Barrel
There are a lot of ways to make a barrel, each adherent to each school has strong opinions on each method.
I’m not gonna talk about that any more than I want to talk about the suitability of a specific caliber for battle. This is not that conversation.
Franklin Mann started out doing his tests in what he called a ‘Sled” rest, with the buttstock of the gun placed in a groove, so he could return to more or less the same place every time. Soon enough, Mann discovered that the variables of using a completed rifle made the experiments he was doing more rather than less difficult.
So he made a series of V blocks and used concentric threaded rings on a series of handmade barrels made for him by such famous makers as Pope. Mann had a setup where he shot down a tunnel made of muslin placed on stands, and into a box filled with oiled sawdust, to be able to carefully capture the trajectory of the bullets, (he placed cardstock every few feet) and the bullets. The mechanism he made to do all this testing shows not that he was an eccentric, but plainly and probably a lunatic. Here’s a picture of the shooting rest and “tunnel” and here’s a picture of some of the barrels he used to test, including some of the knurled chamber/firing mechanism segments.
Mann realized that in order to test only the barrel and the bullet, you had to isolate them from everything else. And that’s what he did, and his results speak for themselves. If you haven’t read the book, you might consider it.
Shooters from then on have understood that there are a bunch of things that can affect accuracy. Pope made a pretty comfortable living tuning single shot rifles with gain twist barrels. Everyone who has ever shot a bolt action knows that as the barrel warms or of the stock absorbs some moisture it can affect the point of impact.
Volumes have been written about free floating barrels, pillar bedding actions. And yet there are still lots of good shooting Mannlicher-Schoenauer rifles out there. Other volumes have been written about barrel harmonics and damping systems and god knows what have you.
Here is the very bottomline: For each barrel out there, there is an optimum load or a series of optimum loads, an optimum round that fits the barrel’s chamber as well as it can. If you place that barrel in a machine rest, and insert a series of optimum loads and fire them at distance X, you will end up with an accuracy that can be measured. Whatever that MOA value is, that is all that it will ever be.
I’m not talking about firelapping or any other methods of accurizing, this isn’t that conversation either. Under controlled circumstances, you will get what you get out of a barrel, and you will never get any more.
In a boltie you can tweak the stock, bed the action, bed the barrel, float the barrel, cork the stock, lap the lugs, any number of things to try to wring the most accuracy out of the barrel. A falling block has a different set of accuracy related components. Break action rifles another set. Doubles- well, doubles aren’t meant for long ranges anyway.
In an AR all of these things have been removed from the process. Installed correctly, the gas tube touches nothing, and cannot exert any kind of force on the barrel. (I can’t speak for piston types) Installed correctly, and manufactured correctly, the front sight cannot exert any kind of force on the barrel. The handguard can only exert a relatively small bit of tension, and there are even “Free floating” handguards.
This is one of the aspects of the design that reveals it’s genius to me. The barrel is held to the receiver by a nut. Nothing else touches it in a way that can affect the barrel’s accuracy. It hearkens back to Mann and his separation of the barrel from all potential external influence.
I see a lot of guys messing with AR’s in their basement shops on youtube. The recurrent themes seem to involve things like squaring the receivers. There is nothing that can be done to an AR receiver that will make the barrel shoot better than the barrel will shoot. If you think this is possible, beware of hucksters selling oceanfront property in Florida. The accuracy of the barrel is a fixed quantity, and messing with the receiver cannot change that.
I’ve heard the argument that “Squaring the receiver aligns the bolt properly so the headspace is perfect” &etc.
Another fun feature of the AR is that the bolt has a bit of play in the bolt carrier. Not a lot, but if you pull the BCG out of your rifle you will discover that the bolt will wiggle a bit in the bolt carrier. This is not a flaw, it is a feature. The bolt itself is designed so it can compensate for the maximum misalignment that can theoretically occur between the receiver and the barrel. So if the barrel is not square to the receiver by .05 of a degree, the bolt will still find the cutouts in the barrel extension and lock up against the cartrige, in it’s chamber.
Oh, about the chamber. Ed Foster send me this missive, and regardless of what you think of me, you should pay attention to Ed. I may know a lot of shit about manufacture, but Ed knows from AR’s. I quote:
Chambering is simple. The MilSpec 5.56mm and the civilian .223 Rem both have identical chambers.
