AR15 jamming issues, assistance requested!!

[jeffC]

Added this question to a thread in the general section, but got no response, so I'll try here, and ask for some assistance. Having a tough time with a recent build, so I'm looking for ideas. Having to re rack almost every round.bullets are getting hung up on feed ramp area. When they do make it into chamber, I can see a good amount of copper sheared off the bullet by the feed ramp, and bullets come out with scratches on them. Also, when clambering using charging handle, if I chamber even a wee bit gently, it will get hung up. I know it's proper tactics to let it rack with full force, but all other ARs I've handled have never got hung up by doing this. Any suggestions. I suspect the lower may be too low, and the mag isn't reaching the height the upper was designed for. It's a custom build, so it's a mutt. Ay and all suggestions will be greatly appreciated


ETA: parts list for those interested
remsport upper
troy bolt assembly
daniel defense barrel
roggio arsenal lower ( I know, bad reviews, but it's what I've got)
different magazines
dmps lpk

pics are of feed ramp, and also what it looks like when the jam happens

 

[mac1911]

1. Try different mags
2. Different ammo
3. Use the lower on another known good upper
4. Use know good lower on suspect upper
I have assembled a few real mutt jobs with used parts ectect. Seems like every other build a bad magazine shows up or ammo?
If all else fails tear it down and inspect each part and compare to a know good rifle. Try to find something that just don't look right.

 

[noxin]

Interesting. I'm having similar issues I originally thought it might be the mags failing to load in all the way.

Are you able to get any to rounds to work? Mine works for the first three or four then wont feed.

 

[dbott63]

As mac1911 stated, it is likely the magazine. Are you using 30 rd prebans? If so have you changed out original springs? I had a couple of mags that would barely feed the first round without jamming. I replaced the old spring with Wolff extra strength springs and no more issues.

It doesn't look like the feed ramps are jacked up. The other thing I would check is the buffer spring / buffer combo. Are they new? The buffer spring may be too weak to properly push the BCG into battery.

 

[jeffC]

I've tried three different mags, one old and two brand new with same results with all. Also, I've fired this with two completely different stock setups on it, one rifle and one carbine, with the same results.

 

[OnTheRoad]

It doesn't look like the feed ramps are jacked up. The other thing I would check is the buffer spring / buffer combo. Are they new? The buffer spring may be too weak to properly push the BCG into battery.

Have a look at the gas tube as well, make sure it's not loose or obstructed. One other thing to check (this one baffled me for awhile once): be sure the buffer is able to travel back its entire length into the tube when the action cycles. I had a build on an A2 style stock and the screw from the back of the buttplate into the buffer tube was a bit too long - the buffer would hit it in its way back and prevent the rifle from fully cycling, causing very similar symptoms.

I'm sure you've checked that the BCG is not binding and is well-lubed.

 

[dbott63]

I've tried three different mags, one old and two brand new with same results with all. Also, I've fired this with two completely different stock setups on it, one rifle and one carbine, with the same results.

Well that eliminates the usual suspects. Have you tried putting the upper on a lower that you know cycles fine usually?...and vice versa with the lower? I have no experience with the lower you used, but like you said, it could just be seating the top of the magazine too low.

 

[jeffC]

No I haven't tried any other uppers or lowers yet. That'll be my next objective on my next range trip. If it IS seating the mag too low, are there any cures for this besides finding a new lower that fits?

 

[dbott63]

No I haven't tried any other uppers or lowers yet. That'll be my next objective on my next range trip. If it IS seating the mag too low, are there any cures for this besides finding a new lower that fits?

Unfortunately I don't think so. I'm not an expert by any means but if the mag is seating too low that means the lower is out of spec. You would probably end up having to scrap that lower. You could always hang onto it to use for one of those 50BMG uppers with the upper mounted magazine assembly.

Someone smarter than I am may come along with other options for you. If the problem ends up following the upper it could be the feed ramps on the barrel....to steep maybe?

 

[KMM696]

It's tough for me to tell from the pics - is there a step up in the feed ramps where it transitions from receiver to barrel extension? It doesn't look bad in the picture, though. Upper/lower swaps on your next range visit will certainly narrow things down.

