Lightweight Build Idea: Am I a kook?

[Janny_Brova]

Just finished a lightweight 18" .308 build with a hunting aspect in mind and I'm gonna be honest... Its making my current 20" grendel feel a bit insecure about itself.
Anyways I have a mind to SBR a KP15 lower with a 12" upper using a faxon barrel, an RTB lightweight bolt carrier, and a wojtek agb... All said it should clock in at ~5lbs

Question is... Is that a dumb combination that is just doomed to have cycling issues? I haven't played with lightweight bolt carriers with grendel in general, but I'm no stranger
to tuning rifles.

[StoneHendge]

Anything is possible as long as you can adjust your gas!

[biodsl]

Anyways I have a mind to SBR a KP15 lower with a 12" upper using a faxon barrel, an RTB lightweight bolt carrier, and a wojtek agb... All said it should clock in at ~5lbs

You should do this.

[lazyengineer]

Put it on a Magnesium lower for bonus weight savings points.

As to the light carrier, I personally prefer running heavy carrier to slow it all down, but if you have an adjustible gas block, that should take care of it. That said, beware that most AR15 adjustible gas blocks use these delicate little screws, that very quickly freeze into place. Making them more or an initial usage setable gas-block, more than actually adjustible. Most blocks are hidding under the handguards, and hard to get to (one reason I prefer a shorter handguard). So my advise is don't go cheap on the gas-block, but get one with a great big adjustment knob, not some tiny little recessed screw.

[A5BLASTER]

Adjustable gas and the rtb lowmass bcg will work fine with a 12 inch barrel and carbine length gas.

I have done several of them. I have used standard carbine bufferand spring as well as my preferred buffer system the jp scs.

Adjust the adjustment screw in the gas block open and then closed every 200 to 300 rounds and it will never lock up on you. I have used the wojtek gas blocks but moved to the SLR gas blocks now.

[Janny_Brova]

Put it on a Magnesium lower for bonus weight savings points.

As to the light carrier, I personally prefer running heavy carrier to slow it all down, but if you have an adjustible gas block, that should take care of it. That said, beware that most AR15 adjustible gas blocks use these delicate little screws, that very quickly freeze into place. Making them more or an initial usage setable gas-block, more than actually adjustible. Most blocks are hidding under the handguards, and hard to get to (one reason I prefer a shorter handguard). So my advise is don't go cheap on the gas-block, but get one with a great big adjustment knob, not some tiny little recessed screw.

I've heard a lot about that sort gas block binding up but I haven't used like that as of yet. I was thinking more along the lines of the one he sells that has the forward facing click-adjustable screw. I've got one on another rifle and it's been working good so far.

[Janny_Brova]

That's good to hear! I'll definitely be going that direction then. I've also heard some good things about the slr gas blocks... I take it is a pretty decent step up?

[raamaudio]

Great fun putting together a low weight 65G

I got a bit nuts into this and ended up with a Faxon 12" barreled pistol that was 4.2 lbs and too much money, selling parts now...and I built one for 60 percent of the cost that was 4.7lbs, same barrel, etc....now I have a 5lb 16" rifle with around the same money into it though cutting it down to pin and weld so 16" total with a linear muzzle device.

I just happen to have a Faxon 12" Gunner barrel with approx 20 rounds through it.

I am running a little under powered but dang fine Leupold 1.5-4 Circle Firedot scope that I loved on the pistol and on my 10/22(nothing Ruger left on it, full custom) with mount less than a pound on my 16" rifle at the moment is just 6lbs scoped. With BUIS, finger stop, etc....6.2lbs. I have parts to make it lighter but prefer to sell them as it is light enough as is. I am looking into a 1-8 scope but that Leupold glass quality in any brand is $$$$ and most are far heavier.

I have the Superlative gas block on it now which is great if going suppressed but I probably will not do so. I have a new SLR gas block I could use, titanium, ouch $$$$, I wish I had bought the steel one then would just go ahead and use it.

[montana]

That's good to hear! I'll definitely be going that direction then. I've also heard some good things about the slr gas blocks... I take it is a pretty decent step up?

Like A5blaster said, it is good to adjust the screw in and out every so often. I put a little kroil oil in it when doing this. I have built competition rifles using a JP SCS, American Gold cassette type trigger, low mass TiN PVD BCG or Cerakote micro slick BCM BCG with the upper BCG channel Cerakote micro slick applied. This cuts recoil friction which allows the lowest setting on the gas port. I personally have not seen any significant difference between the low mass or standard BCG to justify one, others have. I use standard weights with no tungsten weights, which has the optimum recoil impulse with my set up. With a good muzzle comp and the rifle gas blocked tuned to the ammunition, the rifle's recoil is amazing. For hunting or competition shooting, the reliability is fine if the gas block is tuned to the out side temperature. One word of caution, never confuse these rifles with a duty rifle..

[tdbru]

you guys are amazing. i tried to do a "lightweight" 6.5 GR build and it still came in at 8lbs 6 oz. with sling. about 3 lbs less than the 24" HB upper but still, you guys got to 6.2 lbs?? well done. it's been 100% reliable with many various loads. accuracy is another issue however.
-tdbru

[Janny_Brova]

Great fun putting together a low weight 65G

I got a bit nuts into this and ended up with a Faxon 12" barreled pistol that was 4.2 lbs and too much money, selling parts now...and I built one for 60 percent of the cost that was 4.7lbs, same barrel, etc....now I have a 5lb 16" rifle with around the same money into it though cutting it down to pin and weld so 16" total with a linear muzzle device.

I just happen to have a Faxon 12" Gunner barrel with approx 20 rounds through it.

I am running a little under powered but dang fine Leupold 1.5-4 Circle Firedot scope that I loved on the pistol and on my 10/22(nothing Ruger left on it, full custom) with mount less than a pound on my 16" rifle at the moment is just 6lbs scoped. With BUIS, finger stop, etc....6.2lbs. I have parts to make it lighter but prefer to sell them as it is light enough as is. I am looking into a 1-8 scope but that Leupold glass quality in any brand is $$$$ and most are far heavier.

I have the Superlative gas block on it now which is great if going suppressed but I probably will not do so. I have a new SLR gas block I could use, titanium, ouch $$$$, I wish I had bought the steel one then would just go ahead and use it.

Yeah, I played with 1-8x scopes for a while and found that the money required to check the weight, glass quality, and eyebox requirements made them prohibitively expensive. I've actually taken to using 2-7x scopes recently as they offer generous eye relief and great weight saving at a pretty useful magnification range while remaining cheaper for the same level of glass quality.