Com ver Mil brass.. is pressure the same if vel is the same?

[indio]

Hello,

I'm wondering if I'm working up a hot load to keep 155gr Palma's supersonic at 1000yds in a long barrel TR/F Class 308 would it be a bad idea to stick with the Lake City LR cases i currently using (with mild loads) ?

If the velocity is equal would there be more pressure in a case with less capacity and less powder or a case with more capacity and more powder? Or would they be equal?

 

[jonbearman]

For every action is an opposite and equal reaction.This is the first law of physics.

 

[dmickey]

And this answers what question? ???

 

[necchi]

If the velocity is equal would there be more pressure in a case with less capacity and less powder or a case with more capacity and more powder? Or would they be equal?

Your trying to equate two separate things, Velocity and Pressure, they are not linear in comparison. More pressure does not always equate more velocity, other stuff happens in the chamber/throat/bore with various pressure spikes and powder burn.
A better way to wrap your head around it is to think that the lower capacity case may create the same velocity with less powder because of an equal pressure and pressure spike or curve being created.

I'm not real good at explaining the particulars in a way folks understand easily.

Bottom line is you'll need to work up separate charges for the different cases, esp when using mil brass.
Truly accurate 1000yrd loads need a high rate of similarity, each case should have exactly the same capacity, each neck should have the same tention, each bullet and charge needs to be exactly the same.
Can it be done with mil brass ? By all means, Yes. But selective care and measurement needs to be done.

 

[mw0248]

get your hands on 'Modern Reloading, 2nd edition' by Richard Lee; It will tell you everything you should, and should not do; I have been reloading for over 20 yrs, and I still use this book; Information is free; Stupidy/ ignorance is costly;

Just do it right;

 

[KevinThomas]

Indio,

Quick heads up here; LC and other military 7.62 and 30/06 brass tends to run a good bit heavier than their civilian counterparts, and have in turn less capacity. This makes LC brass a fairly poor choice for this particular application, as it limits the amount of powder you can stuff into the case. Most of the better brass used for this type of shooting will have greater internal capacity, thinner walls, etc.. The old WCC 58 brass is still some legendary stuff (damn near worth its weight in gold to LR shooters), precisely because it was so thin walled and had that greater capacity. That's the direction you need to head. You'll need somewhere in the neighborhood of 2950 fps to keep the 155s supersonic at 1,000. LC makes some very good cases (some of the best, for loading 7.62 semi-auto Service Rifles), but it's not a great choice for this particular venue.

This capacity issue, incidentally, is why most of the reloading manuals are so particular about warning handloaders to reduce their loads by 5%-10% to start if they're using military cases. Just something to consider.

 

[expiper]

With the smaller capacity case you get more pressure sooner....so with the larger volume case you can use more powder to get the same pressure and also MORE velocity.....the bigger the case volume the faster you can push em...Roger

 

[markm87]

I've hand scaled powder into .308 cases that I could sort by looking into the case mouths and seeing how high the powder was.

I was stunned the first time I saw how dramatically different .308 internal case volumes can be.

 

[KevinThomas]

markman87,

You realize that the powder wasn't properly settled into the case if you just poured it in with a funnel, correct? I think I did this in one of the Sierra manuals, but it showed the amount of settling that can be obtained by using different methods of charging. In one photo, I dropped a charge of an extuded tubular powder into a 308 case and took a photo of the powder of where the case mouth was filled to. Duping the powder out, I recharged the same case using (as I recall) about a 4" drop tube and the exact same charge of powder. That photo showed the powder coming up far further down in the case neck than the first one. And finally, I repeated this drill using an even longer drop tube and touching the case against a vibrating electric motor (electric shavers work well for this), and photographed the third drop. This time the powder was almost all the way down to the neck/shoulder junction. Same case, exact same charge, just using different methods of dropping the powder, and a major difference in how much free space was left in that case. Makes a big difference here, and doesn't necessarily relate to capacity.

 

[Greg110]

If you will check German Salazar's older blog entries, he answers all your questions.

 

[markm87]

markman87,

You realize that the powder wasn't properly settled into the case if you just poured it in with a funnel, correct?

To a certain extent... yes. But I can drop 20 charges in my Lapua brass and look into them in the loading block and they'll all look about the same.

What I was getting with some MagTech 308 brass was significantly different. I literally sorted the 10 pieces of brass out without seeing the head stamps.

 

[KevinThomas]

Checking the water capacity is the best way to sort here, and will give you a true idea of the relative internal capacities. Problem is, it's time consuming, messy and in general a pain in the ass. Just didn't want you assuming that different levels of powder, or where it came up to in the neck, was a valid means of discerning capacity, especially where extruded tubular powders were involved.

Sounds like you're headin' in the right direction.

 

[PREMOD70]

You'll usually get more case capacity with Winchester brass which usually equates to more speed if that is what you're after.

 

[markm87]

Sounds like you're headin' in the right direction.

Oh I am. I culled all that Brass and we're shooting Lapua only.