new years glossary test

[bam1015]

Being fairly new hear and having gotten much great info on this site, i was wondering if we could compile a one stop thread with definitions of terms. many of you are so experienced that we throw around a lot of Terms that quite frankly confuse the heck out of us newbies...lol...Now ive have muddled through the site and figured out (or guessed at) the meaning of many of the terms but thought we could get a one stop thread with explainations and even pics when ever possible of such terms as : freebore,headspace,bearing surface,fire forming,annealing,jump,jam, and im sure thats only a partial list of which we can add as we go. i think not only as usefull info but also as a safety issue im sure the missinterpretation of some of these terms could be dangerous to some . now im sure some of you will point out some good reloading book that answers all these questions, let me know if there is, but i think some answers from many real world users like on this site would be informative.....and hopefully doesnt start too many arguements....lol

 

[BoydAllen]

Freebore: The part of the chamber that is directly in front of the part that is designed to accommodate the case necks of loaded rounds, and just behind where the rifling starts, usually with an angular transition to full land height. This is not the same as the distance from the end of the case neck to where a bullet makes contact with the rifling.
In this drawing, the freebore measures .188. http://www.the-long-family.com/images/6_5%20284%20Lapua%20Match%20long%20throat.jpg

Headspace: The distance between the bolt face and a standardized reference point in a rifle's chamber, properly measured by standardized gauges. Reference is more commonly made to the difference between what a chamber actually measures and the minimum, which is usually determined by some organization like SAAMI. For rimless bottle necked cartridges the reference point is a circle of specified diameter (which varies with the caliber) that falls somewhere the slope of the chamber shoulder. Semi-rimmed cases use the same method. Rimmed reference the surface that the front of the rim contacts, and belted cases where the front of the belt makes contact. Lacking a generally accepted term to describe it, shooters often mistakenly refer to case or cartridge headspace when they are talking about the clearance between cases and chambers. This does not usually cause problems as long as everyone understands what is meant.

The bearing surface of a bullet is that part that is of sufficient diameter to make contact with the bore as it travels down the barrel. Practically speaking measurement of this may not be from points that are actually of that diameter, but just adjacent to them, and as long as the same tool is used for all measurements there should be no problem with the usefulness of the results.

Fire forming may have more than one meaning. Some cases, such as the PPCs, as made from .220 Russian brass, require that the parent case be fired to form their final shape. In these cases the difference in dimensions before and after may be considerable. In other cases the brass is nominally the same shape as the chamber, but the fit in the chamber is looser than is optimal for best accuracy, and/or the straightness of the case (which may be referred to as concentricity) is not as good as it will be after one or two firings, in the chamber that it is intended for.

Annealing is heating metal to change its hardness. Cases are work hardened by repeated firing and sizing, which may lead to undesirable changes in their characteristics. In the extreme case, necks and or case bodies my split when they become so hardened that they lack the required elasticity to survive being fired. When annealing cartridge cases, strict attention must be paid so that the heads of cases are not softened in the process. This can lead to catastrophic results that very likely would endanger the life of the shooter. I would respectfully suggest that those new to the sport stay away from this operation until they have become thoroughly familiar with all of the details of the subject, keeping in mind that there is a huge amount of bad advice on the subject that is available in print and on the internet. If you want to read good information on the subject, I suggest Ken Light as an excellent source.

Jump is how far a bullet moves, from its as loaded position, to make contact with the rifling.

Jam is a widely misused term. The original, and proper use is the maximum length that a bullet may be loaded to without being pushed back into the case as it is chambered, using the same neck tension that will be used for actual loading. Many years ago benchrest competitors adopted the technique of loading a bullet slightly longer than "jam" chambering the dummy round, or loaded round, if at the bench at a range, or with the striker assembly removed from the bolt elsewhere, and then recording the length, usually measured using a tool that contacts the bullet on its ogive, due to the irregularity of bullet tips. By determining what this maximum or Jam is, one may then easily adjust a seating die to any length less than that.

The corrupted use of this term uses it to refer to any seating that is longer than that which just touches the rifling, the usual being " I seat my bullets jammed .015." The proper way of saying this would be .015 longer than touch or touching. It is not that I think that those who misuse the term are less worthy than those who use it properly, it is just that in most cases we are self taught, and it is highly likely that they have not been exposed to a knowledgeable source.

On this same subject, I generally seat double radius 6mm short range bullets a few thousandths (.003 to .004) off of (or shorter than) jam. Of course this length, will vary with neck tension, and increase in direct proportion to throat wear. Others prefer to reference the point at which bullets touch the rifling, and indeed there is nothing wrong with this system, given that we now have tools available that make taking this measurement much easier than when I first started reloading. I feel confident that the origin of the term jam was well before any of these tools were available.

Of course if anyone disagrees with any of this, feel free to comment, and correct.

