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Post by loggy on Aug 25, 2007 15:10:35 GMT -4
Over years of shooting many different twist MLers i must totally agree with the principle that a longer bullet likes a faster twist and conversely a shorter bullet favors a slower twist.
Anyone have any thoughts???
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Post by batchief909 on Aug 27, 2007 11:26:46 GMT -4
I agree!
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Post by loggy on Aug 27, 2007 19:24:09 GMT -4
I wouldnt expect any different from a BIG TRASH CAN thrower!!! ;D
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Post by zimmerstutzen on Aug 28, 2007 8:50:56 GMT -4
Most definitely, however, there's a bit more to it than that. Long bullets do well in rifling suited to them. Not just twist but depth as well. Rifling that has a depth of more than approx .007 can be too deep for the bullet to fill the grooves and eliminate "blow by" of gases. Blow by can deform the bullets and otherwise cause loss of accuracy. The same can be true for very narrow groove rifling with wide lands. Round ball slow twists are much less finicky about depth of rilfing, provided the velocity of the PRB doesn't just strip through the rifling. Shallow rifling such as .004, can be too shallow to keep the PRB from being just pushed through without spinning. Tearing the patch, deforming the ball and leading to a loss of accuracy. The type of deep round ball rifling that leads to target style accuracy, is terrible for minnie balls and bullets because they can't fill the grooves when fired.
There are some forms of rifling that do better than others for certain purposes. There is square bottom groove rifling, round bottom groove rifling, (no corners for fouling to stick) grooves wider than the lands, and even geometric shaped rifling such as the hexagonal bore Whitworth rifles that took a hexagonal mechanically fit bullet. There were a host of various types of rifling in the mid 19th century. There was rifling that was deeper at the breech than at the muzzle, such as the 1853 Enfield. Some guns even had a "v" bottom groove rifling. About the most complex was that developed by Alexander Henry for the Britsh War Department in the 1860's. It isn't really lands and grooves, but is more a series of convex and concave shapes that spiral through the barrel. Even the wide "grooves" had a raised hump in the middle.
Most modern rifles are simply broached with shallow square cornered rifling grooves. Cheap to make and with todays tolerances, accurate enough. Round ballers usually prefer "cut" rifling, which is generally deeper than a simple broach can do. I have a custom cut round ball barrel that has round bottom grooves that are twice as wide as the lands, as well as being .008 deep. (Very acurate with round balls.)
Then there are barrel chokes. Most rifle barrels are straight through, but the 19th century British, found that a slight constriction of the bore (Which is quite dangerous with hard bullets such as hard cast or copper jacketed) was more accurate with the soft lead and paper patched bullets of the era.
Lastly, there was gain twist, rifling which accelerates in twist as the muzzle is approached. Harry Pope made many of the most accurate rifles of the world in the 1890's to 1930's. But he found that gain twists increased accuracy with small bore black powder loads, but were dangerous with smokeless loads. As I recall, the Italians actually manufactured military rifles with a gain twist.
That is just the beginning of the "rest of the story"
Yep, as a general rule, faster twist, longer bullets! But, that is only part of the factors.
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Post by loggy on Aug 28, 2007 19:02:07 GMT -4
Thanks for the great info zimmer!
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Post by zimmerstutzen on Aug 29, 2007 8:48:13 GMT -4
You asked for thoughts and I gave mine.
In the 1800's some ballisticians actually came up with a formula for the alledged "magic bullet" length. It works to an extent, but doesn't really account for the ballistic co-efficient of the nose shape. The real long range black powder shooters, (1,000 yard distance) tend to use bullets from 525 to 650 grains in 45 caliber rifles and up almost 700 grains ( .1 lbs each) in 50 caliber guns. That is a bullet around two inches long. They take into account nose shape for less air resistance and mass for sheer inertia to carry out 3,000 ft. Often times those guns had false muzzles, a piece of rifled barrel that would slip fit onto the main barrel and was perfectly aligned with the rifling. It would allow the bullet to be swaged into the rifling at loading and then the piece would be taken off for firing. The muzzle crown is then nearly as perfect as can be had, eliminating any deflection at the crown from defects and wear from loading.
British gun makers such as Gibbs and Rigby took long range muzzle loading to a high art form of ballistic science. The bullet had to be heavy enough to carry and stay stabilized that far. They used paper patched smooth sided bullets to reduce the wind resistance of grease grooves and cannelures. Their molds often would be "nose" pour so the bases would be as perfect as possible. They often used grease wads or scrubber wads over the powder and under the bullet so the hot gases of the powder would not deform bullet and also to lessen or cushion against obturation. Those old timers even took into account the effect of barrel temperature during a rifle match and tried to keep the temperature as constant as possible.
Short lighter weight bullets tend to have less inertia, and because of shorter flatter noses worse air resistance than longer bullets. The amount of spin imparted to the short bullet is less relevant because the bullet air resistance and yawl set in and diminsh distance accuracy A Marlin 444 with it's short 250 to 275 grain flat nose bullet is a powerful round to, lets say 250 yards, but an old 45-70 with a 450 or 500 grain bullet initially moving much slower will carry more energy and remain stable to much further distances. Now that rainbow arc is another thing to contend with, but at 500 meters, the 45-70 will outperform a 444 Marlin. (assuming proper rifling, shooter proficiency etc are equal)
As for muzzleloaders, there is alot of carry over from ballistics of breech loaders. Ballistic co-eficients against air resistance, mass inertia and the rate a bullet slows down are pretty much the same after the bullets leave the barrel. Round balls crtainly don't have the same type of mass inertia as the bullets and saboted rounds used in in-lines. But round balls do sometimes have better ballistic coefficients than some of the flat nose wad cutter type projectiles I see in the stores.
