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Posted: 9/6/2026 9:20:46 AM EDT
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Having a nightmare with my 350 Legend specifically built for deer. Anderson lower with unremembered upper brand and BCG. BCA 16" barrel with pistol length gas tube with adjustable port block wide open. Gas port aligned with those plastic alignment thingies. Wish BCA milled a dimple for the bort block. Duramag 10 round 350 Legend mag. The first round chambers fine with the release. However, subsequent rounds fail to feed. The fired round ejects fine, but the next round only gets the nose into the chamber, jamming up the BCG. Needed a Carbine or mid length gas tube instead? Too much friction from the metal mag? BCG issue? Tired of messing with it. So I have 2 choices. One, BCA bolt action complete upper and eliminate the semiauto issue completely. Two, BCA complete upper semiauto and get everything dedicated and tested to work with the 350 Legend. Both are about the same price. |
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What buffer and spring are you using? I’d weigh the buffer and measure the length of the spring, then count the coils. I’d check the BCG for gas leakage. What magazines are you using? The rifle sounds under gassed but hard to say without more info. If the rifle is under gassed going to a lighter buffer and or recoil spring might help get it reliable. Sometimes an over gassed AR-15 can exhibit the same characteristics as an under gassed AR-15. An ejected piece of brass to 1-2 O Clock would tend to indicate being over gassed. I’d try loading the chamber with one cartridge in the magazine and see if the AR-15 cycles. It can be helpful to video the firing sequence to help identify the issue. The most common buffer tube length these days is carbine with a carbine weight buffer and spring. I’d make sure that I was using that configuration before testing again. |
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I should note that previously the AR was short cycling, not ejecting, and occasionally trying to ram the empty with a fresh round into the chamber. The buffer tube is carbine length with a 3 oz buffer. Spring is unknown. 40 winds of 0.071" wire marked in yellow. Tired of messing with it now, so looking at a complete and matched upper, either bolt or "full semiautomatic  ." I just want this working for deer season without wasting more time on it. And yes, it's properly lubed. |
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You can try the modified 350L mags from RRA. I had a 350 that was doing the same thing suppressed and unsuppressed. Tried an RRA modified mag and that fixed most of the problem. I know RRA changed the spring and did some minor matching to the front lip of the mags. |
" I don't sweat, I grease! " ~ FS2000Guy
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I looked at Bear Creek Arsenal web sight and only the 10.5” 350 Legend barrel use a pistol length gas system. The 16”, 18” and 20” barrels use a carbine length gas system. Everything I read indicates getting a 16” pistol length gas system can be problematic in 350 L. I think I would contact Bear Creek Arsenal and see if they will trade barrels. The gas port in a pistol length gas 350 Legend would be pretty large around .093-.108” if you aren’t using a suppressor. It sounds like the gas port is to small for a 16” barrel but most manufacturers that sell 16” 350 Legend AR-15 barrels use a carbine length gas system. I’m unsure what weight a yellow buffer spring is but here are a couple graphics which might help. AR-15 buffer spring lengths.  Ejection pattern graphic for AR-15.  |
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Originally Posted By VASCAR2: I looked at Bear Creek Arsenal web sight and only the 10.5” 350 Legend barrel use a pistol length gas system. It was purchased several years ago. I'm not seeing the barrel on my purchase list, so not Bear Creek. Will have to check out the manufacturer. |
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Originally Posted By RogueSpear2023: Bear Creek Arsenal is probably the issue. Unfortunately, this gets thrown around a lot. Unfortunately, I had the same/similar issue with a BCA complete upper. Tried 180’s, 145’s and 145gr ammo. I got sick of chasing the issue and time constraints led me to replace it with a cmmg barrel. Issues were resolved with no other changes. I’ve purchased 2 uppers from them. 1 runs great the other was the 350. From my experience you have a 50/50 chance of getting a good one.  Take this how you want. |
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Originally Posted By RogueSpear2023: Bear Creek Arsenal is probably the issue. Most every 350 Legend AR post regarding problems ends up being a Bear Creek Build... 350 Legend AR's can be difficult.... Have you tried a different magazine? DuraMags are normally solid...some people have had good luck with lowering the leading front edge of the magazine. Have you polished the feed ramps/bolt face and ejector ? 350 likes a very smooth feeding system. Some M4 feed ramps do not allow enough clearance.. Have you tried a H3 Buffer? That has cured a good bit of issues. Mos-Tek- https://mos-tek.com has a tremendous amount of experience with the AR 350 Legend.. it's been a few years but if you reach out to Aaron he can likely walk you through getting it running well.... I have had a SBR 350 from them for 6 years that runs like a top I know Facebook is frowned upon here...but there is several really solid 350 Legend FB groups where all of you issues have been sorted out.. |
