Interior Bullet Distance/Length vs Pressure

[chiltech500]

Is OAL Really the Right Measure for Powder Loads

I am trying to reason out effects of bullet interior depth, i.e. more inside length = higher pressure round?

The reason this comes to mind is that I compared my Lymans’ last evening for 125 gr lead round with Titegroup and was surprised to see 3.2 gr as the max load vs a chart I’ve used that lists various powders at different bullet types/weights which shows Titegroup 4.0 gr for a 125 gr LCN. (Also, most forum posts speak about 4 gr of Titegroup with 9mm rounds).
The difference between the bullets was OAL as far as I could see, the lower powder charge OAL was 1.15 vs the higher load OAL of 1.125. I do not recall whose bullets they were using for each.

Correct me if I am wrong. When comparing one OAL vs another for pressure and load, the bullet used for measurement needs to be the same. There is no point in comparing say a 125 gr Lee LSWC vs a 125 gr Lyman of the same type (unless the bullet length below the mouth of the cartridge is the same)?

I compared a 125gr LSWC from Mo bullets vs a 125 gr LTC from Alpha Bravo. I measured the distance from the top of the lube strip to the bottom of the bullet. (I maximize OAL for accuracy) and the MO Bullet was .050 longer. To me comparing a load with these different bullets is useless without a chrono. Am I right about that?

 

[rcmodel]

Yes, you are right.

Unless the bullets are exactly the same, as well as the test barrel used, you can't compare them.

rc

 

[GJSchulze]

Lower case volume (after seating the bullet) means higher pressure. With the same bullet that translates to lower OAL. A heavier bullet requires less powder because of greater inertia and a longer bearing surface. Lead requires less powder than jacketed because there is less friction.

Why do you think a longer OAL means better accuracy?

 

[chiltech500]

because the bullet is closer to the rifling, not the factors intended to be discussed in my post

 

[GJSchulze]

because the bullet is closer to the rifling, not the factors intended to be discussed in my post

I know people say this for rifle, but I've never heard anyone say it for pistol. I have no reason to believe one way or the other, but with all the other factors that affect accuracy in a handgun, close to the rifling has to be one the factors that low down on the list. I don't believe 9mm is used for bullseye shooting, so if you are handholding, the gun is far more accurate than you are.

I don't mean to say you people shouldn't pursue accuracy any way they want, but it does seem to me that you should start at the top of the list with what affects accuracy the most and work your way down so that you spend most of your time on things that give you the most bang for your buck.

 

[Blue68f100]

OAL can effect accuracy on a pistol. My 9mm BHP went from 4" groups down to < 2" by only changing the OAL. Every gun is unique.

 

[Tilos]

chiltech500:
As I see it, reloading is a science, with many variables, not something that can be "reasoned out" based on published data, or whether or not it is conflicting.

The reason loads are "developed", is based on ALL the variables involved, with the biggest being a particular gun and all it's parts.

As mentioned, averaging data from different sources is one way to start, and keep in mind you are "developing" a load for your circumstances.

Good luck in you load development,
Ken

 

[oldcelt]

I read an article by someone looking for more accuracy in the 9m/m and found if he trimmed the brass to a uniform lenght it made quite a difference.

 

[GJSchulze]

I read an article by someone looking for more accuracy in the 9m/m and found if he trimmed the brass to a uniform length it made quite a difference

Do you have a reference for that? Does the particular length matter or that it just makes the rounds more consistent? By how much? Given that brass cases vary in weight, not only between headstamps, but within, I question how much difference this can make. If trimming to the same length makes neck tension consistent, than doesn't the varying weight undo this?

 

[oldcelt]

I can't remember where I found this, but I do beleive that consistant oal and head space will make a difference. I know rifle shooters that will check .22lr for rimm thickness and claim it improves their groups.