Reading manual bullet questions

[sydandpaigesdad]

OK I have been reading my Lymans manual and have some questions regarding the load recommendations for the. 308

1st What is meant by OAL, if overall length is it a measure of max. or min.
They have the sieera mk as 2.775" OAL

2nd They have BC:.462 AND SD:.253. What do they mean and why are they important?

Lastly, Ihear people referring to"the lands", what does this refer to and what is the importance?

I know these are elementary questions but I just want to be sure I absolutely understand things perfectly, thanks in advance, God Bless.

 

[Birdhunter1]

OAL is the overall length of the casing and bullet.
B.C refers to ballistic coeffecicient. Basically it is a measure of the aerodynamics of the bullet and how it will be effected by wind drift and how quickly it drops an looses velosity. The higher the BC the more aerodynmaic it is so to speak. As an example my .30-30 loads (125 grain Sierra JHFP @24xx fps) have a b.c of about .119, my .223 loads (52 grain Hornday AMAX @3200 fps) are about .247 and a Cheytac (.408 caliber super long range sniper rifle, supersonic at +2000m) has a bc of about .989.

The lands is the part of steel (or flat spots) between the rifling grooves that are cut into the steel. From the shoulder you have the area where your case necks are, the in front of your case there is a portion of the barrel that is smooth and larger diameter than the part where the rifling starts. Some call this the free bore, what it does is allows space enough for the maximum OAL of factory loaded ammunition. Some factory loads will be shorter than other so a rifle manufacturer has to go by what the longest load that is commerically available that will be placed in that gun. Think of a .243 load with a 55 grain bullet and a 105 grain bullet, big difference in length.

 

[ants]

Hello, friend. Not trying to be difficult, but please go back to the first page of the Lyman reloading manual and read it again. The chapters before the load data explain nearly all of the basic concepts. Then you can read the load data and understand it more completely.

 

[sydandpaigesdad]

Ants You Just Made Me Leave This Forum Thanks For Being A Jackass, If You Didnt Want To Answer You Shouldnt Have

 

[ranger335v]

dad, in defense of ants, I think you missed his meaning.

The questions you asked have been answered far better in many books than any of us can post in a brief answer on the web.

 

[steve4102]

Ants You Just Made Me Leave This Forum Thanks For Being A Jackass, If You Didnt Want To Answer You Shouldnt Have

I think Ant's response was about as nice and sincere as one can get when trying to instill into a new reloader that the first half of the manual should be read over and over. At least he didn't say RTFM or Read the F****** Manual which has been used on this and many other forums several times.
I think you are over reacting, stick around, you'll like it here.

 

[MCMXI]

1st What is meant by OAL, if overall length is it a measure of max. or min.
They have the sieera mk as 2.775" OAL

sydandpaigesdad , we're all here to learn so I hope you reconsider your position of "leaving this forum". Anyway, OAL can be confusing particularly for someone starting out in reloading. As an example, let's say you want to reload for a .308 and you made the smart decision to load 168 grain Sierra MatchKing HPBT bullets. If you refer to Sierra's manual (50th Anniversary Edition) it lists the following specifications.

Maximum OAL: 2.810"
Cartridge OAL for 168gr SMK HPBT: 2.800"

The manual lists 20 different powders for the 168 grain bullet but simply states cartridge OAL of 2.800"

Now let's say you want to get a second opinion and you refer to "Modern Reloading Second Edition by Richard Lee". You look up the .308 Winchester cartridge and the schematic shows the length of a loaded round to be 2.810". The figure doesn't explicitly say "Maximum OAL" though. So now you look up the loads for a 168 grain jacketed bullet and you notice that there's a "Minimum OAL" length listed for each of the 16 different powders but no absolute OAL as in the Sierra manual. Reloder 15 has the Minimum OAL listed as 2.700" and a bunch of others show 2.800". So now you look at another manual, Speer Number 11, and find that they don't list any OAL dimensions either Minimum or Maximum. Confused yet? If so, then welcome to the world of reloading. How can one manual give the Max. OAL and the same cartridge OAL for 20 different powders, another manual list the same value simply as OAL and then list Min. OAL values for 16 different powders and another manual give no information at all about Min, Max or cartridge OAL?

