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New To .40


Chuck Merriam

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:wacko: With all the searches I start to get a little cross eyed.......I am loading to 1.180 OAL and using Winchester Small rifle Primers. #1 How much decrease in pressure do I get by loading longer (to1.180 vs 1.126 or so)? #2 How much hotter will the loads be by using SRP's? You can answer both by telling me the approximate % increase/decrease of Titegroup Powder or what you use. After looking at all the data seems like using close to max. on powder at spec OAL to make major with SRP's and 1.180. I know back the charge down 10% or so and check, but just want to hear from those who have more grey matter on the subject. ;)

Thanks,

Chuck

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:wacko: With all the searches I start to get a little cross eyed.......I am loading to 1.180 OAL and using Winchester Small rifle Primers.  #1 How much decrease in pressure do I get by loading longer (to1.180 vs 1.126 or so)?    #2  How much hotter will the loads be by using SRP's?  You can answer both by telling me the approximate %  increase/decrease of Titegroup Powder or what you use.  After looking at all the data seems like using close to max. on powder at spec OAL to make major with SRP's and 1.180.  I know back the charge down 10% or so and check, but just want to hear from those who have more grey matter on the subject. ;)

Thanks,

Chuck

I use VV N320 which has a similar burn rate, and I get 20 fps more with SRPs than SPPs.

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VihtaVouri used to have a neat little formula in their reloading guide that allowed you to estimate the change in pressure and velocity caused by a known percentage change in powder charge, case volume, and bullet weight. They stopped publishing it a few years ago, probably because people were putting too much faith in the numbers they were calculating, when all the formula was good for was rough approximations for small changes.

What you are asking for in your first question is what a change in internal case volume, caused by seating the bullet to a different OAL, will do to peak pressure. The problem is that, short of actually measuring the case volume of a loaded round (and there are ways of doing it, but none that I know of that are simple) you don't know where you started and where you ended up on the volume. So you are guessing, and when you are talking about peak pressures in a high pressure round, that is a hazardous thing to do. You will, however, definitely have lower pressure for the same powder charge/bullet/primer, the longer you load.

Published data in load books is the safest information to start with. In the forty, one trick is to start with the data for the 10mm, since that is loaded to a length similar to what the forty is loaded out to to chamber easily in the 1911 pattern guns. The problem, though, is that the powders used in competition aren't the ones listed in most manuals for the 10mm or the 40 S&W.

Commonly used recipes for loads for the action pistol sports, found here and from a number of other sites, are GENERALLY considered acceptable for use in a well built gun with a fully supported chamber, although your results could definitely vary and you use such info at your own risk.

Any load you start with, you should work up to. Start 10% below the charge recommended at the OAL listed and work up from there. If your bullet is different from the one listed in the load, even if it is the same grain weight, compare the lengths of the bullets, and compensate in the OAL to give the same internal case volume. A chrono is a must.

For your second question, even though many have not found a consistent difference in velocity using Winchester's WSR's vs WSP's, my experience is very similar to fomeister's, using the same powder, though my spread is a bit less.

My two centavos,

Kevin C.

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Thanks for the info. Never thought to look at the 10mm data. When you load long there is not much data except for this forum. I have an excelent load manual that has bunches of stuff, including hard to find loads with older powders even. I used the 1911Forum alot, but it seems it is out for who knows how long!?!

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