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I have had a Polytech M14-S that has been patiently waiting for me to give her some attention. She was slightly used when I took her home and the Muzzle Erosion (ME) gauge read about 0.3. As far as I could tell the only change her first owner made was to put her in a USGI Fiberglass stock.
However, he did not change out the Chinese Connector Lock.
The Chinese Connector Lock fits flush with the side of the receiver when it’s closed and the Chinese stocks are cut so the wood is against the receiver at that location and the Connector Lock cannot work out while in the stock. The USGI Connector Locks are longer and do stick out of the receiver when closed, and the USGI stocks have a relief cut for this. So if you put a rifle with the shorter connector lock into a GI stock the lock can work loose. I’m not sure if the previous owner was aware of this or not, but the Operating Rod Spring Guide coming out of its place during shooting may have been the motivation for him selling the rifle so cheaply.
Since I noticed this, the first thing I did to the rifle after purchase was to install a USGI Connector Lock and pin. I found the Polytech Receiver’s Connector Lock hole to be undersized a bit. I could manage to get the Connector Lock into the hole but it was too tight to lock or unlock by finger pressure. I put the Connector Lock into the chuck on my minimill so it was holding the portion that would stick out of the receiver when closed and turned it while applying gentle pressure with some 400 grit wet/dry sandpaper. Taking the parkerizing off that area was sufficient to do the job.
The other things I did to the rifle right off the bat was shim the Gas Cylinder Assembly, switch Flash Hiders and install a Stripper Clip Guide, as it appears that the previous owner removed it to use a scope mount.
Everything I have read on the Chinese rifles says that they did an excellent job on the receivers. They are the only option in the US for a drop forged M14 type receiver that does not have a NFA tax stamp attached to it.
However everything I have read about the bolts says they are junk, at least the ones imported into the US before the import ban. A GI bolt will not generally just drop into a Chinese receiver and close. Material must be removed from the rear of the receiver ring, where the bolt lugs bind. Knowing this, I bought the Polytech with the idea of learning how to perform my own GI bolt modification.
In deciding what bolt to use, I tried two different New Old Stock (NOS) GI bolts to see which one would close more. A Winchester bolt won the contest and therefore was my choice for this conversion.
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In the process of doing the GI bolt conversion I removed the barrel from the receiver. One, it’s easier to handle the receiver without the barrel on it. Two, I wanted to deal with the areas of interference from the receiver first and not worry about any possible interference from the barrel itself, at least not yet.
Chinese receivers have a set screw on the receiver ring that must be removed before pulling the barrel or you can bugger up the barrel threads. These set screws are reportedly very soft and can be difficult to get out in one piece. I found a screwdriver bit that fit the thickness of the slot the well, but was too wide to fit into the flathead slot itself, so I modified it with a Dremel and Cut-Off Wheel.
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I placed the modified bit into the slot, slid the screwdriver over it, tapped the screwdriver with a hammer to be sure the bit was fully set into the slot and carefully started removing the set screw. I was in luck this time as it came out in one piece.
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Next I removed the Connector Lock and pin I had installed, as I didn’t want the pin interfering with my action wrench, and once the pin is out the Connector Lock itself can fall out and disappear in the dark recesses of SS’s Man-Cave.
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Note the area where the finish is mostly removed on the Connector Lock, per my polishing for fit.
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Ok now to the press to remove the barrel. Brandon1 donated a barrel vise and action wrench to the SS M14 Build Disorder Society and they work great.
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I put the receiver in a vise lightly clamping down on the lugs up to the rail, just tight enough to secure the thing so it wouldn’t move while I was grinding with the Dremel.
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I tried various attachments and did not take photos of everything I tried, but carefully removed material from the offending areas as smoothly as I could, until the bolt would close. Be careful not to hit the locking lugs! Remember to take your time, check and recheck. It’s hard to put it back once you’ve removed it.
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When I got it really close, it seemed that it was stopping on the curved contour between the receiver ring and the shelf that the lug is supposed to stop on. I compared it with other rifles I had around and decided to carefully reshape that curved transition from the receiver ring to the shelf. Blue Dykem helped determine exactly where the offending areas were and soon I had the bolt fully closing.
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Once I was satisfied with the bolt’s closed position it was time to rebarrel. Note my $7 framing squares in use with Badger’s Timing Gauges.
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Note that I wanted to stick with a Chrome-Lined Barrel for this rifle and had several handy to try in the efforts of determining which barrel would give me the headspace range I was looking for. Obviously there is no way to shorten headspace, and I can only lap a few thousandths or so to lengthen headspace without getting too far into the carburization. I would index the prospective barrel, clean the chamber, insert a 1.630” Go gauge, and note the right bolt lug position to figure which one would be the best for use. None of the barrels I tried would close on the Go gauge, which means the chamber dimensions as is would be too short and I would need to lap the bolt lugs to set back the bolt and effectively lengthen the chamber headspace.
