Welcome to AR10T.com, the world's first forum dedicated to AR-10™ rifles .  We invite you to JOIN our friendly firearms enthusiast forum.

Determining Maximum Overall Cartridge Length

  • Posts: 942
  • Thank you received: 122

Determining Maximum Overall Cartridge Length was created by NightForce

I made up a little system that works well for me and I've been using it for years....

My system consists of the following:

1. An appropriate length cleaning rod
2. A brass jag with a flat tip
3. Washers (2) that are the same thickness that slide over the rod and can be fixed in position using nylon tipped set screws..

This image is hidden for guests.
Please log in or register to see it.



Remember - Every bullet style will result in a different over all cartridge length. When developing a load for a particular rifle your initial measurements must be used using this tip to determine the chambers Maximum Overall Cartridge Length. The tip of each bullet is not the same therefore if you're measuring the cartridge overall length it will be different with each cartridge and you'll be chasing your tail trying to figure out what's wrong. The Ogive on the other had is pretty consistent within a given lot of tips therefore can be used as a repeatable datum with adjusting the seating die.

Maximum Overall Cartridge Length = Distance from the bolt face closed to the tip of the bullet just touching the rifles lands.

Instructions:

1. Slide the first washer on the cleaning rod.
2. Screw the brass jag into the cleaning rod tip
3. Slide the cleaning rod assembly into the muzzle end of the barrel until it comes in contact with the bolt face
4. Slide the washer against the muzzle and tighten the set screw
5. Remove the cleaning rod assembly and add the second washer
6. Remove the bolt
7. Insert the bullet tip into the chamber until it touches the lands.
8. Hold the bullet against the lands with a wooden dowel so it won't move
9. Slide the cleaning rod assembly into the barrel until it comes in contact with the bullet tip.
10. Slide the second washer up against the muzzle and tighten its set screw.
11. With a vernier, measure the distance from the outside of each washer
12. Subtract one washer thickness...

Result = Maximum Overall Cartridge Length

Generally speaking, I like to have about 0.010" gap between the Ogive and the lands. This allows "some" bullet movement so that chamber pressure drops as soon as the cartridge is fired. "Jamming" the Ogive into the lands can cause a dangerous pressure spike if you're working with a maximum load.

Using the bullet above, adjust your seating die until the tip of "this" bullet in a loaded case equals the determined cartridge maximum length minus 0.010. The relative distance from the head of the cartridge to the bullets Ogive should remain constant within 0.002, all else being equal....

In general, the Maximum Overall Cartridge Length will exceed the magazines allowable length and will need to be loaded individually.
The following user(s) said Thank You: MrMarty51, jtallen83, Siscowet, Libertarian623
10 years 1 week ago #37146

Please Log in or Create an account to join the conversation.

  • Posts: 1078
  • Thank you received: 188

Replied by LebbenB on topic Determining Maximum Overall Cartridge Length

Good to know. I imagine this system gives more consistent results with a bolt gun than with a mag fed semi-auto.
RLTW
Last edit: 10 years 1 week ago by LebbenB. Reason: Spelling
10 years 1 week ago #37147

Please Log in or Create an account to join the conversation.

  • Posts: 880
  • Thank you received: 216

Replied by Libertarian623 on topic Determining Maximum Overall Cartridge Length

Great post, a accurate cheap way to measure COAL. On my way to the shop to measure mine. Thanks Nightforce.
10 years 1 week ago #37148

Please Log in or Create an account to join the conversation.

  • Posts: 1227
  • Thank you received: 102

Replied by MrMarty51 on topic Determining Maximum Overall Cartridge Length

That is a very good how to. I like it.
I have three .308 rifles, they are, all three, removable magazine fed, two are semi auto, one is a Ishapore bolt rifle.
I checked the COAL in an AR10 magazine, using a factory MIL. SPEC. cartridge and also with one of My reloads, not a lot of room to wiggle in there. :busted:
BUT, I do have several bolt fed box magazine rifles and I will definetely be using this method on those.
Matter of fact, I have five or six boxes of reloads for the Remington 700, 30-06 that I will check, or, I could say "Double Check" to mnake sure that the booolits is not to close to the riflings. I used a dummy round when I was ready to load up for this rifle and also for two .243s that I have.
Thank You for this most quick and easy way of checking for COAL.
Things is moving fast now.
What`ll You say when Jesus asks, Why did`nt You read My book ???
10 years 1 week ago #37149

Please Log in or Create an account to join the conversation.

  • Posts: 942
  • Thank you received: 122

Replied by NightForce on topic Determining Maximum Overall Cartridge Length

After spending quite a few hard earned dollars on everyone else's design, and being somewhat dissatisfied, I decided to come up with my own. Once I determined the two what I really need to measure the picture became very clear...AND simple!

Thanks guys, my pleasure!


Yes, I agree with you.

Initially I used this on all my bolt guns. Knowing that I would determine the finished COAL, I used this in conjunction with my Redding Competition Seating dies to really fine-tune my most accurate cartridges.

While the AR platform utilizes a box magazine, I was curious to determine just how much farther out the tips had to be seated in order to be .010 off the lands. In each case, in order to achieve this dimension, the COAL exceeds the magazine length so these round need to be loaded individually...

I'm curious to see the difference in accuracy from loads I develop for both single feed and magazine feed.....it will be a good test..
10 years 1 week ago #37153

Please Log in or Create an account to join the conversation.

  • Posts: 1183
  • Thank you received: 147

Replied by Akai on topic Determining Maximum Overall Cartridge Length

Great idea :clap: I'm still learning something new everyday :nicethread:
AKAI
10 years 1 week ago #37158

Please Log in or Create an account to join the conversation.

  • Posts: 3354
  • Thank you received: 547

Replied by Siscowet on topic Determining Maximum Overall Cartridge Length

Good info Night Force. Thanks for sharing.
10 years 1 week ago #37163

Please Log in or Create an account to join the conversation.

Show 'em Off!

Add your rifle to the AR-10 Photo Thread!