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Posted: 8/25/2004 10:52:44 AM EDT
[Last Edit: 9/11/2004 6:45:59 AM EDT by jdgiii]
I have read the FAQ's and have not found an answer to my specific problem. So here's my sob story:

I have recently completed my first build (HOOAH!). Fired 250 rounds UMC 45 gr FMJ (including barrel break in) with no issues. Went the range yesterday, fired @ 60 rounds Q3131A no probs. Then it went to s$#&. Had a ftf. The round was dug into the land in the back of the feed ramp, leaving two crescent shaped gouges in the round. I removed the magazine and the fubar'd round. When I slapped the bolt release it happened again. This time I pulled the charging handle all the way back, released it and the round chambered. The problem then began occurring at least every other round until I quit fooling with it. I took the weapon home and thoroughly cleaned it. I then tried each of my 15 USGI 30 round mags and my usgi 20 round mag. they all had the same result. FUBAR'd rounds. I even tried using different ammo to no avail, as well as tightening th mag catch a couple of turns. No luck. Below are the particulars on my carbine Help!!

RRA flat top upper
RRA lower (no m4 feed ramps)
OLY 16" heavy contour barrel
USGI bolt and carrier
A2 stock, buffer, spring
plain (as in no rails) freefloat hand guard
standard FSB
Link Posted: 8/25/2004 10:53:55 AM EDT
I have had the same problem from time to time and it is always the mag. Put a new spring and follower in them.
Link Posted: 8/25/2004 11:28:42 AM EDT

Originally Posted By jdgiii:
The round was dug into the land in the back of the feed ramp, leaving two crescent shaped gouges in the round.

Do you mean that the bullet tip struck the flat below the barrel ramps in the extension and setting the tip back into the case,

Or, the bolt is slipping over the top of the round (grabing the round after the rim), wedging the bullet tip into the barrel extension, and the bolt climbing over/past the rim and the bolt lugs denting the top of the case (bolt stuck on top of the case with the bullet tip in the barrel extension.

These are two different types of feeding problems, and if we can narrow it down, problem solving will be a lot easier.
Link Posted: 8/25/2004 2:52:30 PM EDT
The round tip is going straight into the ramp and catching in the slots(?) where the bottom two lugs fit. Its doing it on both ramps. The slots where the bottom lugs on the bolt fit seem to have sharper edges than the ones that I've seen pictures of in the AR-15 area.
Link Posted: 8/26/2004 8:03:55 AM EDT
Tried new spring and follower on one mag. No change.
Link Posted: 8/26/2004 8:17:29 AM EDT
Are the feed ramps causing the damage to the cases (tip in the barrel extension, and the bolt against the back of the rim),

Is the bolt causing the dents to the case (climbing over the rim and denting the sidewall of the cases, such as the bullet tip in the barrel extension, and the bolt resting on top of the case)?

Link Posted: 8/26/2004 9:31:27 AM EDT
Link Posted: 8/26/2004 9:42:56 AM EDT
The bullet tip wedges in slots for the locking lugs in the bottom of barrel extension, and the bolt is not resting on top of the case. The bolt is behind the casing like it should be.

Miller, Yes this was with an entirely different mag.
Link Posted: 8/26/2004 3:20:39 PM EDT
High, NEW Guy here. I don't mean to highjack the thread but my problem is much the same. Model 1 sales 16" upper flat top. olympic lower with model one sales guts. The bolt is landing on top of the round and grabbing the side of the case, IN my case Happens with the second round out of the mag regardless of mag choice. The gun is still under 50 rounds total use.
Link Posted: 8/26/2004 5:31:20 PM EDT
I had the same exact problem with three uppers about three months ago. Because the barrels were new Bushmaster barrels, Bushmaster gave me an RMA # and they corrected the problem by lowering and polishing the feed ramp area, thus removing the sharp edges that were gouging the bullets.
Link Posted: 8/26/2004 7:20:10 PM EDT

Originally Posted By Bowhntr6pt:
I had the same exact problem with three uppers about three months ago. Because the barrels were new Bushmaster barrels, Bushmaster gave me an RMA # and they corrected the problem by lowering and polishing the feed ramp area, thus removing the sharp edges that were gouging the bullets.

