here's an article that sums up all the various rifling types i had saved it to my hard drive some time back for reference in the future. i thought it might add something to this thread.
please note i know nothing like these other guys do i just found this article very imformative back then and thought i would share it.
Tech Side
The Crowning Achievement
Building the perfect rifle barrel requires a blend of art and science.
By Wayne van Zwoll
Both chrome-moly and stainless barrels deliver fine accuracy in hunting rifles as well as in target guns. Fluting reduces barrel weight while preserving stiffness.
In the simplest of terms, a barrel is a pressure vessel. High-performance rifle cartridges can generate 60,000 psi, and a safety factor must be built into the barrel so a hot handload or some other variable doesn't cause damage.
There are two main barrel types. Most hunting and military rifle barrels are made of chrome-molybdenum, the steel used in truck axles and other high-stress components. It takes a traditional blue nicely and so is preferred for custom rifles. You'll commonly see it designated 4140. Other four-digit numbers indicate a slightly different alloy--Dan Lilja uses 4142 chrome-moly.
Stainless steel, popular in hunting rifles, dominates competitive rifle games. The stainless in barrels is not the same as that found in cutlery. Barrels of 416 stainless qualify as "rust-resistant." Their high chrome content adds hardness (and makes blueing difficult). A sulphur component makes machining easier. Stainless barrels cost more than chrome-moly barrels of the same quality. Some shooters claim stainless is easier to clean and lasts longer, so it's worth the premium. Super-accurate barrels can be made from both chrome-moly and stainless steel.
Tensile strength and hardness affect barrel performance. Tensile strength is the force required to break a steel rod one inch in cross-sectional area by pulling at both ends. Generally, hardening steel increases its tensile strength. But a tensile rating of 100,000 pounds for a rifle barrel is worthless if the steel is so hard it's brittle. A hardness of 25 to 32 on the Rockwell C scale has proven a useful compromise.
Heat-treating leaves residual stresses in barrels that can be relieved by slow cooling after reheating the blank.
Barrel drilling and reaming haven't changed much over the past century, except for the tooling. Carbide bits and reamers last a long time and deliver a superior finish. The deep-hole drill traditionally used to perforate rifle barrels has a stationary bit; the barrel rotates around it at up to 5,000 rpm. The bit is mounted on a long steel tube with a groove for cooling oil. The hole is commonly drilled .005 of an inch undersize so a reamer can finish the job, leaving the bore smooth and uniform.
Rifling the bore can be done with a cutter, a button or a hammer-forging machine. The cutter, developed in Nuremburg in the late 15th century, is a small hook in a hardened steel cylinder that just fits the barrel blank. The cylinder or cutter box moves through the bore via a long rod that pulls the hook against the bore wall, removing about .0001 of an inch of steel with each pass. After indexing so every groove is shallowly cut, the cutter box is adjusted to deepen the bite. Broaches with multiple hooks in a step configuration speed the process. Rate of twist hinges on the preset rotation of the cutter box. Figure an hour to rifle a barrel with a single-point cutter. It's a low-stress process, but it's costly. John Krieger's best barrels are single-point cut.
Much faster is the tungsten-carbide button, with rifling in reverse. Mounted on the end of a high-tensile rod and rotated by a rifling head set to the desired rate of twist, the button is pushed or pulled through the finished bore by a hydraulic ram, "ironing in" the grooves. To prevent bulging, the tube must be rifled before it is turned down to a narrow taper, which can result in distortion at the muzzle end. Dan Lilja's barrels are button-rifled; he says the smooth interior finish and uniform depth of the grooves give this method an accuracy edge.
Proper crowning of a barrel is critical to overall accuracy. A recess on this muzzle protects the mouth of the bore.
Hammer-forging pounds the barrel around a mandrel with the rifling in reverse. A shorter blank is used because the process lengthens the barrel by about 30 percent. Hammer-forging equipment was developed in Germany to produce barrels for MG42 machine guns. Stainless barrels are difficult to hammer-forge because they're too hard. Substituting 410 for 416 stainless is the solution. Hammer-forging is fast but leaves considerable radial stress, which is tough to remove.
