august 23, 2012 i posted about a gun smith named harrison beane who was selling a bolt and barrel extension with a .473" bolt face that fit into the ar-15 platform w/ no other alterations to the basic system. that post asserted that the "... time had come ..." for such a development, because it would allow the ar-15 to fire cartridges derived from the ubiquitous .308 winchester/7.62x51mm nato cartridge case.
http://wintersoldier2008.typepad.com/summer_patriot_winter_sol/2012/08/an-ar-15-platform-bolt-w-a-473-bolt-face-an-idea-whose-time-has-come-and-which-is-now-reality-.html . please see the live links below the article, for a very inclusive history of all of this.
enter the dpms generation ii ar-15 in .308 winchester. it is the actualization of my position that a .308 caliber weapon could be realized on a basic ar-15 platform, by the simple expedient of increasing the size of the ar-15 magazine well.
go to dpms's website, for a very thorough explanation of what they have done, and the very clever engineering behind it.
for the article below a close friend loaned me the use of his dpms gen ii ar-15 in .308 winchester, and allowed me to take it down and photograph it. he also let me shoot it a bit, and it is a very tractable, very easily handled rifle, and gives every indication of being nicely accurate. that's a hard combination to beat.
this post is a direct comparison of my ar-15 in "jj's brit," with the www.ar15performance.com bolt/barrel extension, and the dpms gen ii ar-15 in .308 caliber.
the basics are easily summarized. the "jj's brit" ar-15 fires a .284 caliber bullet from a shortened 7mm 08 remington case, sized so that it fits into the basic ar-15 sized magazine, which limits overall cartridge length to 2.260".
the dpms gen ii ar-15 is basically identical in architecture to a standard ar-15 from the rear of the receiver right up to the area between the hammer pin and the magazine release, and accepts standard ar-15 parts to the hammer pin, but from that point forward the lower receiver has been widened and lengthened to accept an ar-10 sized magazine, and will accept an overall cartridge length to 2.800".
caption: picture taken from above the lower receiver. the receiver on the bottom is the dpms ar-15 gen ii, and you can very easily see the size differential in the magazine wells, both in length and width. the bottom receiver, on an ar-15 sized platform, accepts the standard ar-10 sized magazine, and the .308 winchester cartridge. the top receiver, in my "jj's brit" ar-15, is limited to the ar-15 sized magazine, and cartridges that do not exceed the length of the standard .223 remington/5.56mm nato rounds.
this is just a beginning. the real difference between the rifles lies in the robust dimensions found in the dpms gen ii's bolt and bolt carrier system. these parts, as compared to the "jj's brit" ar-15, are just massive. (caveat: i've not been into the innards of an ar-10, so i do not have direct knowledge of how large an ar-10 bolt is, but, it would have to be going some to be any stouter than the ar-15 gen ii bolt in .308, ... , the thing is huge, and it maintains the same massive diameter almost its full length. we'll, you'll see.)
let's take a look at the boiler rooms of the two rifles, the place where the forces of the cartridge firing is born.
caption: the bolt carrier assemblies from the two rifles, with the gen ii on the bottom. look at the two pins w/ the flats at their ends, and the holes drilled through them to accept the passage of the firing pins. the gen ii has simply a bigger pin, and this is the pin that cams the bolt in and out of battery against the locking lugs, ... , it has a lot of stress on it, and absorbs a lot of wear, and the gen ii pin is simply more rugged.
look at the two bolts. the gen ii is simply larger, with larger lugs, more engagement surface, and is just a massive cylinder compared to the bolt unit supplied by www.ar15performance.com . (and, i can tell you, the "jj's brit" bolt is far more rugged than the standard ar-15 bolt ... the ar15performance bolt is not downsized in any respect. and, it has absorbed everything i've thrown it, with no problems. and, "jj's brit" is a high intensity cartridge, make no mistake about that. it operates at pressures as high as the .308 winchester.)
another view of the bolts will illustrate how massive the dpms gen ii bolt is. the pictures say it far more clearly than i can express.
caption: the bolt on the left is from the dpms gen ii. it has a .473" bolt face, to accommodate the case head of the .308 winchester cartridge. it has 7 lugs, and they are shaped in what has become a new standard for forming the lugs, designed to better resist stress cracking and the like, from the pressure placed upon the bolt by cartridge ignition. and, the www.ar15performance.com bolt also reflect this progress in design in its .473" diameter bolt face. it is not frail, it is not delicate, and it is pretty robust in its own right.
but, the far greater size and weight of the dpms gen ii bolt as depicted in the picture is no optical illusion. it is massive in comparison to the bolt used to build my ar-15 in "jj's brit."
the design philosophies are the same. and, believe me when i tell you, the "jj's brit" bolt has withstood all i've thrown at it without complaint, and without any indication of stress. it is, in fact, a well built and well designed component.
it just is not as large, nor by inference, as strong as the dpms unit. simple as that.
i have voiced my opinion, many times now, that if the ar-15 has a weakness as against the ak-47 & 74 rifles, it is that its extractor is not as robust and as problem free as the russian/chinese/easter bloc weapon. i am not the originator of that opinion, as the strength of the ak-47 in this regard is well known, and advanced by every person who argues that the ak-47 is a superior weapons system. (i do not hold to that position, for various reasons.)
but, take another look at the dpms gen ii extractor, both in the picture above, and in this following.
caption: the extractor is the strap of metal inletted into the side of the bolt, running back along it for some length, and with the little hook at its front, ... , the little hook goes over the case rim, and when it comes time for the operating system to take the expended & empty cartridge case out of the rifle's chamber upon firing, that little lip & the rest of the extractor do the dirty work.