I was thinking that this might be an option to correct my problem. Thanks.
Link Posted: 8/27/2004 12:45:50 AM EDT

If your having problems with the left hand round out of the mag (second on a thirty round USGI mag) with the bolt climbing over the top, then you have something out of spec. The left hand side of the mag is the catch side, and would be considered the higher side of the mag (the right hand side can cant down due to play in the mag well slot). My guess is that the upper is sitting too high off the lower, the catch is holding the mag too low, or the lug on the left hand side of the bolt is not cut correct. Since I'm MIA in Vegas, mic the distance from the top of the bolt catch to the top of the lower receiver, and post the results. Tweak has the measurement committed to memory; so hopefully, he can chime in with the correct dimension.

To trouble shoot the problem, you may have to swap the mag catch or swap the bolt to see if this corrects the problem using correctly working USGI mags. As a band aid, you might want to get your hands on few SA80 mags, since the catch slot on these mags are known to be milled lower which hold the mag a little higher.

Link Posted: 8/27/2004 12:51:18 AM EDT
I just re-read your first post, and the light bulb over my head finally light up.

Fired 250 rounds UMC 45 gr FMJ

A while back in one of the other forums, some of use went round and round on the M-4 ramps. Since I'm one of these people that tend to hand load some strange configurations to shoot in the rifles, the ramps assisted the longer and shorter than 55 bullets tips in correctly feeding in the barrel threw the feed ramps. On the standard bullets, the length of the Mil tip bullet hits the feed ramps and is feed up correctly, but when you go shorter or longer, the bullet tip has a tendency to hit below the standard feed ramps as they come out of the mag and is either stopped ordeflected with jaming.

When the surfaces of your lower were NIB, this held the mag slightly tighter and higher, but as the rifle started to break in, the mag began have some play and sat a tad lower. In essence, the shorter than standard bullet tips are striking the flat below the feed ramps, and if you check the upper area just below the feed ramps, you will find bullet tip strikes to that area.

The quick resolution would be to just fire 55-grain tips, but like me, this is not a pliable solution. A better solution would be to M-4 the feed ramps (lowering the starting point of the ramps), which allows correct feeding threw the wide variance of bullets that are offered in .224. My guess is that if you get RRA on the phone and discuss the problem with them, they may be able to add the ramps for either little or no charge to you. Also, I'm not a fan of bending mag lips up because this weakens them, so I don't see this as a solution to the problem.

Note: The M-4 ramps are proprietary to Colt, and since they seem to be a little sue happy regarding other manufactures even just using the M-4 name, no one is out right posting that the M-4 ramps are being offer on thier rifles . Instead, the ramps are being cut by hand at latter dates to resolve feeding issues on a need to install basis, and are simple referred to as smith feed ramp improvements. Although this may sound like Colt being petty, the fact is that the M-4 contact is the only thing keeping then alive in the Military market. FN is the new M-16 producer, and had not Colt been awarded the M-4 contract, my guess is that they would have once again been in bankruptcy. The problem that they currently face is that this stay of execution is short lived, and unless they come up with a new proprietary deal to offer, FN will be the demise of them after there proprietary M-4 contract sunsets.
Link Posted: 8/27/2004 1:32:01 AM EDT
Dano thanks for the input. I didn't have a problem with the 45 gr fmj, the problem started with the Q3131A. I don't know how this will change your theory. I'm going to take my rifle back to the amorer who helped me with the build and see what he can do. Thanks again for the help, have fun in LV (Lost Wages). Joel
Link Posted: 8/27/2004 1:38:36 AM EDT
Link Posted: 8/27/2004 1:44:56 AM EDT
Sorry, no digital camera yet. There are no ramps cut into the upper and the ramps on the barrel extension end before reaching the barrel extension/upper seam. It just occured to me that I may need to contact Oly since it is their barrel.
Link Posted: 8/27/2004 1:58:57 AM EDT
My guess is that they look nothing like this,

