March 26, 2019
Photos by Mark Fingar
Whenever a new cartridge comes out, there’s the inevitable internet chatter praising or belittling the new creation. Proponents will parrot the information from the manufacturer and opponents will ask, “What does this do that my (insert preferred cartridge here) won’t?”
One new cartridge that will be generating its share of conversations is the .300 HAM’R. My goal is to answer the question posed above along with an explanation of how this cartridge is possible.
The .300 HAM’R will inevitably be compared to the .300 Blackout (BLK), but there is a huge difference between the two. The .300 HAM’R is to the .300 BLK what the .300 Winchester Magnum is to the .308 Winchester.
Crunching The Numbers
The .300 HAM’R is a cartridge optimized to get the most terminal effects possible out of a standard AR-15. The bolt, magazine and receivers are all what you’d find in any AR-15, only the barrel is different.
The .300 HAM’R cartridge case is .26-inch longer than a .300 BLK case and .04-inch longer than the 7.62x40mm Wilson Tactical (WT). The loaded overall length is just short enough to fit inside an AR-15 magazine.
The 7.62x40mm WT is a cartridge designed by Kurt Buchert and brought to market by Wilson Combat. The problem with this cartridge is the use of bullets with long ogives. Loading long bullets in this cartridge meant that chamber specifications prevented shorter bullets from being seated farther out in the case. The 7.62x40mm puts a lot of bullet in the case, and that significantly limits case capacity.
The “problems” with the .300 BLK are much more numerous when the shooter desires maximum terminal performance instead of the ability to shoot subsonic bullets from a short-barreled rifle (SBR). The .300 BLK was designed to offer better terminal ballistics than the 9mm submachine gun in a package that is the same size or smaller. It succeeded because it shoots better bullets at much higher pressures.
However, when a .300 BLK is loaded with bullets from 110 to 135 grains, there isn’t a lot of case capacity for gunpowder. In fact, there is so little case capacity that almost all .300 BLK cartridges loaded in this bullet-weight range use pistol powder loaded to rifle pressure. It’s all a question of space.
Bill Wilson, of Wilson Combat, knows this and designed the .300 HAM’R to fix it. Unlike the 7.62x40mm, the HAM’R uses shorter bullets in the 110- to 150-grain weight range. These bullets have tangent ogives (the ballistic coefficients aren’t going to be great), so the .300 HAM’R does its best work inside 400 yards.
Choosing the right bullets was the first step, and lengthening the case was the next step. That additional .26 inch of case length over the .300 BLK teamed with the shorter bullets that stay out of the case create enormous powder capacity. All that volume means Wilson Combat has enough room to use honest-to-goodness rifle powder and could fit enough in the case to get close to the maximum safe pressure. With pressure comes velocity.
The Secret Sauce
The .300 BLK’s diminutive powder capacity is why its velocities stink. Sure, you can stuff enough Hodgdon H110 (pistol powder) in there to get to about 55,000 pounds per square inch (psi), but there still isn’t much powder in the case.
Greater powder volume equals more gas volume. Gas volume equals velocity; it’s science. So, fast powders like H110 don’t have a lot of volume because they were designed for use in a pistol case. Those things are tiny, so H110 is compact, heavy and fast. A max-pressure load of H110 won’t occupy much volume, and that’s a problem when you need a high volume of gas to push a bullet at high velocity.
Hodgdon knows their way around gunpowder and invented a rifle powder called CFE BLK for use in the .300 BLK. It was better than H110 because it was slower, a bit bulkier and occupied more volume. Thus, it also yielded more gas volume when it burned. When loading subsonic bullets in .300 BLK, CFE BLK reigns supreme. However, it only does OK when loaded with lighter supersonic bullets.
Once again, the paucity of case capacity means that there isn’t enough room to fit sufficient CFE BLK in a .300 BLK case to reach close to 55,000 psi. The magic Wilson Combat did with the .300 HAM’R meant that suddenly there was an AR-15 cartridge case that had enough room for a sufficient quantity of CFE BLK to hit 55,000 psi with a 125- to 150-grain bullet. Their results were spectacular.
The HAM’R’s case capacity combined with the righteous use of CFE BLK has varying velocity results dependent on bullet weight. Some combinations show significant increases in performance over the .300 BLK, and some performance gains are hard to believe.
