Turning a 16" m4 barrel into a Dissy

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[ARCHIVED THREAD] - Turning a 16" m4 barrel into a Dissy

Posted: 6/23/2005 10:01:22 AM EDT

Have you guys done it and is it hard?
I mean doing it the harder way, installing another FSB and cutting down the current one.

Posted: 6/23/2005 10:11:14 AM EDT

[#1]

FSBs have a 0.750" hole in them. The barrel, forward of the original FSB is somewhat less than 0.750", usually 0.740" or less. That 0.010 or so gap will make for a very sloppy fitting FSB. You may get away with a clamp on style FSB, that can squeeze down to the lower OD. People have used PRI front sights squeezed down forward of the original gas blocks with success in the past.

Posted: 6/23/2005 10:17:15 AM EDT

[#2]

How about drilling & tapping the FSB for set screws?

Posted: 6/23/2005 10:19:08 AM EDT

[#3]

Quoted:
How about drilling & tapping the FSB for set screws?

IMO, is would look like poo and would be very unstable due to the gap between the barrel and FSB, but remember, just IMO.

Posted: 6/23/2005 10:30:49 AM EDT

[#4]

Are the barrels that Bushmaster uses on their dissys some different than "normal" 16"ers? It seems like the M4 profile is the exact same barrel on both the dissy and the patrolman's carbine.

Posted: 6/23/2005 10:41:09 AM EDT

[#5]

Quoted:
Are the barrels that Bushmaster uses on their dissys some different than "normal" 16"ers? It seems like the M4 profile is the exact same barrel on both the dissy and the patrolman's carbine.

www.bushmaster.com/shopping/barrel-assemblies/Images/abbl-16dm4a.jpg

My guess is either the FSB is different or the barrel profile is. I'd lean toward the FSB.

Posted: 6/23/2005 6:34:04 PM EDT

[#6]

There is another issue that I can see also, the trianguler sheet metal deal that goes behind the FSB and holds the front of the HG, on any reguler build the GT keeps it straight, so I'm thinking you need to tack weld it to the FSB, OR put a screw were the GT used to go. Just a thought.

Posted: 6/23/2005 8:37:43 PM EDT

[#7]

Quoted:
Quoted:
Are the barrels that Bushmaster uses on their dissys some different than "normal" 16"ers? It seems like the M4 profile is the exact same barrel on both the dissy and the patrolman's carbine.

www.bushmaster.com/shopping/barrel-assemblies/Images/abbl-16dm4a.jpg

My guess is either the FSB is different or the barrel profile is. I'd lean toward the FSB.

I would think the barrel profile is different, that FSB has the hole for a gas tube roll pin.

Posted: 6/23/2005 9:21:25 PM EDT

[#8]

Why use a FSB at all?

Posted: 6/23/2005 9:38:32 PM EDT

[#9]

Quoted:
Why use a FSB at all?
users.adelphia.net/~masine/A1.jpg

Why do you have a rear BUIS and no front sight? Do you have a rail mounted front sight not in the pic?

Posted: 6/23/2005 9:59:36 PM EDT

[#10]

Quoted:
Quoted:
Why use a FSB at all?
users.adelphia.net/~masine/A1.jpg

Why do you have a rear BUIS and no front sight? Do you have a rail mounted front sight not in the pic?

Damn everybody allways asks that

Just a mock up build to test a 14" midlength gas system.

Posted: 6/24/2005 12:04:12 AM EDT

[#11]

Can someone who really has a factory built Bushmaster Dissipator, please take a closer look at it and give some real info on the diameters and attaching? This speculation is leading nowhere.

Posted: 6/24/2005 12:51:05 AM EDT

[#12]

mongo answered the question in his first post dude, it can't be done with an M4 barrel by using an A2 FSB, you can do it with an A1 FSB if you can find one. the OD of the barrel forward of the FSB seat is SMALLER than the ID of the A2 FSB.

Posted: 6/24/2005 8:45:11 AM EDT

[#13]

Still waiting for someone to measure the dimensions of his Bushy Dissy's barrel at the FSB compared to the gas port. Facts needed.. no guessing, speculations and IMO's.

Posted: 6/24/2005 9:58:37 AM EDT

[#14]

Quoted:
Still waiting for someone to measure the dimensions of his Bushy Dissy's barrel at the FSB compared to the gas port. Facts needed.. no guessing, speculations and IMO's.

No offense.... Cant see the forrest for the trees.
There are several way to do what you wish, and they have all been done before.
*speculation*A bushmaster dissy barrel's forward FSB and barrel dia. would have to be smaller than a compairable M4's, Otherwise the rear "gasblock" wouldnt slide into position.

You have several options: Use a factory dissy barrel, But the rear shaved FSB has troubles clearing some FF tubes.. Use a M4 barrel and find an A1 FSB to ream to final I.D.... Use a cut down 20" which needs gas port work to run correctly.... You can even use midlength barrels in this type of build..

IMHO If your going to use use factory handguards and never will use a FF tube then just go with the bushy dissy barrel.
Flame away.......

Posted: 6/24/2005 10:08:39 AM EDT

[#15]

I've got an M4 profile Dissy from Bushmaster, I'll try to measure the diameter at the FSB when I get home tonight.