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Originally Posted By panthermark: I thought the problem was basically trying to make a straight wall cartridge work in an AR. Needs a lot of TLC. 450BM has been around much longer than 350L. I haven't heard any similar issues about it. It may be personal lack of experience with either cartridge. I've had issues with 350L ejecting, however I think it's related to the Caldwell brass catcher I was using. I bought a Brass Goat clone and we'll see if the problem persists. |
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I'm going to try swapping BCGs with my 556 and some dry lub on the mag and see what happens. After talking to a local gun shop owner, issue might actually be the light weight 124 grain training ammo. After the swap and lube, I'll also try a few rounds of the 165 and 170 grain deer cartridges and see what happens. If that doesn't work, will wait till next year and swap complete upper and mags for 450 Bushmaster. |
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Don't have any pics but the extractor is a huge problem in feeding issues. The round is not slipping under the extractor and that is why the cartridge gets jammed up half way in. Try swapping bolts if you have extras. Or if you have any extras extractors laying around take them with you to try swapping them out at the range. But the pistol gas may be the whole problem. An adjustable gas block and heavier buffers will help to find out if this is part of the problem. The pistol gas was only meant for subs. Not supers. I have had 4 of these and all but the last one were fine. It was doing all of the common issues. After looking over the other guns I noticed the extractors on the other ones had a little more radius on the bottom. I threw in the whole bcg from a working gun and it solved it all. So I bought 3 new bolts and tried all three. They all worked fine. So that one bolt had a bad extractor. I swapped it out and now it too works fine. |
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I have 2 BCA 350L uppers, a 10" and a 16". Both work fine, but when 350L first came out, the not feeding properly was an issue. The most popular fix seemed to be the milling the magazine, I didn't want to do that. I found a little blurb somewhere that said polishing the BCA chamber seemed to fix most issues. I tried that on the 10" first and that worked like a charm, no mods needed to mag. I did that for the 16in and no issues, have done that for 2 friends 350L ar's. I used a .45cal bore mop, put some polishing compound on and used a power drill for bout 10-20 secs. No issues. My 16in is suppressed, no issues with sub or supersonic ammo. Cheap fix that seems to work. My 2c. SY |
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A straight wall cartridge like the 350L has a short dwell time. The gas port needs opened up. I have fixed several 350 ARs by going up one number sized drill bit. Only one required a second round of stepping up. Having done this every single one I have worked on runs fine with standard buffers and springs. The only one I have with a pistol length gas system is my 10.5 Mos-Tek and the port was already enlarged based on his testing. Measure what you have now, look up the conversion to the numbered bits and get the next one larger at Ace hardware. Even a cheaper bit is good enough for reaming out a barrel port once. I would always put an aluminum cleaning rod in the barrel first. You got this. Edit: I jumped on the bandwagon early with this caliber. I was successful in hunting and several of my friends started to switch to 350s as well. I have built several for myself and helped tune up about a dozen others so that is where my knowledge on this comes from. |
| I had a 357 AR Max before it was taken on by Winchester and they changed it to 350 Legend. I also had one of the very first 350 Legend ar uppers made. There was NO load data when I first had mine. We used 357 Max load data and used a combination of dies to load the 350l. We took factory made 145gr fmj rounds apart and loaded them our way. The whole thing with removing the front of the mag was a joke. It did nothing. The tip of the round never touches it, and once past the front of the mage to round touches the feed ramp and the case in the front never comes close to the lip of the mag. Polishing the extractor or beveling the edge of it is one of the main things that works. The other is getting the round to pop up out of the mag faster so the bolt can finish pushing the round in. Sometimes it is just a little tweek to the feed lips on the mag. Other times it can be just trimming them back a hair to get the round out of the mag fast. Other times it is all of it. You just have to understand how this round feeds and go from there. |
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