Sunday, January 29, 2012

AR-15 Gas Sytems and Operation

The AR-15 is a semi-automatic weapon that uses gas from a fired round of ammunition to cause the bolt and carrier assembly to extract and eject the casing of the fired round and chamber a subsequent round from the magazine.  A gas port is drilled into the barrel and located under the front sight base or “gas block”.  The gas from the fired round is channeled through this port and gas block, back through the gas tube (under your handguards), and into the bolt carrier key in order to “cycle” the weapon when fired.  There are three types or designs of “gas systems” for the AR-15 rifle.  In this post, we will briefly describe the benefits and any disadvantages to the three main types, with the purpose of helping our customers decide which design will best fit their needs and application.

CARBINE:  This is the shortest gas system for an AR-15 rifle (the pistol gas system is shorter, but we will limit our discussion here to rifle gas systems).  It is often described as a 7” gas  system, though the actual length is a bit different (these measurements are actually more descriptive of the handguard used).  The carbine gas system if usually found on an AR-15 with a barrel from 11.5” to 16” in length.  This system uses the smallest gas port for a rifle because the pressures from the fired round in this short system are high enough that a larger port is not necessary for the weapon to cycle.  Because of this high pressure, some users believe that this style of gas system has more felt recoil and may cause parts associated with the cycling of the weapon to wear more quickly than with longer gas systems.  The carbine gas system also has the shortest sight radius (distance between the rear and front sight), but is very compact and AR-15 models with a carbine system have been proven in use by military and police units for a substantial time period.

MID-LENGTH:  This medium (9”) length gas system is generally used on 14.5” to 16” barrels and has a slightly longer sight radius than the carbine; this can be beneficial for accuracy when using iron sights.  Also, the longer required length of the handguards can be an advantage for those who desire to use multiple support hand positions; if a railed style handguard is used, there is more space for the location of accessories without having diminished support hand positions.  The gas block/front sight base is located further down the barrel, so a larger gas port is required in order to have enough pressure to cycle the bolt and carrier assembly.  Many users report a lighter felt recoil or “pulse” on rifles with a mid-length system and believe it to cause slightly less wear on parts.

RIFLE:  Typically, this length (11”) of gas system is found on 20” barrels like the M16A2.  It uses the longest handguards, and the much lower pressures at the gas port location so far down the barrel require a larger gas port. 

Dissipator (rifle length gas system on a 16" barrel)

Currently at DTI, our dissipator style of AR-15 rifle (a 16” barrel with a rifle length gas system) has a true rifle length gas system.  Many other manufacturers build this style of AR-15 with a mid-length gas system under the handguards using a low profile gas block; a front sight base (that does not serve as a gas block) is then installed at the typical “rifle-length” location.  The main advantage of this style would be the very long sight radius.  Possible negative aspects include the weapon being a bit “muzzle heavy” and limitations in ammunition selection (see next paragraph).

Many things can affect the cycling and reliable operation of an AR-15.  Multiple variations from the original design have created real benefits for some applications. However, these variations may require additional modifications...or they may create new limitations.  Having a mid-length gas system on a 14.5” or shorter barrel, or a rifle length gas system on a 16” barrel (true dissipator) can necessitate an ammunition selection that produces higher pressures. This is due to the distance for the gas pressure required for cycling to travel before most of it escapes out of the muzzle behind the projectile.  Some of the less expensive ammunition may use lower quality gunpowder that burns inconsistently; this can result in gas pressure that is inadequate for proper cycling.  The weight of the bolt carrier and buffer also play an important role in the cycling of a weapon, so the right combination is necessary for peak performance. 
Hopefully, this post has answered some basic questions about the various gas systems of the AR-15 rifle.  Thanks for reading our blog; if you have any questions related to the AR-15 or any of our products, please contact us and we will be glad to assist you. 

Wednesday, January 11, 2012

The New DTI Extreme Duty Rifle!

So maybe you have heard of DTI, and are considering "pulling the trigger" on a Del-Ton rifle purchase.  The price is great, but you have concerns because the company does not have the brand recognition of the more well known rifle producers.  The most important consideration is that the money you spend will result in a weapon that is useful, valuable, and functional... functional when it matters most.   While we believe this to be true of all of our products (and we go to great lengths to ensure it is before they leave our factory), DTI is introducing a new rifle model designed and offered with the intent to relieve any of the aforementioned concerns. 

