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Posted: 1/11/2009 8:06:29 AM EDT
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Don't know if this one really classifies as "retro", but I need something to think about while 45Bravo is working on my XM177 moderator, so here goes.
I had posted a question a couple weeks ago about a weirdly contoured Colt barrel that I had seen on GB, and someone posted this pic showing some M4 experimental profiles. 
Well that top one caught my eye. I noticed the resemblance to the lightweight 6.8SPC barrel I just received from Cardinal Armory. 
So what upper receivers would the experimental carbines have used? I have a couple of C7's available to use. Or would they have been A2's? Black or Grey? Or since they were experimental can I use what I want and at least be close? |
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http://www.westernfirearms.com/0/wfc/m16/images/40/102.JPG link http://www.westernfirearms.com/wfc/m16?set=40&sz=996x585 Is that a Colt bravo sierra A2 lower? Looks like it's marked burst, and I bet the other side has an A2 roll mark, yet there is no reinforcements. |
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http://www.westernfirearms.com/0/wfc/m16/images/40/102.JPG link http://www.westernfirearms.com/wfc/m16?set=40&sz=996x585 Is that a Colt bravo sierra A2 lower? Looks like it's marked burst, and I bet the other side has an A2 roll mark, yet there is no reinforcements. 
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I'd like to build myself a mock up of the original Model 720 as pictured in the Small Arms Review Colt Model Guide. It has a barrel profile exactly like the current M4 except that the barrel is turned to .575 between the FSB and the front of the grenade launcher relief cut. This leaves the barrel at .750 from the relief cut to the muzzle. It looks strange, it looks different, but it is one of those things that Colt actually tried.
I'll see if I can get a photo of it scanned in the next few days. |
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Are you talking about barrel number two in the above picture? http://i38.photobucket.com/albums/e131/akim85/m4a1_06.jpg This one? ~Augee YES! Augee, that's the one! |
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Are you talking about barrel number two in the above picture? http://i38.photobucket.com/albums/e131/akim85/m4a1_06.jpg This one? ~Augee Bump for late quasi-retro XperiMental-ness I looked at this pic for a minute and thought - his spent brass has no where to go but his face with that tree right there. Then I saw his right thumb - that should feel interesting! ETA: Rock River makes a similar barrel to profile #1 at the top - only midlength. Can't quite tell if the carbine length is a .750 or .625 FSB - I'm guessing .750. 
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Are you talking about barrel number two in the above picture? http://i38.photobucket.com/albums/e131/akim85/m4a1_06.jpg This one? ~Augee Bump for late quasi-retro XperiMental-ness I looked at this pic for a minute and thought - his spent brass has no where to go but his face with that tree right there. Then I saw his right thumb - that should feel interesting! ETA: Rock River makes a similar barrel to profile #1 at the top - only midlength. Can't quite tell if the carbine length is a .750 or .625 FSB - I'm guessing .750. http://rockriverarms.com/images/products/bblcm08.gif Hmmm, that's interesting. It looks like RRA puts a triangular handguard cap on the lightweight, and a round cap on the heavy barrel. What's really weird is that the RRA mid length handguards that I have, won't work with a round cap! |
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That top profile, the one that resembles your 6.8 is the profile that Canada used for the C8 carbine. I've been wanting to get one reproduced so I could make a C8 clone. So the C7 uses a .750 FSB? I thought they were .625" barrels like the 723? Yes, the C7 used the A2 20" barrel with the .750 FSB. It was basically an M16A2 except they retained the simpler A1 sights, brunton bump and full auto. The C8 uses/used a 14.5" lightweight profile, but with the .750 FSB and it has the large flare at the end exactly as pictured in the XM4 photo. I've ofter heard of the C8's referred to as 723's, the odd time I've tried to correct someone but who'd want to listen to the guy who's actually seen and handled these carbines? 
The C8's also used the 2 position buffer tube with the vinyl acetate covered aluminum stock, most still have them but some have been replaced with fiberlite. |
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Leg - wasn't doubting you - all I have read about the C8 was that it was a Colt 725 model and that it had a lightweight barrel. I didn't know it was a light barrel with the .750 FSB.
Thanks for the info - that will definitely help my 725 clone, as I would've done it wrong! |
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That top profile, the one that resembles your 6.8 is the profile that Canada used for the C8 carbine. I've been wanting to get one reproduced so I could make a C8 clone. So the C7 uses a .750 FSB? I thought they were .625" barrels like the 723? Yes, the C7 used the A2 20" barrel with the .750 FSB. It was basically an M16A2 except they retained the simpler A1 sights, brunton bump and full auto. The C8 uses/used a 14.5" lightweight profile, but with the .750 FSB and it has the large flare at the end exactly as pictured in the XM4 photo. I've ofter heard of the C8's referred to as 723's, the odd time I've tried to correct someone but who'd want to listen to the guy who's actually seen and handled these carbines?
The C8's also used the 2 position buffer tube with the vinyl acetate covered aluminum stock, most still have them but some have been replaced with fiberlite. so if I put my 6.8 Lightweight barrel back on the C7 upper, and then use it with my XM177 lower, I'll have a C8? |
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Leg - wasn't doubting you - all I have read about the C8 was that it was a Colt 725 model and that it had a lightweight barrel. I didn't know it was a light barrel with the .750 FSB. Thanks for the info - that will definitely help my 725 clone, as I would've done it wrong! So here I thought I'd have a C8 clone with my Bubbaguns barrel (.625 under the FSB) and now that isn't right either. Is the 723 the same sepc? Anyone know? I know the 723 was 1:7 twist where the 653 was 1:12, and my barrels are .625 (Well, the one out of the package anyway) and are 1:12 but have A2 type sight posts. SR said they weren't 653 replacement barrels - obviously aren't 723 either, so I guess I'll build an Isreali mutt! Love to see some C8 pics BTW Leg. |
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What model, though, exactly? From what I can find (which may be limited/wrong) it appears that the only 1:12 twist 14.5 lightweight barrels are for the 65X series - could it be that replacement barrels for older models were just put out with the newer sights? I would assume that Colt stopped making "obsolete" parts at some point, and it seems that the A2 post would work just as well...
I don't know, I'm just wondering... |
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I'll try and get some photos of the original C8's in a couple of months. Recce Pl are the only guys in my unit that use them and they're all over in Afghanistan at the moment. I've been meaning to take photos for posterity before these things disappear.
FYI Just to add to the confusion, the Canadian rifles don't use an A1 or A2 front sight post. It's a turned straight post that's thinner than an A1, probably closer to a National Match type post than anything else. crackecornish, Yes, you'd have a quasi C8 clone if you stuck your 6.8 barrel on the C7 upper. Go for regular skinny handguards, we still use them up here, even on brand new rifles. No M4 feed ramps to be found either. ETA: Twist rates for all C7 and C8's is 1/7 regardless of when they were made. |
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I'll check them out when I get a chance but the forward assist on all C7 and C8's are round. Believe most these days are small but IIRC they did use the large ones with the side flat initially.
As for the front handguard cap, I believe that it's the plain old round one. We didn't adopt the M203 until much later and even then I only ever saw them on C7's, although some small special units did mount them on C8's. Current C8FTHB's are probably regular round handguard caps as well since the newer Diemaco M203's use a proprietary quick attach mount, which is why the new barrels have that funky profile. |
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