MaineMan2

Conclusion: everyone building one of these rifles needs headspace gauges because the variances in chambers and bolts are too significant. Without going into too much detail, there actually are 3 barrels and 3 bolts here now. The tight chambered Fulton Armory barrel plus 2 Faxon 16" Big Gunner barrels. First, the original Aero Precision nitrided bolt that was so tight in Fulton Armory barrel I had to have them ream the chamber out a bit. I also have a second nitrided AP bolt plus a nickel boron AP bolt that I found on sale. As explained above, one of the Faxon barrels has an OK chamber while the second has what appeared to be a loose chamber - only the original, tight AP bolt passed the NO GO test in that barrel. So the third Aero Precision BCG arrived today and I immediately stripped the bolt, got out the gauges and went to work. This new bolt will not close on the GO gauge in the tighter of the 2 Faxon barrels. It barely closes on GO gauges in the looser Faxon barrel (loosest chamber of the 3 barrels). I don't really need to test it in the Fulton Armory barrel. Perfect! The first bolt stays with the Fulton Armory barrel. The second bolt stays with the tighter Faxon Barrel (passed GO and NO GO tests), and the nickel boron AP bolt will be dedicated to the looser Faxon barrel. Remember that the 308 Winchester GO gauge is 1.630" and NO GO is 1.634". Obviously I have barrels and bolts that have variances of substantially more than 0.004". One of my bolts failed the NO GO test in the looser Faxon chamber, but the newest bolt just closes on the GO gauge in that same barrel. While I haven't tested it yet, it seems safe to assume that the new bolt would fail the GO test in both of the other barrels. I was NOT expecting this much variance in chamber/bolt dimensions.

Actually the Fulton Armory upper will be more of a bench rest rifle. The Faxon barrel upper definitely is hunting.

Before you read this, I am fairly certain the answer is “return the barrel that fails NO GO gauge test.” However, I can swap bolts around so that I have 2 barrels that both pass headspace tests. I’m assembling a second, lighter upper for my first 308 AR build. In This thread I asked if I should have a dedicated bolt for each barrel and the answer appears to be “yes”. My first barrel is a Fulton Armory “medium weight” 18” Criterion barrel (2.9 lbs.) Initially my Aero Precision bolt would not close on a GO gauge. Neither would the bolt from a Windham Weaponry 308 AR. Fulton Armory fixed it so that it closes on a GO gauge with virtually no slop. They specifically call it a “match chamber”. My second barrel from Faxon is a 16” Big Gunner profile. My new Aero Precision bolt barely closes on a NO GO gauge in the Faxon barrel. However, the first AP bolt will not close on a NO GO gauge in the Faxon barrel. Both bolts have what seems like a lot of leeway closing on the GO gauge in the Faxon barrel. So I could assign the first bolt to the second Faxon barrel and pass the NO GO gauge test, then assign the second bolt to the Fulton armory barrel. Is that an acceptable solution or should I get a replacement Faxon barrel?

Thank you!

I am using a Faxon 16” Big Gunner profile barrel for a new upper. Faxon specs say “mid-length” gas tube. Aero Precision mid-length gas tube and M5 upper. Gas tube measures 11-3/4” long. Dry fit barrel in upper receiver, line up gas tube hole with gas port on barrel, and I get this: Looks like a 12” gas tube would be about perfect. Based on: 98’s thread the 11-3/4” gas tube should be correct but clearly it’s not. Using info from that thread, I did find that Armalite’s “carbine” gas tube is 12-1/16” long. Can’t find a “mid-length” tube anywhere I know of that specifies 12” length. Many are mystery parts, and the ones that do list length (like Aero Precision) all say 11-3/4”. Except Armalite itself. Fulton Armory sells a “carbine” length gas tube - given that their “rifle” gas tube is 15-1/2” like Armalite it’s possible their “carbine” tube matches AR-10 specs as well. Should I go ahead and buy a 12” or 12-1/16” gas tube before moving ahead?

Then you might like this 4” Model 66 (no dash) too…

Oh like my grandparent’s address in Cleveland? That’s certainly useful … not.