[G35's feed ramp improvement work]
Link Posted: 8/27/2004 2:12:12 AM EDT
[Last Edit: 8/27/2004 2:13:03 AM EDT by jdgiii]
They look nothing like the picture. They are what I understand to be regular feed ramps. Thanks for all of this help by the way.
Link Posted: 8/27/2004 9:49:56 AM EDT
I just dropped my carbine off with the armorer who helped me build it. I will give a full report of how my problem is resolved when I get it back. Hopefully it is something simple.

Thanks again to all who offered input. It's guys like you that make this such a great website. Later, Joel
Link Posted: 8/27/2004 12:57:54 PM EDT
Depend on the age of the barrel, you may be able to blame Tweak for the problem (he used to work for Oly).

Good to hear that you have someone that can look at the rifle as a complete unit, instead of parting it out to send back to different suppliers. Too many times you get them pointing fingers at other parts that they may not have supplied.
Link Posted: 8/27/2004 3:35:10 PM EDT
Top of Bolt Catch (ramp at hammer face) to upper receiver .2265 Top of Magazine Catch to top of receiver .6975. Thank You for the help.
Link Posted: 8/29/2004 7:14:07 AM EDT
Dano, that is an outstanding photo of your barrel extension. Would like to know how you took it, BTW. A comment on the so-called M4 feed ramps. It is a good idea to make sure that you follow the general plan of ramping the 1911 when you work on your AR. The ramp surface in the upper, if cut that way, should be slightly rearward of the extension ramp; that will leave a small gap or jump between the 2 pieces that prevents bullet nose from digging in. To accomplish this feat, the barrel needs to be taken off and ramped separately from the upper. That's the only way to do it right.
Link Posted: 8/29/2004 11:26:31 AM EDT
G35's work and photo, I just borrowed it,

As far as the ramp goes, yes both the upper and the barrel extension are done, and not just the upper. But unlike the 1911, the barrel extension is a fixed unit to the upper, so they could be ramped as a single unit (milled in a single pass, then polished). On the true M-4, there is a step between the barrel extension and the upper. The whole idea is to just lower the start point of the ramp so a low feed round hits the ramp, and not below it.

Unlike a 1911 set up to hand cycle wad cutters, as long as the tip hits the ramps, the case will follow (no concern of the upper mouth of the flat lip case hitting high and vertical binding.).
Link Posted: 8/30/2004 4:27:11 PM EDT
We haven’t forgot about you.

Do you have access to another Mag catch, and Bolt?

If you can borrow the two from either another rifle or some one else rifle, it will allow you to see if the current ones in the rifle the problem or not.

As for the receiver it's self, the bottom of the mag catch slot should be .9375 +/- .0035 from the top of the receiver, and the slot it's self should be .250 +/- .004.
Other dimensions that you may as well check are the two pivot hole locations to confirm that they too are within spec. Here are the specs for the lower,
(You will need to down load adobe reader to open them)

If the receiver checks out, then it's time to either find a new mag catch to hold the mag higher to solve the problem, or sending the complete upper back for replacement. M1 sales are not a FFL, so forget about sending them the whole rifle to allow them to find the out of spec part(s).

On the upper, there could be a more than a few areas’ that could be out of spec.
To name a few,
The carrier could have too small in diameter, which cause the bolt to ride too high.
The center line from the pivot lugs to the center line of the carrier passage could be too much which causes the entire upper to sit too high off the lower.

