Barrel Wisperers/Gurus help - 5.56 barrel tight spots.

[markm87]

I've been trying to diagnos the cause of pressure spikes/popped primers in a specific Mil Contract M4 SOCOM barrel. So at the advice of Clint at Black River Tactical I got a 5.55mm pin gauge.

After gauging a bunch of barrels, I found that 5 or 6 have the pin gauge stick in the first 1" of the lands.. right in front of the chamber.

I have 2 Colt barrels where the guage passes through cleanly. They are newer barrels. My question is this: Is there some sore of fire cracking that happens with barrel wear that causes the tightness in the same spot of many of my barrels???

 

[SSchnd]

Could be a dreaded build up of carbon in front of the chamber. Do you have a bore scope? Would be a quick look and you would see it and firecracking if several miles on the barrels in question.
Just a thought to check if you have not already.
Carbon Ring will build pressures up and can pop primers. If it is bad enough.

 

[Walt Krafft]

0.2185 gage pin. That will not fit in a lot of barrels. I would never try to send a gage pin through a barrel to check size. There is a good possibility it will get stuck and not come out. You could use a lead slug to search for tight/loose spots. There are lots of causes of pressure spikes in ARs.

 

[markm87]

No bore scope yet. The pin sticks in several of my barrels, in the same spot, but taps right out.

The bullet "jump" on the primer popping barrel is within a few thousandths of the Colt barrel.

I'm going to try some more cleaning and some copper removal too. Bore scope at some point, but I've been spending too much money lately.

 

[fkimble@charter.net]

Tell us more! What bullet? What brand and amount of powder? What primer? Have you done a good cleaning with a brass brush? Do you feel tight spots with a clean patch?

Frank

 

[markm87]

Tell us more! What bullet? What brand and amount of powder? What primer? Have you done a good cleaning with a brass brush? Do you feel tight spots with a clean patch?

Frank

All sorts of bullets and powders. I've been shooting this barrel for years. I honestly can't remember if it was this way when it was new or not.

We shoot a lot of 77 gr SMK, 69gr RMRs, 85gr Match burners, etc. Long range stuff. Any sort of ammo that gets within a few hundred FPS of a 5.56 load starts swiping and popping primers.

Some Wolf SRMs, CCI 41s, Federal AR Match. Powders are H322, N135, and some TAC. I did a 5 barrel chrono comparison with all 14.5s, and this one outshot them all, and even outshot a 16" Colt in velocity.

 

[SSchnd]

I would try a carbon removal liquid (C4 or the other likes) soaking, nylon brushing. Heck I am going to try Thorro Clean for the time soon just to try it. That being the most cost effective attempt to clean out the bore just in case this may be causing a issue with build up over the many many rounds you noted.
Bore Scope like a Teslong is pretty cheap, Just beware once clean you may see things in a bore you just cannot unsee. YMMV

 

[fkimble@charter.net]

Thought you were dealing with a new barrel! Sounds like this barrel may be ready for the tomato patch. They don't last forever. A good cleaning, de-copper, JB. If it still acts up, replace it.

Frank

 

[markm87]

Thanks guys. I re-cleaned it last night and ran some Bore Tech CU2 through it. Very minimal copper fouling.. not much green on the patches.

I put on some magnification glasses and eyeballed the area. Kind looks like the lands are just chattery right there from firing.

I'm leaning back towards the chamber being out of spec (5.56). A bore scope and Ned Christiansen's 5.56 chamber reamer are in the future.

 

[akajun]

I've been trying to diagnos the cause of pressure spikes/popped primers in a specific Mil Contract M4 SOCOM barrel. So at the advice of Clint at Black River Tactical I got a 5.55mm pin gauge.

After gauging a bunch of barrels, I found that 5 or 6 have the pin gauge stick in the first 1" of the lands.. right in front of the chamber.

I have 2 Colt barrels where the guage passes through cleanly. They are newer barrels. My question is this: Is there some sore of fire cracking that happens with barrel wear that causes the tightness in the same spot of many of my barrels???

Ive found that with a good load, popped primers in AR's are caused by certain brands, an oversized firing pin hole, a rough or worn, firing pin tip, or even a buildup of primer metal on the firing pin tip. If you show no other signs of pressure spikes, then try a new or different bolt or firing pin.

 

[Walt Krafft]

If that mil contract barrel is chrome lined it will destroy your reamer.

 

[markm87]

If that mil contract barrel is chrome lined it will destroy your reamer.

Ned reports that he's used his own on a several chrome lined barrels with no issues. Caveat being that it will increase wear on the unit, but he's had no customers report back that a reamer has dulled.

Some other guys reported that they've seen them used in the old Semper Paratus Armorer's course too.

It's honestly cheaper to replace the barrel, but I'm the type who has to get resolution, and experiment and learn something.

 

[RegionRat]

If I were to try and give a friendly suggestion, it would be two details.

Getting a borescope in this era is cheap enough you should already have one. In this context, you would be able to inspect the barrel for abnormal wear, damage, corrosion, or fouling, and make more informed decisions.

The second concept is not meant to insult you or talk you out of trying to learn hands on..., but is based only on what I can see in this thread.
You are not a gunsmith and don't already have the tools, background, or experience.

Based on this, why not just get with a qualified gunsmith who will allow you to follow along the troubleshooting process?

It would be less risky, your learning would be guided, and in the long run cheaper than what tends to happen when folks try to learn this in a vacuum. Hearsay off the internet by trial and error tends to get expensive and there is a high risk you learn nothing and get frustrated with failure.

A well qualified professional gunsmith will already have the facilities, and will guide you so that what you spend isn't a waste. You would be paying them for the education, but you would learn what is right or wrong and why.

So, I am not trying to talk you out of learning and having fun in the process, but the value for the money doing this with guidance from an expert will get you more bang for the buck than trial and error on your own. Good luck either way. YMMV