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Converting lower sear/trip for semi mode m1918 vs A2

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I have a Winchester m1918 with the early buffer. I picked up a ROT Korean era lower (with formed mag guides) to shoot in the Winchester to reduce the wear on the all original Winchester lower. What I found was the gun would function full auto only in semi mode with the ROT lower - and since my main range is semi only that was a no go. In inspecting the parts movement it feels like the rear of the A2 sear (which is considerably longer than the original Winchester sear in order to be actuated by the A2 buffer head) is either binding on the early buffer head, or the rear of the receiver. This is preventing the sear from dropping enough to trip the sear reset in semi mode.


I spoke George (Junkyardslug) from "wwiibarman.com" who educated me that part of the A2 modernization was to expand the area of the rear of the receiver to create a step down to allow the A2 sear additional movement. Here is a photo showing an original and A2 cut rear section that George provided to show the difference:



George suggested that simply removing the sear release stop lever may work to allow enough movement to not bind the sear. I tried that and found no difference.


I picked up a few extra sears and cut one of them short by removing the ears just behind the area where the "sear and stop lever spring" engages the rear of the sear. This modified sear (minus the sear release stop lever) works perfectly now in semi and full settings with the original buffer. I suspect those with A2 BARs could get semi fire in slow mode using this modification.


Here are some photos. Many of the online manuals show the disassembly and re-assembly procedure for the lower. For this procedure I found the depicted procedure for disassembly is not necessary. The counter recoil spring is the challenge on assembly, but using a punch on the opposite side of the pin for leverage makes the job easier.


These are my observations and steps, be warned I am an amateur and new to the BAR - not an experienced gunsmith. Perform at your own risk.


1) Using a brass or steel punch, punch out the sear pin. On one of my lowers, this could almost be done with lateral force alone. On the other (ROT) the parts fit tighter (presumably due to a stronger counter recoil spring) so a few hammer taps were needed. The sear spring (leaf type) may remain in place when punching out the sear pin. With the pin driven out, remove the sear and sear release stop lever.




Showing sear spring removed and installed - this is not necessary to remove but will easily slide to the rear with the sear removed. Lift up the center leaf, hold up with a small screw driver, and slide the assembly off the frame.




Set the sear release stop lever aside, it will not be re-installed. Modify a A2 sear by removing the rear ears (that engage the A2 buffer head). I made my cut just behind the point where the ears stick out from the main body, so the rear of the sear is still supported by the sear and stop lever spring. I used some Birchwood Casey blue to prevent rust on the cut portion of the modified sear:




When installing the modified sear, do not include the sear release stop lever. Use a steel punch to line up the sear carrier and manipulate the punch rearward to slide the sear carrier forward to align the holes. Partially insert the sear pin. Then insert the sear, and punch the sear pin in place.




If removed, replace the sear spring by placing over the sear and sliding towards the magazine catch. If the sear spring remains in place, be sure the two outer leaves of the sear spring ride over the top of the forward ears of the sear when sliding the sear in place prior to pin install, as in this photo (unmodified A2 sear):




Here is a comparison of the early Winchester lower, a modernized lower with the modified sear, and an unmodified ROT A2 lower:






If anyone tries this with a A2 buffer I would be very interested to learn if it reliably works in semi when set to slow mode. I believe it will work based on my understanding of the A2 buffer head in relationship to the A2 sear/sear release stop lever. It is also possible that simply removing the sear release stop lever with an unmodified A2 sear would also produce semi in slow fire mode.


I am not sure if the cut down in the rear of the receive as shown by George is necessary for the A2 buffer to work in an early receiver for slow fire mode (on early receivers). I hope to experiment with that in the future and will report my findings here.


All the best, Nate in MN

Edited by nate129
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  • 4 months later...

I removed the early buffer tube from my Winchester and confirmed what George taught me about the differences in the rear of the receiver, as pictured in the first photo of the above post. My Winchester receiver is original and unmodified and as such the rear "ears" of the A2 sear bind against the receiver interior just forward of the buffer tube threads. This interference point is present even when the buffer is removed from the receiver. This binding point prevents the sear from dropping down low enough to reset, causing full auto only in the F setting. I assumed the A2 overstamp on the modified guns only signified the swap of buffers, but clearly the process also involved modification to the receiver interior forward of the buffer threads as shown above. I did not recall seeing any such info in the BAR bible, Rock in a Hard Place.

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