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Old November 21, 2012, 11:35 AM   #1
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Windham Weaponry - "Compass Lake Chamber" info

A few days ago, I sent an e-mail to Windham Weaponry asking what the differences were between the "Compass Lake Chamber" and other types of .223/5.56 NATO chambers. Here's my inquiry, and the much appreciated response from Erik Winter at WW. The bold type and underlining is mine.


I have a question regarding the "Compass Lake chamber". All I ever see is that the chamber is "slightly smaller" than the Wylde chamber.
Is there an actual drawing, or a spec sheet with comparative values/dimensions for any of .223 SAAMI, Compass Lake, Wylde, AMU and NATO chambers?

Thanks very much for your time.


Hi C,

I don’t have drawings to share but basically the lead in our 5.56 NATO chamber is .0566” and the lead of the 5.56 Compass chamber is .0250”

The mil-spec NATO chamber has a longer lead but has an included taper per inch of .0427” so it results in a much longer but more gradual lead. Our NATO chamber has a shorter lead for achieving much better accuracy than can be achieved with the longer mil-spec lead.

All things being equal you would have about .093” less throat length on the Compass chamber compared to the NATO, and .119” less on the SAAMI
compared to the NATO.

I have tested our Compass lake chambered rifles with 5.56 NATO ammunition and there are no signs of overpressure.

I don’t have any info on Wylde or AMU chambers.

Keep in mind I’m not an engineer and the above information I put together... as it was explained to me by our engineer.

I hope this helps,
Erik Winter
Gunsmithing/Tech Support
Windham Weaponry

So there ya' go. I'd like to again thank Mr. Winter for taking the time to obtain and share this info.

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Old November 21, 2012, 01:39 PM   #2
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I don't really know alot about the differences between all the chambers but Im not sure If I'd be ok shooting 5.56 out of a chamber that has a smaller lead then the wylde .Maybe only commercial 5.56 but the NATO stuff could come from many different countrys and depending on how they are made . Tracers , armor piercing and incendiary bullets all could be longer then your standard 55-62gr commercial bullets . Thats just me and because I have the most basic understanding of the issue I could be playing it to safe .
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Last edited by Metal god; November 21, 2012 at 01:47 PM.
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Old November 28, 2012, 12:13 AM   #3
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I don't blame you for being cautious. If I ever get a Compass Lake chambered gun and decide to shoot some M885 out of it, which actually would be pretty unlikely, I'd be looking really close at the fired primers.
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Old November 28, 2012, 07:51 AM   #4
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If you are buying a varmint rifle for great accuracy why would you want to shoot military surplus ammo in it ? I have never shot military ammo in my AR, I only shoot 223 hand loaded ammo for accuracy. But thats just me. There are guys in our gun club that shoot the Windham Weaponry Varmint Exterminator getting groups of 5 shots in one ragged hole at 100 yards with hand loads and Federal American Eagle ammo. They are extremely accurate rifles.

You can get more info on Compass Lake Engineering here

Last edited by rebs; November 28, 2012 at 07:57 AM.
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Old November 28, 2012, 07:41 PM   #5
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I agree with Rebs.

I have an AR .223 that is carefully loaded for target shooting.
I don't put unnecessary wear and tear on the expensive Krieger barrel with Slobbovian Surplus.

I have a stock AR 5.56 that would be useful in case of societal breakdown. It shoots the cheap stuff well enough to repel boarders.
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Old November 28, 2012, 09:56 PM   #6
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REAL U.S. surplus 5.56 costs more than most commercial .223

If you plan on shooting a LOT of 5.56 - Get the Nato Chamber.
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