So what's going on? The Max. OAL is selected so that the loaded round will chamber in "standard" chambers and possibly magazines (if there's a standard for those). If you exceed that length, the bullet might contact the lands of the barrel before the action is closed. This most likely won't happen on a Remington .308 since the throat is excessively long. Sierra probably developed the loads listed at the given cartridge OAL so that's how they report their data. If a manual lists Min. OAL for a specific powder (as Lee does), you can bet that they developed and tested the load at that OAL and are concerned about a possible pressure increase in the case if you seat the bullet deeper. In the case of Lee, you have the "safe" option to seat the bullet so that the OAL is somewhere between the Min. OAL given and the Max. OAL given. You might ask why Lee changed the OAL for the same bullet but with different powders. It's possible that they were trying to keep the loads within a certain CUP, PSI or velocity range. I have no idea why Speer doesn't list ANY cartridge dimensions. Perhaps their attitude was "if you're smart enough to reload, you're smart enough to figure it out". Like most aspects of human life, reloading has developed over the years in a random, disorganized, non-standardized sort of way. If a group had got together (such as SAAMI) 200 years ago and come up with a set of standards BEFORE we began reloading, maybe every manufacturer and manual would be on the same page (no pun intended). That didn't happen so we're left with the task of making sense of the nonsense.

From Wikipedia ...

BC = SD/i = M/(i *d^2)

where:

* BC = ballistic coefficient
* SD = sectional density, SD = mass of bullet in pounds or kilograms divided by its caliber squared in inches or meters; units are lb/in2 or kg/m2.
* i = form factor, i = drag coefficient of the bullet/drag coefficient of G1 model bullet (G1 drag coefficient = 0.5190793992194678)
* M = Mass of object, lb or kg
* d = diameter of the object, in or m


From me ...

A good "rule of thumb" for BC values for a bullet is ...

Muzzle Engergy *0.5 = BC * 1000 (yards)

... in other words, your bullet with a BC of 0.462 will have half of its initial muzzle energy at approximately 460 yards.

I hope some of this is helpful.

 

[ants]

Thank you 1858, for the patient and thorough reply.

I have 6 manuals from various publishers going back to the 1972 edition of the Shooter's Bible Reloaders Guide. I read them all constantly. That's why I like to offer that very advice. It's what I do myself, and it leaves me with lots of answers and very few unanswered questions.

 

[MCMXI]

ants, I agree with the advice that you gave the OP and it's a pity that he took it the way he did. There's no easy way to learn this stuff. Knowledge and true understanding come with hard work but sometimes we need a little help. As for manuals, the Modern Reloading Second Edition by Richard Lee has HORRIBLE load data but the first 13 chapters (200 pages) are excellent and should be read by anyone thinking of reloading. Sometimes it's better to jump in to get some idea as to what's what THEN read the manual once you know enough to understand what the manual is referring to. I did just that last week at work. I conducted some bullet hardness tests using a Rockwell 524T hardness tester without knowing much about Rockwell hardness tests or the instrument. After obtaining some "data", I read the manual , did some research on the internet and now I feel confident that I can obtain accurate, meaningful and repeatable results when I retest the bullets.

 

[Zeede]

It's odd how he capitalizes the first letter of every word in his rather immature response to some very good advice from ants, yet his original post was written "normally".

At any rate, I don't see how you can read the Lyman's Guide all the way through to the load data and not catch what the OAL is. Lyman is pretty good about pounding certain things into your head. Heck I know one guy who was a nervous wreck about reloading his own stuff after reading the Lyman's Guide

Cameron

 

[Hey_Allen]

RE the capitalization of the first letters, many of the forum software packages will do that to a post when someone types in ALL caps, rather than let them 'shout' at everyone.

I think it looks goofy, but hey, whatever they want to do..

I hope the OP reads any of the follow up posts, as I've found the various posters here to be highly informative, even when I'm not asking questions much!

 

[Walkalong]

We all had a bit of trouble when we first started. Terms we take for granted now we did not have a clue about then. Be paitent, answer questions, try not to make a new reloader uneasy about asking questions. Yea, some of the questions are simple to us, and yea, maybe they could have found the answer by more searching, but they asked us. There is nothing like getting the questin answered vs just reading about it somewhere that instills more confidence in people.

I know these are elementary questions but I just want to be sure I absolutely understand things perfectly, thanks in advance, God Bless.

Now that sounds like sincere appreciation for help with simple questions even before the help is given.

 

[sydandpaigesdad]

Ants a sincere apology

Seems I did indeed overreact, and to be honest I lashed at you wihen, in reality, it was pms from a couple of other guys that got me going. So as a man I admit I was wrong and wanted to put it here for everyone to see. I have and did read the part in my Lymans manual, just wanted to be sure I understood what I was reading, you know double check my brain in a sense. No excuse I absolutely understand and I hope you accept my apology as well as anyone else who may have been offended by my immature display.

