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New Army "Caliber Configuration Study" - BluntForceTrauma - 04-24-2014
I want to run some numbers, making a comparison between this GS Custom 6.5mm 112gr monolithic with a PKM 7.62x54R round.
Any educated guesses as to a realistic velocity from a 16" barrel for a 112gr with at least a 0.523 BC from the 6.5 Grendel case? I'm thinking if we have a Grendelized M855A1 that it would have a similar form factor to the GS Custom 6.5 112gr, perhaps a bit lighter if the steel core is less dense than copper.
John
P.S. I'm going to compare it to a 7.62x54R round from a PKM 25.4" barrel, with a 148gr bullet at 2,717 fps with a 0.350 BC. I've guesstimated the BC, since internet sources vary so widely. Sierra bullets lists a BC of 0.397 for its .308 150gr FMJBT. If I'm being unfair to the Russian, speak now.
New Army "Caliber Configuration Study" - stanc - 04-24-2014
Tony Williams Wrote:A comment on bullet design: it does not necessarily follow that a lengthened bullet has a better Form Factor, if the extra length just goes into the shank, leaving the nose and tail profiles the same.Thanks for that info, Tony. I would note that the M118 Match bullet has a tangent ogive, whereas that of M80 Ball is secant. A better comparison would be to steel-core M59 Ball (left, below), which also has a secant ogive, and weighs approximately the same as lead-core M80 Ball (right, below). Do you happen to know the FF of the M59 bullet?
This can be demonstrated by comparing the 7.62mm M80 with the M118 sniper loading (both lead-cored). The M118's FF is almost exactly the same; it has a better BC simply because it's heavier.
![[Image: M59m80A.jpg]](http://i116.photobucket.com/albums/o15/Cosine1/M59m80A.jpg)
Quote:Extra length can permit a better FF by allowing a longer, more tapered ogive - but only if the COAL permits this.I wholeheartedly agree. We can only hope the military will, too.
The US has a long tradition of designing cartridges with COALs too short to permit the use of high-BC bullets with long ogives. The 6.8mm Rem is perhaps the most extreme recent example of this...
One of the key design points of any new military cartridge should be that the specification must allow the use of long-ogive bullets, since they can provide a significant improvement in long-range performance without any extra power, weight or recoil.
Quote:Apart from slightly longer gun actions and magazines, it provides extra performance at no cost.Yes. It causes me to wonder how much performance would improve by simply increasing cartridge OAL of 5.56 and 7.62 NATO.
On your MG&A forum, Badcow454 stated that the 7.62x51 case loaded with a scaled-up 7N6 bullet would have a 2.94" COAL. Since the FN MAG was originally adopted by Sweden in 6.5x55, which has a 3.15" COAL, it would seem a relatively easy task to adapt MAG variants to use 7.62x51 with long-ogive bullets.
Of course, this concept could also be applied to 6.8 SPC, as well as variations like 6.5 SPC.
Question: What do you get if you scale up the 5.45x39 round by a factor of 1.1?
Answer: A long-loaded 6mm SPC.
![[Image: ak-74-ammunition-for-sale-b.jpg]](http://www.keepshooting.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/a/k/ak-74-ammunition-for-sale-b.jpg)
New Army "Caliber Configuration Study" - stanc - 04-24-2014
HANKA Wrote:I'm going to compare it to a 7.62x54R round from a PKM 25.4" barrel, with a 148gr bullet at 2,717 fps with a 0.350 BC. I've guesstimated the BC, since internet sources vary so widely. Sierra bullets lists a BC of 0.397 for its .308 150gr FMJBT. If I'm being unfair to the Russian, speak now.Speaking now.
Yes, I think it's unfair. One of the SME's on Tony's MG&A forum says he uses 0.406 BC and 2750 fps (for MV from the PKM).
IMO, 0.406 BC for 7.62x54R 148gr steel-core Ball seems reasonable. It's consistent with the middle of the BC range in test data on 7.62x54R.net, as well as published BC's for 7.62x51 147gr M80 Ball.
