Mag and feeding problems

Talk about the AR15 style rifles chambered in 450 Bushmaster.

Moderator: MudBug

Mag and feeding problems

Postby Sesshoku » Fri Feb 07, 2014 11:29 am

Guys, I need to ask for a bit of your expertise. First things first, I'm new to the .450BM, and I'm new to the AR platform, but not new to shooting. So I'll have to ask you to pardon any incorrect terminology.

I have four magazines. Two of them are the Bushmaster factory 5-round mags, which actually only hold four rounds. The other two are ASC 9-rounders that I just picked up from Franklin Armory. I cannot get a single round to feed into the chamber from any of the four of them. I'm also having problems with brass extraction, but I'll get to that in the another comment.

Last week, I field stripped, degreased and used Froglube on everything then took my new 450 to the range for its first shooting session. I tried the factory mag and couldn't get a round to chamber. I looked over the mag and it appeared the half circle they cut in the front of it needed deburring because it looked like the neck of the brass caught up on that. So, I opted to load each round by hand by locking the bolt back, dropping a round in the chamber then releasing the bolt. I looked over the other factory mag and it was the same way. The ASC mags were not as bad, but I couldn't get any rounds to load from them either.

I have since used my Dremel tool and deburred the magazine fronts and ground a bit of a downward bevel into the half circle cut out, thinking that might help the neck of the round glide up into the chamber. I tried loading the rifle today and once again, I couldn't get a single round to load from any of my four magazines. So now my guess, after reading several posts on here about polishing the lips and possibly prying them outward, is the problem is with the lips. It seems like they are holding too tightly on the brass and not allowing the bolt to push them forward. Granted, it's not an educated guess, but I'm at a loss right now on how to make this rifle work. If any of you have any advice on how I can fix this problem, would you please pass it my way?

This photo shows how far (actually not far) the bolt pushed the round out of the mag before it stopped:

Image

Should the tip of the ammo be pointing higher up than this?

Image

Front view before trying to chamber:

Image

Top view before trying to chamber:

Image
User avatar
Sesshoku
 
Posts: 49
Joined: Thu Jan 09, 2014 8:35 am

Re: Mag and feeding problems

Postby Sesshoku » Fri Feb 07, 2014 11:46 am

My new issue is the brass not ejecting out of the chamber. Out of my first 10 shots that day, I had no problems at all. In the next 15 shots, however, 6 of them stovepiped and one failed to even get that far, jamming in the chamber. I attributed this to the very cold temps that morning (it was 15 degrees) thinking maybe my lube was gumming up. But then I started to wonder because I followed the directions on the Froglube and completely wiped everything off all the parts before I re-assembled the rifle. Maybe it was the cold, I don't know. But if that's the case, I doubt Froglube will work for buy intended application of deer hunting, because sometimes here in Indiana, the temps do drop considerably during the deer firearms season.

In any case, I came home and talked to a LE buddy of mine. He told me to check the bolt to make sure I reassembled it correctly. I checked the extractor to make sure I could move it, and I checked the ejector to make sure I could push it in. All seemed to work fine.

Here is a photo of the round that jammed:

Image

Aside from all the damn problems I was having, this photo shows my first 8 shots out of the new rifle at 50 yards. The first two were high left as I was just trying to get it on the paper. The next three were slightly high, and the last 3, well, those made up for my rough start to the day.

Image
User avatar
Sesshoku
 
Posts: 49
Joined: Thu Jan 09, 2014 8:35 am

Re: Mag and feeding problems

Postby Hoot » Fri Feb 07, 2014 1:34 pm

First off, polish the underside of those lips if there's much friction between them and the cases, it will slow down the stripping action. If you hand cycle the bolt forward slowly, as it strips a round,does the bullet or case still catch that circular cutout area? If so, lower the cutout a little further. An alternative approach would be to spread the front of the lips a small amount. That's once you polish those lips. When the rifle is new,it really pays to run the BCA wet until it polishes it's way into where it will ride for the next several thousand rounds. IE break that resistive parkerizing/annodizing coating. You can also just lube it up and hand cycle it over and over to break it in, but that's tedious. These rifles start out pretty stiff when they're new, but they break in over time. A lot of cycling problems, both going forward and extracting, lessen with wear. Mine was pretty crunchy when I first got it and now it's slick.

Here's a gotcha to watch out for:
Make sure your action goes far enough back so that the front of the bolt is picking up the case head, not the body of the BCA. I know this one from experience. Spent hours troubleshooting before it dawned on me that my buffer was bottoming out, not allowing the BCA to come back far enough for the bolt to pick up the case head instead of the body of the BCA. I had changed out my stock from an A2 to an A1 and the A2 butt screw which I reused was a little too long. The buffer kept hitting it, not allowing the action to go back far enough.

