Optimum Charge Weight, then seating depth

[NICKNICK]

Have any of you ever gone the optimum charge weight route to find a "robust" charge weight, and then fine tuned with seating depth? Since loading on or very close to the lands can increase pressure, and loading too far into the case (too short) can increase pressure, what seating depth should you start with?

The advice I'm seeing is that when playing with seating depth, you should reduce your powder charge for safety. However, wouldn't that undo all the goodness of the Optimum Charge Weight?

After settling on a powder charge, should I just be loading to magazine length and incrementally shortening the COAL until I see pressure signs? I'm hearing that the pressure increases from seating depth can be very NON linear, so is there a safe way to do this without blowing anything up?

 

[Sniper Uncle]

I don't know the answers to your questions, however, have you access to QuickLoad? I believe that this program may be able to help you with figuring out pressure curves and spikes.

 

[JoeBUtah]

Have any of you ever gone the optimum charge weight route to find a "robust" charge weight, and then fine tuned with seating depth? Since loading on or very close to the lands can increase pressure, and loading too far into the case (too short) can increase pressure, what seating depth should you start with?

The advice I'm seeing is that when playing with seating depth, you should reduce your powder charge for safety. However, wouldn't that undo all the goodness of the Optimum Charge Weight?

After settling on a powder charge, should I just be loading to magazine length and incrementally shortening the COAL until I see pressure signs? I'm hearing that the pressure increases from seating depth can be very NON linear, so is there a safe way to do this without blowing anything up?

You might want to tweak your thought process just a little bit; this concept of 'optimum charge' as well as 'robust charge weight' cannot be independent of cartridge length.

My approach has been this: find a powder charge/bullet weight combination that works with your rifle using the recommended overall cartridge length specified in your manual(s). If you are loading for a magazine fed firearm, you may need to slightly adjust the OAL for smooth feeding. When I load for my AR, I'm not loading for precision, so I pretty much follow the book specs for OAL. I'd like to be more particular when loading for my Remington MilSpec 5R .308.

My gun happens to like 42 grains of Varget with 175 SMKs at the recommended OAL of 2.80. But that is just OAL: I am not taking into account the dimensions of the chamber and the relationship of the bullet ogive to the lands. Given the curvilinear design of the bullet, the relationship of OAL and distance between the ogive the lands cannot and is not linear: you simply cannot say "Well, if I make my OAL 2.805 then my ogive will be .005" closer to the lands..." For me this is an obvious non-linear relationship; bullet depth to pressure is non-linear as well, but since I can't see, feel, measure it etc, I prefer not to 'play' with it.

Again, my personal approach is not seating depth, but rather jump to the lands. Right now I have several loads waiting to be tested: 42, 42.5 and 43 grains of Varget behind 175 gr SMK . Each charge has two different 'jump values'. Will my accuracy and precision improve? Range time will prove it...

 

[l115a3]

As above mention, Ogive may slightly different due to different lot of bullet.

You should measure rely on BOG (Based to Ogive).


Some lot of 175 SMK seat COAL 2.800" , BOG = 2.233"

Another lot of 175 SMK seat COAL 2.800" , BOG = 2.217"


My LB chamber measure with 175 SMK to touch the land @ BOG = 2.250"

 

[Bob 964]

I have always been to told to start seating depth testing with the bullet touching the lands or jammed into the lands (0.010") and then working toward jumping the bullet. Starting jammed will let you know early in the process whether you have pressure issues. NEVER start jumped and work toward jammed. Read TresMon's sticky entitled "Handloading for long range 3: finding start OAL" for a better explanation.

 

[Deadshot2]

I have always been to told to start seating depth testing with the bullet touching the lands or jammed into the lands (0.010") and then working toward jumping the bullet. Starting jammed will let you know early in the process whether you have pressure issues. NEVER start jumped and work toward jammed. Read TresMon's sticky entitled "Handloading for long range 3: finding start OAL" for a better explanation.

