I was loading some .223 ammo this weekend and was deciding on a OAL for my cartridges. Most of the time I usually go by whatever factory ammo I have on hand.

While measuring a factory PMC XTAC with a 55 gr. bullet, I was wondering how much powder they were using. So I opened the cartridge and poured the charge onto my scale. 25.9 is what the scale read. I'm assuming that means it's a factory 26 grain load with a .1 grain variance.



The bullet itself came in at 54.8 grains which may have lost .1 grains or so by the pliers I used scratching off some of the jacket. So it appears that PMC is using a 26 grain charge of non-canister ball powder. It was very similar to what I've seen from the Federals XM193 charge although the powder was more of a graphite color than a charcoal color used in the Federal cartridges.

A friend of mine recently showed me his custom AR-15 in .300 blackout with a 9-inch barrel and AAC 762 suppressor. I was intrigued to compare it with my HK UMP 8-inch barrel gun. Both are short barrel rifles and when loaded with subsonic ammo, the .300 blackout is very similar is terms of ballistics to the .45 ACP.

Once we exchanged guns and started looking at them I realized it wasn't fair to compare them directly. While both guns were similar, they were also very different. Here is my analysis of each gun along with the pros and cons of each. I also discuss the .45 ACP and .300 Blackout cartridges themselves. Lets start with the HK UMP:

Pros

• Availability of ammo
• Light weight weapon platform
• Easy to clean
• Folding stock for small storage

Cons

• Cost/Availability
• Lack of customizable features
• Lack of long-rage effectiveness

The HK UMP was built with one thing in mind: clearing rooms. It's not a battle rifle which can be used for long distance engagements. My semi-auto version is very light, but quickly gains weight with a 25-round magazine of .45 ACP. Even with the extra weight of a suppressor attached the gun is still well balanced and easy to run with. The use of .45 ACP is great because it is one of the easiest calibers to find ammo for. Due to it's mostly polymer construction, it cleans up quick and easy.

The cost and availability of this gun is brutal. As a civilian, you are forced to go through a USC conversion process. Obtaining the parts needed can be both difficult and expensive. Things like stock length, trigger weight, and magazines are not customizable. You are stuck with what you get and there are no substitutes.

The AR-15 with .300 Blackout is a more versatile rifle. It has a few drawbacks, but overall it is very flexible. Here is my list of pros and cons:

Pros

• Price/Availability
• Wide range of custom parts and features
• Wide range of effectiveness

Cons

• Cost/Lack of ammo supply
• Heavier weapon system
• Harder to clean

Parts for the AR-15 platform are plentiful and cheap by comparison. There are wide-range of trigger, stock, and magazine options. The cartridge itself has several flavors which come in both subsonic and supersonic. 220-grain subsonic loads are very similar to .45 ACP but cost almost double. The 115-grain (or 125-grain) serves as a better cartridge for long range engagements where a 220-grain (or 230-grain .45 ACP) simply can't reach.

The cost and availability of .300 Blackout ammo is the only keeping it from being the new standard cartridge for carbines. This may change over time as more companies have recently started offering .300 Blackout models in addition to the .223/5.56. If you are looking to shoot a lot of rounds, you will need deep pockets or a reloading press. Even if you are loading your own ammo, the cost and availability of .300 Blackout bullets makes it a little difficult. The use of a suppressor with a short barrel AR-15 also has it's drawbacks. There is a noticeable amount of back pressure which results in a very dirty gun. Cleaning the AR-15 is real chore which makes the UMP more attractive in that respect. While you can use a pistol caliber suppressor with .300 Blackout, most use a rifle suppressor which adds more weight to the end of the gun due to its larger and heavier construction.

So in the end, I hope you see why they are not fair comparisons. If I had to pick just one, I would probably choose the UMP conversion simply do to it's use of .45 ACP which is a huge selling point in my book.

Here is a look at installing the Knight's Armament URX 3.1 rail. To do this successfully, you will need the following tools and materials:

• Securely mounted vise
• Upper receiver vise block
• Loctite 242 (or similar thread lock)
• Knight's URX barrel nut wrench
• Torque wrench

They key to installing this rail correctly is having the right tools and taking your time. There are 4 main steps to installing the rail: