MaineMan2

I had assumed that 1-piece scope mounts would always be in alignment and not need lapping. In the process of moving a scope from one rifle to another, I thought “I’ll check this nice Warne mount just to be sure.” I hadn’t checked it when I out it on the first rifle. To my surprise, my Sinclair alignment gauge showed an error with the Warne mount. So I pulled out a Leupold mount that I had bought for another purpose but hadn’t installed yet. The rings on the Leupold 1-piece mount lined up perfectly. The comparisons between the two are interesting, especially considering that the Leupold Mark AR mount (top) cost almost $40 less than the Warne Gen 2 Skelontized MSR mount (bottom). The Leupold weighs 0.6 ounces less according to my scale. No big deal. However, unless you really need to push that optic forward over the handguard, the Leupold has much more solid attachment to the rail. The clamping surface is twice as long and 5 screws are better than 2 IMHO. Those 3 lugs on the underside of the Leupold lock into a Picatinny rail. The cross bolts on the Warne are narrower than the rail slots and allow significant fore and aft movement. The Leupold looks industrial while the Warne looks much more elegant to my eye. Please note that this is a sample size of 1 per mount. The biggest “aha!” for me was the need to check ALL scope rings for alignment.

Back to the video - did anyone notice the world’s weirdest hasty sling grip? Am I the only person who questions “I never change out AR triggers”?

Many thanks to all of you who helped me get this squared away. I thought I’d come back for a wrap up on this build. Total weight is 8 pounds 4 ounces. With an SLR adjustable gas block dialed back, brass goes into a nice circle about 8 feet away at roughly 3:00. To me, consistent ejection and not throwing brass too far tells me the rifle is running well. Based on my experiences here Aero Precision is not precise. You can see the spring inconsistencies above. I had to juggle AP bolts between rifles to get bolt/barrel combinations that passed GO/NO GO tests. Clearly Faxon isn’t any better since they made the barrels; however, variances in the bolts were the only reason I didn’t have to send something back. Then there’s the Aero Precision handguard. I got this model because of weight and no need to mount anything forward other than the front sight. After tearing my hair out and bottoming put the front sight, I figured out that the small forward rail was not coplanar with the receiver rail (using precision straight edge). I really like Aero Precision’s “enhanced” handguard attachment system but this was aggravating.

I have three 308 AR uppers. Two Faxon “identical” barrels and one Criterion barrel finished by Fulton Armory. Three Aero Precision bolts. I had to mix and match bolts with barrels and was lucky enough to find 3 good combinations in terms of headspace. 2 combinations wouldn’t close on the GO gauge. One combination would easily close on the NO GO gauge. Clearly there were variances over .004” between the bolts and barrel chambers. Like powders - only 308 upper on the bench at a time!

Had a great conversation with Alan at Springco. Short version: he doesn’t make rifle length springs because there isn’t much demand. That makes sense. He offered to help me solve this problem but agreed that an adjustable gas block was the best solution. I found it very interesting that he says “each rifle is an example of one” and says that they after need to be tuned individually to get them running right. Based on our conversation, I will not hesitate to use Springco in the future for any build with a carbine buffer tube. We did briefly discuss the difference in length of the two Aero Precision springs. I will not be buying one of those again.

Yesterday didn’t go as planned. I was almost packed up to head to the range when unrelated fecal material hit the impellers. I did go this morning. The Armalite EA1095 buffer spring made a small difference in the ejection pattern, moving it to about 1:30 from 1:00, and the brass was not being thrown as far. I also put a second EA1095 in my good 308 AR build that had the longer Aero Precision spring in it (see above). The ejection pattern didn’t change from 4:00 but the brass was closer together. I understand the guys saying “if it cycles ok and the bolt locks open, why worry?” However, if my buffer weight and spring are both good, then the brass should not be flying forward so much. That tells me the BCG is moving too fast (correct me if I’m wrong about that). One thought that occurred to me is that maybe the gas port isn’t perfectly round. IOW tightest inside diameter looks OK but it lets too much gas through. I’m not sure how to check for that.

New Armalite EA-1095 spring arrived after sunset. Here’s a pic comparing it two Aero Precision “rifle extension” springs: AP spring from “over-gassed” gun on top measures 12” long with 39 coils. Middle spring is another AP rifle spring from a build that works fine, has been assembled for months and shot a lot more. It measures 12-3/4” long, also 39 coils. Bottom is the EA-1095 measuring 13-1/2” long with 34 coils. I need to go to the range tomorrow and see how the rifles run with different springs, but I’m betting the spring was the problem.

Scale and #43 drill bit arrived. Please note - I’m basically keeping notes here at this point. Waiting on Armalite spring and email response from Springco. I am curious though about what potential problems a slightly long buffer might cause. I measured something wrong the other day. The Faxon Big Gunner 16” barrel gas port is between 0.0807” and 0.086”. That should be small, if anything, based on info above. #1 AP M5 enhanced 18” barrel, mid-length gas, rifle receiver extension - works fine BCG 18.5 oz. Buffer 5.3” 5.4 oz. #2 AP M516” barrel, Armalite mid-length gas, rifle receiver extension - ejects 1:30 10-12 feet WW 16” barrel, mid-length gas tube, carbine receiver extension BCG 18.6 oz. Buffer 5.28” 5.4 oz. I do need to put upper #2 on lower #1 to see if the problem is in the lower as we suspect. Finally, I’m not compulsive about where the brass ejects. However, when it’s flying out almost straight ahead and going over 10’ something isn’t right.

If the gas port is the correct diameter, then the problem must be mass of the buffer + BCG -OR- spring. Armalite EA-1095 spring is inbound. So is a scale that should be “good enough”.

Not my Ace Hardware 😜. I called them and #43 was “the only one we don’t have in stock”

Turns out a #43 drill bit is in between the 2 data points I already have so I ordered just that bit.

OK inside of buffer tube is exactly 9-11/16” deep. Buffer measures 5.28” long. 5.6 oz. weight came off Aero Precision site - I don’t have a scale in that range. Checking with every drill bit, etc. I can find, the gas port is between .086” and .093”. Probably close to half way in between. Based on everything I can find here, that is too big for a 16” barrel: I will order a new spring when I order the adjustable gas block. I’m assuming dialing back the gas is in order so correct me if I’m wrong! Need to know if it’s worth it to buy a set of numbered drill bits. May be able to weigh the buffer later. The BCG doesn’t come close to the back of the receiver where the buffer sits at rest (don’t know what that’s called). I know for an AR-15 you need to check and make sure BCG doesn’t hit that bridge before it bottoms out in buffer tube. Clearance for AR-15 should be 2 quarters thick. This was much more.

Took a new 308 AR build for its first range visit today. Ejection is very far forward - about 1:30 - and the cases are flying 10+ feet. Winchester white box M80 ammunition. The bolt is locking back correctly. I only fired single shots as my goal was to sight the rifle in. I’d brought 2 rifles to sight in so I switched to the other one rather than shoot this 308 AR more. My first thought is that I need an adjustable gas block, but let me spell out as many details as I can and get your input. Aero Precision M5 upper and lower receivers, BCG, rifle length buffer tube, and M5 308 Rifle buffer kit. The buffer is 5.3” long and weighs 5.6 ounces. I used the exact same parts with a Fulton Armory 18-1/2” mid-weight barrel. Fulton Armory specs an Armalite carbine AR-10 buffer tube for that barrel, so that is what I used. SLR adjustable gas block in the first build; however, I didn’t need to adjust anything. That rifle ejects about 3:30 and runs like a top with the SLR adjustable gas block wide open. (Using the exact same ammo.) I used a Faxon Big Gunner profile 16” barrel for this new build. Stock Midwest Industries gas block. A normal “mid-length” gas tube didn’t come close to the middle of the cam pin cutout in the upper receiver, so I got the longer Armalite AR-10 “carbine” gas tube. I don’t have the pin gauges I would need to measure the gas port diameter but am guessing that Faxon has over-sized it. So is an adjustable gas port the first step? I’m reluctant to mess with success, but swapping gas blocks between build # 1 and build # 2 might save me a little money.

