renaissanceman

I was hitting them pretty consistently with 75gr BTHP over CFE223 in a 223 last time around, but they wouldn't fall. 198gr 8mm bullets did the trick, but hitting them was rather tricky with Mauser open sights since the target was narrower than the front post. I have no doubt that the 168 launched from a 308 will get the job done.

I have a buddy with a membership to a private range that goes to 500m+ so just trying to be able to pound the knockdown targets on the 500m line with boring regularity.

Just put in notifications for primers of all types on Midway. What good is all the money in the world if you can't buy primers, anyway?

Haha, ok, I'll stick around. I'll be doing load development next. 168gr Hornady BTHP. Wallet in hand, but not much in stock to spend on these days...

Thanks! I'll be a lurking member...once the rifle runs, it's hard to have much to talk about, but I'll be reading in the shadows.

Seems to be fine, I'm working on load development now. It'll cycle min loads with 147gr FMJ bullets, so I think it's got the right size port. Not too gassy, either. Once I've got my pet load, I may tune the gas block down a bit if there's a bit more gas than I like.

Primers are what we need.

Care to share the math if there's a clean derived equation? I'd love to be able to set up a spreadsheet that predicts what is needed based on a QuickLoad predicted port pressure, but I think it'd be decently messy to derive.

All cycling issues have resolved -- it now cycles any ammo you feed it with bolt lockback every time. The recoil is quite mild and the empty cases land at the 4'oclock position about 5 feet from the rifle in a neat little pile. How's that for a happy ending?

Drilled to 0.938". First crappy dewalt bit couldn't handle it, second (new) one cut it smoothly and easily. Kissed it with a 0.125" bit afterwards for a bit of a chamfer to deburr. Bore cleaned and ready to roll, hopefully I'll get cycling and not have to give it another thought.

Will do. Last time I used a high grade bit and it kept grabbing the soft stainless and chipped all to hell on the cutting edges. This time I'll just use a crappy dewalt 3/32 bit on my cordless variable speed drill and take it slower with no guides or any other overthinking shenanigans. It'll probably work without drama and I'll be up and running tomorrow.

I'll take a drill bit to it soon -- I've done one in the past with a hand drill and a 3d printed guide to keep it straight and a 3d printed insert to keep the bit from going all the way through and into the opposite side. Sort of shady, but lacking a drill press...whatcha gonna do? Kinda strange that a rather large and reputable company (Aero) would under-drill a port -- I'm thinking a lot of AR10s are undergassed, despite everyone online seeming to think overgassing is the issue that causes chronic cycling headaches. Of all my buddies who have built one, I've still never seen one just run without issues.

No change. That 0.086" port is probably the culprit, as originally suspected. Any suggestions on what size to drill to? 3/32" (0.0938") perhaps?

The heavy buffer and spring arrived. Now to get to the range to test it.

I finally got around to ordering the heavy buffer. The first time the site's payment gateway was down, and then holidays hit and that was that. Looking forward to getting this thing running.

Can someone explain to me why with such a light buffer installed, my bolt would under-travel like it does in the footage? From my experience with AR15s, it should be much too fast if the gassing is sufficient. I'm tempted to drill the port to 0.093" while waiting on the buffer and spring...

Here's the thing -- I'm not seeing high bolt velocities, and the bolt is getting nowhere near the catch on firing (video shows this pretty clearly). I'm going to correct my buffer issues, but I'm still not sure how the increase in buffer weight will help, unless it helps get the gas impulse to the bolt converted into more kinetic energy to help with the bolt travel rearward against the spring. My gut is telling me after I get a new spring, buffer, and tube, I'll still have to drill the port. We shall see.

I measured, and the internal depth of the buffer tube is 7" (measured by pencil... the tape wouldn't fit...), the buffer is 2.5", and the buffer and spring combo is just shy of 12 inches when removed and the spring is at free length (uncompressed). Where do I go from here?

