Help me understand bottleneck COAL

[44 AMP]

If the recipe says 2.2" OAL, and it assumes my brass is 1.76" long, and I trim to 1.75" and seat the bullet to a 2.2" OAL, I have now reduced the volume behind the bullet beyond what the recipe specified, potentially raising the pressure beyond the never exceed limit.

Am I right here?

No.

Others have explained it, so lets look at a slightly different way. Say You load to 2.2" overall. That's from base of case to bullet tip. Now, what are you changing when you trim brass from 1.76 to 1.75?

ALL you are changing is the length of the case neck. NOT the powder space, just "how far up the bullet the neck reaches".

Trimming the neck is to ensure clearance in the chamber, so the case mouth is positioned where the rifle has room for the mouth to expand and release the bullet. Too long a case means the case mouth is "too far in" and the gun barrel doesn't have the room needed for the case mouth to expand and THAT increases pressure, lots.

The base of the bullet is typically seated even with the base of the case neck, or below, so shaving a few thousandths from the MOUTH of the case doesn't change that.

clear as mud now, right?

[308Loader]

"Make sense...? To anyone?" post #20

No this made no sense. 9mm indexes the case in the chamber off of the case mouth. If the case was abnormally long, the chamber cannot lock up to fire. the OAL of the completed round makes no difference in this equasion.

Bottleneck cases index off of the shoulder in the chamber, too high of a shoulder and the bolt cannot lock up to fire. As HIBC perfectly stated, if the case is not trimmed under max length it "will get jammed beyond the neck of the chamber into the leade. That makes it hard for the brass to expand to release the bullet" as well as "Also, realize your 223 seater die as a crimping feature built into the die. You can cause yourself problems accidently crunching a hard crimp on as you seat your bullets.". If you want to crimp your bullets consistent trim length is critical. I don’t crimp 223 but don’t ask how I figured that out you can bulge the shoulder to the point it wont chamber.

Sorry to beat a dead horse. To me, these things are curtail to understand when reloading high pressure cases. Please don’t rush into something that might get you hurt. Do your homework. I think Uncle nick has some illustration’s that might help.

[nhyrum]

Originally Posted by 308Loader

"Make sense...? To anyone?" post #20



No this made no sense. 9mm indexes the case in the chamber off of the case mouth. If the case was abnormally long, the chamber cannot lock up to fire. the OAL of the completed round makes no difference in this equasion

I never said the imaginary round was meant to be chambered and shot

Simply an exercise in how varying the case length had no bearing on powder capacity. Which was one of the op's concerns.

Yes. The perfectly spherical chicken in a vacuum round would not chamber. That had nothing to do with what I was saying.

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[ghbucky]

I don’t crimp 223 but don’t ask how I figured that out you can bulge the shoulder to the point it wont chamber.

Umm... yeah, I 'figured this out' 2 nights ago

[308Loader]

Sigh... I give up. Chickens in a vacuum and theoretical bullets you cant shoot.

Point I was after is that smashing the brass beyond the neck of the chamber into the leade and or over crimping will have an effect on pressure, accuracy and any other thing that you are trying to achieve with a good hand load. The misunderstanding of OAL vs trim length terminology frightens me. They make books for this, wish people would read more these days. Tube vids don’t always put things into context. The length of your completed round has nothing to do with where you need to trim to.

Good luck, god speed, and be careful what you feed your rifle.

[ghbucky]

308Loader -

I read, and watch the vids, and I come here and ask questions. I have yet to charge a case, because I'm working this stuff out before I do something stupid.

It took a page of people beating it into my head to make sense of it, but it finally worked. So, there may be some hope for me!

[nhyrum]

Originally Posted by ghbucky

308Loader -



I read, and watch the vids, and I come here and ask questions. I have yet to charge a case, because I'm working this stuff out before I do something stupid.



It took a page of people beating it into my head to make sense of it, but it finally worked. So, there may be some hope for me!

We all have to learn. Nobody knew everything, especially from the beginning. Some forget that.

308 reloader, I suggest you use the reading comprehension you talk about and reread this entire thread as to understand what issues the op was asking for help with and what I was saying. The example I used was simply an exaggeration used to illustrate a point that, I thought at least, was one of the things the op stated he/she wasn't understanding

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[308Loader]

Sorry if that came off harsh. We all started somewhere. Please do your homework before you dive into something that goes 3000 FPS+.