View Full Version : M4 Feed Ramp Issue
I finished the assembly of my new lightweight midlength AR-15 yesterday, but I might have an issue. The upper receiver (Spikes) and the barrel (Daniel Defense) are both cut for M4 feed ramps. I was cleaning out the chamber and noticed that the barrel M4 feed ramps look like they might overhang the upper receiver M4 feed ramps. Sure enough, when I run the tip of a paperclip up the ramps, it catches on the left side and almost catches on the right side. So now I know why my Colts appear to have the ramps cut after assembly. At this point I'm past figuring out which part isn't correct (if any). What I need to know is how to remedy the situation. I'm guessing that I have to grind a bit, but I don't want to take off too much and I certainly don't want it to look like Bubba did the job (which is a strong possibility if I don't have the correct tool and directions). Your input to help me solve this issue is appreciated.
BTW, here's my new rifle.
http://s11.postimg.org/q60bdbbz7/Spikes_Zombie_Midlength_left_view.jpg
http://s11.postimg.org/cntf10ztv/Spikes_Zombie_Midlength_right_view.jpg
I learned a bit along the way, so that's always good. It has Spikes upper and lower receivers, a Daniel Defense CHF lightweight midlength barrel, a YHM flash hider, a BTE .625" receiver height adjustable gas block, CMMG lower parts kit, Aim's NiB bolt carrier group and a Magpul stock set. The front end is very light, especially for a midlength.
This is in the wrong section... but this is the reason for choosing quality parts. Quality parts will all be built to spec and will go together without these kinds of issues. I bet the feedramp issue is in the Spikes upper, not the DD barrel assembly. DD is known for quality, in-spec products. Spikes not so much.
Have you had any issues with feeding? Either way, definitely keep the grinder far away. I'm sure it will be fine how it is, but if it were mine, I would replace the upper to prevent something bad from potentially happening.
Wrong section? The Custom Build Forum seemed most appropriate to me given that I custom built this rifle for myself. If there is a more appropriate subforum, I'm all ears.
Regarding the quality of the Spikes upper, I know that I found zero cosmetic flaws with it, but there is most definitely a noticeable cosmetic machining flaw near the muzzle of the Daniel Defense barrel that should not have gone past QC in my opinion. For $225 I figured that I could overlook it. I'm not saying that cosmetics translate to dimensional correctness, but I'm not pointing the finger at Spikes given the machining that I've seen. Regardless, I'm sure I'm not the first to find himself in this situation. Help fixing it would be appreciated, not the you should have bought this, had soandso build it, or just purchased a factory built $2000 rifle kind of second guessing.
Have you cycled rounds through the chamber yet? That should tell whats going on if anything. Take pics of the problem area.
Wrong section? The Custom Build Forum seemed most appropriate to me given that I custom built this rifle for myself. If there is a more appropriate subforum, I'm all ears.
Regarding the quality of the Spikes upper, I know that I found zero cosmetic flaws with it, but there is most definitely a noticeable cosmetic machining flaw near the muzzle of the Daniel Defense barrel that should not have gone past QC in my opinion. For $225 I figured that I could overlook it. I'm not saying that cosmetics translate to dimensional correctness, but I'm not pointing the finger at Spikes given the machining that I've seen. Regardless, I'm sure I'm not the first to find himself in this situation. Help fixing it would be appreciated, not the you should have bought this, had soandso build it, or just purchased a factory built $2000 rifle kind of second guessing.
It says in the title of the forum 'Custom Build Forum': "Show off pictures and specifications of your latest project". You would get proper response under the AR Technical Discussion section.
Anyways, there really isn't a fix other than to replace. Be it the barrel or the upper, if the issue is bad enough, something needs to be replaced. I don't care who builds it, if a part is out of spec, it's out of spec, whether it's DD, Spikes, etc. Most would lean toward Spikes being the problem though since DD has such a great track record. I would call both DD and Spikes to see what they say. I can't speak for Spikes warranty, but DD is top notch.