Ok -- read it in full -- makes sense. I'll start digging into what parts need to be replaced, hopefully tomorrow. Palmetto has been decent for AR-15 kits, everything always ran right out of the gate. This was not intended to be a buget build at all, but I was a bit confused as to what would work and what wouldn't so I ordered a kit. The kit has been a joke, though. Takedown pins were wrong, the bolt catch had a pin rather than a threaded pin, etc, etc. at least the buffer tube and magpul stock might be useful on a 15 at some point... I've never actually seen an AR10 that runs, but against my better judgement I was suckered in. I figured there's got to be a way to get them going, and I'd figure it out. I appreciate the time and expertise you guys freely offer.

I like a man who tells it as it is. I'm getting the picture -- I'll read the thread you linked and then measure when I can. The rifle lives at the farm, not my house, so it's a drive away to go check or I would have already done it. The Palmetto kit uses an AR-15 buffer tube and some janky shortened buffer to make it work. I noticed the spring looked like crap.

Yes, all the factors must be balanced and please correct me if I'm wrong here, but if the gas supply is held constant, doesn't adding more weight to generally slow the bolt speed and thus compensates for an overgassed condition?

How would this explain the bolt under travelling, though? Seems a heavier buffer would make my symptoms worse?

It's an AMT, DPMS pattern. It doesn't seem to be causing any issues.

I'll do that. It's a standard AR buffer tube if I recall correctly.

I'm new to the AR10 world, and I'm having issues with cycling. Bear with me -- there's been a progression of testing on this issue that will be covered in detail (TLDR: skip to video (https://streamable.com/3idj1i) and comment on undergassed symptoms) Parts in build: -Aero upper -20" ballistic advantage barrel, rifle length gas/0.086" port with a Kaw Valley Magnum linear comp, (no suppressor) -Standard BCG (unbranded, from Right to Bear) -Gorilla Machining adjustable gas block with Expo arms rifle length tube -Expo ar10 charging handle -PSA lower parts kit (carbine buffer tube, 2.8oz short buffer, ar10 buffer spring) -Magpul 10 round mags -Running wet with ALG go juice. The bolt can be pulled back by hand and locked on an empty mag. There's about 3/8 of an inch of travel past the stop. The gas tube sits at the halfway point in the cam "half moon" so I don't think that is the issue here. I was shooting 147gr handloads with shooters world tactical rifle powder, all the way from min loads worked up to max, and there is no difference. I first assumed undergassed since I got no lockback on a single round, but from some reading and advice from those on AR15.com, I learned people generally think that AR10s that do not run are are usually overgassed. After reading that, I installed a Gorilla adjustable gas block, and started with it closed and slowly opened it while firing single shots of a mid-range load. It takes 6 turns from full closed to full open, and at 1 turn, the bolt unlocked, but the casing didn't move from the chamber. At 2, it pulled about halfway out. At turn 3, the casings began to eject and fall right below the rifle. Turn 4, 5 and 6 resulted in them landing farther and farther away, with the shells landing pretty consistently about 5 feet back at the 4 o'clock position at full open, similar to before the adjustable was installed. I did not get a single lockback on about 10 shots fired with the block full open. At this point, I'm back to thinking it's undergassed. Quickload shows port pressured in the 14.5ksi range, whereas most 223 loads show port pressures around 20ksi. The 0.086" port is similar to, if not smaller than, what I've seen in AR-15s, and it seems a touch small for a 14.5ksi port pressure. Tactical Rifle is a bit on the faster end for 308 powders, so I'm going to try loading up some 168gr BTHPs over Match Rifle, which is a lot slower. I'm thinking I can get port pressures up to 16ksi or higher with that combination. If that doesn't result in lockback, I'm considering drilling to around 0.089 or 0.0935" and trying again. I've had to a drill port in a big bore AR15 barrel out in the past (357 AR -- 8-12ksi port pressures at carbine length), which fixed short stroking, but I'm not familiar with the quirks of the AR10, other than I've never seen one that just runs without issues that need to be worked through. Later, I shot with the same 147gr handloads, tula of a couple lots, and 168gr bthp loads to see if I could get bolt lockback. I couldn't and I captured 960fps video of all tests. That footage can be viewed here: https://streamable.com/3idj1i Thoughts?