Setting OAL/COL

[MrGiggles]

I made up my first .300 BLK rounds last night. Used Armscor 110gr FMJ projecticles, once fired brass, and 19.5 grains of H110.

I eyeballed the powder level and tried to set the bullets just above it. These projectiles don't have a channellure. I fired 10 of the 35 that I loaded without a hitch. They cycled fine and landed on target.

How does one go about determining a good seating depth? Is there a way to measure the distance to the rifling lands?

My manual lists a maximum length, but that isn't applicable because my projectiles are much shorter than most (round nose) used in this cartridge.

 

[witchhunter]

If it is magazine fed, the COL must allow the round to fit and function through the magazine. This should be your maximum COL. You can set the bullets deeper if you want to experiment with accuracy. Keep the case mouth on the shank of the bullet, not the ogive. A rule of thumb is a caliber's worth of the bullet inside the case, e.g., a .308 bullet should be seated .308 into the case.

 

[Reefinmike]

Google "plunk test". Load a dummy round with a long oal and slowly seat it deeper until it passes the plunk test. Then seat it just a little deeper so that it isn't jamming into the lands of the rifling. I doubt you are going to run into the issue of loading longer than the magazine with a 110gr 300blk. You will have to look it up, but I think that people loading for AR's generally seat the bullet such that the bullet is just barely touching the rib in the magazine. I honestly have broken that rule many times. My 150gr supers are far from touching that rib and my 230gr subs hit that rib and cause the round to bend inward in the magazine a bit. Both rounds function 100% in my AR pistol.

 

[Bart B.]

I've no idea who or why the idea that bullets must be one caliber deep in the case mouth was dreamed up. Nor have I heard any explanation as to why that has to happen that makes sense.

What about boattail bullets? Does the tapered heel have to be part of the dimension? Or is it only the full body diameter (shank) part?

A Sierra 30 caliber 85-gr. rifle bullet's diameter is greater than its base to ogive origin. And the 150-gr. bullet for the military .30-06 ammo had its cannelure about .200" forward of its base. The boattail version used in 7.62 NATO ammo has a shorter shank length behind its cannelure.

People have shot thousands of rounds of 30 caliber 155-gr. BTHP match bullets in .308 Win cases with a lot less than bullet diameter length of the bullet's shank inside the case mouth. Won matches and set records doing it.

 

[steve4102]

For the BO.

Set your calipers to .250

Place the caliper over the nose of the bullet and mark the bullet where your (.250) calipers contact the bullet.

Seat your marked bullet so the mark measures the same length as the bump in the mag.

Like this

https://www.google.com/imgres?imgur...uHOAhUGqh4KHVhnDGEQMwhfKDkwOQ&iact=mrc&uact=8

 

[homatok]

OAL as set out in reloading manuals is, for the most part, really an insignificant measurement. Manual measurement will simply ensure the round is safe to fire in all firearms designed for that round. In reality, each firearm is an individual, so maximum OAL is whatever will fit into the dimensions cut into your firearm! The best way to determine the maximum exact measurement you can use, is to make a chamber cast. A cast of the chamber will tell you exactly what length you can use, always dependent on the length that will fit and function in your magazine. The advice to have at least one caliber of seating depth is to ensure the case has enough bullet to grab onto to keep it in the case during whatever insult it may be subjected to prior to being fired. The “one caliber” is measured in full diameters of bullet, exclusive of any reduced diameter from a boat-tail. Optimal OAL can be determined by considering the use the firearm will be subjected too, i.e. a target round that will only be fired at the range will require less seating depth than a round that will be used for hunting. Hope this helps.

 

[Bart B.]

Steve4102, is that .250" diameter on the bullet ogive where the rifling will contact it in a .300 BLK chamber?

 

[macgrumpy]

I've no idea who or why the idea that bullets must be one caliber deep in the case mouth was dreamed up. Nor have I heard any explanation as to why that has to happen that makes sense

I was told that the idea was that seating the bullet to that depth helped ensure that the bullet stayed aligned with the central axis of the cartridge, theoretically this should minimize the angular offset between the bullet's and the bore's central axes- in other words, the bullet has less chance of wobbling as it moves down the bore, obviously it would be the bearing surface of the bullet that would be of importance if this theory were true. Like all generalizations I'm sure that it's a rule that is just intended to help the average novice get started and I'm sure that none of us would be surprised to hear that it's pretty flexible and not a a fixed requirement.

 

[Bart B.]

macgrumpy,

Bullet alignment to the bore on bottleneck cases headspacing on their shoulders is primarily determined by the case shoulder centering in the chamber shoulder being driven their by firing pin impact. If the case neck's well centered on the case shoulder (best done with full length sizing dies), then the case neck will then be well centered in the bore.

If the case neck has a .002" spread in wall thickness, the bullet will then be .001" off center to the bore. Not to worry about as such ammo shoots as accurate as can be done.

If the resized case has it's mouth too small for easy bullet seating, a lot of force is needed to seat the bullet. If the neck walls are too thin, then bullets that seat hard can bend the case neck making the bullet crooked relative to the case axis. Gelded full length sizing dies (those without expander balls) with their neck diameter about .002" smaller than that of a loaded round typically works best. Very straight necks on case axis and minimal bending, if at all, when seating bullets.

 

[steve4102]

Steve4102, is that .250" diameter on the bullet ogive where the rifling will contact it in a .300 BLK chamber?

It is where any bullet seated this way will feed and fire in the BO.