I will be looking for a bolt carrier group soon. Is there a good reason to spend the extra money for a chromed or nickel boron BCG?? Is mpi/hp tested more important??
AR Bolt Carrier - Phosphated versus Chromed versus Nickel Boron
- Thread starter dreadpirate
- Start date
...and I quote from who appears to be an Internet authority
"Magnetic particle testing only find defects on the surface. It does so because steel is ferromagnetic and the "lines" of magnetization applied in the MT process will concentrate at ALL discontinunities on the SURFACE. This includes all holes, lug corners and any other edges. Such indications are NORMAL. MT's only value here is finding defects on the relatively flat surfaces like the cam pin hole web.
It cannot find defects located deep in the material. And that includes defects in the center of the cam pin hole web, a HIGHLY stressed area. Defects in other areas outside of the lugs and bolt face.
Now, specifications for the military are "written in blood". The MT specification (MT is the proper NDT term, Magnaflux is a trademark process and MPI is military) arose out of the early life of the M16, material science has progressed to make such testing unnecessary IF the proper material is utilized. But if the letter of the TDI is followed, lesser materials and specifically poor processing WILL make life short for any bolt.
ASNT is the most recognized authority in such matters. My experience dealing with ASNT level IIIs with regards to MT and UT is the basis of my judgement and I have had them run MT, PT, RT and UT on some bolts. Their judgements were PT is by far the best NDT for both bolts and carriers due to geometry.
Now for the materials engineering. Bolts with significant defects that are missed by NDT will fail in a very low cycle fatigue regime. That is 1-100 rounds. The failed part's fracture line will show the defect, usually just below the surface along with large areas of ductile faliure.
Bolts which fail in the 101-5000 round counts which fail do not do so from any INDICATABLE defect but from MATERIAL FATIGUE. These failures are noted by the absence of any ductile failure. This is typical low cycle fatigue in the hardened steels used in firearms.
The most common fracture point is the web of the cam pin hole. The most common problem is severity of quench. This is not anything that can be detected by MT/MPI. Buy quality, not specifications. "
Groovy......
My Dad's Savage 775 still shoots/cycles as well as the day he got it over 60 years ago. Bet his wasn't mpi/hp tested.
Fact is...just what do you plan on doing with this AR???
"Magnetic particle testing only find defects on the surface. It does so because steel is ferromagnetic and the "lines" of magnetization applied in the MT process will concentrate at ALL discontinunities on the SURFACE. This includes all holes, lug corners and any other edges. Such indications are NORMAL. MT's only value here is finding defects on the relatively flat surfaces like the cam pin hole web.
It cannot find defects located deep in the material. And that includes defects in the center of the cam pin hole web, a HIGHLY stressed area. Defects in other areas outside of the lugs and bolt face.
Now, specifications for the military are "written in blood". The MT specification (MT is the proper NDT term, Magnaflux is a trademark process and MPI is military) arose out of the early life of the M16, material science has progressed to make such testing unnecessary IF the proper material is utilized. But if the letter of the TDI is followed, lesser materials and specifically poor processing WILL make life short for any bolt.
ASNT is the most recognized authority in such matters. My experience dealing with ASNT level IIIs with regards to MT and UT is the basis of my judgement and I have had them run MT, PT, RT and UT on some bolts. Their judgements were PT is by far the best NDT for both bolts and carriers due to geometry.
Now for the materials engineering. Bolts with significant defects that are missed by NDT will fail in a very low cycle fatigue regime. That is 1-100 rounds. The failed part's fracture line will show the defect, usually just below the surface along with large areas of ductile faliure.
Bolts which fail in the 101-5000 round counts which fail do not do so from any INDICATABLE defect but from MATERIAL FATIGUE. These failures are noted by the absence of any ductile failure. This is typical low cycle fatigue in the hardened steels used in firearms.
The most common fracture point is the web of the cam pin hole. The most common problem is severity of quench. This is not anything that can be detected by MT/MPI. Buy quality, not specifications. "
Groovy......
My Dad's Savage 775 still shoots/cycles as well as the day he got it over 60 years ago. Bet his wasn't mpi/hp tested.
Fact is...just what do you plan on doing with this AR???
- Thread starter
- #3
Ok - here is a BCG with a "cosmetic blem". Is this a bad idea or a bargain??? Is a blemish acceptable for a bolt carrier??
http://palmettostatearmory.com/inde...up-cosmetic-blem-ready-for-duty/category/332/
http://palmettostatearmory.com/inde...up-cosmetic-blem-ready-for-duty/category/332/
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I would jump on it, that is a great price on a BCG. For what it is worth I have a Nickel Boron BCG in mine and probaly would not go that route again as I notice no real improvement over a standard phosphate coated part.
What they said
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