7N6 Data Compilation (As compared to M855)

[win&legend]

Impiracle Accuracy Report

“Back when in SF I choreographed and thoroughly tested a new AK74 and Yugoslav 5.45x39 ammo out to 600 yards. The velocity for a 20 round string was 3090 fps. A base was made replacing the rear sight so a 2X Leopold scout scope could be mounted. It was tested alongside a M16A2 with a Colt 4X scope mounted on the carrying handle. M855 "green tip" ammunition was used in the M16A2.

We (4 shooters) found no trajectory difference between the 2 rounds out to 600 yards. the m16A2 was a little more accurate; 2 - 2.5 MOA vs. 3 - 3.5 moa for the AK74 but at 300 yards (we were on a standard known distance HP range) 100% hits on an E silhouette from prone supported was quite probable with either rifle/ammo. We put several hundred rounds through the AK between the 4 of us shooting and marking each hit at all ranges.

This is just FYI as I know you want more precise data on the trajectory. However, trajectory dat for the M855 round should be very close and at least a good place to start.

Larry Gibson “

5.45x39mm Ballistic Data
(Source: http://www.ada.ru/Guns/ballistic/545x39/index.htm)


Bullet weight - 3.42 grams
initial rate declared by the manufacturer - 870 m / sec
Ballistic Coefficient: 0.282
Height of sight above the barrel: 8 cm
An initial rate, measure chronograph, m / s
919 925 The minimum initial velocity of - 895 m / s
The maximum initial velocity of - 931 m / s
The average initial velocity of - 922 m / s
Average statistical deviation of - ±10 m / s
The maximum difference of velocities - 36 m / s
928 921
931 930
923 895
921 927

Relative reduction in the trajectory
The distance, meter 0 50 100 150 200 250 300 350 400 450 500
Weapon is sighted in at 100 m -4,0 -0,2 -3,6 -11,8 -25,2 -44,6 -71,0 -105,5 -149,6 -204,8
Weapon is sighted in at 200 m -4,0 2,7 5,9 5,2 -10,4 -26,8 -50,2 -81,8 -122,9 -175,2
Weapon is sighted in at 300 m -4,0 7,1 14,8 18,6 17,9 11,9 -18,9 -46,0 -82,6 -130,5


Deviation from crosswinds, cm
The distance, meter 0 50 100 150 200 250 300 350 400 450 500
The wind speed, 1 m / sec 0,00 0,18 0,75 1,75 3,22 5,21 7,77 10,98 14,90 19,60 25,15
The wind speed, 3 m / sec 0,00 0,55 2,26 5,26 9,66 15,62 23,32 32,94 44,69 58,80 75,46
The wind speed, 3 m / sec 0,00 0,92 3,77 8,76 16,10 26,04 38,86 54,90 74,49 98,00 125,77


Energy of bullets at a distance (Joules)
The distance, meter 0 50 100 150 200 250 300 350 400 450 500
Energy Joules 1295 1117 959 819 695 587 493 412 344 288 243
Energy ft-lbs 955 824 707 604 513 433 364 304 254 212 179


Caliber Comparison: energy of bullets at a distance (Joules)

Notes: 7N6 data copied from chart above (see Source for origins), not the original data set of “http://www.ada.ru/Guns/ballistic/545x39/compare.htm”, from which the chart below as originally taken. Consider the following:
7N6 has a BC of approx. 0.156 for G7 model calculated (Source: http://www.calguns.net/calgunforum/a.../t-175550.html). Projectile Weight: 52.9gr, Initial Velocity: 880 m/s (Source: http://www.google.com/search?q=5.45x...icrosoft:en-us)
M855 has a BC of .151 G7 (source: http://www.frfrogspad.com/bcdata.htm). Projectile Weight: 62 gr, Initial Velocity: 940 m/s (Source: http://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO)
Data in “http://www.ada.ru/Guns/ballistic/545x39/compare.htm” contradicts both slight efficiency advantage and expected similar ballistics considering near identical shape and velocity. 100-(.156/.151×100)≈3.3% efficieny advantage. This advantage suggests that over distance the energy carried by 7N6 will eventually overtake that of M855, however the advantage is relatively small. The following data set reasonably resembles the efficiency advantage and expected near identical ballistics. Here we see an approximate 3.3% efficiency advantage averaged over the distance, hence why 7N6 catches up at about 300meters in terms of conserved energy.