Oddly enough, out of all the barrels I tried, the Chinese barrel that came on the rifle was the one that would require the least amount of lapping. I estimated that I could lap to achieve my desired chamber headspace without going more than about .003” into the carburization of the bolt and receiver. I had an excellent muzzle and a visual inspection of the throat showed no chipping or flaking at the lands, so I was good with using the original Chinese barrel.
After rebarreling, I checked the bolt to see if it would still close on empty. It would almost, but just not quite close on empty. Using a flashlight, Blue Dykem and dental floss, I pinpointed the interference at the top of the bolt. The shroud or hood of the bolt was impacting the barrel itself.
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If my headspace was already where I wanted it I would have relieved the barrel at that location until the bolt closed. But knowing that I still had a few thousandths to go by lapping the bolt, and knowing that the bolt would move to the rear when I did so, I presumed that it would make the necessary clearance.
So I lapped until I had the desired chamber headspace, and it did indeed make the necessary clearance at the barrel.
Here’s some photos of the homemade bolt lapping tool I use. Sized, cut, sanded brass case, hammerspring and nylon screw from Lowe’s with the threads taken off by a belt sander (so the shaft of the bolt will fit inside the hammerspring). The nylon screw just happens to be the perfect size to fit the bolt face. These photos are from lapping my SAI after correcting the bolt roller impact defect. The brass case is easy to remove if you size and polish or sand it before using it. If you don’t size it, you may need a broken shell extractor to get it out when you’re done lapping.
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Before performing this conversion job I have lapped a TRW bolt into a LRB receiver, a TRW bolt into a Fulton receiver (both for new builds using chrome-lined GI barrels), and lapped a TRW bolt into a SAI receiver to lengthen the chamber headspace after fixing the bolt roller impact defect (which shortened the chamber headspace).
I believe this Winchester bolt and Chinese receiver was harder than any of the others I had lapped before. It took noticeably longer to remove material than what I had experienced before. I noticed that the Winchester bolt had a lighter dimple (from heat treat test) compared to any of my TRW bolts. Perhaps this dimple is a visual indication to a prospective bolt buyer of how hard the bolt is? It would be interesting to know whether this is so, and if so, how that affects the depth of the carburization. If the bolt is harder does that generally mean the carburization is deeper? If so, those who prefer chrome-lined barrels may wish to use harder bolts to allow for a greater measure of safety when lapping bolt lugs to achieve chamber headspace?
I reassembled her and dressed her in something a bit more fitting, a nice birch stock I picked up from CMP-South…..
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A little refinishing of the stock, bedding, a websling and some park and she'll be ready to go out on the town....or at least to the range.
However, he did not change out the Chinese Connector Lock.
The Chinese Connector Lock fits flush with the side of the receiver when it’s closed and the Chinese stocks are cut so the wood is against the receiver at that location and the Connector Lock cannot work out while in the stock. The USGI Connector Locks are longer and do stick out of the receiver when closed, and the USGI stocks have a relief cut for this. So if you put a rifle with the shorter connector lock into a GI stock the lock can work loose. I’m not sure if the previous owner was aware of this or not, but the Operating Rod Spring Guide coming out of its place during shooting may have been the motivation for him selling the rifle so cheaply.
Since I noticed this, the first thing I did to the rifle after purchase was to install a USGI Connector Lock and pin. I found the Polytech Receiver’s Connector Lock hole to be undersized a bit. I could manage to get the Connector Lock into the hole but it was too tight to lock or unlock by finger pressure. I put the Connector Lock into the chuck on my minimill so it was holding the portion that would stick out of the receiver when closed and turned it while applying gentle pressure with some 400 grit wet/dry sandpaper. Taking the parkerizing off that area was sufficient to do the job.
The other things I did to the rifle right off the bat was shim the Gas Cylinder Assembly, switch Flash Hiders and install a Stripper Clip Guide, as it appears that the previous owner removed it to use a scope mount.
Everything I have read on the Chinese rifles says that they did an excellent job on the receivers. They are the only option in the US for a drop forged M14 type receiver that does not have a NFA tax stamp attached to it.
However everything I have read about the bolts says they are junk, at least the ones imported into the US before the import ban. A GI bolt will not generally just drop into a Chinese receiver and close. Material must be removed from the rear of the receiver ring, where the bolt lugs bind. Knowing this, I bought the Polytech with the idea of learning how to perform my own GI bolt modification.
In deciding what bolt to use, I tried two different New Old Stock (NOS) GI bolts to see which one would close more. A Winchester bolt won the contest and therefore was my choice for this conversion.
In the process of doing the GI bolt conversion I removed the barrel from the receiver. One, it’s easier to handle the receiver without the barrel on it. Two, I wanted to deal with the areas of interference from the receiver first and not worry about any possible interference from the barrel itself, at least not yet.
