Sizeing and case length question.

[holdover]

Ok, I made my first 50 round batch of 223. I used 69 gr sierra match kings HPBT with 20 grains of N133 powder , my over length is supposed to be 2.244

Problem is , its not , there are variance's from 2.240-2.255.

I changed the battery on my calipers to be sure that was not the problem , I am assuming my case lengths may have been off when I trimmed them , (Im not sure)

Never having done this before, I was concerned with the safety of the rounds and Of course I would prefer to be spot on with the C.O.L.

Now having said all that my rounds will cycle though the mag and gun. How much will it affect my accuracy @ 100 yards? and are they safe to use or should I pull them all .

What do you guys think?

 

[MilesTeg]

Case length shouldn't have anything to do with COAL (barring any major oversights). Your COAL is mainly set from your seating die (Some other minor stuff can play a role). With that said if you aren't short stroking it and doing everything correct the 0.015 does seem large to me. My guess is it has to do with the bullets your using. Maybe they vary in length or maybe your seating die geometry doesn't work well with that profile. Meaning the bullet isn't impacting the die inner body (seater plug) in the same place every time.

 

[holdover]

Is there a normally a sleight or acceptable variance? or should the COAL be spot on most of time?

 

[squib]

Is there a normally a sleight or acceptable variance?

Yes, if you measure the bullets with calipers from base to tip you will see the differences.

 

[holdover]

What may be the causes and cures for something like that? I need to troubleshoot the problem

 

[Mosinitis]

This is PERFECTLY NORMAL with these bullets. As you can see they have a ragged non-uniform tip. That's the reason for large variance base to tip. It has no effect on accuracy because all of them contact the lands at the point close to what is called ogive. Base to ogive measurement will be uniform and consistent. You need a special comparator to measure that.

 

[Mosinitis]

What may be the causes and cures for something like that? I need to troubleshoot the problem

No cure is needed, don't sweat it. As long as it fits the magazine, you are good to go.

 

[Mosinitis]

There are what's called meplat uniformers that cut the tips making them more uniform. The value of that is questionable, even among the top shooters, most people don't bother. The tips will be more uniform but at the expense of ballistic coefficient. I have one of these cutter, it sits in a drawer and never used.

 

[Mosinitis]

Aluminum GI mags will accept up to 2.265". Over that value, you are pushing it. Seat the bullets so the longest don't go over that. Less for plastic mags.
It's not sizing that you adjust, it's seating. Bullet seating depth.

 

[kev74]

Something else to keep in mind is that the overall length given in the book is the minimum. You can safely go as long as you want over that.

...and 2.240" is effectively the same as 2.244". So don't sweat it.

I usually have good luck starting with the largest OAL that will run in the magazine.