Quoted:
There is another issue that I can see also, the trianguler sheet metal deal that goes behind the FSB and holds the front of the HG, on any reguler build the GT keeps it straight, so I'm thinking you need to tack weld it to the FSB, OR put a screw were the GT used to go. Just a thought.

There is a short roll pin pressed into the FSB where the gas tube would be to index the metal plate properly.

CD

Posted: 6/24/2005 10:50:28 AM EDT

[#16]

Quoted:
Still waiting for someone to measure the dimensions of his Bushy Dissy's barrel at the FSB compared to the gas port. Facts needed.. no guessing, speculations and IMO's.

I used to own the standard Dissipator (HBAR profile), and the front sight base had the exact same inside diameter dimensions as the gas block under the handguards. From a manufacturing standpoint, I can't imaging why Bushmaster would make the M4 barreled version any different.

Posted: 6/25/2005 12:32:12 AM EDT

[#17]

Quoted:
Still waiting for someone to measure the dimensions of his Bushy Dissy's barrel at the FSB compared to the gas port. Facts needed.. no guessing, speculations and IMO's.

you're a piece of work dude

Posted: 6/25/2005 8:12:17 PM EDT

[#18]

Quoted:
Quoted:
Still waiting for someone to measure the dimensions of his Bushy Dissy's barrel at the FSB compared to the gas port. Facts needed.. no guessing, speculations and IMO's.

I used to own the standard Dissipator (HBAR profile), and the front sight base had the exact same inside diameter dimensions as the gas block under the handguards. From a manufacturing standpoint, I can't imaging why Bushmaster would make the M4 barreled version any different.

Maybe they make a special Dissy M4 or HBAR barrel, because nearly every barrel is smaller forward of the gas block. Some are a few thousandths, others are more.

Posted: 6/25/2005 9:02:00 PM EDT

[#19]

Yup, the M4-Dissy (or other Dissy) is a special profiled barrel that is machined to accept the 750 FSB is 2 spots.
The profile is set up so that there is a shoulder (were the CAR handguard cap would have gone on) that the shaved/ gas block FSB would mount near. The area where the front sight FSB would mount is also set up for the same .750, but there is no shoulder; so the saved/gas block FSB can pass over it.

(As for this next info, I can't remember if its BM on Model 1 Sales or both . . .? . . . but . . . .)
With the shoulder missing for the sight FSB, the handguard cap is held against the sight FSB by using a bolt that is threaded into the unused gas tube hole.

When looking at contoured barrel blanks, you can always tell if the barrel is made for a dissy by the 2 machined areas for FSB.

hope this helps . . .

Posted: 6/26/2005 1:35:39 AM EDT

[#20]

Quoted:
Quoted:
Still waiting for someone to measure the dimensions of his Bushy Dissy's barrel at the FSB compared to the gas port. Facts needed.. no guessing, speculations and IMO's.

you're a piece of work dude

Why? I just wanna know some facts. Is there something wrong about that?

Thank you guys for sharing.

Posted: 6/26/2005 1:48:50 AM EDT

[#21]

Quoted:
Why? I just wanna know some facts. Is there something wrong about that?

you were given the facts at least three times by my count.

Posted: 8/6/2005 7:23:18 AM EDT

[#22]

Quoted:
Quoted:
Why? I just wanna know some facts. Is there something wrong about that?

you were given the facts at least three times by my count.

BravoCompanyUSA was the first one to give facts by my count.

Posted: 8/6/2005 11:24:17 AM EDT

[#23]

your original question, will a m4 barrel work as for a dissapator.

1.

Quoted:
FSBs have a 0.750" hole in them. The barrel, forward of the original FSB is somewhat less than 0.750", usually 0.740" or less. That 0.010 or so gap will make for a very sloppy fitting FSB. You may get away with a clamp on style FSB, that can squeeze down to the lower OD. People have used PRI front sights squeezed down forward of the original gas blocks with success in the past.

2.

Quoted:
mongo answered the question in his first post dude, it can't be done with an M4 barrel by using an A2 FSB, you can do it with an A1 FSB if you can find one. the OD of the barrel forward of the FSB seat is SMALLER than the ID of the A2 FSB.

3.

Quoted:
You have several options: Use a factory dissy barrel, But the rear shaved FSB has troubles clearing some FF tubes.. Use a M4 barrel and find an A1 FSB to ream to final I.D.... Use a cut down 20" which needs gas port work to run correctly.... You can even use midlength barrels in this type of build..

4.

Quoted:
Maybe they make a special Dissy M4 or HBAR barrel, because nearly every barrel is smaller forward of the gas block. Some are a few thousandths, others are more.

5.

Quoted:
Yup, the M4-Dissy (or other Dissy) is a special profiled barrel that is machined to accept the 750 FSB is 2 spots.
The profile is set up so that there is a shoulder (were the CAR handguard cap would have gone on) that the shaved/ gas block FSB would mount near. The area where the front sight FSB would mount is also set up for the same .750, but there is no shoulder; so the saved/gas block FSB can pass over it.

(As for this next info, I can't remember if its BM on Model 1 Sales or both . . .? . . . but . . . .)
With the shoulder missing for the sight FSB, the handguard cap is held against the sight FSB by using a bolt that is threaded into the unused gas tube hole.

When looking at contoured barrel blanks, you can always tell if the barrel is made for a dissy by the 2 machined areas for FSB.

hope this helps . . .