In order to participate in the GunBroker Member forums, you must be logged in with your GunBroker.com account. Click the sign-in button at the top right of the forums page to get connected.
Options
oal gauges and calipers
edg1520
Member Posts: 10 ✭✭
i'll probly wished i'd left them in the damn store but since i bought them i could use a little help.Now you've got an c.o.l.(cartridge overall length)then you got that damn o.a.l.guage and i think its tellin me my barrels taken a poop on me because when i put the modified case adapter in there with the bullet and pushed it forward its over the c.o.l.length so where do my options lie at this point.
bullets with the ring around them are supposed to set in the casing that far arent they thats why its there right?not to be to exact when i pushed the oal gauge in the rings out about an 1/8 to 3/16s or some wheres closemy col is 3.290 and im thinkin it was around 3.331 or some thing close?
bullets with the ring around them are supposed to set in the casing that far arent they thats why its there right?not to be to exact when i pushed the oal gauge in the rings out about an 1/8 to 3/16s or some wheres closemy col is 3.290 and im thinkin it was around 3.331 or some thing close?
Comments
The COL is just a book value as is the OAL. These are SAAMI specs.
You seat the rounds to feed from your magazine and try to get them close to the rifling for better accuracy than a factory round that has to make a big jump to the lands.
That goofy little ring, known as a cannelure, is embossed into some bullet designs so that the neck of the case can be crimped into that groove. This crimping helps keep the bullet in the case while under recoil, at the specified length in order to provide consistent feeding and pressure. Not all bullets of the same caliber, say .30 caliber as an example, have the cannelure at the same dimension simply because they were designed to be used in different cartridges with differing magazine lengths. In essence, bullets designed for use in the .308 Win. will have a cannelure in a different place than a bullet designed for use in the .300 Win Mag.
Chambers cut into rifle barrels can have different designs also, they are not all the same no matter what SAAMI has for specification. The factories often change those designs and dimensions in order to accommodate all factory ammunition safely. Usually, we find that the factory chambers have a long 'leade' or a longer 'throat' which allows the pressure to drop slightly, providing a buffer for potential pressure excursion.
This longer chamber is not an indication of your barrel taking a poop but it does tell you where the lands begin and how far your bullet will jump when seated to magazine length or the length set by using the cannelure.
Accuracy can still be attained when bullets are seated off from the lands. It's just a matter of experimentation with load development.
This is an article by John Barsness attempting to explain a part of your dilemma:
RIFLE CARTRIDGE OVERALL LENGTH
by John Barsness
ONE OF THE TOP TEN questions asked by readers of handloading articles is: "What's the overall length of that super load listed for the .300 Hamburger Magnum?" Apparently there is a widespread belief that somehow overall length (also known as OAL) has a major influence on handload accuracy. Well, it can - but generally not by exactly imitating the OAL of a load developed in another rifle.
Two factors influence "correct" OAL: the distance from the bullet to the beginning of the rifling in front of the chamber, and whether the cartridge will function in the rifle. The first factor usually produces the question.
In general, the closer the bullet to the beginning of the rifling ("leade"), then the better accuracy will tend to be. This is because the bullet has less chance to tip slightly as it makes the jump from the case to the leade, and bullets that start down the bore straightly tend to shoot accurately. This is why benchrest shooters often seat the bullets so that the bullet firmly encounters the lands. Black powder cartridge shooters who favor single-shot rifles often seat cast bullets to they're actually engraved by the rifling.
However, in either case the cartridge doesn't have to function through a magazine, because only a single round is loaded at a time. In fact, some benchrest rounds are loaded so "long" that if for some reason the round has to be extracted without firing, a cleaning rod is used to push it from the chamber. Otherwise the bullet might stick in the throat and only the powder-filled case is extracted. This makes another fine mess, Ollie.
So most of us seat bullets just shy of the lands. About .03 or approximately 1/32 of an inch is considered a good starting place - if the cartridge will function through the magazine. In most modern bolt-actions the chamber leade is cut so that a round loaded with an average bullet seated "short" enough to work through the magazine will be pretty close to the leade, with a little adjustment room.
But sometimes the leade allows for cartridges longer than the magazine. The Weatherby rounds with their well-known "freebore" are a good example. Freebore is a very long unrifled section, or "throat," between the case mouth and the leade. In accuracy theory this is a bad idea, since it gives the bullet more room to tip slightly before entering the rifling.
However, if the throat is only slightly over bullet diameter then accuracy is often very fine. A .30-caliber bullet nominally measures .308" in diameter, and a tight-fitting throat might measure .3085". Several rifles in my collection have "throats longer than the magazine" and all shoot very accurately. Three are Weatherbys chambered for the .240, .257 and .300 Weatherby Magnums, but another is a CZ 550 in 9.3x62 Mauser. In these rifles the length of the magazine is the only limit to OAL.
In tube-magazine rifles (usually lever-action) OAL is controlled by action function. Normally the rounds must fall within a fairly narrow range of OAL, otherwise they'll jam the action. Since crimping's recommended for tube-magazine rounds, most bullets come with a crimping groove in about the right place for most actions, whether the bullet is jacketed or cast. It's almost never a mistake to seat the bullets so that the case mouth can be crimped into the front edge of this groove, though action function should be checked with a dummy round or two to make sure.
Where there is some wiggle room, often a slight adjustment to bullet jump will improve accuracy noticeably. Some cartridge/bullet combinations will shoot better with a little less jump than .03", others with a little more. The Barnes company has long suggested .05" as a starting point for their all-copper X-Bullets, because they are harder to engrave than lead-core bullets. Be aware that less jump usually means more pressure - and more risk of leaving a bullet in the leade when extracting a loaded round.
The reason that the leade-adjusted OAL of a round in one rifle won't often work in another is simple: the distance to the leade varies from chamber to chamber, even in supposedly identical rifles of the same make. When manufacturers make a lot of rifles, they use the same reamer as long as it will last. They start with a maximum size reamer, and run it until it wears to minimum size. Thus your leade may vary slightly from mine, even if both rifles are Rugers chambered with the same reamer. In rifles made by various manufacturers, reamers from different makers will probably be used, which probably means slightly more variation.
There are excellent tools for determining the distance from the bullet to the leade, but this can also be determined with a dummy round. Seat a bullet well out in an empty, resized case, then try to chamber it, working the round through the magazine if the rifle has a magazine. At first it probably won't fit, either in the magazine or chamber, but eventually a point will be reached where it does just fit.
If this is in the magazine, and the round chambers easily, then you now have the OAL for that bullet in that rifle.
If it won't fit in the chamber, keep screwing down the bullet seating stem a half-turn at a time until the round will just fit in the chamber. Now, look at the round closely. The bullet will probably be marked just in front of the case mouth by the rifling in the leade. Take some 0000 steel wool and "erase" these marks, then turn the seating stem in another half-turn and re-seat the bullet. Try the round in the chamber again, then see if it's still marked by the leade. If so, erase the marks again and turn the seating stem down another half turn. Eventually the bullet won't be marked - and since most seating stems are threaded to about .05" a turn, you now have a dummy round with the bullet seated right around .025" from the leade. There's your starting OAL.
thanx guys i was begining to think i didnt get such a good deal on the gun if i was going to have to buy a new barrel for it already i just wanted to make sure the gap wasnt to large because my other rifles a lot closer so thanx again for taken some worry off my mind
nononsense thats a good article thanx for sharing [8D]