Ceratac AR308 kit build round 2

[CRracer912]

I had been wanting a large frame AR for quite some time and ran across this Ceratac AR308 Kit.  The first two hits for searching this kit brought me here; Ceratac AR308, and here; Ceratac AR-308 Build.

Not a lot of info, but thanks to Lane's adventure in building the AR308, and the information he provided as well as 98Z5V and others, I decided to give it a try.  I've had quite a PM with Lane prior to ordering the kit and beyond.  I use a 5Dtactical Jig Pro and a Dewalt DWP611 router, I hadn't bought the jig with the combination AR15\AR10(308) adapters as I'd figured I'd probably just go the PSA route if the day ever came that I wanted to buy a large frame 308.

This worked out fairly well as the Ceratac AR308 takes a different adapter kit for the 5D Pro for a large frame AR than what normally comes with the 5D Pro Combo jig.  On Ceratac's website it offers for sale the Ceratac AR308 adapter for the 5D Tactical Jig Pro, this caught my eye making me wonder why they called there's Ceratac as opposed to 5D tactical.  Going to 5D Tactical's website, and viewing the Combo kit, it clearly states their kit won't work with the Ceratac AR308 lower (otherwise known as an SR762), but an adapter kit is offered that 5D Tactical did make, and sells only through Ceratac, just for this lower.

Ceratac was easy to deal with, both the online ordering and the online support chat, though information they'd provide is limited. I placed the order for the AR308 kit and Jig adapter on the 11th of December, picked it up at the Post Office on the 17th of December.  They have a disclaimer on their website  that says if they are OOS of an item to complete the order, that item will be upgraded free of charge.  Not a lot of options, but I selected 18" Nitride barrel(34.99 upcharge), M-Lok rail(9.99 upcharge)(left it at the 12" standard length).  The BCG was default to Nitride and that carried a 4.99 upcharge. 100% USA made LPK(9.99 upcharge), no sights, standard milspec buffer tube, stock and grip.  The Ceratac Jig adapter was 39.99.

When the rifle was unboxed, I noticed the Standard stock and pistol grip had been upgraded to the Magpul Moe (fixed stock).  I had contemplated getting that upgrade but decided not to add the 44.00 cost. First regret enters here, the buffer tube with the Magpul stock was commercial(I would have preferred milspec for simplicity and ease of changing stocks later down the road.  Everything else was as I ordered.

After further inspection of the parts inventory, it was found to be missing the crush washer for the standard A2 flash hider, no barrel nut shims and only one out of 6 screw for the hand guard attachment to the barrel nut.  None of this was a concern for the price, and the quality of the lower and upper, along with the Nitride barrel was as good as anything else I had from Colt, S&W, AA. However, this morning I placed a call to Ceratac about those missing pieces and there was no issue getting it resolved and I have just received my tracking information for all of it.  The only issue with the Magpul stock was, while the fixed stock fits both commercial and milspec, the clamping adapter at the front is milspec\commercial specific, and my adapter was milspec, which would not slide on the commercial tube at all.  They are sending the shim kit (was supposed to be included and apparently that kit also contains the screws for the hand guard), a crush washer(I was informed they had a new muzzle device that will soon be available as an upgrade over the standard A2 flash hider and they are sending me one free of charge for this issue) along with a commercial adapter for the Moe stock (he offered to send a milspec tube instead, but their willingness to support missing items was handle extremely well and I figured what's it matter with a fixed stock anyways).

Yesterday evening I set out to mill out the lower.

5D Tactical Jig Pro with Ceratac AR308 adapter kit

Rear Jig plate for Ceratac AR308

Front TD holder for Ceratac 308

I tape my lowers to hopefully prevent damage, 5D tactical Jig Pro behind lower

Lower installed in Jig. The front is held secure with TD lugs and an included pin, the rear adapter acts as an end plate on the lower and secure with the vacuum hose attachment

This is my mini machine shop.  It's a heavy table and vise that I move out in the open so I have easy cleanup for all the aluminum shavings. I've attached the pilot hole guide to the top of the jig.  It starts out by drilling a 21/64" hole from the top of the receiver through to the trigger guard area. I really need to get a bench top drill press, would make this much easier.

