AR-15 Bolt issues

[granite1]

Do you grease them occasionally? Looks like they were run dry.

 

[C.E.Smith043]

Do you grease them occasionally? Looks like they were run dry.

I shoot some oil to them before i go out every night. Thats about it.

 

[Ggmac]

Sorry if I missed this . How did you check the back side of the extension ? A Borescope is about the only way without removing the extension .
I'd be checking the receiver extensions out just so you don't damage a new bolt with a galled/ chipped extension .

 

[Rsadams]

9310 is an alloy used in the "better" AR bolts. I would suspect you are correct about the mpi designation. The two together likely means simply mpi tested 9310 alloy.

Good bolts will be stamped HPT/MPI , which stands for high pressure tested/ magnetic particle inspected which is basically in my opinion magna flux for cracks.... I hope that's right we owned an automotive machine shop for 40 years...lol

Not sure if Carpenter 158 steel is the same as 9310 but it's what you want in a good bolt...

 

[C.E.Smith043]

Sorry if I missed this . How did you check the back side of the extension ? A Borescope is about the only way without removing the extension .
I'd be checking the receiver extensions out just so you don't damage a new bolt with a galled/ chipped extension .

I have a shard off of a broken mirror that I've glued to the end of a pencil. You can stick it inside the barrel extension just like a dentist does a mirror into your mouth and see the back side

 

[gunsandgunsmithing]

Good bolts will be stamped HPT/MPI , which stands for high pressure tested/ magnetic particle inspected which is basically in my opinion magna flux for cracks.... I hope that's right we owned an automotive machine shop for 40 years...lol

Not sure if Carpenter 158 steel is the same as 9310 but it's what you want in a good bolt...

"It has been the "Mil-Spec" since. Since the creation of Carpenter 158, the metals industry has continued to innovate, creating new blends of steels. 9310 is a AISI standard grade of tool steel that makes it about ~7% stronger than "mil-spec" Carpenter 158 steels, when appropriately treated.May 12, 2016"