Fine-tuning, and the history

[ni0h]

I finally got into this because of a friend using my garage to mill out an 80% lower, who, on his third try, bought one for me to pay me back for the inconvenience(I still find aluminum shavings).  He never did get one right, but I've had mine ever since, and finally, in March, I bought the completion kit.  I'm ..."handy", so I went as cheap as I could get getting what I knew I wanted, expecting that the kit to be at least a functional set of components that would work together assuming there was nothing wrong with the part I supplied.  It was specifically advertised as compatible with 80% Arms DPMS AR308 lowers.I even added a mag to the order so I'd have that for fitting.  At $549, I was able to get that past my wife.

The kit as specified on the vendor's site was a little vague, but I figured at that price point, they might have an assortment of known-compatible parts and I'd get the detailed list with the shipment, along with specs for torque, a statement that the bolt and barrel were checked for headspacing, etc...  No.

https://moriartiarmaments.com/ar-10-.308-6.5-cm/ar-10-.308/80-kits-en-gb3/20-en-gb2/ar-10-.308-20-shark-rifle-build-kit-w15-keymod-handguard-dpms-rk308-fsk15-20n
 identified every part I recieved as well as I could, based on sizes and shapes and shared sizes and shapes and sent that to Moriarty, and after a few rounds of email with their 2-day turnaround, got them to understand that there was no lower parts kit, and a few weeks later was able to assemble the lower..  Fortunately, that's pretty intuitive.  Test-fit the mag...they sent me an AR15 mag.  They didn't have any AR10 mags so they just sent me that, but at least they took it off my bill.

So, all of that is mostly just to head off the expected cascade of hindsight.  I've figured out that Moriarty is incompetent all on my own and at my own expense.

I've got no torque rod, and another $50 would have been a hard sell with my wife.  I've got no workbench anyway to put a vice on to put a torque rod in.  But understanding what a torque rod does, not needing precise positioning of a hole for a gas block,  and not caring about aesthetics, I torqued my barrel nut to about 50  ft-lb using a 9" vice grips on the barrel just ahead of the nut, and a 1-3/8" combination wrench on the nut and put about 70lb on the end of the vice grips, which, being about 8" from the centerline, should be about 50.  Since people have to choose the nearest position to line up the gas block hole, I knew it's impossible to bring it to any particular spec and all I could find was ranges, all of which included 50.
I believe it's well-aligned(see picture of feed ramps).
No dimpling jig, so I did some really careful pencil and ruler work, and the gas marks around the port showed I was within a few percent of perfect.... but it would stovepipe every time. 
Between installation of gas block and checking pattern was the test fire, done, since moriarty give zero support or backing, with my left hand, wearing full ski goggles along with the hearing protection.  I didn't have sandbags and a string to haul out to the friend's farm, and I had checked the headspacing myself using pieces of very light index card(I had no idea they made them that close to paper) cut to fit inside the bolt face.  The bolt would fully close on one with a perceived bit of resistance at the end and would not close all the way on two, compared to effortless with none.  Obviously, closing on a loaded chamber, with the firing pin on the table beside me.  So, I had pretty good certainty that headspacing was OK before that cautious test shot.

On investigation, I learned that these kits commonly come with an AR15-length gas tube.  On the third try, I got an armalite-spec tube... (why does everyone keep the measurements secret?", placing the end nicely in the center of the bolt pin cutout.  I'm still waiting on the one from Armalite, but fortunately I cought Primary Arms with them in stock, on apparently the one day they had them.

I was disappointed to get no discernible change in function.  So, after trying a heavier buffer and even borrowing an AR15 spring (later in the lockdown where my friend could finally meet me outside), I decided the only thing left to change is the size of the gas port...which seemed really way outside anything I ought to be considering, but a rant by 98V5Z convinced me to go for it.  I went through several bits, starting with the 5-64 that would go in the first few mm but not all the way... and after 3 cycles of the next larger bit, the behavior changed.
It will finally lock back after the last round in a magazine - but it no longer extracts.  Every shot, I have to lock the bolt back and work the next round back into the magazine, remove the mag, drop the bolt, and let it extract the cartridge.
I believe the last drill was 2.06mm.   I was just keeping the packages lined up and going for the next one up, but had a bad bike wreck the evening after the last test and lost track.  Just today I'm finally up to working on it again.

Specs:
20" rifle barrel,

rifle-length gas tube changed to armalite.

generic fixed gas block - .750 journal.
some unknown low-profile upper

Odd low-profile barrel nut.
Some sort of low-profile mlock handguard with full-length top rail.  It attaches by clamping to the barrel nut.

a "shark" muzzle brake.
mil-spec carbine buffer tube, with 308 spring and a 3.8oz 308 carbine buffer substituted to an expo arms 5.3oz 308 heavy carbine buffer.

mil spec trigger.

 

I hate having to describe things as "some sort of", but ... well, that's all I can get for those.  I've spent so many hours on google images trying to make a match. 

 

Think of this as a guy finding parts after the apocalypse, trying to make what he's got work.  I just lost my job, so I can't do what everyone else tells me - "quit being so cheap and go buy a nice new professionally-built rifle".

 

Where things stand:  I have slightly buffed the chamber with ultrafine emory cloth. to ease extraction.  There's a little bit of scuffing on the outside of the brass but my friend tells me it's not excessive - so trying that.  Second intervention - You'd think with my scientific background I would not have changed a variable in the middle of a series of tests - but when I ran out of my first test box of ammo,,which was the cheapest thing at walmart at the time, I bought the close equivalent from another manufacturer because that was the cheapest at the time.  So it's possible that the cycling was solved not by that level of increase in port size, but by the switch from remmington to winchester, both 150gr PSP.  So after sitting down here and seeing these two boxes sitting side by side I finally pulled my head out of my ass and texted my wife who was at walmart at the time.  I'll be interested to see whether the remmington behaves exactly as the winchester does, or if it behaves exactly as before, or something in between - probably not feeding AND not ejecting.