The distance, meter 0 50 100 150 200 250 300 350 400 450 500
7,62х39 2075 1786 1529 1303 1105 934 790 669 572 496 439
5,45х39 1295 1117 959 819 695 587 493 412 344 288 243
5.56x45 1607 1339 1108 910 741 598 478 380 303 245 205

Eng. Relative to 5.56 80.5% 83.4% 86.5% 90.0% 93.7 98.1% 103.1% 108.4% 113.5% 117.5% 118.5%


Note: 5.56x45: bullet weight 3.56 grams, 1006 m / s, 7.62x39: bullet weight 8 grams, 720 m / s
5 Speed of bullet at a distance


The distance, meter 0 50 100 150 200 250 300 350 400 450 500
Speed m / sec 870 808 749 692 637 586 537 491 448 410 377


7N6 Advantages/Equalities as Compared to M855:
Approximately 3.39 J of recoil energy allows for high follow up shot accuracy and controllable fully automatic fire as compared to that of M855 (6.44 J). (Source: http://en.wikipedia.org/wiki/5.45%C3%9739mm)
Low weight per round, allowing higher ammo capacity
Relatively flat trajectory, very similar to M855
While initial energy is lower, due to sligh efficiency advantage, retention of energy out to 300m yields energy levels near identicle for that of M855 round.
Relatively consistent yawing across all effective ranges

7N6 Disadvantages as Compared to M855:
Due to lack of fragmentation at common engagement ranges 150m to 100m or less, does not have as much wounding potential as M855 cartridge.
More limited availble types of loads to civilians (FMJ, HP, SP and V-Max Fragmenting round)
Slightly lower velocity produces a greater arc in trajectory as compared to M855

[Jonny Detroit]

Perhaps i missed it in all that data, but the cross section of the 5.45 seems slightly higher than that of the 5.56. Was it enough to impact the cross wind drift data?

[win&legend]

That may be a possibility, I didn't do a whole lot of research into that portion as my primary concern was energy delivered at the various ranges. There is so much opinion and conjecture out there on this round vs. NATO 5.56 its rediculous. Considering weight, shape and size are extremely close, I would expect similar energy to be delivered (how fast it is delivered can vary quite a bit between the two as M855 is a fragmenting round where 7N6 is a tumbling round), but total amount delivered should be close. M855 certainly has the energy advantage at closer ranges as its a little bit more powerful cartridge than 7N6, however at maximum range 7N6 delivers a bit more, however its performance may be superior at that range because it will still yaw and tumble where M855 will no longer fragment (requires 2700 fps or more to fragment).

This all assumes the data in the tables is a reasonably close approximation for 5.45/7N6. I have no way of validating that it is with absolute certainty. Some of the information for M855 (ballistic coefficient in particular) was taken from actual testing done at the aberdeen proving grounds, so I'm reasonably confident in its validity, but I have no gaurantee of the results in the chart either.

[Jonny Detroit]

Only one way to find out... wait for a windy day. Thanks for the math brother.

[20nickels]

If that's the Larry Gibson I know there is truly little he doesn't know about firearms.

[win&legend]

I don't know him, but what was said and the way it was described seemed very credible. I also found some more information regarding 5.45 accuracy. Much of the accuracy issues can be attributed to the sights (in particular the short sight radius). Nutnfancy (i have found quite a few threads of 5.45 and 7.62 users who had similar results) did a review on GI sights for an Arsenal SGL21 (7.62) and achieved about 1.5 MOA at 100 yards from the bench. Considering that 7.62 is typically not known for extremely high accuracy (although it is certainly good enough for its effective range and purpose), that is very impressive. I believe 5.45 should be capable of a little better or at least the same given the same opportunity. So its not far off from 5.56 (which contrary to common believe is about a 1 to 2 MOA cartridge given standard military cartridge and M4 rifle, certainly its capable of more with matched rounds and match grade barrels) and more than good enough to hit the intended targets within its effective range (more than 300m enough energy is lost that its effectiveness will likely become spotty, same with 5.56 as can be seen by the energy left after 300m in both rounds).

