Need Help Finding Max OAL

[1SOW]

I feel dumb but can't find the max coal for my first JHP load. .355", MG 124JHP bullet. I've done this a number of times and loaded 10K FMJRN bullets and it worked as advertised.

I'm using my CZ75B barrel chamber(CLEAN) as the gage. I push an MG124JHP into a shot case and seat it fully in the chamber. I pull it out carefully and measure OAL. I do several times to make sure it's fairly consistent. "IT APPEARS TO FULLY SEAT(TIGHT) AT ABOUT 1.135".

I subtract about .1" and use an empty case and seat & crimp a bullet to this new oal. I then 'drop' this test load in the chamber , make sure it drops in freely, and try to rotate the case to insure it's not hitting the leade/rifling. If it does (hasn't before now) I shorten it in .005 increments till it's loose in the chamber.

I've done all this (several times )and thought I had it. Tried it again and it wouldn't rotate. Tried it again and it rotated but was very hard to rotate. My cases are sized exactly the same as thousands of FMJ I've shot.

I painted the bullet with a black magic marker and tried again 3X!.

I'm not sure I know what the rub 'line' on the bullet is telling me.---see my pic

I'm down to 1.12" COAL (the pic)and still not sure if it's clear of the leade.

SOMETIMES it WON'T ROTATE by hand

SOMETIMES it'STICKS' in the chamber slightly when you try to pull it back out.

Can someone tell me if that's the leade making that scrape just above the case mouth? or what.

What "should" be a good COAL for this bullet in a CZ chamber.

I really would appreciate some advice.

Edited February 7, 2010 by 1SOW

[The Antichrome]

In my Shadow, I run MG JHP 124's at 1.100 ...really short.

I arrived at that length from conversations with Angus (and other CZ'ers)

on the cz forum. It has worked perfectly for me.

Edited February 7, 2010 by The Antichrome

[1SOW]

In my Shadow, I run MG JHP 124's at 1.100 ...really short.

Thanks Antichrome. I have heard 1.1 and 1.105 should run in a 75BCZ, but I really wanted just a little more COAL if my chamber will hold it.

I shot 10 today at 1.105, they shot okay but ran a little fast with 4.0 grs of n320. I never did get the round to be free-moving in the chamber. The cases ARE sized fine (identical to the FMJs I've been running) and did drop in, but they still felt too tight moving the round by hand.

Edited February 7, 2010 by 1SOW

[tac_driver]

In my Shadow, I run MG JHP 124's at 1.100 ...really short.

Thanks Antichrome. I have heard 1.1 and 1.105 should run in a 75BCZ, but I really wanted just a little more COAL if my chamber will hold it.

I shot 10 today at 1.105, they shot okay but ran a little fast with 4.0 grs of n320. I never did get the round to be free-moving in the chamber. The cases ARE sized fine (identical to the FMJs I've been running) and did drop in, but they still felt too tight moving the round by hand.

I don't have a CZ but i'm curious what your crimp measurement is. I crimp to .376. Hornady has a similar profile with their 124gr. HP-XTP, and their minimum tested OAL is 1.060

[fltbed]

Finding your OAL

Things you’ll need:

1. Dowel rod that fits down your bore. (cleaning rod will work in a pinch)

2. Exacto knife, razor blade or scribe.

3. Dial calipers

With the action closed, insert the dowel rod through the muzzle till it’s resting against the breach face and scribe a line on the rod at the muzzle.

Now insert the bullet you plan on loading into the chamber and hold it against the rifling with something. (another piece of dowel rod, cleaning rod, etc.)

Reinsert the dowel rod till it’s resting against the nose of the bullet and scribe another line on it at the muzzle.

Measure the distance between the two lines and you now have the maximum OAL for that bullet in your chamber. I normally back off my OAL another .010 or, if it's real long, to the max OAL that will function through the magazine.

I know there are other ways of determining OAL that are more precise and more expensive, but I’ve always found this method more than adequate for my needs.

Hope this helps.

Jeff

PS I have found a lot of TC design’s that copy the ogive of Hornady’s XTP to require a really short OAL.