9mm Pistol Chamber Variation and Its Effect on OAL

[Gnnut2]

I drew a diagram illustrating a loaded round using an average case length and on the actual bullet dimensions. From these references I calculated the seating depth, bullet projection above the case mouth, and the vertical distance for the propellant.

• Those are good steps. Of all the concerns, the height of the powder matters the least. Nice to know, but very few powders really care about "compressed loads".

Wobbly, I've read many negative comments about using compressed loads for the 9mm Luger. My understanding is the greatest concern is compressing fast burning propellants. When ignited it burns so fast that it needs room in the case to prevent an explosion. This is my interpretation only based on reading various articles. I have loaded many bullets using compressed loads in my .41 mag and .45 colt revolvers, along with several rifle loads. I have never had a bad experience, but I ALWAYS use a published recipe. Please share your thought on the science of 9 Luger and compressed loads.

• You also need to calculate in some excess to cover your own cartridge variations due to the fact that as a novice reloader, YOU will introduce OAL variations. Very few novice reloaders can hold an OAL goal to +/-0.002", it's going to be more like +/-0.010". This comes under the heading "Poop Happens".   

Wobbly, you have called me out on this one! I have never achieved uniform consistency when seating bullets. There always seems to variation. I seem to fluctuate mostly +- 0.002 from my target and occasionally it'll vary by -0.005-6. I don't know where the gremlin is hiding, but can you help me find him?

It's interesting to note the latitude that a generous chamber offers, but on the other hand you don't have the bearing surface for the base of the bullet that a shorter chamber offers.

• Generous chambers allow you to use strange shaped bullets, and that's about it. The blunt nosed RMR bullets being a prime example. Their RN and JHP are great bullets, but not a strong choice for the CZ (as much as I hate to say this because as a company, I really like RMR).

• The 9mm Luger cartridge likes its bullet seated fairly deeply, so in generously proportioned chambers this "space" is usually wasted, in that the maker is giving up some accuracy. To get that free accuracy, you'll most likely be seating deeply regardless of what the chamber allows. So loading for the CZ is actually a stronger position, when you own multiple brands.

Thanks, Wobbly, this is nice to know about the great CZ pistols.

[George16]

I sort by head stamp in order to minimize variance in OAL. This will make the biggest change in OAL. However, you will still get a little variance due to the different lengths of the bullets themselves.

[Wobbly]

I sort by head stamp in order to minimize variance in OAL. This will make the biggest change in OAL. However, you will still get a little variance due to the different lengths of the bullets themselves.

Sorry, bullet length does not affect OAL. And on a progressive press, case lube probably makes the biggest difference in OAL.

During the assembly process, the cartridge is compressed by a press which only applies pressure to the head of the case and the meplat of the bullet. Therefore any variation in case length OR bullet length only affects the amount of bullet insertion, but never the OAL.



You can clearly see this in the cartoon above. Instead of "light, medium and heavy" bullets, just imagine these as "short, normal and long" bullets of the same weight. In the same brass, longer bullets simply seat deeper. Longer cases simply sit higher on the platen or shell holder, thus increasing the seating depth.

Variations in OAL come from...
• Not using slow, consistent seating pressure. This is most common in novice reloaders.
• Not using case lube, especially in progressive presses
• Not lubing the press
• Not using a seating anvil that fits the bullet's ogive
• Variations in brass hardness between brands, because this introduces variations in required insertion force

 

[painter]

I'd disagree that if you're seating off the ogive there could be very slight variations in the bullets length from ogive to tip. You see this often with Speer Gold Dot's. Not so much with RN bullets.

That might give you variations in the .001-.002" range, but not the variation that new reloaders see from inconsistent operation, or process.

Carry on.

[Wobbly]

I'd disagree that if you're seating off the ogive there could be very slight variations in the bullets length from ogive to tip.

You caught me !

Full Disclosure: It helps that I own a metal lathe and can make seating anvils that precisely fit all my bullets.

[painter]

I'd disagree that if you're seating off the ogive there could be very slight variations in the bullets length from ogive to tip.

You caught me !

Full Disclosure: It helps that I own a metal lathe and can make seating anvils that precisely fit all my bullets.

I'm off to buy a lottery ticket.

[George16]

I'd disagree that if you're seating off the ogive there could be very slight variations in the bullets length from ogive to tip.

You caught me !

Full Disclosure: It helps that I own a metal lathe and can make seating anvils that precisely fit all my bullets.

Nice to be able to modify those seating anvils to fit your bullets precisely.

 I’ve seen new reloaders not realize that the Dillon seating Die anvil has two different profile to accommodate both Rn and FN. they either use the FN profile for RN bullets and vice versa.

[Gnnut2]

Variations in OAL come from...
• Not using slow, consistent seating pressure. This is most common in novice reloaders.
• Not using case lube, especially in progressive presses
• Not lubing the press
• Not using a seating anvil that fits the bullet's ogive
• Variations in brass hardness between brands, because this introduces variations in required insertion force

 

Wobbly, these are good tips. I have been pondering the causes of inconsistency and I can see where an anvil made to conform to the ogive would yield consistent results as long as the ogives are consistent. As painter said, if the ogive varies it seems to me that it could affect the OAL because the contact points will vary. What do you think about cutting one designed to only contact the meplat? This may not work with a round nosed bullets but it may with any of the flat nosed varieties including hollow points.

