HK vs. AR Accuracy

[USMCsilver]

Just wondering what I should expect. I can almost pinhole 3 rounds at 30m from a 14.5" Bushmaster and was wondering if a HK93 will be as accurate (because one should arrive around noon today). I know that 30m is nothing, but that isn't a bad group when it looks like a ragged hole from .308 instead of 3 little holes from a .223.

I guess what I am really getting at is -- Will it group an inch at 100 yards?

 

[keens]

I don't know, but I am major jealous...Hope you enjoy the H&K...let us know how it shoots. Awesome weapon IMO...

 

[Tamara]

Never shot one for groups. I wouldn't expect AR-type accuracy (as you noted, commercial AR's are freaky accurate for service-type rifles) but it'll be no Kalashnikov, either.

 

[Adam Firestone]

I must respectfully disagree.

As with all rifles that use a rotary locking system, the AR-15 is going to have a measure of torque during operation that distorts the bolt/barrel interface during the moment of firing, thus inducing a measure of inherent, non-predictable, dispersion.

The same is true of the AK design, but magnified by the moving mass of the piston over the barrel which adversely affects barrel harmonics.

Conversely, the HK/CETME design moves straight to the rear with no torquing at all, and there is no moving mass above the barrel. The HK/CETME design is therefore capable of greater inherent accuracy than either the AR or the AK designs.

Of course, this is all academic; we're talking about differences notable only when the rifles are fired from a mechanical rest, not from a human whose heart is still beating and thus inducing unpredictable dispersion.

When built to the same standards, and in the same chambering, all are capable of similar real world performance. I'd stack a KTR-03V against an AR or an HK93 any day of the week.

 

[Handy]

As with all rifles that use a rotary locking system, the AR-15 is going to have a measure of torque during operation that distorts the bolt/barrel interface during the moment of firing, thus inducing a measure of inherent, non-predictable, dispersion.

This doesn't follow. The bolt is locked and static at the moment of firing, so torque is not a factor until extraction, when the bullet is beyond the muzzle. On the other hand, the HK rifle blowback operated, so it is essentially creating headspace while the bullet is still in the bore. This doesn't seem to be an issue, but is certainly more palpable than what the bolt on an AR does AFTER the bullet has left the muzzle.


HK roller rifles can be very accurate, but HK93s came in either 1:12 twist or 1:7, which will be a factor, depending on bullet weight. Chamber dimensions, barrel weight and a number of other pedistrian factors also weigh in. If you adapt to the HK concentric sight system, you'll be able to make the rifle perform. 55 gr. or less for the 1:12, 62 gr. for the 1:7.

At the 30m you asked about, I can't imagine any .223 rifle not putting them all in the same hole. 200 yards is a much better yardstick.

Enjoy.

 

[Adam Firestone]

This doesn't follow. The bolt is locked and static at the moment of firing, so torque is not a factor until extraction, when the bullet is beyond the muzzle. On the other hand, the HK rifle blowback operated, so it is essentially creating headspace while the bullet is still in the bore. This doesn't seem to be an issue, but is certainly more palpable than what the bolt on an AR does AFTER the bullet has left the muzzle.

No sir. The AR's BREECH is locked at the moment of firing. The bolt carrier is moving to the rear and the bolt turning prior to the bullet leaving the muzzle - this is where the torque comes into play. The breech hasn't unlocked because the bolt hasn't rotated far enough before the time the bullet exits the muzzle and the pressure drops.

While I don't think the HK/CETME system "creates" headspace (isn't that defined by the position of the moving parts when they are at rest in the "locked" - a tough word to use in a delayed blowback system - position?), I don't think that's germane.

The point is that the HK system moves straight to the rear, thus disturbing the barrel less than either the AR or the AK, and contributing to the HK/CETME systems greater potential accuracy.

But, as you pointed out, machts nichts. Any of them will shoot better than most mortals can.

 

[Lycanthrope]

Well..all I know is that it's expected for a good AR service rifle to print at least .5 MOA and many easily do better.

Torque or not, can the HK live up to it? I think that's the question.

 

[Master Blaster]

No sir. The AR's BREECH is locked at the moment of firing. The bolt carrier is moving to the rear and the bolt turning prior to the bullet leaving the muzzle - this is where the torque comes into play. The breech hasn't unlocked because the bolt hasn't rotated far enough before the time the bullet exits the muzzle and the pressure drops.

Sorry have to disagree with you here is why:

On an AR with a 20" barrel the gasblock is 6" from the end of the muzzle, the gas that moves the bolt carrier rearward enters the gas block and the gas tube via a hole in the barrel under the gas block. The gas does not enter the gas tube until the bullet has passed the hole in the barrel. The firing gas is traveling at the same speed as the bullet, so the bullet has 6" to travel at 3200 fps before it exits the muzzle. The gas at 3200 FPS has to travel 14" to reach the gas key and begin the carrier in its reaward movement. In other words the gas pulse is 8" from the carrier key when the bullet exits the muzzle.

