A lot of guys lust for the elusive USGI op rod to put on their M14 clone/build. And why not? The GI geometry ejects the shells neatly at 2 o'clock and the fit and finish on a GI rod beats the pants off the Norinco op rods, which while very functional, aren't exactly head-turning. Some of the chinese oprods are also very poorly fitted and rattle around right out of the box, perhaps moreso than a worn our USGI rod would.
When I first started doing GI builds on Norinco M305 guns, it was back in the late 1990's. Up to around 2005 or so, I had to do a lot less fitting to make a USGI oprod run right on a Norinco receiver. Around that time, the Chinese started machining their receivers slightly differently and also started machining their oprods a little differently as well (more on that later). I'm not sure why the change was made, and why there is a difference at all, given all these receivers were forged and at least partially machined back in the early 1990's. But nevertheless, between 2005 and 2007, more receivers started showing up with a thicker receiver sidewall just above the op-rod guide track, wth slightly different op rods than what I used to see. On the 2009-2014 guns, it now seems rare to find a receiver that will take a USGI op rod as a drop-in part.
Some vendors are offering op rod fitting as a service nowadays, and if you are NOT mechanically inclined, let me start by saying I recommend you use their services to have GI parts fitted to a receiver. These parts are expensive and you don't want to ruin good parts. But for those who do their own work, or aspire to, I thought it would be interesting to exaplain op rod fitting.
FIRST RULE OF OP ROD FITTING - DO NOT START BY FILING ON THE OP ROD TAB!!!
It's really rare that an op rod tab is too large to fit a Norinco receiver - more often than not, the tab is worn and already a little undersized, though it might be tighter fitting than a norinco oprod - those are loosey-goosey. Op rod tabs can be welded back up if you stoof one up, but it's expensive and not for the amateur gun plumber, so just don't file your op rod tab unless you've tried the easy stuff first. A new in wrap op rod tab could need filing, but chances are you don't have a new op rod.
So first, a word about how the receivers changed. if you measure a USGI receiver to see how much the receiver side wall sticks out above the op rod track at its thickest point, it will measure about 0.100". If you take the same measurement on a recent Norinco, this dimension will be between .110" and .120". That is why many GI op rods will barely go into the track on a Norinco, if you can get it to go in at all, and it will bind badly. The GI oprod was designed to have less than 5 thou clearance between the interior radius and the receiver side wall, so a GI rod will be at least 5 thou too tight.
Also, Norinco receivers look to have been broached along this surface. It's cost effective and does the job, but if you run a straight edge along the surface, you'll see it isn't straight and will have high and low spots. If you are going to re-park your receiver anyhow, I usually draw-file this surface with an 18" mill file like this:
This is not a wearing part of the receiver, so there are no concerns about cutting through surface hardness or anything. Once fitted, the op rod should NOT touch these surfaces, else you've done something wrong. Draw filing makes it less likely a well-fitted op rod will rub or bind on the receiver side wall.
Now you have to do a little filing on your op rod. When I took these photos I was fitting a TRW op rod with a like-new tab to a Norinco. (PS: I did not have to file the tab, and you likely won't have to either!!!)
The Winchester is taken off my LRB and did not need fitting. (The tab looks like that because I had it built up, top and bottom, with weld and dressed it back to make it a little tighter than spec as the gun is set up as a NM rifle). LRB receivers use the USGI exernal dimensions, so a USGI oprod will fit without any work. I showed the Winchester rod so you can see how an un-modified rod looks.
The Norinco in the middle is what I call a recent production chinese op rod, in this case a 2013 made part. Because the side wall is now thicker on Norinco guns, they machined a flat above the tab to provide clearance.
The top rod is the TRW I fitted. Notice I flied the usual USGI curved surface flat, just like a Norinco oprod. This is usually the only filing you need to do to make most USGI op rods fit Norinco receivers. This does not affect the function of the oprod and it can still be re-fitted to a non-chinese receiver later a this clearance area is not critical to how the gun functions.
Note: You only file the flat above the top of the op rod tab, and you file it parallel to the back of the op rod tab. Take your time and fit often to see if the rod is binding anywhere in the receiver. Make sure the op rod guide is on the barrel and pinned in place when you check for fit and function. You can;t put material back on easily, so go slow and try fitting it often.
Here is the back of the same three op rods, from left to right: TRW, Norinco and Winchester.
