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First Firing of 1st LR-308 Build


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The excitement of finally firing my LR-308 build after months of waiting for parts in the mail was soon tempered by ftf/fte problems.

But first the good news, it didn't blow up in my face on the first round fired.

I was using Winchester 7.62 and .308 ammo as pictured. All the 7.62s failed to eject. All the .308s ejected but failed to feed the next round. But ALL would feed and eject using the charging handle. So it would seem to point at short stroking due to gas pressure or buffer problems.

I'm using an adjustable gas block and kept screwing OUT the adjustment screw (I'm assuming OUT is what you do for more pressure) but did little or no help. It's possible the gas block hole is misaligned with the barrel port but the set screw is in the dimple on the barrel.

I lubed the bcg quite heavily.

I've also included pix of the fte and the ends of some of the 7.62 and .308 cases, if that helps. The ends of the 7.62s seem to show some heavy extractor markings.

The problem with working on guns is if you don't have a place to shoot on your property, you have to go to the range to test any fixes you did to find out if they work. My nearest range is 40 miles away and that slows down the progress. And you have to take all your AR tools with you.

One other thing, the bolt catch would sometimes work and sometimes not work. if it worked, the catch release would not work. I've had doubts it and replaced it already but no better. When installed, should the catch lie flat on the lower's surface? With pin inserted, it doesn't. See pix.

Below are links to the parts I'm using:

Sadlak Adjustable Gas Block

Aero Precision Upper

ALG Defense Trigger

AR-Stoner Gas Tube

Hexmag Magazine

CBC 20" Barrel

Mercury BCG

Luth-AR Buttstock/buffer/tube/spring

A side note: the red dot optic was so far off I wasn't even hitting the paper at 100 yds. It was shooting so high a range employee came to me to let me know I was hitting their rails above the targets (indoor range). Oops. I couldn't see where they were hitting. Moved the target to 35 yds and finally got one on the paper and was able to adjust the optic to hit where I aimed.

 Thanks for reading this long post. Any advice will be appreciated.








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You should always start at 25 yards or so with new sights to make sure you’re in the range you need to be before sending to 100 to fine tune…especially in an indoor range. That’s just proper range etiquette.  For the rifle, we’ll need more info. Double check your gas block is aligned, and while it’s off measure the size of the gas port. Take a look and make sure your gas tube ends in the middle of the cutout in the upper receiver. Measure the internal depth of your buffer tube, then measure and weigh (in ounces) your buffer.  Some may want to know length of spring and coil count. Let’s start with those as it’s usually one or more of those items. You say you were well lubed, but run it dripping for the first handful of outings. 

Edited by DNP
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Alright, thanks. I’ll try to get those measurements. Port size may be difficult since I have nothing that will measure it. I’ll have to rely on barrel manufacturer’s specs.

As for gas block alignment, the set screw on the bottom is in the barrel’s dimple. So if it’s slightly off , how do you tell?

As for the range screw up, most of my range time has been with handguns and iron sights. Never realized a new red dot sight could be that far off. A learning experience, indeed.

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53 minutes ago, Harveyshot said:

Port size may be difficult since I have nothing that will measure it. I’ll have to rely on barrel manufacturer’s specs.

I wouldn't recommend that.  I just ran into two barrels from Ballistic Advantage that were undersized.

If you have a Harbor Freight(or some other cheap hardware store) nearby and $20 to spare, you can pick up one of these to use for measuring.

Numbered drill bit set

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4 minutes ago, unforgiven said:

Harbor freight drill bits are not the best spend a little more for a better bit. Just my 2 mags. There are deals to be had there but bits aren't one of them. From my experience with them.

They are fine for measuring purposes(which is all I intended in my post), but I certainly wouldn't recommend them for actual drilling.

@HarveyshotNotice what I linked to are numbered drill bits.  They have more iterations of sizes between the "normal" drill bit sizes, which is why they're good for measuring gas port holes.

Link to drill bit chart showing "regular" and numbered drill bit sizes.

