I am considering making the change from lead to copper/copper derivitive bullets. I have read that copper (Barnes/Nosler/new Hornaday) are, in general, more sensitive to loading techniques particularly seating depth than are their lead counterparts.
Are there any "rules of thumb" that can be suggested to facilitate the transition to copper from lead bullets in 7mm-08?
I'm not sure if you are moving from cast bullets (what is usually meant by "lead bullets") to gilding metal jacketed bullets, or are talking about moving from lead core jacketed bullets to copper solids? Each of those steps up raises start pressure. Higher start pressures means higher peak pressure for a given powder charge. This varies with your gun's specific chamber and bore dimensions. Simply obey the old rule of thumb that any time you change a reloading component (case, primer, powder, or bullet) you back your loads off 10% and work up watching for pressure signs.
Solid copper bullets are less dense than jacketed lead core and cast bullets. That means they are longer for a given bullet weight which means they need a faster barrel twist to keep them stabilized.
I should have been more precise in my initial post. I intended to say that I was moving from conventional lead core bullets to solid copper bullets and understood that copper bullets needed to be seated deeper (because of their relative length) and that accuracy tended to suffer until that "sweet spot" for copper had been determined. Any suggestions as to how to back into the revised seating depth...or is it purely a trial/error process?
I have just reloaded some test loads for my 270 using Barnes tsx. I used the given coal but from what I have heard on other forums .o50 to .030 off the lands are best.
The greater seating depth just refers to the fact the bullet base has to go in further to get the same COL as a same-wight, same-style bullets of the denser lead core construction. If you are loading singly, you can touch the lands with them, same as any other bullet. They will raise start pressure though, owing to being harder, so you need to back the load down maybe 20% from max and work up if you are doing that? If you start with the usual .020" off the lands, the normal 10% backing off max load should be adequate to start. Adjust deeper in 0.005" increments toward 0.050" off the lands until you find a seating sweet spot somewhere in that range. Then start working the powder charge up to find the charge weight sweet spot. Also try around 1 caliber into the case neck if the bullet's greater length hasn't put it there already?
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