New Army "Caliber Configuration Study" - stanc - 04-24-2014
HANKA Wrote:I want to run some numbers, making a comparison between this GS Custom 6.5mm 112gr monolithic with a PKM 7.62x54R round.I'll hazard a guess of 2550-2600 fps, based on 16" velocities @ http://www.alexanderarms.com/images/pdfs/grendel_ballistics.pdf
Any educated guesses as to a realistic velocity from a 16" barrel for a 112gr with at least a 0.523 BC from the 6.5 Grendel case?
New Army "Caliber Configuration Study" - BluntForceTrauma - 04-24-2014
Obviously, I want to put the 65G in the best light, and am jealous of any competing data, so let's just get that on the table now. Having said that, I intend to have very strong rationales, openly and objectively argued for my data.
What is the rationale for your SME's data about 7.62x54R? I'm skeptical that his BC is better than Sierra's, given that Sierra is actually tested, has a denser lead core that sheds velocity slower, and has a secant ogive. Got a link to his data?
I'm gonna go with 2550 fps for the 112gr 65G @ 0.523 BC (this is a conservative BC because that's the 2400 fps BC). Comparable 110-115gr 6.8 loads get about 2550 fps from a 16".
John
New Army "Caliber Configuration Study" - stanc - 04-24-2014
HANKA Wrote:Obviously, I want to put the 65G in the best light, and am jealous of any competing data, so let's just get that on the table now. Having said that, I intend to have very strong rationales, openly and objectively argued for my data.ARRRRRGH! I just spent two hours composing a reply, only to lose it all because of the forum's %&@#ing auto-log out!
What is the rationale for your SME's data about 7.62x54R? I'm skeptical that his BC is better than Sierra's, given that Sierra is actually tested, has a denser lead core that sheds velocity slower, and has a secant ogive. Got a link to his data?
I'm gonna go with 2550 fps for the 112gr 65G @ 0.523 BC (this is a conservative BC because that's the 2400 fps BC).
Okay, abbreviated version.
SME apparently does a lot of official government testing of military small arms ammo, and is held in high regard on Tony's MG&A forum.
Links to SME's 7.62x54R LPS data:
* BC http://forums.delphiforums.com/autogun/messages/?msg=5922.7
* MV http://forums.delphiforums.com/autogun/messages/?msg=5922.9
Did a lot of searching, but was unable to find any manufacturer listing of .311" bullet of required weight and shape. Closest fit is Nosler .308" 150gr E-Tip, a solid copper bullet (much closer in material density to steel-core LPS) with boattail and tangent ogive. BC = 0.469, so I still think 0.406 is reasonable for the LPS.
Am skeptical that BC of a 110-112gr, 6.5mm military ball projectile will get above 0.480 (if even that high), but I nevertheless look forward to seeing your ballistic comparison.
![[Image: nosler_etip_bb_580.jpg]](http://www.huntingtons.com/store/images/D/nosler_etip_bb_580.jpg)
New Army "Caliber Configuration Study" - BluntForceTrauma - 04-24-2014
Here are my charts for a 6.5 Grendel carbine with commercial off-the-shelf lead-free projectile versus a Russian 7.62x54R PKM machine gun, based on the following assumptions:
6.5 Grendel: 112gr GS Custom copper monolithic (0.523 BC) @ 2550 fps from 16" barrel.
PKM: 148gr 57-N-323S mild steel core (0.381 BC) @ 2725 fps from 25.4" barrel.
As with models for the global warming debate, one's models depend on one's assumptions and initial inputs, but I think mine are defensible. Data was generated using the online JBM Ballistics Calculator and charts were made after inputting the data into an Excel spreadsheet.
The news here is how well a 6.5 Grendel CARBINE stacks up against the threat medium machine gun.
While starting out slower, the 6.5 Grendel velocity starts beating the PKM after 300 yards. 6.5 Grendel hits harder at range, aiding penetration.