You'll note the TRW and Norinco op rods are now flat above the top of the op rod tab, while the Winchester op rod has a continuous gentle curve to it from the bottom of the op rod tab to the top of the hump. This rod will not fit a chinese receiver unless I were to alter it to match the TRW op rod I fitted.
I hope this helps someone out
Happy shooting.
When I first started doing GI builds on Norinco M305 guns, it was back in the late 1990's. Up to around 2005 or so, I had to do a lot less fitting to make a USGI oprod run right on a Norinco receiver. Around that time, the Chinese started machining their receivers slightly differently and also started machining their oprods a little differently as well (more on that later). I'm not sure why the change was made, and why there is a difference at all, given all these receivers were forged and at least partially machined back in the early 1990's. But nevertheless, between 2005 and 2007, more receivers started showing up with a thicker receiver sidewall just above the op-rod guide track, wth slightly different op rods than what I used to see. On the 2009-2014 guns, it now seems rare to find a receiver that will take a USGI op rod as a drop-in part.
Some vendors are offering op rod fitting as a service nowadays, and if you are NOT mechanically inclined, let me start by saying I recommend you use their services to have GI parts fitted to a receiver. These parts are expensive and you don't want to ruin good parts. But for those who do their own work, or aspire to, I thought it would be interesting to exaplain op rod fitting.
FIRST RULE OF OP ROD FITTING - DO NOT START BY FILING ON THE OP ROD TAB!!!
It's really rare that an op rod tab is too large to fit a Norinco receiver - more often than not, the tab is worn and already a little undersized, though it might be tighter fitting than a norinco oprod - those are loosey-goosey. Op rod tabs can be welded back up if you stoof one up, but it's expensive and not for the amateur gun plumber, so just don't file your op rod tab unless you've tried the easy stuff first. A new in wrap op rod tab could need filing, but chances are you don't have a new op rod.
So first, a word about how the receivers changed. if you measure a USGI receiver to see how much the receiver side wall sticks out above the op rod track at its thickest point, it will measure about 0.100". If you take the same measurement on a recent Norinco, this dimension will be between .110" and .120". That is why many GI op rods will barely go into the track on a Norinco, if you can get it to go in at all, and it will bind badly. The GI oprod was designed to have less than 5 thou clearance between the interior radius and the receiver side wall, so a GI rod will be at least 5 thou too tight.
Also, Norinco receivers look to have been broached along this surface. It's cost effective and does the job, but if you run a straight edge along the surface, you'll see it isn't straight and will have high and low spots. If you are going to re-park your receiver anyhow, I usually draw-file this surface with an 18" mill file like this:
This is not a wearing part of the receiver, so there are no concerns about cutting through surface hardness or anything. Once fitted, the op rod should NOT touch these surfaces, else you've done something wrong. Draw filing makes it less likely a well-fitted op rod will rub or bind on the receiver side wall.
Now you have to do a little filing on your op rod. When I took these photos I was fitting a TRW op rod with a like-new tab to a Norinco. (PS: I did not have to file the tab, and you likely won't have to either!!!)
The Winchester is taken off my LRB and did not need fitting. (The tab looks like that because I had it built up, top and bottom, with weld and dressed it back to make it a little tighter than spec as the gun is set up as a NM rifle). LRB receivers use the USGI exernal dimensions, so a USGI oprod will fit without any work. I showed the Winchester rod so you can see how an un-modified rod looks.
The Norinco in the middle is what I call a recent production chinese op rod, in this case a 2013 made part. Because the side wall is now thicker on Norinco guns, they machined a flat above the tab to provide clearance.
The top rod is the TRW I fitted. Notice I flied the usual USGI curved surface flat, just like a Norinco oprod. This is usually the only filing you need to do to make most USGI op rods fit Norinco receivers. This does not affect the function of the oprod and it can still be re-fitted to a non-chinese receiver later a this clearance area is not critical to how the gun functions.
Note: You only file the flat above the top of the op rod tab, and you file it parallel to the back of the op rod tab. Take your time and fit often to see if the rod is binding anywhere in the receiver. Make sure the op rod guide is on the barrel and pinned in place when you check for fit and function. You can;t put material back on easily, so go slow and try fitting it often.
Here is the back of the same three op rods, from left to right: TRW, Norinco and Winchester.
You'll note the TRW and Norinco op rods are now flat above the top of the op rod tab, while the Winchester op rod has a continuous gentle curve to it from the bottom of the op rod tab to the top of the hump. This rod will not fit a chinese receiver unless I were to alter it to match the TRW op rod I fitted.
I hope this helps someone out
Happy shooting.
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