If the lower is out of spec, and not sitting the mag in the right spot, yeah, you're kind of screwed on that lower. It would mean the cuts for the mag catch assembly are in the wrong place. It's not impossible to fix, but the shop time involved in making an oversize mag catch and cutting the lower to match is not at all cost effective for a common item such as an AR lower. Easier and cheaper to replace it - if the lower is the problem.

 

[atilla]

i also can't quite tell--run your finger along the feed ramps... if you feel anything other than smooth, you're probably going to have to work that out.

 

[Supermoto]

i also can't quite tell--run your finger along the feed ramps... if you feel anything other than smooth, you're probably going to have to work that out.

I agree, looks like the m4 ramps on the receiver are over cut. The sharp edge could be shaving the bullet

 

[Billsail]

I agree, it looks like there is a lip where the barrel meets the receiver. In the second (blurry) it looks like the bullet was stopped at that point. If that's the case, maybe you can get to it with a fine tip Dremel grinding bit to smooth it out a little. Go easy.

 

[jeffC]

Ok, so after a battery of tests and trials, I've decided that the bcg is scraping the hammer, and slowing down the motion to the point where it's not having the power to rack another round. What I've got it there now is a cheap-o dpms lpk, which included the trigger assembly. Can anyone suggest a hammer that is known for being a little more low profile, for situations like this?

 

[Maximus Slade]

I have seen this failure before. If you still haven't fixed it, pull out your carrier group and check that the carrier key (the dohig on top of the BCG) is mounted tight and bolts staked.

A buddy of mine bought a brand new Stag. He put a mag or two through it and it started to jam up like that. We tried swapping mags, ammo, and buffer tube. We pulled out the BCG and found that the carrier key was loose and binding the whole assembly causing the group to fail to travel fully.

 

[Billsail]

The rearward motion of the BCG resets the hammer back to the "cocked" position. It has to scrape the hammer to push it into position. If it is making contact with the hammer in its forward travel, it is more likely your lower is out of spec, but still possible your hammer has too much height. If you decide to trim off some height, remember you will be reducing its weight, thus reducing the impact on the firing pin. Most likely it won't be much.

 

[jeffC]

Stupid ****ing Roggio arsenal. I should have researched this company before I bought it. Turns out they sold a ton of junk lowers then shut down shop, as to not be held accountable for the shit they produced. I'm gonna shave off a hair off of the hammer and if that doesn't work I'll just bite the bullet and buy a quality tried and true lower. Thanks for the info everyone. And it IS noticeably scraping during forward travel, to the point where the travel visibly slows down a small bit.

 

[Supermoto]

Stupid ****ing Roggio arsenal. I should have researched this company before I bought it. Turns out they sold a ton of junk lowers then shut down shop, as to not be held accountable for the shit they produced. I'm gonna shave off a hair off of the hammer and if that doesn't work I'll just bite the bullet and buy a quality tried and true lower. Thanks for the info everyone. And it IS noticeably scraping during forward travel, to the point where the travel visibly slows down a small bit.

The hardening on the hammer is very thing. I wouldn't reduce it

Did you take the hammer out and then it feed correct?

 

[Another_David]

Try this:

1.take the upper off
2. remove the bolt carrier group (BCG)
3. remove the bolt from the BCG
4. put the BCG back in the upper without the bolt
5. slide the BCG in and out of position

does it rub anything? It might "click" slightly as the gas tube inserts into the gas key but it's shouldn't stop completely

if there's an obstruction you may need to tighten the gas key and/or bend the gas tube into the correct position

 

[jeffC]

The hardening on the hammer is very thing. I wouldn't reduce it

Did you take the hammer out and then it feed correct?

I imagine you meant "thin". Which makes me say.... "Whoops"
i took off a minoscule amount of metal off the hammer with a dremmel, and polished up the area I worked on. I then cycled 30 rounds through it with much much better results. I'll have to take it to the range tomorrow or the next to be sure, but I think this may have done the trick.

 

[atilla]

if you end up needing a hammer, post or PM me... i MAY have one. i am not sure if i already gave it away though.

 

[MJ1]

It's what they do.