The difference between the civilian and military barrels is in front of the chamber. The .223 has .025 freebore @ .225 diameter and a 1.5 degree leade cone into the rifling.
The military tube has .060 freebore @.226 diameter and a 3 degree leade into the rifling, to accomodate the much longer ogive on the tracer round. The extra long tracer projectile is also the only reason the military uses a 1 in 7 twist. The 1 in 8 works better with both the 62 grain green tip and the Mk. 262 77 grain load. Better accuracy with the 62, and lower pressures with the 77.
The “compromise” chamber I’m most familiar with is the modified Wilde chamber found on Roy Piontek’s E.R. Shaw barrels, a just about “min” chamber with .032 length freebore x .225 diameter, and it shoots like a dream with everything I’ve put down it. It maintains the military 3 degree leade angle, and that seems to have been the critical pressure control mechanism. I concede it might cause some problems if fired continuously with tracer, a hot loaded and brutally dirty round, but what sane person shoots tracer in a good barrel anyway?
I’ve received the exact same comments on the Wilde chamber from Jim, and it appears to be the perfect advice.
As we’ve already discussed, the bolt, barrel, and barrel extension make the accuracy of the barrel. I have not tried this, but I have a solid feeling that if I were to take those three parts to the range, put the barrel into a suitable vise, chamber a round and put in the bolt, then tap the firing pin, it would shoot just fine. (I don’t imagine it would do the components any good, though I can’t see as it would do them a good deal of harm, either)
So the receiver is just a sort of a carrier for the barrel, with an area for the bcg to reside.
If the barrel extension doesn’t have parallel surfaces on the mounting ring, that could cause the barrel to be misaligned with the receiver.
If the barrel extension isn’t internally square to the barrel, that could cause a different type of misalignment.
If the front of the receiver isn’t square to the baore, that can cause yet another type of misalignment. And if the internal threads of the nut are not square with the seating surface, this can cause misalignment or looseness. It seems that these are the sort of problems that all the home gunsmiths I see online are attempting to correct.
Why on earth would you want an improperly manufactured part in your firearm? Those potential problems are manufacturing defects, and the best thing to do with parts that are improperly manufactured is to send them back to their manufacturers with some explicit directions as to their placement. You cannot make a silk purse out of a sows ear.
In any event, the bottomline is still the barrel, extension, and bolt. Those pieces together provide the accuracy, the rest of it just carries them around and makes them convenient to use.
Here’s the thing: Having a loose or improper fitting barrel/receiver interface will cause the sights to move or not line up properly or repeatably. This will not allow you to use the accuracy that the manufacturer put into the barrel. At Prof Hale’s place I was assaulted by people who just KNEW that fucking with the receiver was going to make the barrel shoot more accurately. This is voodoo gunsmithing, pure and simple, and to represent it as anything else is bullshit.
Now, I will gladly concede that making that receiver fit the barrel tightly will make sure the sight can be made to point at the thing the barrel can hit much more reliably, but again, why deliberately use an out-of-tolerance part, if max accuracy is your goal?
The way the barrel fits into the receiver is critical, so those dimensions have a tighter tolerance. The slot at the top of the receiver is critical for bolt alignment. The depth of it has to allow room for the receiver to grow. The nut is steel so that it expands at the same thermal rate as the barrel, so it doesn’t cause the threads in the receiver to lock up. This is not because it can affect the accuracy of the barrel, which it cannot, but because it affects the tightness and repeatability between the receiver (Which is where the rear sight or optics are mounted) and the barrel. If the optics are not in a rigid and immobile relationship to the barrel, there is no way you will shoot accurately.
This is all some pretty damned fine engineering, but there are a lot of things you can’t even see. Mr Foster points out something I knew but maybe you don’t: Flip the upper up on it’s forward pin. See the hole for the back pin? It’s a slot. It’s not round. It’s just a little bit longer than it is tall, and the reason is to prevent the upper from binding when the receiver warms while being shot.
