Project - 300AAC Blackout Mini-14!!

Brobee

Brobee

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Hi there!

PART I

For whatever reason, I LOVE the mini-14/30 platform as an all-purpose semi-auto rifle. I gleefully play with my .223 guns shooting my run&gun course from 400meters down to 100 meters on Steel Silhouettes, and I've enjoyed boar and deer hunting with both the 7.62x39 and 6.8SPC guns.

One thing that's troubled me about the 7.62x39 guns though are the magazines. The factory 5 round mag seems to always have trouble with the last round, and while I've never needed it hunting it's always bugged me. I also did not like that I had to have two stashes of expensive mags....factory 5/20s for the .223 and factory 5/20s for the 7.62x39 (with no factory 5/20s available fo rthe 6.8SPC). Then when the 300AAC blackout started taking off I was pretty interested...I might be able to standardize my magazines, and brass supply could be simplified significantly too if I could get set up to make cases from .223.

So early in the year I got motivated and set out to try. I first tackled brass, and some will remember threads I posted on my process early on. It's become quite a bit more efficient now, but brass is not the focus of this thread...:)

I'm lucky enough to have a good shooting buddy who's day job is to run a high-tech production machine shop, manufacturing oil tools here in Alberta. We've enjoyed shooting our mini-14's together enough that he also caught interest in the Blackout Mini, and committed to putting his considerabe skills and machining capacity behind the project....so it was time to look for barrels!

That proved to be more frustrating that one would have thought...after waiting for months (after being told it would only take a couple weeks), I expanded our search scope and was surprised to learn that there is a barrel maker operating right here in Alberta! Ron Smith works from his amazing workshop out on his family farm less than an hour north of Calgary. Amazing! After a couple of phone calls, he agreed to make me three .308 diameter 416 Stainless rifled barrel blanks. We settled on a 1 in 9 twist, for reasons I can explain later.

Boy was I excited when I got the call inviting me to drive up and pick up the barrels! But that excitement paled by comparison to how I felt when I opened the door to his shop and walked in for the first time. There stood Ron, labouring over his rifling machine as he put the finishing touches on my last barrel blank:

02BarrelBlankMaking.jpg


He spent about an hour with me touring me through his shop, and it was FANTASTIC. He told me that he personally made the rifling machine about 45 years ago, and that he's cut rifling on many, many thousands of barrels over the years.

01BarrelBlankMaking.jpg


This is the machine he uses to gun-drill the stainless blank, and then chase it with a reamer to make sure the hole is perfect.

03BarrelBlankMaking.jpg


And here are the finished barrels (with a couple more laying there ready for their new owners):

04BarrelBlankMaking.jpg


It was pretty much the most awesome experience I've had this year, and I'm super grateful to have lucked out and found such an interesting guy. I can hardly wait to drive back out to show him the finished project...

More to follow in Part II....

Brobee
 
300 AAC Blackout Mini-14
PART II

So with my barrel blanks burning a hole in the back of my vehicle, I drove as fast as legally possibly over to my shooting buddy's shop. We carved out a bit of time in our schedules and got to work. Ok, he did pretty much all of the work from here on....I just yacked up a storm and again watched in awe.

As an aside, I was thinking about posting this in the gunsmithing section, however neither one of us are trained gunsmiths; rather we are interested enthusiasts. We use our mini-14s primarily as black rifle play toys, and given the cartridge we were using I figured I'd post here in the black rifle section as general interest story for the AR boys also playing with the 300 blackout.

So anyway....while waiting for the barrels that would never come, we'd ordered headspace gauges and reamers, all of which had showed up many moons ago, so we were ready to get going!

Step 1.1 - Measure the headspace of all the .223 donor guns as they came from the ruger factory. This would allow us to set our reference points for the barrel shoulder/barrel mouth as it relates to the bolt face and would be important when figuring out how to headspace the new barrels. We were working with three donor guns, and it turns out the factory ruger headspacing is very very very consistant - all three measured somewhere between 0.002 to 0.003 longer than 1.4636 SAAMI .223 GO. To measure this I have a special set of 12 headspace gauges, starting at 1.4636 GO and then each getting bigger by 0.001. Dave down at Pacific Tool and Gauge made them for me, and they are super handy when trying to determine exactly the headspace of any .223 gun. You can see these gauges in one of the pictures below. We can tell how long the chamber is by watching the bolt lugs....the bolt would completely close on 1.4656, but would close like 95% on the 1.4566 gauge. All three were bang-on close together.