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
User avatar
Hoot
 
Posts: 3367
Joined: Tue Feb 09, 2010 9:34 am
Location: Minnesota

Re: Mag and feeding problems

Postby Sesshoku » Fri Feb 07, 2014 2:12 pm

Thank you for the help, Hoot. I will polish those lips this weekend and see if that helps anything. When I tried to load the rifle this morning, it did not appear that the front of the round was catching on the circular cut out, but rather, it looked more like the lips held the round at such an able that the bolt couldn't push it forward. When trying the factory mags, the bolt could barely move the ammo forward - maybe 3/8 inch. With the ASC mags (from Franklin Armory) the round went a bit farther before it hung up. It cleared the circular cut out but still did not make it into the chamber as it appeared to hang up on the lips. Here is a photo of the ASC mag after trying to load with it:

Image
User avatar
Sesshoku
 
Posts: 49
Joined: Thu Jan 09, 2014 8:35 am

Re: Mag and feeding problems

Postby helidude350 » Fri Feb 07, 2014 2:25 pm

I second hoot on the buffer situation .
I can't chime in on the frog lube, but if things are sticky, that will do it.
Maybe try 1 or 2 rounds in a standard pmag or plastic sig mag.
That would take the mag issue out of the equation .
Or single feed it and drop the mag before firing, taking the mag out of the equation.
helidude350
 
Posts: 394
Joined: Sat Sep 25, 2010 1:53 am

Re: Mag and feeding problems

Postby commander faschisto » Fri Feb 07, 2014 7:34 pm

Looking at your side view pic of the loaded mag, it sure looks like the feed lips are holding the rounds TOO nicely horizontal, thus causing the case mouth hang-ups. The feed lips should be opened (slowly and gradually) until the exposed round is in a slightly "nose up" position, just a couple degrees above perfectly horizontal. It is possible to go to far with this adjustment, and you'll have the mirror image of the problem, with the round missing the chamber to the high side and jamming. Try the search function on the site here; there have been several discussions early on of the adjustments needed for the mag feed lips. Basically, horizontal is too low, and will snag on the mag....too high of an up angle will miss the chamber mouth and jam at an angle in the receiver.
Isa Akhbar!
NRA Life Member
Oklahoma Rifle Association member

Heavily armed; easily pissed.
User avatar
commander faschisto
 
Posts: 1272
Joined: Tue May 31, 2011 6:32 pm
Location: Oklahoma City USA

Re: Mag and feeding problems

Postby Hoot » Fri Feb 07, 2014 9:48 pm

commander faschisto wrote:Looking at your side view pic of the loaded mag, it sure looks like the feed lips are holding the rounds TOO nicely horizontal, thus causing the case mouth hang-ups. The feed lips should be opened (slowly and gradually) until the exposed round is in a slightly "nose up" position, just a couple degrees above perfectly horizontal. It is possible to go to far with this adjustment, and you'll have the mirror image of the problem, with the round missing the chamber to the high side and jamming. Try the search function on the site here; there have been several discussions early on of the adjustments needed for the mag feed lips. Basically, horizontal is too low, and will snag on the mag....too high of an up angle will miss the chamber mouth and jam at an angle in the receiver.


+1 on the mirror image problem if they're over-expanded. More often than not, that is the way they came from the factory in the past. Perhaps they've gotten better at controlling that deviation. Polishing them actually affords a little relief in itself just from removing manufacturing burrs and whatever paint they use to coat them. The faster the round is able to be stripped, the more it is inclined to go nose up when it gets to the feed ramp. This brings up another possibility and that is polishing the feed ramp. I actually do that on every upper before the first round goes down the tube as a matter of general principle. Many that I've seen both for myself and others, have the same rough anodizing finish as the rest of the receiver, however some are already polished pretty good. I forget if the 450b has M4 ramps in the receiver or not without going downstairs and looking. That's the part that I'm most concerned about having a rough finish. The portion of the ramp in the barrel extension is generally pretty smooth, assuming they do not parkerize it.

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
User avatar
Hoot
 
Posts: 3367
Joined: Tue Feb 09, 2010 9:34 am
Location: Minnesota

Re: Mag and feeding problems

Postby dec » Wed Feb 12, 2014 8:12 am

So after having a perfect range session with my new 450BM and discussing the problems that sesshoku was having with him, I decided last night to go out and hand cycle a few rounds just to make sure everything was fine with my rifle. Right out of the gate, I was getting the exact same problem as he describes above, which again is odd because it was fine when I was shooting the other day. I right away was noticing deep scratches into the brass from the feed lips on the mags.