Bottom line since the bolt is riding over the top of numerous mags is that the mag is being retained too low in the rifle. The quick solution is to figure out how far higher the mag needs to sit higher in the lower to get the bolt in the right position, and find a mag catch to correct the problem. The correct solution is to break out the mic, and find the components that are out of spec, and replace them with the correct parts.


(Speak mode) Since we as the builder of the rifle are actually the smiths, then it is our responsibility to fit and function testing the rifle. Granted that the parts should be within spec from the supplier, but that would only be in a perfect world. Time and time again, we often see posts of how numerous rifles are assembled in a few minutes, and for the most part, function from the start. On some suppliers, you end up paying more for the parts, but have a better chance of the parts working together as a system. If the game plan was to build a rifle for the least amount of money possible, then often this requires more work than just dropping it parts, with that being to confirm that the parts will work together as a system. The reason that I use the word system, it that in fact, the only true mil- spec part for the AR-15 rifle is those parts that can be used on both the military M-16 rifle and the AR. From there, it's just of matter of following what Colt designed for the semi auto rifle parts (SP-1). Fact is that some suppliers maintain these standards better then other, and should be one of the considerations of which you buy your kits/ parts from.
Link Posted: 8/30/2004 5:05:10 PM EDT
G35 should get an award for that photo - I am completely impressed. With a little computer animation you could get the cartridge-eye view of being chambered and fired. Anyway as far as ramps go, the general idea is not reserved for a particular type or shape of ammo. Whenever 2 separate parts come together to form a mechanical ramp, there is the possibility that the bullet somehow will dig in right at the margins no matter how smooth both parts are made. In order to prevent digging in, you simply create the ramp with a small step so the bullet nose cannot touch the critical area at all. I just use the 1911 example because that's how they are all made (at least the ones that feed correctly).
I'm sure that your polished feed ramps work beautifully, and that you can feed a wider range of ammo in that gun.
Link Posted: 8/30/2004 8:42:02 PM EDT

Originally Posted By Dano523:
My guess is that they look nothing like this,

[G35's feed ramp improvement work]

nice ramps ya got there
Link Posted: 9/1/2004 10:48:32 PM EDT
I'm afraid that I'm having the same type of trouble with my M-16. I have a M16A1 Colt lower that has been converted back to semi only by removing the auto sear and selector switch. My department issued me a 11.5 inch A2 upper that I am unable to advise the manufacture. It had quite some rust near and around the gas tube and barrel extension that I had removed by a trained gunsmith. The stock was switched with a RRA 6-postion stock and a Tango Down battle grip was installed. I was having problems with the rifle failing to extract/eject spent rounds but I placed a D-fender o-ring in the extractor spring and now it extracts great. Now, the problem is that some rounds are striking the feed ramp and its pushing the tip of the bullet into the casing. My gunsmith advised me to junk the upper and get a new one but due to my department's lack of available funds for such a trivial matter as a patrol/duty rifle, I can't do that.....yet. Would polishing the feed ramps help? By the way, this problem (ftf) occurs mostly with 55 grn fmj ball but 62 grn fmj works well (or atleast better). Any ideas? Thanks.
Link Posted: 9/1/2004 11:07:48 PM EDT
Link Posted: 9/2/2004 1:55:09 PM EDT
There are no markings on the upper that I could find. My gunsmith had no idea who's upper it belonged to either. It came with no bolt or carrier. I used the bolt/carrier from my M-16A1. I was told if I changed the gas tube to a pigtail it would make the gun reliable. How would a Colt barrel help? Thanks for the info.
Link Posted: 9/2/2004 2:22:49 PM EDT
Do you have a telescoping (carbine) buttstock ? If so, you might want to try a heavier buffer.
Link Posted: 9/2/2004 7:26:14 PM EDT
Okay, I used a buddy's Colt M-16A1 lower that had a heavier buffer installed and it ran through 2 mags (28 rds each) with one malfuction which was a fail to feed with the right side shell being lodged/jammed into the lower part of the upper receiver just a frog hair from the feed ramp. I cleaned the weapon and there is some wear on the metal below the feed ramps. My gunsmith stated that he has heard that barrels under 11.5 had problems but that 11.5 should be fine. My tactical team leader feels confident that the gas tube is the one to blame. I will get to the range with some new ammo asap to try again but I have urban rifle school next week and I NEED a reliable rifle. Once again, thanks for all the input and advise.
Link Posted: 9/2/2004 10:24:56 PM EDT
Link Posted: 9/3/2004 12:15:58 AM EDT

