Improperly cut chamber? (Update - Range Report)

AR/M4 AR Technical Discussion
1

Hi All,

I have a S&W M&P15a that I purchased last month. I am having problems manually extracting live 5.56x45mm rounds from the gun using the charging handle (see my original post here https://www.m4carbine.net/showthread.php?t=37339).

After doing some more testing this weekend, it seems like the chamber on my gun might be too short for the 5.56x45mm ammo. My gun functions fine with commercial .223 Rem ammo. I do not have this problem with .223 Rem factory loads.

However, with my 5.56 ammo (Federal and Pvri), the cartridges are slightly longer (2.250" vs 2.210") and I often get stuck live cartridges which are difficult to extract manually.

The ejected live cartridges often have scratches on the FMJ bullet and now I’m thinking its due to a tight/improperly sized chamber/throat.

I had this problem once with a pistol that had a stainless barrel. The manufacturer took the pistol back and rereamed the chamber and the problem was solved. However, with my new AR, I have a chrome lined steel barrel.

What is the correct way to address this problem? Do I need a new barrel, or can a chrome lined barrel have its chamber re-reamed (then relined)?

Thanks in advance.

Cynergy

** Please scroll down to my post from 9/23/09 for an update on the gun **

2

We have had these allot at work. You can send it off to like ADCO and they can fix it. You can rem the chrome lined barrel and chamber. You can also send it off to the manufacture. There have been allot of company’s selling these barrels like this. Just improper machining.

3

Also i know that some might disagree but look at what feed ramps you have on there and what barrel extension you have also. If you mix match them in the wrong combanation it might have this effect. I have only seen it once but I changed the barrel extension and it work after that.

4

Dude the chamber cleaning had no effect? Don’t get me wrong it very well could be a tight chamber I am just trying to trouble shoot over the net I don’t have eyes on the problem. It is normal for the bullets to have scratch marks from being chambered my LMT leaves 2 scratch marks from just below the bullet tip to almost the crimp groove on the bullet it is from the barrel extension bolt lugs could this be the scratches that you are talking about?

5

Ned has a gauge used to check chambers I would check it before I would cut it.
http://www.m-guns.com/tools.php
S&W do not normally have this problem but it could happen just don’t want to jump the gun.

6

da fuck is this?

7

:confused: My LMT does not have mixed barrel extensions M-4 upper with m-4 feed ramps and M-4 barrel extension. scratched bullet everytime. No problem it is just the way it is.

8

cynergyou,

Had something similar happen, the thread is here:

https://www.m4carbine.net/showthread.php?t=33817

I wasn’t going to “live with it”, and I wasn’t going to pay someone to fix it since it is still under warranty. I contacted SW, shipped it back and they did several fixes on it. The details are in the thread, but I can tell you one thing, they re-worked the chamber! And they were a pleasure to deal with (FedEx wasn’t but that was another story).

My only suggestion is call them, don’t email them. Took three days for them to get back to me on email, which is not acceptable in the digital world!

9

Thanks Fellas for the replies.

Unfortunately, cleaning the chamber did not help. I cleaned the chamber twice before I went back to the range. At the range, I would chamber a round, then try to extract it manually. For the first couple of rounds from the mag, it was not too difficult to extract the rounds manually using the charging handle. However, after firing only a few (maybe 3 or 4) rounds the problem reappeared.

My rifle does have the M4 feed ramps on the receiver and barrel extension and they look like they are cut properly and are nice and smooth.

I will try to give S&W a call this week after the holiday and see what they recommend.

Thanks again for your replies.

10

Well, I ended up sending my gun last week to S&W. I received a call from a very helpful fellow in their long gun department. He was working on my gun. He was extremely helpful.

The fellow explained that he had inspected my gun and he and a coworker ran several mags of various commercial ammo through my gun without any issue. He ran a lot of .223 (mostly Black Hills), but also two different brands of 5.56x45NATO (XM193). He was not able to reproduce the problem. He and an engineer took some measurements, he checked head space (using a 5.56x45 NATO gauge) and everything looked OK.

