these discussions are entertaining I am yet to see anything that looks like a weapon system specification. Before one can even discuss the cartridge one must define the mission. What range, what target, what protection level, what dispersion. Decisions on projectile energy must be underwritten by the required level damage within a known and defined target, thus one can shift mass, caliber and velocity as variables but only in consideration of the recoil level imposed by the weapon weight. This now in turn drives the projectile construction which then in turn provides the envelope for the casing. The engineering decision then becomes a balance of the operating system type, pressure and weapon weight, and then finally drops to barrel length.

But it all starts with hit probability and range, followed by an accurately defined and scientifically backed target description.

In consideration of the Wolf projectile for the steel case, this was a balance for a economical construction of projectile with good external ballistics for shorter barrels. The primary goal was economy everything else was secondary. Given the space envelope a lead free 110 grain projectile with a Bc value approaching 0.480 is quite feasible. The lead free construction can be used to advantage when considering protected target types typical of the modern battlefield. What is less inviting for the Grendel is the PPI for a mid life upgrade unless powder technology for insensitive propellant advances in the same timeframe.

[stanc]

The three things that a GPC would need is a BC over .500, muzzle speed of 2500 fps and potential to be used in the M16/M4 platform. But my question would be whether there is ANY advantage of going to a larger caliber (ie 7mm), of using a longer case than what we have in the 6.5 Grendel. How close is the Grendel in potential to becoming the GPC?

Bill Alexander estimates the Wolf 100gr FMJBT to have a 0.390 BC, quite a bit lower than the 0.500 you cite as necessary.

A larger caliber (6.86mm or 7mm) may be required for a GPC to have adequate terminal effects, particularly with lead free bullets.

[stanc]

Of course they are. :/ Thanks for the info Stanc I was unaware of that. Is there some advantage I don't know about or is it purely the tree huggers bull s***t.

I think it's mainly the latter.

[JASmith]

Of course they are. :/ Thanks for the info Stanc I was unaware of that. Is there some advantage I don't know about or is it purely the tree huggers bull s***t.

I suspect both factors are at work.

Lead and copper are both a lot more expensive these days, which drives one toward steel as much as possible for military bullets. Sporting bullets are a different story.

Also, making the environment a matter of religious principal makes a lot of folks to blindly accept that even mildly toxic materials are to be eliminated. Whether elimination of lead, for example, from bullets makes diddly squat difference is beside the point. The fact that "lead is poisonous when large quantities are consumed" makes it one of the metals to be eliminated.

The anti-gun community takes advantage of the Pb-phobia by pushing for legislation to prohibit lead bullets for hunting and indoor practice. Suitable replacements are a LOT more expensive, raising the threshold for participating in our sport.

[Trooper]

While these discussions are entertaining I am yet to see anything that looks like a weapon system specification. Before one can even discuss the cartridge one must define the mission. What range, what target, what protection level, what dispersion. Decisions on projectile energy must be underwritten by the required level damage within a known and defined target, thus one can shift mass, caliber and velocity as variables but only in consideration of the recoil level imposed by the weapon weight. This now in turn drives the projectile construction which then in turn provides the envelope for the casing. The engineering decision then becomes a balance of the operating system type, pressure and weapon weight, and then finally drops to barrel length.

But it all starts with hit probability and range, followed by an accurately defined and scientifically backed target description.

In consideration of the Wolf projectile for the steel case, this was a balance for a economical construction of projectile with good external ballistics for shorter barrels. The primary goal was economy everything else was secondary. Given the space envelope a lead free 110 grain projectile with a Bc value approaching 0.480 is quite feasible. The lead free construction can be used to advantage when considering protected target types typical of the modern battlefield. What is less inviting for the Grendel is the PPI for a mid life upgrade unless powder technology for insensitive propellant advances in the same timeframe.

Three weapons: the PDW of the common soldier as currently manifested in the M4, a DMR (markmans rifle) with 20" barrel and a light MG like our SAW (M249). Currenly both the US and the UK infantry squad have an PDW (M4 or the Enfield for the UK) in 5.56x45, a SAW in 5.56x45, a DMR in 7.62x51 and a medium MG in 7.62x51. That is four weapons with spare parts and two seperate magazines, two MGs with seperate belts. Thus the desire to have a General Purpose Rifle that could be the PDW (16.5" barrel) or the DMR (20" barrel). Afghanistan has put targets out at 500 meters, too far to be effective with the 5.56x45. Thus the need for the DMR and med MG in 7.62x51. Plus both Iraq and Afghanistan have buildings made of brick and stone which tend to not be effected by the lighter 5.56x45.

I am putting together a piece, which I will post here, on the GPC/GPR.

[Nukes]

Has there been any rational discussion explaining why lead going back into the ground from which it came is a problem? Even with regard to the claims of finding lead shot in waterfowl, I do not recall any convincing evidence of harm. Did I miss something?

A second question—is there anything important to know about the interior ballistics of lead-free ammunition, anything that, vis-à-vis safety, should influence chamber dimensions, etc.?

[stanc]

Has there been any rational discussion explaining why lead going back into the ground from which it came is a problem? Even with regard to the claims of finding lead shot in waterfowl, I do not recall any convincing evidence of harm.

What does it matter? The decision to go lead free has been made. Plan accordingly.

A second question—is there anything important to know about the interior ballistics of lead-free ammunition, anything that, vis-à-vis safety, should influence chamber dimensions, etc.?