I know I am ignoring the spring resistance, and the gradual rise in pressure that happens as soon as the gas from firing enters the gas tube. But the Bolt carrier does not begin to move until after the bullet exits the barrel. The AR was designed to work that way.

 

[Adam Firestone]

But the Bolt carrier does not begin to move until after the bullet exits the barrel. The AR was designed to work that way.

This CANNOT be true. The entire reason that there is a locking mechanism on ANY gun - be it a 1911A1 or an AR is to ensure that there is a delay in the opening of the bolt until the high pressure period has ended. If the bolt carrier didn't move until the bullet had exited the muzzle, no locking mechanism would be necessary. On the AR, the CARRIER begins to move, and the bolt begins to rotate prior to the bullet's exiting the barrel, but the BOLT does not begin to move to the rear until the bullet has exited the muzzle. Same principle applies to a 1911A1 - the slide and barrel begin to move to the rear upon firing, but the slide does not begin to move independently until the bullet has exited the muzzle.

PS - the gas in the tube is moving MUCH faster than the bullet in the barrel.

 

[keens]

This is making my head hurt, but it is interesting...

 

[Handy]

Adam,

MB and I know what we're saying, think about it. Unlike a 1911 (recoil) or an HK (blowback), gas rifles do not use the direct energy of firing to function. They use tapped off gas to perform the same funtion as a slide action shotgun: Unlock the bolt, then drive it back. (In fact, Brownings first autoloader was a modified pump action shotgun.) Until that gas can get there and works on the bolt carrier, nothing's moving.

As to the HK, I'm not referring to the bolt gap, which is what HK refers to in their manuals as "headspace". What I'm referring to is that the casing and bolt begin to move backward out of the chamber upon firing. The roller delay slows this "blow back", but the fact is that the case shoulder doesn't have a chamber shoulder to press against for most of the cycle - the case is busy pushing the bolt backwards. This would normally tear the cases apart, but the case is floating on an equalized jacket of gas due to the flutes. This is a controlled process, so reasonable accuracy is indeed possible, but it is not the same as the accuracy one might get if the gun allowed neck sized cases, for instance.

 

[Marko Kloos]

HK roller-lock rifles are generally more accurate than an AK, but not as accurate as an AR.

Consider that the vaunted PSG-1, the most accurate of the roller-delayed blowback HKs, is a sub-MOA rifle, but only barely. That's not bad for a semi...but not unattainable for an AR-15 at a tenth of the price.

 

[USMCsilver]

Wow -- I didn't realize that this would spark such a debate. It has been interesting, and a bit helpful, to say the least.

Anyhow, just picked her up and figured I'd share my new addition to the family:

 

[OBIWAN]

Very Nice

Did you get me one too???

Please.....

Damn......

 

[Handy]

That's a $150 or so HK53 flashhider you got on there.

 

[JohnKSa]

The gas is almost certainly moving faster than the bullet. The bullet is restricting the movement of the gases behind it. The gas moving down the gas tube is not restricted by the bullet and it could easily be moving faster than the bullet.

That said, it has a good bit farther to go than the bullet and the tube is small and has some bends which will slow it a bit. Besides, even when it gets where it's going, it doesn't IMMEDIATELY start unlocking the bolt, it has to move the carrier back a bit before the bolt begins to turn.

I agree with Handy that the bolt is not beginning to unlock before the bullet leaves the muzzle.

Consider that the vaunted PSG-1, the most accurate of the roller-delayed blowback HKs, is a sub-MOA rifle, but only barely.

Is that really true? I've seen some groups quoted at longer range that are well below half-MOA... Hearsay only, but from more than one source.

 

[USMCsilver]

Handy -- That's a $150 or so HK53 flashhider you got on there.

It isn't the 53 hider I don't think. I believe the 53 to be about 1-2" longer. However, I am pretty postive that the one I have is not too cheap.

Here's the 53 hider, I think...; BTW, that is NOT my rifle:

 

[Tamara]

JohnKSa,

Is that really true? I've seen some groups quoted at longer range that are well below half-MOA... Hearsay only, but from more than one source.

With my meager skillz, I never got measurably below 1 MOA with either of the PSG-1's I've had serious trigger time on with any factory load, including Federal Gold Medal Match.

 

[JohnKSa]

That's kind of sad...

You'd think for 10 grand they could make it shoot as well as a $65, hundred year old Swedish Mauser.

 

[Adam Firestone]

More on the technical later. . . but. . .

WRT the M96 Mauser. . . .remember, back then, they were made by craftsmen who cared. The time and effort and hand fitting that went into those rifles in the early 20th century would make them cost well into the four digit range today.