View Full Version : AR Upper Questions
Okay here we go,
I bought one of those Superior Arms stripped lowers from AIM like 2 months ago. I bought it just to have it and eventually build something. It is my first AR and first AR build.
So I stumbled upon a lower parts kit at the gun show in WPB 2 weeks ago for a good price. I picked it up. I assembled the lower, no sweat. Now I am focused on the butt stock and upper. I think I am going to go with a Magpul CTR collapsible stock on a 6 position buffer tube.
I have begun focusing on the upper now and I have questions.
I would like a 16" barrel chambered for 5.56 and a flat top receiver. I plan to put on a full floating quad rail, perhaps a Troy or Daniels unit. I am probably going to go with some kind of red dot with a magnifier for optics but would like to have a flip up sight as another option. I want a barrel thats threaded so I can choose which flash suppressor I want to use.
Here are the questions:
1) What does a higher twist ratio in the barrel accomplish?
2) How important are M4 feed ramps?
3) Is stainless or Chromoly a better choice for the barrel (non fluted)?
4) Should I use a gas block or an A2 front sight?
5) What is the deal with the "f" marked A2 front sight?
6) What tools will I need to assemble an upper?
7) What is the difference between a 16" carbine barrel and 16" medium barrel?
Umm I think thats it. This is not going to be a long range shooter but I would like to build a nice tactical rifle, useful to perhaps 100 yards.
I was thinking about going with a complete upper but I want to build instead.
Thanks for all the help.
Here are the questions:
1) What does a higher twist ratio in the barrel accomplish?
You can create a whole section on the science of twist rate since it will lead directly into ballistics. Since we are only talking .223/5.56 NATO, we don't need to go into the science but there's a boatload of stuff to read if you do. From what you are describing as a type of AR you are looking to build, you are going to find the 3 most common twist rates: 1/7, 1/8, 1/9 with 1/7 being the fastest twist rate. If you plan on firing 55 grain or lighter .223 mostly, then you need to go with 1/9 (or even slower). US military ball ammo is 62 grain and is best fired in a 1/8 or 1/9. If you plan on lobbing heavier rounds, it becomes more important to impart a faster twist for stability where a 1/7 works best. The problem with firing lighter rounds in a fast twist barrel is that it might cause jacket separation and even bullet disintigration in flight because the spin is too fast and your barrel is going to wear out faster. The best all around rate if you plan on shooting a wide range of ammo is 1/8.
2) How important are M4 feed ramps?
It was added to the M4 as a design enhancement for better feed reliability with what could possibly contaminate a magazine in the field. Just make sure your upper has the M4 cuts already before you buy a barrel with it. If it does then you should only install a barrel with M4 cuts. Putting an non M4 cut barrel on a M4 cut upper will cause feeding problems or bullet deformation while chambering. If you don't have it, then it's best to find a non-M4 cut barrel but you can still get away with using an M4 cut barrel. Technically, it really is the barrel extension that we are talking about, but most people will buy a barrel complete with the extension installed.
3) Is stainless or Chromoly a better choice for the barrel (non fluted)?
Another topic that will garner reams of discussion. Most match target barrels are SS since it is considered strongest and most durable. Chromoly is very common and is considered the minimum standard. Chromelined Chromoly steel is where they add a chrome alloy plate to the entire interior of the barrel. It adds a corrosion barrier and adds greater wear resistance to a standard Chromoly barrel. Now, in order to add the chrome plating, they will overbore the bore and rifling to acheive the proper dimensions. This is were people will argue that the chrome plating can never be perfectly consistant, so it will always be less accurate than a SS or chromoly barrel. There's always a trade off. Basically, if you are not building a match rifle and you do get lazy and not clean your rifle after every range day, then chromelined is for you.
4) Should I use a gas block or an A2 front sight?
Some people don't like to see the front sight in their view when using non magnified optics. Others think aesthetically, it just looks cooler to have a full length rail covering a low profile gas block. Basically, define the look you want to go after and choose either. The A2 sight is going to give you the strongest sight/gas port option out of all of them.
5) What is the deal with the "f" marked A2 front sight?
Slightly taller shelf and milspec. For most people, it is a non issue, but technically, if you use a milspec BUIS with a non-F marked A2 FSB or vice versa, you might not be able to acheive elevation zero.
6) What tools will I need to assemble an upper?
At minimum, a barrel nut wrench, torque wrench, proper punch to install the forward assist roll pin if you have to, and possibly ring expander tool if you have to remove the delta ring to install a free float rail. The rail alone may require a strap wrench, allen wrenches, screwdrivers, etc. and punch and hammer to remove an A2 FSB to install a gas block if the barrel assembly you buy already has one installed and you want to go another route. Oh, an some quality grease for the barrel nut thread.
7) What is the difference between a 16" carbine barrel and 16" medium barrel?
It is where the gas port is located on the barrel. I can't recall the exact dimensions, but it's somewhere around 7" from barrel chamber end (without the extension) for the carbine and 10" for the middie. The majority of the parts/components out there are geared towards the carbine set up.
Perfect, thanks Phil. I really appreciate you taking the time to read all that and reply with all the info you gave. For tools I guess all I need is a barrel wrench, have all the other stuff. Very cool. I cant wait to get started.
