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Posted: 11/23/2006 9:51:52 PM EDT
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The ArmaLite AR-15 had a 1/14 twist, as was standard for .224 center fire rifle barrels. Colt placed the AR-15 into production in December of 1959 after purchasing the rights and AR-15 trademark name. Colt did not have rifle barrel manufacturing capability so Winchester was subcontracted to make AR-15 barrels. These Winchester barrels were 1/14, broach cut, and 6 groove. Thanks to Victor of US Anodizing www.usanodizing.com/ and CaptRichardson I recently had four 601 barrels to study:  Top barrel has only one marking, a small partial triangle shaped stamping in between the legs of the FSB (Front Sight Base):  Scottmon's 1/14 twist barrel is identical to this one: www.ar15.com/forums/topic.html?b=3&f=123&t=300554 Second barrel down has three markings. An M & S stamped between the legs of the FSB. Took the FSB off this one and found no marking under it:  A small partial triangle shape stamped in between the legs of the FSB on the opposite side:  Also has a standard Colt C in Square proof stamp on the breach of the barrel:  Barrel second from bottom has two markings. M & S stamped in between FSB legs:  Small partial triangle stamping on opposite side. This appears to be the standard Colt Varified Proof in triangle stamping used on later Colt's through about 1965, but only partially stamped.  Bottom barrel has been refinished, and has several markings. M stamping between FSB legs:  W stamped at TDC behind handguard cap:  FSB hides another W, also note that the gas port is counter bored, and the TDC marking (none of the other barrels had the TDC marking, and the other one I had the FSB off of did not have a counter bored gas port):  Here is another example with the M & S stamping, photo courtesy of Victor:  Another one. This one also has a W stamp, but in a different spot then the above example:  photo by Model_One Another C in Square:  photo by Model_One This one has a M1 stamp, something not found on any of the others:  photo by Model_One As noted in TBR (THE BLACK RIFLE) the Model 601 was chambered differently then later Colt rifles. These barrels are chambered with significantly shorter leade/throat then was used from the Colt Model 602 through current production. With the exception of the bottom barrel these gauge a 0 with my commercial T/E gauge. 602 and later barrels gauge a 1.25 when new with this same gauge. The bottom barrel exhibits significant throat erosion, so it's T/E reading is not relevant to the topic. Top three barrels are turned to the same outside diameter as was it's replacement the Model 602, and the later 603/604/SP1/etc. These barrels are all around .575" in diameter in front of the FSB. Bottom barrel is around .565" in front of the FSB. TBR indicates that Colt increased the diameter of the AR-15 barrel beyond ArmaLites original specs. Based on the barrels I have inspected it is apparent that this change occurred during Model 601 production, meaning the bottom barrel is of earlier manufacture. Considering the earlier vintage of the bottom barrel it is safe to conclude that gas ports were originally counter bored, and that this feature was later dropped. While the standard 1/14 .224 barrel twist was quite successful in commercial firearms it did not serve the AR-15 well. M193 ammunition utilizes a boat tail projectile rather then the more common flat base. Boat tail bullets have less bearing surface to engage the rifling of the bore then flat base bullets of the same weight. The result was that the 55 grain FMJBT bullets were on the edge of stability when fired from the AR-15. Because of these factors accuracy problems plagued the Model 601 and a twist change to 1/12 was approved July 26th, 1963. Tgus was kind enough to share some pictures of the barrel on his approximately 10,000 serial numbered 601. This is one example of a 1/12 twist Model 601 and it's barrel markings:   Model 601 production ended in 1963 and was replaced by the Model 602. For the sake of comparison the Model 602's barrel was stamped with the Colt Verified Proof marking. This was a VP in triange and was placed betweent he legs of the FSB on the right side:  To differentiate the newer 1/12 twist from the former 1/14 Colt stamped a 12 about an inch from the muzzle. This was done on 602 barrels and on later rifles and was replaced by a C (chrome chamber) stamp in the Fall of 1967:  The three top 601 barrels in addition to the 602 barrel and early 603/604/SP1/etc have a mirror image C stamped at the TDC of the barrel extension. The earlier 601 pictured at the bottom lacks this stamping. Have info/pic on another that is stamped M1. Need to get with the owner to posts pics, or maybe he will jump in........ |
 Where do you guys find those?? More importantly..where do you guys find the left side green handguards!?  Still only have the right side and my barrel/upper are gonna be on their way soon.(using a 1966 1/12 twist barrel..I know, I know..it's not a 601 barrel but I cant find one and I dont have unlimited funds for this rifle..it's as close as I can get with my money. Smooth FSB, roll-pinned bare steel swivel, etc) |
A stash was recently found at KY Imports, details here: www.ar15.com/forums/topic.html?b=3&f=123&t=300554 The other two detailed were purchased off Ebay, back in the day.
Take a close look, there are no green left side handguards pictured. I took the picture in such a way to make it look like they were there. Left handguards are very rare. |
Think it'd be worth it to try to get one from them? Or is it just luck of the draw and I'm more than likely to get a regular upper? |
Can't give up that easy. To find something rare you are going to have to pursue it, as with any other hobby. Try and find a rubber coated AK74 buttplate, when you do let me know how many decades that took, hehe. |
LOL yeah. Well of course I'll still look but it's not the highest thing on my list of things to get for this 601 anyway. Who knows, maybe I'll get lucky on egay someday. 
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Thanks a Million EKIE! As always an outstanding piece of work. It does not happen very often but I do get lucky on a rare occasion, and thanks to Scottmon I got real lucky and scored those (3) 1/14 601 Barrels. Based on my conversations with KY Imports that was a 1-Time find, and I bought all of the 1/14 Barrels that they had, so no more for now, but I will keep checking back. I still have not figured out how those Uppers came about? All 3 of those Barrels were on 603 / Forward Assist Uppers which makes no sense. I could understand a 601 Upper rebuilt with a newer 1/12 Barrel, but I don't understand why someone would put an old 1/14 Barrel on a new Forward Assist Upper? Thanks again EKIE for sharing all of your outstanding work, and thanks again Scottmon for the great tip. "Capt Richardson" |
Maybe someone less informed than us on such matters had a bunch of barrels and uppers laying around and put them together and some just happened to be 1/14" barrels? |
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