A little grease on upper prevents the castle nut from galling the aluminum threads and makes assembly easier.
A BCM Gunfighter charging handle improves leverage.
Lay the flat-top receiver and handguard on a flat surface to be sure that they are properly aligned before installing screws and torquing them down.
Wilson Combat’s Accu-Tac AR flash hider sports an external profile and accurizing flutes that improve muzzle harmonics.
February weather in North Texas was typical for the time of year. As the sun dropped toward the horizon, the temperature dropped below freezing. I sat in a comfortable box blind overlooking a hog feeder. A Wilson Combat AR-platform rifle stood leaning in a corner while I watched a doe and two fawns search for acorns.
Wild hogs befuddle me. Most of the time I can a glimpse a whitetail’s rack and tell you what it will score within 5 inches, but trying to guess a hog’s size is one of the most difficult tasks. I should have taken a clue from the blonde boar’s age, when I spied him in thick brush beyond the game feeder that stood 80 yards away. He stood motionless within the tangle of briars for more than five minutes, studying his surroundings before edging toward the feeder. When he finally walked under the feeder and started scrounging for corn, I still couldn’t judge his size as he stood knee deep in a muddy hole. On cue an hour before dark, the feeder rained corn on the waiting boar. He fed for 20 minutes while I studied him through the riflescope. Without another hog beside him to compare size, I didn’t prepare for a shot. It was the first hunt of a three-day outing, so I wasn’t in a hurry to do my part in thinning the hog population.
Without warning the boar trotted from beneath the feeder and disappeared. Less than a minute later, a sow and her eight piglets trotted up to the feeder and started chowing down. Within five minutes the crowd had swelled to nearly 30 hogs of all colors and sizes. I examined the biggest hogs under the feeder and realized that the first solitary hog was larger than any of the porkers now shuffling around. Darkness fell, and the hog lights cast an eerie red glow on the now vacant feeder. Stepping from the darkness, the solitary blonde boar returned to feed in peace. That’s when I determined that he was definitely big enough to rank trophy status. I settled the crosshairs on his shoulder and squeezed off a shot. Even though the rifle was suppressed, the 7.62x40WT (Wilson Tactical) round cracked loudly and put the hog into a pile.
It wasn’t until the boar got a ride to the skinning shed that I truly learned his size: long tusks and his 235 pounds were evident, and a post mortem showed that the 110-grain Barnes TTSX was more than a match for the boar’s thick hide and gristle-shielded side. That introduction to this new cartridge was a real eye-opener. Several months later, I got an assignment to dig deeper into this new cartridge. The first order of business was to get Bill Wilson, owner of Wilson Combat, on the telephone—I wanted the originator’s thoughts on the new round. We discussed and compared the new 300 AAC Blackout to the 7.62x40WT. “If you want to shoot subsonic loads, then the Blackout is a good choice, but the 7.62x40WT really shines when you want to shoot high-velocity bullets with plenty of punch,” Bill Wilson said. When he suggested that I build a complete upper in this caliber to learn more about the round’s capabilities, I agreed.
The Upper Build
A few days later, UPS delivered a package that contained new brass: Barnes Bullets’ new 110-grain TTSX bullets, a couple boxes of Wilson Combat’s loaded ammo and the parts needed to build a complete upper receiver. The upper receiver build was straightforward. I installed the ejection-port dust cover first to get that out of the way. Next came the forward-assist plunger. A roll-pin holder made starting the forward-assist retaining pin much easier than trying to start it any other way. The same tool type was also employed to install the roll pin that holds the gas tube in a low-profile PRI gas block. (I later replaced the gas block with an adjustable PRI gas block so I could fine-tune the gas pressure. The inside of the handguard required a bit of filing work to clear the slightly larger gas block but only took about 10 minutes to complete.)
Next came assembling the barrel to the upper receiver. I struggled with the barrel tensioning nut and finally decided to grind down the jaws of an adjustable wrench to get the jaws narrow enough to fit the flats on the tensioning nut. I tensioned the nut by feel, just indexing the handguard’s rear screw holes when the handguard was perfectly level with the Picatinny rail on the upper receiver. If I recall correctly, torque specs for a barrel tensioning nut range from about 55 foot-pounds to 70 foot-pounds, but to be this precise you’ll need a dedicated tool that will allow the attachment of a torque wrench.
