9mm COL too short?

[Bozrdang]

I've been loading Acme 115 gn coated RN bullets with 6 gn of BE-86 at 1.127 COAL for about a year. I decided to try some Acme 124 gn RN bullets instead and the dummy round needs to get down to 1.103 before it will pass the plunk test in my two CZ barrels. The Acme 124 gn has a rounder, less pointy tip than the 115 gn bullet so it makes sense that it needs to be shorter but I just want to make sure I'm not too short. I plan to run 5.1 gn of BE-86.

Any potential problems with that? Is there an absolute minimum that you should never go under?

 

[Steve C]

Increase in bullet weight will always increase pressure if using the same charge level used with a lighter bullet so load data for the new bullet weight needs to be followed. Whenever one makes changes in bullet weight, type or brand loads need to be worked back up from start levels. Just make sure you use a start level load, -10% below max published load level for the bullet weight, and work your load up watching for pressure signs or until you find the most accurate loading. A proper start load for BE-86 with a 124 gr bullet would be 5.2gr that is -10% from the max load of 5.8gr listed by Alliant.

What shortening your OAL using the same bullet weight and thus the available case volume does to pressure is mainly a guess. It can increase pressure substantially or it may make no or little difference depending upon powder used. The start load level would be a safe starting point for different bullets of the same weight and different seating depths.

 

[rcmodel]

As long as the bullet ogive is still outside the case, it isn't too short.

You didn't say how short short is going to be??

But Allient lists 5.7 BE-86 with a 125 LRN seated 1.120" as a MAX load, so you should be OK unless it's MUCH shorter then that.

rc

 

[Bozrdang]

Steve C - I get all that. I'm asking specifically about the COAL.

 

[Bozrdang]

As long as the bullet ogive is still outside the case, it isn't too short.

You didn't say how short short is going to be??

But Allient lists 5.7 BE-86 with a 125 LRN seated 1.120" as a MAX load, so you should be OK unless it's MUCH shorter then that.

rc

I listed in my OP that I had to get down to 1.103 for the dummy round to pass the plunk test. That's why I'm concerned,

I also corrected a typo in the OP. I intend to start with 5.1 gn of BE-86, not 5.5 gn.

 

[Smitty79]

I had some SNS coated 124s I had to load to 1.05 for a CZ. I had feeding problems.

 

[hdwhit]

From the 9mm Parabellum entry in the Speer Manual #11 (published 1987):

"For best functioning, load ... to an overall length of 1.100 with 125 grain bullets."

And this, speaking of the need to ensure proper neck tension so that bullets did not get forced deeper into the case:

"But more important, loads that produced 28,000 CUP went to 62,000 CUP when bullets were purposely seated 0.030" deeper!"

You are currently reporting a powder load just below the indicated starting load for this caliber and bullet weight and your COL is slightly longer than the minimum suggested by Speer so in my opinion you should be okay.

I would suggest loading 10 rounds this way and firing them to see what the results are and then adjusting the load and COL from there.

 

[Steve C]

I'm asking specifically about the COAL.

As RC said, "As long as the bullet ogive is still outside the case, it isn't too short."


If you are worried about the shorter OAL feeding and shooting from your CZ, it should work just fine. Often even an empty case feeds so shorter OAL's isn't generally an issue. Range testing will be the determination of that. So load up some and head to the range. There is a lot of things in hand loading you just have to try a few first to make sure they work. IF they don't work, that's why a bullet puller is a good thing to own.

If you are worried about potential over pressure due to the shorter OAL then make sure you use the start load and work up procedure of your new component mix.

 

[Handloader109]

Not used those bullets, but have had some issues with my cast and powder coated. The way I did it was kept at the lowest starting load and tested for function. If they worked, and shot well, That was my load. I creap up if needed for function and accuracy. I've had to load to 1.060 with Lee rn. Just watch load, start low and you should be OK.

 

[LiveLife]

Acme 124 gn has a rounder, less pointy tip than the 115 gn bullet so it makes sense that it needs to be shorter but I just want to make sure I'm not too short.

124 gr RN comes in two typical RN profiles - stepped with more pointed nose or non-stepped with more rounded/shorter nose (see comparison picture of Missouri vs Dardas RN bullets above).

While I use 1.125" OAL with stepped RN bullets, when using non-stepped RN with shorter rounded nose profile, I need to use 1.080"-1.100" to fully chamber without hitting the start of rifling (see comparison of loaded OAL below).

 

[Rule3]

CZ's have a very short "leade and do not like any bullet with a fat rounded profile. I was using MBC small ball and had to seat them real short. I do not know about Acme but suspect the same thing.

Here is what MBC says about their bullet.

http://missouribullet.com/details.php?prodId=51&category=5&secondary=8&keywords=

Put some black marker on the bullet and drop it in the barrel you will see where it is rubbing.

Adjust your powder charge to start load

 

[ArchAngelCD]

You should be fine with a 5.1gr charge @1.100" OAL according to all the numbers. You are correct to be concerned about pressures in the 9mm. Small changes can change pressures, sometimes by a lot in such a small case.

 

[Bozrdang]

I loaded 20 test rounds with 5.1 gn BE-86 and a 1.066 COL. I'll test them at the range tomorrow.

I had to go that short to get them to pass in my CZ P09. I was initially only testing in my 75b and my SP01. I then remembered that the P09 was the tightest.

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