Determining correct OAL?

[jakeb]

Hey Guys,

I'm about to start working up some loads for my G19 (KKM Barrel).

I'm seeing a lot of different load data where the OAL is different from one another.

What would be the most appropriate way of determining what OAL to use for a load? I don't have a chronometer.

My loads will consist of:

Starline Brass

124gr MGB

WSP Primers

TiteGroup (4.0, 4.1, and 4.2 drops)

Any help would be appreciated.

Thanks!

Jake

[Duane Thomas]

There's really no one, correct answer to that question. I use 1.150" if it matters. I know some people run shorter OALs but find the slightly longer 1.150" feeds a bit more smoothly - in my guns.

You really do need to somehow access a chrono if you're going to know what your load is actually doing, velocity and power factor-wise. You can't rely on guesswork or book published statistics. There are just WAY too many variables at play here for that to work.

[jakeb]

I'm mostly looking for a practice/plinking load. I'm new to IDPA/IPSC at my club and would like to figure the most economical/safest 9mm load recipe to get me up to speed.

[Sarge]

Hey Jake. If you have not been welcomed to the forums yet, then welcome.

As much as I detest the phrase, "the search function is your friend", it really is the best way to find what you are looking for in this case. Or just start reading the whole 9mm reloading section. But a 124 MG CMJ with 3.8 TG should get you pretty close to 125 PF with an oal of around 1.14. I needed 4.2 in my M&P but glocks can be faster. After loading several thousand rounds I finally saw the light recently to check your reloads for fit in your actual barrel. Most here will tell you to load as long as possible to fit magazines and chamber without the bullet touching the rifling. But the above numbers should get you pretty close. Be careful and read some good reloading manuals and this forum and you will learn a ton.

Good luck.

[jakeb]

Thanks Sandman and Duane!

In further reading (using search and google site search) I've come up with the following...

Seating depth and OAL/COL can affect pressure and velocity. So starting it would it be safe to assume that I load my cartridges at 1.14" with different powder charges until I find my sweet spot with the powder charge. Once this is done I can begin testing (with a chronometer) deeper seating depths and see what comes up the best.

Does this sound like a safe way to proceed?

[Darrell]

The MG 124 JHP touches the rifling on my G17 @ 1.193. My load is 4.0 Tightgroup, with Mg 124jhp at 1.120 crimp .3785. for IPSC. My accuracy load is 5.4 of Power Pistol for my G34. Some people like to load as long as possible to fit the mag, but in my experience every bullet has a sweet spot. MG 124 JHP for me the sweet spot was 1.120.

Gun Bullet WT Pwdr Wt Primer cas OAL AVG ES SD PF Gp size

G17 Atlanta 147 ? W/W 1.100 898 24 5 132.0 3.42 15.00 25 yd bench .3765 crimp

G17 Bayou 125 Clays 3.40 Magtec W/W 1.150 0.0 5.33 15 yd benched 10 shot group 9/18/2009

G17 M. G. CMJ 147 T. G. 3.20 Magtec W/W 1.100 867 25 7 127.4 2.63 3-5 shot 20 yd

G17 M. G. CMJ 147 T. G. 3.40 Magtec W/W 1.100 894 40 9 131.4 2.65 3-5 shot 20 yd

G17 M. G. CMJ 147 T. G. 3.60 Magtec W/W 1.100 930 30 8 136.7 2.75 3-5 shot 20 yd

G17 M. G. JHP 124 P.P. 5.2 W/W mix 1.120 1051 37 10 130.3 2.26 10 25 yd Ransom 88deg 6/12/08

G17 M. G. JHP 124 P.P. 5.4 W/W mix 1.120 1079 40 12 133.8 2.73 10 25 yd Ransom 88deg 6/12/08

G17 M. G. JHP 124 P.P. 5.6 W/W mix 1.120 1110 34 10 137.6 1.76 10 25 yd Ransom 88deg 6/12/08 Best Group

G17 M. G. JHP 124 P.P. 5.8 W/W mix 1.120 1128 52 16 139.9 2.10 10 25 yd Ransom 88deg 6/12/08

G17 M. G. JHP 124 P.P. 6 W/W mix 1.120 1163 41 14 144.2 1.88 10 25 yd Ransom 88deg 6/12/08

G17 M. G. JHP 124 T. G. 4.10 W/W Mixed 1.120 1107 40 12 137.3 3.21 10.00 25 yd Ransom 85deg 4/11/08

G17 M. G. JHP 124 T.G. 4.00 Magtec R-P 1.120 0.0 3.75 15 yd benched 10 shot group 9/18/2009

G17 M. G. JHP 124 T.G. 4.00 W/W W/W 1.120 1073 30 11 133.1 2.60 10.000 25 yd Ransom 88deg 6/12/08

G17 P. Delta FMJ 124 A. S. 4.20 W/W mixed 1.150 1028 31 9 127.5 2.02 10.00 20yd 10 shot avg, 70 deg windy W/O flyer

G17 P. Delta FMJ 124 N320 4.20 W/W Mixed 1.150 1052 33 10 130.4 3.70 10.00 25 yd Ransom 85deg 4/11/08

G17 P. Delta FMJ 124 N320 4.20 W/W Mixed 1.150 1047 68 18 129.8 4.50 10.00 25 yd Ransom 85deg 4/11/08

