Tag Archive for bolt carrier group

AR 15 Basics – Bolt Carrier Group – BCG

Along with your barrel, your Bolt Carrier Group is the “Heart” of your AR rifle. So choosing the right one is very important to the overall quality and dependability of your rifle.

The “Mil-Spec” or industry standard for BCG’s are as follows …… Carpenter 158 steel, shot peened, gas key secured with grade 8 fasteners, chrome lined and parkerized. While there are some variations and options like different coatings, these standards will be the same for most BCG’s on the market.

One of the first things you want to look for in a BCG is that it’s been MPI and HPT tested. MPI stands for “magnetic partical inspected” and HPT stands for “high pressure tested” …… basically these are tests to help determine if there are any issues with the BCG such as cracks or hairline fractures that could cause failures. These tests are also use on barrels as well.

Now many companies test their BCG’s in these ways but some companies “Batch” test their BCG’s which basically means that for every batch of BCG’s they produce, they only test one BCG. Definitely something you’ll want to check into when purchasing. Companies like BCM, Daniel Defense, Spike’s Tactical & Palmetto State Armory are examples of companies who individually test their parts.

Next you’ll want to check the staking of the gas key on your BCG. Now this can be pretty hard to do if your buying online so do your research on the different companies to find out who has a good reputation in this department.

For those that don’t know what the staking of the gas key is, I’ll explain. The gas key is the part of the BCG that comes into contact with the gas tube coming from the gas block on the barrel and it is what the gas blowing back from the barrel comes into to contact with to cycle the action of the bolt. Because of all the pressures associated with this and because the gas key is attached to the rest of the BCG by two small hex bolts, it’s inportant that those bolts are properly “staked” into place to prevent them from backing out or loosening due to the pressure and causing a failure.

The next thing you’ll want to take into consideration is wether or not your getting an AR15 style BCG or an M16 BCG. The differences are noticable at the rear of the BCG where the top and bottom of the M16 style BCG are the same length adding weight and stability to the action and also slightly slowing down the cycle rate which of course is preferable for full auto rifles. The AR15 style BCG has the bottom rear of the BCG cut back to reduce weight and cost of the BCG.

Now while most civilian shooters won’t notice the difference between these two types of bolts, now days the two kinds of bolts are so comparable in price that you might as well just go for an M16 style BCG.

One final thing to keep in mind is the chrome lining. Some companies advertise chrome lining on their BCG’s and some don’t, but keep in mind that chrome lining in the body of the BCG where the bolt rides and inside the gas key is an industry standard. So while you may not see it advertised, I’m not aware of any company currently manufacturing a BCG without chrome lining.

So thats its, those are the basics. There are some customized options out ther like specialty o-rings and ejector springs that you’ll sometimes find on some BCG’s but for the most part those are upgrades or customizations and aren’t a part of your standard BCG.

AR15 Basics of Buying or Building

If you’re a first time buyer or builder of the AR platform there are a few tips that hopefully might help you out in making your purchasing decisions for either your parts or a complete rifle.

The first thing to remember when buying an AR …… most of the parts being used, no matter what the name your buying, either came from the same place or were made using the same equipment and made to the same specifications if your buying a “milspec” rifle.

Now if your going for a higher end rifle that has stricter tolerences and is built to a higher standard for more accuracy (although those companies sell milspec rifles as well) then thats a different story.

The next thing we need to understand is, what is “milspec” for an AR rifle. First off, there are only 2 companies that know what true milspec is or create true milspec rifles and those companies are FN & Colt because these are the only 2 companies that have government contracts and create true milspec rifles.

Most of what we in the civilian market call “milspec” is really just an industry standard chosen to get as close to true milspec as possible without the government inspection process. These industry standards include things like …..

