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Experience is a cruel teacher, gives the exam first and then the lesson.
Absolutely nothing broken on my rifles but I do resemble an "unfortunate soul" now and then![]()
Air, it's a 30mm 6x24 Osprey scope and while decent enough I'll probably install one of my Super snipers on the rifle if it proves accurate enough while shooting it for the first time today. Also, I installed an old red dot Bushnell scope I had laying around for quick acquisition, it works well because it's canted to the left of center thus allowing left eye aim and/or right eye on the larger scope, if bot eyes remain open. I am hopeful that I'll be able to zero it to the right enough to appropriately shift POA/POI.
Vegas, why goofy look? I liked the purposeful, embedded larger trigger guard, sling attachment, and the shape of the Stark grip that's why I bought & installed it. Only thing different I'd do with them while manufacturing is to rubberize them more.
I also polished the trigger group to drop it from an 8lb to a now very crisp 5.5-6lb trigger pull.
So there appears to be an AR manufacturers chart somewhere that we all must worship? Typical of the "follower" mentality crowd....pun intended.
A few more pics from this morning:
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Last edited by gcp; 07-20-13 at 06:02.
Long story short:
MPI - Magnetic Particle Inspection Process of inspecting the barrels/bolts for defects that might shorten the lifespan of the part
HPT - High Pressure Test. Use of an M197 test cartridge (or equivalent) to test bolts/barrels at 70K PSI.
Shot peened - use of small pieces of "shot" to relieve the stress on the surface of a metal.
Also, proper spec materials like use of Carpenter 158 on the bolts, 4150 CMV barrel steel or FN proprietary "Machine Gun Steel." Stainless steel barrels, depending on the type and manufacturer, can be good to go. A search of the manufacturer on this site will probably turn up some info.
Quality parts will use fully MPI and (most of the time) HPT barrels and bolts. Some companies forgo the HPT on their bolts (Noveske for example) and there is some debate as to whether it is necessary as it could shorten the lifespan of the bolt. Not going to take a side one way or the other as that's a different discussion, different time.
Anyway, sometimes PSA lists uppers and BCGs without listing whether or not the bolts are properly inspected and/or tested. Such as this one. While it is made of the proper materials, there really isn't a way of knowing if the bolts are MPI/HPT or not. But they also have ones with the proper testing like this one which details the process.
And other times, you'll see something like 8620 used like here which is not the official "mil-spec" steel that is supposed to be used and also note the listing does not include any inspection process.
Barrels used by PSA are mostly FN manufactured varying from 4150 CMV steel to CHF "Machine Gun" steel. Many, if not most are listed as having MPI and HPT done so you are generally safe with PSA. But from time to time you get something like this listed which does not specify.
So as stated before, just check the specs on what you are picking up. PSA has an industry rep here on this board and they are pretty active over on Arfcom as well for specific questions about their products. They are generally pretty good about answering questions about the specs.
Also, here's a few other threads to check out:
https://www.m4carbine.net/showthread.php?t=7355
https://www.m4carbine.net/showthread.php?t=56063
https://www.m4carbine.net/showthread.php?t=7009
https://www.m4carbine.net/showthread.php?t=50559
Experience is a cruel teacher, gives the exam first and then the lesson.
munch, I am familiar, do understand, and speced out my upper/lower/BCG for MPI/HPT/shot pinned.....before purchase. Too early in the morning and I didn't make the abbreviations connection. As an engineer I very much appreciate well thought out specs/charts and fully comprehend their purpose in life, as long as they are properly understood and utilized by the user.
Last edited by gcp; 07-20-13 at 08:15.
I would think twice about polishing the trigger. Once you get through the thin surface hardening it will begin to wear fast, to the point of being unsafe over enough time. If a lighter, smoother trigger is needed I would save up for a Giessele trigger. It's your gun though, just my 2 cents.
As far as chart worshipers go, you would do well to familiarize yourself with it, couldn't hurt. Looks like a successful build, congratulations.
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