Most likely it is just fine. Post some pics of the problem area.
depends on how much overhang you a looking at? If it is slight, then the Dremel or Foredom may be your best choice. Very careful cut and polish to match. If it is more pronounced then a new upper receiver may be indicated? Close up pictures may be helpful?
Here's a picture. I had a hard time getting it to focus, so it's the best I could do.
http://s8.postimg.org/41z7fp0et/Spikes_Zombie_M4_Feed_Ramps.jpg
I'll try to get some time over the next couple of days to test the feeding, extraction and ejection.
SeriousStudent
09-02-14, 22:18
Moved to the appropriate sub-forum.
Judging from the picture, it doesn't appear to be an issue unless you are having feeding problems. If manually cycling the rifle checks out, then try live fire testing.
My level of knowledge is not to the point where I can give you any advice about feed ramp issues, but I can tell you that your ironsights are currently installed backwards.
I'll just make sure that I'm looking through them backwards when I shoot the rifle. Seriously, I just took them out of the package and stuck them on for the picture. Not that they're in any way complicated, but I obviously need to learn how they work.
I'll just make sure that I'm looking through them backwards when I shoot the rifle. Seriously, I just took them out of the package and stuck them on for the picture. Not that they're in any way complicated, but I obviously need to learn how they work.
I would also look and see if you have a special gas block because Troy makes a rail mounted front sight and a gas block mounted front sight and I'm 99% sure you installed a rail front sight on a gas block. Zeroing will be an issue with that setup, unless your gas block is at rail height??
I would also look and see if you have a special gas block because Troy makes a rail mounted front sight and a gas block mounted front sight and I'm 99% sure you installed a rail front sight on a gas block. Zeroing will be an issue with that setup, unless your gas block is at rail height??
The BTE gas block that I installed is rail height. It was very difficult to find a 0.625" rail height gas block. BTE's was the only would that I could find at a reasonable price. It's definitely the same height as the receiver because I timed it by turning the rifle upside down to rest both it and the receiver top on a flat surface.
http://bte-usa.com/images/product-pictures/gas-blocks/bte-rec-ht-gas-block.jpg
http://bte-usa.com/parts/receiver-rail-height-gasblocks.htm
Although I have not had a chance to shoot the rifle yet, from everything that I've seen I'd recommend the BTE gas block.
Ned Christiansen
09-04-14, 09:00
Well if there's a step there may not be an issue but there is certainly a potential issue. It's not as it should be-- the compatibility between barrels and receivers with M4 feedramps seems spotty. If it were me I'd give it the old Bubba grind but that's not for everyone especially when you have carefully selected and painfully paid for what you thought ought to be a good combo.
I monitor two AR's that have M4 uppers and non-m4 extensions, so there is an overhang of more than 1mm, and in several thousand rounds there have been, to my surprise, no feeding issues. They'll get fixed eventually but until then they are a running experiment that sofar has told me that maybe the whole M4 feedramp thing is not a huge part of M4 reliability.
Run a bullet tip up the feed ramp. If there's hesitation, you have a "clicky". If it feeds correctly, and gives you no issues, you may decide to ignore it. A number of things could cause it, but there are only two fixes...replace receiver or barrel until they fit together right, or alter the feed ramp on the barrel.
If you choose to fix it, understand that feed ramp geometry is what it is for a reason, and if you do it wrong, it may ruin the barrel, the receiver, or both.
If you have the extension ramps hanging over the receiver cuts NEVER try to cut the ramps with the rifle assembled. You will never get the hesitation removed, and you will remove the feed ramp anodizing. You must measure or mark what needs to be addressed while it's assembled, then do your modifications with the barrel out. You may polish with a dremel and a cratex wheel. Polish ONLY with a dremel--no cutting, unless you are a dremel GOD.
I did some hand cycling and it seems to feed fine. So Ned, as you've suggested, it might not be an issue even though it's obviously not right. I took a look at an AR15 that I built about eight years ago. It has a Stag upper receiver and a Sabre Defense M4 barrel. It has an overhang that's actually worse. However, the rifle has been 100% reliable. I took a look at a couple of factory built Colts that I have. The metal at the M4 ramps is unfinished, so it appears that Colt cuts the ramps (or at least polishes them) after assembly.
