Ceratac AR-308 Build

[98Z5V]

This is the ultimate:   

https://forum.308ar.com/forum/125-raleys-tech-corner/

You would have been looking for this one:

 

TECH NOTE 96 HEADSPACE 110404 Rev 1 Final.pdf

Edited September 29, 2018 by 98Z5V

[Lane]

That is what I was looking for. I guess I had seen all the information in Tech Note 96 before; but it's good to have a refresher. I still have a lot of reading to do in Raley's Tech Corner, but now I have time to do that...

I thought about the masking tape method and would almost prefer to go with paper or cardboard as I suspect they are held to a higher tolerance standard in terms of thickness. In the end I'm just going to order the proper gauges in a few days when I have money available to do so. It's not worth taking a risk since the old timer who agreed to take me hunting wants to fire it too. I figure I might as well get .223/5.56 gauges as well, and take this seriously from now on. I already have them for 7.62x39 since AK barrels require the headspace to be set as they are pressed into the trunnion. It really seems like all the gunsmiths ran for the hills in other states when the NY SAFE Act passed a few years back; and I can hardly blame them. I suspect much of the future work they would have done here would have been neutering guns for law abiding citizens which is totally heartbreaking to do. I cringe every time I grind the threads off a perfectly good barrel (but that is the letter of the law in this state).

That puts me out about a week before I'll be able to test fire the AR-308 kit; but you better believe it will be 100% by the time the gauges show up. No sense wasting any time in that respect. All in all I feel it is a good thing; because now I won't have any reason to rush through any of the finishing work that is left. It looks really good so far, and the only other thing I really need is a scope for it. I'm thinking a 3-9x40 is a pretty good jumping off point in that respect.

[98Z5V]

55 minutes ago, Lane said:

It looks really good so far, and the only other thing I really need is a scope for it. I'm thinking a 3-9x40 is a pretty good jumping off point in that respect.

I've had fantastic success with the Primary Arms 4~14 First Focal Plane scopes.  For the heavy 5.56 guns and the .308s, this one in particular is absolutely great:

https://www.primaryarms.com/primary-arms-4-14x44mm-riflescope-acss-hud-dmr-308-223-reticle-pa4-14xffp308

[Lane]

Nearly finished now. I spent a few hours today finishing up the fire control group. Everything works as it should; safety is safe, disconnector functions without a gap, and the trigger has good throw. I only have to finish assembling the other lower parts which is very quick. I'm currently waiting for the lady of the house to get home so she can watch (she still isn't done with her own AR-15 build).

The pistol grip as attached is not NY legal but I'm considering options and using it to hold in my selector detent pin. My first AR-15 has a sawed off grip but I'm not sure that is ideal on the larger .308 build. The AR-15 lower sitting on top of the AR-308 has an upside down pistol grip on it which looks a lot like a Sparrow grip. I'm not sure those are 100% legal here but the local gun shop sells them. Unfortunately that upside down install requires drilling and tapping the lower along with all the grip modifications. I'm not quite ready to commit to that on my .308, but I also don't like paying $50 for a NY legal grip.

I ordered the .308 headspace gauges so they should be here late this week or early next. Only other thing I need in the short term is a stock of different ammo brands for the test firing/break in.

Today I looked at the entire selection of scopes at Primary Arms and picked the same scope you recommended 98Z5V. I was all ready to post the link here and ask about it only see it matched the link you already had posted. That will be my next purchase when funds allow. 

[Lane]

I finished up the build today in anticipation of the .308 headspace gauges arriving tomorrow. I decided to go with a fixed magazine so that I could keep the pistol grip and telescoping stock (shouldn't have ground off the barrel threads after all). I just didn't feel comfortable with a compromise grip on such a large firearm. I also stocked up on ammo for the break in, though I'm not sure yet how much I'll actually shoot through it tomorrow.

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. 

Unfortunately with a pinned magazine the bolt face catches on the back of the magazine follower when returning home on an empty magazine. I'm not sure if it is common practice to carve a slight ramp to allow that action or if I should baby it and push it down every time I want to close to bolt after emptying the magazine. I nicked one of my AR-15 magazines the other day from doing the same thing and it doesn't seem to affect operation.

