Ceratac AR-308 Build

[Lane]

Thank you, I'm quite happy with the way it turned out. I hope it does help someone else in the future as I got quite a bit of help from this forum along the way. So many great topics to read about here, and some things came up I hadn't even considered with previous builds. As nervous as I was to ruin a $10 part; my adjustable gas block conversion worked out, and has held up to my light shooting so far. I also had no idea the buffer weight could make such a difference, which is something I have yet to experiment with further as time goes on.

For now though; I'm simply focused on getting it sighted in the best I can, and spraying bullets out the barrel before hunting season opens in less than a week. Yesterday I nailed six rounds through the same hole in a paper target, so I think I'm in good shape. 

[98Z5V]

8 hours ago, Lane said:

Yesterday I nailed six rounds through the same hole in a paper target, so I think I'm in good shape. 

 

I'd hunt that, brother - without hesitation.  

[CRracer912]

Hi all, first post here. Signed up just to thank the author of this thread for all this information on the Ceratac 308 kit.

I've been wanting to do an 'ar10' for some time now. My oldest son has a PSA PA 65, but I think I'd just as soon build and 80%, and I really like the price point of this kit. I use the 5d tactical jig, so I'd probably just get their kit for it.

I was curious about some of their options. The lower kit has a USA upgrade and a no fcg. I don't suppose the no fcg option would include USA pins and springs. 

As for the hand gaurd, I take it that the barrel nut has to be indexed for the gas tube, did I read that right? 

I think I read in the other Ceratac thread that you could use an armalite or dpms barrel in any ar10 upper, but I was previously under the impression that those two use a slightly different barrel extension, any input on this?(in case of future barrel replacement)

Anyways, awesome thread, answered a lot of questions about the kit that I had floating around in my head.

[Lane]

31 minutes ago, CRracer912 said:

Anyways, awesome thread, answered a lot of questions about the kit that I had floating around in my head.

I can try to answer at least some of your questions. You might want to search around the forum for answers on the barrel extension. My recollection is that only the nut and upper receiver threads are different, but I don't have anything to compare with myself.

The no FCG option is new, but they have a live chat feature on the website that runs during business hours. Should be able to get that answer in a few minutes when they are open tomorrow. I will say the $10 savings is laughable regardless of how many parts are removed. I would gladly buy the trigger and hammer from you for $10 if there are too many other parts missing with that option.

The barrel nut is not indexed for the gas tube; the gas tube passes over top of the nut entirely. When tightening the barrel nut you simply align the holes so the hand guard (when mounted) aligns with the upper receiver rail.

 

[CRracer912]

Ok, didn't think about the hand gaurd attaching points being reason for you having to add the second shim, makes sense.

You're right, 10 bucks ain't much to know off, I've just got a bunch of mil spec triggers from my ar15's, I'll never use them. If omitting it doesn't get the USA hardware, I'd get the fcg..

I'm in the process of browsing threads now.

 

Thanks!

[CRracer912]

As was mentioned by the OP, Ceratac offered a kit for the lower to use with the 5D tactical ready jig pro.

Thought it was odd that Ceratac listed it as 'ceratac'.

A little investigation on 5D's website showed that the mult platform jig pro does not accept the SR762 lower and that they offered an adapter kit for that style of lower through Ceratac.

I only mention this as the original thread that lead me here was questioning what actual lower Ceratac was selling. I saw it was figured out throughout that thread, but wanted to add what I'd found direct from 5D tactical.

[Lane]

7 minutes ago, CRracer912 said:

SR762 lower and that they offered an adapter kit for that style of lower through Ceratac

I found the same information on the 5D tactical website and also asked them some pointed questions. Then with some help from this forum, I cut mine without the jig based on a measurements from an early Matrix Aerospace lower (Matrix Aerospace made the lowers for Ruger's SR762). The fire control group turns to be different in both vertical and horizontal position which is why standard 5D and other jigs are not compatible.

18 hours ago, CRracer912 said:

The lower kit has a USA upgrade and a no fcg. I don't suppose the no fcg option would include USA pins and springs.

I used the live chat to ask about the no fcg option. Turns out they omit all of those parts, no pins, hammer, trigger, disconnector, or associated springs. 

[CRracer912]

You had better luck with live chat than I did. Being in CST, I probably tried it before they were open.

I've got some ar15 lowers coming from them, first time ordering from them(Ceratac), supposed to be here Monday. When I get those done, I'm gonna get the AR308 kit. Should go fairly smooth since you all covered the need for heavier buffer and adjustable gas block. I'll just mod their gas block as you did.

It'll be my first 308 in the AR pattern, and I'll be doing a lot of comparison between dimensions of the upper/lower with that of my son's PA65, rail height, TD pin location etc.

[Lane]

22 minutes ago, CRracer912 said:

I've got some ar15 lowers coming from them, first time ordering from them(Ceratac), supposed to be here Monday.

I've done a few of their AR-15s and have no complaints. What are your plans for those?

22 minutes ago, CRracer912 said:

It'll be my first 308 in the AR pattern, and I'll be doing a lot of comparison between dimensions of the upper/lower with that of my son's PA65, rail height, TD pin location etc.