the dpms gen ii ar-15 extractor is simply massive in comparison to the www.ar15performance.com extractor. as to size, and inferentially ultimate strength and pulling force in taking a fired case from the chamber, there simply is no issue involved, the dpms unit is far more suitable for the job.
the dpms website goes to some pains to explain that the extractor fabrication and metallurgy has been improved, and that the extractor function has also been improved, over previous ar-15 standards. i am not a metallurgist, and i am not competent to comment on that.
but, i can comment on what i see. in comparison to previous ar-15 sized extractors, is is simply huge. in comparison to the harrison beane supplied extractor from ar15performance, it is simply huge.
look back to the picture before this. the comparison is simply inescapable.
not only is the bolt bigger in the dpms gen ii rifle, but, the bolt carrier as a unit is far more massive.
caption: the bottom picture is repeated.
but, in this case, it does no harm, and it just points to a simple fact, in handling a bigger round, that shoots a bigger & heavier bullet, bigger is better. the larger bolt carrier has more mass, it weighs, more and it slows down the extraction and ejection cycle, and makes feeding a new cartridge into the chamber a much surer and more predictable occurrence.
bigger, heavier, is better. a good little man beats a sluggard big man, it's been proved many times. a good big man beats a good little man. and, that's been proved many times. it's why you won't find too many 180 pound pulling guards in the ranks of nfl linemen.
simple as that.
i've been talking "big," "robust," "massive," "heavy," and all those things. by doing so, i hope that i have not created a false impression. that being, of course, that the new dpms gen ii ar-15 in .308 winchester shares a fault found in most ar-10's chambered to .308 of being an overweight and cumbersome pig.
it does not.
i am going to tell you something that you may not believe after you've been privy to a trip through the innards, the "boiler room" of the dpms gen ii as compared to a standard ar-15, and that is the dpms gen ii is a very trim, very compact, and a rifle that is light in weight.
in simple point of fact, the dpms gen ii is lighter in weight than my "jj's brit" ar-15. the dpms gen ii is a bit longer in the receiver, but, just by about 1/2 inch, and it is far heavier in the bolt carrier/bolt assembly, but overall it is lighter than my "jj's brit." this is due, in the main, to a slightly trimmer and somewhat shorter barrel, 16" as compared to 18" or so in the brit, but, the fact is, the gen ii is just a far trimmer and handier rifle than a standard ar-10, and weighs maybe a pound more than a light weight ar-15.
the handling is just identical. ar-15 to ar-15. they handle so much nicer, so much easier, than an ar-10 that it just is not even funny. i am 5'8" and about 165 pounds. i'd just as rather zip around the dance floor w/ julia roberts, as meryl streep. (oh, yeah, i am sure they'd have something to say about me that wasn't entirely kind, as well, but, life is just damned tough, you know what i mean? people are just no damned good, and just judgmental assholes. sorry ar-10, that's just the way it goes. i didn't make us who we are, and i am not going to contribute to making us any better and/or nicer. that's just the way it is.
caption: the two rifles, side by side. can you tell them apart?
the dpms gen ii ar-15 in .308 has the more slender barrel, while the "jj's brit" ar-15 has been left in the bright, and never blued. and, the dpms gen ii has the shorter hand guards, they being the carbine length unit from magpul, while the "jj's brit" ar-15 fore end is a little longer, in an "intermediate" size.
and, did i mention, that the dpms gen ii is just a tad lighter than my ar-15. not by a great amount, but, it is easily perceived that it is lighter.
so, is the dpms accurate? yes. is it as accurate as "jj's brit." not on the day that i shot it, but, it's owner has not had a chance to wring it out, nor to develop loads for it. i can tell you that the dpms gen ii will shoot circles around any ak-47 or sks ever built, and will do it with 155 to 168 grain ammunition, as opposed to the sov bloc standard 123 grain bullet. 168 grains at 2550 to 2600 feet per second at the muzzle for the .308 winchester, versus 2350 feet per second from a 123 grain bullet as the standard loading in an 7.62x39mm soviet (model 43) round.
now, i am not abandoning an advocacy of my "jj's brit" in my ar-15 (the necessary parts supplied to me by www.ar15performance.com). it is a good, solid gun, and it has not broken in tough use. it took some time to get it all sorted out, but, it has been used hard, put away wet, and shrugged off all the abuse.
my little "brit" shoots a 130 grain bullet at an honest 2500 feet per second at the muzzle, which is far superior to the russian model 43 as shot in the ak-47. (and, if i could load the cartridge to an overall length of 2.600" or so, and shoot it in a dpms gen ii rifle allowing the longer length, it would shoot that same 130 grain bullet to an honest 2600 feet per second, or i would shove a peanut down the center line of main street in milton freewater on my hands and knees with my nose, for .... you get the picture. it would beat the living snot out of a 6.5mm grendel any day of the week, loaded to equal pressures. all other things being equal. oh, goodness, i can hear the teeth gnashing. but, hey fellas, physics is physics.)
my little "brit" is not the cartridge a .308 winchester is, however, by any stretch of the imagination. not in sheer power. but, i believe it a far better balanced cartridge for the average infantryman. and, my little parts-sourced-harrison-beane created concoction is a fine rifle. i am not giving it up.
ah, the dpms gen ii ar-15 in .308 winchester is one very sweet, sweet, sweet shooting and handling rifle. dpms has hit the damned ball out of the ball park.
well, enough metaphor mangling for one evening. i am done.
john jay @ 04.29.2014