Bullet seating depth

[BruMatt]

This may be one of those "forest for the trees" things but it just escapes me. If pressures are determined in part by bullet seating depth, and if different brands/types of bullets have different base lengths, why don't we factor in the difference in determining the overall cartridge length? For instance, if I have a round nose lead bullet, 200 grain and a flat nose 200 grain if I seat each by the same amount of bullet in the case, the pressures, and therefore the load data, should be the same.

Is there some standardization in where manufacturers put the crimp ring? It doesn't seem to always conform to the depth requirement in the load data sheets? Nor does it seem to be a consistent distance from the bottom of the bullet.

Help me out please. What am I missing?

 

[SMSgt]

"... if I seat each by the same amount of bullet in the case, the pressures, and therefore the load data, should be the same. "

Yep, you'd think so. There is little "standardization" in reloading data, each bullet and powder manufacturer having the own set of powder loads and COLs. Each uses different test standards, some using guns with a barrel length of "X" inches, others using test barrels of "Y" inches.

I prefer my COLs to be on the long side as long as they feed and chamber well. I haven't had any issues with them once I establish a COL that suits my firearms.

 

[jazzman452]

Most reloading manuals show the manufacturer and part number of the bullet used when giving OAL specs. That's why I try to stick to the bullets listed and not buy any that are odd weights or sizes, just makes it easier for me.

Jim

 

[Jellybean]

I don't think I'm understanding your questions right, so this may sound a little off.

There is a lot of mis-information available on the 'net about seating depth and pressures and it's easy to get confused on the issue. There are many factors that may have an affect on pressures and seating depth is just one of them. If you plan on loading near maximum pressure levels you need to understand these factors and how they relate to each other, or just do as the reputable loading sources tell you and start low and work your way up while watching for warning signs of high pressures.

 

[Nevada Ed]

Most bullet makers put the crimp on their bullets so they come close to standard OAL for that caliber.

Of course the style of nose on either lead or jacketed copper bullets will vary, as well as the amout of bullet below the crimp area, so this is a +/- of the actual measurement thing but the finished product should be very close to factory specs.

 

[blujax01]

The way I see it the bullet manufacturer knows best. Of course this means that the well-armed reloader needs to have manuals for every bullet they process.
The upside is that I have a perfectly good excuse to obtain more reloading manuals!

 

[mikld]

Also, that's why OAL is bullet specific...

 

[jepp2]

This is more of an issue with cartridges that have less case volume under the bullet with more variation in OAL (9mm is the most sensitive due to the low case volume and great OAL variation of 1.010" to 1.169").

You are on the correct track with bullet seating depth rather than OAL. Some earlier loading manuals listed bullet seating depth. But it is very easy to calculate. A resource that will assist you can be found here.

 

[ArchAngelCD]

The slight differences in bullets is one of the reasons we have starting charge weights and max charge weights for powder. Start at the low end and your reloading will be safer. The COAL for any load is useless unless you are using the same exact bullet they use in the recipe and the brass is trimmed to the same exact length they are using.

 

[MichiganScott]

Is there some standardization in where manufacturers put the crimp ring? It doesn't seem to always conform to the depth requirement in the load data sheets? Nor does it seem to be a consistent distance from the bottom of the bullet.

Hodgdon lists 24 .30 caliber cartridges. The cannelure (proper name for crimp ring) has to be a bit of a compromise. When you consider all the manufacturers and how they may target certain different segments of the shooting community and all the different bullet weights and shapes available in each caliber, it's easy to see why standardization will never happen.

 

[125JHP]

I think you are on the right track and should continue your quest. As mentioned, older manuals listed the seating depth instead of an oal... for a reason. I think the oal developed when there were only a few types of components available and people were trying to match standard factory loadings to save money. Since then, the garden has bloomed.

For many bullets I do exactly what you are talking about. If there is a crimp ring then I try to use that as my guide but still be aware of how much lead is in the case when looking at load data from different sources. For most semi auto bullets, I try to calculate my OAL based on a reasonable estimate (aka guess) of how much shank the selected bullet has, how much of that shank is in the case and what the 'normal' OAL of that caliber is. My OAL will fall where it may but is usually in the acceptable normal range. You will be looking at balancing pressure, mechanical functioning and velocity for charge/bullet weight when doing all this, so there are affects in multiple directions by changing it (that's why you need to understand the ramifications). Measure a few different bullet shanks to see what I mean and pull some factory ammo to see how deep they are seated (after measuring OAL). Take a look at this thread, where I did just that.

http://smith-wessonforum.com/reloading/238285-couple-obscure-9mm-loads.html

For 9mm, depending on the bullet, I find a seating depth between .18" (XTP) to .28" (some 147gr JHP) into the case gives me acceptable performance and OAL in the above areas. Some variance will apply to special cases such as short bullets, hollow base or longer projectiles with a long shank.. YMMMV

 

[BruMatt]

Thanks guys for the great information. My question was poorly written (I shouldn't try to write something technical at 3 in the morning) but the responses were great. What triggered the question was the difference in OAL in the Hornady book for 44 spl 240 SWCs at @1.46" and the other books and lists for that round at 1.5" to 1.55". When I measure the length of the bullets from Hornady and MO Casting they are close to the same. I also wonder about what difference in pressure the seating depth makes. I have typically loaded longer than the minimums.

