Bolt is not returning to battery

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Bolt is not returning to battery

Postby mcurbo » Sun Mar 18, 2018 2:18 pm

Hello. I am admittedly new to this, so bear with some less than intelligent questions or descriptions. I know there have been some issues with getting the 450 BM to feed reliability. I bought 3 mags off of ebay that was "supposed" to be for the 450, 458, and 50 BW. I haven't had enough range time to confirm that theory, but the limited experience I have with them makes me believe they are feeding correctly. I went through 63 rounds my first day I took the gun out and the only problem I had was with a couple of failure to ejects. Playing with the gun, I noticed the bolt does not seat well into the feed ramps and I assume that might be some of my problem. I looked at my other guns, and they will seat regardless of the travel of the BCG, but the 450 BM will only do it if I really pull the charging handle back and let it snap back. I may be barking up the wrong tree, but I wanted some of you more experienced guys and gals to chime in. I called myself greasing the BCG pretty good and focused on the bolt after what I saw it was doing. Can I polish the teeth on the bolt, or should I just hope it wears in with use? Thanks in advance.
Mike
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Re: Bolt is not returning to battery

Postby Texas Sheepdawg » Sun Mar 18, 2018 2:36 pm

Welcome to the group. I will just say that it may need some break in time. There is a way to lap the bolt to the barrel but I will let more experienced folk field that option.
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Re: Bolt is not returning to battery

Postby Texas Sheepdawg » Sun Mar 18, 2018 2:38 pm

You may also consider completely disassembling the bolt and extractor to see if any debris is hung up under the extractor. That will make for an overly tight return to battery
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Re: Bolt is not returning to battery

Postby Bmt85 » Sun Mar 18, 2018 2:56 pm

Who is the manufacturer of the upper, or if it's a build, what parts were used?

When you ran it the first time out, would the bolt stay back on an empty mag after firing the last round?

Are there marks on the rims of the fired brass from the extractor?

It sounds like a new build or upper. Some can be tight and require a little more break-in. I wouldn't grease anything. Strip the bolt carrier, degrease it, then oil the crap out of it, and shoot it. I would also degrease the upper receiver, barrel extension, and barrel. Just make sure you remove any oil in the chamber and barrel before you shoot it again. I always run new builds wet for at least the first outing, usually 2 or 3 though.
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Re: Bolt is not returning to battery

Postby mcurbo » Sun Mar 18, 2018 4:39 pm

WOW! Thanks everyone for a quick response. The upper is a Radical Arms. I realize it is cheap, but I liked the price and I wasn't fully committed to the idea of a big caliber. As far as marks on the rim from the extractor, I can't say for sure. Again, I am new to this. I have shot a lot of rounds over the past few months through other uppers, but they have all been steel casings and I had no reason to look at them. I am thinking about trying to reload the 450 BM, so I actually have my spent rounds to look at. They all have a mark on the rim, but it is more of a black mark rather than a deformity in the brass. I did notice considerable cuts in the casing from the feed rails (I assume), but I can't say for sure about the rim and extraction. As far as the bolt-hold-open, I only had one instance when the bolt did not stay open when the magazine emptied. As far as the grease, I can definitely degrease it, but I was using EWG grease which I was under the impression was just a heavy lubricant. Again, I realize everything on YouTube is not correct, but it was recommended for new guns...

Thanks again for everyone's help,
Mike
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Re: Bolt is not returning to battery

Postby mcurbo » Sun Mar 18, 2018 4:43 pm

Forgot to address the dirty bolt option. I tore it completely down before I fired it and again lubed it with EWG. The BCG was unbelievably rough/scratchy when I first took it out of the box. Most of that has resolved, but I still think the return to battery should be better...
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Re: Bolt is not returning to battery

Postby Hoot » Sun Mar 18, 2018 8:22 pm

Black phophated finishes are notorious for taking a while to slick up. That's one of the reasons that nitrided bolts and carriers are so popular. Well, that and easy cleanup. The same applies to barrel extensions. All you can do is keep on shooting them wet with lube and wiping off the displaced phosphate and powder residue slurry after each time out. Some members have resorted to sitting watching TV or whatever else they do with disposable time and hand cycling the bolt repeatedly. A lot cheaper than each cycle costing you a round. Some actually dope up all the mating parts with JB Compound or one of the other bore cleaners containing mild abrasives and then hand cycling. It accelerate the displacement of the phosphate on mating surfaces. The caveat there is thoroughly cleaning all the abrasive off when you're done. The latter method will break in an upper in one evening at the price of a really anal cleaning job afterward. I'd go as far as not double, but triple cleaning just to make sure. Don't forget in between the gas rings! Ideally, you'd take them off before starting but they're PITA to get off and back on. ;) Then there's "The Meltdown" using a Dremel and some Cratex rubber tips. That's a lot more attention to detail and Dremel manipulation, but ultimately the fastest method, not including waiting for the Cratex tip order to come in the mail. Lots of them available on Ebay. As unlikely as it seems, putting rotary abrasives in your action, its pretty hard to overdo it with them, provided you have A cool hand, A keen eye and Horse Sense.

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Re: Bolt is not returning to battery

Postby mcurbo » Mon Mar 19, 2018 6:26 am

Thanks Hoot for the very thorough reply.
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Re: Bolt is not returning to battery

Postby Bmt85 » Mon Mar 19, 2018 4:17 pm

I looked up the specs for Radical's 450B, and I'm curious about a couple things. What length barrel did you get? I noticed that it says the 20" barrel has a rifle length gas system. If you have the 20" barrel, and it indeed does have the rifle length gas system, I think we just found your problem. If not, then we will figure it out.

It says your BCG is melonite, so it may take a bit more to break in, if it's tight. Keep an eye on the gas key screws. I have a .223 upper from Radical (couldn't pass up the deal), One of the things I noticed is that the staking on the gas key screws isn't great. So far mine has held up, but I don't have many rounds through it. Seems to be common with their uppers, and some have had them work loose. Not too common, but still keep an eye on them.

I would ditch the grease for now, and run oil. Even if its hoppes. As Hoot stated, your going to remove it and add it a few times. After it's running, then try the grease.

One last thing, they state they have a 1:14 twist. That's way more than needed.
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Re: Bolt is not returning to battery

Postby Texas Sheepdawg » Mon Mar 19, 2018 5:09 pm

Bmt85 wrote:

One last thing, they state they have a 1:14 twist. That's way more than needed.


Totally agree. That’s a pressure event waiting to happen. Unless you’re sending 200 Grain bullets or lighter.
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