And that's all that should ever be asked of those rounds, those cartridges are intended for short and medium range applications, they are not high powered long range cartridges like 54R/30-06. I think that its rediculous when people compare them to higher calibers because that was never the intention. I really wish I could see some official testing comparing the two with a full data set for each, energy, velocity, drop for all current 5.45 and 5.56 cartridges.

[Jonny Detroit]

Odd that they are often boat tailed.

[Cy4ka]

I'm going to shoot ballistic gel blocks with 5.45 7n6 and 5.56 to compare this summer but I don't know what grain to use for the 5.56, I'm thinking 62gr M855. What do you think?

[Jonny Detroit]

That would be the natural choice i think.

[irierider]

great stuff, some is over my head!!

[win&legend]

I second the choice for 62gr. You could also try 77gr (not sure what the designation was, but there's a 77gr mil. round), I've come across 5.56 advocates who seem to think that round produces "miraculous" results. It would be interesting to see how those two perform comparatively at 100m and 300m ranges.

Also, it should be noted that most russian military 5.45 cartridges have a much stronger emphasis on penetrating armor than 5.56 US military cartridges. M193, M855, MK262 were all designed designed for use on unarmored or light armored targets, where if you look at russian military 5.45, almost all of russia's current cartridges are armor piercing to some degree. They are designed to take out soldiers wearing body armor where most 5.56 cartridges are not (I do not believe we have ever been in a major war where we having to fight soldiers wearing armor was a common occurance, correct me if I'm wrong, starting at WWII, Korean War, Vietnam, 1st Gold War, 2nd Gold War/Iraque War).

The 7N6 bullet has a 1.43 g (22.1 gr) steel rod penetrator. Since 1987 this penetrator is hardened to 60 HRC. The latter 7N6 cartridge can penetrate a 6 mm thick St3 steel plate at 300 m and 6Zh85T body armour at 80 m. 7N6 bullets have a red identification ring above the cartridge neck.

The 7N10 "improved penetration" cartridge was introduced in 1992. The size of the steel penetrator was increased to 1.76 g (27.2 gr) and the lead plug in front of it was discarded. In 1994 the 7N10 design was improved by filling the air space with lead. Upon impacting a hard target, soft lead is pressed sideways by the steel penetrator, tearing the jacket. The 7N10 cartridge replaced the previous variants as standard Russian service round and can penetrate a 16 mm thick St3 steel plate at 300 m and 6Zh85T body armour at 200 m. 7N10 bullets have a violet/purple identification ring above the cartridge neck.

The 7N22 armour-piercing bullet, introduced in 1998, has a 1.75 g (27.0 gr) sharp-pointed steel penetrator and retains the soft lead plug in the nose for jacket discarding. 7N22 bullets can be identified by their red identification ring above the cartridge neck and a black tip.[6]

The recent 7N24 "super-armor-piercing" cartridge has a penetrator made of tungsten carbide. The 7N24 round is loaded with a a 4.15 g (64.0 gr) projectile containing a 2.1 g (32.4 gr) penetrator which is fired with a muzzle velocity of 840 m/s (2,756 ft/s) yielding 1,464 J (1,080 ft·lbf) muzzle energy.

Considering most of these rounds were developed during cold ware or slightly post cold war, I think the US soldier or soldiers of other developed countrys were the traget they were most concerned with. It seems to me they were willing to trade off some soft tissue damage for the ability to inflict soft tissue damage when having to shoot through armor. If that was not the case, they would be using soft points, hollow points (available from silver bear, wolf and Tula) or a fragmenting round to inflict much greater soft tissue damage like M855. Some seem to think Russia misunderstood the M193 and M855 wouding affects for being the result of tumbling. Considering those wounds look quite different and it would not be too difficult for them to have shot a target with M193 and found that he round fragmented, I highly doubt that is the case. They chose consistency and penetration over high damage at close range but moderate damage at long range. Different methodology is all, I don't think one is always better than the other, both have their merits.

I've seen a few posts of large white tailed deer (one was a 10-point 200lb buck, single shot to the chest with 7N6, ran 80 feet and dropped dead, another was an 8-point buck shot with 55gr silver bear Hollow Point, single shot to the chest, droped dead on the spot, guy said when cleaning it there were only a few small pieces of heart and lung left in tack, everything elses was soup). Deer are much more resilliant to fire arms than humans (I can't count how many videos I've seen of deer being shot and then running for miles before dropping, even with large caliber like 30-06, youtube has one being shot with .50 cal, still ran couple hundred feet before dropping!), so if it works that good on them, I'd say it works on the other.

