How do you the perfect COAL for your pistol?

[gregjc9]

I hope this hasnt been beat to death already here, but I havent been able to find my answer.

I recently picked up some Unique to try in my 9mm. For the past year, I've been reloading my 9mm with 115gr plated RN with 5.4gr Power Pistol, and a COAL of 1.156. This combination has been working very well.

I was going through my Sierra manual, for Unique with 115gr RN it suggests a COAL of 1.100 Doing a little more research, I found an article on OAL that was for rifles, but was intreguing none the less, and was wondering if the same process could be applied to pistols.

So I thought I might try and find the "perfect" COAL for my CZ 75SA (my IDPA and range gun). Using the method in the attached pic, I found that with a dummy round at the max COAL of 1.169, it appears to just headspace correctly. Slightly longer COAL and distance from the case rim to the barrel is greater than the headspace of the empty case.

So using slightly less than the max COAL as a starting point, does it make sense to make a batch of loads, decreasing the COAL by some amount, like 003?

1.168
1.165
1.162
1.159
.
.
.
.

Or am I overthinking this?

EDIT: All this is assuming mid-range loads, taking into consideration the impact on pressure a short COAL can have.

[Miata Mike]

I will be watching this thread and see what comes of it. I loaded up a small batch of 9mm at almost the max of 1.169. I grabbed a random Federal FMJ and measured and just replicated.

After I shoot them I plan on working on shortening the OAL and reducing the powder from 4.5 grains of Bullseye to 4.0 and see how they feel. I think having a little more seating depth will keep the Berry's 124 grain RN bullet in place better.

I wish I would have started reloading way before the snow started to fly and hunting season here. Now I have to deal with finding my brass in the snow.

[jbrown13]

Here is an explanation that is posted on another forum that is about as clear and understandable as can be. This is that author's opinion and I just offer it as grist for the mill. See post No. 15 in this thread: http://glocktalk.com/forums/showthread.php?t=1293939

I couldn't figure out how to copy and paste it here, for which I apologize.

[k4swb]

What I like to do is, first seat the bullet (one with no crimp groove) to where it has a good support/case grip. This is very subjective and can vary greatly from bullet type to bullet type. Once I am satisfied with the case grip, I then check the depth in the barrel. I really like to find the bullet just touching the rifleing at this point so I can increase the depth just enough to be a few thousands off the rifleing. Hard to do with some short bullets. Once I am again satisfied, I then make sure the rounds work in the magazine. This would be the longest OAL for that round I could use in MY gun. Usually this shoots the best in MY gun. From there, if needed I may play with deeper seating but I have found that the longest COAL I can reliably get to function in MY gun is almost always the best functioning and most accurate.

[jepp2]

I start by determining the MAXIMUM COAL for the bullets I use in my various pistols. The PERFECT COAL is a different goal.

I find the rod system shown in the bottom (not the top Hornady Lock-N-Load system)of the picture to work best for me in determining the MAXIMUM COAL. I realize that headspace can impact this, but what I really what to know is how far out can I seat the bullets and not touch the rifling?



I keep a MS Word table by bullet by pistol of the max length I can load. I know that 1.169" will fit in all my magazines (Winchester White box is loaded at 1.169").

To allow my reloads to be shot in any of my pistols, I let the shortest length in my table to determine my max COAL I load for that bullet in that caliber. This is so I can shoot the reloads in any pistols in that caliber.

From there I adjust if necessary for proper functioning.

Then I record seating depth for that COAL. When considering loads, I try to determine seating depth used in the published data. I do this by using the length of the bullet used in the testing and record the seating depth in my loading manual. Since my seating depth is usually less, then I adjust powder charges as required.

Always remember seating depth changes can significantly change peak pressure. And COAL may be the same for different bullets of the same weight, but the seating depth may be different for those bullets due to the profile.

[gregjc9]

Here is an explanation that is posted on another forum that is about as clear and understandable as can be. This is that author's opinion and I just offer it as grist for the mill. See post No. 15 in this thread: http://glocktalk.com/forums/showthread.php?t=1293939

I couldn't figure out how to copy and paste it here, for which I apologize.

Great article, thanks!! That is pretty much what I have been doing to determine my max COAL. But I just wonder how the OP came up with .015" as the minimum amount to back off the max COAL? EWAG?

I have read having some amount of "jump" to the rifling yields better accuracy. Maybe in pistols such as 9mm and 45ACP this is all that's needed?

This also clarifies for me the need to go through this excercise for the different bullet mfgrs I might order from. They may all be the same weight and type, but the ogive is slightly different, which will yeild different max COALs.

[WESHOOT2]

Since reliable function is paramount, I first choose an OAL that provides it.
Then I vary a bit for accuracy.

I have determined that a great compromise OAL is 1.130--1.155".
Most of my ammo runs around 1.140".


My latest load utilizing a Penn 125g LRN is running at a super-short 1.065". Reliable and real accurate.......

Testing continues.

[wncchester]

"So using slightly less than the max COAL as a starting point, does it make sense to make a batch of loads, decreasing the COAL by some amount, like 003?"

Your premise is good but you really don't need to be so tenative in steps. Moving down by 10 thou (the thickness of three sheets of paper) for a few rounds would be faster and the fininished ammo would still be as precise as any handgun would ever see. Few of us bother with seating steps smaller than 5 thou for precision rifles and they are MUCH more finicky than any handgun.

Well, the tiny but high pressure 9mm IS more pressure quirky than the larger, lower pressure .45ACP. Maybe your 3 thou test steps would be better for that little European thing.

[dahermit]

Or am I overthinking this?

Yes. OAL is critical for top accuracy in regard to rifles. With a 9MM (Autos), function is the priority, which has already been mentioned.

[gregjc9]

Quote:
Or am I overthinking this?

Yes. OAL is critical for top accuracy in regard to rifles. With a 9MM (Autos), function is the priority, which has already been mentioned.

I thought I might have been. Some great info, and I still learned a few things, so thanks.