New Cartridge Developments and Implications for Dismounted Infantry Soldiers

[stanc]

Have you ever done a weight analysis of 6.5x55 Swede with 140gr versus 7.62 NATO, assuming equal weight links?

I don't have precise weight for 6.5x55, but with a 140gr bullet, it has to be heavier (due to fatter, longer case) than the 7.62x51 w/147gr projectile (392gr).

So, if you're hoping for a weight reduction, ya ain't gonna get it by switching to 6.5x55. :eek:

[LRRPF52]

stanc,

Not suggesting 6.5 Swede as a cartridge as I feel it's COAL is too long. I'm just interested since it has performance that I like, and there are existing military 140gr loads for it that can be used as a reference. Since it has a .480" base diameter versus the .476" for 7.62, it would be able to use the same links and provide a theoretical weight comparison. I'm not sure how much the extra 4mm in narrower neck brass will affect the weight between the two cases, but it doesn't matter for what we're looking at. Rough figures show 7.62 147gr weighing 700gr more per 100 rounds of ammo, which is only .1 pound more than the Swede based on bullet weight alone.

This would represent the top limit in weight for a new LMG cartridge, and would penalize the SAW gunners heavily, so I would steer away from it on those grounds as well.

LRRPF52

[stanc]

I'm not sure how much the extra 4mm in narrower neck brass will affect the weight between the two cases...

The neck doesn't matter. It's the 4mm longer rim-to-shoulder length where the extra brass affects the weight.

...but it doesn't matter for what we're looking at. Rough figures show 7.62 147gr weighing 700gr more per 100 rounds of ammo, which is only .1 pound more than the Swede based on bullet weight alone.

Again, you can't look at only the bullet weight. The fatter, longer 6.5x55 case is sure to make up that 7gr difference in bullets.

At best, 6.5x55 matches the (392gr) 7.62x51 cartridge weight. At worst, 6.5x55 is a few grains heavier.

But, if logical analysis doesn't convince you, I've asked some people who should be able to weigh a loaded round.

[stanc]

Okay, I got the following reply from an acquaintance.

The Swedish manual "Ammunitionsregister för Armen" shows the weight of 6,5 m/94 Sk ptr with projectil M41 as 22.9 grams. I weighed a specimen headstamped / 7 / / 8 / 027 made by Norma with CNCS Spitzer bullet and it weighted 23.9 grams (369.1 grains).

Seems it's much lighter than my logic said it ought to be... :o

So, using the book value (22.9 grams), 100 rds of linked 6.5x55 would weigh 0.54 lbs less than a belt of 7.62x51.

[LRRPF52]

stanc,

I suspect something like a 6.5x47 Lapua on full auto would be a barrel burner, but that is the direction the performance objectives would most likely lead. If a Grendel could match 7.62 M80 out to distance, that would be great, but getting the projectiles to speed is the problem. I'm just anticipating those that will say that they have a certain perceived or real performance of M80 ball at 700m, 800m, 900m, that the Grendel clearly does not, as far as hard impact on target goes.

If the requirements were reduced to say that it equals 7.62 trajectory only, then there is probably some room past 600m to argue in favor of the 147 impacting certain targets vs. an undetermined mass-produced 6.5 round of lesser weight. That's why the 140gr 6.5 military bullets interest me. I would not want the x55 case length for the reasons stated previously.

It is interesting to note that the 6.5x55 Swede with 140gr Norma Spitzer probably weighs less than the 7.62x51 M80 with 147gr, given the differences in case dimensions. The Norma might have a lesser powder charge weight as well, since it doesn't take as much to get a 140gr going 2600fps from a tighter neck when compared with what it does to get a 147gr going over 2800fps, and the Swede needs a slower-burning powder to push that bullet with its long bearing surface.

LRRPF52

[stanc]

So, do you plan to do any barrier penetration tests of 6.5x55 vs 7.62x51? Would love to see the results.

Attached:
6.5x47
6.5x55
7.62x51

[JASmith]

Gents,

There may be some prudence in separating bullet design from cartridge design. For example, the hype about the M855A1 suggests that it tends to put a hole in thicker steel than does the 7,62X51 M80 in some circumstances. We can go very small in bullet and cartridge size and get interesting results: http://www.cbjtech.com/sida.asp?sida=5_Downloads. The penetrator in this 6.5mm cartridge is a 4mm diameter tungsten rod.