Still waiting for the funds to pick up a scope, but I'll rock the polymer iron sights in the mean time. They worked just fine on my AR-15 for the short time I didn't have a scope on it.

[Lane]

Fed Ex rolled up early in the day with new headspace gauges among other things. I tore everything down and the go gauge was just a bit snug; the no go gauge wouldn't allow the bolt to close with any reasonable amount of coercion. I put it all back together and then decided to double check it for extra peace of mind; same results. 

It was then that I began to notice how loose the gas rings were inside the bolt carrier. There wasn't any significant friction and the bolt moves in and out with a gentle shake of the assembly. That just didn't seem right to me so I did a few searches but didn't find specific information about the .308 right away. I'm also not sure how different it should be from an AR-15. The other thing I noticed was the gas rings are actually a continuous coil, and not three separate rings. It looks like it could be adjustable by stretching the coil out a bit. 

I contacted Ceratac about the issue and am awaiting a reply. They said it should come within the hour so I can't complain about speed. I just didn't want to go ahead and test with live rounds if it should actually be nice and snug. 

I fooled around with the bolt catch issue late last night and have it completely resolved now. I noticed marks on the top of the bolt catch and ended up removing a tiny amount of material on the back side to allow for reliable operation locking it back with the charging handle. The magazine follower doesn't actually catch if the bolt catch button is pressed in all the way when sending it home. In the end I found a post in a California guns forum about adding a slight ramp to the magazine follower, which I also did as a precautionary measure. It didn't take much shaving to get it working smoothly with or without depressing the bolt catch manually.

[Lane]

So I didn't hear back from Ceratac within the hour they specified. That would be fine if it weren't Friday evening, but I know they won't reply before Monday now. I found the specs over in Raley's Tech Corner:

MCFARLAND GAS RING ACCEPTABLE OD DIMENSIONS

·         AR-10 = .656 - .659

I measured mine three times and got between .6500" and .6495" with a caliper that can read half thousandths, just what I was expecting. The OD was out of spec by 6 thousandths and definitely too small to be contacting the bolt carrier. While I couldn't find any mention of this process elsewhere; I took it upon myself to adjust the coil. I happen to have ring mandrels around so it wasn't too difficult. I knew I would have to overshoot to get it to stretch considering I was well below the low spec. I stretched it to about .665" which is right around a US 3-3/4 band size, and then flipped it over and did it again. I was careful to keep all the coils together and work it slowly so it wouldn't bend out of axis and deform the thin metal. 

It worked, and I now have a McFarland gas ring that is within spec, and back in the gun. It feels much more normal and provides a bit of resistance on the way in and when rotating the bolt. It's nowhere near as tight as any of my AR-15s, but that seems to be ok. Only now it's dark outside so I'll have to wait until tomorrow to give it the live fire test I had planned for today.

I didn't find any horror stories attributed to catastrophic failures from worn gas rings, only cycling problems and jamming. I presume it might have been fine to run it that way, but I wasn't positive if the ring would grow or shrink when hit with the pressure. I also wasn't sure where all the extra blow by would go, I would prefer not to get a face full of hot gas if it were too much.

[98Z5V]

You're doing great on this thing, man - fantastic. 

[Lane]

First and foremost; I survived a live fire test. I was a bit cautious given everything I've been through with this build. Unfortunately it's incredibly hard to aim through peep sites with a motorcycle helmet on, so I took that off after the first three rounds. I loaded one round first of 150 grain Federal, then two more rounds after that.

The third round chambered and then I couldn't pull the bolt back to eject it. I'm not even sure why I thought something was odd, maybe it didn't cock the hammer? I manually cocked the hammer with the gun taken down since I couldn't get the round back out for inspection; then it fired just fine. The bolt was definitely still closed tight at that point. I loaded three more rounds of 180 grain WInchester Super X and those all fired without issue though the brass was about 2 o'clock where the others were more like 3 o'clock. 

Inspect my brass if you don't mind. Are those light primer strikes? Should I take another hair off the front of the lower receiver to give the hammer a bit more swing? The marks on the neck seem normal to me for such a new build. I usually run enough steel case ammo to chamfer the edge of the locking lugs which clears those up early in the break in process.

Any other thoughts?

[98Z5V]

Brass looks good - no light strikes there.

