Bear Creek Arsenal 450 Bushmaster Upper Feeding Issues

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I slapped my new best Creek 350 upper on an aero lower, added a scope and a 5 round mag from the manufacturer bear Creek recommends and went shooting. At 100 yards with a solid field rest I got 1.5 inch groups with ball and 170 grain hornady interlocks. So far, so good.
The issue is feeding from the mag. At first it jammed every round. After a mag or two it got better, but about half the time it would feed the first two or three rounds and then hang up. I fired 50 rounds total, so this could just be a matter of needing to be broken in. What else should I be looking at to troubleshoot this?
Is the bolt riding over the cartridge? Is the hitting the ramps and stopping? Is the cartridge jamming at an angle going into the chamber?
Need more detail how it's jamming. Most AR feeding issues are magazine problems
Seems to be jamming at an angle going into the chamber. I would have bought CMMG mags, but Bear Creek specified ASC mags as preferred.

Last edited: Jul 31, 2020
Check the feed ramps on the barrel. BCA can be a little rough there.
OK, what am I looking for? What do I do? Dremel?
Just check for jagged edges, sharp spots, anything the bullet could be catching on. If there appears to be anything that would cause issues, email BCA & get a return authorization. They may turn out some barrels that would be better used as tomato stakes, but their customer service is excellent
In today's environment I must say I am kind of reluctant to return it. Who knows when or if I will get one back? I will have a look. The upper shoots really well. Inch and a half groups from a compromise caliber at 100 yards with a field rest and a mil spec trigger on the lower is a lot better than I expected.
@troy fairweather any tips for this gentleman?
Get rid ot the ASC mags and get Magpul, Okay and Colt mags
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Ks5shooter Contributing Member
How about cmmg? This cartridge requires specific mags, not standard 556 ones.
Reading comprehension! I missed that this upper is a 350. I have no experience with this caliber. My earlier advice is for ARs in 5.56 and it goes without saying, it doesn't apply in this case.
All the ASC AR mags I've used had problems. Others have reported problems with ASC AR mags as well, especially the ASC mags that came with the S&W MP10.
I did a bit of research. It looks like 300 Blk mags can be modified. Here's what Wilson says- https://shopwilsoncombat.com/AR-Style-Magazine-350-Legend-15-Round-Polymer-Lancer/productinfo/TR-350LMAG15/
Here's a YouTube video. Haven't had a chance to watch it myself, I gotta run down to the hangar and swap batteries in one of our helicopters-

CMMG mags might work
Ya I'd double check the feed ramp, polish the underside of the mag lips then it not do some tweaking to the feed lips. I still don't think they have the age 100% yet. I think a 223 May may work with 2 or 3 in it.
OK, so I finally got this rifle out to test again. I bought some CMMG mags to see if the quick, easy fix would work. With FMJ ammo, it fed flawlessly. With the Hornady 170 grain interlocks it hung up agout every 5th round. The Hornady has a noticeably longer OAL and an extended pointy tip compared to the ball, so I suspect that the length/shape of the bullet may be hanging up. A shame because they are extremely accurate. I may try the 160 grain Federal fusions and see if they do any better. I have been impressed with the accuracy of fusion ammo in other cartridges.
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Demi-human maybe likes firearms a little bit…
For an AR, magazines are, an expensive, consumable. If it don't work, throw it away.
Or since they're brand new, sell them or give them away to a friend.
Or bend the lips a smidge more, fill them with metal shavings and give them to an enemy.
I had the same problem you did with my Bear Creek Arsenal 350 Legend barrel. To be fair it wasn't assembled by them, it was just their barrel and bolt. Several different mags and I had the same issue as you even with the same Hornady ammo. First thing I did was grind down the front of the mag a little and round that edge off. It helped some but to get mine feeding 100% with any ammo I've shot I ground and polished very judiciously on my feed ramp effectively turning the ramp into one very large angled ramp not 2 small ones with a hump in the middle. I would first suggest reaching out to BCA and let them deal with it if they aren't helpful then bust out the dremel.
At this point, I am looking at toting this thing in the field as soon as September 2, so I am not messing around with it any further. The Hornady shells are purely hunting ammo and will be a low round count proposition for me. I don't think I have ever fired more than two rifle rounds at any big game animal, so I will live with it for this season. After big game season is over I may use the rifle with FMJ for shooting beavers (a 22LR is NOT enough for a 40 pound animal with a massive skull) and it cycles those just fine. My wish list for this thing is an upgraded trigger (probably a Larue single stage) and a feed fix, but it will have to wait at this point. Complicating all of this is that I am staying away from crowded ranges and as soon as any big game season starts it is illegal for me to be walking around in the woods to sight in with any centerfire rifle over .23 caliber.
While I agree that mags are usually the source of AR feed issues assuming there is enough gas to lock open on the last shot, mis-matched barrel feed ramps and uppers can cause the issue too.
See: https://www.thehighroad.org/index.php?threads/about-ar-feed-ramps.812232/#post-10389926 for a nice photo showing the differences.

Seems these mismatches become more common during supply shortages.
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Demi-human maybe likes firearms a little bit…
I thought that was a requirement for larger than thirty caliber bullets, especially those that are not spire pointed.
My 450 Bushmaster has a single feed ramp receiver and barrel extension.
One still set for .223 would definitely put the kibosh on larger bullets.
At least you can hit the woods, @brewer12345.
That was exactly my thought too. Difference is that the 450BM is a single stack mag and the 350 Legend uses double stack. Maybe that's why they stuck to an m4 style feed ramp.
I did see where CMMG 350 Legend barrels have a single feed ramp and people say their CMMG uppers work so I copied that design and applied it to my BCA barrel. It works 100% now.
I don't have any experience with the 350 legend, but my experience with other AR calibers leads me to believe a standard m4 feed ramp would not work well for a 350 legend. If I got a barrel with m4 ramps I would enlarge them with a 3/8" egg shaped carbide bit.
Buy yourself a CPD mag for the 350 Legend & your problems will go away. Most people don't realize they can't use a normal mag with the 350 Legend.
If you go to grinding on your barrels feed ramps you may void your warranty.
I hope this helps me. I just tried my new 350 upper from BCA and it is a jammomatic. It will not feed and the bolt will not lock back on the last round either. I emailed them, and they asked me to send it back to them. We will see.. I tried a modified Pmag and the DuraMag that came with my Ruger bolt 350. I did order another Duramag just to try too.