JaxChris
07-13-2009, 02:37 AM
From what I've learned, if you're shooting 70gr+ rounds then you need the 1/7 twist rate. If you're only shooting 69gr and less, then 1/9 twist is fine. Many people that build seem to prefer 1/7 if they can get it for the same price as a 1/9 counterpart.
For the M4 ramps, Phil is absolutely correct but I just felt like clarifying. If your Upper Receiver has M4 ramps you must have an M4 barrel extension on your barrel. If your Upper Receiver does not have the M4 ramps, then you can use either barrel extension just fine. My recollection of the M4 feed ramps is that they were designed to assist in full auto feeding from the more violent carbine-length gas system.
Dan, on the last question, were you referring to gas system or barrel contour? I ask this because gas systems are typically called pistol, carbine, mid-length, rifle - while barrel contours come as M4, CAR4, lightweight, medium, heavy. So asking carbine to be compared with medium made me wonder if you were asking for the difference in the barrel contours of the M4 (or CAR4) and the medium.
If so, the M4 barrels are heavy contour from the gas block forward, with the notch out front for the M203 grenade launcher loop, and has a lightweight contour under the handguard. The CAR4 contour is similar to the M4, but is not lightweight under the handguard. The medium contour is like the CAR4 but lacks the M203 notch.
The rest I won't touch as Phil has explained more than I know. =)
From what I've learned, if you're shooting 70gr+ rounds then you need the 1/7 twist rate. If you're only shooting 69gr and less, then 1/9 twist is fine. Many people that build seem to prefer 1/7 if they can get it for the same price as a 1/9 counterpart.
For the M4 ramps, Phil is absolutely correct but I just felt like clarifying. If your Upper Receiver has M4 ramps you must have an M4 barrel extension on your barrel. If your Upper Receiver does not have the M4 ramps, then you can use either barrel extension just fine. My recollection of the M4 feed ramps is that they were designed to assist in full auto feeding from the more violent carbine-length gas system.
Dan, on the last question, were you referring to gas system or barrel contour? I ask this because gas systems are typically called pistol, carbine, mid-length, rifle - while barrel contours come as M4, CAR4, lightweight, medium, heavy. So asking carbine to be compared with medium made me wonder if you were asking for the difference in the barrel contours of the M4 (or CAR4) and the medium.
If so, the M4 barrels are heavy contour from the gas block forward, with the notch out front for the M203 grenade launcher loop, and has a lightweight contour under the handguard. The CAR4 contour is similar to the M4, but is not lightweight under the handguard. The medium contour is like the CAR4 but lacks the M203 notch.
The rest I won't touch as Phil has explained more than I know. =)
Thanks Jax,
I was indeed asking about the gas port location as it relates to where the front sight/gas block will be positioned and which length hand guard to use. I think I will go with the standard carbine length. I like the look of the medium because it moves the sight forward and seems to fill the barrel out more but it also seems to limit your choice more on the barrel selection.
With regards to the M4 ramps, I did read that you needed an M4 barrel if the receiver had the M4 cuts. I guess my question was more along the lines of will I get more feed jams in a carbine length rifle without going with an M4 barrel/receiver combo or will it not make a difference?
I guess my question was more along the lines of will I get more feed jams in a carbine length rifle without going with an M4 barrel/receiver combo or will it not make a difference?
IMHO, you'll be better off with M4 cuts for reasons pretty much like your barrel choice. Uppers with M4 cuts are more readily available and in many cases, cheaper. That said, I've actually modified standard uppers and filed and polished M4 cuts for a couple of my personal A/R's to perfectly match the M4 feed ramps on the barrel extension as they are many times not perfectly matched.
The M4 cuts are more sought after also. Meaning if you need to sell, it should be easier to sell.
JaxChris
07-15-2009, 10:16 AM
Phil, are you saying you've "added" M4 ramps to an upper receiver? I thought that was a big no-no to cut. Or you mean you cleaned up bad factory cut ramps?
If you're comfortable with cutting that stuff I'm wondering if you'd be willing to do a job down the road if I can't get a shop around here to do it. I'm wanting a Stag Left-hand upper for one of my builds but I was recently informed that Stag doesn't do M4 ramps on their upper receivers, even though their barrel extensions have them.
Phil, are you saying you've "added" M4 ramps to an upper receiver? I thought that was a big no-no to cut. Or you mean you cleaned up bad factory cut ramps?
If you're comfortable with cutting that stuff I'm wondering if you'd be willing to do a job down the road if I can't get a shop around here to do it. I'm wanting a Stag Left-hand upper for one of my builds but I was recently informed that Stag doesn't do M4 ramps on their upper receivers, even though their barrel extensions have them.
Yup. It's a big no no to prevent knuckle heads from FUBARing their uppers. It does require the right files and magnified goggles and the actual barrel for proper fitting. I then polish it up and aluma black the notches for a factory look.
Yup. It's a big no no to prevent knuckle heads from FUBARing their uppers. It does require the right files and magnified goggles and the actual barrel for proper fitting. I then polish it up and aluma black the notches for a factory look.
Damn you Phil, holding out on me again. Guess what you will be showing me now.