Funny thing is I don’t remember new phone numbers at all. I can rattle off my first cell phone number from 1990 and my home phone from the ‘60s in an instant but don’t know the California # my daughter got a couple years ago. I know the area code but the rest is in my cell phone…

I’m surprised by this conversation. Don’t doubt you at all, but a refund is where I’d go too. I had a headspace problem with a Fulton Armory barrel and bolt. “Bolt won’t close on GO gauge.” ”Headspace gauges vary and we use Forster.” So I buy a Forster headspace gauge and still no joy, although it did seem very close to closing on the second GO gauge. (Note: I now have both Forster and Clymer 308 headspace gauges but can’t remember which came first - they might have been using a Clymer gauge) ”Send us the barrel and bolt and we will make it right.” FA reamed a thousandth+ more out of the chamber and re-polished it very nicely. Bolt just closed on my first GO gauge and a tiny bit more loosely on the second GO gauge. I paid for shipping and second set of headspace gauges. Oh and turnaround was just about as fast as it could be. Was this ideal? No but the end result is excellent, and I never felt like I was talking to someone who didn’t build rifles. P.S. I was going to use a Wilson Combat 16” Ranger barrel for a new upper but they went out of stock just before I finalized my plans. Your story makes me happy in an odd way - 16” Faxon Big Gunner barrel should arrive today.

Thanks - did not have that in long-term memory.

I like that “parts that slide together should ride together.” Thanks

My first 308 AR build ran like a top out of the box. Only problem is it weighs 12-1/2 pounds with scope. So I’m assembling a second upper using a Faxon 16” Gunner profile barrel and Aero Precision upper receiver (to match AP lower). I used Aero Precision’s “enhanced” upper and handguard in the initial build. However, I’m using AP’s normal upper and lightweight S-One handguard this time. That alone will save 1/2 pound according to AP. Is it OK to swap a BCG and especially bolt back and forth between barrels? Read somewhere that the bolt and barrel extension lugs wear together and sort of need to be mated. I’m not shooting competition and seriously doubt I’ll top 1,000 rounds a year - probably more like 500.

Ian just uploaded a great video on Forgotten Weapons that answers this question. The most fascinating thing to me is that originally the bolt carrier was really long and included what is now a separate part - the buffer. This confirms my thoughts that it is the combined weight of the BCG and the buffer that matters. (Please ignore the optical distortion in the pic.)

I originally bought a 3” S&W Model 66-4 new around 1990. Had no idea it was a limited production run - I just loved the balance and feel of the gun. Fast forward 25 years. My daughter moves out to LA and suggests that she’d like to be able to protect herself. Of course? What gun would you like? Oh that really nice revolver. Ugh… but of course I gave it to her. After a couple months my quest for a replacement went into high gear and I eventually paid up for another 66-4. Apparently my illness went into remission but came back this year as you will see below. Model 66-2 Model 66-3 Model 66-4 (second one) I do have the nice wood stocks for the 66-4 but the Hogue Bantams are great for shooting and this is NOT a safe Queen.

Thanks guys!

Good question! I instinctively went with 15” handguard for longer sight radius, but that hardly applies in this context since there will be an optic. Extra 3” weighs 1-1/2 ounces more. Optics Planet would change order but doesn’t have 12” black and neither does anyone else that I can find quickly. I do prefer to have the gas block covered.

Update: finally getting off the ground with this project. I contacted Aero Precision and asked about the weight of their “enhanced” receiver and handguard vs. their regular M5 upper and an Atlas S-One handguard. Guy surprised me when he said that the enhanced setup weighed 1/2 pound more. Yes, it’s really solid but 1/2 pound? Not for this build. Here’s what I’m thinking about for a critical parts list: Aero Precison M5 lower & upper receivers, Atlas S-One 15” handguard, BCG, rifle length buffer tube kit. Faxon Big Gunner profile 16” barrel with “mid-length” gas system (Does anyone know if I need to find an odd length gas tube for this?) Haven’t decided on trigger yet. Rifle stock?

