Discussion On Custom AR-15 Barrels
BY Herschel Smith
5 years, 5 months ago
Custom barrel manufacturers like Obermeyer, Krieger, Lilja, Hart, Douglas, Schneider and other companies which go by the maker’s last name, are your best assurance of good quality. That’s not to say that other maker’s barrels―let’s call them “semi-custom”―don’t shoot as well, but it is to suggest a lower element of risk involved in your satisfaction. I think it’s wise to request a stainless steel barrel since they will, on average, shoot a little better for a little longer.
It would be nice if a materials engineer and/or a highly experienced gunsmith would weigh in on this, but that’s not my understanding. My understanding (which might be flawed) is that a SS barrel will be more accurate out of the box, but that whereas another barrel might last for 25,000 rounds, a SS barrel will last for 15,000 rounds before needing to be replaced. Again, if my understanding is wrong on this, it would be good to know it.
The chambering option that probably gets the most thought about and worry over is throating. Throating, let’s say here for simplicity, controls the distance of a bullet; bearing surface to the origin of the lands of the rifling. Almost always, a rifle shoots best when a bullet at least starts near the lands, if not on them. If the bullet has to travel through space before engaging the rifling, that’s called “jump,” and that’s an issue of concern. Since there is such a difference in comparing length of short range and long range bullets for this rifle, some compromise has to be met. Essentially, getting less jump for the shorter 68- to 77-grain bullets fired from magazine-length rounds means that the longer 80-grain bullets used at 600 yards will be seated more deeply into the case (which will reduce powder capacity). Short or long? Either, or anything in-between for that matter. It doesn’t really seem to matter. Why even talk about it? Why not? Everyone else does. What they’re not really talking about, though, is who’s shooting what scores with various ideologies. That’s because AR-15s shoot just as well at 200 and 300 yards with all the different “magazine” bullets, regardless of where those bullets are sitting with respect to distance from the lands. What matters to 600-yard performance is that the shooter knows how to experiment and adjust the amount of jump the 80-grain bullets have, and that discussion is for another article.
Someone care to elaborate what’s he’s talking about here?
On May 13, 2019 at 11:18 pm, Ratus said:
The stainless steel used to make barrels is “soft” (ie. Better for machining with less tool wear) so cut rifling is more precise and easier to finish. If you are interested in a barrel for competition shooting at targets for score then a high priced “named” barrel is for you.
On the second part, he’s talking about how chamber dimensions affect accuracy when shooting ammunition that has an OAL the is too long to fit in an AR15 magazine.
Again, more competition specific frippery that doesn’t really matter to most of the people looking for a good general purpose AR15 barrel.
If you want me to elaborate more on this just let me know. (Caveat, I’m not an expert in this or any other field. Just someone who has read a lot and has shot a bit)
On May 13, 2019 at 11:31 pm, Ratus said:
Here’s some links to the very good interview by InrangeTV with Faxon about barrel making.
Faxon Q&A: Barrel Manufacturing, Nitride vs Chrome lining
https://youtu.be/e2X1iaQbjg8
Faxon Q&A #2: Barrel profiles, length, fluting
https://youtu.be/yF4g2CWtjOo
Faxon Q&A #3: Twist rates, stress, break-in, gas ports
https://youtu.be/R3FDLiWMUTc
Faxon Q&A #4: Chamber types, heat dissipation, headspace
https://youtu.be/ZDvLrvEAhkM
Also a short video testing a modern pencil barrel vs an original Colt pencil barrel
WWSD: Pencil barrel Stress & Heat Zero Testing
https://youtu.be/QTovPt4weIs
On May 14, 2019 at 4:46 am, Bill said:
What Ratus said… First off, I’m neither a Gunsmith, nor an Engineer, but I have competed in long range rifle, and have a good experience base with ARs, even building them for various purposes. So…
The whole “jump to the lands” discussion is purely a Mid to Long Range Competition issue. Competitors have generally (not universally) found benefits to loading their bullets “into” (touching) the lands in the throat of the barrel (thus eliminating the “jump” to the lands when fired, and more importantly aligning the centerline of the bullet with that of the bore). This can also create pressure issues in the rifle & has to be done with care. Nothing about it should concern an AR builder at all, …unless he’s building specifically for long range (which I would not with std AR cartridges).
