Over at the firearmblog there is a link to some pics of some Australian guys practicing before deployment. At least one of them has a 12" hk417. His buddies has what seem to be different 5.56 ar's with M4 length barrels.

Both the scar and the 417 come with barrels that are shorter than an m4 barrel. Could anyone please explain to me what the advantages of this is when there are lighter and lower recoiling 5.56 rifles availible? It's obviously worth the recoil and blast to the guys using them, but why?

The same rifle with same length barrel has less range and penetration.

Both .7.62 and 5.56 were designed for 18 +/- barrels, and tend to lose a decent amount of energy with shorter barrels.

Still, a 12 inch 7.62 is going to have more horsepower than a 14 inch AR, and depending on what one is shooting at/what range, more penetration.

I believe the ballistic solution for 7.62 is 16-18 inches and 5.56 18-20 inches (meaning the powder is almost completely consumed getting 95+ % most out of the round).

Your mileage and beliefs may vary.

The 6.8 SPC and .300 were designed to be more efficient in shorter barrels (but they do benefit from longer tubes too).

My 16" AR has at most 1200ft lbs at the muzzle. My 16" Scar 17 has right about 2400+ so twice the muzzle energy with the same length barrel.

My 14.5 AR tops out under 1100 ft lbs and I haven't chronied my 17 with a 14 inch barrel but I feel its safe to say it has about twice the energy again.

Take that out to 300 yards and a 75g TAP has 630lbs left and a 155g Amax has 1330lbs left.

.308 over better short barrel cals because of logistics I guess lol

Do you really believe that everyone in the military knows about guns and ballistics?

It's  likely that the guy picked it because the cartridge is bigger, or he likes the balance or ergonomics or just to be different or whatever.

The next time I see a Green Beret talking about racking the slide on a 12GA for HD, Im going to get it on video, and make ARF heads explode.

by the same aspect, aren't they just issued a weapon... not really a lot of choice in the matter. and for high speed low drag types who do have multiple weapons, mission directives will state which member carries what.

or at least that has always been my understanding. I'm just a joe nobody though.

For the Aussies, I couldn't tell you. In the US mil, it depends on how "special" you are. If you have rank, a position of authority, or are in a "special unit" odds are pretty good you have more flexibility in selecting your weapon, and gear than the average E-3 11B. As a trend, the US mil is getting more lenient on allowing some shooter preference.

My DSA OSW (10 inch FAL) is 2 ft long and has 30 rounds of 308.

That will get me out to 500 m easy and it will cut through brush much better than any 223 which will fragment once it hits a small branch. I have seen 223 key hole after going through one dry wall. The second dry wall about 6 inches apart had a key hole.

223 is effective when it hits something directly. If it hits something first it fragments or tumbles.

The Army is? I was in Afghanistan in 2013 and you weren't allowed to change anything on your weapon. The only guys that could use other weapons or make any mods were SOF. Where did you get that information? Are you in the military or are you just talking out your a$$?

LOL

So YOUR unit didn't allow any changes, so it MUST be that way for EVERYONE but SOF right?

When I was in Afghanistan, plenty of Company Commanders allowed lots of shooter preferences including optics, mags, grips, furniture, ect. Not to mention, that now most units allow Soldiers to arrange their gear however they want. Not that long ago, everyone was told exactly where and how everything would be carried.

In addition to SOF doing pretty much whatever they want, Generals, and their PSD carry whatever they want, by regulation.

So you've been on the site for over a year, and don't know how to tell site verified .mil? Maybe you just aren't that observant, and that's why/how you missed the glaring amount of non standardized weapons in the modern Army.

Was there when 173rd, 10MD and 3ID were there. Worked with 6-8 Cav and group on occasion. They were not allowed to change their weapons configurations except maybe group. Mostly was M4 with Aimpoint or ACOG, PEQ15, surefire on Knights RAS. Maybe some commanders allowed it but its rare. The Army is getting more restrictive not less. Compare Viet Nam with todays army and you're going to tell me the army is getting less restrictive? Even group had pretty standard M4s. Maybe Specter optics or 10 inch barrel. Hell... I have better weapons at home than 90% of our soldiers had including group. In 2010 to 2013 everything got more restrictive including ROE.

