Polytech M14S rear sight replacement question

[DaveInGA]

Howdy Folks,

Years ago, I picked up a side stamped receiver Polytech M14S, s/n 21,### brand new in box, cosmo and all. Replaced the bolt and non-functional flash suppressor with a USGI SA replacement bolt (lapped in) and USGI NM flash suppressor. Rifle functions and shoots good, head space and lockup excellent with new bolt. The original chinese sights worked "ok", but looked and functioned roughrough, so made plans to replace it in the future as well.

Flash forward in time to today. I was browsing for M1 Garand parts on the CMP for sale forums and saw the Italian made (Beretta) M1 Garand rear sight complete assemblies for sale NOS in cosmo for a reasonable price shipped to my door. Word is out there were very well made sights and to USGI specification, so I ordered a set for the Polytech M4S I have, figuring no "originality" would be disturbed putting them on my Polytech.

Installed the rear sight assembly on my M14S. Sight went on pretty much normally with no issues (I greased it properly.) but as I was getting it adjusted, I noticed a couple oddities with the windage knob.

The knubs (I apologize, I don't know the proper name.) on the windage knob that fit into the cut grooves in the receiver slots to lock the knob as you adjust it are not as wide as the original chinese sights, so there is some slop in the lock in. You can wiggle the windage knob back and forth in the slots. The original chinese sight did not have this problem. Also, normally you have to crank the split nut down all the way, then back off some to get the windage knob to turn. In the case of this one, it would turn with the split knob cranked down as far as I could turn it in with my screw driver.

I'm wondering if you guys have seen this and is it a problem or not. If it's a problem, what's the solution? Buy another windage knob from another manufacturer and if so, which one?

Thank you for your help. This website was a great help to me years ago when I just got the rifle.

 

[45ACPKING]

I've run into that same issue on a number of rifles. Only using garand sights tho.
Never had it happen using GI m14 .... But then again, could just be luck of the draw.
Chinese sights are metric and the garands are not... Could this be the reason? Maybe the garand windage knobs engaging surfaces are different..... Hmmmmm .... Gonna consult my manuals

 

[DaveInGA]

I've run into that same issue on a number of rifles. Only using garand sights tho.
Never had it happen using GI m14 .... But then again, could just be luck of the draw.
Chinese sights are metric and the garands are not... Could this be the reason? Maybe the garand windage knobs engaging surfaces are different..... Hmmmmm .... Gonna consult my manuals

I don't think it's a metric issue. I do think you may be onto something and may have solved the problem with the M14 vs. Garand windage knob engaging surfaces. The chinese sights are copies of the M14 sights and the windage knob engagement surfaces are longer when compared to the Garand windage knob, so perhaps the M14 windage knobs are as well. Looks like I'm going to be buying an M14 windage knob. Luckily, those are less expensive than Garand windage knobs.

I'm thinking a quick measurement with a set of calipers of the nub of an M14 windage knob and a M1 windage knob that fits into the slots on the receiver would resolve the question pretty quick. I have Two M1 rear sight windage knobs from two different manufacturers, but I don't have any M14 windage knobs that are known to be M14 windage knobs.

 

[DaveInGA]

I couldn't find my two spare windage knobs of course, lost in the man cave black hole some where. But here's what I did find out:

I have an older Polytech M14S, s/n 21### and the nub/engagement surface length measurements seem to be 0.16" long at the top and 0.23" at the base for the windage knob.

I also grabbed the Italian (Beretta made) USGI surplus sight assembly installed on the rifle and measured it's . the nubs are 0.153" at the top, with a long slow leading slope and a steep following slope and measuring 0.164" at the base nub. So fairly narrow compared to the chinese windage knob.

The specification for the slot of the "X" is 0.160" +/- 0.008." My Polytech slot measures 0.174" at the bottom of the slot or about 0.006" over the maximum specification.

I'm now wondering if the older chinese rifles or just the older Polytechs had/have wider slots. Mine has been in the U.S. a long time. From Lee Emerson book, the receiver was manufactured between 1988 and 1993. The rifle was sold here in the US between December 1993 and February 1994.

What I'm seeing here is with the receiver being over the maximum specification and a Beretta windage knob being narrow, there is definitely some tolerance stacking to the point this Italian USGI windage knob would have slop/hysteresis if used on this rifle.

 

[DaveInGA]

Found a resolution to the issue. Received a windage knob for a BM59 rifle today. The bosses on it were as wide as the original polytech windage knob, so fit the receiver well. They also fit the Beretta M1 rear sight assembly I had put on. Issue resolved and now windage knob slop/hysteresis feels about the same as my 1950's built M1 rifle. So if you want to replace your rear sight, but the new windage knob feels too sloppy, it's likely a BM59 windage knob will resolve the problem for you.