The barrel question is endless, and opinions are like -err- “rearward orifices”; everyone has one & they all stink in one way or another.
The AR platform is so versatile that what is “good” or “bad” depends mostly on your intended use of the rifle. What’s good for a patrol rifle will not be for a varmint rig, or a historical replica. Decide what you want to end up with, then build it. The guy you quoted is thinking solely about competition; a fairly narrow requirement set.
On May 14, 2019 at 10:04 am, Bram said:
Are Polygonal rifle barrels dead? I always used to hear about the advantages and would have thought they would be popular in this age of expensive customization.
On May 14, 2019 at 12:17 pm, Georgiaboy61 said:
Re: “The chambering option that probably gets the most thought about and worry over is throating. Throating, let’s say here for simplicity, controls the distance of a bullet; bearing surface to the origin of the lands of the rifling. Almost always, a rifle shoots best when a bullet at least starts near the lands, if not on them. If the bullet has to travel through space before engaging the rifling, that’s called “jump,” and that’s an issue of concern.”
To second what others have covered, a competition-type stainless steel barrel with a Wylde or similar “tight” chamber is generally what someone doing CMP/NRA high-power rifle would want. It isn’t necessarily best for a general-purpose platform.
Military-specification rifles and carbines are built with generous chamber dimensions since they may be called upon to fire a wide variety of ammunition, whose length, weight and construction may vary considerably. This is also the case for any select-fire weapons platform since full-auto operation also calls for generous chamber and throat dimensions for optimal reliability.
Bullet “jump” from the cartridge case (neck) to the lands-and-grooves does not always spell less-accuracy. Some rifles shoot certain loads extremely-well even though there is considerable distance between the projectile and the barrel grooves. The dimensions of the bullet itself, the uniformity of its case, the chamber throat and more – all influence accuracy and reliability.
For most shooters, the only practical way to discover whether your particular cartridge/bullet and rifle combination “likes” jump or not is to do real-world (empirical) testing at the range.
Having provided the usual disclaimer that every rifle is different, it is standard practice amongst metallic reloaders to increase COAL (cartridge over-all length) by seating the bullet further out in the case neck, so that it has less distance to travel to engage the rifling. Again, the “sweet spot” is best determined by experimentation.
The time/effort required for such experimentation benefits long-range or other precision shooters, but is probably not worth it for the typical carbine user, most of whose shots fall inside 100 yards. There just isn’t enough of a payoff realized by shrinking its groups from 1.5-2 inches at 100 yards, to 0.75 inches at the same distance. As always, ask yourself: “How much accuracy do you need?” and don’t let the perfect be the enemy of the good.
On May 14, 2019 at 12:23 pm, elysianfield said:
Ratus,
I once manufactured precision rifle barrels…in the early ’90’s. The answer as to whether 416SS barrels are “more accurate” than various steel offerings was a simple matter then;
“How many stainless steel barrels were successful in the National Bench Rest competitions?
…None. All the winners used chrome-moly barrels. May be different now?
On May 14, 2019 at 3:32 pm, Georgiaboy61 said:
@ elysianfield
No kidding!? The things one learns in everyday life…. thanks for the info.
On May 17, 2019 at 2:45 pm, Guest said:
In the case of 5.56mm the point is moot. A milspec 5.56mm chamber has 0.162″ of unrifled “leade” in front of the chamber as a means of boosting velocity while reducing maximum pressure peaks. You can’t seat any .224″ diameter bullet I know of anywhere near the rifling, not at cartridge overall length that will fit in an M16 magazine.
I am aware that benchrest shooters have long favored seating the bullet in such a manner that it just barely kisses the rifling when chambered. You can’t do this here.