Durability of the Carbon Fiber AR-15

[lukemayo]

Hey guys, I have just purchased a Bushmaster AR 15 from Buds (.223/5.56). I am very pleased with this rifle, however, I heard from the dealer when I picked it up that I had to be careful with certain types of ammo since it was carbon fiber and sometimes it explodes under certain pressure. My question, if this is something I should be worried about, is what kind of ammunition should I be steering clear? And, has anyone had this happen to them? Only the lower is made of carbon fiber.

Thanks.

 

[LJ-MosinFreak-Buck]

Well Carbon Fiber is said to be as strong, or stronger than steel. Other than that, I couldn't tell you.

 

[blackDdefense]

I would not worry to much about ammo exploding the weapon. If it is just the lower that is carbon fiber shoot all you want. The only concern I have heard of is the longevity of the lower at the pins (trigger pin, hammer pin, take down and pivot pin). Keep a watchful eye and see the the holes start egging out after long periods of time and lots of rounds fired. For the average user, it should be fine. I would like an update after you have shot it for a long time to see if my theory is correct.

 

[Bartholomew Roberts]

The part of the AR15 that contains the pressure is the barrel extension/barrel. Anything that escapes that is likely to do a number on the receiver whether it is aluminium or carbon fiber, so I wouldn't worry about "exploding" too much.

One issue that has popped up in the past with carbon fiber receivers is the nose of FMJ rounds poking small holes in the receiver underneath the feed ramps of the barrel extension and eventually leading to feed issues. My understanding is that Bushmaster solved that issue a while back though and it is mainly an issue with the early Professional Ordnance labeled ARs.

 

[451 Detonics]

This is the common failure point of these rifles...the weight of the bolt slamming into the barrel is just plain tough on the locking ring area.

 

[lukemayo]

Thank you for your feedback. As always, this website is very helpful!

 

[kwelz]

Bad idea. Just saying something is stronger doesn't really tell the whole story. There is no question that an weapon can be made out of a number of materials. Steel, Aluminum, Carbon Fiber, Polymer, etc. However that weapon generally needs to be designed with that material in mind. I would buy a SCAR or ACR all day long because they were designed with that material in mind. I would never buy an AR made out of these materials however.

 

[lukemayo]

Not really sure what you mean kwelz. Are you saying the only material in mind when they thought of the AR was a metal?

 

[4thPointOfContact]

At the time the Armalite Rifle was designed, yes, the only material they had in mind was "7075 aluminum" there weren't any suitable polymers in widespread use at the time.

Now days, you could plug in the 3D printer and have a lower produced in a matter of minutes, although I still wouldn't trust its long-term durability if the dimensions were directly translated from aluminum to ABS plastic. I'd at least want thicker dimensions in all walls and probably aluminum bushings for any pins.

 

[kwelz]

Correct 4th. You have a different design philosophy when using different materials. Polymers for instance can be just as strong but are also more flexible and wear easier.

 

[451 Detonics]

Also the name Carbon Fiber is rather misleading as it is not made from carbon fiber but is a polymer with random carbon fiber threads in it.

 

[scythefwd]

carbon has better tensile strength than steel, BUT it doesn't handle shock nearly as well as steel or AL.

 

[chris in va]

Good point about the carbon reinforced polymer vs carbon fiber.

 

[G.barnes]

Carbon fiber is as strong as steel if it's real and good. Real and good are expensive. You can make a decently strong carbon fiber for cheaper but it's not the same. It's like thise car hoods the one for 400 dollars fall apart in a year or two and one that lasts is 1300 dollars.

 

[Greenmachin3]

As someone who has worked with carbon fiber on a daily basis, I can tell you that the bushmaster isn't carbon fiber but carbon reinforced polymer. Technically, carbon fiber is a carbon reinforced polymer, because the polymer is the resin, but that's another story. The bushmaster isn't what you'd call CF

You see carbon fiber at the very pinnacle of manufacturing in automotive and aerospace, why? Because it's that good. In Formula 1 racing it is used for just about every part including the driver's crash box and HANS device. In next gen fighter jets it's used in load bearing areas etc. It doesn't fatigue like steel and especially not like aluminum. You can literally bend a piece of CF over and over within tolerances and it won't show signs of fatigue. The problem? It's very expensive. Extremely expensive. ~$75 a yard for dry CF with resin separately, $160+ per yard for pre-preg depending on the weave and thread count. That's not including autoclaves vacuum pumps, etc.

If you did a layup of carbon fiber to make an AR receiver with the appropriate weaves and thread counts in the right directions with the right layering it would be quite an expensive piece. However, it would be a strong as steel at a fraction of the weight. You also would see failures in aluminum and steel receivers well before CF receivers.

The biggest problem with CF is cost and speed of manufacture. Even with the latest resins and autoclaves, it takes a few hours for a layup to be cured enough to use as a part. BMW just spent $100s of millions developing a way to mass produce finished CF parts inexpensively because they eventually want to build entire cars out of the stuff at a lower price than using aluminum and steel.

Rant over about that.

Would I buy an ar-15 with a plastic upper, even if it's glass, kevlar, or carbon reinforced? No. I would go the standard route and lighten the gun in other areas.

 

[Gordon]

Well I bought my first Ca. Legal non registered AR last month. It was a Bushmaster Carbon 15 with a sealed mag bottom and it has the forward assist and uses standard AR lower parts. I milled open the mag well, giving it a nice wide bevel AFTER I put a bullet button on itand I blocked a Magpull 20 round mag to 10 rounds. It IS Kali legal though and because of the bullet button option allowing lots of S&W and other off list guns in lately only paid $500 for it . Some one had put a float GG&G railed fore end on it! but it was unfired. I like the 16" plus Izzy brake 1/10" barrel for M193 and varmint loads for my .223s.
I detail stripped it and put an extractor mod kit in , staked the carrier with my tool, and staked the stock ring after putting on a GG&G single point adapter and an H-1 buffer. It had a decent trigger pull and everything looked ok in the lower. I decided to go light and put a C-More railway on it I got for $199 with a 4moa dot on e bay. I put an Israeli made foregrip with a mechanical activation of a 3 cell Surefire plastic LED light for another $99 from Israel. It came with a decent BUIS . I have only run 200 rounds thru it when I sighted it in and I got 2" 100 groups after sighting in at 25 yards I ran some fast 10 shot strings of the 55 grain ball at the end to see what happened when it got hot. I only had one FTF in the first mag load and it ran like the energizer bunny for the other 199 shots.
I have 4 legally registered AR preban AWs so I got this one in an effort to get something real light I would not have to keep locked up and not supposed to share here in Ca. :scrutiny . All the women seem to really like the sub 7 pound weight -loaded, and the C more seems VERY easy to get on target for the newbies.
So bottom line, until my Bushmaster Carbon 15 has a failure as pictured above I will enjoy it as my 'trainer' AND as a VERY lt weight CAR $800 with all the good quality bells and whistles.