So I began "polishing" the feed lips on both of my mags and I removed the finish on the feed ramp and began polishing that. None of this helped. I lubed up the BCG very generously. Again, no help. I cycled and cycled and cycled the BCG by hand ... still nothing.

Finally I said the heck with it and got out a pair of needle nose pliers and began slowly opening up the feed lips on the mags, starting at the front end and working my way back to give the bullet a more nose up look. It took some serious tweaking, but after about 90 minutes of fine tuning, I got both mags to allow every round to be stripped as I let the bolt slam forward. They do not seem to miss high as they come out of the magazine as of right now. We will see after some more range time and things polish up on their own. I can always tweak them back down if need be. The weather has been brutal here and shooting time has been next to none. It is supposed to warm up tomorrow and I hope to get out and run some rounds through this thing again.

I did get one mag from Bushmaster that was fabricated too fat. It was so thick that even when empty it would not fall free of the mag well (a mag well that has had 1000+ rounds of .223 run through it). When loaded with ammo the mag expanded further and getting the mag out was a chore. I actually had to take a 4" grinder to both sides of the mag and remove about 1/2 the thickness of the metal just to get it to fall free when loaded. After doing that and adjusting the feed lips it is working properly.

I know this ... I am very disappointed that a $800 upper and $40 each mags must be "tweaked" to this degree and $200+ in ammo must be shot just to "break" all of this in. I'm all for breaking in and not shy when it comes to working on my own stuff, but this whole set up is the roughest out of the box gun that I have ever had. Very frustrating.
Derek Craig
dec
 
Posts: 23
Joined: Mon Nov 25, 2013 8:34 pm
Location: Ashley, Indiana

Re: Mag and feeding problems

Postby Hoot » Wed Feb 12, 2014 9:59 am

Mag spring tension can be a factor. This is a matter of personal preference, but I remove any excess lift tension that is not needed by removing turns from the bottom of the springs. I don't drop my mags in the soup and expect them to come up firing, so I use just enough tension to get the job done under the conditions I normally operate in. single stack mags have different needs as opposed to staggered ones. Just sayin'...

I don't recall having to mess much with factory mags as a matter of necessity way back when I got mine in 2010. Perhaps Bushmaster and/or their OEM have tweaked the design to yield greater profits. They are owned by an investment capital firm now. I did mess with mine as a matter of learning and experimentation. Aftermarket mags modified to work in a 450b are a different matter. They need a little more hand fitting

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
User avatar
Hoot
 
Posts: 3367
Joined: Tue Feb 09, 2010 9:34 am
Location: Minnesota

Re: Mag and feeding problems

Postby Texas Sheepdawg » Wed Feb 12, 2014 10:17 am

I ran into this problem back couple years ago, where the screw the screws into the back of the buffer tube that holds to stock on was about a quarter inch too long and it was creating the same problem except a little more severe. I could not even get the bolt to lock open. This was after a recent replacement of a limb saver but pad that came with a screw already included. It seems the screw was too long and the buffer was actually bottoming out, hitting the screw and not allowing the BCG to go back far enough to strip the next round properly plus it was not even allowing the BCG to lock open.
Also, from looking at your pictures, it seems that the lips on your magazines, the forward part of those lips seem to be a little too tight. I believe Hoot has you on the right path. And yes these uppers are pretty tight when they're brand-new so you may need to run the bolt carrier a little more wet than normal until it breaks in. What I used all my bolts during break-in was a lubricant called Dura lube and it seemed to be working very well for my 6.5 Grendel and also, (when it was brand new), my 450 bushmaster.
And yes, once again I agree with who that sometimes the magazines springs may be a little too tight. Some of the springs in the magazines have excessive compressed sections of springs down at the bottom of it. But the more I look at your pictures the more I'm starting to think that those magazine lips are little too tight at the forward end of the lips.
-Texas Sheepdawg
Join us on FaceBook https://www.facebook.com/groups/Texas.Sheepdawg.Patriots/
http://youtube.com/c/TexasSheepdawg21
NRA Life Member
Image
User avatar
Texas Sheepdawg
 
Posts: 3869
Joined: Fri Nov 05, 2010 10:55 am
Location: North Texas

Next

Return to AR15 Style Rifles

Who is online

Users browsing this forum: No registered users and 3 guests

cron