+1

Another caveat. Only make ONE adjustment at a time. Either work with powder charge OR seating depth. Playing with a lot of variables at the same time will tend to make your head explode, not being able to figure out which change was really responsible for the success or failure of he load.

 

[NICKNICK]

+1

Another caveat. Only make ONE adjustment at a time. Either work with powder charge OR seating depth. Playing with a lot of variables at the same time will tend to make your head explode, not being able to figure out which change was really responsible for the success or failure of he load.

So should I pick a COAL first (either magazine length or ogive .XXX" from the lands), hunt for a powder charge, choose the powder charge, then start adjusting COAL shorter (further from the lands) while keeping powder charge constant?

 

[Bob 964]

Yes --- once you determine the optimal powder charge weight, you then test that charge weight at different seating depths.

 

[Sniper Uncle]

All this information is very good. But, if you are trying to figure out where to head, you can cut out some time by using QuickLoad to point you into a good direction. I have tried a myriad of powders---well, at least 7-8 in my 30.06. To load test all these takes forever. I just started playing with values in QuickLoad, and you can figure out a lot of stuff by data that has all-ready been collected and codified. Then, you can choose a powder that matches what you are trying to do, and start load testing with that. You can see theoretical differences with seating depth, and what it should do for your pressures. This way, you have a good idea what should happen, and can test to verify. QuickLoad can help you choose powder, find starting charge weights, and then figure out what you consider good things to try with seating depth. I have found QuickLoad to be somewhat conservative in its charge weights when compared to my manuals. I do check them also, just to be sure that I am not overlooking something.

 

[SPAK]

My personal practice is to stay off the lands at least .005". Almost all of my loads are .010" -.020" off the lands. There's enough inconsistency in base to ogive and oal of bullets that being closer than .005" will increase the likely hood that some of you loads will be on the lands and some just off...

I don't like jamming bullets either, and once you've opened an action to find all the powder dumped into your action you'll do he same. Soft seating usually requires light neck tension to work well, but again you risk the powder dump if you ever have to extract a live round.

Start .020" off the lands, Once you find your ocw move in and out +\- .005" but I wouldn't get any closer than .005" off the lands and personally I would stop at .010" off the lands. Depending on your particular bullet of choice, You should be able to find your fine tuning spot between .040" and .010" off the lands if you properly selected your ocw....

 

[glock63]

I start at .010 off the lands as well. Nearly every bullet I have tried in my custom .308 has shot well there. I have no desire to seat into the lands, and don't shoot bullets that require it.

 

[Deadshot2]

So should I pick a COAL first (either magazine length or ogive .XXX" from the lands), hunt for a powder charge, choose the powder charge, then start adjusting COAL shorter (further from the lands) while keeping powder charge constant?

This was summed up best by a fellow shooter who seems to win everything he enters (when he shows up the other shooters start to bet on who will be "second"). His words are "you play with the powder charge to get close then fine tune with the seating depth". Most seem to agree that he highest pressures are present when the bullet is jammed for any given powder load. Once you find your "pressure limit" move the bullet back in small increments to adjust now for the "barrel timing".

To move to the next stage, read this:

http://www.the-long-family.com/optimal barrel time.htm

 

[fx77]

Start with the Jam (bullet touches lands) and find the OCW
with the smallest groups
then back up the bullet from the lands in small increments 1-1.5 thousandths til you find your best group or the quality deteriorates...
This way U avoid over-pressure.

 

[heytonyman]

I've found that in most factory chambers, seating to the lands is will be no-where close to fitting in the magazine. If you're stuck with a long throat and a short magazine, the best you can do is load them as long as will fit in the magazine for OAL, but seat your bullets measuring base to ogive for best consistency. Of course load a handfull and check the COAL variations to ensure that they will indeed fit in the magazine.

For most rifles with long throats the difference between a .130" jump and a .140" jump is null. It comes down to a jump-tolerant bullet at that point.