Why AR barrels have "step-down" in diameter ? (PIC)

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[ARCHIVED THREAD] - Why AR barrels have "step-down" in diameter ? (PIC)

G35 Joined Sep 2001 Posts 889 EE Offline TX, USA	Posted: 3/11/2005 8:21:28 PM EST Why do AR barrels have this "step-down" in diameter ?

MisterPX Cap'n Bumpalot uses dial-up. Joined Mar 2004 Posts 1757 EE Offline WI, USA	Posted: 3/11/2005 8:33:27 PM EST To fit a standard industry wide sized muzzle attachment. A light barrel will actually step up to that size.
	Spec. for life in the Nasty G who knows that there is no such thing as a stupid question, only stupid people.

G35 Joined Sep 2001 Posts 890 EE Offline TX, USA	Posted: 3/11/2005 9:12:53 PM EST [Last Edit: 3/11/2005 9:14:05 PM EST by G35] But why would someone want to slip-on a muzzle device when the barrel has threads ? I could see having the step-down on a barrel without threads...no threads, but there would be a step-down to accomadate a slip-on attachment.

Zak-Smith Practical Shooter Joined Nov 2002 Posts 3281 EE Offline CO, USA	Posted: 3/11/2005 9:18:47 PM EST Nobody mentioned "slip on" except for you. Some muzzle attachments have a collar that protrudes rear of the shoulder, like the Smith Vortex FH.
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p35hp Joined Oct 2004 Posts 3 EE Offline KY, USA	Posted: 3/12/2005 6:20:53 AM EST Some muzzle attachments have a collar that protrudes rear of the shoulder, like the Smith Vortex FH................Does this mean that I'd have probs mounting on a barrel w/o a step down?

Troy

Joined Nov 2000
Posts 20809
EE Offline

CA, USA

Posted: 3/12/2005 7:28:32 AM EST

The reason for that step-down is to ensure compatibility with muzzle-launched rifle grenades. Because the M203 was adopted not long after the M16 was in the US, you don't see a lot of rifle grenades here, but many other countries still use them often, and a few non-lethal devices are designed around the same concept. Most countries don't have the budget to buy a bunch of specialty weapons, so they have to be able to adapt what they've got (a rifle) to do what they need.

NATO-standard 22mm ID rifle grenades.

-Troy

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StormSurge

Joined Sep 2001
Posts 2144
EE Offline

CA, USA

Posted: 3/12/2005 6:35:41 PM EST

Originally Posted By Troy:
The reason for that step-down is to ensure compatibility with muzzle-launched rifle grenades. Because the M203 was adopted not long after the M16 was in the US, you don't see a lot of rifle grenades here, but many other countries still use them often, and a few non-lethal devices are designed around the same concept. Most countries don't have the budget to buy a bunch of specialty weapons, so they have to be able to adapt what they've got (a rifle) to do what they need.

photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=2908
NATO-standard 22mm ID rifle grenades.

-Troy

...and so mutations pass into the orderly cycle of evolution!

coldblue Team Member Joined Jan 2002 Posts 604 EE Offline FL, USA	Posted: 3/13/2005 3:46:52 AM EST Many years ago, when I asked Colt engineers this question, they stated that it was to use existing fixturing that holds the barrel when it was chrome plated.
	ColdBlue sends...

bsbg

Opinion worth what you paid for it.

Joined Mar 2001
Posts 3732
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NH, USA

Posted: 3/13/2005 4:32:52 AM EST

Originally Posted By coldblue:
Many years ago, when I asked Colt engineers this question, they stated that it was to use existing fixturing that holds the barrel when it was chrome plated.

Typical manufacturing reasoning

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Duffy Member of GGC (Gucci Girl Club) Joined Jan 2001 Posts 5425 EE Offline USA	Posted: 3/13/2005 5:07:03 AM EST It's a good thing we humans don't have a build-in handle on our heads to facilitate child birth
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redfisher

Member

Joined Nov 2002
Posts 2826
EE Offline

FL, USA

Posted: 3/13/2005 5:31:18 AM EST

Originally Posted By Duffy:
It's a good thing we humans don't have a build-in handle on our heads to facilitate child birth

That is very funny, duffy.

I swear I actually expelled (something..

.) when I read that!

back to the question and the 'existing fixturing'

Do non-chromed barrels NOT have this step down, or are all barrels configured this way just in case they are to be chromed?

mongo001

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Joined Mar 2003
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MI, USA

Posted: 3/13/2005 5:40:32 AM EST

Originally Posted By p35hp:
Some muzzle attachments have a collar that protrudes rear of the shoulder, like the Smith Vortex FH................Does this mean that I'd have probs mounting on a barrel w/o a step down?

You might. I've taken the collar of a few Vortexs and other FHs to fix this problem for a few people.

This post edited for typos and grammatical errors.

Thinking twice and posting once.<img src=/images/smilies/anim_rolleyes.gif border=0 align=middle>

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BattleRife

Joined Jan 2001
Posts 145
EE Offline

CAN

Posted: 3/13/2005 9:13:43 AM EST

Originally Posted By coldblue:
Many years ago, when I asked Colt engineers this question, they stated that it was to use existing fixturing that holds the barrel when it was chrome plated.

That doesn't stand up to analysis.

I will be making barrels at the rate of a thousand a day, and so I have a thousand chroming fixtures, and I expect to make 1-2 million barrels.

Does it make more sense to add an extra machining step to each of ONE MILLION barrels;

Or to remake / rework one thousand fixtures, and leave the barrels alone?

When you have that kind of volume, you can afford to do it right.

Ross

Joined Nov 2000
Posts 3311
EE Offline

VA, USA

Posted: 3/13/2005 4:03:43 PM EST

The rifle greande explanation is correct. The M16 series uses a spring collar that fits behind the FS. When the Grenade is slipped on the NATO std 22mm diameter FS, it compresses the spring fingers into this step-down area. This keeps the Rifle Grenade from slipping off the end of the rifle while you're moving around.

You have to replace the spring collar after shooting so many number of grenades.

Ross

[ARCHIVED THREAD] - Why AR barrels have "step-down" in diameter ? (PIC)

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