He asked me to send some of the ammo that I was having problems (primarily Pvri Partizan) which I did. He received the ammo this week and called me today. He did a bunch of testing with my gun. He shot a mix of Black Hills .223 (to warm up the gun) and also my Pvri Partizan 5.56 NATO and was able to reproduce to some degree my problem. The gun operated properly during the semi-auto cycle, but he did notice that sometimes it was difficult to manually extract a round using the charging handle.

The fellow Dykem-ed some rounds and hand fed them into the chamber (to avoid scratching the Dykem on the feed ramps and dropped the bolt. He noticed some very light rifling marks on the bullet tip. He also measured my Pvri 5.56NATO and compared it to their 5.56 NATO and found the shoulder of the Pvri ammo to be slightly wider with a diameter that was approximate 2 to 3 thousandths of an inch larger.

Anyway, to resolve the problem, he rebuilt the upper completely using a barrel that had the chamber carefully flex honed. He explained that the flex hone tool is used to smooth the chamber out, and since it is such a very fine grit, it does not strip the chrome lining, it merely smooths the chamber and polishes it. He pointed out that all of their barrels receive a flex honing as part of the machining process. He also took the time to manually do the flex honing (the standard factory process is automated) to ensure that the chamber was smooth.

Afterwards, he tested the new upper and everything seemed to run smoothly. He was able to shoot through the rest of the ammo without any noticeable issues manually extracting the live cartridges. He was even able to run two of the test cartridges that I had sent to him that got stuck in my original M&P upper. These cartridges extracted properly when he pulled the charging handle and everything seems good as far as he can tell.

Anyway, I should be receiving my rifle withing a few days. I was really impressed with S&W’s customer service. This fellow was very patient and really took time to explain to me exactly what he did to check my rifle and what he did to remedy the problem. The turn around was pretty quick. The day he got my gun in, he started to inspect it and debug it and he called me a day later to update me and inquire about the ammo I was using.

I am looking forward to receiving my M&P back from the factory and I am fairly confident the issue has been resolved. The person who worked on my gun told me to make sure that I call back after I have had a chance to shoot the gun and to let him know if the problem looks resolved.

Thanks for everyone’s replies in this and my other post. I will update the board once I have had a chance to shoot the gun and run it through its paces. I am extremely happy with S&W’s customer service.

11

Glad it worked out for you. Sounds very similar to the fixes they did to my rifle. When they send it back to you they will include an invoice with a list of their fixes. Will you be so kind as to post that list so that I can compare it to the one I received?

I too was very impressed with S&W’s customer service. When a company makes a large number of any product (no matter the quality of the manufacturer or the parts used) certain pieces slip past the QC. Most if not all show malfunctions early on. In the oil industry they call it Infant Mortality Rate. S&W has proven from what I have read, and what I have experienced with them personally to be very willing to address any issues that may happen with their products, adding even more points to the quality of the M&P.

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dmcmanus - i agree. i’m glad they stand behind their products.

i’ll be sure to post a list of the fixes they made to my rifle when i receive it.

13

I finally had a chance to take my S&W M&P 15 to the range recently. Smith and Wesson was extremely helpful and efficient through the whole process. Even though I got my gun back this past fall, I didn’t really get a chance to shoot my reworked AR because of family commitments and then because of hunting season and the holidays. However, I finally got a chance to shoot a bunch of ammo through the gun and the problem has been rectified.

The gun looks great with the new upper and it shoots well. I tested it at 25, 50 and 100 yards and its accuracy is on par with my Colt 6920. I did not have any problems using the Prvi 5.56 55 gr ammo that gave the original upper some problems. They provided me with a brand new upper. Even the folding rear sight was brand new. I can tell because on my original upper, I chewed/scratched up the slot on the mounting screw of the rear sight after I had Loctited the threads. The upper on my gun looks completely new as the technician said it was. They also gave me some free Magpul 30 round mags for my troubles.

Anyway, I am very happy with this gun and very pleased with S&W’s response to my problem. They were extremely courteous, efficient and helpful.