Differences in bullet diameters for .284 cal

[BK7saum]

I turned the necks on my 7mm SAUM brass to measure ~.3134 for a .315 chamber reamer (expecting the chamber to be a hair bigger than the .315). I used the hornady 162 amax as the template bullet for setting up my neck turner. When I loaded up my 180 JLK bullets the necks measure .3140.

Well I pulled the bullets and turned down the necks a little more. What I found out was there was what I feel is a large variation (at least more that I expected) in .284 bullets from various manufactures.

Remington factory 140 core-lokt measure .2834 (pulled from factory ammo, brass necks turned and bullets/powder reloaded).

Hornady 162 amax bullets measure .2839.

JLK 180 bullets measure .2844.

I guess it definitely pays to measure the exact bullets you are going to use when neck turning brass. I didn't expect more than .0002" difference in bullets across the board from any of the bullet companies. .001" is what I found today.

Anyone else noted .001" differences in bullet diameters between companies.

 

[ChrisGarrett]

Re: Differences in bullet diameters for .284 cal

It's not uncommon to have a variance of +/- .0005" in bullets. They're man made, mass produced items.

That's why some of us don't want to run tight (neck turn) match chambers, too much to worry about.

Chris

 

[BK7saum]

Re: Differences in bullet diameters for .284 cal

The only other semi-tight neck rifle is a 6x47 lapua with a no-turn neck for Lapua brass. I think it is .003 or .0035 over loaded neck diameter.

The reamer used was a .315 and I was hoping that it would be a no-turn chamber. Most brass for my other 7mm calibers measures .310 and .311 for loaded round neck diameters. However, SAUM brass has necks of ~.015 instead of .013 necks of some of the more common calibers. I didn't realize this at first and when I did find out I decided to stay with the 7 SAUM and the .315 reamer. So I turned the necks to give clearance. When I received the JLKs, I didn't measure and it turns out they were larger than I anticipated.

No problem now, I just had to turn the 100 pcs of brass a little bit more.

 

[Fuzzball]

Re: Differences in bullet diameters for .284 cal

Sounds like you are assuming the book max cartridge neck diameter mathches the chamber neck diameter? Not so. The chamber typically will be 2-4 thou larger than the ammo.

If you want to know your chamber neck diameter you would do best to make a chamber cast but you can get very close by simply measuring a fired case neck and adding a thou to account for springback.

Whatever your actual chamber size is, if the loaded ammo is no larger than the fired diameter you are fine.

 

[BK7saum]

Re: Differences in bullet diameters for .284 cal

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">Sounds like you are assuming the book max cartridge neck diameter mathches the chamber neck diameter? Not so. The chamber typically will be 2-4 thou larger than the ammo.

If you want to know your chamber neck diameter you would do best to make a chamber cast but you can get very close by simply measuring a fired case neck and adding a thou to account for springback.

Whatever your actual chamber size is, if the loaded ammo is no larger than the fired diameter you are fine. </div></div>

Not really assuming book max neck diameter matches anything. One drawing I saw showed a .3201 diameter. Brass is usually a few thousandths smaller than book dimensions and factory chambers are sometimes a few thousandths larger. Based upon 7mm08 and 7mm Rem Mag brass on hand, I wasn't sure how much thicker the SAUM brass would be. Both the 7mm 08 and 7mm RM measure .310/.311 loaded. Was hoping that SAUM brass necks would be about the same, but they are .3145-.315 loaded for Rem. Factory ammo.

Would have been nice if they measured .312 or .313 loaded. Then I would have had a no-turn neck. I don't mind turning necks, especially if it gives me a little better accuracy.