5.56 SPR Upper Build Steps & Tools: 16" Rosco K9 Intermediate Gas Barrel + BCM Demo Upper + KAK 13" Handguard

[WeR0206]

The use case for this build is a low cost shorter length SPR made with some parts that I already had on hand except for the barrel and gas block.

Amazon list for tools/supplies mentioned in the videos/thread:
https://www.amazon.com/hz/wishlist/ls/3QMZQX5CVKWR2

Build videos 6 part series:

1. AR-15 16” SPR Upper Build 5.56 (1/6): Taking Barrel Measurements and Checking Headspace
   
2. AR-15 16” SPR Upper Build 5.56 (2/6): Installing Dust Cover and Forward Assist
   
3. AR-15 16” SPR Upper Build 5.56 (3/6): Installing Barrel Into BCM Thermofit Upper
   
4. AR-15 16” SPR Upper Build 5.56 (4/6): Torquing The Barrel Nut and Attaching Gas Tube To Gas Block
   
5. AR-15 16” SPR Upper Build 5.56 (5/6): Installing Gas Block, Muzzle Device, and Handguard
   
6. AR-15 16” SPR Upper Build 5.56 (6/6: Things To Check Before Test Firing
   

Build list (note re: pricing, some of these parts were purchased during Holiday sales):

• Upper receiver: BCM Demo Upper (# FLAT-TOP-UPPER-M4-DEMO) ($50) (thermofit)
• BCG: Radian Enhanced Nitride BCG (# R0081) ($179)
• Gas tube: Rosco Intermediate Nitrided Stainless Steel Gas Tube (comes with barrel)
• Gas block: Rosco .750” V2 Set Screw Gas Block (# ROS-NGB-002) ($38)
• Barrel: Rosco K9 16” 1:7 Intermediate 5.56 Nitrided 416R Barrel (# K9-16-HY-556-7-I) ($135)
• Handguard: KAK 13” Handguard (# MO-441-1010-006) ($110)
• Muzzle device: Cross Machine Tool Tactical Combat Flash Comp (QPQ Stainless) ($79)

Total cost: $591

Barrel inspection notes:

• Weight: 34.6 oz (2.2 lbs)
• Gas system length: Intermediate
• Gas port size: 0.088”
• Gas block journal: 0.7505”
• Barrel Extension: 0.9975”
• Headspace gauge check (on fully stripped Radian bolt):
  • 1.4636”: closes
  • 1.4646”: doesn’t close
  • 1.4686”: doesn’t close
  • 1.4736”: doesn’t close

Link to AR-15 upper build tools post:
https://www.youtube.com/post/Ugkxl7ASgT3q4m5A1T9gGwWvzNZD85zbZXqC
Link to AR-15 upper build steps post:
https://www.youtube.com/post/Ugkx-OnosmRoszGgOf4Z-qEJY6IQqnokqAE3

Build steps:
Part 1:

1. When the barrel arrives clean the chamber and bore with 91% Isopropyl alcohol then take measurements for weight, gas port size, gas block journal, and barrel extension
2. If you have a borescope, inspect the barrel and take pics/videos to document the initial state of the barrel. If you do see something like weird coloration, damage on the lands/grooves/crown/etc. still try shooting the barrel. If it doesn’t shoot and you think it’s from a documented defect you can always send the barrel back in to the manufacturer
3. Using a 1.4636” min headspace gauge and 1.4736” field gauge make sure the chamber is within min/max headspace specs by checking if a fully stripped bolt will close/twist on the gauges
4. If multiple stripped uppers are available find the one with the tightest fit on the barrel extension (I prefer thermofits)
   
   Part 2:
5. Once the upper is selected (if needed) install the dust cover and forward assist
   
   Part 3:
6. Clean the barrel nut threads, inside of upper, and barrel extension with some alcohol to remove any debris, etc. before installing the barrel into the upper
7. If building an accurized upper that’s not thermofit apply Loctite 620 to barrel extension then slide it into the upper (optional: apply a little aeroshell to the barrel nut threads to protect them from the loctite)
8. If thermofit, heat upper threads with heat gun on high for about 2 to 2.5 mins then quickly slide the barrel into the upper making sure it fully seats. Wipe any excess loctite from the barrel nut threads and inside upper near barrel extension
9. Allow upper to cool (note the loctite needs 24 hours to cure before shooting)
   