Gonna take a few rounds to fully break it in, so shoot the piss out of it, well-lubed of course.  VERY well lubed.

[Lane]

Absolutely. Those first few shots were simply a function test. I like to run very few rounds through, and then strip it down to look for wear or anomalies. Luckily outside of prime whitetail hunting season, I can simply walk outside my door and start blasting. 

Today I uncovered a few things and I'm not totally sure all of what parts are at fault (hammer pin problem). Furthermore I thought long and hard about posting another failure; but I think it's best to admit it for the good of anyone else who attempts a first build. The torque specs on the barrel nut are higher than an AR-15, but in the past I had mangled an aluminum AR-15 barrel nut trying to get it to align the rail on the hand guard. That one warped badly through the rear set of attachment screw holes; note the barrel nut for this AR-308 is made of steel and not aluminum.

I went out to shoot a four more rounds and had two fail to fire; though they did fire on the second try. I grabbed a magazine's worth of steel case Tula after that and had three more fail to fire, only to note that my hand guard moved and the barrel nut came loose. Full stop. Thinking back I knew I needed to readdress that, but never took those parts back off again. Right away I removed the gas block, snaked out the gas tube, and ended up adding back the second shim that came in the kit to make it torque down correctly. The hand guard is again aligned but that was a big mistake; luckily I'm still here to talk about it.

I also noted aluminum deposited on the front of the hammer where it was contacting the lower receiver. Turns out those Matrix Aerospace measurements were dead on. I had originally left the pocket a little shy because the hammer already stood proud when installed. Tonight I milled off the rest (using an end mill in my hand to shave it slowly), exactly to the measured line. The hammer no longer makes contact during normal operation. It wasn't much extra, but it does offer further proof that the Ceratac really is a copy of that design. 

Finally; in researching these light strikes (those last three Tula rounds are barely dented, and didn't fire on a second try either; so I left them outdoors); I noticed the hammer holds the pin very tight. So much so that the pin rotates in the lower with the hammer movement. I tried putting the pin in a drill and giving it some 1000 grit paper on the center portion; that didn't help. I also tried a needle file in the center slot where the hammer grips it to keep it from walking; that didn't work either. Tried spinning the hammer on the pin in the drill with oil; still too tight. I am not sure how much further to go with that monkey business. I'm more than likely going to buy new pins and a hammer from a different source. I'm sure I can polish the pin really well and run it through the season if it keep it well oiled; but after checking my AR-15s and verifying they DON'T spin the pin, I'm not eager to chew up my lower.

I didn't figure out how to get the anti-walk part out of the hammer or loosen it up, but that may be an option. I'm not sure a drill bit or reamer is a good idea as it might leave a flat which could cause other problems. I will likely re-appropriate a hammer and pin from another build in the short term so I can continue the break in process. Tomorrow is rain so that won't likely be until Monday.

Everything is back together at the moment and ready for more minus that hammer issue. The only other wear I noticed was on the flat sides of the cam pin where it contacts the upper. It might need a bit of grease in the short term during break in as it's already turned silver. I think that might be what had kept me from opening the bolt on the first failure to fire round. It's caught a few more times when charging but slid free more easily since then.

[Lane]

I took it apart and cleaned everything thoroughly later last night which gave me a closer look at a few things I mentioned above. On the plus side; during live fire testing the bolt always locked back on an empty magazine so that seems to be in good shape.  

The cam pin did indeed take a nick off the notched opening in the upper receiver next to the end of the gas tube. It appears that improved cam pins are available with more rounded edges. The one I have isn't rounded very much on the corners, and not different on one end from the other. After cycling the action a few times the cam pin gets turned to one side enough that it is possible that rotation is impeding the firing pin. I didn't see any noticeable damage on the firing pin itself but I polished the long area with 1000 grit for good measure. 

The forward assist paw was catching on the side of the bolt carrier in some circumstances and had already worn itself quite a bit. I added some oil and cycled it manually while twisting the forward assist in both directions. It seems to be much better now and doesn't lock up the bolt up anymore.

