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reading manual... questions
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sydsdaddy
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OK so Igot my lymans manual today and reading andwhen looking at their loads for a .308 using 168gr sieera matchking bullets and I have a couple of questions about the measurements information given, may sound dumb, but maybe I am.

They have 2.775" OAL, is this over all length or something else, cant find it explained in the manual, if so max. or min.?

Also BC:.462

SD: .253

What am I looking at here, and why is it relevant?

OK finally what is meant when one is talking of the" lands" and why is it important.

Like I said pretty dumb, I just dont want to have any confussion. Thanks, God Bless.


John 3:16
 
Posts: 31 | Registered: 21 September 2008Reply With Quote
Slowpoke Slim
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First of all, NONE of your questions are dumb. Anyone who says they are needs their *sses kicked for being a jerk. NEVER be afraid to ask questions about reloading.

OAL is Over All Length of loaded cartridge. In your manual, it is the seating depth that they seated that bullet to for those loads they developed for the manual.

BC is Ballistic Coefficient. It is a brainiac formula used to determine how easily a bullet "slips" through the air, and is mainly used in comparison between different bullets to assist a loader/shooter choose a bullet that may have better long range characteristics for less drop and less wind deflection off target from crosswinds.

SD is Sectional Density. This is a simillar brainiac formula derived number to compare penetration characteristics between similar bullets to help the loader/shooter determine which bullet may give them the penetration they need for a given game animal.

The "Lands" refer to the "high spots" on the rifling in the barrel, and is often used when speaking about the chamber/throat area of the barrel and at what distance the bullet will contact the lands, how much "free bore" or distance the bullet travels on ignition of the cartridge before it engages the rifling and begins to spin.

Feel free to PM me ANYTIME you have any questions about reloading, if I don't know the answer, I'll find it for you or point you to the proper reference point to find it.

Never stop asking when you have questions, everyone has questions sooner or later.


Si tantum EGO eram dimidium ut bonus ut EGO memor
 
Posts: 1147 | Location: Bismarck, ND | Registered: 31 August 2006Reply With Quote
Jim C. <><
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quote:
OAL is Over All Length of loaded cartridge. In your manual, it is the seating depth that they seated that bullet to for those loads they developed for the manual.

Correct. Many seem to think the book OAL is something engraved in stone and deviation will cause some great danger. That isn't true.

Use the book OAL to develop your own loads for best accuracy by varying charges in small amounts. When you get your best accuracy, then vary that OAL a bit each way (move in maybe .010" steps but don't jam the bullets into the rifling) to see if accuracy improves. It often does.

Don't be concerned about exposing what you don't know. All of us had to start exactly where you are. Many of us are here specifically to help others get past that stage safely.

SD - In these days with a great variety of premium bullets, the Sectional Density of a bullet is largely irrelivant as a predictor of perfomance on game.
 
Posts: 1615 | Location: South Western North Carolina | Registered: 16 September 2005Reply With Quote
Winchester 69
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My Lyman's 47th has a glossary. Wonder why they've dropped it? It's only two pages.
.
 
Posts: 1184 | Registered: 21 April 2007Reply With Quote
308Sako
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quote:
Originally posted by sydsdaddy:
OK so Igot my lymans manual today and reading andwhen looking at their loads for a .308 using 168gr sieera matchking bullets and I have a couple of questions about the measurements information given, may sound dumb, but maybe I am.

They have 2.775" OAL, is this over all length or something else, cant find it explained in the manual, if so max. or min.?

Answered already, it's the length that Lyman used for their work up. YOU DO NOT HAVE to load to this length.

Also BC:.462 Answered, a mathmatical way of describing the bullets ability to maintain it's velocity.

SD: .253 Yup, already answered by SPS.

What am I looking at here, and why is it relevant? The questions you asked are very pertinent to your understanding of the loading process and the actual cartridge as a functioning system. Pressure of gases is directly related to volume and how far a bullet is seated into a case directly affects volume. The distance a bullet is from the land s is another factor which is worth considering, but functioning through your rifle's magazine or action is a more primary concern. for singleshots, then you are free to load to what might be considered non-standard lengths. A manual gives you "their" components and "their" results, you should always follow the advice of starting lower and working up for many to be learned lessons.

OK finally what is meant when one is talking of the" lands" and why is it important. The raised portion of the rifling just past the chambers throat or leade... as answered above. It is a good point of reference when recording notes on your loads, such as -.040 from the lands or + .010 into the lands. Many benchrest shooters consider contact when the bullet will show small square marks from where this contact is made. Works for me and is consistant.



Like I said pretty dumb, I just dont want to have any confussion. Thanks, God Bless.






Member NRA, SCI- Life #358 28+ years now!
DRSS, double owner-shooter since 1983, O/U .30-06 Browning Continental set.
 
Posts: 3611 | Location: LV NV | Registered: 22 October 2002Reply With Quote
sydsdaddy
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Thanks so much guys for all the help so far. Im sure Ill be back.


John 3:16
 
Posts: 31 | Registered: 21 September 2008Reply With Quote
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