I saw a "special" bayonet advertised that will work on the 16" carbines.

It had a weird extension below the regular handle to make it longer.

My choice of pre-ban AR is going to depend on whether or not it will accept the M7 and M9 bayonets.  I've seen so many variations between the bayonet lug and flash hider, I wonder what is standard for the bayonets.

What do I need to look for to make sure I don't have problems?  Thanks!

I've seen what you're talking about. The cheapest place I've seen them is on Ebay.
www.deltaforce.com
sells them.
But if I were you, I'd get a 14.5" barrel with a fixed flash suppressor to avoid the problem all together.
That's what I'm doing for my M4, but it is being sent to GG&G for their flipper.
Hope this helps.
-Steve

MN227,

The thing is, M7 & M9 won't normally fit on a 16" (you already know this) so it is really dependent on the extension.  All the bayonet lugs I have seen first hand are all the same, and I stick with flash hiders that are mil-spec in outside dimension.  I think that leaves F/H like Colt, Gem-Tech, AAC, KAC, Vortex, and maybe Phantom?  Probably others too.  I bought one of those M7 Bayonets from PreBanArms/Cuzco for 16" carbines, and it is really nice.  The bayonet is a real Colt and the extension is made very well and finished perfectly - it all looks like factory.

The standard for bayonets, flash hiders, and bayonet mounts is a matter of mil-spec dimensions.  Except for those barrels with a funky flash hider or muzzle brake, I don't think you will have a problem.

P.S. I also have an M7 bayonet that fits the original Bushmaster 5.5" flash hider (mounted on a 11.5" barrel).  I don't know where you get those cause the flash hider is larger than a standard F/H I think.

Got a good picture of the lug extension?  

Hey thanks!

I can see another topic here is covering this.

I'm looking at an Olympic shorty, ad states it is a 10" with a 6" flash suppressor.  It looks like a standard diameter, so I am guessing this will work.  

As a rule, what brands/variants won't take the standard bayonet?

Thanks!

I REALLY like the Bushmaster 16in pre-ban A3 with the ARMS S.I.R., this would HAVE to be mil-spec for M7 M9 bayonets right?  

It's just some companies use "too short" length handguards/gas systems which pull the gas block further from the flash suppressor?

Not really, but here is 16" M7 Bayonet pic from the [url]www.prebanarms.com[/url] website.
[img]http://photos.ar15.com/ImageGallery/IG_LoadImage.asp?iImageUnq=7865[/img]