   Part 4:
10. Before torquing the barrel nut down examine the area where the barrel extension feed ramps match up with the feed ramps in the upper. Use a toothpick, etc. to see if there is any snag when going towards the barrel, if so use a file to smooth it out
11. Apply aeroshell 64 assembly grease to the barrel nut threads and shoulder of barrel extension
12. With upper secured internally by the lugs with Midwest Upper Receiver Rod, Magpul Bev Block, etc. season the barrel nut threads by tightening close to torque spec and loosening a few times then torque barrel nut based on handguard manufacturer’s specifications (KAK says 35-55 ft-lbs, I use upper end)
13. Attach gas tube to gas block using Midwest Industries lower receiver block and White Oak gas tube spiral roll pin with 5/64 punch
    
    Part 5:
14. Attach gas block with cup tip set screws @ 15-20 in-lbs then verify gas port alignment w/ scope. After test fire replace cup tip screws with knurled tip screws and optional threadlocker (Loctite 246 or Rocksett) then make witness marks on screw heads
15. With upper secured internally via the lugs, oil the muzzle threads and attach the muzzle device (torque to ~15 ft-lbs). Note if muzzle device will be used as a suppressor mount don’t put any oil and instead add a few drops of Rocksett to the muzzle threads before attaching muzzle device (let cure for 24 hours before use)
16. Attach handguard by following manufacturers specs re: use of threadlockers, oil, etc. on handguard screws and torque specs. Witness mark each screw head (use Vibra-tite VC-3 or Loctite 246, KAK spec: alternatively tighten each screw until you get 45 in-lbs)
    
    Part 6:
17. Before test firing check the following: gas tube is far enough inside of upper, carrier mates well with the gas tube (no hang ups or friction), m-lok screws aren’t touching the barrel or gas block, check bolt extractor rotation on pin, and check if firing pin has any friction sliding inside of bolt
18. Attach upper to lower and do a full function check and test fire

Threadlockers and grease:

• Assembly grease (for preventing different metals from galvanizing together, used on barrel nut threads, etc.):
  • AeroShell 64 Grease ($10)
  • TW25B Gun Grease ($20)
• For gas block screws:
  • Rocksett or Loctite 246 (high temp/oil resistant)
• For bolt carrier gas key screws:
  • Loctite 246 (high temp/oil resistant) or Vibra-Tite 121
• For muzzle devices/suppressor mounts:
  • Rocksett
• For handguard screws, scope bases, etc.:
  • Vibra-Tite VC-3

 

[Cascade Hemi]

Single use knurled 10-32 set screws, torqued to spec, are a better solution than rockset (or equivalent).

 

[WeR0206]

Single use knurled 10-32 set screws, torqued to spec, are a better solution than rockset (or equivalent).

I agree. I use cup tip to do a function check and if everything works well I swap them out for knurled tip screws. Just edited the OP to specify this.

 

[flogxal]

Good point on degrease before threadlocker, any oil/grease tends to render the threadlocker useless. I've had fasteners come loose in other situations (mountain bike fasteners) where I'd missed some oily residue. Knew a guy who crewed in top fuel 1/4 mile who was obsessive about threadlocker prep with that big bomb of an engine!

 

[TonyTheTiger]

Very interested to see how that barrel does.

 

[WeR0206]

Very interested to see how that barrel does.

Yeah me too, if I can get 1.5-1 moa 5 shot groups from a $135 barrel (labor day sale) I’d be thrilled.

Preston Moore’s channel did a review of this exact barrel recently (it seemed to like the heavier bullets better and was terrible with winchester 55gr plinking ammo but its pretty horrible with most barrels):

 

[WeR0206]

Just uploaded part 3, installing barrel in thermofit upper

 

[TonyTheTiger]

Yeah me too, if I can get 1.5-1 moa 5 shot groups from a $135 barrel (labor day sale) I’d be thrilled.