The part of the bullet that picks up the spin from the rilfing is the side. Perhaps with a bore rider nose part of the nose also pickes up spin. The length of the bullet isn't necessarily all picking up spin from the rifling. Where the nose doesn't contact the riling, that really doesn't count as length. So an optimum projectile has both the necessary length against the rifling to maximize the twist, as well as a ballistically more efficient nose cone.
Now most of this really doesn't matter to PA hunters who rarely get a shot over 80 yds. Hopefully it will explain what may be necessary for you if going out west and you want to shoot an antelope at 350 yds with a muzzleloader. Most buffalo hunters preferred to be at least 300 yds away from the herd and could proficiently take neck shots out to 450 yards all morning. Those little 300 grain projectiles in the stores just wouldn't reliably do the job out of a black powder gun.
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onager
lodge member
Posts: 244
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Post by onager on Aug 30, 2007 16:24:26 GMT -4
Ow!........My head hurts!
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Post by zimmerstutzen on Aug 31, 2007 14:57:47 GMT -4
There are guns that load powder and ball from the front, there are guns that load from the breech and guns that load in between. There are even guns that take powder through the breech and bullet from the muzzle. There are several types of ignition, wheel locks, match locks, flintlocks, percussion, needle fire, rimfire, centerfire and electric. There is rate of twist, shape of rifling, width of rifling, variable twist, variable rifling depth and variable bore width, bullet nose, barrel temperature, barrel float or lack thereof, There's patched round balls, bullets, paper patched bullets, gas checked bullets, jacketed bullets, solid points, hollow points and expanding points; variable lengths of bullets, then powders, wads, grease cookies, and strength of prime, and variable rates of powder burn and variable pressures of powder burn. Variable air drag on the bullets, bullet velocity, open sights, peep sights, sight radius, scopes, x-tubes, length of barrel, inertial mass of the projectile then there are single triggers, single adjustable triggers, single set triggers, single action double set triggers and double action double set triggers. Slope shooting, level shooting, shortrange, mid range long range,
It is merely selecting the optimum combination of variables appropriate to the shooting discipline.
I don't believe it gets any simpler than this.
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onager
lodge member
Posts: 244
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Post by onager on Aug 31, 2007 16:06:17 GMT -4
Loggy. Please, never again ask "anyone have any thoughts?" And Never a greater understatament. "I don't believe it gets any simpler than this" ;D ;D ;D ;D Seriously, I do appreciate the expert comments.
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Post by loggy on Aug 31, 2007 16:10:12 GMT -4
LOL Onager!!!
It took me a couple years to understand the "basic principle" that Longer bullets like fast twists and the shorter bullets like slow twists. ;D
Zimmer sure added some addl good info for sure!!!
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Post by berkscoflinter1 on Aug 31, 2007 17:30:43 GMT -4
I know better than to jump in here on this inline thread, but I just received my latest Cabela's flyer, and I find the TC Triumph they're advertizing, an interesting rifle. Is it worth considering, or is it way beyond an old flinter's capabilities? I would promise to keep it in the back corner of the closet. Is that Zimmer awesome, or what!
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Post by loggy on Aug 31, 2007 18:49:16 GMT -4
Berks, you cant go wrong with ANY TC In-line!!!
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Post by zimmerstutzen on Sept 6, 2007 8:48:40 GMT -4
I don't know how many of you have heard of Harry Pope. He made specialty target rifles that took muzzle loaded bullets. Once the bullet was seated, a cartridge full of powder was inserted into the breech. He was probably the most gifted target gunsmith that ever drew a breath. Of his rifling and twists he said:
“My rifling has eight wide grooves, which are on a radius about three times the radius of the bore, and has the corners rounded out, so dirt is easier removed, and it is cleaner in use. This groove is cut just deep enough to clear the bore in center and give a depth at corners of about .004 inch,…. which is ample depth and works cleaner, and leaves less to depend on upset of the bullet, and is therefore more reliable. The lands are very narrow (about one fifth to one sixth the width of the groove.) The bullet is made with a base large enough to fill the grooves completely, and the body is practically the same diameter as the bore. This gives a form that is gas tight, loads very easily(being assisted in this by the narrow lands and choke bore) and on upset, instead of the body of the bullet meeting only sharp lands and those cutting into the body of the bullet more or less unequally, it is held to place by the nearly flat center of the broad groove and swells out into grooves equally and perfectly central: consequently is accurate.
…I have fired 130 consecutive shots in ten shot strings….. The largest of the groups was 3.75 inches, the smallest was 1.8 inches. All but two of the shots would cut into a three inch circle. (at 200 yds)
Barrels are cut with a pitch (twist) correct for the bullet they are intended to use. Shorter bullets can be used in a barrel cut for the longer one, but not the reverse.
All calibers, except the 25 are guaranteed to shoot within a 2 ½ inch group at 200 yds with the muzzle loaded bullet. ”
Note: lands one sixth the width of the grooves would in a 32 cal barrel would measure only .017 of an inch wide and the grooves would be .106.
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