OAL question

[Micro man]

Been doing some 45ACP loading lately and am running out of round nose bullets.
Which brings me to my question, I have 45ACP bullets that are the same weight but differ in the nose configuration. My manual lists oal for a JHP and I have a flat nose etc. is there a rule of thumb folks use to take into account when deciding what oal is correct?

Thanks Micro man

 

[Jim Watson]

You could measure the bullet and the case and do the arithmetic to figure seating depth and start there. Adjust as required for smooth feeding.

 

[44 AMP]

is there a rule of thumb folks use to take into account when deciding what oal is correct?

Yes, the "correct" OAL (loaded length with bullet) is what doesn't jam the bullet into the rifling, and fits and feeds in your gun, from the bottom of the magazine to the chamber.

 

[Aguila Blanca]

is there a rule of thumb folks use to take into account when deciding what oal is correct?

Yes, the "correct" OAL (loaded length with bullet) is what doesn't jam the bullet into the rifling, and fits and feeds in your gun, from the bottom of the magazine to the chamber.

That's the correct answer insofar as feeding from the magazine is concerned. However, it offers nothing useful regarding a potential need to adjust the powder charge.

What determines whether or not the powder charge needs to be adjusted is the seating depth -- the depth to which the base of the bullet extends into the case. Let's assume that your new flat-point bullet is generally the same shape/profile as the previous hollow-point you were loading. From a feeding perspective, using the same C.O.A.L. should result in the new bullet feeding reliably.

But the new bullet, being a flat-point, is solid, whereas the old bullet was a hollow-point. It's unlikely that the overall length of the two bullets will be the same, even though they are the same weight. That means if you load the new bullet to the same C.O.A.L., the seating depth will be different. If the seating depth is greater, you will have less case volume, and correspondingly higher pressure. If the new bullet is shorter, the seating depth will be less, resulting in lower pressure and possibly not enough recoil to cycle a semi-automatic action.

When changing bullets, unless you were loading at or near a starting load, it's always a good idea to start over and work up the load for the new bullet.

 

[jetinteriorguy]

Take the new bullet and load one extra long with no primer or powder. Then do the plunk test. Keep seating deeper a little at a time, I do 1/2 turn, then plunk again. Keep doing this until the bullet plunks, then seat it .010” deeper and start your load work up from there. I personally avoid a compressed load, I measure how much of the bullet is seated into the case and compare it to the powder in the case to avoid compression. I also watch for pressure signs.

 

[74A95]

Take the new bullet and load one extra long with no primer or powder. Then do the plunk test. Keep seating deeper a little at a time, I do 1/2 turn, then plunk again. Keep doing this until the bullet plunks, then seat it .010” deeper and start your load work up from there. I personally avoid a compressed load, I measure how much of the bullet is seated into the case and compare it to the powder in the case to avoid compression. I also watch for pressure signs.

Why the paranoia over a compressed load?

 

[44 AMP]

That's the correct answer insofar as feeding from the magazine is concerned. However, it offers nothing useful regarding a potential need to adjust the powder charge.

No, it doesn't speak to adjusting the load, nor was it meant to. It's a specific answer to a specific question about length.

Adjusting the powder charge due to a change in length is a different, though related topic.

And, its not always needed, though it never hurts to check.

 

[jetinteriorguy]

It’s not ‘paranoia’, as I stated it’s just a personal choice. If you want to run a compressed load, that’s your personal choice. I’ve never seen any advantage to a compressed load in a handgun, all of mine shoot fine and function fine without doing so and I’m plenty happy with that. See page 40, bottom left hand corner of the Lyman 50th Edition Reloading Handbook, novices should avoid the use of compressed powder charges. By the nature of his original post I’m assuming the OP is a novice. You can also refer to page 63 on compressed powder loads and the bright yellow highlighted words CAUTION.

 

[Unclenick]

Micro man,

The general formula for seating depth is:

Seating Depth = case length + bullet length - COL (Cartridge Overall Length*)

What you are trying to do by controlling seating depth is control how much space the powder starts burning in. If case lengths vary, but head thickness is consistent, then using the formula with each case length is going to produce varying powder space. The best practice is just to use the SAAMI maximum case length and ignore your actual length as this will put the bullet base a consistent distance from consistent head thicknesses, making powder space consistent. With the .45 Auto, that SAAMI length is 0.898". So the formula becomes:

Seating Depth = 0.898" + bullet length - COL

Once you have found the seating depth for one bullet, you then find it for other bullets of the same weight and construction** but different length by rearranging the formula to:

COL = 0.898" + new bullet length - seating depth

One caveat with all this is that not all cases do have the same head thickness. Wall thickness can also differ below the normal range of seating depths, as, for example, the reinforced case made by Starline for 45 Auto +P loads. The arithmetic works precisely only with cases that match the cases used in the original load data. The way the difference is handled is to have you always start with the lowest load in the tables you are using and work up in steps that are about 2% of the maximum charge weight on the table, watching for pressure signs.

A second caveat is that some bullets, seated to the correct COL to match the seating depth of other same-weight, same-construction bullets, may not result in smooth feeding. If you have to seat a bullet deeper to get correct feeding, start the load workup looking for pressure signs all over again. In some instances, this will make an important difference. In some, it makes no difference because the primer is unseating the bullet before the powder starts to burn, making the actual powder space bigger than as-loaded. This is why you are stuck with working loads up to see if they are right in your gun.



* COL, COAL, OAL all mean the same thing. The letter "A" in some initials harks back to pre-1950s spelling when overall meant "taken altogether" while over-all meant a total length. The first form has the initial "o.", while the second has the initials "o.a." You see the hyphenated spelling in pre-1950 dictionaries. Still, by the time Webster published its 3rd edition in 1961, the hyphenated form had been dropped, and both meanings had come to be spelled as the single compound word overall. So, today, most load manuals use C.O.L. and the obsolete pre-Korean war spelling initials, O.A.L. and C.O.A.L. are used in fewer places. Often, manuals drop the formal inclusion of the periods between letters. But any of those forms work to communicate what you mean to other reloaders.

**Same construction means both cast or both jacketed with lead core or both copper solids or both moly-coated, etc. Different types of construction take different amounts of pressure to start them into the lands of the rifling, resulting in different peak pressures.