i do not know how many people realize it, perhaps most, perhaps very few, but one of the reasons the ar-15 rifle gives such good accuracy is that the rifle functions very precisely during its operation cycle. in short, it usually does everything in the very same way, shot to shot.
this makes a difference? oh, yes, indeed.
for example, the first shot out of a magazine, whether fed from a bolt locked open and then dropped on the top round, or fed with the bolt drawn from a closed position and then loading the first round, is usually just a bit out of the group from all subsequent shots. it is just the minuscule difference in the way that round is fed into the chamber that impacts its, ... , uhm, ... , point of impact.
so, when getting an ar-15 up and running, you want to get repeatable precision in function to achieve accuracy. this "repeatable precision" is also nice if you want to have a good round in a target competition, or, if you want to live in combat, for instance.
relative to that latter point, i have been experiencing jams in the operation in my ar-15 birthed as the "jj's brit." (trademark asserted.)
if you have been following along in this series of articles, you will know that i have attributed these jams (which "interrupt" the operating cycle, to put it mildly) to the less than perfect function of the magazines i have been using to feed the little "brit."
caption: an empty "brit" next to a loaded one on the left, and an empty .308 next to a loaded one on the right. to get the loaded "brit" into the chamber of my ar-15, the empty must first be ejected quickly and smartly from the action, so that the bolt may pick up the fresh/loaded round from the top of the magazine, and shove it into the chamber.
this is a violent and quick occurrence.
any delay, no matter how slight in getting the empty out of the way, will cause a mechanical malfunction, known "affectionately" as a "jam." the empty cannot be impeded on its exit from the action.
eliminating this "impedance" is what this post is all about.
the jams have been of a type. they usually occur with an empty sticking mouth out from the ejection port, lodged in front of the bolt face and over a following round which has got its nose into the chamber, but halted when nature dictates that two objects cannot occupy the same (limited) space at the same time.
out with the bad air, in with the good air. that sort of deal. you cannot get another round into the chamber via the space above the magazine until you have gotten the fired and empty round out of it.
well, i have to tell you, i was not making a measured progress solving the problem of why this was occurring.
until yesterday.
i had taken the rifle to the local shooting range to let a couple of local gunsmiths/gun purveyors see the little gun in action, and to fire it. the long and the short of it being, that they did, and they did. and, while firing it, the rifle jammed several times as described, much to my consternation.
and, one of them observed, you've got to make the ejection port a bit bigger, because the fired case is being delayed from ejection as it is either snagging on or being obstructed "on it's way out" because it is hitting the edges of the ejection port.
we cleared a jam, and then took the rifle down, examining it.
and, sure enough, towards the back portion of the ejection port were the tell-tale brass smudges/leavings of the cases hitting both the upper and lower edges of the port. once this was observed, it was obvious that the rear, e.g., fattest or thickest, portion of the case was being hindered on its way out of the gun. and, the front of the bolt face was hitting it while picking up a fresh round, and shoving both the rear of the empty and the rear of the fresh round at the top of the magazine forward at the same time. predictably enough, this stopped when the whole mess ran out of room to go forward.
jam. necessitating drawing the bolt back, dropping the magazine from the magazine well, and then shaking the empty and the fresh round partially in the chamber clear of the rifle.
a pain in the butt in competition and recreation, and potentially fatal in a fight. not good under any circumstance.
the remedy. well, the ejection port is the size that it is. so, the only remedy to eliminate this obstacle to impeccable functioning was to make the ejection port large enough to allow the spent case an obstruction free exit from the action, in a quick fashion, to clear the action above the magazine to allow feeding the next round.
quickly.
so, after discussion with tim, a gunsmith at double diamond gun shop here in milton freewater, it was decided that i take the trust dremel tool, and a small hand file, and remove some material from the top of the ejection port.
which i did.
this is a bit tricky, and not to be done with the heavy or injudicious hand, because that port of the receiver is also where a raised rail on the bolt carrier rides on the interior portion of the upper receiver. this is just above the upper portion of the ejection port.
so, i got out the trust dremel, and a small bastard cut file, and started to remove material above the port. first, i "broke" a sharp edge on the interior of the receiver, and took it down. then, i did the same to the edge on the exterior of the receiver. finally, using the dremel just a bit, and the small file just enough, i then rounded that edge to both the "broken" sharp edges, to make a nice rounded profile on that surface, and leaving a larger dimension for the empty case to be ejected from the action.
caption: the ejection port of my ar-15 in "jj's brit."
look to the top of the port, and you can see that the ejection port top rail has been opened a bit, and that the surface has been made rounded and smooth, with no sharp edges to catch a departing empty case as it is being ejected.
the bolt carrier is the part with the little notches cut in it, near the bottom left of the ejection port. look to the top of the ejection port, and you can see very clearly the edge of the little raised edge of the raised pad on the bolt carrier, upon which the carrier rides in the interior of the upper receiver.
if you are at all familiar with the ar-15 rifle, you will know just how much/or how little material has been removed from the ejection port.
this all was smoothed by a folded piece of 220 grit wet/dry sandpaper, held in a modern infinitely flexible soft malleable stylus, e.g., the paper on the end of my finger. i must tell you, that the whole thing went off with a hitch, leaving a very nice and smooth rounded surface, and a slightly larger opening to the ejection port.
prior to this, a person could not see the raised rail on the bolt carrier on the interior of the receiver. i have removed enough material from the ejection port that now that same person can just see the sharp edge of that rail, but, obviously, not the much else of its bearing surface, just above the port. a judicious job on my part, in my estimation.
please be advised. i am not aware of a manufacturer on this earth, if presented with my subsequent complaint that the receiver has cracked at the ejection port, who who not utter & declaim the words, you idiot, your warrantly is voided. you caused this, and we ain't paying for it.
your choice. if you follow this procedure upon making your own "jj's brit" (trademark asserted), you have the choice. legality versus function. and, all that implies.
i have chosen function over financial prudence. if you get this far, i expect that you will be faced with the same choice.
john jay @ 05.11.2013
p.s. how did the procedure work? well, it is a bit early to say definitively just yet, but, the removal of the material at the top of the port has had a seeming salutary effect. i have test fired the rifle, obviously not a great deal, and no "stovepipe" jams have re-occurred.
and, i know for a fact that it has changed the operating cycle. previously, empty cases were ejected a bit "forward" of the ejection port, and not directly out to the side as i would prefer. well, after removing this material, the empty cases are landing discernibly more towards the side of the rifle, indicating that as a physical fact that the empty cases are not being delayed in their exit from the rifle.
i may yet take just a sconcy of material from the bottom port, "breaking" a sharp edge to the outside or exterior of the action, and not going to the interior of that rail at all. we'll see. i may not do this, as there just isn't much meat on this portion of the ar-15's upper. if i don't "have" to, i won't. why "fix" it, if it ain't "broke," at this juncture?
caption: pretty self explanatory. an ar-15 upper and lower receiver, showing the work done on the ejection port of the upper receiver. it's a nice little rifle, and getting more reliable step by step.
we'll keep you posted.
Valuable. Being distributed. Thanks. (Perhaps you meant "'without' a hitch"?)
Posted by: Jorge_Banner | May 12, 2013 at 12:23 PM