Speer Reloading

Which bullets can I use instead of what is listed in my manual?

I am very new to reloading so I need some help. I have a Speer Manual #14 and it only has Speer products. If I wanted to use Hornady or another manufacturer how would I determine what bullets to buy? Should I just shop by the size and use a slightly lighter load or should I buy another manual?
BTW my main hunting rifle is a 1943 Mk. 4 No.1 Lee-Enfield chambered in a .303 British. No offense to Bear Crap’s response but the website listed doesn’t include .303 British. My mistake for not adding that to begin with.

The rule of thumb is you use the same bullet weight.

I strongly advise you to buy the Layman reloader guide book. It has tons of information for reloading ammo.

Edit;
Im sorry about that. Seems their site has changed and I didn’t check it out well enough duh!

I advise you to buy the manual for each powder company and bullet manufacture. I have one and here is a bit from it;
.303 British
150 grain Hornady SP InterLock bullet, 42.2 grains RL-15 powder, Win. WLR primer, Hornady brass. MV 2600 fps in 25.25″ barrel. (Based on the Hornady Handbook, Sixth Edition.)
174 grain Hornady SP InterLock bullet, 46.4 grains H414 powder, Win. WLR primer, Hornady brass. MV 2400 fps in 25.25″ barrel. (Based on the Hornady Handbook, Sixth Edition.)

WARNING! Never go by data given on a forum including the data I just gave you. Its 4 am and I could have made a mistake. That was just to give you and idea.
But as I said you go by the weight of the bullet. If your load data says so much of type *X* powder with type*X* primer and a 180 gr bullet that means any jacketed bullet that weight.
There are other important thing like overall length of the round, length of casing, etc etc, that’s important.
I still can find free load data from the powder companies and you can trust that. Here is one for example;

http://www.hodgdon.com/basic-manual-inquiry.html

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