Discussion in 'Handloading and Reloading' started by orpington, Nov 20, 2021.
The gas check provides protection of the bullets base & can be loaded to higher pressures.
If the heavy bullet is going the same speed or slower than the lighter bullet, that too would make sense.
Of course if the data is from more than one source, that’s almost a guarantee they won’t be the same.
I have some books that lists different starting/max loads for the same bullet, seated to the same depth using the same powder. This H110/W296 (same powder) data as an example.
Different lot of powder, different environmental conditions on the days tested, different measuring equipment…
To sum up your questions...
Increased bullet weight does, indeed, increase pressure. That's why you will see load charges go down for a heavier bullet, when comparing apples to apples... that is, say a Hornady jacketed bullet vs a Hornady jacketed bullet.
Gas checks seal the base of the bullet, much like a jacketed bullet obturates... increasing pressure with a better seal. The benefits of a gas check are two-fold... besides a better seal, you can generally drive gas checked bullets for this reason, and as was mentioned, reduce leading from a hot flame front.
Cast bullets can run from very soft (pure lead) to very hard (typically called 'hard cast.') There are benefits to both... depending on what your purpose is for the bullet, and how fast you plan on driving them. Again... generally speaking, soft lead bullets cannot be driven over the generic threshold of 1200fps (or even less...) without leading and other problems. Harder cast bullets can... I regularly drive non-gas checked cast bullets into the 1800's, and gas checked cast over 2200fps.
There are also exceptions... like the .45 Colt. A generic .45 Colt load won't drive any bullet over 900fps (or thereabouts, depending on the weight) but there are firearms that can handle heavier loads, and data is provided for those specific firearms... using the very same bullet in some instances.
I believe I was comparing data from different publications and hence my confusion. Further research reveals that these publications consistently appear to decrease powder suggested starting grains and max loads as bullet weight increases. However, there is variation using the same bullet weight and a different publication.
As was pointed out by jmorris and Charlie, if all things were equal, but they're not. Even barrels made connectivity will produce differences.
The books are guides, not absolutes. That is why we start low and work up, verses picking a weight and going for it. Works the same with lead, my alloy and cast 432-640 bullet might be softer than yours or either might be a plain base or GC'ed. Either way the only data might be a Lyman manual. That said, for a 260gr cast bullet with a similar profile across the board "should" have similar start load data.
Will your alloy and firearm be the same as ours or theirs, nope so we work with what we have recipes for.
A few other things to look at... are each data sets finer details. Things like which primer, is it a test firearm or a test barrel (2 VERY different things!) and the length of the barrel. As .41 suggests... every set of load data you see is really valid, just valid for what the tester that day found using their components in their particular environment. Testers also have different end goals for data... accuracy vs velocity, or pressure over burn characteristic... even something as esoteric as case fill.
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