I know we stickied the 9310 Bolt thread in Tech, but if this discussion develops further, I’d love to see this as “easy to find.” Great info if we can confirm “generics” that work.
I know we stickied the 9310 Bolt thread in Tech, but if this discussion develops further, I’d love to see this as “easy to find.” Great info if we can confirm “generics” that work.
Actually, no.
The gas key screws are not standard MS cap head, socket screws.
The screw, per drawing number 8448508 is a 1/8 socket, 8-32 UNC-2A.
All military standard cap head socket screws in 8-32 UNC use a 9/64 hex wrench.
Screw, 8448508 has a thicker head wall thickness, and has more specific strength requirements. There used to be a specification for such thick walled cap screws, but it was cancelled a long time ago.
Last edited by lysander; 04-12-21 at 11:07.
You know, I find it a wee bit amusing that people get all excited about the addition of a tenth of a percent (0.10 %) of molybdenum to the steel used in the bolt, yet blithely glossy over the steel composition of other parts.
Commercial cap screws made to ASTM A574 or NAS 1352 standards are made from one of several steels, AISI 4137, 4142, 4145, 4340, 8740, 5137, or 51B37M.
The gas key cap screws (8448508) are specified to be made from AISI 4037.
So, what it's all steel with the same yield strength, right?
Well, the strength and hardness are the same but their are other properties that might have a bearing on the behavior of the screws and explain why Colt's was so specific in material choice. The elongation at break is 5%, and 36% reduction in area for 4037, the other alloys have values in the 17% elongation and 53% reduction. This means that 4037 is a very "stiff" alloy, in takes a lot of force to stretch the material a small amount
Also, the required torque on these screws in 58 in-lbs, which means the stress in the threaded portion of the screw is 157,800 psi, that is very close to the yield strength of the material. So, additional loads, say from the gas pressure, might push the stress into the region of plastic yield, which means the screw will stretch and stay stretched. AISI 4037, with its low elongation, will stretch and set to a smaller percent that the other steels.
Oh, but is it not also the case with Carp 158/AISI 9310? No. The mechanical properties of Carpenter 158 and 9310 are remarkably similar, elongation being 13% and 15% and reduction being 49% and 52% respectively. Impact properties are also very similar.
So, what's on my bolt carrier? Screws made to ASTM A574, simply because no third party sells real 8448508 screws, that I know of, even some of the one advertised as "Colt's" had 9/64 socket wells. If the screw has a 9/64 socket well, it is not the correct part, it should be 1/8 inch.
I purchased spare gas keys from BCM. They came with the screws. When buying gas key screws separately I go with the OCKS screws.
Last edited by prepare; 04-13-21 at 04:06.
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The TM doesn't call for any sealant to be used when installing the gas key.
There doesn't seem to be an industry standard or SOP in regards to using a sealant?
Last edited by prepare; 04-17-21 at 16:54.
You won't outvote the corruption.
Sic Semper Tyrannis
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