These suggest that arbitrarily setting a bullet weight or caliber may lead us away from very interesting and possibly compelling solutions.

[LRRPF52]

stanc,

I don't see a need to test the 6.5x55 Swede specifically, as long as we can get .260 Rem or 6.5x47 Lapua to duplicate the velocity with 140gr bullets we're interested in. I think those Swede's are somewhere in the neighborhood of 2600fps, so that is easily attainable since I get 2850fps with 130 VLD's right now from a 22" .260 AR10. 6.5BR would also be another one to look at. If it's easier to use a readily-available 6.5 Swede rifle with readily-available 140gr Swedish Mauser ammo, that could be helpful. I have several friends that own those rifles in Finland, as well as 7.62 NATO rifles and machineguns there, so we could possibly conduct those tests this summer and winter.

Otherwise, I need to try some of the 140gr military-compatible bullets that are available in my .260, and I'm having a hard time finding them. I'm neck-deep in a lot of other work right now, so any suggestions in the right direction would be great. I just checked Midway, but couldn't find any 140gr 6.5mm FMJ's. I wonder if we could locate a source for just the 140gr Swedish military projectiles, separate from the loaded cartridges.

Basically, I'm thinking of testing the 140's versus the M80 ball at 500m, 600m, and 700m on some common mediums. Then we could work backwards in bullet weights with 6.5's if the 140's prove superior to the 147gr 7.62 NATO, which may seem like a foregone conclusion, but should be done on an unbiased assumption, since results are what matters.

I want to combine thin metallic barriers simulating light-armored vehicle skin, with some type of semi-fluid medium behind them to demonstrate both armor-defeat capabilities and follow-on affects to tissue simulant. I think we'll be able to incorporate these tests into one of the various sniper training events there, or my shoot schedule here.

LRRPF52

[LRRPF52]

JASmith,

That 6.5x25 is an answer to all my concealed carry dreams. I've been a big fan of the 7.62x25 for a long time, and have actually drawn out some 6.5x25 concepts, but was limited by COAL and lack of available mags. This eliminates all those obstacles. That will have profound effects on PDW/pistol and SMG's if adopted. That tungsten penetrator on the armor door is eye-opening, if factually-represented. That will also cut weight significantly for my summer guns when clothing is less and thinner. Wow. I've had plans to custom-build a 1911 with a modified frame that will take Cz-52 mags, but there is no need for that if I can get this. It will also make the Bizon with helical mag a totally new animal...should probably stop talking now...

This still presents us with some potential problems for a LMG though, since sabots don't have the same accuracy potential, as you will notice with the 10.2cm groups at 100m, and 17.8cm groups at 200m, unless one would be willing to seriously decrease hit probability at 400m and beyond. A sabot-based system might be acceptable for a belt-fed weapon if the accuracy spread were figured into the shot-dispersal benefits of traditional machine-gunning, which could be mitigated with constant recoil since the gunner can basically walk rounds onto target very quickly. Hmmmmm....

LRRPF52

[stanc]

Otherwise, I need to try some of the 140gr military-compatible bullets that are available in my .260, and I'm having a hard time finding them. I just checked Midway, but couldn't find any 140gr 6.5mm FMJ's. I wonder if we could locate a source for just the 140gr Swedish military projectiles, separate from the loaded cartridges.

Midway offers the Lapua 144gr FMJ.

I don't know of sources for Swedish military 140gr FMJ bullets only. If you specifically want such, probably have to buy mil surplus ammo and pull the bullets.

The S&B site does show that they have 140gr FMJ projos (in boxes of 100), but I couldn't find a source for these in the US. Also, they look to have a slightly rounded tip, where the Swedish mil bullets are much more pointed.
http://www.sellier-bellot.cz/ammo-compon...ullets.php


Wolf and Prvi market 6.5x55 w/139gr (flat-tipped) FMJ.

