M9 bayonet, Long tang vs Short tang

[Misfit-45]

Hi Folks and Happy New Year!

Ever since I have seen and collected the M9 MPBS, I wondered and somewhat marveled at the design of the handle and tang arrangement; the fat rod screwed onto the relatively small tang of the blade. When I learned about the USMC long tang version, I read and heard the universal opinion that the long tang was a much better design. I presumed they were talking about the strength of the design rather than the ease of construction. I am no engineer and would not know how to calculate a strength comparison between the two systems, but I would think that BUCK would know everything about it. I was hoping that someone would be able to tell me from their research which design is the stronger of the two and by how much. Is it a matter where both are about the same, or is the short tang M9 simply an over engineered, but flawed system? Not to be dismissed is the rather fragile screw tap at the end of the long tang version.

In my opinion, when all the pieces of the short tang M9 go into place and are properly torqued, they should be as strong or stronger than the long tang version. Especially when the handle is pressed against the cross guard (even though it’s “just plastic”) there is tremendous leverage against bending of the blade.

Maybe I’m wrong and maybe it makes little difference, but I don’t think I could find a better place to ask the question. The pictures below of the long tang version M9 are taken from another web site and are not my own. Thank you very much.
Marv

The next question to be answered is Which is stronger, the Phrobis M9 or the OKC 3S?

[Oldsmithy]

only the first few threads (equal to the diameter of the screw) actually provide strength so in the tensile direction they should fail at the same load, assuming they are the same material and diameter. The longer the tang the stiffer the part will be with a bending load both because the tang is "thicker" and because the moment on the joint it closer to the end of the grip, so in that instance the longer tang will be stronger both in the blade direction and perpendicular to it.

Your pictures seem to show the USMC is the short tang not as per your text. The only advantage to the shorter tang is is weighs a little less.

[Misfit-45]

Thanks for addressing my topic. That is interesting about the first few threads determining the tensile strength of the tang. (the amount of "pull strength" of the tang) In any event, tensile strength is not going to be an issue for the soldier or marine.
Yield strength is more important to the user. How much can the bayonet bend before permanent damage, or breakage. If you were to place the M9 bayonet between two cement blocks and applied weight to the cross guard, how much weight would have to be applied to permanently bend or break the bayonet? In the bayonet trials used to select the M9, it had to withstand a dead lift of 400 pounds without developing a permanent set. The Phrobis passed, but I wonder how much weight it would take to damage the bayonet...and which bayonet system, long tang or short, would take the most weight. That's the ultimate question I'm asking. Which one is strongest?
As for the short tang M9 bayonet being lighter, how can that be when the fat round tang used in the short tang M9 probably weighs more than the tang of the long tang M9? I'd be curious, if you have both bayonets, if you could weigh them and see which one weighs more?
In regard to which bayonet I used in the pictures, I was comparing the two USMC versions of the M9, since it was the Marines that ordered the long tang version for testing. They must have liked the long tang since they adopted the OKC3S.
I did not mention the Phrobis name in my first text as you suggest, however, I probably should not have posted the text in the Phrobis M9 section of the forum. I did that because the original design of the MPBS M9 was "Phrobis", and that ultimately is the system that is "on trial" here. Thanks again for the response.
Marv

[Oldsmithy]

As I said the long tang will be stronger in bend as the change in section is further from the bend point so will see less bending stresses

[pwcosol]

My understanding is the USMC was looking for two things in the 1993 trials bayonet which they wanted over the standard design. One was a solid tang which they believed would be stronger than the threaded tang. They also preferred the bayonet not be able to be disassembled by Marines in the field, hence the riveted tang variant. As one can see, the other pattern with screw tang is likely much weaker because of insufficient thickness of the tang (to the degree the screw threads are partially exposed). I surmise this would have been rectified had the design gone thru additional improvements.