303 British Measurements

[blackthorn]

I would appreciate it imensely if someone could please tell me what the Maximum case length measurement and the "trim too" length measurements are for the 303 British cartridge.

Thanks.

[john hayslip]

Hornady says 2.222 and 2.212 inches.

[longbow]

SAAMI:

http://www.saami.org/PubResources/CC_Drawings/Rifle/303%20British.pdf

No surprise, same as Hornady.

Longbow

[blackthorn]

Thank you.

[Dale in Louisiana]

google is a wonderful thing: I found wikipedia.

http://en.wikipedia.org/wiki/.303_British

dale in Louisiana

[303Guy]

Not all 303 chambers are the same length. There is a minimum clearance required and if it might improve accuracy one could determine the actual length and trim accordingly. On the other hand, if you have more than one 303 or your ammo might end up in someone else's rifle it might be prudent to trim to spec. Then again, my one rifle with a shorter chamber which got a case from a longer chamber didn't blow up or even show any signs of pressure because the throat entry was big enough. I didn't do it deliberately, I just wasn't watching case length and found the case mouth slightly crimped. I have to trim.

[ukrifleman]

Lee's Modern Reloading give a max trim length of 2.222, I trim fire formed brass 0.010 below max and then neck size, remembering to keep any fire formed, necked sized cases dedicated to the one rifle.
ukrifleman.

[Larry Gibson]

Why not do a simple chamber cast (parafin wax will do nicely) of your rifle? That way your case will fit your rifle.

Larry Gibson

[blackthorn]

Thanks again to all who replied. Here is the deal---I was given a fair amount of once fired casings. I have several 303 rifles, so what I want to do is to FL size one time and then start fitting cases to each rifle and neck size from there on. I found the max at 2.222 but did not find the "trim too" measurement, thus the original question. From what you all have said it appears I should use ten thou below max (or there about). A chamber cast of each rifle is definately in the works (eventually).

[ukrifleman]

If you are going to chamber cast, push a plug at least 9" down the bore and get a bore diameter as well.
ukrifleman.

[303Guy]

No, the nominal case length is 2.222 so trim to that length if at all. The main consideration in trimming is to square the case mouths. Some clearance is required on firing and sometimes the case elongates. If you are going to fire-form with cast boolits then trim after. Check which cases are interchangeable (one chamber is bound to take any of the others) to make sure the longest case is safe in all rifles it will chamber in. Have a look at chamber specs and work out the 'normal' mouth clearance. If you want to play it safe then 2.222 is the length you want, no less. Remember that sometimes cases shorten. If a case keeps lengthening you need to find out what's causing it. That changes case volume over time and the shoulder moves into the neck base area causing the dreaded 'dough-nut'. Sometimes the dough-nut can be used as a boolit seat but chances are it will be uneven anyway.

The significance to us as booliteers is the boolit can upset into that gap then get swaged down again. I can't see that as being conducive to accuracy although it may do no harm. I get that sometimes and the gap appears to be about 2mm.