 

[PDL]

If you had Quickload you can change whatever variable, (like seating depth) and see the differences in pressure. And you might be supprised at how little a change can make big differences in pressure.

Bullet makers as well as powder makers have online load data for their products.

 

[Jellybean]

I think you're reading too much into this. As stated the increase in pressure will depend on the case capacity, but there are many other things that have an impact on pressures that the manuals don't even list. Chamber/barrel dimensions, bullet design and construction, general differences is firearms used, differences in atmospheric pressure, temperature, differences in loading tools and techniques, lot to lot variations in components used and etc. What a manual lists as safe may not be safe at all when loaded by someone else if enough of the above meet at a "worst case scenario" circumstance.

Loading manuals are a guide to get you started, they are not a recipe book. Owning a manufacturers manual for every bullet you use is nice for anyone that actually reads the whole book because they will give you information specific to their products, but it isn't needed to work up a good load. The OAL Hornady gives is based on the design of their bullet and has no real bearing on any other brands. The difference in pressure you might get from using another bullet with a different seating depth is only a part of the difference of all the above possilbe factors. The Hornady bullet is swaged which means it is probably softer than the MO castings. Are both bullets in question the same diameter? How do their respective bearing surfaces compare? All of these need to be addressed, not just seating depth, and the best way to do this is simply to start at a reduced or "starting" load and work your way up to a safe load.

 

[dickttx]

When I started reloading in the latter part of the 60's it was mostly for rifles. You would pick a load from a manual, then acquire the bullet, primer, powder and case used and assemble the round. Even the loads for my 25-06 AI were listed in the Ackley manual.
After nearly 40 years of not, I started again a couple of years ago, handguns only.
Just about the only bullets I have used are Precision Delta jacketed, and Missouri Bullet Co. lead, with a few Berry's and Ranier's. None have any loading data so I have done a lot of searching.
I came to the same conclusion as the OP and 125JHP--the amount of the bullet in the case should be the controlling factor.
On another forum someone maintains a database or 45 ACP bullets where people have measured the length of the full diameter of the bullet. They measure by blackening the sides of a bullet, then using a razor blade to scrape the black off and measure resulting clean spot.

 

[Nevada Ed]

If your loading the same weight bullet there is little reason to worry since the ammout of bullet base that goes into the brass does not change that much with the lighter bullets.

The larger bullets that take up 50% of the case may be something different but I have yet to load any of these
except the 148 HBwc in my 38 spl.

Here is a picture of a sierra JHC, and two old style,Win SJHP and a Rem SJHP, to show you the difference and why some bullets need different OAL's.

 

[BruMatt]

Thanks Nevada Ed, for the examples. If you look at bullet #1 and bullet #3 (assuming they are the same grain weight), I would tend to use the same load data and crimp to the cannelure of each as long as I was not below the minimum OAL. Bullet #3 would fill the casing a fair amount more than bullet #1. That would change the performance relative to the load data. But the real question is, "Does the reduction in case volume for bullet #3 cause a significant increase in pressure so I am wrong in using the same laod data for both bullets?"

 

[blujax01]

...

Loading manuals are a guide to get you started, they are not a recipe book. Owning a manufacturers manual for every bullet you use is nice for anyone that actually reads the whole book because they will give you information specific to their products, but it isn't needed to work up a good load.

Sorry J.B. I have to disagree. "Recipe books" is exactly what they are.
I agree (and the recipes state) that you don't start at the top of the prescribed amount of powder.

While one can work up a load from scratch, some of us don't have the patience to use trial and error and learn that some powders are better suited than others - and some are not suited at all - for different caliber handguns.

For the person who wants "off-the-shelf" recipes for ammunition, or want a good jumping off point for further exploration, in my opinion the bullet manufacturers manuals are the primary source.

 

[Jellybean]

...But the real question is, "Does the reduction in case volume for bullet #3 cause a significant increase in pressure so I am wrong in using the same laod data for both bullets?"

It may, and you might be.

Depending on if everything is the same but the seating depth and if you are using a maximum, or near maximum, load. And it could be even worse depending on which powder you are using as some are less tolerant to excessive heat and pressure as others.

And just for the record, if you take a loading manual printed by bullet no. 3's manufacturer, load it exactly as they say and with the same brands of powder and primers and go directly to the maximum, or near maximum load, you might still get a significant increase in pressure over what they printed.

 

[Nevada Ed]

Pressure with a revolver...........

Cylinder I/D,cylinder gap, type of primers,powder burn rates,posion sensitive (?),outside temeratures,type of crimp,moisture with powder , scale correct etc. etc.............

We are lucky if they work with the correct data !!

Mercy.