Michael

 

[Hud]

sydandpaigesdad,

Interpretation of responses has sometimes ruffled my feathers as well, ...happens to all of us, but you get my vote as a stand-up guy for your appology.
You could have just left, which would have been a loss for all of us.
I hope you stay, because you will one day be fielding questions from new folks with your personal knowledge & that gained by being a member of this forum.

Regards, Hud

 

[ants]

No problem, friend. How are Syd and Paige? I hope everyone is fine.

If you haven't had a chance to discover it yet, go to the Hornady web site and click on the Ballstics Resource button in the center of the home page. Spend some time wandering through it, I am always amazed at the wealth of information they have.

Did you get the answers to your questions?

The OAL listed in load data can be seen as the Minimum overall length for that particular bullet and gunpowder charge as tested by that particular laboratory (obviously each different laboratory tests a different OAL, so you gotta pay attention carefully). It is an easy way of gauging how deep you can seat the bullet into the brass case, because you don't want to seat too deep. The deeper you seat the bullet, you decrease the volume available for the gunpowder explosion. If the volume is too small, the explosion can be far too extreme. So the Minimum OAL is a handy guideline to stay on the safe side, but remember that it is always specific to a particular bullet and gunpowder charge. If you use a different bullet, it is wise to choose a longer overall length. Most of us choose a relatively long overall length that seems to work best for the gun and its magazine. No need to use the minimum OAL just because it is printed in the data table. [Sometimes OAL is called COAL. The C stands for Cartridge.]

BC is Ballistic Coefficient. For those who shoot for maximum accuracy at very very very long ranges, the BC can help estimate the bullet's ability to maintain velocity by avoiding drag and turbulence. For super-long-range shooting, it helps determine how long the bullet will remain at supersonic speed before it transitions down to subsonic speed. During the transition, the shock wave overtaking the bullet from the rear can knock the bullet off course. For most of us shooting at about 200 yards or less, BC isn't a big deal unless you want to make a big deal out of it.

SD Section Density is often used by some people to estimate how a hunting bullet will penetrate game (let's be civilized and assume you're shooting at non-human bodies). Other things being equal (like impact velocity, bullet design and material, etc.) the higher the SD number, the better the bullet's penetration. In other words, a skinny bullet of a given weight tends to penetrate better than a fat bullet of the same weight, because it concentrates the same force on a smaller area of the target. Some large game with thick skin and heavy bone requires penetration to get to the internal organs, smaller game with thin skin does NOT require extreme penetration. Also, some believe that the fat bullet (lower SD) will hit harder and impart its energy more quickly, which they believe to be favorable for those bipedal non-game targets.

When they cut the rifling in a barrel, the deep groove is called the 'groove' and the high part is called the 'land'. Obviously the grooves and lands stretch in a twisted helical pattern down the entire bore, but you may have seen the word 'land' in regard to the beginning of the lands right where the chamber transitions to the rifled bore. There is a general principle in high-accuracy shooting that it is valuable to build up a certain amount of pressure behind the bullet before it starts moving out of the brass case. By loading the bullet so it almost touches the beginning of the lands at the end of the chamber (usually about 0.020" before the lands) you can use the lands to help hold the bullet in the case a little longer to let the pressure build up. [This is my own personal advice, but if you don't have a rifle and ammunition and optical sight and shooter capable of maximizing the last 1 percent of accuracy at extremely long range, seating the bullet up near the lands will do virtually nothing for your shooting performance. All the other uncontrolled variables will greatly overshadow it. But that is just my own personal opinion. Your experience may differ.]

If you visit that Hornady site, spend some time at the section called 'internal ballistics'. It's pretty cool. I don't know if they cover this same material, but they tell you a lot about how the powder discharges into hot gas, how the hot gas expands, how the bullet engages the lands, how it travels down the bore, how the brass case behaves during discharge, and lots of cool stuff.

 

[Claude Clay]

too complicated,
the lands am what the sailor wants to see after being at sea for too long.
say good-night gracie

 

[ants]

Good night, Gracie

 

[Walkalong]

Good night John Boy.

 

[ilike223s]

If your reading and using the lyman reloading book, it explanes every question you have,take your time,if ur reloading be safe not sorry.Read all you can find,