Okay so I had no intention of building an AR, and especially not a 7.62x39 AR, but the opportunity to buy a barrel was presented on the EE last year and it was too good to pass up, and so the build began. I thought I would build it, have some fun and then sell it, but thats not how this story went, I dont think I could part with it now after seeing how it shoots!
PARTS BREAKDOWN:
UPPER:
Brass-aluminum forge upper receiver (square mark on right side) NEW
16" TNW barrel - gas port is not in a standard position (was a gas piston system barrel) used
Rifle length gas tube (had to be trimmed to fit for non standard gas port which is closer to midlength) used
Midwest Industries set screw low profile gas block (used)
Free float forend and barrel nut from Remington R15 painted black (used)
Ice arms phosphate FA bolt carrier (new)
DPMS 7.62x39 bolt (new)
DPMS charging handle (used)
Firing pin (not sure brand) (new)
A2 flash hider ½-36 thread (not sure brand) (new)
The scope is a Redfield revolution 3x9x40 (new) on a Burris PEPR QD 1” mount (used)
LOWER:
Blue line sale receiver (new)
DPMS LPK (new)
DPMS stock/buffer/spring/tube (new)
XCR 7.62x39 mags (new)
I also needed tools so I picked up a NC star multi AR wrench and a clamshell style upper vice block
ASSEMBLY:
Assembling the whole thing was pretty fun/educational, but there were some challenges:
-The barrel does not have a standard gas port location because it used TNW’s proprietary gas piston system.
Luckily one of the gas block’s set screws holes lined up perfectly with the 1st hole that is recessed in the barrel where the piston system was clamped down, so I know it will stay put. I screwed the set screws on the gas block down without applying loc tite for now in case I had to take the whole thing apart.
-I did not have a crush washer for the flash hider, so I just attached it hand tight for now (seems to stay put).
-The barrel nut was torqued to 42-43 lb/ft with my torque wrench before it aligned to the next gas tube hole.
-The free float forend is also just hand tight for now.
-For the lower I had issues inserting the bolt catch pin and it was ruined in the process, so for now the bolt catch is kept in place by a crappy nail (seems to work fine). No trigger guard until I find an enhanced winter guard.
What it looks like assembled:
FIRST RANGE TRIP:
I did not have any 7.62x39 mags so I was just using pmags with 2 rounds loaded and this seems to work fine, but with 3 rounds would jam on the 2nd shot. Also did not have the PEPR at this point. Ammo used was norinco 7.62x39 non corrosive surplus because there was no way I would be disassembling the gas system after shooting corrosive to clean.
I expected light strikes based on reports that surplus primers are hard and that the firing pin for 7.62x39 should be longer, and this is exactly what happened. It would go like this: boom, boom, click, manually extract, boom, click, extract, boom, click, extract, click, extract, boom..... not exactly an enjoyable experience.... Upon inspecting the cases that did not fire, it seems like these are the ones that have primers recessed quite a bit more than the ones that fired.
Another thing that happened after about 50 rounds is that the bolt would no longer go into battery. Turns out that the ice arms carrier has a gas key that was phosphated on the inside or is undersized (don’t get me started on the non existent staking!), so the fouling from cycling built up and did not allow the carrier to close over the gas tube.
Reliability aside, there was a silver lining none the less, 25 yard 5 shot groups (yah I know big f-ing deal) looked like this:
BUT then I went down to the target I set up around ~100m and was shocked to find this:
Now the group as a whole isnt anything special (10+ shots), but a lot of these were touching! Turns out this rifle has some potential! But this is what you have to keep in mind: I was shooting standing, front of rifle supported by a bag, stock supported just on my shoulder and the DPMS trigger is far from excellent or smooth. I was not prone, or even sitting, no bipod, no rear bag, and the scope wasnt sighted at all (did I mention there was also a snow storm out?)
I didnt see the target until the end of the day when we were cleaning up and was very impressed, I can just imagine how this group will look if I get into sitting/prone with a bipod, rear rest, or improved trigger or some premium ammo or handloads (no plans to handload at the moment).
FIXES AFTER 1st RANGE TRIP:
Before I did any further accuracy testing, I had to correct the reliability which meant eliminating light strikes and gas key issues. I modified the firing pin by hand filing the shoulder/collar, as well as the tapered end near the tip of the pin, I also sanded down the "tail end" of the bolt.
These mods allow the firing pin to protrude a bit more and ignite the surplus primers.
I sanded/filed the inside of the gas key so the key closes over the gas tube even after fouling.
2nd RANGE TRIP:
I finally picked up some XCR 7.62x39 mags so I can load 5 and 10 rounds reliably (they work great, no feeding issues). I got to sit this time (still not ideal as you can see in the pic), and shot 100m groups that I think are pretty impressive for a semi auto and considering the shooting position/rest/trigger/ammo.
This was the best one, but the others were not that much worse. (same as 1st pic)
I still got 8-9/10 rounds firing with the firing pin mod, and for the ones that did not fire, I noticed that the primer was recessed pretty deep into the casing. The fired cases that I picked up, I noticed that the primer was mostly flush. I will have to further file the firing pin end so it protrudes a few more thousands on an inch. The rounds with light strikes I then fired without issue in my friends new XCR.