Here's the 5D tactical router base installed on the Dewalt DWP611.  The two pins are the initial pins attached to the base plate, and they trace the FCG pocket guides on both sides of the lower opening.

The Jig Pro uses a 'Readymill Pro' end mill that is installed in a custom made Arbor that screws directly to the shaft of the router, no collet required.  The Jig router base plate has a bearing installed that the ready mill slides up and down through, I assume to provide lateral support during cutting. Here is a picture of the router on top the jib with the endmill placed in the pilot hole, ready to make a cut.

Here, the first stage is complete.  That means the endmill has been adjusted to maximum depth, using the built in depth guide where the '1' is located.  Those marks are the recommended cutting depth increments, but I cut that in half to a third, for me it's not a race and I'm telling myself that by doing this, I'm making my endmill last longer and not putting any undo pressure on the router/bearings. Whether that's true or not, IDK.

Once the first stage is complete, I remove those short pins on the router base plate and install the mid length pins and continue on down until I've reached maximum cutting depth of the 2nd guide, then I switch to the longest pins and finish out the trigger slot hole.  Here it is after the 3rd stage is completed.

[unforgiven]

Outstanding brother , I like your approach. I am a big fan of making it work. 

[CRracer912]

Thank you! Posting some dimensions before I forget...

Just eyeballing the lower in the jig, I was concerned with how much material was going to be left behind the bolt catch, as well as the depth.  I placed a call to 5D Tactical and told them I had bought the Ceratac AR308 and their Ceratac 5D jig adapter.  I was assured that they had tested it 100% for dimensional fit, so with that in mind, I put it together and went at it. The entire milling process above including setup took about 2 hours taking my time.

I didn't cover the drilling of the safety selector or the FCG pins, but with the lower installed in the jig, you can see the alignment holes through the thick aluminum side plates, they have steal sleeves installed.  Safety selector uses a 3/8" drill bit and will go in one side and out the other and right in to the guide on the other side of the jig.  The FCG pin holes are 5/32" and drill from each side(my bit wasn't long enough to go all the way through nor would I want to with that small of a bit. All drill bits were included with the 'Ready Mill Pro' kit that is selected depending on the router you have.

This is the thickness behind bolt catch after milling. .212 for those with trouble reading upside down:)

I just use a black sharpie in all the drilled holes, I don't worry about the inside.

FCG installed as well as bolt catch for reference.

Lower assembled with buffer tube as well as upper assembly(less barrel, obviously) and installed to lower

 

The 18" Nitride barrel has a gas port hole that measured .081", since it is such a small hole to measure I used a couple drill bits to double check.  A 5/64" was a tick small(.071) and a 3/32" was too big(.093), so I'll assume my measurement is pretty close. The barrel is also dimpled for the gas block. Since I've got a smaller gas port hole in the barrel than what Lane had in his, I'll probably initially only add a heavier recommended weight buffer, and not worry about an adjustable gas block for now.

According to 5D tactical, and Ceratac, as well as my measurements.  The upper is a bit unique in that it has the Armalite slant, but the DPMS barrel threads with 16 pitch.  And according to Ceratac and 5D tactical it would utilize the 'high' profile handguard for DPMS.  The tang is somewhere in between what a low DPMS and high DPMS measure. I'll be changing out my oldest son's barrel on his PA65 early next year and will be able to see how the Gen 2 PSA PA10 upper hand guards compare. Fit and finish, this Ceratac is nicer overall than my son's PA65.  I've noticed on his, the BCG is apparently rubbing the threads of the buffer tube entry and the front edge of the tube assembly. Just cycling this Ceratac by hand leaves no marks, but it's obvious the way the lower is made that there is more clearance where the BCG enter the buffer tube.

The Nitride BCG is a nice smooth finish, the FA does engage and I hadn't noticed any drag of the FA on the bcg during cycling.  I tried a loaded Magpul Mag (with 6.5 creedmoor) in the lower, it slides in smooth and locks easy, but it's snug enough it didn't drop free with that loaded 20 round mag.  The Bolt was not marked MPI anywhere that I could find, nor is it advertised to be as far as I recall.

I'm on hold now until my other missing pieces arrive so that I can finish the upper assembly.