Edited by RacerX
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Just now, RacerX said:

They are fine for measuring purposes(which is all I intended in my post), but I certainly wouldn't recommend them for actual drilling.

Makes sense, they are good for one cut if they don't snap. They have deals on saws, welders, drill motors. 🍻🍻

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The reason you can not trust Manufacturers specs is there is no mill spec for 308 or large framed AR's and there cousins and brothers  they are all different . and I just about tell you now that I bet yours is undersized it happens all the time it and gas tubes are two of the main culprits along with wrong buffer...

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Well, mistakes do happen and I've done a few builds with Ballistic Advantage barrels now, with no issue.  Both of these barrels were ordered at the same time, so presumably they were part of the same batch.

Based on the gas port size they had (0.086") I would almost bet that someone was previously drilling/reaming mid-length barrels and forgot to change the bit when switching to rifle length.

I just chalked it up to a good lesson.  I will always measure the gas port from now on, before assembling.

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When you take the gas block off, you should see a little carbon around the hole. It will be very apparent if you can see that on there…should make a ring around the gas port as the hole in the gas block is bigger than the gas port hole. If you haven’t put enough rounds through it to see that…try this: Mark where your gas block sits when set into that dimple, and then rotate it 180. The hole drilled for the dimple should be in the same location as the gas port. 

You really do want to measure the gas port for yourself. Then you know for certain. 

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As I start the tearing down, here are some findings.

Gas port size: larger than 5/64 and smaller than 3/32 which is what it should be according to posts here and other places. 0.0935”/#42 falls between the two fractions above.

Here is a pic of the gas tube in the upper. Seems to end in the right place.

But I think the real culprit may be the bcg lubrication. The bcg was dry and the bolt would barely move in and out of the carrier. So much for thinking I lubed it enough.

Man, these DI systems are extremely dirty. And that was after only about 30 rounds. Excuse my ignorance but my only AR experience is with an AR-15 I built six years ago with a gas piston system. I would have done that with this one but they’re just too expensive.

On to the buffer assembly.

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I’m sure it’s good on your rifle, but the internal depth of the buffer tube is a good number to know.  

Lube that thing up and go put 100 rounds through it. Soaking wet. Start with your gas block wide open. Make it run, and tune it down from there if needed.  My rifle took a while for the parts to mate up and run reliably. Break in is definitely needed on these guns. They aren’t as foolproof as most of the 5.56 variants. 

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Back from the range with an update.

After about 50 rounds,  she almost did perfectly as far as feed and eject go. Near the end there were a couple of ftf and fte. Broke it open and oiled it some more. Didn’t help. Then I remembered DNP saying start it with the gas block wide open so I opened it quite a bit (didn’t want to lose that screw at the range) and that seemed to work.

So thanks everyone for all the advice.

The remaining  problem now is the bolt catch that isn’t catching with an empty mag inserted. I would put two rounds in a mag and fire off both but no catch. Did this many times. At first it would catch if I used the charging handle but at the end it wouldn’t. When I look at it with the gun open it just doesn’t seem right. If you can see it in the pic, the catch is barely making contact with the follower when the mag is fully inserted. The one pic shows it with the mag almost fully in. There are other pix of the catch in the original post.

 I’d appreciate anyone showing their bolt catch. Thanks.




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Aero Precision. Never actually tried out their bc on a functioning rifle, just didn’t like the way it moved so little and sat cocked in the lower.

Does everyone’s bc sit that way?

Ordered a Luth-AR bc and it did the same. Although, when trying the bc out a few weeks ago (just manually operating the bcg), it worked. All the parts we’re pretty much dry.

I’ll try the Armalite one and hope for the best. Thanks.

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Thanks for that link, jtalien83, but it just added to my confusion.

I’m starting to think I’ll have to buy one of every make and model and try them all. That little nub on my current bc, that the follower pushes up, barely makes contact with the follower. I think the 10a might be a viable choice because it ‘looks’ like that nub is wider and more towards the end of the bc but they are hard to find.

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