The only other thing I noticed was a series of marks on the bottom of the bolt carrier. I counted them and it pretty well matches the number of rounds I have fired so far. I've included pictures of that because I can't see why that is happening off hand. They are spaced very differently and one distinct group on the ramp, and another on the flat area. There is no significant wear on the top of the hammer and some of them appear too wide to have been caused by the hammer. I don't see anything else that could be hitting it that far back though. I don't see the hammer move at all when closing the upper.

Finally; it kicks like a mule. I didn't notice it while wearing leather but when shoulder firing later it left a nice bruise. I don't have a rubber pad on my butt stock or anything else to damp the force. Am I just a Nancy or do I want to look at tuning the buffer system as time goes by? I already cleaned the back of the buffer bumper but there was some indication it could be hitting the back of the tube. I will mark it with a Sharpie marker and see if wears any away the next time I run some rounds through. Looks like the rain might be short lived today so I might get time to run a few more boxes.

[Lane]

Short update here. I have still been trying to figure out what is going on with my bolt carrier and why it's getting slammed by the hammer. I found this thread over in another forum and it's really the only thing I've found so far:

https://www.ar15.com/forums/ar-15/Bolt_Carrier_Hammer_issues/66-555373/

Near the bottom; the post on 12/8/2011 show a picture of a hammer with an L cut at the top. Has anyone seen this before? I'm still not entirely clear even after reading the thread what is actually happening. Perhaps the initial bolt carrier group cycling back is bumping the hammer a bit; then the hammer returns, hits the bottom of the carrier and rides it before finally cocking on the trigger or catching the disconnector? They seem to indicate that some damage could be done but I'm just not sure what the deal is here. I've included pictures of my firing pin in the carrier, and the hammer to compare with those other pictures. 

I put some Dykem on the hammer, closed the upper an pulled the trigger while it was still wet. Looks like the hammer is hitting the firing pin square and then drags on the rounded edge of the pin before hitting the ramp when manually charging. Obviously all that happens faster with a bullet cycling the bolt carrier. 

Any thoughts? Has anyone seen this before? Should I just notch the trigger and call it a day? The last reply I got from Ceratac Monday was pretty cagey in regards to the gas ring problem; they refused to offer specs and said it needed to be measured with precision equipment. They did offer to RMA the bolt carrier group but I declined since I already fixed the problem. I'm not sure what they would say to me about this considering I didn't buy their jig. It's certainly not something that would go away even if the hammer were a few tenths of an inch lower (which it really couldn't be). 

In other news I think I got a bad box of Tula ammo; had four fail to fire out of a box of 20 which has a date code of 09 02 90. 

[Lane]

I am back here to answer my own question and ask another. I inspected things a bit more closely and found similar damage on an AR-15 with a new lower attached. What do you know, they both have damage to the tail of the disconnector where the hammer hook is hitting. Seems like that trips the disconnector long enough to bounce the hammer back off the bolt carrier group. Searching for that problem indicates they are likely over-gassed and could be resolved with an adjustable gas block, heavier buffer, or stiffer spring.

Are these good candidates for a stack of quarters? How will I know when I have enough? I also have to place a few parts orders, so I'm not opposed to any of those other solutions. 

[Lane]

Looks like I might have screwed myself with my gas ring fix. It appears JP Enterprises sells an "enhanced" gas ring similar to the McFarland but looser; listed for DPMS/KAC builds. No diameter specs that I can find, but that explains a lot of things. Too bad Ceratac didn't want to provide the specs (even when they replied Monday), because all I could do was guess. 

I think I'm going to have to buy one and measure it. I suspect it could fix my disconnector/hammer contact issue by letting more gas blow by. Will find out later this week I hope. 

[98Z5V]

If you need heavier buffer information, I can go over all that stuff with you, in spades.  I'll need details of your setup,that I'm sure you are able to provide.

Type of recoil system - rifle or carbine (collapsible stock).

Internal depth of receiver extension.  Relaxed length of the buffer spring, coil count, and wire diameter.  Buffer length and weight.

Type of barrel - 18" midlength gas, 16" midlength gas, 20" rifle gas,etc.  Barrel gas port diameter.

That's the necessary info do get into gassing and reciprocating weight/spring strength.