ETA: a year ago I considered crimping unnecessary for 308 Winchester. However, my recent research indicates that more and more people are recommending crimping for gas operated, semiauto rifles. Including a tech at Hornady I spoke with yesterday. Roll crimp for bullets with cannelures. Taper crimp or no crimp for bullets without a cannelure.

Those videos aren’t available on Brownells/Sinclair anymore. However, they are on YouScrewed.

I’m wrestling with another Aero Precision lower and that takedown spring is driving me nuts again. So I found this video: They say to cut off much more of the spring than I had done. Plus now I know why they don’t give you a shorter spring for the rear takedown pin.

PMags. I like Aero Precision S-One handguards. The way they connect to the upper receiver is solid, if a bit fiddly the first time you install one. Weight is very good and that is important to me. However, if I wanted a beast of a handguard that could really take abuse I might look elsewhere.

Agree on WW customer service and bang for the buck with Windham Weaponry ARs. My 308 AR from them has DPMS pattern receivers. Bought 1 or 2 years ago.

Thanks!

Does anyone use a Flex Hone to polish the chamber on a new barrel or is that only for when you have problems? How about lapping the barrel during break in? Thanks, Chip

Bingo!

The horse has been beaten post mortem; however, sometimes a video is worth a thousand words. I typed up the following to get my own understanding squared away. It may or may not be useful to anyone else. At 4:40 in This video you can see the expanding gas entering the chamber inside the BCG. For a moment, the bolt is pushed forward by gas pressure at the same time the BCG is pushed backward. This reduces pressure on the bolt lugs while the cam pin is rotating the bolt out of battery. When the BCG has moved backward far enough for gas rings on the bolt to be forward of the vent holes in the side of the BCG, the gas pressure inside the BCG is released and the bolt can move backward with the BCG (under inertia now). This reflects the genius of Eugene Stoner IMHO. It also demonstrates the critical timing involved in getting this system to operate correctly. Now look at the carrier key/gas tube connection during that cycle. If the gas tube were a bit too long, it’s OK. More gas will be released through the holes in the side of the BCG from that chamber inside it but the BCG and bolt can still keep moving backward. However, if the gas tube is too short, the gas seal between the carrier key and the gas tube could be lost BEFORE the BCG gains enough momentum to move backward as fast and as far as it needs to. (Please note that the gas tube could be so long that it bottoms out in the carrier key, preventing the bolt from fully locking into battery and that would be “bad”.) Another video at 3:15 shows the gas system and bolt at work. (Turn sound down unless you like really bad heavy metal music) BTW that first video does an excellent job of showing how the trigger, hammer, disconnector and auto-sear operate. The handoff of the hammer from the disconnector to the trigger always gave me the creeps but it makes complete sense for select fire.

Thank you again. I was not familiar with DSG, but they were the only place I could find the correct Armalite ‘“carbine” gas tube at 12-1/16”. Someone please tell Faxon this is how it SHOULD look! Armalite part number is anyone needs it; last digit is a “5” I did check to make sure that this longer gas tube isn’t bottoming out in the gas key with the bolt closed. It’s not even close - the gas tube could go at least 1/4” further into the gas key on the BCG.

Good points! When I was sorting things out with Fulton Armory, the guy there told me that they used only Forster headspace gauges and my testing with a Clymer gauge didn’t matte - so I bought Forster gauges too. I can tell you from direct experience that my Clymer GO gauge is a tiny bit longer than my Forster. I can’t remember which was which but the NO GO gauges are different too. Rex is right - you can have variances in reamers, in barrel extensions and in bolts. I’ve never had a headspace problem with an AR-15 but these 308 beasties…

Ha! Read THIS THREAD for fun and games with headspac