Nothing that I know of. But, I'm not an expert on the subject.

[Tony Williams]

is there anything important to know about the interior ballistics of lead-free ammunition, anything that, vis-à-vis safety, should influence chamber dimensions, etc.?

The key issue with lead-free bullets (by which I mean with some mix of copper and steel - tungsten is too expensive for general use and has its own toxicity issues) is that they are less dense than lead. So if you just keep the same bullet shape you lose weight and therefore BC, other things being equal. To keep the weight and BC the same, the bullet has to be longer. This can cause problems with ammo packaging (the longer bullet may leave less space for propellant) and even stability issues, since a tighter rifling twist may be needed. In fact, with a 6.5mm bullet you might find that a lead-free 123 grain is beginning to push the envelope as far as the maximum length/diameter ratio for spin-stabilisation is concerned - especially when you bear in mind that a tracer bullet will be required, and they are less dense still so tend to be longer than their ball equivalents.

Taking all of that into consideration, lead-free bullets are a PITA for achieving high-BC bullets in a compact 6.5mm cartridge.

[Michael]

I'd love to see the Geneva convention thrown out and our Marines and Soldiers only be regulated by the Constitution and the UCMJ, allowing a HPBT GPR, but I don't see that happening anytime soon.

We have been using HPBT ammo for the last couple of years http://bulletin.accurateshooter.com/2010...5-56-ammo/. It isn't match grade, and is more designed for penetration, but we have been using it

Can only speak for myself, but last couple of tours I did ('08 and '09) there was 77gr Match ammo available. Primarily for DM, but in my units, we were able to outfit most of the folks a couple of times.

[BjornF16]

The "open tip match" (OTM) gets around the Hague Convention primarily because al Qaeda isn't a "contracting party" to the Hague Conventions...not sure if NATO would adopt the round.

http://avalon.law.yale.edu/19th_century/dec99-03.asp

Then there is also this "opinion": http://www.thegunzone.com/opentip-ammo.html

[stanc]

The "open tip match" (OTM) gets around the Hague Convention primarily because al Qaeda isn't a "contracting party" to the Hague Conventions...

Actually, that isn't really why, although I suppose it could be used as a legal rationale. IIRC, the US JAG authorized use of Sierra MatchKing hollowpoints mainly on the technicality that they were not designed to expand in flesh.

And BTW, the US is also not a signatory to Hague Declaration III. :eek:

...not sure if NATO would adopt the round.

Just offhand, I don't know of any NATO nations (other than the US) that use hollowpoints. Being Hague signatories, the Europeans tend to abide strictly by the letter of the law (in contrast to the US). Some of them have even gone so far as to modify construction of their FMJ projectiles to try to eliminate fragmentation in soft tissue.

[BjornF16]

Actually, that isn't really why, although I suppose it could be used as a legal rationale. IIRC, the US JAG authorized use of Sierra MatchKing hollowpoints mainly on the technicality that they were not designed to expand in flesh.

That rationale is the second link I provided.

And BTW, the US is also not a signatory to Hague Declaration III.

However, HD III (1899) was the basis for other "findings" or agreements to which we ARE signatories, notably Hague Declaration 1907, Section IV, Article 23e which basically says the same thing. (The US considers HD III section relating to explosive bullets to be a part of international law as it is closely related to HD 1907 Section IV, Article 23e.) The second link I provided also gives other Treaty agreements to which we are signatories.

The bottom line is that the Law of War constraints upon the US include not using bullets designed to fragment or expand upon contact (this is routinely taught in Law of War "classes" which we had to routinely take). The OTM bullet does not meet this criteria (as outlined in the finding I provided).

Finally, these conventions to which we are signatories are obligatory between warring parties who are both/all signatories. As soon as a non-signatory is introduced, the limitations are removed. Al Qaeda is NOT a signatory, and therefore we wouldn't be held to those restrictions (and my original post is still correct).

[Tony Williams]

The Hague provisions have effectively been rolled up into the Geneva Conventions which are considered to be binding on any country engaged in warfare, so the debates about who signed what are rather academic.

The key phrase is "bullets designed to fragment or expand upon contact". The US position has been that their OTM bullets are not designed to expand (and in fact usually don't), just as the M855 is not designed to fragment - these characteristics are just accidental side-effects.

[stanc]

I am putting together a piece, which I will post here, on the GPC/GPR.

How goes it with this? I'm hungry for something new.

[bwaites]

The Hague provisions have effectively been rolled up into the Geneva Conventions which are considered to be binding on any country engaged in warfare, so the debates about who signed what are rather academic.

The key phrase is "bullets designed to fragment or expand upon contact". The US position has been that their OTM bullets are not designed to expand (and in fact usually don't), just as the M855 is not designed to fragment - these characteristics are just accidental side-effects.

Generally true. Of course we are not fighting a country, so the Hague and Geneva conventions don't apply anyways! We are fighting criminals who fit into the criminal class known as "terrorists".

[stanc]

Generally true. Of course we are not fighting a country, so the Hague and Geneva conventions don't apply anyways! We are fighting criminals who fit into the criminal class known as "terrorists".

- Not all of the people we're fighting are terrorists. Some are patriots waging guerilla warfare against foreign invaders.

- AFAIK, the US JAG rulings on hollowpoints like the SMK and SOST rounds authorize their use against not only criminals and terrorists, but also lawful combatants (i.e., members of national armed forces). Other countries JAG equivalents have ruled such projectiles are illegal. They can't both be right.