Achieving maximum case life 101 The dimension of the chamber and the dimension of your dies has everything to do with case life. Let's take a look at 308 Winchester. Pull up and print the below for reference. http://www.saami.org/pubresources/cc...Winchester.pdf Particularly notice the tolerances allowed on cases and chambers. Notice there is a datum line .200” up from case rim calling for .4703 and the tolerance is minus .008” which means a factory case can be manufactured from .4623 to .4703 and still be in tolerance. In actual practice I don’t think you will find any new 308 commercial cases smaller than .465” and I believe one will find all LC Match unfired cases to be .468”. Now look at the chamber drawing at bottom at which calls for .4714 + .002 so a SAAMI chamber can run .4714”-.4734” at that datum and I have seen rifles that give birth to cases that measure .475” ! ! ! ! ! Best scenario here is obviously a LC Match case at .468 being fired in a chamber that is .4714 so you have an expansion of .0034”. Worst case is a commercial case at .465 fired in a chamber of .4734” or worse. Now, look at case neck variations you can get with such chambers. .3442 +.002 is authorized for the chamber and the loaded round neck at .3435-.008” so you can have .3355 case neck and a .3462 chamber neck. In ammo, I have measured LC Match M118 that runs .338 on the neck and commercial ammo is a tad smaller and varies but I have found nothing larger than .338 on commercial ammo but then again there are so many and I don’t buy factory loaded ammo to hunt with. It is well known the more a case expands from fired dimension the more the brass is “worked” taking it back to what FL dies produce. That brings up other problems. .308 dies I have size .4680-.469 and I have one that FL sizes at .471” as I don’t want to “work” the brass any more than I have to. I see hundreds of references to small base dies which beg the question if all 308 dies size base dimension to .468-.469 and the smallest chamber base (fired case) dimension is .4714” how much smaller do you need? I don’t own an SB die and never have. Thus, what is one to do to obtain maximum case life? Bear in mind I am talking bolt gun chambers here and not parking lot (M14/M1A) chambers. I have 308 reamers that give me a base dimension of .4685-.469”. Thusly, commercial cases only expand .004” and LC Match expands .0005" or .001" so when it comes out, my fired cases run around .4683” which means the brass has not visibly moved but can be measured. When it is sized, the base does not move. Thusly, the brass more or less retains its factory dimensions. I have reamers that cut four neck dimensions: .337, .339, .344 and a SAAMI spec reamer. Rifles chambered with .337” reamer will just chamber Winchester cases with 168 Sierras. Rifles chambered with .339” neck dim reamer will just chamber LC Match and all the commercial I have found. Next to be considered is the distance between the case head and the case shoulder. Look at the chamber drawing and you will find 1.630 +. 010” range. GO Gages (min) are .1630 and NO GO are normally .1.636 and FIELD SERVICE is 1.640” Thusly on a new factory rifle you will normally see 1.632 - .1.634 and I have seen new factory rifles close on 1.636 NO-GO Gage. OK get out your MOTION SICKNESS BAGS and look at headspace dimensions for ammo is .1.634 -.007” so you can have max forward movement of the shoulder go form .1.627 to 1.636 or .0066” range. Again talking bolt gun here and not parking lots. I headspace my rifles to give me a fired case of 1.631–1.632" so when I FL size I can adjust my die to give me a loaded length of 1.630–1.631", which means the shoulder is barely moved. I call this the 222 Rule, which means the case moves no more than .002” at base, neck or headspace. Now, what does this give me for case life? Well in 308 using LC Match brass I have run tests where I did nothing to the cases and got 90 to 100 loadings. On commercial cases, I discard Federal at third firing and Winchester at 6 to 10 firings when the primer pockets get loosened as I don’t want to cut my bolt faces with the plasma jet-like leakage around the edge of the primers. On 30.06 I run .467 base dimensions and .469 on another and I have one 30.06 LC Match case I have loaded 157 times and still waiting for more. ALL 30.06 ammo I have ever measured new unfired is .465” at the base. Based on this and the feel of the primer pocket on this case I can get maybe 20 loadings and then I will move to Wolf Primers which are a tad larger than ours and will snug up the “feel” when seating. Based upon the cost of 500 new cases these days, this will pay for one to buy a custom reamer for bolt guns that give tighter dimensions and longer case life and if you like to shoot the reamer pays for itself quickly and it is good for many chambers especially if you use a rougher first. Ray Steele who built all the US Secret Service sniper rifles and the match-winning rifles they used for many years is the one that got me on the above chambers about 30 years ago and I bought my reamers from the same place he got his to his drawings and as well his personal reamers. Ray passed a couple years back and I miss him greatly. He was not only a top-flight rifle smith but a former member of US Palma, Dewar and Pershing Teams and to my knowledge only two people have been on all three, the other being Larry Moore. Prior to going to the Secret Service, Ray built all the ammunition test rifles at Frankford Arsenal. He designed the reamer used to chamber the rifle that holds the 1000 Yard Any Sight record and as of this writing is still listed on NRA website. I have a reamer made to Ray’s drawing for the 300 Win mag which has tolerances to give max case life as well. OK, I fully realize a tight neck can lead to high pressures and the way to make sure all your loaded ammo will fit in such chambers is you take a piece of barrel the same caliber you are shooting or the muzzle section that is normally cut off a blank and run your custom min dimension reamer in the chamber end until the shoulder is cut about .100" and stop. Next, reverse the barrel stub in the lathe and trim it back until you see the end of the case neck and leave the shoulder. This will give you exact information on where your neck is in relation to overall length. The gage is left in the die box and I gage every round loaded to make absolutely sure no interference fit is going in and have never had a case that would not go in my NECK GO GAGEs. Bottom line is I have one set of 500 30.06 LC MATCH brass that I have been running since 1982 and they are on their third barrel and all were cut with same reamer I got from Ray Steele.