If you have a digital IR thermometer, you can pump a few dozen rounds quickly through your AR, and note the temperature change, and measure the diameter of the pin and the length of the slot, and use that to determine what alloy the upper is probably made from. Congrats, you just reverse engineered that part of the design.
Additionally, and i don’t know if all uppers are like this, mine and several others I’ve seen have had the slot canted at a slight angle. This means as the upper warms, it fits a little more tightly to the lower. That slot is a little piece of brilliance there, it really is.
I’m not concerned about the suitability of this as a battle rifle, I’m really, really not. That discussion is for other people. I’m talking about the incredibly complex and well thought out design of what in the end is a very simple mechanism, and one that is not just elegant but a blast to shoot. Thanks, Gene. Nicely done.
21 comments Og | Uncategorized
I’ve been telling people this for 7 years now. I am frequently roundly castigated as an idiot for it.
Of course, I am also castigated as an idiot for believing in the superiority of external coil spring tensioned extractors with wear lifetimes in the millions of rounds; to internal tension leaf extractors with wear lifetimes in the thousands of rounds.
Oh and then there’s the fact that I tell people that if their magazine springs are properly designed and manufactured they will not take a shorter set or wear out prematurely when their magazines are kept loaded to their proper capacities (at least not after the first few times they load the magazine. Some spring makers don’t preload their springs before shipping them to the magazine makers); and should have a cycle lifetime of at the very least tens of thousands of cycles, if not hundreds of thousands or millions.
Somehow, this is impossible to believe; though the many springs in various industrial machines surrounding us, and even in automobiles; have cycle lifetimes in the billions.
The fact is, most people simply do not understand basic engineering; and no proof you can present them with will overcome their “common sense”.
I don’t disagree with anything here.
Here’s the thing: Having a loose or improper fitting barrel/receiver interface will cause the sights to move or not line up properly or repeatably.
And here it sounds like you are admitting that there are other factors in where the bullet goes besides the barrel, extension, and bolt. That is all I, and I think Res Ipsa, were saying.
No, that’s a lie. I made it very clear in my posts at Prof hale’s that the barrels accuracy is just that. period. And I made it very clear that your accuracy would suffer in my very first comment on the subject; it was clear that Res knew more than me about everything (Which, of course, he does not) and had anyone bothered to READ THE WORDS I WROTE instead of being fools, you might have seen this:
“Unless, of course, you’re talking about the relationship between the barrel, receiver, and optics changing, which is a different story altogether. It makes sense that an upper which is square to the threads would work much better, because the barrel could heat up and move around- but that’s the nature of alloy parts anyway.”
That was in my very first comment on the subject, and I have described in detail how any why it works, and i have described in detail how every point Res made to me was either a: Stupid, or b: an outright lie.
From the very beginning I made the statement that the barrel, barrel extension, and bolt were all the accuracy the firearm was ever going to get, and that is still true, and all the voodoo bullshit Res came forth with was simply that.
Here’s what I’m ‘admitting’: i was correct from my very first comment on the subject, and not one person has had the balls to stand up and say I am not, and be willing to prove it. period. Everything else is falsehood.
I shot many thousands of rounds in HP rifle competition. When the AR came along I studied the design and came to the same conclusions you have. No need to spend hours fooling with the receiver other than making the sight consistent and repeatable. I just bought a Kriger barrel used a Wylde chamber and installed it with a floating hand guard. They all shot better than the shooter and I know that to be true because we had a cradle to test them in. That cradle can make a shooter feel really bad about his ability.
Blind, when I see how accurately the barrel can shoot and how accurately I cannot, it is very humbling.
I will confess to being completely bumfuzzled the first time I saw a heavy benchrest rifle (in this case, a Sako action hucked up to a barrel in .22-250) where the truck-axle barrel was bedded and the action was free-floated…
There’s so much voodoo in benchrest shooting I am amazed that anything gets shot at.
I guess, at the end of the day, it’s the results that speak, right?
I am not lying. You have stated that the barrels quality will set an upper bound to the gun’s accuracy. I agree.
But that is not all there is to it.
You said:
Despite any advancements in anything you state, the critical stuff all takes place inside the barrel. if there is something that will change that, that does not involve machining something inside the barrel,I’m pretty sure that I can make a similar case that changing the air pressure in my trucks tires can effect the bullets flight.
