Home Forums Hunting & Shooting AR and Tactical Rifles Tac 20 build (pic heavy)

I found myself in possession of most of the parts to slap together another AR upper, and happened across a set of 20 Tactical dies by Hornady so I thought I'd try one. I'll be machining the barrel from a Black Hole Weaponry blank, so I thought I'd post some pictures of the process here for anyone who might be interested. (And I figure it's fair to call this a "build", since I'm actually making the barrel myself.)

Here's the parts I'm starting with, still need a handguard. AAC receiver, some sort of nitride BCG, generic adjustable gas block, and a Fail Zero barrel extension. The truck axle is a 24" .20 cal 1:10 blank; basically a solid bar with a rifled bore. Pardon the low light cell phone pic.


This'll be a work in progress; I've just started and will be working on it as time allows so I'll update the thread as I go. I'll add a few more pics below though.

Looking forward to seeing how it turns out. Are you going with a BHW blank primarily based on getting a good deal, or do you think they’re on par with other quality SS button blanks? Say Shilen, Criterion, X caliber level...

I’m asking because I’ve had a couple of AR barrels from them that shot well, but I don’t see BHW mentioned nearly as often on rifle forums as I did a few years ago

A little about the cartridge itself - for those who don't know, the 20 Tactical is just a 223/5.56 case necked down to 20 cal, and the shoulder is pushed back to 30 degrees. The body/shoulder junction doesn't really move, so it doesn't take much to bump the shoulder back, and it gives a longer neck. Velocity numbers often quoted online for 24" barrels are 32gr @ 4200 fps and 39/40gr @ 3900 fps, essentially duplicating the 204 Ruger but with plentiful 5.56 brass and plenty of room in an AR magazine. Those numbers might be a little optimistic, but we'll see.

One thing I've discovered in my online research of the 20 Tactical, and then actually sizing my own brass, is that most of the "internet wisdom" about this cartridge vs the 20 Practical is wrong. Most discussions about it claim the Practical is so much easier because you can use 223 bushing dies and swap bushings. However, that assumes you're already using bushing dies, and also requires several steps to neck down with bushings. The same sources claim the 20 Tactical is difficult to bump the shoulder back, and many list fireforming as another downside. I'm pretty certain most of those are just repeating what they've read without any experience with the 20 Tactical.

With these Hornady 20 Tactical dies, forming cases is done by just one pass in the sizer die. That's it. It doesn't even take appreciably more effort than just normal 223 case sizing. The case length shrinks by about .004" on all the different headstamps I've tried so far. None had any trouble with the shoulders, including Winchester brass, and no fireforming is required. For my uses this is ideal, because I intend to just start loading with processed 223 brass, and don't want to turn case necks, fireform, or mess with necking down in stages with a bushing die.

20 Tactical on left vs 223 on the right.


20 Tactical vs 223 brass


a small handful of different headstamps sized to 20 Tactical, with one 223 case on the left

Walter - good question, and the answer is a little of both. BHW's retail outlet has a number of blanks in stock and ready to ship for reasonable prices, but I've used several of their barrels now and have been very impressed with them; they're accurate, fast, and foul as little as any other barrels I've ever used. I think you don't hear of them partly because the 3-groove "polygonal" Caudle rifling is just different and scares people off, but I've had really good luck with it in 6.5 Creedmoor and 243 LBC.

Also, I've been doing machine work since the mid-90's, but this BHW blank is one of the nicest barrels to machine that I've ever worked with. Partly that translates to good bore and chamber finish, but it's also just a pleasure to work with.

Thanks for the answer and for the informative post

Before I started on the barrel, I figured I'd check bolt lug contact in the barrel extension, and lap the face of the upper receiver.

Wrong bolt in this pic (that's a Grendel bolt), but you can see how the bolt and barrel extension lugs interface in an assembled upper:


Bolt lug engagement was adequate but not ideal. You can see less contact on some of the lugs; this was a result of the receiver face being slightly out of square.


My lapping fixture in the receiver. The fixture is a Brownells receiver extension, I bored out and pressed on a large nut, then turned the face square for lapping.


Where the lapping action happens:


Results of the first pass are pretty good. Could stop there but might as well take it a little further. We're looking for bright white lapped area all the way around, or close to it:


I'm calling this done. Looks like a low spot at 3:00 on the face of this receiver, but we have enough contact everywhere else that it won't matter:

Neat project & should be a great round; really great that one pass through the sizing die get's the job done.

I'm sure it will turn out well; good luck with it & keep us posted on the results.

MM

This looks like a great thread! Thanks for posting and keep it going.

