9mm 115gr RN vs HP OAL

[CZDave]

Hi everyone!

I just started reloading Rainier HPs tonight and realized the OAL of these rounds is much less than the Berry's 9mm 115gr RN DS bullets ive been using. I'm new to reloading and have only done 9mm so far.

The oal of the Berry's mentioned above has been 1.150 to 1.168. The Rainiers I started on tonight were at best 1.0 and most were far less.

My question is what should be the overall length of a hollow point?

TIA

czd

 

[GLOOB]

I went through this just the other week, myself. The answer is that maximum OAL may depend on your pistol. Take your barrel out and test to see what is the maximum OAL that will fit with that bullet, and then calculate the distance of case space from the back of the bullet. If there's less case space than the load data you are working with, back off the recommended loadings and work your way up. But OAL of less than 1" sounds quite short, indeed.* I would be cautious while working up a load with those. My 124 grain Berry's HP's measure around 1.04-1.08", depending on the gun.

From what I have read, smaller case volume may result in higher pressures when near max loadings and especially with faster burning powders.

*BTW, from your ID and sig, I take it you have a CZ. They are known for having short throats. You might consider looking for a HP bullet with a curved ogive shape to allow a longer OAL for your hotter loads.

 

[Tilos]

try this:
With the barrel removed, drop a bullet in the barrel, followed by an as fired case (not resized, not belled).
The case will slide over the bullet and stop when it gets to the step in the chamber.

Carefully remove the bullet and case as an assembly, and measure the OAL, while finger pinching the bullet/case junction to limit any movement.

That OAL measurement represents the MAXimum as the bullet was touching the rifling, and something shorter (-.020") will chamber but needs to be checked for mag function also.
Try it, and good luck.

 

[CZDave]

Thanks for the input guys. I ended up running a dummy round thru my gun to make sure it would cycle. Hodgdon's recommends 1.125 (jacketed) so that is about what I started with and it seems to work. I'll run off a sample and see how it goes.

 

[rfwobbly]

Dave -
You've gotten some good info there, especially the how-to details from Tilos. If the 9mm you are reffing to is a CZ, then those pistols have extremely short leade and each new bullet will require this same procedure.

The chamber measurement minus .020" will set the bullet back off the rifling and account for any bullet-to-bullet variations your reloading press may deliver. It's important that you understand we're not merely asking you to simply 'be off the rifling' by that huge amount.

When 9x18 ammo gets to around 1.000" a lot of guns start to have feed issues. So you definitely want to figure out what the longest cartridge you can use safely is going to be. Typically it's the conical nose FP bullets that give the most trouble in a CZ.


As a secondary step, you may wish to take your Berry OAL of 1.150" and subtract the Berry bullet height. This will tell you where the base of the bullet is. Then do the same for your new Ranier HP bullet.



If both bullets are 115gr and since both bullets are plated, this will give you a fair insight into the comparative chamber pressures and velocities. For instance, if the HP seating depth is substantially higher than the RN (as per the RH picture), then you'll have an indication that more powder may be required to achieve similar pressures and velocities as the RN. Follow? While not a hard and fast reloading law, you will gain useful safety checks on your load assumptions. And more safety is always gooder.


So the placement of the bullet's nose contributes to feeding, and placement of the bullet's base contributes to chamber pressure. Both useful measurements to gather and track.

 

[rfwobbly]

Thanks for the input guys. I ended up running a dummy round thru my gun to make sure it would cycle. Hodgdon's recommends 1.125 (jacketed) so that is about what I started with and it seems to work. I'll run off a sample and see how it goes.

Dave -
Sorry to miss you while I was typing.

The recommended pistol OALs in reloading manuals only mean 'this is the pressure and velocity we got when we did this exact load.' But if you'll read the fine print, you'll see that what they used for testing is not even a pistol, but a "test barrel" clamped in a vise.

Therefore they are not recommending that OAL, they are merely reporting the pressures for a load at that OAL. Do you understand the difference?

YOUR OAL is determined by how YOUR bullet interfaces with YOUR barrel. This as per the method Tilos gave you. IF your OAL comes up close to the Hodgdon OAL, then you are free to use their load. But Hodgdon is NOT telling you that OAL will run in your gun. They can't. It's impossible. There are simply too many barrel-bullet combinations available. Follow?

Hope this helps!

 

[CZDave]

You didnt miss rf - Im still thinking about your last post. I understand so far but doesnt feeding a round in, then ejecting tell me whether that oal will work for my barrel ?

 

[rfwobbly]

Dave -
First, let me apologize. I forgot to welcome you to THR. Welcome aboard, sir!

The way you're doing it is a common test, but not a great one. (And here I assume you've marked up the bullet nose with a marking pen, like a Sharpie Marker, and didn't see any evidence of any touching on the "test cartridge".)

Think about this... What if your one and only "test bullet" has missed the rifling by .001", BUT the cartridge length variation your press delivers is + or - .003" ?? In that case the cartridges you produce at +.002 and +.003 will be touching.

Or the converse. What if you measure and find out the cartridge could have been .040" longer? That could decease the chances of a "compressed load" or possibly be enough to end a feeding issue.

So your present method tells you "you missed", but it doesn't tell you "by how much". That's like wearing a blind fold at a rifle match. You shoot and the RO says "You missed". If that's all the information he gives you, then how can you ever correct or improve?

Hope this helps!