The 6.5 Grendel's trajectory drop is neck-and-neck with the PKM until it pulls ahead after 650 yards.
The 6.5 Grendel drifts less at all ranges in crosswinds; this is key for getting on target faster.
As is to be expected, 6.5 Grendel doesn't match or exceed the energy of the bigger cartridge until after 800 yards.
John
New Army "Caliber Configuration Study" - nincomp - 04-25-2014
HANKA Wrote:P.S. I'm going to compare it to a 7.62x54R round from a PKM 25.4" barrel, with a 148gr bullet at 2,717 fps with a 0.350 BC. I've guesstimated the BC, since internet sources vary so widely. Sierra bullets lists a BC of 0.397 for its .308 150gr FMJBT. If I'm being unfair to the Russian, speak now.
I tend to believe the fellow on the the MG&A forum. He has access to a range with doppler radar measuring equipment, and had been a missile designer. Ballistics is his job.
I eventually got the russian photo of the 7.62x54 LPS and the Sierra 150 FMJBT pretty much to scale (what a pain). As you would expect, the steel cored bullet is longer. You can see that the ogive on the LPS is longer and it has a longer boattail. This makes the form factor pretty much the same as the Sierra. This is what I meant in my earlier post.
I have heard that GS Custom's BC's tend to be optimistic. I find it odd that I never saw those bullets being used by long range competitors. Based upon the published BC's they would have been idiots not to.
[ATTACH=CONFIG]5081[/ATTACH]
New Army "Caliber Configuration Study" - Tony Williams - 04-25-2014
HANKA Wrote:I'm thinking if we have a Grendelized M855A1 that it would have a similar form factor to the GS Custom 6.5 112gr, perhaps a bit lighter if the steel core is less dense than copper.
Forgive me for being picky, John, but the Form Factor is unaffected by bullet weight or the density of the materials - it is only concerned with the shape. The weight of the bullet is taken into account in calculating the Sectional Density which is then multiplied by the FF to get the Ballistic Coefficient.
New Army "Caliber Configuration Study" - BluntForceTrauma - 04-25-2014
Tony, perhaps I wasn't clear, but what I meant is that I'd like to postulate a 6.5 M855A1, with its two-part copper and steel construction, that exactly matches the shape or form factor of the 6.5mm 112gr GS Custom monolithic in order to preserve that bullet's BC, as nearly as possible.
Photo concept attached.
Nincomp, thanks, valid points. The 7.62x54R BC of 0.381 I quoted is, supposedly, translated from Russian military manuals. I might add that it could simply be the GS Custom bullets are too pricey for competitors?
Anyway, as always, my main point is that these hypotheses look promising and I wish I had money to burn playing them out!
John
New Army "Caliber Configuration Study" - stanc - 04-25-2014
Nice work, John! The graphs illustrate the ballistics quite nicely.
But, since I think the GSC bullet gives an overly optimistic basis for comparison, I ran my own tables, using the 110gr Barnes brass solid (second from right, below) as a military ball surrogate.
![[Image: 04-1.jpg]](http://i583.photobucket.com/albums/ss273/Gunwritr/04-1.jpg)
6.5 Grendel LMG: 110gr Barnes banded solid (0.452 BC) @ 2550 fps from 16" barrel.
7.62x54R PKM: 148gr 57-N-323S mild steel core (0.406 BC) @ 2750 fps from 25.4" barrel.
Data was generated using the online JBM Ballistics Calculator.