Got started on the barrel, and will be reaming the chamber tonight or tomorrow.

Truing up the barrel with a fitted bore rod. This required turning a tool steel rod to .1993" to fit the bore in this barrel. The barrel is held only by the first tooth of the chuck jaws (blank is oversized so I turned a locating ring that is centered to the bore), and located at the rear with a spider. This allows me to adjust the angle of the barrel in the chuck to align the bore. Usually this is done with a 4-jaw chuck, but I got lucky with this very well zeroed 3-jaw. I adjusted the spider until neither indicator needle moves when rotating the chuck.


Located at the rear by a spider:


Facing the blank:


Chamber end of the barrel is ready to thread. The section to be threaded is .810" OD x .620" deep, and will be threaded 16 TPI to match the barrel extension.
That second step sticking out of the chuck is the 1" OD the barrel will be at the chamber end before tapering or stepping down the profile. Lots of material to remove from this 1.25" blank!


This pic shows the raised ring in the blank where the first tooth of the chuck jaws grip:


This is a different barrel, a pre-chambered BHW blank in 243 LBC, but it shows what the 20 Tac chamber end will look like after machining, before the barrel extension is attached.

One more update before the holiday weekend; got the barrel threaded and chambered, pics below.

I like to stop after the first light pass with the threading tool (only a few thousandths deep) to double check the thread pitch; easy to correct it now if it's wrong, but a lot harder later.


Threads are complete so the barrel extension threads on with a close fit. This is also the time to adjust the barrel shoulder to "time" the barrel so that it points either up or down, rather than off to one side; just a little accuracy trick that usually gets skipped in production barrels.



Now time to ream the chamber. This reamer has a floating pilot, so I chose a pilot that is a close fit to the bore. The Caudle rifling in this barrel has a larger bore (not groove!) diameter than standard, at .1993", so I used the largest pilot available at .1986"; not quite as close fitting as I'd like but close enough to work well.
With a small reamer like this, there isn't a lot of room for chips, so I only cut about .060" at a time and then retract the reamer to clean the chips out. It does get tedious, but gives better results than just ramming the reamer into the bore till it's done. I use lots of cutting oil on the reamer.


Part of chamber reaming is setting headspace, this is the equipment needed to do that. Go/no-go gauges, a good caliper (and also feeler gauges, not shown), and the bolt and barrel extension.


Setting headspace in AR barrels is actually pretty easy when done this way - by screwing the barrel extension on over the bolt and Go gauge, the gap between shoulders of the barrel and extension can be measured. This measurement shows that I need to advance the reamer another .3585" deeper to close on the Go gauge.


Headspace is now correct, with the bolt able to close on the Go gauge (as shown) but not quite on the No-go gauge. In this cartridge, the difference between the Go and No-go gauges is .003", so I chambered .002" deeper than the Go gauge. The sizing die will be adjusted to match that setting of course.

Yodering,

Where do you buy your barrel extensions, and bolts at ?
I’ve been thinking of making my own 204 ruger barrel for my AR’s, I have the lathe, but only do bolt work right now.

I’m looking forward to seeing pictures of drilling the gas hole in the barrel.

After chambering is complete, I cut the feed ramp. A lot of commercial barrels cut the feed ramp deeper, but I prefer a shallower angle for more case web support. I cut a 30° angle to .100" larger diameter than the chamber (.050" per side).


The final step is to lightly polish the feed ramp and break the sharp edges with emery cloth, and burnish the chamber. I use 0000 steel wool wrapped on a bristle brush for burnishing; we want a tight fit that will apply lots of pressure.


Final result - a clean smooth chamber and feed ramp with no detectable roughness or rings in the chamber.


That concludes the chambering part of this job. What remains is to profile the barrel, size & drill the gas port, and thread the muzzle; I'll share progress of those as they happen but it may be a few weeks from now.

I get my barrel extensions from Brownells. This one is a Fail Zero extension (about $25) but I have had really good results with the uncoated steel extension Brownells sells for ~$18.

I don't have a favorite source for bolts, usually just shopping around for whatever fits my needs.

That 204 Ruger barrel would go pretty much identically to this 20 Tac. I highly recommend the blanks from True Sporting Arms (that is BHW's retail outlet); they had this 1.25"x24" 20 cal 1:10 blank on sale for well under a Benjamin even after shipping, although if you pay full price they are fairly expensive. This is one of the nicest machining barrel blanks I've worked with though, it makes the machine work a real pleasure.

All my parts for builds have come from White Oak Armament or White Oak precision, I used to buy barrels chambered with bolts from them... not that I have my own lathe I could do it myself, however I’ve never seen anyone drill the gas port yet... so I have reading too do. I have built multiple HP competition AR’s so I have all the other piece parts, and as you showed headspacing the barrel extension isnt’ much different that you do with a bolt gun.

