Cracked bolt > Maintenance & Cleaning

Posted: 4/15/2007 11:58:03 AM EDT

I was cleaning my AR after a trip to the range. After applying solvent to the bolt I saw what looked like a piece of hair or dust on the side of it. A closer look revealed a fine crack through the side of the cam-pin hole, ejector side.

So, I need a new bolt.

The gun is a homemade job bought secondhand, last year. It has a DPMS lower, but I don't know about the upper or the bolt assembly. I have had no problems with it except an occasional failure to lock back on an empty mag--the ramp on the bolt catch shows significant wear.

If anyone could suggest where to get a new bolt or bolt catch, I'd greatly appreciate it.
Also, I have a few questions:

Should I replace the entire bolt assembly--extractor, ejector, rings, etc.?
What about the carrier? Will any bolt fit safely and properly in any bolt carrier?
Does the headspace need to be checked?
Is there any other safety concern that would cause me to have a gun smith look at it instead of just buying a part and dropping it in?

Thanks for any info.

Posted: 4/15/2007 12:30:39 PM EDT

[#1]

Quoted:
If anyone could suggest where to get a new bolt or bolt catch, I'd greatly appreciate it.
Also, I have a few questions:

I just purchased an entire new bolt with carrier from Operation Parts. Very nice MP tested bolt too.

Should I replace the entire bolt assembly--extractor, ejector, rings, etc.?

You can, and save the extra parts as spares.

What about the carrier? Will any bolt fit safely and properly in any bolt carrier?

Yes, any standard bolt will fit any standard carrier.

Does the headspace need to be checked?

It’s always a good idea, especially on weapons with higher round counts.

Is there any other safety concern that would cause me to have a gun smith look at it instead of just buying a part and dropping it in?

No, I think you’ll be fine. Bolts break at the weakest point which is often the lugs or at the cam pin hole as yours did.

ETA: Pics. And it’s good that you caught that crack when you did. That is one reason why I get a big kick out of these threads where people brag about how fast they can clean their AR. It’s not a race, and your not only cleaning you should also be inspecting as well.

Posted: 4/15/2007 6:19:18 PM EDT

[#2]

Thanks, QUIB.

Posted: 4/16/2007 2:35:30 AM EDT

[#3]

Quoted:
Thanks, QUIB.

Your welcome.

Posted: 4/16/2007 3:07:16 AM EDT

[#4]

You can get a new bolt lots of palces. But ADco has them for about $45.00 and cheap shipping. That was the cheapest last time i was looking for one. Except DPMS from brownells and i wont use DPMS bolts.

Posted: 4/16/2007 5:17:16 AM EDT

[#5]

look in the EE, i got a good deal on a Colt M4A1 MP bolt there

Posted: 4/16/2007 3:09:35 PM EDT

[#6]

height=8

Quoted:
You can get a new bolt lots of palces. But ADco has them for about $45.00 and cheap shipping. That was the cheapest last time i was looking for one. Except DPMS from brownells and i wont use DPMS bolts.

Why?

Also, what's MP?

Posted: 4/16/2007 5:49:44 PM EDT

[#7]

Quoted:
Also, what's MP?

From the net:

Magnetic-Particle inspection

Magnetic particle inspection processes are non-destructive methods for the detection of defects in ferrous materials. They make use of an externally applied magnetic field or DC current through the material, and the principle that the magnetic susceptibility of a defect is markedly poorer (the magnetic resistance is greater) than that of the surrounding material.
The presence of a surface or near surface flaw (void) in the material causes distortion in the magnetic flux through it, which in turn causes leakage of the magnetic fields at the flaw. This deformation of the magnetic field is not limited to the immediate locality of the defect but extends for a considerable distance; even through the surface and into the air if the magnetism is intense enough. Thus the size of the distortion is much larger than that of the defect and is made visible at the surface of the part by means of the tiny particles that are attracted to the leakage fields.
The most common method of magnetic particle inspection uses finely divided iron or magnetic iron oxide particles, held in suspension in a suitable liquid (often kerosene). This fluid is referred to as carrier. The particles are often colored and usually coated with fluorescent dyes that are made visible with a hand-held ultraviolet (UV) light. The suspension is sprayed or painted over the magnetized specimen during magnetization with a direct current or with an electromagnet, to localize areas where the magnetic field has protruded from the surface. The magnetic particles are attracted by the surface field in the area of the defect and hold on to the edges of the defect to reveal it as a build up of particles.
This inspection can be applied to raw material in a steel mill (billets or slabs), in the early stages of manufacturing (forgings, castings), or most commonly to machined parts before they are put into service. It is also very commonly used for inspecting structural parts (e.g. landing gear) that have been in-service for some time to find fatigue cracks.

Posted: 4/17/2007 2:21:20 AM EDT

[#8]

Quoted:

Quoted:
You can get a new bolt lots of palces. But ADco has them for about $45.00 and cheap shipping. That was the cheapest last time i was looking for one. Except DPMS from brownells and i wont use DPMS bolts.

Why?

They had a bad run a few years back and were breaking more often then other brands. I had hoped they resolved the problem. But our local police later bought a bunch of DPMS rifles, DPMS' largest govt contract ever at the time in fact, and those rifles suffered many bolt failures even though the rifles were very low round count. It was a big enough problem they scrapped the DPMS rifles and changed vendors.

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