The 110-grain bullets showed an increase of right around 160 feet per second (fps) over bullets of the same weight fired out of a .300 BLK. (All barrels used in testing were 16 inches long.) The problem the 110-grain bullets face is they aren’t heavy enough to get over 50,000 psi, so the additional case capacity gets a good but not great velocity gain.
Spectacular changes occurred with the 125-grain bullets. That bullet weight had an increase of 306 fps over the .300 BLK at the same bullet weight from identical barrel lengths. The combination of a bullet with the correct weight to hit right around 55,000 psi with the maximum load of CFE BLK combined for a huge gain in velocity.
Designed To Be Accurate
If you ever want to start a fight about why some of the older cartridges don’t stack up, get the chamber print and give it some scrutiny. Free bore is one area in particular where modern cartridge designs excel. Free bore is where the bullet sits when the cartridge is chambered, but short of where the rifling begins. The problem with having too much slop in the free bore is the bullet can yaw or twist prior to engaging the rifling. When that happens, the bullet’s center of gravity forcibly changes upon impact with the rifling, which causes accuracy to suffer.
Wilson Combat designed the .300 HAM’R with a free-bore diameter of .309 inch, half of what’s found on the .308 Winchester. The rifle I tested shot exceptionally well, and getting the free-bore dimension correct is a big part of that. Any cartridge designed over the last 10 years will usually stay to the .001-inch addition or less, which is another reason why modern rifle/cartridge combinations shoot so well with a wide range of bullet weights.
The other reason the .300 HAM’R shoots so well is the angle of the leade (where the chamber transitions from free bore to rifling). It’s set at 1.5 degrees, which is the optimal angle for most modern bullets. That angle, combined with the tangent ogives of the bullets Wilson has loaded into their ammunition, combine with the free-bore dimensions to create excellent accuracy.
With some of the velocities that Wilson Combat is getting from the .300 HAM’R, I expect there will be some speculation on the chamber pressure of factory-loaded ammunition. All Wilson ammunition stays between 48,000 and 58,000 psi. The 110-grain bullets can’t get over 50,000 psi with CFE BLK, it’s only with the 135-grain bullets and heavier that you can get up to 58,000 psi. I think those are excellent pressure numbers for an AR-15 cartridge, especially since the .300 HAM’R utilizes a midlength gas system on the 16-inch barrel I tested. The 18- and 20-inch barrels utilize an even longer intermediate gas system. Both system lengths allow chamber pressure to drop more than a carbine system would allow before the bolt starts the extraction process.
I encourage readers to go to Wilson Combat’s website to explore the copious information available on the new .300 HAM’R cartridge. Wilson Combat has published a lot of data from their research on what it has to offer. The velocity and energy numbers they’ve posted are very similar to what I saw during my own testing, so their comparisons are pretty accurate and very informative.
The test rifle I used for the .300 HAM’R evaluation was the Wilson Combat Ranger. This rifle is an excellent multi-purpose model that is a good choice for everything from self-defense to hunting.
All of Wilson Combat’s AR-15 rifles use bolts made from 9310 steel. AR purists will say that Carpenter 158 was what Eugene Stoner specified, and while that’s correct, that was in 1957 for a rifle-length gas system that used ammunition loaded to a maximum pressure of 50,000 psi — times have changed.
The 9310 steel is an alloy that includes vanadium and aggressively regulates the sulphur and phosphorus content. The vanadium gives the steel a tight, irregular grain that better resists cracking, and the sulphur and phosphorus give it a degree of insensitivity to the heat-treat process, which makes it more forgiving.
Wilson Combat also makes the barrels for all of their 5.56 and .30-caliber offerings. They start with a bar of steel, drill the hole, hone it, rifle it with a button, contour the barrel and do all of the chamber work. Along the way, they also handle all of the heat-treating and stress relieving. This is an incredibly sophisticated manufacturing process that they do completely in-house, and it speaks well of the company’s capabilities.
The range time I spent with the .300 HAM’R shows what happens when a company like Wilson Combat sweats all the details and does all the legwork like they did with both rifle and cartridge.
Not only was the rifle exceptionally accurate, the cartridge offers unrivaled terminal performance from the AR-15. It doesn’t matter if you’re shooting critters or steel, nothing will hit them harder than the .300 HAM’R.
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