I'm not comparing it to Vietnam, WWII, or the revolution when you brought your own guns. Im comparing it to pre-GWOT.

Now that the number of troops deployed is getting smaller, everything is trying to go back to the way it was. Still it is FAR less restrictive than it was 15 years ago. If you weren't in prior to, or at the beginning of the war, you wouldn't be able to appreciate how much better it is now. I agree that we could have more options, but all that stuff costs money, and requires training for proper employment. I doubt that will continue to improve now that the budgets are all getting cut, and the garrison derp is back.

I've worked with 6 different Brigade units closely in 3 deployments. All of them had infantry or Scout units that were given non standard weapons, or were allowed to make modifications. All SF, SOF and PSD had whatever they wanted. A lot of them choose to carry close to standard configuration M4's.

At the beginning (12 years ago) I'm sure the rules might have been overlooked. As we draw down things are getting more garrison like. I know at least one guy that took his own weapon but it looked like a standard M4. I carried an M4 and M9. Wish I could have taken my Sig 516 with suppressor and Glock17. Or my Para FAL or a SCAR. I did get to handle and shoot the G36, Sig550 and CZ Bren 805 (Czech soldiers weapons). Would take a SCAR or M4 over them.

I always wondered about the effectiveness of the short 762x51's as well.  I stamped my SCAR 17 and have both a 13" and 16" barrel.  I generally keep the 16" on the rifle.  The 13" while cool-guy approved seems like it would end up about as effective as 762x39 but bulkier and heavier.  I have no idea how the ballistics are by the numbers.  If guess between 1800 - 2100 ft/lbs range in energy.

Pretty sure about anything out of a 13 inch barrel is still over 2000ft lbs and the 130g load made specifically for the short barrel scar is supposed to be around 2750 fps and almost 2200 ft lbs.

oh easy, Mk319 130gr OTM =2700fps from 13" barrel, that's why

If you slap a supressor on a 12" barrel, won't that have similar ballostics to a 16-18" barrel? (Although the actual length would likely be as much as 20"). I used to think suppressors slowed down the bullet, but that was from reading about older barrels that bled gas to slow hypersonic ammo to subsonic speeds. Now I am under the impression that the bullet will remain pressurized in front of burning powder longer, which should give it better ballistics than without a supressor. (Consider that each baffle may only slow about 15% of the gasses per inch).

Anyways, regardless of ballistics, if one were to shoot supressed .308, then you probably wouldn't want An 18" barrel in the field, because the suppressor would make it as much as 26" long, and heavy. So shorter barrels seem like they have their place, albeit for special purposes.

I wouldn't think the .308 with a short barrel would be a good choice for house clearing, due to the recoil. A 5.56 would certainly be lethal enough at that range, be lighter, faster to point, and could carry more ammo too.

These weapons (417 and scar heavy) are favored in SOF units in the sniper/DDM role. The shorter ones excel at this role in engagements in urban/built up areas where engagement ranges are generally shorter. Since they are more compact, they are more user-friendly as far as keeping the overall length to a minimum- this becomes especially apparent when a suppressor is attached, or when conducting activities like parachuting, fast roping, or engaging targets from platforms like boats or helicopters. The 7.62 round is far superior to any 5.56 round in terminal performance and flight characteristics in windy conditions, and especially in scenarios where a shot must be taken through a glass barrier- a frequent situation when operating in urban environments, whether it be auto glass or windows in a structure.

So he can have a cool looking, expensive ak47 equivalent?

To be able to put a can on it and have it be not so damn long.

Mk319 laughs at you

I'm building a 14.5" 308 AR FWIW

Please texas tony stop spreading the lie about 308. 308 losses about 25 fps per inch. Not a big deal.