I don’t think that is true. Things like barrel bedding matter on a bolt gun. The equivalent on an AR would be slop in the fit between the upper and lower or bearing faces being machined out of square.
Because the gun moves while the bullet is in the bore. If the pin is bearing one way on the first shot, and bearing differently on the second there will be an impact when the recoil takes up the slack.
You can visualize this by imagining that fit being extremely loose, and what it would feel like to shake the gun, with all the weight in the magazine connected to the lower.
This could have an effect on which way the barrel is pointing when the bullet exits, due to the vibrations produced.
Even more extreme, the hammer that hits the firing pin is connected to the lower, and hits the pin contained in the upper. If the fit is loose the upper will move. The barrel is no longer pointed where you aimed it.
These types of things could keep you from getting the accuracy a good barrel is capable of.
Wrong. Prove it or admit youre making shit up.
Og,
“There’s so much voodoo in benchrest shooting I am amazed that anything gets shot at.
I guess, at the end of the day, it’s the results that speak, right?”
As best I can determine, benchrest rifle is to shooting as Top Fuel is to automobile racing. In both, the guy behind the trigger when the light goes green is the smallest variable in the win.
Giraffe,
“The equivalent on an AR would be slop in the fit between the upper and lower…”
Given a machine rest, you could take the lower completely off an AR without affecting its accuracy.
The “Accu-Wedge” is sold to suckers who don’t know how the gun works.
A friend’s TN Air Nasty Guard unit traded in nearly unused M-16’s for retread FMF M-16A2’s that were worn to bare silver aluminum. You could read the Sunday NY Times through the gap between the uppers and lowers. All the good shots still qual’ed Expert.
“Og, no need to reverse engineer anything. The material is 7075 aluminum, ”
Indeed. It’s actually a kind of a textbook example of how that works.
I’ve spent a lot of time making temp or one use fixtures out of t6061, it’s a hoot to work with. (Made a pair of fixtures to cut the tails off coins to solder the heads together a while back, and people are STILL borrowing it, I intended to use it ONCE. We have customers that make billet car wheels out of it.
“If you haven’t read the book, you might consider it.”
Consider it considered.
I’m going to look for some porn.
Y’know, the Mauser American used an AR type rotating bolt, but I don’t know whether it locked up into a barrel extension, a-la Stoner, or into a more traditional receiver lockup.
Take that Mauser design with it’s straight-pull bolt, and operating using the Stoner barrel/extension/bolt dynamics. But, residing within the blue steel n’ wood and traditional lines of every Fudd’s favorite Bambithumper.
That’d be a hellva rig; I’d want one!
Sounds like a project for ya, Og, on those days you’re bored and got nuttin’ else to do?
Jim
Sunk New Dawn
Galveston, TX
If the object is to put’em in the same hole at a hunert, all of my Savage 10s do that outa the box.
If ya wanna smoke the guy at 900 yds, call in air.
What about the differences in expansion of the materials? Where the barrel meets the receiver, steel on aluminum. Cold, you have a tight fit. But as you warm it up does the receiver expand faster than the steel barrel and thus produce slop (non-repeatable) barrel alignment?
I once had a 16″ bull barreled Oly Arms that would out preform everyone that ever shot the damn thing.
Every time I thought I’d seen it do it’s best, I’d let someone else shoot it. Just WOW.
It lives at my dad’s house now. Maybe I’ll trade him a lighter weight upper/rifle and get it back from him. Hmmmmm. All of this accuracy talk makes me miss it dang it.
Given a machine rest, you could take the lower completely off an AR without affecting its accuracy.
sure. when the machine rest is not given, I believe it matters.
When the machine rest is not given, it still does not matter. And that is the issue I have with “belief” People believe the damnedest dumb things, like the Hale-Bopp idiots, or the Occutards or democrats. belief is what you have when you aren’t willing to learn facts.
I followed this conversation, at some points feeling like I was a stone age savage listening to a relativity discussion between Al Einstein and Stevie Hawking.
I’ve only ever really been about practical shooting, I admit it.
So, I’m with Skip.
Shit, John, you know a million times more than I do about this stuff, I just approached the whole thing from how an engineer sees things.