Dolomite_Supafly wrote: ↑Sun May 19, 2019 6:26 pm
There is zero reason to run brass at 1.368" unless you like to practice malfunction drills or like having random pressure spikes. Also, having to trim every time you reload gets tedious.
For at least 8 years, and thousands of rounds, my brass has been cut at 1.350". I have yet to have a problem. I toss or loose the brass before I have to trim.
Okiedelta wrote: ↑Thu May 23, 2019 10:55 pm
I assume you are referring to dellet’s earlier post. All my brass is trimmed to 1.358 to 1.360. The fired Hornady brass measures 1.358 on average. I’ve got a Sheridan slotted gauge and the 1.358 still leaves a small gap between the case mouth and the end shelf in the gauge. I don’t know how short is too short, but i would guess that too much gap between the end of the case mouth and the chamber ledge could lead to the bullet pushing some small brass off the end of the case mouth.
This is one of those arguable things in handloading, so I’ll argue the other side.
First thing is that the neck stretches very little, and most chambers have more than enough room to keep the neck from pinching the bullet, as long as the brass is sized properly, and that’s the problem. I would say something like 95% of people assembling cartridges are not “properly sizing” their brass. That includes probably 99.5% of people following the directions that came with the die.
For the most part, contact with the shell holder and 1/4-1/2 turn more, will set the shoulder shorter than SAAMI spec. Giving the cartridge less body and more neck. If the neck is longer than SAMMi spec, it is more likely to pinch the bullet. It’s not overall case length that determines when the pinch happens in a bottleneck cartridge, it’s the length of the neck. In the 300 Blackout the the distance from the datum line, where the neck contacts the chamber to the end of the neck space in the chamber is about .295”. This allows a case length of 1.378”,
if the shoulder is in the correct location.
If the case is formed like in most dies set by contact plus 1/X turn, the shoulder is often placed .010”+ Shorter than it needs to be, If that happens it will headspace off the rim, instead of the shoulder.
Trimming to less than SAMMI max will be required.
The problem with trimming shorter than needed is it increases the speed and amount of carbon build up in front of the neck. Unchecked this will first cause accuracy issues then safety issues. Carbon build up can pinch a neck and cause a pressure spike just as easy as the chamber. A carbon ring is unpredictable where and when it will be a problem. The part of the chamber that will cause this to happen is constantly moving farther away from the case neck dur to erosion, basically getting safer all the time.
Necks do not grow very fast in a properly sized piece of brass, and even less of that happens when firing. The lengthening happens when sizing. The diameter stretches to fit the chamber and most growth in length happens at the bottom end of the case. During sizing, the diameter shrinking down forces the brass forward. Since the die stops this flow at a fixed shoulder point, it pushes everything into the neck increasing the length.
The body of the brass expands to fit the space between the shoulder and bolt face every time you fire. If it stretches .010” you will push that much brass into the neck on the next sizing. If it only stretches .001”, then only that much is forced into the neck.
So how often you need to trim depends on how much you size your brass. Low pressure subs will stretch less and therefore need less trimming, even when improperly sized. I would suggest properly sized supers require less trimming, than improperly sized subs.
