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Posted: 8/12/2008 12:12:54 AM EDT
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I've always had a particular likening to vintage rifles and retro ARs are no different. I thought it would be great to assemble a pseudo 607 rifle as my first retro and started doing some research. Now I must admit, I've never actually seen a 607 in real life and I've always assumed the 3.5" moderator was nothing more than a blast cup that directed muzzle blast down range. Then the other day while trying to find specs on it to recreate it (or something similar) I came across a picture of one cut in half and it looked like there was a cone shaped blast shield welded to the front of it, similar the AMD muzzle break but without the side ports. It also seemed to have rings inside of it, like baffles but with excessively large pupils. This led me to wonder why exactly the 3.5" moderator was given a silencer designation by the ATF. Anyone care to bring me up to speed on exactly how the 3.5" moderator was designed, how it functioned, why the ATF ruled the way it did, etc. I like lurjing here because I lack the knowledge to contribute but this topic hasn't seem to come up in my reading here. If it's a taboo subject, I apologize, but I think this is one of those circumastances where I won't find the answer by searching alone. Thanks in advance. |
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It was not simply a long flash hider, it is indeed a suppressor of sorts with baffles designed to reduce muzzle blast from the 11.5" barrel to a more manageable level (similar to that of the 20" barreled rifles) and to hold the pressure long enough for the rifle to function properly. ATF declared it a suppressor because it reduces sound by approx 2db. |
IIRC, WA-Tom made a copy of the 3.5" mod...Maybe Tom could elaborate...  FWIW, I've seen pics of a 4.375" mod that looks like the 607 mod...the inside of the muzzle end is cone-shaped, like the style the OP described...Don't know what the guts look like... 
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| The 607 moderator was basically like the 177 type except they didn't put any flash holes on it in front of the baffle stack/chamber. Another poster got it right, ATF decided to call these a silencer and created the ruling that if it reduced sound by even one DB it was a silencer. Now we all know logic and ATF don't always walk hand in hand, but they mostly decided to rule this way because the moderator, when attached onto a .22LR weapon does in fact serve as a crude silencer, with reduction in the 15-20DB range. Given a choice I would take a dedicated, purpose built .22LR silencer any day over a Colt moderator, but they are regulated as silencers and until they are ruled otherwise that is what they are. |
In looking for the picture again, I came across this picture:  I believe this is the one you are talking about. This was NOT the image I found earlier but can't find now. The one I had was a perfect cross section with the entire moderator cut in half, where as these have what appears to be 90 degree wedges taken out of them one showing the external of the core one showing the internal of the core. The image I saw was of a 3.5" moderator and looked similar but didn't have the slot cuts for the flash suppression and was shorter. It was also on a brown background and had a complete moderator (or maybe the top half) above it instead of a seperate moderator. I am still looking to try and find that moderator again. From the sounds of it, it seems that it was a long flash suppresor with a blast chamber and a crude diffuser which wasn't meant to suppress the sound as it was to make the weapon less hellish on the user and people next to them. I didn't even think about cycling issues because of it, which is interesting. Do 607 rifles with the A1 flash suppressor have more cycling issues than the 607s with moderators, or were other modifications done to enable to the gun to fire without the moderator? VAAR thank you so much. PM coming real soon. Thanks so much for the quick response guys. The only thing holding me back is that Nodak is out of stock right now but I think that just gives me an excuse to make all the parts and test fit them on one of my other ARs while I wait. |
Hmmm, maybe I will try my TSI XM Moderator with a 22lr conversion to test it....Nice! |
Too hard to engrave also 
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