So, I'm not yet asking for specific help yet - just giving the background and hoping someone sees something I missed, wants to call me a fool...whatever.
I'll try to get this site logged in on my phone so I can send decent pictures.  The camera on the computer with the good keyboard is my borescope.

[ni0h]

whoop.  That's a long one.  Like I said - "the good keyboard"... lets me blither.

[98Z5V]

15 minutes ago, ni0h said:

 

That's a very bad combination, right there.  The feed ramps in that extension need to be chopped up, and blended with the ramps in the receiver.  That's the worst possible combo, right there.  Dremel Chainsaw Sharpening Bit will do it.

Edited June 20, 2020 by 98Z5V

[shooterrex]

Soft point ammo doesn't feed well in the rifles for the most part. FMJ or the plastic tipped feed better.

[ni0h]

3 hours ago, 98Z5V said:

That's a very bad combination, right there.  The feed ramps in that extension need to be chopped up, and blended with the ramps in the receiver.  That's the worst possible combo, right there.  Dremel Chainsaw Sharpening Bit will do it.

Wow. I was looking at the lead lint and wondering if that was a problem. 
longterm a problem, right?  Short term, getting the feeding and ejection working, irrelevant?  
I’m building a hunting rifle that I hope is never asked to empty all 10rounds in an emergency but I want it to if I ask.

 

28 minutes ago, shooterrex said:

Soft point ammo doesn't feed well in the rifles for the most part. FMJ or the plastic tipped feed better.

Thanks. Once I get it to eject and feed at all, that sounds like the appropriate loading under the bed. Mag and bcg in the safe. 

[98Z5V]

1 hour ago, ni0h said:

Wow. I was looking at the lead lint and wondering if that was a problem. 
longterm a problem, right?  Short term, getting the feeding and ejection working, irrelevant?  
 

That's an All-The-Time Problem, right there.  If anything at all feeds, I'd be surprised.  That's one sharp edge, on each feeding side, waiting to slice into evert single projectile tip that tries to get out of that magazine. 

That needs fixed first.  Very first.

[ni0h]

On 6/20/2020 at 8:49 PM, 98Z5V said:

That's an All-The-Time Problem, right there.  If anything at all feeds, I'd be surprised.  That's one sharp edge, on each feeding side, waiting to slice into evert single projectile tip that tries to get out of that magazine. 

That needs fixed first.  Very first.

Thanks.  In fact, feeding has not been a problem, but - I've bought the right stones and am waiting to borrow a friend's tool to smooth that up.
That's just a perfecting thing.  I've emery-clothed the chamber lightly and am hoping it will extract next time I get to test.

[ColinGSeries]

On 6/20/2020 at 10:49 PM, 98Z5V said:

That's an All-The-Time Problem, right there.  If anything at all feeds, I'd be surprised.  That's one sharp edge, on each feeding side, waiting to slice into evert single projectile tip that tries to get out of that magazine. 

That needs fixed first.  Very first.

I just checked my receiver and barrel feed ramps after reading this post, and I have M4 ramps on my barrel and receiver BUT it appears that the receiver feed ramps are not quite "large" enough, as they stand proud of the barrel feed ramps. Should I look to dremel them down to match the barrel, or just shoot and observe to see if it causes problems?

[98Z5V]

5 hours ago, ColinGSeries said:

I just checked my receiver and barrel feed ramps after reading this post, and I have M4 ramps on my barrel and receiver BUT it appears that the receiver feed ramps are not quite "large" enough, as they stand proud of the barrel feed ramps. Should I look to dremel them down to match the barrel, or just shoot and observe to see if it causes problems?

That situation isn't as severe as the other way around - M4 receiver and non-M4 barrel extension.  That one is a house-wrecker.  Your feeding will improve, if you match the receiver to the feedramps in the barrel extension, that's for sure.  My recommendation is the Dremel, and the Dremel Chainsaw Sharpening Bit.  It's a long, thin stone.  It'll make short work of the aluminum on the receiver, and it's pretty easy to match the ramps in the extension.  The steel extension keeps you from messing it up.  Don't even worry that it might turn out bad - it won't.   This is what you're looking for - almost every ACE Hardware in the country carries these things:

[ColinGSeries]

14 hours ago, 98Z5V said:

That situation isn't as severe as the other way around - M4 receiver and non-M4 barrel extension.  That one is a house-wrecker.  Your feeding will improve, if you match the receiver to the feedramps in the barrel extension, that's for sure.  My recommendation is the Dremel, and the Dremel Chainsaw Sharpening Bit.  It's a long, thin stone.  It'll make short work of the aluminum on the receiver, and it's pretty easy to match the ramps in the extension.  The steel extension keeps you from messing it up.  Don't even worry that it might turn out bad - it won't.   This is what you're looking for - almost every ACE Hardware in the country carries these things:

Thanks! My SnapCaps are coming today so I can do some initial feed testing. I already have a great Dremel and I'm sure my Ace stocks these. I'm assuming these are 455 grit from the package, so should I also look into some finer-grit sandpaper for finish polishing?

[98Z5V]

9 hours ago, ColinGSeries said:

Thanks! My SnapCaps are coming today so I can do some initial feed testing. I already have a great Dremel and I'm sure my Ace stocks these. I'm assuming these are 455 grit from the package, so should I also look into some finer-grit sandpaper for finish polishing?

That 455 is just Dremel's part number for the package.  When I end up doing this, I hit it with a polishing compound afterwards.  That takes care of it.