From a max load back to a resized case?

[Mark611]

I know this has probably been asked here before but I'm gonna ask for some expert advice on this for my own good! I've been reloading 7.62x51mmNato cases in my 308win Savage bolt gun, most of my data I've been using has come from a book from Stephen Radgwell, titled Reloading 7.62x51mm Military Brass: in this book is info on how to safely reload 7.62nato to be used any bolt action rifle, but he starts off using fire formed cases to develope his data, so my question is without going back thru the whole process of load development again due to the limited resoures in todays world can somebody help me here? Let's say I have a max load of 40.5gn's of Varget using a 175gn Sierra Matchking from my 24'' 1&10 twist barrel, using a fire formed and neck sized only case, I'm happy with the #'s from my chrony and I have no pressure signs to worry about and all is good! now say I have 400 full length small base sized cases I want to reload, Where do you think I should start my powder charge @ to try and safely keep my same velocity's and pressures at? any ideaslightbulb I'm wanting to load up some ammo for storage, thanks guy's!

 

[Red hunter]

Do you have a head space gauge? Check the difference in case size. If they are close, say .001 to .003. I dont think they will have the same point of impact due to the case difference. They may be close but not one that I would stick in my rifle and expect to hit at an extended distance.

 

[Mark611]

yes I have a L.E.Wilson drop in gauge that will show proper case sizing and head space, and I also have a Hornady comparator tool with the head space gauge bushings to measure the difference in the head space of full length or small base or fired cases, my concerns are internal volume, I'm looking to try and get as close to the same velocity's from the fired cases compared to the full length size with over pressuring the full length sized cases I started off with the case in new condition as the came from IVI, they were small base sized to begin with, I sorted them and full preped and also turned the necks to make them as uniform as possible before I loaded them, I've only worked with about 100 pieces of this brass so far and started off loading them at the lower end of the loads suggested in Steve's book, I thought maybe someone might have gone thru what I'm looking to do and it may save me some trouble of going thru the testing again I know the poi will be off some but I'm not concerned about that I can always resight without allot of shooting to rezero,gun)case volume is where I need help, thanks guy's

 

[Deleted member 46119]

I think you are asking a question that is somewhat difficult to answer.

Correct me if I don't get this right, I'm gonna restate your question:

What changes do I make to the powder charge to get the same POI from a new lot of brass that is not fire formed to my chamber?

If that is the question, it's a physics problem and it takes data, lots of data. All that data is something that may not be available. An example is "case volume".

There is the data of case volume of your fire formed brass vs. the case volume of your small base sized brass vs. dynamic case volume as the round goes through the burn, expansion, bullet release cycle in the chamber.

IMHO: All anyone can say is "If it were me, I'd..."

So, not recommending it to you but if it were me, I'd:

Make a 'short' ladder of 3 cartridges of each at .2 increments, starting 1grs below the known to work well load. Chron these and check POI. Pick the one that is closest to the known good load, assemble the remaining cartridges and shoot away.

If I had a "match", I'd stick with the already fire formed brass.

 

[jasent]

No short cuts in this hobby, I'd load up 10 rounds starting below your load and watch for pressure, you may find that you can load your normal load,maybe not. I'd GUESS that you can but as mentioned they prob won't have same poi or speed because of the brass having room to expand. Difference may be minimal, Better to shoot up 10 rounds than have a problem.

 

[SidecarFlip]

BTW, Sierra recommends powder charges in once fired military brass to be one haf to one grain LESS than the normal charge in all instances. That comes right from the Sierra loading manual, 5th edition.

I'm sure they have a solid reason for that. Sierra does extensive ballistics testing on all types of brass/projectile combinations. They have a state of the art 300 meter underground test range below their facility in Sedalia.

I load Sierra projectiles almost exclusively with the exception of Hornady V Max in 22 caliber.

 

[Mark611]

Thanks for the replys! I guess what I'm asking is if my max load is 40.5gn's of Varget with the 175gn SMK's with fire formed cases @ 2550fps with the Nato brass, and I'm trying to get close to the same velocity's with the same brass that has been small base sized that is unfired without over pressuring the the unfired cases, I'm looking for a good starting point should I start a grain weight under this max load or should I go more than a grain? I have not noticed any real pressure sign's with the 40.5gn loads, I feel comfortable @ this loading and don't feel the need to push it any further it's still SS! 1k yds according to my data? thanks for your help!

 

[Deleted member 46119]

BTW, Sierra recommends powder charges in once fired military brass to be one haf to one grain LESS than the normal charge in all instances. That comes right from the Sierra loading manual, 5th edition.

I'm sure they have a solid reason for that. Sierra does extensive ballistics testing on all types of brass/projectile combinations. They have a state of the art 300 meter underground test range below their facility in Sedalia.

I load Sierra projectiles almost exclusively with the exception of Hornady V Max in 22 caliber.

Fits with my suggestion.

 

[jasent]

I'd suggest 5% at least