Step 1.2 - Make a barrel vice sleeve and receiver wrench for the mini-14:

05ReceiverWrench.jpg


Step 1.3 - Use a highly sophisticated lever to torque off receiver from barrel (this is an example of why we are unqualified to post in the gunsmithing section):

06PipeWrench.jpg


And the result - no damage to the receivers when spinning them off the barrels! You can also see the .223 headspace gauges in this photo:

07ReceiverHeadspaceGauges.jpg


Step 1.4 - Use the same headspace gauges to understand how consistant the relationship is between the shoulders and breech faces of the factory barrels:

08HeadspaceDetermine.jpg


This was quite interesting - the design and execution of the mini as they come from the ruger factory is such that the gauge representing the headspace of the gun (in our case 1.4656) was precisely flush with the breech face of the barrel for all three of the donor guns. How convenient is that!?!?!?! Provided we could replicate the exact distance between the barrel face and the barrel shoulder, it would be a piece of cake to headspace the guns, requiring that we cut the chamber until our 300BLK GO GAUGE sits exactly flush with the barrel end, and then go another 0.002 or 0.003 for it to be semi-auto safe.

So my buddy set out to make his plan, and did up a bunch of drawings to use for CNC programming:

09Drawings.jpg


More to follow in Part III....

Brobee
 
300 AAC Blackout Mini-14
PART III

The next step was getting the .308 barrel blanks ready for profiling in the CNC machines. We wanted to make sure that the bores were precisely true with the outside profile, as we needed to be able to chuck up the barrels from the outside and still be spinning/turning them around the axis of the bore.

Step 2.1 - Set the barrel blank up, centered around the bore using a live center:

10TruingBlankSetup.jpg


Step 2.2 - Turn the outside so that it would be as close to true as possible in relation to the bore.

11TruingBlank.jpg


Step 3.1 - As per Ron Smith's instructions, trim off at least 4 inches from the chamber end of the blank, and take the rest from the muzzle end. We targeted 18.6 inches to give us a bit of breathing room.

12LengthRoughCut.jpg


Step 3.2 - Back to the manual lathe where he took another 0.050 facing off the breech and the muzzle:

13FacingTruing.jpg


14Facing.jpg


Step 3.3 - Cutting the Crown.

15Crowning.jpg


Now it was time for the CNC profiling work....stay tuned for Part IV!

Brobee
 
300 AAC Blackout Mini-14
PART IV

Now we were ready to do the barrel profile on the CNC machine. My buddy has a "Special Projects" CNC lathe, named such because it's where most of our special gun projects get done. In order to keep his business running, I am not allowed to go anywhere near any of the other CNC machines that are busy spitting out oil tools. *sigh* someday maybe I can talk him into the mega-big-bore project...:)

Step 4.1 - Chuck up blank in CNC lathe and touch tool off the breech as our primary reference point:

16ProfileTouchOff.jpg


Step 4.2 - Program CNC lathe to cut profile.

17ProfileProgram.jpg


Step 4.3 - After quadruple-checking everything, run the back half of the profile. I was amazed how fast this went, and how awesome the finish was when done.

18ProfileRun.jpg


Here's how they looked after they came off the first profiling operation:

21Thread.jpg


Step 4.4 - Program, check, and cut the other half of the profile:

20Profile2.jpg



Step 5.1 - Back to the manual lathe for reaming out the chamber. He did this very slowly with lots of measuring along the way:

22ReamChamber.jpg


Step 5.2 - Check chamber depth with headspace gauge, using the end of the barrel as a reference point. Here we still have another 0.040 to go to get to SAMMI 300BLK GO. We ultimately went an additional 0.002 beyond this.

23CheckReamerDepth.jpg


Step 6.1 - Make sure to go home on time to attend my Daughter's 7th birthday family celebration. This is where my photo report flies off the rails a bit, as I took the camera with me. My dedicated buddy kept going, so when I arrived the next day he had already put them back on the CNC lathe to cut the inner relief profile on the chamber end for the extractor and bolt face shroud, re-attached the receivers, properly them up, and located/milled the gas bushing recess and gas port. So when I got back the following morning, the assembled barrelled actions were waiting:

24AssembledAction.jpg


Actually finding something I could do, I cleaned up the flash off the factory castings (you can see the pre-cleanup flash around the receiver in the photo above) and we set about to assemble the guns. We pressed on the origional ruger front sights, and then spun on A2 flash hiders on the 1/2x28 threads he'd cut on the muzzle end when doing the profiling work. We assembled one gun for testing, equipping it with an ultimak rail and an Aimpoint ML3 2MOA. Off to the range we went!

Preliminary Range Report to follow in Part V...

Brobee
 
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Cool project!

Looking forward to part IV!

EDIT: Blarg. You posted part IV in the time it took me to read the rest of the thread. CURSE YOU!!!!
 
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