I would love to try this thing prone and with some better ammo and a better trigger, I bet I can get all the rounds touching no problem! Never experienced this sort of accuracy with the ol’ SKS.
PARTS BREAKDOWN:
UPPER:
Brass-aluminum forge upper receiver (square mark on right side) NEW
16" TNW barrel - gas port is not in a standard position (was a gas piston system barrel) used
Rifle length gas tube (had to be trimmed to fit for non standard gas port which is closer to midlength) used
Midwest Industries set screw low profile gas block (used)
Free float forend and barrel nut from Remington R15 painted black (used)
Ice arms phosphate FA bolt carrier (new)
DPMS 7.62x39 bolt (new)
DPMS charging handle (used)
Firing pin (not sure brand) (new)
A2 flash hider ½-36 thread (not sure brand) (new)
The scope is a Redfield revolution 3x9x40 (new) on a Burris PEPR QD 1” mount (used)
LOWER:
Blue line sale receiver (new)
DPMS LPK (new)
DPMS stock/buffer/spring/tube (new)
XCR 7.62x39 mags (new)
I also needed tools so I picked up a NC star multi AR wrench and a clamshell style upper vice block
ASSEMBLY:
Assembling the whole thing was pretty fun/educational, but there were some challenges:
-The barrel does not have a standard gas port location because it used TNW’s proprietary gas piston system.
Luckily one of the gas block’s set screws holes lined up perfectly with the 1st hole that is recessed in the barrel where the piston system was clamped down, so I know it will stay put. I screwed the set screws on the gas block down without applying loc tite for now in case I had to take the whole thing apart.
-I did not have a crush washer for the flash hider, so I just attached it hand tight for now (seems to stay put).
-The barrel nut was torqued to 42-43 lb/ft with my torque wrench before it aligned to the next gas tube hole.
-The free float forend is also just hand tight for now.
-For the lower I had issues inserting the bolt catch pin and it was ruined in the process, so for now the bolt catch is kept in place by a crappy nail (seems to work fine). No trigger guard until I find an enhanced winter guard.
What it looks like assembled:
FIRST RANGE TRIP:
I did not have any 7.62x39 mags so I was just using pmags with 2 rounds loaded and this seems to work fine, but with 3 rounds would jam on the 2nd shot. Also did not have the PEPR at this point. Ammo used was norinco 7.62x39 non corrosive surplus because there was no way I would be disassembling the gas system after shooting corrosive to clean.
I expected light strikes based on reports that surplus primers are hard and that the firing pin for 7.62x39 should be longer, and this is exactly what happened. It would go like this: boom, boom, click, manually extract, boom, click, extract, boom, click, extract, click, extract, boom..... not exactly an enjoyable experience.... Upon inspecting the cases that did not fire, it seems like these are the ones that have primers recessed quite a bit more than the ones that fired.
Another thing that happened after about 50 rounds is that the bolt would no longer go into battery. Turns out that the ice arms carrier has a gas key that was phosphated on the inside or is undersized (don’t get me started on the non existent staking!), so the fouling from cycling built up and did not allow the carrier to close over the gas tube.
Reliability aside, there was a silver lining none the less, 25 yard 5 shot groups (yah I know big f-ing deal) looked like this:
BUT then I went down to the target I set up around ~100m and was shocked to find this:
Now the group as a whole isnt anything special (10+ shots), but a lot of these were touching! Turns out this rifle has some potential! But this is what you have to keep in mind: I was shooting standing, front of rifle supported by a bag, stock supported just on my shoulder and the DPMS trigger is far from excellent or smooth. I was not prone, or even sitting, no bipod, no rear bag, and the scope wasnt sighted at all (did I mention there was also a snow storm out?)
I didnt see the target until the end of the day when we were cleaning up and was very impressed, I can just imagine how this group will look if I get into sitting/prone with a bipod, rear rest, or improved trigger or some premium ammo or handloads (no plans to handload at the moment).
FIXES AFTER 1st RANGE TRIP:
Before I did any further accuracy testing, I had to correct the reliability which meant eliminating light strikes and gas key issues. I modified the firing pin by hand filing the shoulder/collar, as well as the tapered end near the tip of the pin, I also sanded down the "tail end" of the bolt.
These mods allow the firing pin to protrude a bit more and ignite the surplus primers.
I sanded/filed the inside of the gas key so the key closes over the gas tube even after fouling.
2nd RANGE TRIP:
I finally picked up some XCR 7.62x39 mags so I can load 5 and 10 rounds reliably (they work great, no feeding issues). I got to sit this time (still not ideal as you can see in the pic), and shot 100m groups that I think are pretty impressive for a semi auto and considering the shooting position/rest/trigger/ammo.
This was the best one, but the others were not that much worse. (same as 1st pic)
I still got 8-9/10 rounds firing with the firing pin mod, and for the ones that did not fire, I noticed that the primer was recessed pretty deep into the casing. The fired cases that I picked up, I noticed that the primer was mostly flush. I will have to further file the firing pin end so it protrudes a few more thousands on an inch. The rounds with light strikes I then fired without issue in my friends new XCR.
I would love to try this thing prone and with some better ammo and a better trigger, I bet I can get all the rounds touching no problem! Never experienced this sort of accuracy with the ol’ SKS.
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