The notes you made on the bullet contacting the internal taper of the case is interesting. I have never even had that scenario on my radar. You fellows on this forum don't miss a trick. Now I have to figure out to ensure that I do not violate the case taper when seating my bullets.

[painter]

The most important dimension wrt accuracy/consistency of your loads is seating depth. The minor variation in OAL due to ogive to meplat dimension are completely inconsequential.

Reloading is not rocket science. It's all about process. Try not to over think it.

[Wobbly]

The notes you made on the bullet contacting the internal taper of the case is interesting. I have never even had that scenario on my radar. You fellows on this forum don't miss a trick. Now I have to figure out to ensure that I do not violate the case taper when seating my bullets.

Easy !

Don't ever load 147gr bullets. 

[Gnnut2]

Points well taken gentlemen. Don't over analyze, and no 147 grain bullets for my CZ pistols.

[Wobbly]

I have been pondering the causes of inconsistency and I can see where an anvil made to conform to the ogive would yield consistent results as long as the ogives are consistent. As painter said, if the ogive varies it seems to me that it could affect the OAL because the contact points will vary. What do you think about cutting one designed to only contact the meplat?

I make new anvils for the Dillon dies all the time. Dillon really doesn't have a good answer for conicals such as the Hornady XTP and TAP, and the Precision Delta JHP. In those I push on the ogive and not the meplat. This because 1) there really isn't enough physical support to push straight-on. Yes, you'd get really good OAL reading and low variations, but the nose of the bullet would simply collapse to different degrees depending upon how fast I swung the op lever.

2) Besides simply pushing on the bullet, one of the other jobs of the seating anvil is to Center the bullet in the case. The bullet can't fly straight if the axis of the bullet is not loaded onto the axis of the cartridge. That point is a LOT more important than OAL.

So a correct fitting anvil is doing 2 important jobs.

[Gnnut2]

Wobbly, thank you for contributing to my continuing education. I can see how increasing the contact surface area while seating the bullet will provide better  bullet centering in the case. I agree that's much more important than the OAL

[Philintheblanks]

I have been pondering the causes of inconsistency and I can see where an anvil made to conform to the ogive would yield consistent results as long as the ogives are consistent. As painter said, if the ogive varies it seems to me that it could affect the OAL because the contact points will vary. What do you think about cutting one designed to only contact the meplat?

I make new anvils for the Dillon dies all the time. Dillon really doesn't have a good answer for conicals such as the Hornady XTP and TAP, and the Precision Delta JHP. In those I push on the ogive and not the meplat. This because 1) there really isn't enough physical support to push straight-on. Yes, you'd get really good OAL reading and low variations, but the nose of the bullet would simply collapse to different degrees depending upon how fast I swung the op lever.

2) Besides simply pushing on the bullet, one of the other jobs of the seating anvil is to Center the bullet in the case. The bullet can't fly straight if the axis of the bullet is not loaded onto the axis of the cartridge. That point is a LOT more important than OAL.

So a correct fitting anvil is doing 2 important jobs.

Junior Partner here: I can't reply to your message or post a personal message to you, nor even email the administrators to ask for help. I keep getting error message which perhaps is a polite way of telling me I am drooling while awake. So I'll do it the hard way. I am asking you about used Dillon equipment and about the anvils for seating fp and swc bullets. You're welcome to reply privately.

[George16]

I have been pondering the causes of inconsistency and I can see where an anvil made to conform to the ogive would yield consistent results as long as the ogives are consistent. As painter said, if the ogive varies it seems to me that it could affect the OAL because the contact points will vary. What do you think about cutting one designed to only contact the meplat?

I make new anvils for the Dillon dies all the time. Dillon really doesn't have a good answer for conicals such as the Hornady XTP and TAP, and the Precision Delta JHP. In those I push on the ogive and not the meplat. This because 1) there really isn't enough physical support to push straight-on. Yes, you'd get really good OAL reading and low variations, but the nose of the bullet would simply collapse to different degrees depending upon how fast I swung the op lever.

2) Besides simply pushing on the bullet, one of the other jobs of the seating anvil is to Center the bullet in the case. The bullet can't fly straight if the axis of the bullet is not loaded onto the axis of the cartridge. That point is a LOT more important than OAL.

So a correct fitting anvil is doing 2 important jobs.

Junior Partner here: I can't reply to your message or post a personal message to you, nor even email the administrators to ask for help. I keep getting error message which perhaps is a polite way of telling me I am drooling while awake. So I'll do it the hard way. I am asking you about used Dillon equipment and about the anvils for seating fp and swc bullets. You're welcome to reply privately.

You need to have 25 posts to be able to send a pm. Keep on posting worthwhile replies and posts and you’ll get to 25 in no time.

Or you can go the easy route by posting replies such as “welcome” “me too” etc 😆