_______ 65G _ 762 ____ 65G _____ 762 ____ 65G _____ 762 ___ 65G __ 762
Range _ Drop _ Drop _ Windage _ Windage _ Velocity _ Velocity _ Time _ Time
(yd) ___ (in) __ (in) ___ (in) _____ (in) ____ (ft/s) ___ (ft/s) ___ (s) ___ (s)
000 ____ 0.0 ___ 0.0 ___ 0.0 ____ 0.0 ____ 2550.0 __ 2750.0 __ 0.000 _ 0.000
100 ___ 48.4 __ 44.7 ___ 0.8 ____ 0.8 ____ 2356.8 __ 2525.8 __ 0.122 _ 0.114
200 ___ 90.5 __ 84.0 ___ 3.5 ____ 3.5 ____ 2172.0 __ 2312.4 __ 0.255 _ 0.238
300 __ 125.2 _ 116.7 ___ 8.1 ____ 8.2 ____ 1995.5 __ 2109.3 __ 0.399 _ 0.374
400 __ 151.1 _ 141.6 __ 15.1 ___ 15.3 ____ 1828.1 __ 1916.9 __ 0.556 _ 0.523
500 __ 166.6 _ 157.0 __ 24.6 ___ 25.0 ____ 1670.6 __ 1736.1 __ 0.728 _ 0.688
600 __ 169.7 _ 160.8 __ 37.0 ___ 37.8 ____ 1524.5 __ 1568.6 __ 0.916 _ 0.869
700 __ 157.7 _ 150.5 __ 52.5 ___ 54.0 ____ 1391.8 __ 1416.9 __ 1.122 _ 1.071
800 __ 127.8 _ 122.8 __ 71.5 ___ 74.0 ____ 1274.8 __ 1284.0 __ 1.347 _ 1.293
900 ___ 76.4 __ 74.0 __ 93.9 ___ 97.9 ____ 1176.0 __ 1173.5 __ 1.593 _ 1.538
1000 ___ 0.0 ___ 0.0 _ 119.8 __ 125.5 ____ 1097.3 __ 1087.7 __ 1.857 _ 1.804
Energy @ 1000 yards
65G: 294 ft-lbs
762: 389 ft-lbs
New Army "Caliber Configuration Study" - BluntForceTrauma - 04-25-2014
Thanks, Stan, for taking the time to generate the data points. So, worst case, our carbine is still almost going neck-and-neck with their MMG?
Something went awry at the 700-yard mark on your drop data?
John
New Army "Caliber Configuration Study" - stanc - 04-25-2014
HANKA Wrote:Thanks, Stan, for taking the time to generate the data points. So, worst case, our carbine is still almost going neck-and-neck with their MMG?Yeah. Much better than I expected. It looks to me like a 65G LMG would be quite capable of going up against a PKM, even without a super-streamlined bullet.
Quote:Something went awry at the 700-yard mark on your drop data?No, the numbers are correct. I guess I really should've changed the column heading from "Drop" to "Trajectory." I ran it using 1000 yards as the zeroing distance, in order to show the height above ground the bullets reach en route to 1000 yards.
New Army "Caliber Configuration Study" - stanc - 04-25-2014
Was curious what difference there'd be to use G7 instead of G1 BC's, so I re-ran the tables. Makes little difference in trajectory and wind drift, but definitely affects velocity.
6.5 Grendel LMG: 110gr Barnes banded solid (0.232 G7 BC) @ 2550 fps from 16" barrel.
7.62x54R PKM: 148gr 57-N-323S mild steel core (0.208 G7 BC) @ 2750 fps from 25.4" barrel.
