Noob questions - 9mm and Lyman 49th edition


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Scuba_Steve
October 7, 2012, 03:41 PM
I have been reloading .45acp for about a month with good results. I am now starting to reload 9mm and have some quesitons I didn't run into with the 45acp reloads.

1) I am loading 124gr. Montana gold JHP. The lymnan book has 125gr. JHP listed. I assume I can use these suggested starting grains, correct?

2) The schematic for 9x19 shows an OAL of 1.169, yet the tables show a much shorter OAL, 1.075 for 125gr. JHP. I'm assuming 1.075 is the absolute minimum, not recommended length, correct? (my research shows people seem to use 1.120 - 1.150 length for these bullets).

3) For each table of load recommendations by bullet weight, they have the letter in bold "BC" and "SD" what does this stand for?

Hope these quesitons are not too dumb, I really have done my research and could not find answers to these questions.

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rcmodel
October 7, 2012, 03:49 PM
1. Yes.

2. 1.169" is the SAAMI MAX length for any bullet shape. Longer then that will not fit any many pistol magazines.
The OAL shown with each bullet is what the load was tested at, and probably what you should use until proven otherwise. The Sierra 125 JHP they tested has a very short ogive, or nose, and if seated longer would jam into the rifling in many pistol chambers. A bullet with a more gradual ogive shape such as a RN could be seated longer without contacting the rifling.

OAL is entirely dependent on the bullet design, and some will be shorter then others because they have a different ogive shape, weight, or construction.
For instance, comparing a FP and a HP of the same weight and manufacture will find the HP to be longer then the FP.

3. BC =Ballistic Coefficient.
SD = Sectional Density.
There is some discussion of BC on page 76 of the Lyman manual.
In simple terms, the higher the number, the more streamlined the bullet is.

The formula for SD is on page 453.
In simple terms, bullets with a higher SD number and similiar construction will penetrate better then one with a low number because they are more "arrow like"..

rc

tightgroup tiger
October 7, 2012, 05:25 PM
You can go longer than the advertised OAL per bullet your using but obviously don't go shorter.

Other then what RC said you will find out that the chambers in a lot of 9mm's have different lengths in the bullet leade. I spelling it wrong on purpose so you know I'm not talking about the bullet.

For instance my Keltec pf-9 has a maximum leade of 1,075 for a 124gr Hornady XTP because longer than that will jam the bullet into the rifling of the barrel causing problems , where my Ruger SR-9, I run the OAL out to 1.135"and they will work fine, because my PF-9 has a much shorter bullet leade than the SR-9.

RC always says to take the barrel out of the pistol and drop a loaded round in the chamber, if it drops in and goes plunk, and dumps right back out again, it not to long of a OAL, as long as you still have good neck tension.

In his words, use the barrel for an OAL gauge since that's what your shooting out of anyways.

If you load for several 9mm's and want your ammo to work in all of them, then use the barrel with the shortest leade for you OAL and you can't miss.

srtolly
October 7, 2012, 05:39 PM
Glad I found this post. I'm loading .40 and .45 now and just starting 9mm and had the same questions. Thanks.

CZ57
October 7, 2012, 07:15 PM
As rcmodel points out, the SIERRA 125 has a very short ogive. One reason I use the data where they loaded it as a worst case scenario for 124,125 gr. JHPs in 9mm. The bearing surface is about as long as you'll find at this weight causing the highest amount of friction in the bore and almost always loaded shorter than many other JHPs in the same weight class.

For a good 124 gr. JHP, I suggest the 124 gr. Remington JHP which has a rounded ogive and can be loaded longer, they can also be purchased in bulk packs. How long it can be loaded is determined by the leade of the barrel in your gun. When I can, I like to use Vihta Vouri's recommendation for OACL at 1.142"/29mm. For CZ pistols I had to load them shorter at 1.122"/28.5mm. I drive them hard with Ramshot Silhouette and Vihta Vouri 3N37 I used prior to switching to Silhouette. www.ramshot.com ;)

Scuba_Steve
October 7, 2012, 08:47 PM
Thanks to all for the straight up answers. I never thought I would reload, but between the $ crunching, a new winter activity, and the opportunity to learn, I am really enjoying this new hobby.

I have much to learn, but it has been a great way to enjoy some quiet and productive time alone.

moto_stevo
October 8, 2012, 10:20 PM
As stated use your barrel as a gauge. Drop a new bullet in and use a spent casing ( before resizing) and slide it down over the bullet until it seats down as far as it can go. Carefully pull it out and measure. Do this several times with several casings to get a good average number. Then deduct .015", and that is YOUR max OAL for THAT bullet/barrel combo

bds
October 8, 2012, 11:59 PM
as rcmodel and others posted, determining the Max OAL (http://www.thehighroad.org/showthread.php?t=506678) using the barrel is a good start.

Once you determined the Max OAL, you next need to determine the OAL that will reliably feed/chamber from the magazine when the slide is released - I refer to this OAL as the Ideal OAL. As some posted, this may be the same or shorter than the Max OAL and may vary for different pistols. I load for multiple pistols and often use the OAL that will work in all the pistols reliably. Note that this "working" OAL will often be different from the OALs in published load data as using the OAL in load data WILL NOT ensure your finished rounds will reliably feed/chamber in YOUR pistols.

Once you determined the OAL that works in your pistols, then you can conduct a full powder workup from start charge to determine the charges that will reliably cycle the slide and produce accurate shot groups.

srtolly
October 9, 2012, 12:44 AM
I'm with Scuba Steve, great winter activity to keep out of trouble with the wife. I am appreciate the info on max OAL, I never thought it could be done that way. Something to do tomorrow now.

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