The DTI  Extreme Duty model is MIL-SPEC.  This rifle features a 16" M4, 1X7 chrome lined barrel that has been high pressure tested (HPT) and magnetic particle inspected (MPI) manufactured by Fabrique Nationale d'Herstal (FNH-the largest supplier of small arms to the US military). This hammer forged barrel is well known for both of "out of the box" accuracy and longevity. Other important features include:

Chambered in 5.56 X 45 NATO

Upper and lower receivers are MIL-SPEC, forged 7075 T6 aluminum, hard coat anodized

MIL-SPEC phosphated 8620 steel bolt carrier with a HPT/MPI tested
Carpenter 158 bolt that is heat treated and plated; chrome-lined carrier interior and key (properly staked and sealed)

M4 handguard with double heat shields and aluminum Delta ring assembly

M4 rifling profile and feed ramps

M4, five-position buttstock with MIL-SPEC buffer tube

Troy Industries flip-up rear sight

Ships with sling, 30 round magazine, buttstock cleaning kit, and hard case

At an MSRP of $989.00, the DTI Extreme Duty rifle is a top tier, ready for anything weapon at an amazing value.  This weapon will be available for purchase in early 2012.  Thanks for reading our blog...check back often for more news and information pertaining to the AR-15 platform and feel free to contact us anytime with any questions you may have about the AR-15 and our products.

Link to Outdoor Life review on the DTI Extreme Duty Rifle

Sunday, January 1, 2012

An Introduction to AR-15 Nomenclature

The AR-15 is a great weapon to have for competitive shooting, hunting, and defense or work, but its different operation and configuration can be confusing to people new to the platform.  To help with all the nomenclature specific to the AR-15 platform, we thought it may be beneficial to offer a brief dictionary for those who are interested in seeing if this excellent weapon will meet their needs.

Lower Receiver-The lower half of an AR-15.  DTI offers lower receivers in 3 formats: stripped, complete (with installed lower parts and grip), and complete with buttstock.  This is the part of an AR-15 that is subject to the ATF performing a background check before it can be transferred to a customer through an FFL dealer.  All other parts of the AR-15 are simply considered “parts” and can be sold directly to a customer.

Upper Receiver-On our website, this typically denotes the upper receiver itself (we use the term “custom uppers” or “barrel assemblies to describe a complete upper receiver half—from upper receiver to muzzle).

A2 Upper Receiver-An upper receiver with an integral carry handle/rear  sight.                                           

Flat Top Upper Receiver-An upper receiver that does not have an integral carry handle/rear sight or rear sight of any kind, but rather a picatinny rail for the attachment of sights or optics (also termed an A3 or A4/M4 style upper by others).  DTI offers them with or without M4 feed ramps.  All of our flat top uppers have “T-Marks”, which are white, etched numerals on the rail so that sights that have been “sighted-in” and later taken off can be reattached at their previously “sighted-in” position.

M4 feed ramps-A flat top upper receiver that has extended feed ramps machined into the upper receiver for more reliable feeding of all types of ammunition, especially when the weapon is excessively dirty. 

Front sight base/FSB-the triangular shaped base mounted by taper pins on our barrels.  There are two designs available at DTI.  Standard front sight bases are used with A2 upper receivers, and F-marked front sight bases are used with flat top upper receivers for proper rear/front sight alignment.  The front sight base serves as a “gas block” to channel the gas from the fired round back through the gas tube and into the bolt carrier key to cycle the bolt assembly for ejection and subsequent feeding of the next round.  There are other styles of "gas blocks" available for AR owners whose application would be better served by not having a typical front sight base.

Chrome moly/chrome-lined barrels-All DTI barrels are produced from chrome moly vanadium steel.  We also offer many of these same barrel styles with a chrome-lined bore and chamber as an optional feature.  Many experienced AR-15 users and designers believe that a non chrome-lined barrel may be more accurate, but chrome-lined barrels may have greater longevity.  As with any choice regarding AR-15 options, the user’s particular application is the most important thing to consider when deciding which barrel will best suit his or her needs.

Barrel Twist Rates-The number of revolutions in inches in the rifling of a barrel.  At DTI, we offer chrome moly barrels in a 1X9 twist rate, and most chrome-lined barrels in both 1X9 and 1X7 twist rates (Example: a 1X7 twist rate barrel would have one revolution of the rifling in every 7 inches).  The prominent "train of thought" is that the faster twist rate (1X7) is more accurate with the heaviest bullets (62-77 grain), while a slower twist rate is better with lighter weight bullets (45-62 grain).  DTI rifles with a 1X9 twist rate tested and featured in major weapon publications have produced sub-MOA accuracy with heavier bullets, however.

post ban AR-15 with crowned muzzle, no bayonet lug, and fixed stock
Pre Ban/Post Ban-While there may be other nuances involved, “pre-ban” typically denotes an AR-15 with a bayonet lug, flash hider, and collapsible stock.  Most “post-ban” rifles, uppers, barrels, not have a bayonet lug on the front sight base, have a crowned muzzle on the barrel or a permanently attached muzzle brake/compensator, and a fixed stock.  The “ban” refers to the AWB (assault weapons ban) enacted under President Clinton’s administration and allowed to expire during President Bush’s administration.  Some states and even local areas have similar laws still in effect.  It is best to visit your state’s DOJ website or inquire at a local gun dealer regarding what is a legal configuration for the AR-15 in your area.

If there are any other terms that are unfamiliar or any questions you may have, please contact us.  Whether by email or phone, we will do our best to answer your questions accurately and in a timely manner.  Our customer service and sales department has a genuine desire to make sure you understand the items we sell and ensure anything you may order will meet your needs and application.  (20120101)