Brass length vs accuracy

[Kelly Timoffee]

Haven't been able to find much info on it, just wondering from others experience if they are getting accuracy variance between cases different in length.

ex. mine is trim to 2.025" and max is 2.035"

so, does using one case that has been trimmed to 2.025" and one that is say 2.034" effect accuracy, I can see possible chambering changes, but to me,I can't figure that one would have pressure changes or such to effect accuracy as long as OAL is consistent.

Please correct me if need be.

 

[mmattockx]

Case length doesn't matter, as long as it will chamber properly. As you note, OAL and distance from the ogive to lands is far more important to accuracy. If you are crimping, then case length becomes important to obtain a consistent crimp.

Mark

 

[Mystic Precision]

As was said, as long as the case is short enough so it can expand without jamming into the leade, you are good to go.

10 thou is the usually trim range and I purposely used cases that were all over the map just to see what would happen - nothing.

However, get a few thou too long and it can do some real exciting things.

Jerry

 

[Kelly Timoffee]

Perfect, thanks guys, it was just something in the back of my mind I was unsure about.

 

[tbough]

I was playing around with a Sinclair chamber length gage in my Sako 243. I was getting a length of over .050" longer than trim to max. Are these things to be trusted?

 

[Mystic Precision]

The best way to know for sure is to take a chamber cast and measure that directly.

Gauges can give inaccurate values if you are indexing off the wrong part of the chamber ie the gauge is actually measuring the leade not where the case neck on the chamber is cut.

Also, as a barrel wears, this 'line' may blurr as the chamber and throat wear out.

For case length, as long as the case doesn't jam, you are ok.

Bullet seating depth vs the throat/leade is another story but this can be much better monitored.

Jerry

 

[tbough]

Thanks Jerry, many rounds through that barrel so maybe that's what I'm seeing.

 

[CyaN1de]

You want to stay at least .020 away from the actual end of the chamber. If the chamber measures 2.050 for instance then your MAXIMUM case length will be 2.030.

 

[farmnut]

I was playing around with a Sinclair chamber length gage in my Sako 243. I was getting a length of over .050" longer than trim to max. Are these things to be trusted?

Exactly, most people trim too much but unless you have a gauge you just don't know. I make my own gauges and it has been my experience that all factory maximum lengths are way on a safe side. I would say for accuracy you want your brass same length.

 

[sunray]

Case length by itself won't affect accuracy or pressure. Having loaded ammo that is different lengths because of it can affect accuracy though. Case length is important in a semi-auto. Not as much in a bolt action.
"...over .050" longer than trim to max..." Trim, chamfer and deburr. They're safe to use, but sooner or later they'll cause the bullet to stick in the rifling. That can cause the bullet to be pulled out when you open the bolt.

 

[ykkid]

Actually, case length is one of the determinants in the shape of the pressure curve as the powder burns. since case length variations are manifest in variations in neck length,a nd therefore amount of friction contact between bullet and neck, the longer the neck, the higher the resistance of the bullet to initial movement. Ergo, the burn curve changes, the burn rate changesm the effective pressure changes, and the vibrations as the bullet scoots down the pipe cange. Sometimes to no apparent detriment, and sometimes to group enlarging effect. All those folks who need magnifying glasses to detect how many bullets passed through the hole ensure their cases are all the same length.