G17 P. Delta FMJ 124 N320 4.30 W/W Mixed 1.150 1061 44 11 131.6 4.40 10.00 25 yd Ransom 85deg 4/11/08

G17 P. Delta FMJ 124 N320 4.30 W/W Mixed 1.150 1058 20 6 131.2 6.80 10.00 25 yd Ransom 85deg 4/11/08

G17 P. Delta FMJ 124 P.P. 5.40 W/W Fed 1.120 0.0 1.85 1.60 10 shot group 15yds and best 9 4/3/2009

G17 P. Delta FMJ 124 T. G. 4.00 W/W W/W 1.120 0.0 1.70 1.10 10 shot group 15yds and best 9 4/3/2009

G17 P.Delta JHP 124 WSF 4.80 W/W PMC 1.120 0.0 3.00 9.00 ransom Rest 25yd 4/16/09

G17 P.Delta JHP 124 WSF 4.80 W/W W/W 1.120 0.0 2.55 9.00 ransom Rest 25yd 4/16/09

G17 P.Delta JHP 124 WSF 5.00 W/W W/W 1.120 1090 25 7 135.2 2.15 9.00 ransom Rest 25yd 4/16/09

G17 Precision 147 231 3.00 W/W Mixed 1.110 0.0 1.80

G17 Precision 147 231 3.20 W/W Mixed 1.110 0.0 2.50

G17 Precision 147 231 3.40 W/W Mixed 1.110 0.0 1.60

G17 Zero JHP 121 T.G. 3.50 W/W W/W 1.120 0.0 1.92 5shot 20 yd

G17 Zero JHP 121 T.G. 3.70 W/W W/W 1.120 0.0 2.04 5shot 20 yd

G34 M. G. JHP 124 T. G. 4.00 Magtec R-P 1.120 1113 58 13 138.0 1.51 5 shot gp bench @ 15 yds 10/15/2009

Edited November 19, 2009 by Darrell

[Sarge]

Thanks Sandman and Duane!

In further reading (using search and google site search) I've come up with the following...

Seating depth and OAL/COL can affect pressure and velocity. So starting it would it be safe to assume that I load my cartridges at 1.14" with different powder charges until I find my sweet spot with the powder charge. Once this is done I can begin testing (with a chronometer) deeper seating depths and see what comes up the best.

Does this sound like a safe way to proceed?

Like Duane said you really need to find a chrono to use but I know that can be easier said than done. But to just plink and practice or even to shoot a local match just look up some recipes for the 124 MG and go from there. 1.14 oal falls within the realm of a common oal for 9mm with that bullet.

OAL does(not can) affect pressure so be careful with shortening things up when the time comes.

[BMartens]

I found a little trick to help determine a good starting OAL for 9mm. I pulled a bunch of factory rounds apart and found that almost every single OAL left a very consistent amount of space in the case for powder. It averaged out to .203. If you measure the bullet you are loading and add that to the case length and the subtract .203 you will have an excellent starting OAL. This has worked with every 9mm bullet I have tried so far.

Example

.563 bullet length

.750 standard case length for 9mm

1.313

-0.203

1.110 Starting OAL

.580 bullet length

.750 standard case length for 9mm

1.330

-0.203

1.127 Starting OAL

This is just a good starting point. As mentioned by many, there are dozens of variables that you will want to consider and one big one with Glocks is what OAL the magazine will handle.

If the measurements above comes out longer than the max OAL of 1.169 then start at 1.169.

In order to find what is the absolute best for your gun and your load you will need access to a chronograph and then you can fine tune everything. For USPSA want you want is 100% reliability first, then the best accuracy you can get. Running is number 1 for this game.

I've never tried this with any other caliber, yet, but it seems to work wll with 9mm.

[Wheeljack]

I read where the 9mm shell is the same thickness down .300 from the mouth, but I measured some shells to .275. So I figure the shell length, plus the bullet length less the .275 is the minimum COAL for the bullet. Your figures are good for starting loads but loading heavy, long bullets I use my figures to make sure I'm not squeezing the base of the bullet. Your figures give me a over 1.169 length. So in that case I use a size between minimum and maximum and with 125gr bullets I could use your formula. Thanks.

[MemphisMechanic]

You'll see the "plunk test" or "spin test" mentioned in lots of posts here.

They amount to the same thing. Crank out a few dummy rounds (no powder, no primer, everything else fully completed) and drop them into the chamber on your gun's barrel.

If they drop in cleanly and spin freely, they're not long enough that they're wedged in the lands of the barrel - stuck in the rifling, in layman's terms.

If you load longer than your gun's chamber, you'll be driving the bullet into the lands or pressing it farther back into the case each time the gun feeds a new round. Sometimes this feeds okay, but it's never the safest or most reliable way to proceed.

Edited July 10, 2016 by MemphisMechanic

[mikeAZ]

A simple OAL checker... Make a dummy 9mm round up but don't crimp, put it into the chamber and let the side slam the round down (Do a couple of times). Subtract .005/.0010 "that should be your near ideal OAL with freebore. At least buy a calliper so you will know the length of the round ($10@ Harbor Freight). Threw the years, I've found the shape of bullets vary from maker to maker, thus the OAL length will change with no changes to your press.....