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New M4 chambering issues


mont1120

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Had a new M4 .223 built for 3 gun, and it ran great for two matches, and now I am having serious case issues. It has a Proof research barrel and a Dixie Works receiver. It was set for .223 Wylde. I reload my own ammo, and case gauge every round. The rifle just started to refuse top go into battery about every 3rd round. I had to slam the butt to get the stuck round out. The case does not matter, I had PMC brass, Lake City, and Winchester. When it happens, hitting the forward assist does not help.

 

I took pictures of rounds that were painted in Perm marker, and found a series of three concentric scratches in differing spots on the brass. (See pic). What in the world causes this. None of the rounds fails a Williams chamber gauge, and my DPMS eats them like candy. The rifle is super accurate and I have run out of ideas. Brand new ammo does the same thing.

 

As you can see in the picture, this set of marks can be found near the top of the round, or closer to the rim. Any ideas? The snow has melted and it is time to get some rifle time in.

223 b.jpg

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How does it work with factory ammunition?  If it runs with factory ammo then it's your reloads that are the issue.  What spec case guage are you using .223 or 5.56?   Are you gauging the sized brass or loaded ammo, you should be checking loaded ammo.  I'd just send it back for that kind of money if it did not run with factory ammo.  If you have to use the forward assist, you should not shoot that round. 

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I may have had the same problem but not quite as bad.

 

I installed a new barrel January,  Super accurate but would jam on seven or eight rounds out of 100. These were my reloads (I don't shoot much factory .223/5.56).  Once jammed I had to mortar them out.

 

I reset my trimmer and cut an extra .015" from the case length.   New length was 1.735".  Loaded bullet length is still 2.250".

 

With the short case I've had no more stuck cases.

 

Bill

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I would buy a JP Enterprise case gauge, it is made with a finish chamber reamer and checks body diameter. I use a Hornady cartridge case headspace gauge to measure the fired case length and resized length. But I use the JP Enterprise gauge as a final check of the loaded rounds plop test.

 

PPHWn7L.jpg

 

Below a Wilson, Dillon and JP Enterprise gauges with cases inserted backwards, and as you can see the JP Enterprise is the only gauge that checks body diameter.

 

KSB3ZvP.jpg

Edited by bigedp51
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Thanks for the replies men, here's what I have.

 

The same issue is present with factory loads, but not as bad. Maybe 1 out of 8.

 

Brass length is 1.76, OAL is 2.19, but that's because the ogive is set to crimp the round on the 55 grain Hornady's. I use a Williams case gauge and I reject any rounds that will not go flush into the gauge completely. The shoulder measures .357. I use standard Lee .223 dies. I also used completely resized brass, not just neck sized since none of these rounds have been fired through this rifle.

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if your brass and loaded cartridges meet specifications

 

what is curious is that it used to run great for "2 matches" but now having error.....  sounds like mechanical failure/error

 

maybe the problem is the rifle/mag?

head space?

blem in chamber? 

bad extractor? other bolt/bcg error?

 

 

 

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Well, I think I will send it back for repair, my rounds still run flawless in my old DPMS which has well over 5K rounds through it. Its way beyond my abilities to fix if the group here does not know of any quick fixes. Now I have not used a new mag, is that something that could cause it? Again, the same rounds in the same mags run great in another gun.

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same rounds different gun.......

 

it took me a while to figure it out   but had some (bought) reloads that were jamming in a friends new gun but ran in mine..

 

long story short...  finally measured some of rounds not yet chambered in his rifle...  turns out reloads were off   by avg .0018   when dropped in case gauge...  unless you have really good eyes or ran a straight edge over loaded case gauge,  i missed these b sight alone .... i found out by using stand  comparator on a loaded case gauge   turned out ammo not passing case gauge....  it appears that the first slam rifle either resized ammo or chamber in my gun is looser....

 

before you send it back  take a real close look at reloaded cartridges before you chamber in rifle with  stand comparator   if you can get hands on one.   check sized trim legnth and if loaded cartridge is proud in case gauge.   You may need to dual down sizing die.....

 

if i didnt get any data from stand comparator.   i was going to buy jp gauge like big ed suggested

 

 

Edited by biglou13
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Your chamber may be on the tighter end of spec. Possibly chambered when the reamer was new. What do you use to set headspace on your brass? Try chambering a piece of brass that is 2 or 3 thousandth too long with the extractor and ejector removed from the bolt. If it doesn't fit bump it back a thousandth at a time until it chambers and extracts easily.

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  • 2 weeks later...

Have you checked headspace of the bolt to bbl extension? Only two things I know of can cause this if factory ammo gives the same symptoms.  Case shoulder (usually just reloads), tight chamber or tight headspace of bolt. Not a magazine issue. 

Edited by mpeltier
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I was having a similar problem on my only rifle with .223 Wylde chamber.  All of my reloads looked good in a Dillon case gauge.  In practice and general shooting, it seldom happened because I wasn't ejecting a live round.  But, it was happening on every stage of a recent match.  I checked with factory rounds, and they ran fine.  After some reading here, I reset my sizing die by turning it down about a full turn.  I now have no more problems with my reloads.   

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I use a Hornady cartridge case headspace gauge and measure a fired case and then bump the case shoulder back .003 to .004.

 

Below a fired case from my AR15 rifle before sizing, after sizing the shoulder is pushed back .003 to .004

 

H0SXHH8.jpg

 

Below is my JP Enterprise .223/5.56 case gauge, it is made with a Wylde finish chamber reamer and is the only case gauge I know of that checks case body diameter.

 

And after the cases are loaded I use this gauge for a final "plop" test. Meaning the loaded cartridge is dropped into the gauge all the way then tilted and the loaded round must drop out of the gauge.

 

PPHWn7L.jpg

 

Bottom line I'm loading for three AR15 rifles and a bolt action Savage .223 and with the Hornady gauge and the JP Enterprise gauge I have never had a failure to feed or eject.

 

Meaning with the correct gauges to check headspace length and body diameter you should not have any problems. And again the standard Wilson type case gauges do "NOT" check body diameter. And your resized case diameter should be .003 to .005 smaller than your fired case diameter for reliable extraction. Meaning if it fits the JP Enterprise gauge the case diameter is small enough to chamber correctly.

Edited by bigedp51
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  • 1 month later...

Sooooo, wanted to let all of you guys know the results. A very tight chamber is the reason they were sticking, the shoulder on my reloads was just a hair out of spec, and the should would not chamber all the way, getting stuck, After firing a couple of hundred PMC factory rounds without a single failure, I went back and checked the difference. I looked at know rounds that would fail, and re-checked them in a case gauge. 

 

Sure enough, the rim as not 100% flush in the groove of the gauge. These rounds will fire in my DPMS all day long without a hitch, but the Proof research barrel is cut that tight that it would not accept the bulged shoulder. Thanks for all the responses, and as usual, you guys are right.

 

Live and learn................

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