NEWS | Nov. 12, 2020

M2A1 Machine Gun: When Is the Flat Spring Needed?

M2A1 machine gun
Photo courtesy of TACOM​
Don’t know if your M2A1 machine gun requires the flat spring, PN 5140428? Here’s some help. The flat spring, NSN 1005-00-514-0428, PN 5140428, on the bottom of the M2A1 machine gun’s receiver is to be used along with the legacy M3 tripod traverse and elevation (T&E) mechanism, NSN 1010-01-151-6227, PN 5830128.
flat spring PN 5140428
Part Number 5140428 – Spring, Locking, Elevating Mechanism

T&E mechanism PN 5830128.
Part Number 5830128 – Mechanism Assembly, Elevating

Look at the image below.  The flat spring (1) is secured by the breech cam nut (3) and extends between the rear T&E mounting brackets on the bottom of the receiver (2).
Location of Flat Spring on M2A1 Receiver
Location of Flat Spring on M2A1 Receiver

In the next picture, you’ll see that the spring is made to secure the M3 tripod’s T&E mechanism (1) parallel to the bottom of the receiver when the weapon is removed from the M3 tripod (2).
M2A1 with the M3 tripod
Part Number 8403398 – Mount, Tripod, Machine Gun: Cal .50, M3
In contrast, the M205 tripod, NSN 1005-01-586-5702, PN 13046100, doesn’t share this feature.

If your unit was issued the M2A1s without flat springs and you use them in a mounted role, or with the M205 tripod, they don’t require the elevation mechanism locking flat spring.
If units still utilizing the M3 tripod, NSN 1005-00-322-9716, PN 8403398, have been issued an M2A1 without the elevation mechanism locking flat spring, contact Jack Kopmann at Picatinny Arsenal to request the missing flat spring. He’s at:
The flat springs, PN 5140428, are to be installed by a 91F small arms artillery repairer or a civilian equivalent.  They need to follow TM 9-1005-347-23&P (Jul 11) to correctly install them.