I’m building a “light weight” 308 AR starting with Wilson Combat’s 16” Ranger barrel (32.4 oz.) It has their “intermediate” length gas system, so I know I have to get their intermediate length gas tube. Going to use their lo profile gas block too just to reduce the risk of compatibility issues. My first 308 AR build was successful using a Fulton Armory barrel and bolt in an Aero Precision BCG. However, I did have to send the barrel back to FA because their bolt wouldn’t close on 2 different GO headspace gauges. I paid shipping and they reamed the chamber a thousandth+ more and re-polished it. I’m going to use upper and lower receivers from Aero Precision again because they worked well and I now know about the little quirks there. Rifle buffer tube, spring and buffer Aero Precision BCG weighs 18.24 oz. Wilson Combat BCG weighs 18.6 oz. CMC 308 AR BCG weighs 18.4 oz. AR Stoner BCG 17.7 oz. and Faxon has an “OEM overrun” BCG at 18.7 oz. Here is my question: should I get the Aero Precision BCG or am I better off with the Wilson because that’s where the barrel is coming from as well? Wilson doesn’t sell 308 AR bolts separately. Cost is $290 for Wilson vs $230 for AP. I listed those weight differences because AP seems to be at the bottom of the range and Wilson near the top - 0.36 ounces doesn’t seem like enough weight to make a difference but …

WIndham Weaponry 16” barrel with Eotech holographic sight plus Eotech 3.5x magnifier 9.0 pounds Aero Precision M5E receivers, handguard, rifle length extension tube, buffer and stock, Fulton Armory “mid-weight” 18.5” match barrel between 10.5 and 11 pounds with Vortex Viper PST 1-6 Gen 2 scope. I do not want to hump around in the woods for hours with this thing. For comparison, my Springfield Armory Scout with 18.5” barrel and older Leupold FX-II 2.5x scout scope weighs 9.5 pounds however, that is with a “synthetic” stock that I affectionately refer to as “Gumby”. note: no magazines in any of the 3

Thanks. I read that whole thread again and had missed the part where 98 talked about adding 4 oz to his bolt carrier to get proper function after changing buffer weights. I notice that people tend to talk about buffer weights without considering the spring. It too is part of the system and 98 refers to the original DPMS 308 having a special spring to make their system work. I’d already thought about this because we routinely experiment with different springs in semiauto pistols. You can’t change the reciprocating mass there…

I’m surprised by the variations in weight for bolt carriers for 308 ARs. Sons of Liberty has an LR308/SR-25 BCG that only weighs 12 oz. Yes, I realize that the SR-25 was a different firearm but it was designed by Stoner if I’m not mistaken. Also isn’t the LR308 the first DPMS pattern 308 AR? JP Enterprises offers light weight, variable weight, and a “full mass” bolt carrier for 308 ARs. They state that the full weight version weighs more (15.31 oz. Excluding than a standard DPMS pattern. Aero Precision and Wilson Combat BCGs weigh about 18 ounces, but that includes the bolt itself, cam pin, firing pin, and cotter pin. After the rifle fires, isn’t it the combined mass of the BCG and the buffer what determines how fast the action will cycle? If I’m correct there, then it seems you would have to compensate for a lighter BCG with either a heavier buffer or less gas. Am I missing something? What is the weight spec for a “standard” DPMS bolt carrier or BCG? JP specifically limits their low mass bolt carriers to competition shooting…

Thanks! That’s great to know. Did you say earlier that Ballistics Advantage is the OEM for Aero Precision barrels?

I just discovered that Ballistic Advantage offers a discount if you buy a barrel and BCG from them at the same time. Haven’t confirmed that they check headspace so please verify…

Actually it’s 5.6 oz. according to AP website.

I had the same problem with an Aero Precision bolt and Fulton Armory barrel (Criterion blank). Fulton Armory had me send bolt and barrel to them. They said that the bolt would close on their GO gauge but still reamed approximately 1000th (according to them) more off the chamber and polished it again. Bolt now closes on my Forster GO GAUGE. Please note - this barrel is described as “match quality”. IOW the chamber is deliberately tight and I had tolerance stacking. Also, FA specifically stated that they only use Forster headspace gauges for whatever that’s worth. Also DO NOT USE CARTRIDGE to check headspace. That’s just wrong. Cartridge dimensions are deliberately spec’d slightly smaller than chambers. Think about it - they need to be.