Edited October 11, 2018 by 98Z5V

[Lane]

I am a bit curious what you think of the other options in this case. I decided to attack it from all angles since I don't know if I screwed up the gas ring or of there is something else wrong out of the box. The barrel is 18" which is an upgrade from the stock 16" and I don't believe they replace any other parts when you do that. In fact I have a 16" and 18" AR-15 build from them and nothing is different other than the barrel length and gas tube length. 

The AR-308 kit has a 3.8 oz, 2.55" long buffer; 11.125" spring with 35.5 coils, buffer tube 7.125" exterior with adjustable stock. They call it a mid-length gas system and the tube length is about 11-3/4 (but it is still staked in the gas block at the moment), with the 18" barrel. Gas port size measures a very consistent 0.096" from all angles.

I already ordered the gas ring from JP Enterprises which is likely to be the smaller .650" diameter. I also ordered and adjustable gas block and some buffer weight. I figured it was worth trying each individually before believing the whole system broken out of the box. First gas ring (if it is indeed the smaller size and fits), then the buffer weights with my modified gas rings, and then old buffer weight with adjustable gas block. Some of those parts are likely to end up in other builds later but I want to know as much about this as possible and have it running top notch before November rolls around.

I actually ordered that scope too but from a third party company who claimed to have a single one in stock. Primary Arms is backordered until sometime in November and I can't wait that long with hunting season approaching. I'm not sure it's going to actually show up though; it didn't ship out today like I expected it would. If it is indeed unavailable I will have to get a refund and pick something else in the short term.

Let me know if I need to look at anything else. I left everything apart after measuring the gas port size. No plans to fire it again for another week given the number of marks on the bolt carrier. I'm thinking of using Dykem to cover them up for later testing before I go wild and polish them off (once it's working right). That other parts are all about a week out at this point.

[98Z5V]

That's a large gas port for an 18" midlength gas barrel - quite large.  It's too big.  One thing is gonna fix that, and it's an adjustable gas block, dialed down.  That thing is overgassed for sure, and the buffer is too light.  Those two things are fighting each other, for certain. Overgassed and weak recoil system.  I'll bet that thing just pounds your shoulder.

That buffer is light - you need something 5.4oz, or close.  I need the internal depth on that receiver extension, not the OAL.  At 7.125", it's not gonna be the longer one, for sure, but you need to see if it's short - it should be 7.000" internal depth - but it should also have more than a 0.125" end on it - that thickness is an issue, overall, if it's a true 7.000" internal depth. Spring doesn't look bad for length, or coil count - but what's the wire diameter?  You are looking for something around 72-thou for wire diameter.

Measure the internal depth if the extension with a tape measure - bottom it,but you wanna read the tape that the top of the extension, where it ends at the top of the lower receiver - not at the bottom, by the FCG pocket.

Edited October 11, 2018 by 98Z5V

[Lane]

Sounds like I was barking up the right tree at least. Would those specs be even close to appropriate with a 16" barrel? No idea what size gas port Ceratac puts in that one. 

The marks on the bottom are the bolt carrier are something fierce. I can only imagine how hard it's throwing the hammer back down. I actually ordered new hammer pins because of some noticeable damage on the inside of my existing one.

I got a sick bruise from only a few rounds on the first test fire day. Having fired more since, I've only made it worse.

Internal buffer tube is exactly 7.00" as you mentioned; to the flat top not by the buffer retainer. Spring is exactly .072" wire diameter.

Seems like just the gas ring isn't enough to throw it off this far. Perhaps it is a bad setup out of the box?

Edited October 11, 2018 by Lane
A word

[98Z5V]

Your buffer spring is okay, then.  So is the receiver extension internal depth, for that system.  The buffer, at 2.550" is 0.050" long, but that's not an issue in cycling - the weight of the buffer is an issue.

Can you put up a pic of the buffer?  If it's 3.8oz, it's probably an aluminum body with two tungsten weights inside.  That's about the only way to get that combination.  If you can pound out the roll pin from the end, and break it down - that will help here - because I have solutions, depending on what's inside it. 

Don't stick a magnet to the outside if it, and tell me it's a steel body - a decent magnet will attract to an aluminum body, through the steel weights inside.  If I could invent an aluminum magnet, I'd retire. That's my "velcro" right there.

