6mm bullets

[Trakker]

Can someone confirm to me that the Lapua 6mm bullets are a few ten thousandths undersized - therefore we see some tighter barrels out there for 243/6mm projectiles? Or did I hear FUD at the range?


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[ar15barrels]

FUD.

[Trakker]

6mm bullets

Ok thanks. So why the various bore sizes for 243? I see those on bugholes website for Bartlein barrels.
.236 vs.237. Does it matter?

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[MongooseV8]

Yeah they make 0.243 bullets that are a "few ten thousandths" smaller diamter. You can choose between 0.224 and 0.204. Hehe

But seriously dont put too much faith into what you hear at the range.

[LynnJr]

They actually do make 243 bullets in various diameters and most barrel manufacturers sell barrels just for them. Krieger and Bartlein make a 0.236 bore and a 0.237 bore.
Most custom bullets with a flat base have a pressure ring that is fatter than the rest of the bullet.
The heavy Lapua 6mm bullets are considered a thin bullet in Benchrest Shooting circles.
Hopefully the pressure ring shows up in the picture.
The Lapua 105gr Scenar is a very uniform bullet and ultra-accurate, but the max diameter is 0.24285, compared to 0.2433+ for some other brands. Accordingly the Scenars may prefer a tighter bore.

[ar15barrels]

So why the various bore sizes for 243?

It's the same as for most other calibers.
If you go to a larger bore, you upset the bullet less while engraving the lands.
Upsetting the bullet less leads to better accuracy.

Bore diameter is the SMALLER diameter of the two diameters present in a rifle barrel.
Groove diameter is the LARGER diameter of the two diameters present in a rifle barrel.

The smaller you go on the bore, the more bullet upset and therefore the more pressure you get.
When you are limited to factory ammo, pushing the pressure higher by tightening up the bore will give you more velocity.

You see this done more often in 308's to get more performance.

When you are handloading, you can make the bore bigger so that it does not disrupt the bullet as much.
This would lower the pressure/velocity of factory ammo, but will not matter to a handloader who can simply adjust the powder charge to get the pressure/velocity that they want.

[LynnJr]

Ok thanks. So why the various bore sizes for 243? I see those on bugholes website for Bartlein barrels.
.236 vs.237. Does it matter?

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Drop a marble down a snug piece of pipe and that marble will get to the other end faster and straighter.
Drop it down a looser fitting pipe and it will bang all around before it exits.
If you do the same thing with a bullet here is what happens.
A thin bullet in a large bore will bounce around excessively and the end result is lost accuracy.
Reverse that so you are pushing a thick bullet down a tight bore and you are excessively squeezing the bullet causing it to deform more.
Pick your bullet first then pick the cartridge that will push it at the velocity you need then order up the appropriate barrel.

[Trakker]

Ok thanks. I have 1000 scenars and 1000 bergers. Will give it a try.


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[bubbapug1]

Definitely issues with 6mm bullets and barrel diameters.

Read about it here.

http://bulletin.accurateshooter.com/2007/05/6mm-match-bullet-diameters/

I also ran into this same issue. I switched from smk's to noskers and my groups went from 0.5" at 100 yards to 14". (Or more) at 100 yards. Unfortunitky I did so at the exact moment I changed a scope mount and blew a ton of time and ammo trying to get the mount to work. The mount was fine. I took some smk's I had loaded previous to the switch and bingo...problem fixed. That was with a 6mmbr. The noslers work great in a 6x47 I have however.

[Whiterabbit]

Hopefully the pressure ring shows up in the picture..

Hi Lynn,

I've had great luck taking pictures of stuff like this. What I do is hold up a loupe to the part, and take a picture through the loupe.

It actually works really, really well.

Here's an example of when I needed to share pictures of a factory sear I was working on:

[Flouncer]

What is a loupe ? I know I can google it but that is not as fun as getting a stranger on the internet to explain what they are trying to say in English.

[ar15barrels]

What is a loupe ? I know I can google it but that is not as fun as getting a stranger on the internet to explain what they are trying to say in English.

A small magnifying glass that you can pinch with your face to hold it to your eye.



There are also folding versions which you simply hold like a regular magnifying glass.



Then there are ones intended for use on light tables to view negatives and slides: