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Old August 4, 2011, 11:57 AM   #12
Join Date: March 4, 2005
Location: Ohio
Posts: 10,221

Yes, sticky extraction is a classic pressure sign, and was used by Elmer Keith has his chief indicator of when a load had got past its safe limit. The general rule of thumb is, when you get sticky extraction, back the charge down 5%.

What happens is steel is more elastic than brass. Pressure expands the two together during firing, but the steel can expand beyond the elastic limit of the brass and still return to shape. When the pressure is high enough, the steel does expand that far, then returns to shape over top of the now permanently stretched brass. That causes it to clamp down over the brass and even partly resize it. So, it becomes akin to having a case stuck in a sizing die with no lube.

It is not at all uncommon in revolvers for the primer and brass to show no other pressure sign. This is because the outside of the chamber wall in a revolver cylinder is so thin it will stretch excessively before the other brass pressure signs show up. In a bolt rifle, on the other hand, when sticky extraction begins the other brass pressure signs are already present.

One last thing: It was reported by Elmer Keith and Skeeter Skelton and others that they often got higher pressure from lead bullets than from jacketed bullets when working up maximum loads in revolvers. Even though the harder jacketed bullets produce higher pressure in lower loads by increasing start pressure, lead bullets in a revolvers can be upset into the forcing cone, making them temporarily far oversize and acting as an expanding seal. Until pressure builds high enough to swage them the rest of the way in, they aren't picking up much added velocity. Than causes a higher portion of the powder to burn earlier in the bore so the peak pressure is reached before the bullet has gone as far down the barrel; before there has been as much burning space expansion. That means the peak happens in a smaller volume, raising its pressure value.

You don't have to use hard bullets with H110/296, but you will hit higher pressures sooner if you don't. If you read Richard Lee's book, you'll note the 5 step rule assumes a 10% load span, so the steps are 2% of maximum charge at most. That's not a bad limit for pressure testing, as it will raise pressure somewhere around 5% per step which should is acceptable for pressure testing. If you get load data where the starting load is less than 10% smaller than the maximum load, then switch to 2% steps.
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