i am done building the ar-15 made to chamber "jj's brit," the project finished with the addition/substitution of a few components designed to make function more reliable, and the rifle a bit more robust.
the rifle now just chugs along reliably, digesting all the various hand loads i feed it w/ monotonous regularity.
substitution of upper receiver. the rifle was originally built with an upper receiver from dsa arms, inc. it worked well enough, but i had some concerns that it's its structural integrity might have been compromised when i widened the ejection port to allow the larger "jj's brit" to be ejected from the rifle. to be more specific, i was concerned that the right receiver rail below the ejection port might crack under the repeated stress of firing.
one day i walked into my friendly gun smith's shop, and, sitting on the display case was a very heavy ar-15 upper receiver. i inquired, learned that it was made by dpms, that it had languished in the parts bin for years, and that it could be mine for $100.
i bought it. took it home. and, widened the ejection port even more than i had done to the dsa arms receiver, having absolutely no concern that i might weaken the right receiver rail below the port.
caption: look at the "shiny" portion below the bolt. the receiver rail compared to a normal ar-15 receiver is very thick here, "massive" being a suitable word to describe the construction of this upper receiver.
i used a very high tech method to make this modification to the receiver. i simply put an abrasive wheel on the dremel tool, and had at the thing, removing stock until i was satisfied that a "jj's brit" spent cartridge had room to get out the gun after firing, to make way for a new cartridge to go into the chamber. and, when i had done that, i used a file to dress things up, and thing progressive then progressively finer grits of hand held sandpaper until the surface of the cuts was smooth and shiny.
hey, sometimes simple works pretty well.
the addition of a heavy bolt carrier. one of the issues with the reliable function of an ar-15 is the timing of the initiation of the ejection/extraction/feeding cycle of the operating system of the rifle. if the rifle starts to operate "too late," there may not be enough energy left of that imparted to the bolt carrier to fully cycle the gun. this is seldom the problem.
what is more often the problem is that the rifle is "over gassed," and that the operating system begins to function before pressures in the breaching area of the rifle have fallen sufficiently to allow the spent cartridge to be extracted properly from the chamber: if breach pressures are too high, the cartridge case has not had a chance to shrink/spring back from the chamber walls to which they have been forced against, and when the extractor pulls on the cartridge rim to clear it from the chamber, the case resists, sometimes results resulting in case rims being ripped asunder when the case remains, and the operating system goes back. this is not good. even if the case is extracted without damage from the chamber under this scenario, the mischief caused by too much pressure continues to exert itself to compromise the function of the rifle.
if pressures are too high in the chamber, then too much velocity is imparted to the bolt carrier, and, oddly enough, not enough time is given to the spent case to exit the ejection port and to clear the action. what happens is a real pain in the butt for the operator of the rifle. the bolt carrier comes back, the spent case is still pivoting away from the face of the bolt, and before it can be thrown clear the bolt begins to travel forward to pick up a fresh round from the magazine, which it does. so, now the bolt is traveling forward toward the chamber with a round that sticks its nose in the chamber, and the bolt is also pushing the spent round forward at the top of the bolt face, with the spent round sticking straight out the side of the rifle.
this cannot go on forever. sooner than later things stop, with the fresh round partially in the chamber area, and the spent round compressed down upon it with enough force to partially crush the case walls of both rounds.
this is called a "jam." in this case, a stoppage is caused because of the ancient and hoary old observation from mechanics, that two materials cannot occupy the same space at once.
what is the cure?
well, you can lower powder charges, or use a powder appropriate for the task, to make sure pressures are appropriate in the chamber when the bullet clear the barrel and extraction begins. (this is not as easy as it sounds, and doing this presented one of the great obstacles to the creation of the first semi-automatic infantry weapons. people finally gave in to what was inevitable, and began to use powders with appropriate burn rates to get residual gas pressures down below 2500 to 4000 lbs per cubic inch, in the breach/cartridge case, or in that neighborhood. it is interesting to note that as a matter of physical/mechanical fact, that the bullet has passed the gas port that drives the operating system, and has left the bore, "long" before this happens.)
enter les baer. less baer is a very well known person in the gun trades in the united states, and he make quality parts for ar-15 rifles. one of the things that he sells is a very robust bolt carrier.
i got a les baer heavy bolt carrier and installed it into the "jj's brit" ar-15.
the idea is simple. and, it stems from the law of inertia. when a thing is at rest, it tends to stay at rest. and, the heavier something is, the more force is required to make it start moving, e.g., to overcome its inertia. when pressure is imparted to the bolt carrier via gas pressure, it takes a while for the bolt carrier to begin moving. and, here is the key to the application here. that little "while" that it takes the bolt carrier to begin moving and to begin initiation of the operating cycle, is a "little while longer" when the bolt carrier, and other components of the bolt carrier group, are a little heavier.
in short, the heavier bolt carrier slows down the initiation of the ejection cycle.
and, the heavier bolt carrier, being harder to start, and requiring more force to stay moving, slows down the velocity of the bolt carrier group significantly.
well, i cannot tell you in units of time, the ability to measure this is simply beyond my means.
but, i can tell you that in terms of function, the slower operating bolt carrier system gives the spent case sufficient time to clear the ejection port and be on its way to the ground, so that it has done so before the bolt carrier begins to move forward to pick up a fresh round from the gun's magazine.
no more "stove pipe" jams.
caption: this is the top of the ejection port, showing again material having been removed from the ejection port to allow better egress of the spent cartridge case upon firing a round. we've covered that.
what i would like you to do is to click the little "+" sign locating the cursor, when it covers the picture. if you do that near the rear of the bolt, you will see an enlarged view of the bolt, to include the little "furrow" machined longitudinally in the bolt, and passing through the upper hole in the bolt.
this is a signature identification of a "les baer" heavy bolt, or so i believe. as with all les baer products, it is extremely well made and robust. and, in this instance, heavy. and, in this instance, heavy is good.