Thanks great information. In the posts.

OP great post thanks

I'll definitely post some pics of that when I do it. It's fairly simple with the right tools. I do it in the mill so controlling the depth is easy, and stepping up the size in small increments with sharp drill bits minimizes the burr on the inside. Sharp drill bits are the key though; I only use them a couple times for gas ports and then replace them.

Outstanding!

Love the pics!

This is a great thread !
You remind me of my now passed on retired NASA machinist friend.
He was very anal about whatever he did.
Made me some awesome shooting rifles.
This is very informative about ar's.

Ever get you stock back ?

No........

Another update - barrel profiling and installing the barrel extension.

I didn't take many pictures of barrel profiling, was too busy dodging chips. (just turning the blank down from 1.25" to 1" makes a lot of chips, then profiling started from there.) I kept the profile simple - 1" at the shank, .875" to the gas block, .750" at the gas block and .746" to the muzzle. I may add some flats or fluting later, but not at this point.
Note the different chips piled up - piles of golden bronze C and 6 shapes from roughing with heavy cuts, and then fine curly silver hair from the finishing cuts.


Piles of this stuff everywhere, including my pockets, hair, and they stick in your shoes. I had to clean the floor after every pass down the barrel. The gold/bronze color is from heat; if we were pushing a little harder the chips would be blue and purple.


A bit of polishing with emery cloth and then Simichrome on a paper towel cleaned up the barrel to a nice shine. (I don't use shop rags on the lathe, but paper towel can just rip if it gets caught instead of winding up your fingers/hand/etc.)
BTW that ugly chunk of cardboard back there was to keep chips and cutting oil off of the wall, but it fell down during my project and I didn't bother to fix it.


No pics of contouring or polishing the front end of the barrel, so on to crowning the muzzle. I cut an 11° target crown on this one and finished the OD with a small chamfer.


A little polishing, and the crown is done (sorry for the fuzzy pic):

On to installing the barrel extension permanently. I made this barrel vise years ago, and it's pretty out of the way attached to a workbench in a back room so I've never bothered to move it. The two 5/8" fine thread grade 8 bolts give LOTS of clamping pressure, and with a properly fit set of steel blocks it'll handle 175+ ft-lb easily without slipping or marring the barrel. I make those steel blocks for each barrel size by boring a hole through a solid block then sawing it in half. With a smooth finish in the blocks, it doesn't even scratch the polished surface of this barrel.

I use red 271 Loctite on the barrel extension threads, and torque to 100 ft-lb. Torque is applied via 1/2" drive torque wrench and that Brownells barrel extension tool pictured at the beginning of this thread (in the receiver lapping post).


Installing the extension pin is straightforward. I just cut a piece of 1/8" O-1 drill rod (annealed, not hardened) to .185" with a chamfer on both ends, and tap it in place. The barrel extension hole is sized to be the right press fit for 1/8" rod.

Comment on this part - some companies install hardened pins here. I don't like that because I've had to fix a couple that cracked and broke (from abuse, but still). An annealed pin is much easier to remove if it's damaged, and O-1 is plenty strong even in its softest state. This pin is only there to locate the barrel in the upper so the feed ramps are lined up, it should never be stressed by barrel or muzzle device installation (one reason I really do not like receiver blocks, use an extension tool / reaction rod instead).


This barrel is now ready for drilling the gas port hole, that'll come in the next update. The top barrel is my extra 243 LBC blank, still unprofiled at 1" diameter.

Gas port drilling

When I drill a gas port, I like to drill a matching set screw dimple to help with gas block alignment. To do this, I like to use a collet block, which is simply a precision ground block that holds a 5C collet in the center to allow repeatable positioning of a part in different orientations. I used a square collet block for this job, with a 7/8" 5C collet (that's why I turned the barrel to .875", rather than .850" which I don't have a collet for). I also use a stop on the vise jaw, so I can bump the collet against that to repeat the same position when the collet block is removed and replaced in the vise.

Aligning the barrel in the collet is important too; I mostly do this by eye and align it so the barrel extension pin is straight up. That can be checked in the mill once it's all in place.



Using an edge finder, I can locate both sides of the barrel to find the center. This one is an audible edge finder so it clicks when it jumps out of position as it finds the edge, that's a convenient feature.


With the center of the barrel located, I locate the barrel shoulder at the gas block journal, and move forward .300" to the gas port location.