Chinese receivers have a set screw on the receiver ring that must be removed before pulling the barrel or you can bugger up the barrel threads. These set screws are reportedly very soft and can be difficult to get out in one piece. I found a screwdriver bit that fit the thickness of the slot the well, but was too wide to fit into the flathead slot itself, so I modified it with a Dremel and Cut-Off Wheel.
I placed the modified bit into the slot, slid the screwdriver over it, tapped the screwdriver with a hammer to be sure the bit was fully set into the slot and carefully started removing the set screw. I was in luck this time as it came out in one piece.
Next I removed the Connector Lock and pin I had installed, as I didn’t want the pin interfering with my action wrench, and once the pin is out the Connector Lock itself can fall out and disappear in the dark recesses of SS’s Man-Cave.
Note the area where the finish is mostly removed on the Connector Lock, per my polishing for fit.
Ok now to the press to remove the barrel. Brandon1 donated a barrel vise and action wrench to the SS M14 Build Disorder Society and they work great.
I put the receiver in a vise lightly clamping down on the lugs up to the rail, just tight enough to secure the thing so it wouldn’t move while I was grinding with the Dremel.
I tried various attachments and did not take photos of everything I tried, but carefully removed material from the offending areas as smoothly as I could, until the bolt would close. Be careful not to hit the locking lugs! Remember to take your time, check and recheck. It’s hard to put it back once you’ve removed it.
When I got it really close, it seemed that it was stopping on the curved contour between the receiver ring and the shelf that the lug is supposed to stop on. I compared it with other rifles I had around and decided to carefully reshape that curved transition from the receiver ring to the shelf. Blue Dykem helped determine exactly where the offending areas were and soon I had the bolt fully closing.
Once I was satisfied with the bolt’s closed position it was time to rebarrel. Note my $7 framing squares in use with Badger’s Timing Gauges.
Note that I wanted to stick with a Chrome-Lined Barrel for this rifle and had several handy to try in the efforts of determining which barrel would give me the headspace range I was looking for. Obviously there is no way to shorten headspace, and I can only lap a few thousandths or so to lengthen headspace without getting too far into the carburization. I would index the prospective barrel, clean the chamber, insert a 1.630” Go gauge, and note the right bolt lug position to figure which one would be the best for use. None of the barrels I tried would close on the Go gauge, which means the chamber dimensions as is would be too short and I would need to lap the bolt lugs to set back the bolt and effectively lengthen the chamber headspace.
Oddly enough, out of all the barrels I tried, the Chinese barrel that came on the rifle was the one that would require the least amount of lapping. I estimated that I could lap to achieve my desired chamber headspace without going more than about .003” into the carburization of the bolt and receiver. I had an excellent muzzle and a visual inspection of the throat showed no chipping or flaking at the lands, so I was good with using the original Chinese barrel.
After rebarreling, I checked the bolt to see if it would still close on empty. It would almost, but just not quite close on empty. Using a flashlight, Blue Dykem and dental floss, I pinpointed the interference at the top of the bolt. The shroud or hood of the bolt was impacting the barrel itself.
If my headspace was already where I wanted it I would have relieved the barrel at that location until the bolt closed. But knowing that I still had a few thousandths to go by lapping the bolt, and knowing that the bolt would move to the rear when I did so, I presumed that it would make the necessary clearance.
So I lapped until I had the desired chamber headspace, and it did indeed make the necessary clearance at the barrel.
Here’s some photos of the homemade bolt lapping tool I use. Sized, cut, sanded brass case, hammerspring and nylon screw from Lowe’s with the threads taken off by a belt sander (so the shaft of the bolt will fit inside the hammerspring). The nylon screw just happens to be the perfect size to fit the bolt face. These photos are from lapping my SAI after correcting the bolt roller impact defect. The brass case is easy to remove if you size and polish or sand it before using it. If you don’t size it, you may need a broken shell extractor to get it out when you’re done lapping.
Before performing this conversion job I have lapped a TRW bolt into a LRB receiver, a TRW bolt into a Fulton receiver (both for new builds using chrome-lined GI barrels), and lapped a TRW bolt into a SAI receiver to lengthen the chamber headspace after fixing the bolt roller impact defect (which shortened the chamber headspace).
I believe this Winchester bolt and Chinese receiver was harder than any of the others I had lapped before. It took noticeably longer to remove material than what I had experienced before. I noticed that the Winchester bolt had a lighter dimple (from heat treat test) compared to any of my TRW bolts. Perhaps this dimple is a visual indication to a prospective bolt buyer of how hard the bolt is? It would be interesting to know whether this is so, and if so, how that affects the depth of the carburization. If the bolt is harder does that generally mean the carburization is deeper? If so, those who prefer chrome-lined barrels may wish to use harder bolts to allow for a greater measure of safety when lapping bolt lugs to achieve chamber headspace?
I reassembled her and dressed her in something a bit more fitting, a nice birch stock I picked up from CMP-South…..
A little refinishing of the stock, bedding, a websling and some park and she'll be ready to go out on the town....or at least to the range.