"spikes tactical" heavy recoil buffer. you cannot see it, but inside the little tube that the adjustable stock slides back and force upon, there is a spring. this spring compresses when the bolt carrier moves back under the impetus of a lot of gas pressure, and when that pressure bleeds off, the spring takes the energy it has stored, releases it by coming out of compression, and the bolt carrier group moves forward stripping a new round from the gun's magazine, and chambering it under considerable velocity.
caption: this isn't the best picture in the world, but, you can see the little tube behind the receiver that the stock mounts upon. inside that tube, unseen, are a couple of very important parts, ... , the recoil spring, and the recoil spring buffer.
in the text, we are talking about a buffer from "spikes tactical," which operates because of its increased weight, as compared to ordinary ar-15 buffers, to slow down the operating cycles speed, (often caused by too much pressure.)
all of the discussion above w/ regard to the les baer bolt carrier applies to another part i installed in the rifle to slow down the operation of the bolt carrier, to improve the ejection and extraction of spent cartridges.
"spikes tactical" makes a heavy buffer, which rides inside the bolt return/recoil spring operating in the tube behind the receiver. it's operation is simple. it does nothing, except to slow down the initiation of the ejection/extraction cycle, and to slow down the speed of the bolt carrier group during that cycle.
it does it by increasing the inertia that the bolt carrier group must overcome to begin, and to keep, moving. it is as simple as that.
again, i cannot quantify in units of time how much it does this. i can only tell you that in terms of function, it does it.
finally, the unsung hero's of the whole deal. there are two little parts internal to the rifle, which you cannot see in the above illustrations. they are one small spring, and one very tiny spring. the small string powers the "ejector" button, a little round pin that protrudes from the face of the bolt, and operates against base of the cartridge to pin wheel it from the bolt face and clear of the ejection port. the very tiny spring pushes against a pivot to hold the lip of the extractor in the extractor group of the cartridge case, long enough to let the ejector spring impart its spinning moment to the cartridge case.
if the ejector spring is weak, it doesn't push hard enough against cartridge to spin it free of the rifles action.
if the extractor spring is weak, it doesn't hold the cartridge against the bolt face long enough for the ejector spring to do its work. if the extractor slips, then the ejector is pushing against air, instead of the cartridge.
in short, nothing happens.
the rifle was upgraded with quality springs.
it seems to have had a salutory effect upon the reliability of function.
in sum. that's it.
that's what i have done to make sure that the ejection/extraction cycle works better.
it seems to have worked well. i struggled for a long time to get the ejection/extraction/feeding issues of the rifle working better, so that i have a rifle that functions without interruption from failure to feed properly, or from failures to extract and eject the spent case to make way for the insertion of fresh rounds into the chamber.
it all seems to have worked, because now the rifle works with hand loads of varying intensity, as i experiment with getting just the right load for various purposes.
i am more than a big smug about all this. mr. john garrand worked for 16 years to make the m-1 battle rifle functional and reliable, and he had at his disposal the entire resource of the springfield national armory. various manufacturers of ar-15 and ar-10 rifles have never seemed to quite get the knack of making an ar-type rifle function.
so, i am very pleased, to say the least, that my little cartridge, the "jj's brit," functions very well indeed in the little ar-15 rifle i built for it. i could have made this round function through an ar-10 sized rifle with less difficulty, but, then i would have been left with an overweight pig of a rifle, which i wanted dearly to avoid.
i now have a little ar-15, no heavier than a run-of-the-mill ar-15 in .223 remington/5.56mm nato, which chambers a significantly more powerful, and generally useful, round.
john jay @ 08.31.2013
harrison beane. at www.ar15performance.com , who makes and sells the barrel extension and bolt face with a .473" dimension, that made all this possible.
my friend the gun smith. he resides in montana, wishes to remain anonymous, but without his machining skills and vast knowledge base this thing simply would not have got off the ground. he cut and chambered the barrel, head spaced the barrel extension and bolt, and built the upper receiver assembly. he also nursed me through getting the magazines to work, and his cautions kept me from pursuing many the idiot's path. thanks, don, for a job very well done.
drew458. at www.barkingmoonbat.com, he has provided invaluable help in figuring out the best powders, with the most suitable burn rates, for use in "jj's brit."
frank barnes, and ken waters. frank barnes designed the .308x1.5" cartridge and did a lot of work on it, and ken waters wrote extensively of the best powders to use, and the appropriate charge weights, to achieve safe and appropriate levels of ballistic performance.
the brits. in the early 1950's the british designed the .30/280 british, perhaps the best intermediate infantry round ever designed. we'd be shooting it now, had america not forced the brits to drop it.
lewis potter. a gun writer and shooting sports authority in great britain, mr. potter has kept the original brit alive, and championed it as a deer/stag stalking rifle. one of my great frustrations in this project has been that mr. potter has never commented upon it, or seen fit to contact me in response about it.
i would still like to hear from him.