Drilling the gas port - from research online it sounds like the appropriate gas port size for this barrel length and cartridge is usually between .088" and .093". I drilled first to .076" and then stepped up to .082"; that reduces the burr on the inside of the hole. I'll test fire it at .082" and step up the size to .088" or larger if needed.


With the gas port drilled, now I flipped the collet block upside down to drill the set screw dimple. The mill table position is unchanged, so this dimple is directly in line with the gas port, as desired.


With that part finished, I removed the barrel from the collet block and cleaned the bore in preparation for test firing.

Fun side note - in cleaning this 20 caliber bore, I discovered that it's a nice tight fit for Q-tips (I use a lot of those for cleaning shop projects). With the shop air nozzle stuck in the chamber end, that barrel will shoot a Q-tip through a cardboard box at close range. I may have wasted some time firing Q-tips around the shop.

Thought I'd show what I use for barrel installations, this is the fastest, easiest, and most secure method I know of, and doesn't stress the upper receiver at all. It's great for removing/installing muzzle devices too.

1/2" drive breaker bar in the vise. I made this one from a broken 1/2" extension, but a regular breaker bar or even a ratchet works too.


Barrel extension tool sits on the breaker bar


Upper receiver and barrel sit on the extension tool. This allows easy visibility of the gas tube hole for barrel nut alignment, and all of the barrel nut torque is reacted straight into the barrel extension rather than twisting the upper receiver.


Installing the gas block - note the dimple under the rear set screw hole; that hole is directly in line with the gas hole in the gas block, so lining up the set screw with the dimple automatically aligns the block with the barrel's gas port.


Double checking gas tube length - looks just right. (compare it visually with the half-circle cutout in the upper for the bolt cam, should be a little past center)
I also spend a little time tweaking the gas tube if necessary so it lines up with the gas key on the carrier without bumping or flexing.


Upper is assembled and ready to test fire. I won't bother with the handguard until the gas port is the correct size.


Oops, wrong chambering for this upper. This'll never work.

Thanks for the comments guys!

Like your work.

What brand of lathe do you have?

It's a Jet 13x36, belt drive model from 1991. I wish it was the gear drive model just for faster speed changes, but otherwise really like it; it's a good lathe for gunsmithing work. The 1.5" spindle bore means plenty of room for barrels and actions, and when building my Form 1 suppressors I often use 1.5" stock so that's an important feature.

I bought a matching Jet mill from the same guy, that is a clone of the 9x42 Bridgeport.

Final assembly and test firing happened this weekend.

For final permanent assembly, I decided to use a BCM upper since this'll be more of a precision rifle. (This was originally a left-over parts build, but has morphed into two complete uppers with the extra parts I picked up along the way.) I like the BCM uppers because they are a tighter fit to the barrel extension, and are usually a couple thousandths press fit rather than the typical loose slip fit of most uppers. Heating the upper with a heat gun expands it enough to install the barrel:


I stamped the cartridge and twist rate on the barrel as well. This isn't a fancy way to mark the barrel, but is quick and expedient, and I'm more interested in function than looks on this one anyhow. I do mark a line on the barrel to index the stamps against, and always test each stamp on a piece of scrap first (note the aluminum block near the top of the pic). Stamping a letter upside down is embarassing, testing on scrap helps avoid that. Stamped letters always look a little bit drunk, but IMO this one looks worse in the pic than it does in person.


Inital test firing went pretty well, other than the chrono not picking up any readings. Cycling was just a little sluggish though, with the bolt not locking back on most loads, so I stepped up the gas port size to .089" (from .082").


Indexing the gas port hole is pretty simple - I use the previous .082" drill bit in the chuck backwards, and use the drill bit shank to locate the hole. When the drill bit can enter the hole without any deflection, it's centered. This is accurate to within a thousandth or so if a guy is careful.


Final assembly is complete. Blue #243 Loctite was used for all scope, handguard, and gas block screws, as well as between the gas block and barrel for sealing. Green #620 was used between the handguard and barrel nut per Midwest's instructions. The rifle is topped with a 3-9x HD SS on a 20 moa riser. Still couldn't get reliable velocity readings, but the rifle cycles well with both 32 and 40 gr V-max over TAC, 2460, 8208, and Benchmark.


Just for fun I fired a 32gr V-max @ ~3900 fps (if the 2 chrono readings are correct) into this 5/16" steel plate. Shown for comparison is an impact crater from a 75gr 5.56. It's not a completely fair comparison, 24" vs 16" barrel, but the 75gr 5.56 won't punch through from a 24" barrel either. Max loads with that 32 gr V-max should add another ~200 fps or so.


I'll follow this up with some velocity and accuracy results when I can, but for now this build is done. Thanks for reading.

