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Posted: 5/14/2007 10:28:22 AM EDT
| i _beleive_ that most alum uppers will no fin the carbon 15 lower. the clearances are not the same. You should give BM a call to find out for sure. I have a complete carbon-15. it is VERY strong and super lightweight. i love it. i recently had a little mishap, the buffer tube was bent. the threads on the tube broke, but the carbon fiber threads were fine. i was quite happy to only replace a buffer tube and not a whole lower. |
I've heard the same re: mixing carbon 15 and "normal" AR parts. |
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My first AR was a BM M-4 style Carbon-15. I had issues with it but eventually turned it into a dependable rifle. I wanted to turn it into a flat top and the cheapest route I found for that was a CMT upper delivered to my door for $99.00. I have 3 standard uppers that fit that lower just fine. The CMT, a Stag (CMT makes/is Stag) and a post 1974 Colt M-16 upper. They all fit and function perfectly. Where you'll find a problem is trying to fit a Carbon-15 upper on a standard lower. PS - The only advantage is the weight difference. If you're looking to build the lightest rifle you can then you can trim a few ounces off with one. |
What issues did you have? |
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I had a similar question, where I wanted to replace the barrel on mine. Here is their response. Bushmaster has changed the design and parts used to build the new Carbon 15 rifles and pistols. They now have 5.56mm chambers rather than the tighter chambers used before which helps with the extraction problems that were experienced before. The gas ports have been changed as they were oversized causing the systems to run too hard leading to cycling problems and had too much felt recoil. The gas blocks had overpressure bleed holes that are no longer needed with the correct gas port sizes. Buffer recoil pad has been changed so the pads do not come off under fire causing cycling problems. The new buffer pad also does not put excess strain on the charging handle when pulled to the rear. The old barrel extensions would not allow the use of an AR15 bolt. They now use standard AR15 bolts and modified barrel extensions as they were producing bolts and extractors out of the wrong material which was prone to breakage. The new barrel extensions do not allow the bullet tips to come in contact with the Carbon 15 material to eliminate feed problems. The lower receiver parts are now Bushmaster AR15 parts which are of a better quality than the aftermarket parts that were being used. On serial numbers 6200 and higher the upper receiver barrel nut threads were changed to the same as the AR 15 type barrel nuts so AR type barrels with modified barrel extensions could be installed. The POI firearms and lower serial number Bushmaster upper receiver used a larger diameter barrel nut thread. Upper and lower receivers have added material for strength. The forends are now ribbed. The buttstocks have an added rib at the bottom. The 21S and 97S models now have threaded barrels for AR15 type flash suppressors and muzzle brakes. The upper and lower receivers will now interchange with AR15 receivers so there are more options available to shooters. It does require that the same bolt carrier and buffer system used with the lower receivers be used if interchanging upper or lower receivers. For example if you place an AR15 barreled upper on a Carbon 15 lower you must use the shorter bolt carrier and buffer system. If you place a Carbon 15 barreled upper on an AR15 lower you must use the longer AR15 bolt carrier. Other upgrades and options are on the drawing board and will be announced when they are available. |
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Most of the above information sounds like it was written shortly after BM took over the bankrupt Professional Ordinance and started making changes to the Carbon 15 line. The PO units used a different bolt, carrier, barrel extension and I'm not sure what other non-standard AR parts.(Probably springs and buffers,too.) I bought mine in 2004 after the ban and by then it was an all standard AR parts rifle. As far as the current lower (mine included) you can use any standard LPK in it. I took the barrel assembly off the Carbon 15 upper and installed it on a CMT flat top upper. I'm using the same bolt and carrier from my Carbon 15 in the CMT upper. The current rifles can use all the same parts as an aluminum AR. Some of the parts such as the takedown and pivot pins as well as the safety selector are plastic (polymer, carbon 15 or whatever) to further lighten the rifle. I replaced my safety selector with a standard one because I didn't like the look of the plastic one. Like I said in my previous post, I can slap any of my uppers on the Carbon-15 lower and it fits great and functions perfectly. I tried the reverse of trying to fit the Carbon upper to a standard lower and it's not going to work without some filing or modifying here or there which I have no intention of doing. I'll probably eventually reassemble the whole rifle with a superlight barrel but that's low on my priority list at this time. Someone in a previous thread asked about the issues I had and how I corrected them. The feed ramps on the barrel extension looked nothing like the feed ramps on my other AR's. Maybe it was a transitional type of feed ramp style they were trying on the Carbon rifles. I don't know. That was 2 1/2 years ago and I haven't looked at the feed ramps on any others since I bought mine but I dremeled mine to look more like a traditional feed ramp. That seemed to do the trick and she's been running good since, especially in the new CMT upper. |
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