The best method I have found to level a flattop upper receiver that has a handguard with a top rail is to lay the assembled parts on a perfectly flat surface when tightening the retaining screws. I use a steel welding table for this purpose. With final assembly of the upper complete, I substituted a Bravo Company BCM Gunfighter Mod 4 charging handle for a mil-spec one. Next, I attached the upper to a BCM complete lower fitted with a six-position recoil tube. For a fire control group I selected a JP Enterprises single-stage EZ Trigger tuned to break precisely at 3 pounds. Completing the build was a Tactical Intent TI-7 Tactical Buttstock. (For those not familiar with Tactical Intent, they’re a division of P&S Products, which has decades of experience providing mil-spec weapons parts.)
Once the upper receiver build was completed, I went to the range and started testing my own handloads. It was toward the end of deer season, so I carried it in the woods every chance I had.
Bill Wilson has invested a lot of time in building handloads for his pet 7.62x40WT rifles. “This blue-polymer-tipped Barnes TTSX bullet was specifically made for this cartridge,” Bill Wilson said. “The crimp groove in the bullet is placed precisely at the point that will allow the maximum overall cartridge length of 2.6 inches, which is also the maximum length for a standard 5.56 NATO magazine.” I learned, from loading heavy .308 bullets for the 300 BLK/Whisper to fit an AR magazine, that the cartridge’s overall length is limited by not only length but also the contact of the bullet’s ogive with the magazine’s side support rib. When using polymer Magpul magazines, there’s a simple remedy: I removed the spring and follower and used a flat file to remove about half the height of the rib, giving the bullets clearance on the sides to move freely.
Wilson’s cure for what I experienced with the Magpul magazines is to sell Lancer magazines instead. The Lancer magazines feature a modified (de-ribbed) body to enhance reliability with the 7.62x40WT cartridge. Made in the U.S., the Lancers have translucent, polymer bodies that are impact-resistant through a wide range of temps. Sportsmen will appreciate them.
Kicking Up Dirt
My first trip to the range resulted in erratic performance from my handloads and the Wilson Combat factory loads. At first, I thought the failures to feed were due to underpowered handloads, but when I fired the Wilson factory loads, I had trouble with those too. Shortly thereafter I pulled the barrel off the upper and shipped it back to Bill to have the gas port opened up. After I got the upper back and reassembled my gun, I got nearly foolproof feeding and ejection during my next trip to the range.
My first handload was 20.8 grains of H110 driving a 110-grain Barnes TTSX. Federal small-rifle Match primers were used for all of my handloads. When I switched to IMR 4227, velocities dropped with the 110-grain TTSX. While working on several articles on the 300 BLK, I acquired several hundred Remington 125-grain bullets made to expand at lower velocities. These bullets’ noses exhibit pink-polymer tips. Since these new bullets were delivered in bulk, I took the time to weigh and sort several hundred of them. I found that the bullets ranged in weight by nearly 2 grains. I sorted them into groups of bullets within 0.1 grains of one another and loaded those over 17.8 grains of H110. Another bullet used in Advanced Armament Corporation’s development of the 300 BLK is a 125-grain hollow point that received a charge of 17.7 grains of H110. I produced two loads with Nosler’s 125-grain Ballistic Tips. The first load was 23.5 grains of AA1680, and the second was 17.8 grains of H110. The last load was Hornady’s 130-grain Spire Point with 19 grains of H110. This load turned out the best five-shot group of the day, measuring 0.67 inch.
These represent starting- and mid-range power loads. I’ll continue testing to find the ideal loads. Anyone wanting to work up loads for this round should back off these and the loads suggested by Wilson Combat by 10 percent and then work up. The 7.62x40WT gets a lot from a .30-caliber bullet in an AR platform. The ability to make inexpensive cases from military-surplus brass is a big benefit. If you try it on whitetail-sized game, you will learn too, that it’s an adequate killer. For more, visit wilsoncombat.com or call 800-955-4856.
Description: Experience 0.5-MOA precision with Smith & Wesson’s newest AR rifles - the M&P15...
by Jon Sundra / Oct 15, 2013