Since however, 7N6 does not fragment, shot placement is MORE critical where M855 it is not AS critical within its fragmentation range because of the amount of soft tissue damage. Outside of its fragmentation range shot placement is just as critical as 7N6, if not more so because although M855 will yaw like 7N6 when it doesn't fragment, its a shorter bullet compared to 7N6, which is very long, so tumbling produces more damage than M855 in that respect.

Here is what brassfechter says about 5.45 in their testing: "The 5.45x39mm cartridge is ballistically similar to the .223 Remington. Mainly found chambered in AK74 rifles, we highly recommend this cartridge and weapon for self-defense use. Both expanding and FMJ ammunition is available for this cartridge and the expanding and military surplus FMJs can be counted upon to disable a target given adequate shot placement."

Here is what they said about 5.56, both M193 and M855: "Seeing service in Vietnam and up to the present day, the 5.56x45mm cartridge is popular both with world militaries and sportsman worldwide. Even with FMJ ammunition, a rifle firing the 5.56x45mm cartridge is able to defeat soft body armor and incapacitate the target behind it."

I'm not seeing much of a difference, are you? Seems to me that either round is relatively similar with slight variances between the two which are attributed to their intended role. I think as far as Assault Rifle class cartridges go, either 5.56 or 5.45 are about on par. What's far more important is choosing the proper load for the application and having the training to affectively utilize the capabilities of the cartridge/rifle. For 5.45 there are available Soft Point, Expanding Hollow Point, Rapid Fragmentation (Hornady's V-max is for small game as its fragmentation is at a much shallower depth than M855) and FMJ. I'm not aware of many other types except match grade for target shooting. So my conclusion based on this data, personal recomendations of those who are actually in the military and used 5.45 in combat (US army national guard in this case) and the various examples I think 5.45 just as effective as 5.56. So go with whats best for you based on cost, availability any other relevant criteria.

[maxxmojo]

Right on thanks for posting all this, I've been looking for hard number comparisons between the two for a while. There just doesn't seem to be alot of info out there on 7N6.

Originally Posted by Cy4ka

I'm going to shoot ballistic gel blocks with 5.45 7n6 and 5.56 to compare this summer but I don't know what grain to use for the 5.56, I'm thinking 62gr M855. What do you think?

I'd think the 62gr M855 would better match the ballistics for a comparison to 7N6, but it may be interesting to see how 55gr M193 performs as well. Hell if you can, shoot all three.

[concha]

I'm not understanding the reference to shot placement being MORE important with 7N6.

5.56/.223 ammo was designed to fragment but as I understand it has suffered with ever-shrinking barrel lengths that have negatively impacted velocities and thus the ranges at which the bullets will fragment.

7N6 was designed to tumble/yaw. I understand that it will do so after only about 3 inches after impact and over a much wider distance range than 5.56/.223 will fragment. So with 7N6 you get a longer bullet that tumbles almost immediately and creates long, veering wound paths. Is that that less effective/desirable than a bullet that will fragment over only a limited range?

[Jonny Detroit]

In optimum range the 5.56 fragmenting rounds create so much soft tissue damage that it is almost irrelevant where the bullet lands. The end result will be incapacitation or death. Where as the 7n6 round would have to tumble through something important.

[allesennogwat]

The Germans first designed armor piercing bullets with lead in front of the hardened steel core in WWI. The purpose of the lead tip is to prevent the bullet and its core from glancing off at an angle to the armor. The soft lead is suppose to deform upon impact, holding the steel core with its point pointing into the armor for best penetration. It's not so much about peeling the bullet jacket away as it is to keep the bullet core pointed towards the target as it impacts.

[concha]

Originally Posted by Jonny Detroit

In optimum range the 5.56 fragmenting rounds create so much soft tissue damage that it is almost irrelevant where the bullet lands. The end result will be incapacitation or death. Where as the 7n6 round would have to tumble through something important.

Someone mentioned earlier that M855 needs at least 2700 fps in order to fragment. The ballistics charts I'm seeing show that beyond 100 yards, you are beginning to drop below that velocity. And the tables I saw were for a 20" barrel whereas most ARs are 16", thus losing somewhere in the range of 100-200 fps.