Boyd Allen

 

[bam1015]

Freebore: The part of the chamber that is directly in front of the part that is designed to accommodate the case necks of loaded rounds, and just behind where the rifling starts, usually with an angular transition to full land height. This is not the same as the distance from the end of the case neck to where a bullet makes contact with the rifling.
In this drawing, the freebore measures .188. http://www.the-long-family.com/images/6_5%20284%20Lapua%20Match%20long%20throat.jpg

Headspace: The distance between the bolt face and a standardized reference point in a rifle's chamber, properly measured by standardized gauges. Reference is more commonly made to the difference between what a chamber actually measures and the minimum, which is usually determined by some organization like SAAMI. For rimless bottle necked cartridges the reference point is a circle of specified diameter (which varies with the caliber) that falls somewhere the slope of the chamber shoulder. Semi-rimmed cases use the same method. Rimmed reference the surface that the front of the rim contacts, and belted cases where the front of the belt makes contact. Lacking a generally accepted term to describe it, shooters often mistakenly refer to case or cartridge headspace when they are talking about the clearance between cases and chambers. This does not usually cause problems as long as everyone understands what is meant.

The bearing surface of a bullet is that part that is of sufficient diameter to make contact with the bore as it travels down the barrel. Practically speaking measurement of this may not be from points that are actually of that diameter, but just adjacent to them, and as long as the same tool is used for all measurements there should be no problem with the usefulness of the results.

Fire forming may have more than one meaning. Some cases, such as the PPCs, as made from .220 Russian brass, require that the parent case be fired to form their final shape. In these cases the difference in dimensions before and after may be considerable. In other cases the brass is nominally the same shape as the chamber, but the fit in the chamber is looser than is optimal for best accuracy, and/or the straightness of the case (which may be referred to as concentricity) is not as good as it will be after one or two firings, in the chamber that it is intended for.

Annealing is heating metal to change its hardness. Cases are work hardened by repeated firing and sizing, which may lead to undesirable changes in their characteristics. In the extreme case, necks and or case bodies my split when they become so hardened that they lack the required elasticity to survive being fired. When annealing cartridge cases, strict attention must be paid so that the heads of cases are not softened in the process. This can lead to catastrophic results that very likely would endanger the life of the shooter. I would respectfully suggest that those new to the sport stay away from this operation until they have become thoroughly familiar with all of the details of the subject, keeping in mind that there is a huge amount of bad advice on the subject that is available in print and on the internet. If you want to read good information on the subject, I suggest Ken Light as an excellent source.

Jump is how far a bullet moves, from its as loaded position, to make contact with the rifling.

Jam is a widely misused term. The original, and proper use is the maximum length that a bullet may be loaded to without being pushed back into the case as it is chambered, using the same neck tension that will be used for actual loading. Many years ago benchrest competitors adopted the technique of loading a bullet slightly longer than "jam" chambering the dummy round, or loaded round, if at the bench at a range, or with the striker assembly removed from the bolt elsewhere, and then recording the length, usually measured using a tool that contacts the bullet on its ogive, due to the irregularity of bullet tips. By determining what this maximum or Jam is, one may then easily adjust a seating die to any length less than that.

The corrupted use of this term uses it to refer to any seating that is longer than that which just touches the rifling, the usual being " I seat my bullets jammed .015." The proper way of saying this would be .015 longer than touch or touching. It is not that I think that those who misuse the term are less worthy than those who use it properly, it is just that in most cases we are self taught, and it is highly likely that they have not been exposed to a knowledgeable source.

On this same subject, I generally seat double radius 6mm short range bullets a few thousandths (.003 to .004) off of (or shorter than) jam. Of course this length, will vary with neck tension, and increase in direct proportion to throat wear. Others prefer to reference the point at which bullets touch the rifling, and indeed there is nothing wrong with this system, given that we now have tools available that make taking this measurement much easier than when I first started reloading. I feel confident that the origin of the term jam was well before any of these tools were available.

Of course if anyone disagrees with any of this, feel free to comment, and correct.

Boyd Allen

That is some great input and exactly what i was wanting ,i hope others respond with more terms that need good definitions and as i thought you have shown missunderstanding of some of these terms "could" be dangerous to unschooled users.....i have one question...if i set up a bullet .015 longer than touch, when chambering the round will it normally just push the bullet back into the case or will it push the bullet into the rifling ...or depends on neck tension as to which it does?

 

[BoydAllen]

Different ogive shapes are able to be pushed into the rifling different amounts. If you like doing experiments, seat a bullet long, in a case that has been sized as you would for shooting, measure the OAL, first off of the tip of the bullet, and then off of the ogive, with the appropriate tool, and then chamber the case/bullet and after unchambering it remeasure it, recording all measurements. (If the measurements didn't change you didn't seat long enough.) Be sure to LIGHTLY grease the engagement surfaces of your bolt lugs before chambering. Next use what ever method you like to determine what bullet seating depth has a bullet just touching the rifling. Measure this length off of the ogive after you have seated another of the same bullets in a similarly sized case so that it just touches the rifling when the case/bullet is chambered. Now, subtract the touch length from the jam length, and post the difference, the bullet, and the difference in the diameters of the case neck before and after seating bullets (the latter measured over the bullets pressure rings if that applies).