Good barrels have been produced with all three rifling methods, but makers argue the merits of each. Button proponents even disagree on whether to pull or push the button–or whether it makes any difference. One thing is certain: Cutters and buttons must move smoothly and at a constant pressure through the bore.
Accuracy depends a great deal on rate of twist, which must be tailored to the bullet. Fast-pitch or sharp-twist rifling is required for long bullets at modest velocities. A short bullet driven fast requires less spin. There's some latitude: A 1:10 pitch (one rotation in 10 inches of travel) works for a variety of bullets in the .30-06. Barrels for .223s used in long-range shooting have a very fast pitch–1:9 to as sharp as 1:7–to stabilize 65- to 80-grain bullets. Gain twist, or an increase in the pitch of the rifling toward the muzzle, used to be favored by some riflemen. Lilja once employed gain twist but found after many trials that it failed to deliver measurably better accuracy than barrels with a uniform twist rate.
Rifling type and bore finish have a lot to do with accuracy. Generally, barrels with shallow grooves shoot tighter than those with deep grooves because they distort the bullet less. But shallow-groove barrels don't last as long. Land size is a trade-off, too. Narrow lands distort the bullet less and create less drag but also burn away faster. Reducing the number of lands, a maker can keep them wide while minimizing distortion and drag. Land configuration has long been debated, with no definitive answers: Witness the two-groove Springfield barrel and Marlin's 16-groove Micro-Groove rifling.
A barrel's groove circle must be concentric with the bore and land corners free of irregularities. Some uniform roughness in land and groove surfaces may actually prove beneficial because a very smooth surface increases friction that can pull jacket material from bullets as effectively as the tool marks in a rough bore. Conventional wisdom is that a uniform surface ripple of 10 to 20 micro-inches delivers the best accuracy. Careful lapping of the bore can deliver a properly smooth bore. Kenny Jarrett's super-accurate barrels are hand-lapped–a process that can take hours. But other makers say the process isn't necessary, given a careful rifling job.
Bore uniformity after rifling can be measured with an air gauge, a probe that is moved through the barrel with constant air pressure recording variations from specified dimensions. Shilen's air gauges are sensitive to 50 millionths of an inch. John Krieger recommends that every barrel be trimmed at least an inch at the muzzle when fitted to the rifle because the tooling used in bore finishing can leave a slight flare at the ends. Krieger barrels are lapped to just under 16 microinches in the direction of bullet travel. They're held to a tolerance of .0005 of an inch over nominal groove and bore dimensions, but the dimensions are uniform to within .0001 of an inch. Pac-Nor (button-rifling) and H-S Precision (cut-rifling) specify tolerances of .0003 of an inch for the bore diameter. Pac-Nor limits variation in groove diameter to .0001 of an inch.
MidwayUSA
5875 Van Horn Tavern Rd.
Columbia, MO 65203
(800)-243-3220
www.midwayusa.com
You might also consider choking a barrel if you're shooting lead bullets, as in a rimfire rifle or a competition airgun. Parallel bores are considered top choice if you shoot jacketed bullets.
How do I know all this stuff? I read a lot and ask questions. Most well-known barrel-makers now have web pages, some of which offer barrel-making insight as well as catalogs. If you want only to know where to buy the best barrels, your research gets easier: Midway USA. This shooter-supply outlet has paid attention to the results of benchrest competitions that test barrel accuracy. The logic is simple: To sell the most accurate barrels, stock those that bring home winning scores.
In the 2003 USRA-IR50/50 Nationals, for example, 39 of 87 top competitors used Lilja barrels. Of the best 20 shooters in 10.5-pound centerfire benchrest competition, 16 favored Shilen barrels. Shilen also ranked most popular in the 13.5-pound class. Hart barrels showed up almost as often on heavy rifles and have been a top choice of smallbore shooters for decades. Krieger barrels, the Cadillac of contemporary cut-rifled barrels, finished a close third in the latest postings. Douglas barrels appeared on both centerfire and rimfire lists, having served riflemen for a half-century in 50-yard matches to 1,000-yard competition.
If marksmen with big stakes in one-hole groups use these barrels, Midway reasoned that hunters and competitors will want them. Of course, these are not the only brands to consider when you're shopping. Some barrels, such as those by Kenny Jarrett and H-S Precision, are less widely distributed but offer superb performance.