 

[jtallen83]

28 minutes ago, CRracer912 said:

I've noticed on his, the BCG is apparently rubbing the threads of the buffer tube entry and the front edge of the tube assembly.

Could be the carrier is hitting those threads because the buffer has too much room and isn't stopping it short like it should. I stopped that in my Matrix build with two quarters in the tube before replacing the spring and buffer.

[98Z5V]

 

Good work, man.    

[CRracer912]

Some more dimensions from the buffer tube assembly (commercial)

internal depth is 7 5/16", Buffer is 2.552" in length(weight is 3.837 ounces), spring is 10.5" in length(34 coils plus a double coil at each end)

[willbird]

1 hour ago, CRracer912 said:

Some more dimensions from the buffer tube assembly (commercial)

internal depth is 7 5/16", Buffer is 2.552" in length(weight is 3.837 ounces), spring is 10.5" in length(34 coils plus a double coil at each end)

Are you sure you did not make a typo ?? 7-15/16 would be the same as my PA10 with a 2.5" buffer length.

[CRracer912]

No typo. This is a carbine commercial buffer tube. I took that measurement for Lane, who has same rifle kit, but with a milspec buffer tube having a 7" internal depth. He's having an issue of not being able to lock the bolt back by pulling charging handle and pressing bolt catch, though it will hold open with last shot onemtpy magazine.

I know what you are talking about, my oldest son has a PA65, the buffer tube is nearly an inch longer than a standard carbine milspec buffer tube, and allows the use of a standard length buffer instead of these shorty buffers.

Primary arms sells the armalite tube that is 8".

[98Z5V]

5 hours ago, CRracer912 said:

Some more dimensions from the buffer tube assembly (commercial)

internal depth is 7 5/16", Buffer is 2.552" in length(weight is 3.837 ounces), spring is 10.5" in length(34 coils plus a double coil at each end)

 

3 hours ago, willbird said:

Are you sure you did not make a typo ?? 7-15/16 would be the same as my PA10 with a 2.5" buffer length.

Both those internal depths are bad, and won't work for anything.  It eihter needs to be a 7.000" internal depth for an AR15 extension, or 7 5/8" internal depth for the Armalite AR-10 Carbine extension (and known like parts).

Those two numbers you guys reported above won't work for anything.  Well, they'll make great paperweights.

Edited December 19, 2018 by 98Z5V

[willbird]

I’m as usual smoking crack ? 6-15/16 :-), 7-15/16 would take a lot of quarters 

[98Z5V]

6 15/16" doesn't meet the 7.000" internal requirement for an AR15, brother.  It's short.  Can that thing, for real...  

[willbird]

49 minutes ago, 98Z5V said:

6 15/16" doesn't meet the 7.000" internal requirement for an AR15, brother.  It's short.  Can that thing, for real...  

I'm going to see how it all stacks up when my BCG arrives some day, if it is too shallow the bolt will not lock back, pretty simple ;-).

I shoved the tape measure in there again, I do get 7" on the bottom side.

Right where the keyway is.

Bill

[98Z5V]

You need to measure opposite where that keyway is - at the top of the extension.  There are alot of extensions are flared out at the bottom, to better capture the buffer retainer.   Can't really tell from that pic, but the bottom, near the keyway, looks flared out there. You need to measure opposite that, at the top of the extension, as it would be mounted in a lower receiver.  Look at this one, for example - not only is it extended at the bottom - that HAS to be slotted for the buffer retainer:

This one is definitely extended at the bottom, to capture that buffer retainer better:

Your bolt will still lock back - the face of the bolt travels further back, beyond the bolt catch, than that 1/16" of difference will make - but it might not pick up the next round from the mag, or something else weird - especially in a .308AR...

That 7.000" internal depth is from a real TDP - Technical Data Package - the real blueprint, for the M16 and M4.  I don't get why manufacturers think they can "just get close" or whatever they are thinking, and you as the consumer will have a fully functional weapons platform.  You'll have issues with it, in some sort or fashion, if it's short - or long.  Then, we'll be trying to figure it out.  I had functional issues on one that was 7.100" internal depth, from a very well known, highly reputable manufacturer.  Once I figured it out - it went in the trash.

