243 1000 fps

1.  What is the application?

2.  You want a subsonic 243, correct?

3.  Will you be shooting suppressed?

4.  What is the barrel twist rate?

I have a 243, love it, but push it faster rather than slower.  My fist concern will be twist rate to stabilize the bullet for subsonic use.  

In general, since you are not looking for velocity, the larger the bullet, the better (since  1/2  mass x velocity squared gives you the kinetic energy, and the v is set, making the m bigger makes the KE bigger.)

And if you aren't running suppressed, it is mostly a wasted adventure.  Subsonic is much louder than in movies, even suppressed it is not hollywood quiet most of the time.

In the end, I am still wondering about application.

Lastly, it looks like that rifle is a semi-auto, I know nothing of the action but do know that taking an action meant for supersonic ammo and putting subsonic through it often results in failures to extract, eject, feed, and generally  function reliably.  Subsonic rounds produce far less gas pressure than do their supersonic counterparts, and the actions often don't have enough pressure to operate correctly.

In short, the whole thing might be fraught with peril, it might be worth doing, but it probably won't be nearly as easy as you might think.

you mentioned some great questions, I will have to dig deeper.

When you mentioned the application, are you meaning, : Hunting, sport?

it will be used for hunting. 

Weapon: remington 7400 -  243 rifle

does it matter on grain of bullet to have 1000 fps. or is it all depending on the rifle? 

Howdy the islander,
Welcome to the OT forum.

Making subsonic and reduced load ammunition is tricky business. If done incorrectly, a rifle can be wrecked and safety put at risk.

Are you already proficient at hand loading ammunition?

Perhaps we are trying to overcome a language barrier, but your question about bullet weight alone and your responses to questions imply that you are naive and really don't know anything about hand loading, or loading reduced velocity ammo. Forgive me if I am wrong. I do not choose these words to insult you, but only to help you. There are many here who can help you, but I must stress that you MUST have a high level of understanding about what you are attempting.

.243Win @ 1000fps might be achieved with a variety of bullets and powder combinations, but probably can best be achieved with the heaviest weight bullet which will stabilize in your bore. A heavy bullet @1000fps can best be reached by using one of the double- base pistol powders, but that low speed is achieved with non- typical low chamber pressure and runs the risk of making a load which will stick a bullet in the bore, or create a "detonation" condition, either of which can harm your rifle, or you and bystanders.

If you already are an accomplished hand loader, then there is a wealth of information available online about making reduced load rifle ammunition. My best advice is to learn all you can from all online discussions of reduced loads and then learn some more.

By all means, if you see fit, keep the info and questions coming, as this can turn into a discussion which will benefit many people. Again, what I've said is only to help you and not cause you embarrassment, or insult.

Have shot some sub .243 use trailboss due to case load a little dirty but nice and easy to load never a double charge possible.

would share this with you.

You have had some great responses to your post!

I have loaded a heavy gr. .30 sub I think it were a .220Gr and only 1/3 of the bullet actually cleared the bore I loaded them down too low as a starting load could have caused issues. Didnt take into consideration cold bore cold day cold case.... DUMB DUMB DUMB DUMB on my part...I still have the bullet as a reminder.

Some subsonic (maybe 75%) some supers loaded pretty hot (25%) never factory, never middle of the road.  I have found to get more than the book safely by just learning the rifles and lockups...

I know guys that only shoot "The Load".

I also know guys that load Trailboss every day and in every way (as recommended) and are safe in doing so by following the posted link.  

(I myself have tried double base and triple base high energy powders like n560-n570 and have found them to be my favorite but still use a donut powder like Trailboss due to bulk density) 

Trailboss is a great way to get comfortable with "Reduced" loads...

Extremes of loading can be really tested with the .243WIN.  Can be fast can be slow can be light weight can be heavy weight.  You must know the stability as posted above!!!

Not as many loads as for the .458WM but the .243WIN. has some wide range of capabilities as well.  

I will share that the .243 almost made it as a military cartridge and did very well in the FBI trials and was proven to be able to have very effective terminal ballistics.