It is extremely likely that Colt uses S2. I know AAC uses S2. I am not sure who else, but if anyone really wants to know, you can collect samples and pay for testing - that is the kind of thing that could make gun magazines great - if they actually reviewed guns.
I bet the results would be surprising as to who uses what.
To be perfectly honest I’m more worried about a cam pin wearing out before and extractor pin.
And have you ever seen an extractor pin fail, bend, or break before the bolt gave out due to fatigue? Excluding cases of KB’s due to whatever reason.
From some of your posts, I almost wonder if you plan on starting a business as a steel distributor. Distributing all those crazy hard to find steels that no body needs enough of to justify purchasing a 25,000 pound lot.
Maybe we could do a group buy. 25000 pounds of steel would make about 7,000,000 pins give or take a pin or two. Figuring a cost of $10 per pound a pin would only cost about $0.035 for the metal, maybe another $0.035 for fabrication, say seven cents a pin. Cheap. I’ll take two dozen.
I have seen a few of them tweak or bend. But, in the bigger scope of things I don’t know how important it is. It’s always a good idea to keep things like this on hand.
S7 is probably good enough to not have any problems and I have not heard of any. I picked S2 for AAC pins because I felt it was worth it to use the best material known. The govt uses it because it is in the TDP. It makes me wonder how many “MPI” bolts use S7.
As for cam pins breaking - we engineered around that - our cams pins have lower stress levels and I would not expect one to ever break.
I have seen but few extractor pins break. I’d have thought years ago when D-Rings started to became de rigueur that, if extractor pins were already stressed to near the edge, that increasing extractor tension by XX% would cause many more to break. They seem to be adequately sized for the application, is my conclusion… and/or adequately sized so that the dif between S2 and whatever else is not critical. Just at a glance, I view the span of the pin, in other words the width of the cut for the extractor, as proportionally OK to the size of the pin.
Not to say there are not bad pins… since there’s bad everything else, there surely are bad extractor pins. I’ve seen at least one that was simply 1/16 too short. I’ve seen maybe two that were broken (and as I recall no effect on function) and one that was soft enough to have been bent slightly (again, no effect on on function).
So the real question is, who besides Colt, and AAC use S2 tool steel for their extractor pins?
Next, does anyone besides Carpenter make S2?
Are there any steel distributors that supply the steel in sane quantities for the smaller firearms manufacturers out there?
While I appreciate RSilvers for pointing out this finer detail of making a quality AR, he makes it sound like getting the proper steel is damn near impossible. There have to ways manufactures get the steel they need in smaller lots without breaking the bank.
They seem to use S7 when they cannot get S2. Likewise, companies that are too small to get C158 tend to substitute 9310. While I know S7 is not as good, it is not bad. And while I don’t think 9310 is as good, it is not bad. Not chopped liver by any means.
Part of the demensional design of the parts, was dictated by some of the overall goals related to why the weapon was designed. Such as weight and size requirements. The exotic materials allowed them to design smaller parts that had similar durability to a larger assembly made out of lesser materials.
One of the other variables that dictated some of the design choices was manufacturing capability. This likely played a role with bolt lug design, and why companies like KAC are able to make stronger bolts that fit in roughly the same space. Machining was more difficult and time consuming back when the AR15 was designed. Along with it being more difficult to manufacture parts with smooth radius’ (radi?) with exacting tolerances.
While manufacturing technology has advanced since that time, I would be suprised if there aren’t steels available today that could be substituted for these parts, and be stronger/more able to cope with the loads, than the steels originally chosen for the parts. I mean surely metalurgy has advanced since the 50’s
I’ve asked this question several times and have never received a satidfactory answer. I am pretty certain Eugene Stoner didn’t have the metals that are currently in the TDP when he designed the AR(s) in the 50’s. The TDP has evolved over the last half century.
I can’t speak to the material history of extractor (the marginal information is quite blurry) or the extractor pin (no print on hand) but my bolt print which is a 27APR70 ARDC, redrawn from Colt’s J61538 Rev. E w/C, has as its Revision B a change to (1), which is the material call in the marginal information, dated 01SEP70, the note “See EO HRD 02197-3”. So, as far back as APR70, the print specified C158. The date of the last revision is 80-02-13.
The extractor print calls 4140 or 4340 gun quality on this extractor print but the last visible Revision date on it is 06OCT70 and the latest is a blurry 87-02-1?
