6.8 SPC AR-15 muzzle flash and barrel lengths.


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Hammerhead6814
November 12, 2010, 12:11 AM
I'm building an AR, 6.8 SPC and gas piston system. I'm going all out.

One thing that's bothering me though is what I'm seeing on youtube. Out of a 16 inch barrel it looks like 6.8 AR's turn in flamethrowers.

To the point, what barrel length and flash hider will do away with this? As I said I'm going all out, money isn't an issue.

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longdayjake
November 12, 2010, 10:35 AM
A lot of it is powder choice. Some powders will burn too slow through the barrel and only ignite once the bullet has left the barrel. Usually flames can be cut down simply by using a faster powder or maybe just a powder that isn't prone to large flashes. All flash hiders are going to be pretty similar in how well they hide the flash.

If you want to make sure all the powder gets burned inside the barrel then go with a longer barrel. However, the 6.8 crowd usually points to the fact that 6.8 is better out of shorter barrels than the 6.5 grendel. If you are going to go with a really long barrel you might as well go with the 6.5 because it will give you as much and more than a 6.8 with a long barrel.

It looks as though 18" barrels are becoming popular among the 6.8 crowd. I don't know why but it seems to be the case. If I was buying a fighting gun I would buy a 16" 6.8. If I was buying a long barrel accuracy tuned rifle I would buy a 6.5. In fact, that is what I did. I own a 6.5 and a 6.8 for those purposes. What is your main purpose for the gun?

Tirod
November 12, 2010, 12:52 PM
Even the 5.56 from a 14.5" requires a flash hider. What wasn't said was whether they were removed for the video. It makes a nice Hollywood statement on video to screw off flash hiders and let the flames roar.

There are also a lot of vids on youtube that show exactly which flash hiders do a decent job of completely eliminating flash. There are quite a few on the market now, and plenty of compensators that do it well, too. For a 6.8, you will need the larger .308 versions, as the 5.56 won't let the bullet pass thru. Most of them come with the larger thread.

Barrel length should be optimized for the use, not vice versa. It doesnt really say much to repeat it's an all out gun. That's more chest thumping about a credit card limit than defining how it will be used. The 6.8 was specifically designed for assault rifle use from a 14.5" barrel out to 450m. 16" is the actually the most common barrel, with midlength gas. Some are making 18" to emulate the Squad Designated Marksman, it really doesn't add much for the two inches, just a few dozen more feet per second in speed. Using different ammo will do that, but it still doesn't say what the target will be at what range.

If it's a long range, 400 to 600m gun, get a 6.5G and you get the benefit of the ballistic coefficient working to keep speed up. Works great on paper, and takes smaller game with ease. If it's to be used under 400m, it's not really a paper gun, it's a hunting rifle. That's where the 6.8SPC shines, as it has more speed with the slightly lighter bullets, out of a 16" barrel that is easy to work with, compared to the Grendel's 20-22". It why deer and hog hunters prefer it.

Aside from being an all out and very expensive showpiece, what will you actually shoot with it? That determines not only what barrel length, but what caliber. As for gas piston, it's unnecessary. It does nothing to add to reliability, only expense.

68wj
November 12, 2010, 01:47 PM
I have seen lots of weird stuff on youtube too:D. I wouldn't be too concerned here though. I have a YHM flash hider on mine and don't notice any flash in the day. I haven't had a chance to shoot at night though.

As for the 16" or 18" question, if I had to guess, I would say it is due to the increased adoption by hunters. I fell into that catagory so maybe I am just speaking for myself. I looked at the figures and knew that a 16" barreled 6.8 would do anything I needed it to. However, my time in the woods with longer barreled rifles made me uneasy so I compromosed with an 18".

Rokman
November 13, 2010, 01:50 AM
I'm taking my midlength 18" WOA barrelled 6.8 to the deer woods this week. It has a Troy Medieval meat pulverizer on it and this combo has worked pretty well for me. I haven't shot any game with it yet, but I'm hoping to soon.

cracked junior
November 13, 2010, 11:30 AM
rock river 16 inch 6.8mm. just has the stock flash hider on it. never seen any flames. even in low light.

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