Seems that the advantage for the AR platform are close range fragmentation, slightly better accuracy and lighter weight.

For the 74, you get less recoil (and thus better target reacquisition), better effectiveness of the bullet's designed purpose (yaw/tumble) over a far wider range and greater reliability/ruggedness.

[win&legend]

I would agree that M855 is more effective at close ranges (100m or less for standard M4) with POOR shot placement compared to 7N6 because it does create a very large wound channel. However at ranges beyond its fragmentation (80 to 100 ish meters for 14.5" barrel, 100 to 150 meters for 16" and 20" barrels respectively) its damage is inferior because of the bullets length, it will tumble and yaw similar to 7N6, but its consistancy to do so is less and its a much shorter round. The physical projectile is quite short compared to 7N6. Shot placement with 7N6 is more critical, but I would definately not say that you have to hit a vital organ (heart, lungs or head) to incapacitate. 7N6 striking any bone is going to shatter that bone and tear up tissue reasonably.

On the other hand M855 suffers from light barrier penetration issues, because of its high volatility for fragmentation, at close ranges shooting through hard light barriers, such as automotive glass, most of the round fragments as it strikes the glass.

One of my good friends from high school was army nation guard and went to Iraq for 1 year. He told me that when they had to shoot through automotive glass that they would typically have to hit their targets 4, 5 or 6 times because the M855 rounds were fragmenting before reaching the target. He also said that he and some others from his group had eventually acquired some AK105 series chambered in 5.45 and took with them on some missions. He told me that the 7N6 would typcially incapacitate or eliminate the intended target in 1 or 2 shots at all effective ranges and when shooting through light barriers such as automotive glass (because the round did not fragment).

Its give and take, one is not necessarily always better than the other. Also I am quite sure the russians could have designed a fragmenting round if that was their intention, Hornady did with 5.45 V-maxx, so 5.45 fragmenting rounds are quite possible. I believe they chose to design a longer tumbler instead of a short fragmenter because it was more consistent and had better hard light barrier penetration capabilities. Its simply a different design methodology with different goals. Also a non fragmenting FMJ is more likely to pass through one target and strike another, Russia's military doctive has been everything in excess, a hale of bullets if you will. I do think they recognized the necessity for accurate aimed fire in some cases as well though, the 5.45 is remarkably similar to 5.56 in a lot of cases. I think we can conclude that both 5.56 and 5.45 are equally effective with respect to their intended uses. Neither round is large enough in physical size to mitigate the necessity for proper shot placement in many cases. Also I came across some really good and hard to find data. Here is the updated ballistic coefficent table below as developed by the US army in their testing.

BRL Test Data Table
(Source: http://forums.delphiforums.com/n/mb/...-42&msg=4639.1)

The lower the form factor number, the more aerodynamic the shape with lower drag coefficient.

Dia. Wt. G7 FF G7 BC
5.45x39mm Soviet .220 53.5gr .929 .168
5.56x45mm M193 .224 55gr 1.308 .120
5.56x45mm M855 .224 62gr 1.172 .151
5.56x45mm Mk262 .224 77gr 1.177 .186
5.56mm BRL-1 .224 66gr .858 .219
5.56mm AR-2 FABRL .224 37gr .845 .126
6.5mm Norma BT match .264 139gr .922 .309
6.5mm Lapua Scenar** .264 123gr .950 .265
6.8mm Hornady Vmax* .277 110gr 1.107 .185
6.8mm Sierra MK* .277 115gr 1.338 .160
7.62mm NATO M80 .308 147gr 1.105 .200
7.62mm M852 HPBT .308 168gr 1.177 .215
7.62mm M118 Match .308 173gr 1.096 .239
7.62x39mm M43 .311 123gr 1.165 .156
7.92x57mm sS* .323 198gr .965 .281
7.92x57mm sS* .323 198gr .906 .299
.338 Lapua FMJ LB* .338 250gr 1.000 .313
.338 Lapua Scenar* .338 250gr .926 .338
12.7mm M33 ball .510 650gr 1.050 .340
All data taken from US Army BRL tests except for those with asterisks.
* Data with asterisks was calculated from advertised BCs or info from internet sources. There were two sources for 7.92x57mm sS data.
** Data from Bryan Litz