We even had one guy here try to argue that the 7.000" internal depth on an AR15 carbine receiver extension was "the starting point..."  WTF?!  It's not the starting point, beginning point, "almost point" - is it THE point that you need to hit on an AR15 Carbine receiver extension.   There's no plus or minus, when you want it to operate as designed.

This is the very reason I use 3 out of 4 Armalite AR-10 Carbine Recoil Systems in the guns I have - the genuine parts, from the specs from the real designer of this platform, will not have this issue.  The other 1 out of 4 is using something different, in a 7.000" internal depth mil-spec AR15 carbine receiver extension, so I could test that system out with other known good parts. And it works, in the .260 Rem. That's exactly where my own endorsement of the Sprinco Orange spring comes in, when you use a heavy 2.500" buffer (gotta be damn close to 5.4oz weight).

People give me alot of shiit for this receiver extension BS and recoil system BS that I go through, and I don't get that stuff wrong.  The numbers that really work, are the numbers that I preach.  When something funky is happening with weapons operation, I can trace that down pretty quick with a few measurement details. That goes for recoil systems, and gas systems.

Off that box now... 

Edited December 20, 2018 by 98Z5V

[willbird]

I'm just down to try the frikking thing :-). Might be that my BCG never shows up....and I will never know ;-). The tube I have looks to be 1/16" shorter on top than on bottom.

 

 

 

 

Bill

[CRracer912]

Got my missing pieces in today and finished assembly of the rifle.

Use a carry handle rear sight to line up upper and hand guard, in the process I realized the T marks aren't spaced properly between upper receiver and hand guard. Won't be an issue for me, but others might have issue with that.

Threw on a set of Magpul flip ups for test firing and see how close to zero the barrel is with the receiver. Maybe I'll get a chance to try it out this weekend.

When I called about missing pieces, the guy offered to send a new muzzle device they just got in that will be listed with this kit as an 'upgrade' in the near future. If pictured below on the left.

 

[CRracer912]

If it's functions the way it should and shoots relatively well, I'll end up changing the trigger to either a RRA varmit trigger or a Larue MBT.

I'll try it out as is initially, but I've got a KAK buffer and an Odin adjustable gas block that may end up in/on it if necessary.

[98Z5V]

23 minutes ago, CRracer912 said:

 

That came out as a damn nice looking rifle, man!  Great job on that! 

[willbird]

Yes it does look nice ?

[CRracer912]

Thanks! I handed it to my son, the one with the PA65. His first words were 'thats lite!' lol. 

He's got a 1-6x30 scope, but even without it, it's heavier, we'll have to weigh them.

[unforgiven]

What a cool dad , the family that plays together stays together. ?

[CRracer912]

4 minutes ago, unforgiven said:

What a cool dad , the family that plays together stays together. ?

Don't get me wrong, I didn't give it to him!?

I did get him(and brother) in to this several years ago, bought him and his younger brother there first AR15. Ones 19, the oldest 20. His plans for his 21st birthday is a road trip to Wichita to some gun stores so he can buy his first pistol.

[unforgiven]

Being involved with Hunter's Ed when parents decide to get the kids involved. That speaks volumes about the kids in that they could be trusted. 

[CRracer912]

Took each one to Hunter's education when they'd turned 13. Anytime they could get outside firearms education (from someone other than me), I was all for it.

The youngest, not so much interested in hunting, but likes target shooting and Clay's. Have taken both coyote hunting, the oldest deer hunting a few times. I live in the country so seldom have to leave the property to hunt (cept for better duck hunting).

They've had friends out to shoot who would otherwise never get the chance. And now that they're older most of their same friends still come out to shoot, except now they have their own gun and ammo!

[unforgiven]

Outfukinstanding brother 

[CRracer912]

Specifications for the upper and lower seem to be hard to come by for this upper/lower set.

I stumbled across an upper and thought the rear Tang, angled rear cut looked familiar. It was from Genisus CNC, so I googled and found this.

https://genesiscnc.com/product/genesis-308-upper-receiver/

They also have an 80% lower that says it takes everything from the DPMS LPK except the rear take down pin.

The upper is described to accept the DPMS barrel nut and has the DPMS high rail height, which it what Ceratac and 5D tactical had said they thought the Ceratac upper accepted as well