Neck Clearance in F class?

[Dusty Stevens]

The old mentality was more neck clearance led to premature neck failure. People always just go with what they hear rather than test it. Truth is your brass wont last that long. Your necks may fail due to too much clearance but you woulda had to devcon your primers in about 32 firings before that.

 

[Laurie]

A long time ago, my local gunshop who had close links to the then UK Norma importer, got in thousands of rounds of Norma 308 Win loaded with 150gn PSPs and was selling them cheaper than I could handload the cartridge with Sierra MKs or Lapua B-series Lock-Bases. There was 'something wrong with the brass and it can't be reloaded' my friend the shop owner said. He had trouble moving them despite the price and I ended up clearing his stock at a further discount, pulled the bullets and used them up over the years and much more quickly used up the powder which was probably a bulk equivalent to the old and excellent Norma 201. The brass was carefully deprimed and the primers reused (never had a misfire and they produced good ES values depsite the mishandling!). So I had around 1,000 new 'faulty' cases which I found worked fine but would see neck splits after four or five firings in my Ruger 77V or TR (Fullbore to Americans) rifles. This it seems was the problem - the necks were too thin and when fired in a standard factory chamber and sized with standard dies soon became overworked.

Anyway (cutting a long story short), when FTR came along many years later I discovered I still had a few hundred cases in a box in the loft and now I was into case weighing, neck measuring, neck turning, and bushing dies. Around half had necks around 0.013" or same as Winchester 308 and could mostly be used as a no-turn. The other half were in the 0.012 - 0.0125 band the odd one reading even below 12 thou'. I ended up neck-turning them to 0.012" and sizing with a .330" bushing. At 0.332-0.3325" neck O/D, the pundits told me I was wasting my time shooting them in a 0.344" chamber. Well, they shoot very well indeed and with bushing sizing + Sinclair's E22 mandrel neck expander, I've junked them for slack primer pockets and never a one for a neck problem. After a while the penny dropped that these were the famous Norma 160gn cases from one particular production lot in the early 1980s. With very thin brass they have even higher capacity than Winchester. The fireformed brass water capacities for the three makes in my then FTR rifle were: Lapua 56.1gn; Winchester 57.0gn; Norma 57.4gn. GB 'Match Rifle' shooters had sought them for a while because of this extra capacity, but had found them insufficiently robust for the very hot, heavy bullet loads they've used since long before George Farquarson invented F-Class.

I only use the survivors occasionally now, but that's not because of their performance, rather I do 90% of my 308 shooting with Lapua 'Palma' brass and my older traditional LRP Lapua cases don't get much use either. Yes, 10-12 thou' total neck clearance is almost certainly more than desirable, but it performs much much better than many people will accept.