Also, I doubt most people being shot anywhere in the torso, arm or leg are going to be terribly able to fight. The amount of pain alone will likely incapacitate, let alone the physical damage that may inhibit functionality and both rounds are more than adequite for what most of us will use them for, target rifles, hunting and home defense. So I would suggest based on all of this information that you choose whatever suits you budget and preference best. Some have other 5.56 rifles so that may be a better choice and cost per round is not as much of an issue while others may have other 5.45 rifles or cost/authenticity is more relevant. Performance wise I don't think one is better or worse. FMJ non-fragmenting, Hollow Points, Soft Points and Fragmenting rounds are available to both calibers. Tula, wolf and silver bear each make one or more of the above types mentioned and are reasonably widely available. So i'd choose based on those criteria.

[bryjcom]

I think we are comparing apples to oranges here. The 7n6 was tested in a 16" barrel and the M855 was tested in a 20" barrel.

I think the 7n6 is a better round when matched up against a similar barrel.

tested a new AK74 and Yugoslav 5.45x39 ammo out to 600 yards. The velocity for a 20 round string was 3090 fps. A base was made replacing the rear sight so a 2X Leopold scout scope could be mounted. It was tested alongside a M16A2 with a Colt 4X scope mounted on the carrying handle. M855 "green tip" ammunition was used in the M16A2.

[allesennogwat]

Even with tumble and yaw, the wounds created by non-fragmenting .22 caliber rifle bullets are about equal to handgun bullet wounds. A .22 caliber rifle bullet has to fragment to make any sizable wound. Boat tail 7.62x39 bullets aren't much better. Flat base 7.62 bullets do benefit from tumble and yaw without fragmentation. Flat base .22 caliber rifle bullets would still have to fragment to improve the wounding though. German 7.62 NATO bullets tend to fragment while American-made 7.62 NATO bullets do not fragment well.

[win&legend]

Hence the reason I believe shot placement is critical with any 7.62 battle rifle cartridge or 5.56/5.45 assault rifle cartridge that is a FMJ type. A shot to a vital organ (head, heart or lungs) will incapacitate or eliminate any target with the first shot. Also shot placement is even more critical when having to use AP rounds against armored targets because the penetrator is much small diameter (also very hard and does not deform or expand) than the initial projectile. Thus once the penetrator punches through the armor, its the only portion left to strike the target behind. But even a smal diameter penetrator to the heart, heat or lungs will incapacitate or eliminate a target consistently.

The type of load is also very important. 5.56/5.45 Hollow Points do plenty of damage as evidenced by the following: http://www.ar15.com/archive/topic.html?b=1&f=5&t=792333. In my experience deer can take a lot more physical punishment and keep going compared to a human, google deer shot by .50 cal, the thing still ran a good 100 yards before dying even with a .50 cal! That 5.45 HP round dropped that 8-point buck on the spot and it was reported upon cleaning the deer that the there were only a few small pieces of heart and lung left, everything else was destroyed.

[Scott7891]

I can't believe no one has pointed it out yet but Yugoslavia never manufactured or issued 5.45 ammo. They made 5.56 for export but no 5.45.

[win&legend]

Originally Posted by bryjcom

I think we are comparing apples to oranges here. The 7n6 was tested in a 16" barrel and the M855 was tested in a 20" barrel.

I think the 7n6 is a better round when matched up against a similar barrel.

There's another post I made just a while ago about 5.45 performance, Deuce45s is a site for a company that develops loads for military and law enforcement use. They did quite extensive testing on 5.45 and 5.56. Both were testing with 16" barrels, 5.45 was tested using Russian 7N6 in an Arsenal SGL31 and 5.56 was tested using issue M855 cartridges in an M4 with the 16" barrel (I don't recall the mfg). The muzzle velocity in the M4 using the M855 catridge was 2750 fps average where the muzzle velocity of 7N6 was 3060 fps average. Considering that both cartridges are nearly identicle, I believe a big part of why 5.56 does not perform as well as expected in M4's is not just due to the shorter barre, but rather the design of the fire arm. 5.45 is a lower energy cartridge, by about 20~25%, and its specified muzzle velocity (2900 fps) is about 200 fps lower than 5.56 (3100 fps). However those are for the cartridges under ideal conditions. The AR platform uses a direct gas piston for operation, this piston is fed as the round is initially being accelerated down the barrel, so a substantial portion of the pressure generated is diverted to driving the piston almost immediately. With a Kalashnikov type gas piston, the round is at the end of the barrel and chamber pressure is much lower before the piston is driven back, thus more of the energy from the cartridge goes directly to accelerating the projectile and for a much longer period of time before it is diverted to cycling the bolt. I would expect an AK chambered in 5.56 to perform at higher velocities than an M4 (of equal length barrels) chambered in 5.56 if this is indeed the case (i'm not an AR expert, but I believe that is how the system functions).