[LRRPF52]

stanc,

Thanks for that. I just requested some sourcing for those Swedish Military 140's via contacts in Finland. That's a pretty popular cartridge over there, and Europe as a whole of course. I'm looking at the 6mm BR, which has a water capacity of around 38-39.5grains. I'm thinking a more ideal cartridge for what we're looking at would have a narrower base diameter like the Grendel at .444", with more cartridge length for powder capacity, and would give a better over-bore relationship for barrel life if used with a .264" bore. Basically, a longer base-to-shoulder Grendel would seem ideal at this point, given that we aren't limited by mag-length. If closer to 40 grains of powder could be used, that would get the 6.5's going much faster.

The .260 is way too spacious in case capacity for long bullets at least, and a slightly-narrower case would help with barrel life as mentioned, in addition to soldier carrying capacity for space.

LRRPF52

[stanc]

I'm thinking a more ideal cartridge for what we're looking at would have a narrower base diameter like the Grendel at .444", with more cartridge length for powder capacity, and would give a better over-bore relationship for barrel life if used with a .264" bore. Basically, a longer base-to-shoulder Grendel would seem ideal at this point, given that we aren't limited by mag-length.

6.5x45 Czech?

[Tony Williams]

Basically, I'm thinking of testing the 140's versus the M80 ball at 500m, 600m, and 700m on some common mediums. Then we could work backwards in bullet weights with 6.5's if the 140's prove superior to the 147gr 7.62.

That sounds great, but it might be as well to spread the ranges somewhat to give a more complete picture: something like 200m, 500m and 800m. Logically, the performance of the 6.5mm relative to the 7.62mm should get steadily better with increasing range.

That 6.5x25 is an answer to all my concealed carry dreams.

One of my favourite guns is the B&T MP9 in 6.5x25. I had the chance to shoot it in Sweden a couple of years ago (Carl-Bertil Johansson invited me over, because I had suggested that it might be a good combination). I wrote an article about it which was published in the Fall 2010 Small Arms Defense Journal. There's also a brief note about it at the end of this article: http://www.quarry.nildram.co.uk/PDWs.htm

I have that piece of armour with a hole blown through it on my desk (see below):

[Tony Williams]

6.5x45 Czech?

Or, to put it another way, Cris Murray's 7x46 necked-down to 6.5mm?

[stanc]

Or, to put it another way, Cris Murray's 7x46 necked-down to 6.5mm?

That, too.


I wonder if Murray is still working on the 7x46 project? Last I heard -- about a year ago -- was that he was starting to convert an MG42 to fire the 7mm UIAC. But, his web site seems to no longer exist, and a search only turned up this year-old article: http://www.thefirearmblog.com/blog/2010/...cartridge/

[Tony Williams]

I wonder if Murray is still working on the 7x46 project? Last I heard -- about a year ago -- was that he was starting to convert an MG42 to fire the 7mm UIAC. But, his web site seems to no longer exist, and a search only turned up this year-old article: http://www.thefirearmblog.com/blog/2010/...cartridge/

I met Cris last year at NDIA, and last heard from him in November when a test of his converted MG 42 was imminent. I've sent him an email to enquire about progress.

[Tony Williams]

I've heard from Cris. He's fine and trying to finish a prototype assault rifle. Microsoft stopped his Windows live web service and he hasn't got around to replacing it yet, but he's happy to answer question directly.

He'll be at the Indianapolis NDIA meeting next week, if anyone's going (I won't be this year).

[LRRPF52]

Tony,

Do you know if Chris worked at the AMU at Benning? Was he ever in the National Guard? This guy sounds a lot like someone I knew who was involved with the 6.8 SPC development, but I lost his contact info. You can PM the response.

The 7x46 would seem ideal for a case, pushing a 6.5 of sufficient weight at a sufficient velocity to give good downrange performance. It would require strong brass, and if a small rifle primer could be activated reliably in extreme cold weather conditions, that might be the ticket.

LRRPF52

[Tony Williams]

I've PM'd you.

[LRRPF52]

Gents,

Reading about the 7x46mm some more, it looks like the choice of 7mm might have something to do with the pressure limitation objectives of keeping it under 50k psi with a 130gr going 2650 fps out of a 16.5" barrel, which is a sensible objective for a repeating rifle or machinegun.

A 6.5mm would add a lot more pressure than a 7mm due to the increased bottle neck, but it remains to be seen what characteristics this 46mm length case with a narrower base would have. It's worth looking into I think.

LRRPF52