need help with load info

[jtech]

I am very new to reloading and would like to load Horandy's match 75 gr. bthp for a ar 15 that has a 1-7 twist.
I've checked my lee and lyman manuals and neither is using this exact bullet. The lyman manual I have is the 48th edition, it lists the hornady A max with a oal of 2.39 and sierra hpbt's in 69 & 77 gr's with a oal of 2.60. I know the oal will effect pressure from what I've read ( I can't measure it). I assume the oal difference between the sieera 77 grnr and the hornady A max 75 grnr is bullet shape. Is there a way to calculate a safe starting load or is there a published safe starting load?
Thanks in advance from another newbie!

[jtech]

SORRY for the typo sierra oal is 2.26 not 2.6 in the lyman manual.

[sk330lc]

75gr BTHP  2.250"  C.O.L.      From Sixth & Seventh Edition Hornady manuals..    Or MAG length.

A safe Starting Load is the Lowest start point in your manual. They show the same loads for the 75GR A-max and the BTHP.  Start Low and work Up Looking for presure signs. Your Lyman manual explains well what to look for.. Take it slow check everything over and over.  Be safe. 

[jtech]

The load for the A max may be the same but it is loaded to a longer oal which will effect pressure, 2.39 if memory serves. There has to be a reason, dependent on bullet shape not all 75 gr. bullets are the same. I'm new to this but there has to be a reason the manuals list different oal's and pressures. More or less bullet in the case will change everything or will it not?

[sk330lc]

You are right about COL changing pressures..  I'm sorry what I ment by the Loads being the same was. They show the Powder weights Being the same. The COL are Diff.  The 75gr A-max is a Much longer Bullet.
 If your going to use Hornady Bullets Buy a Hornady manual.  If your going to use Sierra Bullets Buy the Sierra Manual.  Both are very good books, alot of great Info.  Well worth the money in the end. plus you don't have to take my word or anyone else interpretation of the manauls.  Or bad spelling

[stimpylu32]

jtech

Yes the COL will affect your pressure to some extent , as will bullet shape . Bore bearing surface = more drag = more pressure .

However using the A-max data for the BTHP will not be a real problem provied you start at the starting load level and work up slowly .

Other factors will also come into play as it pertains to pressure , the powder burn rate , the powder charge , the powder fill of the case , the primer you use , the amount of throat in the chamber , the cut of the chamber itself ( high or low spec ) , all these will have an effect in what your load does .

The most important thing to remember is that Handloading is not an exact , as you can NEVER get the same load / gun combo that was used to find the listed load data because things change .

Just use safe loading practices as outlined in the manual's and you will be fine . 

stimpy

[jtech]

  Thanks all, that puts it in the perspective I was looking for. Time to get another manual! I was trying to figure out how to use a starting load from a Lee manual for a 75 gr. jacketed bullet (It doesn't list which bullet) that is loaded to min. oal of 2.25 (mag length). Figured I might be asking for trouble.
  Stimpy, thanks, don't know why I hadn't thought of using the A max starting load, but that solves my dilema. Very appreciated! I'd realy rather not discuss spelling for obvious reasons  .

[BBF]

Keep in mind that the Hdy info for their Srvice Rifle has a  1 in 9 twist.