So, in conclusion the 5.45 round doesn't need to be as high energy as 5.56 to achieve the same results, thus it has additional attributes such as substantially reduced recoil and cost with the same performance. Its not so much the cartridge, but the platform's more effective use of the cartridges available energy. Same thing applies to cars, you could have a 300 HP turbo 4 cyl that outperforms a 550 HP high compression V8 if the car the V8 is in has poor gearing ratios that do not utilize its energy output effectively or if the car the V8 is in weighs proportionally more than the car the turbo 4 is in.

[bryjcom]

Originally Posted by win&legend

There's another post I made just a while ago about 5.45 performance, Deuce45s is a site for a company that develops loads for military and law enforcement use. They did quite extensive testing on 5.45 and 5.56. Both were testing with 16" barrels, 5.45 was tested using Russian 7N6 in an Arsenal SGL31 and 5.56 was tested using issue M855 cartridges in an M4 with the 16" barrel (I don't recall the mfg). The muzzle velocity in the M4 using the M855 catridge was 2750 fps average where the muzzle velocity of 7N6 was 3060 fps average. Considering that both cartridges are nearly identicle, I believe a big part of why 5.56 does not perform as well as expected in M4's is not just due to the shorter barre, but rather the design of the fire arm. 5.45 is a lower energy cartridge, by about 20~25%, and its specified muzzle velocity (2900 fps) is about 200 fps lower than 5.56 (3100 fps). However those are for the cartridges under ideal conditions. The AR platform uses a direct gas piston for operation, this piston is fed as the round is initially being accelerated down the barrel, so a substantial portion of the pressure generated is diverted to driving the piston almost immediately. With a Kalashnikov type gas piston, the round is at the end of the barrel and chamber pressure is much lower before the piston is driven back, thus more of the energy from the cartridge goes directly to accelerating the projectile and for a much longer period of time before it is diverted to cycling the bolt. I would expect an AK chambered in 5.56 to perform at higher velocities than an M4 (of equal length barrels) chambered in 5.56 if this is indeed the case (i'm not an AR expert, but I believe that is how the system functions).

So, in conclusion the 5.45 round doesn't need to be as high energy as 5.56 to achieve the same results, thus it has additional attributes such as substantially reduced recoil and cost with the same performance. Its not so much the cartridge, but the platform's more effective use of the cartridges available energy. Same thing applies to cars, you could have a 300 HP turbo 4 cyl that outperforms a 550 HP high compression V8 if the car the V8 is in has poor gearing ratios that do not utilize its energy output effectively or if the car the V8 is in weighs proportionally more than the car the turbo 4 is in.

The AR system uses a direct impingment system. There is no piston.

The only thing that the AR moves during firing is the bolt carrier and spring which are light when compared to the massive bolt carrier/piston of the AK74. Therefore you could make the conclusion that the AK needs to divert more gases to operate the action, not the AR.

Also, the AKs tend to be over gassed to begin with, which would mean you would loose even more velocity. The AK gas system is also VERY sloppy with lots of gaps, air leaks etc, which would lend itself to the conclusion that you would need to divert even more gases to operate the action. The AR system is nice and tight with a small little tube coming off of the gas block and going directly into the bolt carrier..

Further more the AR and the AK have the gas ports relatively in the same position. In other words I don't believe the bullet location in the barrel and when they start to gas the action really matters.

In conclusion I don't believe the gas operated guns really divert all that much pressure to the system enough to really affect velocity. I had heard internet rumor that with the M14 system there is practically NO loss of velocity over a bolt gun.

Basically what I'm saying is the 5.45russian is a quicker round than the 5.56, when compared with equal barrel lengths.