That gas port diameter - I completely trust you on your measurement.  It's too fucking big for that barrel combo - WAY too big.  When you're approaching 0.100" in gas port diameter, that's damn dear 16" rifle gas territory, right there.  It's WAY too much for an 18" midlength.  WAY.  You should be closer to 0.070"~0.075" on an 18" midlength.  That can't be reversed, at it's size.  Only way to solve that one is adjustable gas block, choked down.  I'm not kidding on that part. 

You have two things going on here. WAY overgassed, and a light buffer for a "normal gassed" .308AR.

Please break down that buffer, pics before and after.  I can solve the buffer part pretty easy.  Adj gas block is needed to solve the giant gas port in that barrel...

Edited October 11, 2018 by 98Z5V

[Lane]

So; this looks to me like the cheapest possible parts imaginable. I punched out the roll pin and there aren't any weights inside. It is a solid mass with a bumper pinned on. It very much sticks to a magnet, and has taken enough damage to the rear end to confirm it is likely made of solid steel. Looks like simply buying weights might have been a bit premature.

I have an adjustable gas block ordered and that is likely the first of the new parts to show up here. It should be pretty easy to drive out the roll pin on my existing gas block since I've already done it once before. 

[jtallen83]

4 hours ago, Lane said:

 

It appears from the face of the buffer that it is not contacting the carrier when the receivers are closed, shouldn't be roughed up that much. Could also be the solid buffer is bouncing on the back of the carrier? Odd that it shows wear in the center like that?

[Lane]

jtallen83: The center wear appears to have been caused by the tails for the slot in the bolt carrier which allows passage of the buffer retainer. They have since been polished smooth, but were originally very sharp and closed on the buffer right there every single time. Since I have a fixed magazine, that opening and closing happens a lot. The outer ring does appear to have a lot of damage too, but I'm not shocked given how violently it is being sent back being so over-gassed at the moment. 

Wrote this part earlier, but have been crafting it and didn't click "Submit" until just now: 

I have been considering my options since this buffer doesn't appear to be very serviceable (by adding weights). I didn't find a lot of empty buffers available, and heavy buffers aren't all that cheap. Since I ordered tungsten weights, I think I might try to make a few buffers while I'm waiting for other parts. I already dumped a bunch of money in gun parts and a scope earlier today.

I have plenty of 1" 6061 aluminum round stock on hand, and just Tuesday a buddy of mine handed me a large piece of bronze rod for no apparent reason. My only concern is how fast I can remove material with my small lathe. It turns aluminum fairly well with a bit of patience. Not sure how it will hold up to a hulk of bronze (at least it's pretty round). It should even turn steel at an even slower rate. I have time and materials on hand; worst case is I end up with some paper weights and still have to buy a heavy buffer. I think the bronze might make tuning weights easier with less tungsten; and what good is a "build" if I didn't make some part of it?

The one thing I'm still a bit unsure about is how the buffer length plays a role. It doesn't seem like the bumper is designed to be bouncing off the back end of the tube regularly. I had earlier marked my 308 buffer bumper with Sharpie and didn't see much if any wear markings, even with my current setup. Can I use a buffer that is shorter than normal in an AR-15 if the weight is correct? I'm thinking about re-appropriating this 308 buffer in one of them to resolve the same problem on a lesser scale (very light marking on the bolt carrier), those AR-15s had come with a 3 oz buffer which a bit longer than this one. I suppose I could turn an extension just the same if length actually an issue. Is the bumper actually supposed to give the end of the tube a light tap every time? I'm simply not experienced enough with tuning to know yet.

[jtallen83]

The buffer should tap the bottom of the extension, not real hard but it should make contact. Buffers and extensions that are out of spec can leave too much travel and allow the carrier to strike the receiver at the extension threads, quarters in the extension are an expedient fix for that, I have 75 cents in my Matrix build.

[Lane]

I had asked about quarters in the 308 earlier, and I wasn't sure if they were appropriate for my current situation. At the moment I have a bunch of stuff coming in the mail, but don't want to annihilate my bolt carrier with the hammer smashing for no reason (it also harms the lower).

Sounds like I shouldn't try this short buffer in an AR-15; at least without some compensation in terms of tube length?

At this point I'm committed to whatever it takes. At the same time, I want to learn how each of these components interact with each other.