Preston did a review of this exact barrel recently (it seemed to like the heavier bullets better and was terrible with winchester 55gr plinking ammo but its pretty horrible with most barrels):

I have no idea who or what a Preston is, but be sure to let us know how it shoots!

 

[Trigger Monkey]

I have no idea who or what a Preston is, but be sure to let us know how it shoots!

Preston Moore youtube channel, he does accuracy testing of various barrels using 30 round groups from multiple types of ammunition. He provides the data and compares that to other barrels he's tested using a metric of max distance to get all A zone hits.

It's not bad content, probably helped sell more than a few SOLGW 16" SPR barrels.

 

[WeR0206]

I have no idea who or what a Preston is, but be sure to let us know how it shoots!

Haha, I should’ve been more specific, Preston Moore’s youtube channel is what I was talking about. I hope to get this build done, ammo loaded (likely 77gr SMK with ar-comp in LC brass), and head to the range within a week.

 

[WeR0206]

Video for part 4: torquing barrel nut and attaching gas tube to gas block has just been uploaded and added to OP

 

[TonyTheTiger]

He provides the data and compares that to other barrels he's tested using a metric of max distance to get all A zone hits.

Huh, that sounds like a way more interesting way to compare barrels than normal. I can only watch so many seconds of people measuring groups with calipers before I fall asleep.

 

[Cascade Hemi]

I have no idea who or what a Preston is, but be sure to let us know how it shoots!

Spoiler alert, the barrel performs (in the video) relative to it's price. Not totally horrible, not awesome, just ok.

From my experience, nitrided barrels benefit from being cleaned out with an abrasive, such as Iosso, before firing. You can see the chamber build up from nitriding in the video.

 

[WeR0206]

Spoiler alert, the barrel performs (in the video) relative to it's price. Not totally horrible, not awesome, just ok.

From my experience, nitrided barrels benefit from being cleaned out with an abrasive, such as Iosso, before firing. You can see the chamber build up from nitriding in the video.

When examining the barrel I cleaned it with a parker hale jag and patch soaked with iso alcohol and it had tons of orange debris/coloring on it. More than any other type of barrel. I may hit it with some iosso or jb if I get any funky results during first range trip. Not expecting too much from this build since it’s 90% from spare parts except for the barrel and gas block, but like I said if I can get less than 1.5 MOA 5 shot groups I would be thrilled.

 

[TonyTheTiger]

Spoiler alert, the barrel performs (in the video) relative to it's price. Not totally horrible, not awesome, just ok.

From my experience, nitrided barrels benefit from being cleaned out with an abrasive, such as Iosso, before firing. You can see the chamber build up from nitriding in the video.

I did have the video playing in the background earlier today. Without really paying attention I think I gathered that it shot well enough with good ammo and so horrible with WWB that it brought the average way down?

 

[Cascade Hemi]

When examining the barrel I cleaned it with a parker hale jag and patch soaked with iso alcohol and it had tons of orange debris/coloring on it. More than any other type of barrel. I may hit it with some iosso or jb if I get any funky results during first range trip. Not expecting too much from this build since it’s 90% from spare parts except for the barrel and gas block, but like I said if I can get less than 1.5 MOA 5 shot groups I would be thrilled.

The orange color is nitriding salts. The nitrided surface is incredibly rough, you'll feel the Iosso cut through the top layer.

Manufacturers claim theres no break in for nitrided barrels. I actually think the break in period 300 to 500 rounds because of the shit left from nitriding. The barrel settles in faster after Iosso.

 

[WeR0206]

The orange color is nitriding salts. The nitrided surface is incredibly rough, you'll feel the Iosso cut through the top layer.

Manufacturers claim theres no break in for nitrided barrels. I actually think the break in period 300 to 500 rounds because of the shit left from nitriding. The barrel settles in faster after Iosso.

Thanks for the heads up. I think I have some iosso or Rem 40-x laying around. Curious to see what happens without any paste during first session then hit it with paste in between 1st and 2nd session.

 

[WeR0206]

Build is complete. Just uploaded part 5. Next up is making some handloads for barrel break in.

 

[WeR0206]

Part 6: final checks before test firing