Reduced utility of .308 in shorter barrels?

[Tspeis]

While a few specific loads do fragment at higher velocities (generally above 2700 fps), the vast majority of 7.62x51 mm FMJ projectiles do NOT fragment at any normal velocities in barrels 26" and less.

Except for certain mission specific tasks, I prefer .308 rifles with 16-20" barrels--this offers excellent terminal performance with the common early upsetting 130-155 gr projectiles, as well as good accuracy with the 168 & 175 gr loads match loads. The recent KAC SR25 EM and LaRue OBR with 16" barrels are superb examples of this type of rifle.

Doc or anyone who might know more about the subject at hand,


Any idea what the terminal ballistics of the 165gr and 175gr loads mentioned would be like when fired from a 12.5" barrel? Do you have an estimated effective range on such a rifle/ammunition combo? I know it's a pretty broad question, just trying to get an idea here.

With this, the 12.5" HK417 and SCAR H CQC come to mind. The advertisd muzzle velocity for the 12.5" HK417 with 175gr M118LR is 709 m/s (2,326 fps). Would one be able to load such rounds to achieve higher velocity without overpressure issues or is that typically a no no?


Tspeis

[tkoglman]

Sorry for jumping in late on this one.

I have an HK51 with an 8.3" barrel. I did some un-scientific testing. I shot large 40 gallon water jugs with various rounds to see what would happen. XM193 55gr. 5.56mm rounds would penetrate, on average, 22" and reliably split into two fragments along the canneleure(sp?). 110gr. Hornady TAP .308 would penetrate 20" and completely fragment. I know that its not supposed to matter, but the 5.56mm rounds would cause just a tiny ripple on the water surface while the .308 rounds would actually explode the containers.

Recoil was light from the HK51. Muzzle flash at night with the TAP ammo wasn't bad at all with an HK flash hider. No more than an M14 shooting ball. Surplus ball ammo was a fireball.

[DocGKR]

"Any idea what the terminal ballistics of the 165gr and 175gr loads mentioned would be like when fired from a 12.5" barrel?"

Yes, some idea.

"Do you have an estimated effective range on such a rifle/ammunition combo? I know it's a pretty broad question, just trying to get an idea here."

It will likely have no fragmentation potential by 200 yards and just yaw over. In general, the 175 gr SMK has better terminal effects when impacting above 2500 fps. Below is a 175 gr SMK hitting at 400m when fired from a 24" M40A1:



The whole reason why loads such as the 155 gr TSWG OTM and 130 gr Mk319 Mod0 were developed is for use in shorter 12-16" barrel 7.62x51mm weapon systems--why would someone choose to use a 175 gr SMK in a .308 SBR when better options are available?

"With this, the 12.5" HK417 and SCAR H CQC come to mind. The advertised muzzle velocity for the 12.5" HK417 with 175gr M118LR is 709 m/s (2,326 fps). Would one be able to load such rounds to achieve higher velocity without overpressure issues or is that typically a no no?"

You would NOT likely be able to load to higher pressures and still have a durable weapon system, not to mention keeping propellant pressures within reasonable levels and stable at environmental extremes.

[rkba01]

Doc, do you have by any chance any data on the German 7.62x51 ammo?


This is all I could find:

Bullet design is AB22 whose terminal ballistic performance in tissue is unique from most other 7.62 NATO FMJBT Ball bullet designs. Rather than pitching up 90 degrees, then pitching backwards another 90 degrees and exiting backwards, AB22 pitches up 90 degrees then breaks into two parts at the cannelure, similar in performance to M193 5.56 NATO Ball.
Source: http://www.afte.org/forum/smf1/index...22903#msg22903

[Tspeis]

Yes, some idea.



It will likely have no fragmentation potential by 200 yards and just yaw over. In general, the 175 gr SMK has better terminal effects when impacting above 2500 fps.

The whole reason why loads such as the 155 gr TSWG OTM and 130 gr Mk319 Mod0 were developed is for use in shorter 12-16" barrel 7.62x51mm weapon systems--why would someone choose to use a 175 gr SMK in a .308 SBR when better options are available?



You would NOT likely be able to load to higher pressures and still have a durable weapon system, not to mention keeping propellant pressures within reasonable levels and stable at environmental extremes.

Doc,

Thanks for the info. Please check your PMs when you get a chance.


Tspeis

[DocGKR]

This might have some useful info: http://www.ar15.com/forums/topic.html?b=3&f=16&t=382340

[TiroFijo]

Wow! It seems not all steel jacket 7.62 NATO ammo is created equal... sadly the germans changed their bullets on purpose, to avoid fragmentation.

DocGKR, what is the reason the DAG ammo fragments at much lower velocities (=extended ranges)? Thinner jackect?

Have you tested this bullet?
What is the bullet weight and velocity (they should comply with the NATO standard)?
What is the performance of this DAG ammo against common intermediate barriers, compared to gilded metal clad bullets?

It seems that bullets like this present a very cheap and simple alternative to enhance terminal ballistics in this caliber, are there any downsides?

[SLAP]

Wow! It seems not all steel jacket 7.62 NATO ammo is created equal... sadly the germans changed their bullets on purpose, to avoid fragmentation.

[...]

Do you know this for sure?

[DocGKR]

Yes, as did several other European nations.

[SLAP]

Do you know when? A rough time frame would be fine.

Thanks

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Wounding patterns of military rifle bullets by Martin Fackler




I'm desperately trying to get my hands on the "Deutsches Waffenjournal" report.