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Posted: 3/11/2005 9:21:28 PM EDT
Why do AR barrels have this "step-down" in diameter ?

Link Posted: 3/11/2005 9:33:27 PM EDT
To fit a standard industry wide sized muzzle attachment. A light barrel will actually step up to that size.
Link Posted: 3/11/2005 10:12:53 PM EDT
[Last Edit: 3/11/2005 10:14:05 PM EDT 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.
Link Posted: 3/11/2005 10:18:47 PM EDT
Nobody mentioned "slip on" except for you.
Some muzzle attachments have a collar that protrudes rear of the shoulder, like the Smith Vortex FH.
Link Posted: 3/12/2005 7:20:53 AM EDT
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?
Link Posted: 3/12/2005 8:28:32 AM EDT
Link Posted: 3/12/2005 7:35:41 PM EDT

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!
Link Posted: 3/13/2005 4:46:52 AM EDT
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.
Link Posted: 3/13/2005 5:32:52 AM EDT

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
Link Posted: 3/13/2005 6:07:03 AM EDT
It's a good thing we humans don't have a build-in handle on our heads to facilitate child birth
Link Posted: 3/13/2005 6:31:18 AM EDT

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?
Link Posted: 3/13/2005 6:40:32 AM EDT

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.
Link Posted: 3/13/2005 10:13:43 AM EDT

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.
Link Posted: 3/13/2005 5:03:43 PM EDT
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
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