[ApexinM3]

As the title of the thread states, I am considering the conversion of my M4 to a SBS (legally, of course). I was told by my gunsmith that there is a possibility of failure to cycle due to the shortened length of the barrel unless full house loads are used (i.e. 00 buck, slugs).

I know that Benelli makes a breaching version of this weapon, however I do not know if there is any physical difference between the M4 with 18.5" barrel versus the 14" breaching version other than the obviously shorter barrel length.

Anybody out there with experience on this? Any help would be greatly appreciated!

[kingjoey]

It would depend on the distance between the gas port and the end of the barrel. On the M4 the gas port is at about 12.5" down the barrel IIRC so you'd have 1.5" after the ports to give you your dwell time. Some gas systems will cycle fine with that much time, some won't. Usually higher pressure loads will cycle the action more reliably when dealing with a short barrel setup. You may end up having to have the gasports drilled up a size or two to allow enough gas to come in during that dwell time to cycle the action.

[627PCFan]

Dear god man Im just cringing at the idea of you doing that to a $1400 gun. Buy a mossberg :what:

I think you wouldn't get enough pressure for a long enough period to cycle the weapon if you cut it short to the gas ports.

[ApexinM3]

Trust me, I'm none too keen on the idea of hacking the barrel either, but(!) the Benelli Barrel is virtually impossible to find as they are not sold to civilians. I may just buy another barrel from Benelli, but I imagine they will be super expensive. Joy.

I thought about the Mossy way, but I'd really like the Benelli to be short barreled as I use it more.

[627PCFan]

And when you do complete the transformation I wanna see this thing. Im down in Calvert-

[10 Ring Tao]

The guys on arfcom are very well versed with SBS's and other NFA toys.

I've also seen plenty of threads on the shotgun you mentioned, so there is a good chance someone has asked the same exact question you have, or actually done it.

http://www.ar15.com/forums/forum.html?b=6&f=1

[mtgale00]

The location of the gas port on the breaching barrel is identical to the 18.5 inch full size. One major problem exists with converting your M4 to an SBS. Benelli does not sell M4 spare parts for the shotgun, period. So the question is, is it possible to remove the retention lug, re-locate it and re-weld it without destroying it or the barrel? There may be a gunsmith willing to risk it but are you?

The Entry/CQB model was imported with an 18.5 barrel. Benelli welded the front sight and retention lug in the "SBS" position and the barrels were shortened after they landed in the USA.

[ApexinM3]

Dang, this is getting complicated. I was hoping for a simple chopmod sans barrel swap, it looks like I am getting myself into something deaper. Joy. Gonna place a call to Benelli tomorrrow to see what options exist. I'll keep you all informed...

[SigForLife]

You might want to check out this thread: (pretty wicked at 12")

http://www.benelliusa.com/forum/showthread.php?p=89173

[Gixerman1000]

On the M4 the gas port is at about 12.5" down the barrel IIRC so you'd have 1.5" after the ports to give you your dwell time.

No it's not, the two gas ports are just past the chamber, only about 4-1/4" down the barrel.

http://img.photobucket.com/albums/v238/Gixerman1000/Mis/100_9664.jpg

Benelli may use different gas regulator plugs and/or different pistons with their entry model M4 but I doubt it.

The 12ga is a low pressure round with for the most part max pressure and velocity reached in the first 8" to 12" of barrel length anyway, because of this I would say a 14” barreled M4 would function pretty much the same as an 18.5” barreled M4 as the gas regulator plugs would also help compensate.

[ApexinM3]

Interesting info, to say the least. I am signed up for the Benelli Armorers school at the end of July so I will ask while down there. Thanks to all for the help so far!

[GunTech]

Its a lot easier with am M1. Just cut the barrel wherever you want. I opted for 10.5 inches.

http://guntech.com/shotgun/m1s90.jpg

[tacshooter6.8]

I Have An older Benelli M4 barrel that i was going to convert but life got in the way again...If anyone is interested let me know...It is an older barrel with four ports marked "low recoil". I was going for compact with the most rounds, so not shooting 3" was no big deal(that's what my original barrel is for). Any way asking 650.00 + Shipping...pm me if interested.

[OOOXOOO]

Aww... GunTech beat me to it.