5.56mm chamber (shoots 5.56 or .223)

11595E Barrel Steel

Manganese Phosphate finish barrel

F-marked front sight

Standard threaded 1/2 x 28 tpi barrel for muzzle device

Forged A2 front sight base w/ bayonet lug

Barrel is machined from chrome-moly, high vanadium steel and hardened to a U.S. government Mil-spec of Rc 26-32

The barrel, and all external steel parts, are manganese phosphate finished IAW 5.3.1.2 of Mil-STD-171, the U. S. government’s recommended protective finish for steel

Barrels are .950 diameter under the handguards .750 under the front sight base (standard M4 contour barrel)

Forged A3 upper reciever made from certified forgings, hardcoat anodized IAW Mil Spec A8625, Type III, Class II, black per No. 37038, Table IX with nickel acetate seal, as per the Mil-spec

Buttstock tube is the mil spec thickness 1.145″ OD

M4 style feed ramps

So those are some of the “Milspec” specifications that most manufacturers are adhering to, but they are basically just industry standards, but for our purposes we’ll just use the term “milspec” as the closest you can get to a true milspec rifle is something from Colt and it still won’t be true milspec.

So if u are just getting something milspec, its all the same as far as parts quality. You may have some differences like types of finishes or chrome lined barrel or not, or a different barrel twist depending on what u go with but thats pretty much it.

Most of your recievers are going to come from the same places like Cerro Forge, FNMI or Colt then they are just marked for the company who buys and finishes them.

Most lower parts kits are all identical unless your installing a Geissele trigger or something similar (you’d be suprised how many companies use DPMS lower parts kits in their rifles) so there’s nothing to worry about there.

Most barrels are going to be either Mossberg, ER Shaw, DPMS or FN

Remember that all these parts may have a certain name stamped on them but that doesn’t make them different from most of the other parts out there that may have come from the same place or at least manufactured using the same proccesses and equipment to create those parts to the same milspec/industry standard.

The biggest issue with buying an AR has nothing to do with parts ……… its all about assembly, pick a company that has a good reputation for assembling rifles the right way, who MPI & HPT test there parts and who have a good customer service/warranty service. Some of the best companies in those catagories are suprisingly DPMS & Spike’s Tactical (although I know alot of people think Spike’s is overrated ….. they do have great customer service and they test all their parts, not just batch test)

As far as options go, a few of the bigger options that you’ll want to take into consideration are barrel twist, barrel & gas system length, chrome lined vs non-chromed lined barrel and barrel contour.

The twist rate is going to depend on what weight ammo your shooting, since the most common, most available & most affordable round is going to be 55 grain I’d recommend a 1:9 twist (which basically means that the rifled grooves in the barrel that spin the bullet make one complete revolution around the inside of the barrel every 9″ inches ….. a 1:7 would be every 7″ inches) getting a 1:7 twist works better for heavier bullets like the 62 grain.

As for the chrome lined vs non chromed lined option, thats a personal choice. Chrome lined usually tend to be easier to clean, have better extraction and if u use alot of different loads on your rifle it can help with reliability. Non chromed lined barrels are going to be more accurate but reqiure a little more effort to clean.

Now for the barrel/gas system length decision, this is one that has so many options that its an article in and of itself. The most popular and reliable will be the 16″ barrel with a carbine length gas system or the 20″ barrel with a full length gas system.

Lastly the barrel contour decision has just as many options if not more than the barrel length and gas system options but the standards are …….

M4 contoured barrel (most popular on the 16″ carbine version)

Bull/Varmint barrels (great for any length but mostly for target or small game shooting)

Heavy barrel (a good solid barrel that has a bit of a longer life than most but adds a bit of weight to the front end)

Light or “pencil” barrel (great at weight saving but if your an active shooter I wouldn’t recommend this as its has a shorter life as far as round count goes)

Remember that you don’t have to spend $1500 bucks to have a good quality AR and building one yourself can definitely help save you some money on a quality build.

Well there you go, those are the basics as I see them, hopefully it helps out a little when making your decision to buy or build your AR rifle.