At this point I'm not going to disassemble it to resolve the issue unless it proves unreliable during actual live fire. Thank you everyone for your input. BTW, the sights are now oriented correctly. I'll let ya'll know how it shoots.
556BlackRifle
09-05-14, 11:33
Shoot it and report back. I've seen this before and it's never been an issue.
At this point I'm not going to disassemble it to resolve the issue unless it proves unreliable during actual live fire. Thank you everyone for your input. BTW, the sights are now oriented correctly. I'll let ya'll know how it shoots.
Take the firing pin out and carefully rack a few new live rounds through it. Then inspect the cases and bullet tips. Look for deformation of the bullet tip and scratches. If anything looks out of the ordinary act accordingly.
Shooting it will tell you if there is an immediate issue. Put about 200 rounds through it. Change up ammo, and magazines. Try using the magazine as a vertical grip also as a test. You want to test to make sure the geometry of the magazine under stress does not choke the feeding. Be reasonable. If it doesn't choke you are probably OK.
If you cannot stand it the way it is I would follow the advice of the SPQR476. Disassemble and use a Cratex wheel to take it down slightly. There are Cratex wheels that are just about exactly the size to fit into the ramp so you will be less likely to deform it. Caution is the word on that.
OR you could buy a nice BCM M4 upper from Grant.
JBecker 72
09-05-14, 12:19
Don't tell someone to remove the firing pin from a carrier and then cycle rounds. That's how you get a cam pin cocked sideways and a locked up rifle.
Don't tell someone to remove the firing pin from a carrier and then cycle rounds. That's how you get a cam pin cocked sideways and a locked up rifle.
That is probably true. I forgot to tell him to insert a piece of solid 12 gauge copper wire (with insulation off) to hold the cam pin straight. I use a firing pin with the end cut off. Thanks for the correction.
JBecker 72
09-05-14, 14:03
That is probably true. I forgot to tell him to insert a piece of solid 12 gauge copper wire (with insulation) to hold the cam pin straight. I use a firing pin with the end cut off. Thanks for the correction.
No worries, just didn't want to see someone lock up their rifle. I've seen at least 3 threads on TOS in the past few years when guys took the firing pin out not knowing it's what holds the cam pin in proper alignment.
Dremel that smooth and you won't have to worry about. Just be careful. The steel is harder than the aluminum.
If you've never used a rotary tool before don't learn on your rifle now! Get some practice on something you care less about..
Don't tell someone to remove the firing pin from a carrier and then cycle rounds. That's how you get a cam pin cocked sideways and a locked up rifle.
I have much more experience with AK's than AR-15's. With an AK it's not as easy to remove the firing pin, but once you do you can hand cycle without fear of popping off a round. I don't like the idea of hand cycling cartridges through an AR-15 with the firing pin in place. What do ya'll do to eliminate the possibility of a slam fire?
What do ya'll do to eliminate the possibility of a slam fire?
Dummy rounds. That's the surefire way to cycle a round with no potential discharge.
Will filing the tip off of a firing pin work or with that cause some other sort of problem?
JBecker 72
09-13-14, 15:37
Will filing the tip off of a firing pin work or with that cause some other sort of problem?
That would work, but again, it's not a good idea to hand cycle live ammunition. Just get some dummy rounds.
OK, any suggestions for which ones work and hold up best?
JBecker 72
09-13-14, 16:18
I have some from Magpul that work very well.
I have some from Magpul that work very well.
I have the Magpul dummy rounds too and they do hold up well. I've worked on a lot of old milsurp rifles, and I always make sure to have dummy rounds for function checking. Same goes with modern rifles too. The wrong firing pin protrusion on an old bolt gun could really mess up someone's day if not checked. A lot of old milsurps have been Bubba'd on, and I don't take the risks that Bubba would.
This may sound like a stupid question, and it may even be slightly off topic, but would there be any issues by the opposite situation to the OP's?
i.e. The receiver feed ramps being further back than those of the barrel extension?
I wouldn't imagine this being a problem, but do not know for certain.
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