DIY Dissipator barrel from M4 carbine?

[WallyGeorge]

Hello all,

Here's a question for the more experienced AR smiths/builders on Calguns: Could I make a "Dissipator" style barrel out of a Stag 16" M4 style barrel and an extra front sight? Will the A2 front sight attach with just the taper pins and no barrel step to set against?

I have a pile of unused parts (rifle hg, hg cap, A2 sight) that I was hoping to assemble into a long sight radiused yet lightweight carbine gas barrel. To keep the handguard cap from rotating, I was going to either weld or bolt the cap to the front sight through the unused gas tube hole.

Does this sound like a plan, or a major waste of time/energy?

Thanks for your input!!!

[bwiese]

In theory you could.

I think you'd have to do some lathing on the new area where the FS/GB would now attach. Unsure if the M4 bayonet 'step down' might interfere or look kludgy.

For the rear existing FS/GB you'd just grind down the front sight tower to fit under the A2 handguards. [Unclear if this would fit under various rail handguards, most of those use special low-profile gas blocks.]

If you had the skills/tools/time it might be worthwhile.

You might be best off just selling your bbl and getting fair value out of it and buying a CMMG or Bushmaster Dissipator bbl.

[WallyGeorge]

Think your right about this one. It would end up cheaper to buy the "right tool" the first time...

[chuck762]

The problem is the barrel diameter in front of the sight is smaller than .750 which gas blocks/front sights fit. They run anywhere from .740 down to .720 from the ones I have worked on.

I have read a few posts online bushmaster uses a undersized front sight for their dissipator barrels but have never seen one in person to verify. Could be BS.

It could be done but it would be easier and cheaper to sell off your barrel and buy the one you want.

[AJAX22]

+1 on selling the barrel and buying the right stuff.

It could be done, (probably be easiest to use a pencil barrel FSB and use a lathe to cut a new profile on the barrel) but it is a really bad idea in that it will kill the resale value of the upper. If you REALLY wanted to you could probably swap your 16 inch M4 upper straight across (or + a bit of cash) for a dissapator without making a kluge out of it.

[aplinker]

The dissipator was the dumbest design ever...

16" carbine with a heavy barrel, then they stick another sight on - making it even heavier. BM just did it cause it was CHEAP.

I like the long sight radius, too, but it's otherwise ridiculous.

[hybridatsun350]

The dissipator was the dumbest design ever...

16" carbine with a heavy barrel, then they stick another sight on - making it even heavier. BM just did it cause it was CHEAP.

I like the long sight radius, too, but it's otherwise ridiculous.

First of all, my Bushmaster Dissipator is an M4 profile barrel.

Second, how is it cheaper? It requires that two "gas blocks" be mounted on one barrel. Sounds like more work to me.

[bwiese]

The dissipator was the dumbest design ever...

16" carbine with a heavy barrel, then they stick another sight on - making it even heavier. BM just did it cause it was CHEAP.

I like the long sight radius, too, but it's otherwise ridiculous.

I do like my Bushy Dissipator but the heavy bbl is a bit too heavy.
They also have a Dissipator M4 that has the lighter profile bbl.

A happy medium might be the MedCon bbl profile from CMMG - stiffer & less whippy than an M4 bbl but still nicely balanced.

The longer A2 handguards + sight radius are indeed handy.

[bwiese]

Second, how is it cheaper? It requires that two "gas blocks" be mounted on one barrel. Sounds like more work to me.

Extra gas block may well be cheaper than extra lathe time turning the thinner bbl.

[chuck762]

Extra gas block may well be cheaper than extra lathe time turning the thinner bbl.

Turning a barrel profile on a CNC lathe takes very little time or effort.
A gas block costs more since BM uses a cut down forged standard sight/gas block which requires a few more operations.

[WallyGeorge]

I like the long sight radius, too, but it's otherwise ridiculous.

Yep, I'd like the extra sight radius as well as it seemed like a "fun" project...

[dfletcher]

I had a Model 1 Dissapator for a while & sold it, it was OK I just didn't have any use for it.

Anyway, Model 1 uses a 16.5" heavy barrel with the carbine length gas tube. The "real gas block" is a low profile located under the guard & is held in place with 2 taper pins. I'd think that if you take off the top of a standard sight you'd be fine using that. The handguard is held in place with a handguard plate and this 1913 gas block: http://www.model1sales.com/item-deta...TOKEN=26992511

It's steel and once you snug it up it won't move, of course it serves no purpose as a gas block but just as a forend retainer.

[triaged]

Just cut down the sight into a low profile gas block and get a long free float tube. Put a BUIS on the tube.

Something like this but with the sight on the tube.

http://www.ar15.com/forums/topic.html?b=3&f=118&t=398114

[aplinker]

Extra gas block may well be cheaper than extra lathe time turning the thinner bbl.

exactly... they were using heavy barrel blanks - no lathe time.

The other gas block is small and cheap.

The handguard length is nice, too - especially compared to a carbine, but with the advent of 16" mid-lengths... that's the way to go.

[ar15barrels]

The problem is the barrel diameter in front of the sight is smaller than .750 which gas blocks/front sights fit. They run anywhere from .740 down to .720 from the ones I have worked on.

I have read a few posts online bushmaster uses a undersized front sight for their dissipator barrels but have never seen one in person to verify. Could be BS.

Ding Ding Ding...
We got a winner.

Bushmaster does indeed use undersized front sight bases and pin them on.
I have not seen these for sale as component parts though.