Looking good.

Hope it shoots tight groups.

Haha me too! It'll be embarassing if it doesn't, after all this work!

Thanks.

Thanks for putting this up, competence can make for a compelling read. And thank you for taking the time to make those well composed and informative photographs. Good gun writing lives here.

Great job, great pics & great narrative.

Thanks for taking the time to post it all up.............that in itself takes a while.

MM

Wow, that looks fantastic. thanks for sharing all those details.

...where knowledge and skill converge. Now that is a 'build'.

Thanks for the comments guys. This is the stuff I enjoy doing, much more than debating brands and headstamps.

MontanaMan - glad to do it. I've thought of documenting one of these in the past, but happened to have time to post while making this barrel so it all worked out. About half my rifles have my own barrels like this, but usually I'm too busy to take pics and write it all down. Hopefully this might help someone else who's making their own barrel for the first time; I didn't include every detail but tried to capture the basics anyway.

I haven't had a chance to test any loads for accuracy yet, but did burn some powder finding max loads for a few different bullets, as well as poking holes in steel.

Out of a bunch of different powders I tested, I'm liking XTerminator the best so far based on consistency, how it runs the rifle, and velocity. No surprise given the excellent results I've had from it in 5.56 and lighter bullets. Max loads for good brass life at this point appear to be ~3,850 fps with the 40gr V-Max and 39gr TNT, and ~4,180-4,200 fps with the 32gr V-Max.

20 Tac with those three bullets shown here alongside a 243 LBC with 95gr VLD


I plinked some steel to see what happens with the 32gr V-max load. Looks like I'll probably need to restrict this one to at least 200+ yards on my AR500 steel targets.

Great post. Thanks for sharing.

Thanks for this posting.
You did an awesome build, and showed so much to learn from.
Hats off to you sir.

Yondering, any more on this one?

Actually was just loading some more ammo for it last night. I should take some pics of accuracy targets but haven't done that yet (I really prefer shooting longer distance at steel and other targets once I figure out a load); however, I found it shoots the best (and IMO very well!) with the 40gr V-max over 31gr of Lever for 3917 fps avg at the muzzle. I ran a seating depth test with varied powder charges at each depth, and found that 2.255" OAL shot really well at 100 even with a full 1.3gr variation in powder charge, so I'm loading in the middle of that range and calling it good. I did confirm through a lot of testing that Lever is THE powder for the 40gr V-Max in this rifle; nothing else ran as fast or shot as well.

The 32gr V-Max shot reasonably well with X-Terminator, but struggled to pass 4100 fps without really pushing the brass, and at that speed it gives up a lot to the 40gr load so I didn't bother with it further.

The 24gr NTX is an interesting one I've been experimenting with. There is factory data for it in the 20 Tac, like the Sierra manual, but if you really look at the numbers and powder choices is severely underloaded and hampered by powders that are too slow and fill the case before reaching full potential. Since I've got a pretty full selection of Ramshot and Accurate powders I did the wildcatter thing and started messing with those, stepping faster in burn rate until things fell into place with AA2200. The max load with that one put that 24gr NTX a bit over 4,800 fps (no joke) but I found a decent accuracy load in the low 4,700 fps range. That one doesn't shoot as well as the 40gr V-Max, and loses steam fast, but it's a neat little bullet to fire at warp speed. It also has almost no perceptible recoil other than the bolt carrier movement; it feels like less than my 22 Hornet.
An interesting side note though is that even though it's doing almost 1,000 fps faster than the 40gr loads, it doesn't penetrate steel plate any better. I think that powdered copper core is just so frangible that it comes apart too fast. I did find one example when I had my target mounted to a cardboard box that it split the side of the box and fully fragmented within ~3 inches of entry on just the cardboard.

Anyway, it's a really fun round and a blast to shoot in the AR. It's very low recoil compared to the 5.56 which is already pretty mild, and is an absolute laser beam within ~300 yards. Also, as usual I'm really happy with this Black Hole barrel. I've got another build to post up when I get time; this one is a 19" octagon barrel in 243 LBC, set up as a mid-light weight walking rifle in the AR15 platform. That one includes a thumb surgery story too since I did a very dumb thing and found out what the bone looks like under my thumbnail.

Thanks, the cartridge intrigues me.

Sorry about the thumb.

What an awesome thread! Incredibly informative and incredibly disheartening.....I realize how stupid I am since all this machinist talk is Chinese to a dummy like me. Pictures really help me to understand the process.

Great thread Yondering....thanks for taking the time to explain, with words and pictures, the process of truly building an AR. You’re quite the craftsman! 👍