Looks like the PA65 is a DPMS style lower with a curve at the receiver extension instead of a diagonal cut of the AR-10 style SR762 type lower that Ceratac sells. That will certainly limit, if not rule out interchangeability. There are a few threads around here with a comparison image of the two side by side, but I couldn't find one of them quickly. 

[CRracer912]

2 minutes ago, Lane said:

I've done a few of their AR-15s and have no complaints. What are your plans for those?

I won a larue barrel and chose the 18" predatAR, so one of the lowers will finish that build.

I've got a 24" Grendel upper that needs a home as well as a 7.62x39. I have a bad habit of buying random pieces that interest me that are on sale, then feel the need to make it complete...

[Lane]

6 minutes ago, CRracer912 said:

as well as a 7.62x39

This is my next build actually. I purchased a Polymer 80% lower out of curiosity (and since Ceratac didn't have a sale on aluminum anymore). I will likely swap lowers around so that particular one isn't on a 7.62x39; but, I've been eyeballing my options for that build. I want an AR without a gas port drilled in the barrel so I can legally have a pistol grip installed in NY.

I'm just now finishing the wood on a Traditions .50 cal muzzleloader, and slowly working through an AK build. Seems like you might have the building bug as well...

[98Z5V]

This thread is turning into an absolute goldmine, @Lane - you've done one hell of a job on the information gathering - and the posting of it all - and for certain, on the execution of the machining. 

 

Edited December 11, 2018 by 98Z5V

[CRracer912]

On 12/7/2018 at 10:50 PM, Lane said:

. I want an AR without a gas port drilled in the barrel so I can legally have a pistol grip installed in NY.

 

Could you just install a gas block in reverse to seal up gas port? I know some that do this to make a single shot out of their AR.

[Lane]

From a functional standpoint; yes, you could easily turn the gas block upside down. From a legal perspective it wouldn't fly here in NY state. If the firearm were to come under the scrutiny of police, the examiner is allowed to disassemble and reassemble as they see fit; the catch is they aren't allowed to do any gunsmithing. Without a gas port drilled in the barrel it couldn't be assembled as a semi-auto, with the gas block upside down it could. Having a semi-auto capable firearm with a pistol grip would make it an unregistered assault weapon (same with any other attached "feature"). 

[CRracer912]

Well, that's a bummer about the laws there.

I've got one of the Ceratac ar308 kits ordered. I can either start a new thread when it arrives and I start the lower mill process, or piggy back here(might be nice to keep it all together?)

[Lane]

On 10/4/2018 at 8:59 PM, Lane said:

The only thing I am at all concerned with is the bolt catch. For some reason it is floppy in the slot, and I have a hard time getting it to catch the bolt with the charging handle. I even put a shim behind the catch in the lower to hold it as far forward as possible. That slot came already milled so I'm not sure which part is out of spec. I have to slam the charging handle back as hard as I can to get it to catch. I can't tell if the charging handle doesn't allow me to throw the bolt back far enough, or I'm actually slamming up against the buffer bumper. The only thing I can imagine doing is grinding down the bolt catch a tiny bit on the back side so it catches more easily (or a hair off the bumper if that's it?). I'm going to test fire it first and see if it works that way; I'm hoping it will break in on it's own or perhaps work just fine when shooting.

So I finally decided to go after this problem again... I reviewed the notes I had posted during the build, measurements of the spring; and loads of other threads here over the passing years. 

It finally occurred to me that the only problem I could be having was the spring. I referenced the spring coil diameter I posed early on, and used a calculator to multiply it by the number of coils. Sure enough; the compressed spring would be longer than the whole buffer, not just the part where the spring is allowed to work.

Without even taking apart the gun to check; I ordered a Springco Orange spring. Again; I had read enough here in other threads around here to know that was going to be my solution. 

Spring arrived, and it went to install it. First thing I checked was how far the original spring would compress on the buffer. I could still stick my finger in the end and feel at least 1/4", maybe 1/2" before touching the buffer bumper. Sure enough; it was binding up and making it impossible to ever hit the buffer bumper in the gun. Also nearly impossible to lock the bolt back with the charging handle, since the bolt couldn't travel far enough back unless I slammed it really hard jamming up the coils in the buffer tube. 

Dropped in the Springco Orange spring, replaced buffer. Locks back with ease, and plenty of room to spare. At this point I think I'll revisit the adjustable gas block next time I fire it. I might be able to close it up a bit more with the proper spring. Might not. But I'll be sure to pay attention either way. Is there a preferred sealant for that grub screw on an adjustable gas block? Is Loctite blue enough?

This should be the last thing I needed for this build. Quite frankly it was working before, albeit a bit violently. It would lock back on an empty magazine which meant it was binding up the spring enough to clear. Looking closely at the old spring, there are some wear marks on the coils where it was wearing from that friction. 

Springco Orange spring on top, original spring supplied by Ceratac on the bottom. 

[98Z5V]

Coil-bind is a motherfucker. Every single time.  This is exactly why I state that companies that don't make full guns, shouldn't be allowed to make gun parts in the first place.  Specialty companies that only make a single part - like Sprinco - those guys ONLY make springs, period, for guns - they get a pass, because they only do that ONE THING and know what they're doing.

All these other companies make hard parts - and don't even know how the guns really work in the first place...