stupid pressure question…..

[762willdo]

i was wondering i currently shoot black hills match brass in my match rifle .308 but have on hand several thousand LC LR .7.62 brass and was wondering if i switch will it effect accuracy?
I have matched up the fps exactly by dropping one grain, but will the pressure profiles be the same, in short if represented by a bell curve will the pressure spikes overlap exactly? if they don't then i would expect it to change POI some.

thanx!

 

[tctender]

Re: stupid question…..

If the velocities are the same the pressure curve should be same or at least close. I would shoot some and see if any difference is showing up.

 

[762willdo]

I intend to but can't for a week and a half due to work and was just wondering……

also i'm no genius but i'm pretty sure the pressure curve and velocity have very little in common...

 

[chkunz]

I intend to but can't for a week and a half due to work and was just wondering……

also i'm no genius but i'm pretty sure the pressure curve and velocity have very little in common...

I am no genius but I can tell you that the pressure curve and velocity have a lot in common and I stayed at a Holiday Inn once.

The LC brass is very good brass so drop the charge one grain because the brass is a little thicker than the Black Hills brass and then drive on. If you load the LC brass to the same velocity as the Black Hills ammo then you will be within one MOA on POI.

 

[chkunz]

i was wondering i currently shoot black hills match brass in my match rifle .308 but have on hand several thousand LC LR .7.62 brass and was wondering if i switch will it effect accuracy?
I have matched up the fps exactly by dropping one grain, but will the pressure profiles be the same, in short if represented by a bell curve will the pressure spikes overlap exactly? if they don't then i would expect it to change POI some.

thanx!

One other point, there is more to MV than "the peak pressure spikes overlapping exactly". The MV is a function of the area under the pressure time curve. Your question demonstrates that you do not have a firm grasp of the fundamentals of internal ballistics. That is ok, we all started where you are and we learned by studying. You have come to a good place to learn. Keep the questions coming and you will get great help in learning.

 

[Joe R]

T-REX said:

The LC brass is very good brass so drop ......

IMO for 308 the LC brass is the best brass there is bar none. However, if you want to use LC brass you have to be prepared to anneal and use some brute force, because the stuff is tough. The other thing when resizing you have count to ten Mississippi, to give the stuff time to reshape itself, because it is so tough. If you are interested in precision (we are on Accurate Shooter) I recommend you turn necks. I do it once before I fire it and again after two firings. After that you are on easy street. It's a bit of work but it is well worth it.

I'm pushing 200 grain bullet well over 2,700 fps without any issues. When I was using Lapua cases the primers would fall out after two firings and I'd get expansion in the extractor groove. With the LC I'm on my 5th firing without any problems and I believe they'll go at least 15 times around. I like shooting not reloading, so once I prep the brass I want it to last more than a few firings. Less time prepping brass, more time shooting. YMMV.

Kindest regards,

Joe

 

[Nvreloader]

One item I would do is to get an average H2o capacity's of Both cases you plan on using,
as the internal case capacity's can and will cause problems,
if they are not real close to each other.

If you have QL, you can check the spec's and see the results etc, IMHO.

Tia,
Don

 

[the long shot]

i was wondering i currently shoot black hills match brass in my match rifle .308 but have on hand several thousand LC LR .7.62 brass and was wondering if i switch will it effect accuracy?
I have matched up the fps exactly by dropping one grain, but will the pressure profiles be the same, in short if represented by a bell curve will the pressure spikes overlap exactly? if they don't then i would expect it to change POI some.

thanx!

You can have pressure problems and not have velocity/POI problem so they are separate issues. See my thread on "Blowing primers with mild load" I am using Black hills brass and despite having FPS withing 50 of each other my IMR4350 and Varget loads are showing two different pressures.