BCM based SPR upper Mod 1ish

[Tangotag]

Finally, some money coming to go into this project.
The "bolt up system" on the DD lite is too much of a detractor for me so it's either DD M4 or Knight FF RAS.
But am leaning heavy to the Knight FF RAS 12" with price being about the same.
It is 6.2 oz heavier than the DD M4 12" but too many Mod 1 pictures in the last couple months are killing me.
The PRI Stainless Gas Block might be a good match for the barrel.
I think now taper pinning the gas block with a single 2/0 stainless taper pin is the plan. I already have the 2/0 reamer and need the gas block in determining the length in the pin to order.
Once the gas block is mounted the barrel will be media blasted and coated in Flat Black GunKote.
The A2 flash hider will work for now. I don't indend on getting a Ops Suppressor but may machine my own Ops style brake and collar for the recoil reduction and look.
Final high dollar scope option will have to be determined after I test out the barrel and my abilty in a reality check.
BUIS will be either Knight-Micros or Troy with an HK style front but after the barrel starts punching holes in paper.
Anything I overlooked? Before I spend some money.

[Pk14]

I'm getting to the same point on an SPR build (funding) - any consideration for the TRX Extreme 13" rail? Aside from a piece of rail on the bottom for the bipod and (possibly) a front hand hold, and maybe a short section on the side at some length for a QD sling mount (although I've seen top rail mount sling adapters out there), what do folks hang on SPR side rails to justify the real estate / weight?

Cheers,
Pk

[Sam]

I am leaning toward using the Daniel Def. M4 12" rail for length and lighter weight.

I am not sure which low profile gas block to go with and could use some thoughts here.

Gas block, go steel or stainless steel?

Nice start to your project sir.

I use the DD M4 12" rail on my SPRish upper. I'm happy with it. The bulk of the weight isn't in the rail, it's the barrel, it weighs a ton Mine doesn't have the mechanical sights, but I don't intend to use it for any other purpose except shooting paper targets at longer range.

I use a low profile gas block, it's not stainless steel.

Please share pictures with us when your project is completed.

[Tangotag]

I guess I jumped the gun posting 2 days ago.

UPS delivered today a $48 "discontinued stocking", "1 only" Vltor SS Gas Block set screw model I ordered from DPMS at the end of December.
I had figured that it went to someone else when they sent me in the first week of January about half my order without the Gas Block, everything was back-ordered.

A little reflection, my goal is only for building a tack driving mid-range tier 1 SPR upper.
That whole MK12 Mod 1 is an expensive pursuit to do it exact. Being the Knight non-micro BUIS at $380 for front and back and the Ops Brake and Collar at $180. I already went with the BCM 1:8 barrel, not a Douglas 1:7 and having a BCM upper and BCG, not Colt. So not building a Mod 1 seems more logical.

Noveske uses the Vltor Gas Block so it must be GTG.

Pk14 you make an interesting point on the TRX. I am interested in the Standard Rail version and have emailed Troy with a couple questions. The TRX Extreme, being so thin, would not work for me shooting in all other positions than prone.
The TRX Extreme Standard Rail is 24 oz. where the DD 12" M4 is only 13 oz. The DD 12" M4 is the heavy contender or I should say the lightest weight most likely solution I go with.

[Pk14]

Tangotag -

I'm not sure where the weight data comes from for the Troy Standard vs Extreme however, there's a pretty good thread on the subject here:

https://www.m4carbine.net/showthread...extreme+weight

I saw the weight of the 13" Extreme rail + nut at 12.6 oz. Granted, adding needed rail pieces will move the rail weight up quickly, however, I can't see much more than a section of bottom rail for a bipod mount and a small side section for a QD socket for the sling. At that point its about the same weight as the DD Lite 12".

What kind of use do you see where the rail may be too thin? I still haven't found too many examples of needed side rail real estate on SPRs outside of some folks overseas.

Cheers,
Pk

[Tangotag]

I screwed up the terminology for the Troy rails.
"The Chart" has TRX Extreme 13" at 11.43oz. and TRX Standard 13" at 24oz.
I have held a TRX Extreme and know it's too small for my use when shooting from a non-prone position.
The diameter of use for me is more of a personal preference. I plan to put on the rails, Magpul XTM panels for hand hold shooting positions. I have some big hands I am working with.
For the rest of the rails there is a front BUIS, bipod mount, some sort of foward sling mount location, and an occasional flashlight mounted for any varmint dusk to dawn shooting.
Having full rails leaves me some flexability in positioning these items as needed.

[Pk14]

Fair enough, thanks for the clarification - good luck with the build and I'll certainly join the others here in looking forward to the finished pics.

Cheers,
Pk

[Tangotag]

New update, project changed yet again. I reviewed a few of my other ARs and did a little swaping.
I took the money for the DD M4 rail and picked up a DD lower package from Grant that will be used for finishing other projects and freeing up a BCM lower for this SPR.

I had a 12" Lightweight YHM rail, that is only 1.8 oz heavier than the DD M4, on this chopped 20" to 16" pencil weight under the handguards.
This one is now back to A2 flashhider & handguards with a standard M4 buttstock. It's now a decent lightweight for my girls to shoot at IDPA side-matches.





I think the rail and ACS will work much better as a SPR in this configuration.
GK GunKote flat-black is on order. After it arrives, the barrel gets lightly blasted to matte up the surface matching the Vltor Stainless Gasblock then a couple light baked coats of paint. The gas tube and front rail will also get a paint and bake too in the end.
I would doubt that the GK will do any harm for the gas tube so why not make it all black.

Now for some accuracy testing, maybe some handloading too, and picking up a bipod mount. Finally settling in on a high-powered optic solution.

[docsherm]

The gas tubes get very hot and have a tendency to turn paint different colors. I take them off when painting.

[Tangotag]

Originally I had some reservations on painting the gas tube, I don't think painting the tube will cause it any harm.
I have a carbine that has a considerable amount GunKote Flat Tan overspray coated on the gas tube and is it still holding in original color.
GunKote can take 500F to 800F on the high end. At least that is what they claim in their Technical Data Sheet and that it is used for dissipating and transferring heat.
Hopefully I won't find myself the need for any rapid fire in defensive shooting of match ammo enough to melt the paint.
Though, in that case the paint would be my least concern.