The defender works at this point but sorry to sound like a dummy but were does one get power springs for the extractor? Please keep in mind that this rifle is a M-16A1 on a form 10 that belongs to a police department. I can advise my team leader as to what I feel is right to do with the weapon as far as repairs or modifications but I don't have the last word. Cost is also a issue in that the M-16s were basically given to us by Uncle Sam (thanks!). We had to spend a portion of our initial funding just to convert the rifles to semi only and the "mystery" upper was "found" in one of our weapon lockers just collecting dust. We have two new M-4s but the remaining rifles are vanilla M-16A1 and so, too bulky for entry use. If the 11.5 is worthless, I'm back to square one not to mention back to my HK .45 but I feel that if I can get the right information/advice, maybe I could salvage the upper and have a entry rifle I can depend on. I have a budget but its not very large ($200 max) so the things I need have to come before the things I want (surefire, eotech, etc)
I have no tools as to work on a AR nor do I feel confident on working on a department's already malfunctioning upper. Based on this info, can the upper be made to function 99.99999 percent of the time for under $200? to answer your other questions, I have access to my Sgt's M-4 so I can make the class and Lt. T. Earnhardt is the instructor (local class but great instructor!). Thanks!
Link Posted: 9/3/2004 4:21:43 AM EDT
[Last Edit: 9/3/2004 4:26:08 AM EDT by Tweak]
Link Posted: 9/3/2004 6:00:10 PM EDT
Thanks for the information and time. So, I need some slapping around huh?he
Link Posted: 9/4/2004 2:29:37 AM EDT
Link Posted: 9/4/2004 10:49:34 PM EDT
Link Posted: 9/7/2004 10:57:38 AM EDT

Thanks for all your help. I got your email and forwarded it up my chain of command. I have no idea when or even if it will be approved. I'll let you know asap when the word from on high comes down. In regards to the 20" uppers, would it be more cost effective to purchase new 14.5 barrels and switch out or just trade in the complete uppers? As of right now, all our rifles fuction with the exception of mine (of course!) so I'm the only one complaining (as if that ever works). I'll give you a call when they make a deceision. Later.
Link Posted: 9/7/2004 3:21:18 PM EDT
Link Posted: 9/7/2004 6:06:15 PM EDT
[Last Edit: 9/7/2004 6:09:25 PM EDT by dmuldrew]
Link Posted: 9/7/2004 9:46:34 PM EDT
Link Posted: 9/11/2004 6:50:55 AM EDT
I had my gunsmith take a look at my carbine. It turns out that the buffer spring that I put in the weapon(bought the A2 buttstock assembly used offf of the EE) was a weaker power than standard. He also polished the feed ramps a bit. It runs like a singer sewing machine now. Thanks again for all of the input and assistance. I guess this can be a word to the wise to check out what you are buying off of the EE. Especially if you are using the weapon for duty.

Link Posted: 9/11/2004 9:33:54 AM EDT
I informed those who make important deceisions and they agreed to have the upper "looked at" by another gunsmith. The feedramps were polished and I returned from the urban rifle class yesterday. I had my team leader's M4 on standby but I had zero malfunctions through 750 rds of 55 grn fmj. If the weapon fails again, I'll let you know, but at this point, it works. Thats all they need to know to end this debate. Thanks for all the assistance and information.
Link Posted: 9/11/2004 11:31:40 AM EDT
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