Data was generated using the online JBM Ballistics Calculator. (Traj = Trajectory)
_______ 65G _ 762 ____ 65G _____ 762 ____ 65G _____ 762 ___ 65G __ 762
Range _ Traj __ Traj _ Windage _ Windage _ Velocity _ Velocity
(yd) ___ (in) __ (in) ___ (in) _____ (in) ____ (ft/s) ___ (ft/s)
000 ____ 0.0 ___ 0.0 ___ 0.0 ____ 0.0 ____ 2550.0 __ 2750.0
100 ___ 48.6 __ 44.9 ___ 0.8 ____ 0.8 ____ 2360.4 __ 2530.0
200 ___ 90.9 __ 84.3 ___ 3.4 ____ 3.4 ____ 2179.1 __ 2319.9
300 __ 125.9 _ 117.3 ___ 7.9 ____ 8.0 ____ 2006.4 __ 2120.5
400 __ 152.3 _ 142.5 __ 14.7 ___ 14.9 ____ 1841.0 __ 1931.2
500 __ 168.3 _ 158.3 __ 24.0 ___ 24.4 ____ 1682.3 __ 1750.6
600 __ 172.1 _ 162.8 __ 36.2 ___ 37.0 ____ 1529.6 __ 1577.8
700 __ 160.9 _ 153.2 __ 51.8 ___ 53.2 ____ 1383.4 __ 1412.7
800 __ 131.5 _ 126.1 __ 71.3 ___ 73.6 ____ 1244.8 __ 1256.8
900 ___ 79.6 __ 76.9 __ 95.4 ___ 99.0 ____ 1117.6 __ 1114.6
1000 ___ 0.0 ___ 0.0 _ 123.9 __ 129.2 ____ 1043.0 __ 1036.0
Energy @ 1000 yards
65G: 266 ft-lbs
762: 353 ft-lbs
New Army "Caliber Configuration Study" - Tony Williams - 04-25-2014
HANKA Wrote:Tony, perhaps I wasn't clear, but what I meant is that I'd like to postulate a 6.5 M855A1, with its two-part copper and steel construction, that exactly matches the shape or form factor of the 6.5mm 112gr GS Custom monolithic in order to preserve that bullet's BC, as nearly as possible.
Photo concept attached.
That bullet looks very good, John. It's simpler than the M855A1 because it doesn't include the half-jacket, but inserts the steel penetrator straight into the brass body. It looks like a half-way point between the bullets which ARDEC made for their calibre comparison tests a few years ago (which had a smaller steel element IIRC), and the RUAG HC bullets which are mostly steel penetrator with a smaller brass "shoe" around the base (see below). My only concern with these designs is the potential effect on the BC of the join between the steel and brass bits, and whether the steel tip is so easy to work to the optimum shape.
![[Image: RUAG%20HC.jpg]](http://www.quarry.nildram.co.uk/RUAG%20HC.jpg)
By the way, talking about efficient Russian designs take a look at the bullet from the experimental Russian 6 x 49 Unified round - it weighed only around 5g (77 grains) - shown here next to the 5.45 x 39:
![[Image: 6x49wa.jpg]](http://www.quarry.nildram.co.uk/6x49wa.jpg)
Finally, just to illustrate the issue over bullet length and form factor, here's a selection of 5.56mm military bullets: 55 grain M193, 62 grain M855, 62 grain M855A1, 77 grain MK262. You can see the length issue with the lead-free bullets, and the fact that despite its extra length, the MK262 FF is actually no better than the M855's - it improves in long-range performance only by being heavier.
![[Image: 556.JPG]](http://www.quarry.nildram.co.uk/556.JPG)
New Army "Caliber Configuration Study" - BluntForceTrauma - 04-25-2014
Those Russian bullets are creatures of ballistic beauty!
John
New Army "Caliber Configuration Study" - nincomp - 04-25-2014
Those clever Russians, they made the 6mm bullet with the rifling grooves already pressed in. I bet that makes it go even faster!
New Army "Caliber Configuration Study" - stanc - 04-25-2014
I always did like that 6x49 round.
New Army "Caliber Configuration Study" - BluntForceTrauma - 04-25-2014
I know you've long championed the 6mm SCC. And it is commendable that it is the one concept the Russians seemed most interested in as an alternative. What, if any, do you see as drawbacks to the concept as a replacement for both 5.56N and 7.62N?
John
New Army "Caliber Configuration Study" - stanc - 04-25-2014
If you mean my 6mm Optimum (below), one of the drawbacks that come to mind is the same as for 6.5 Grendel and 6.5 GPC: Increased weight and size relative to 5.56 NATO.
Another, perhaps more important issue, is that barrel life would likely be very low.
![[Image: Jul_31_001.jpg]](http://www.g2mil.com/Jul_31_001.jpg)