Discrepancies in reloading manuals

[smlake]

The Alliant Powder reloading data website calls for a maximum load of 7.2 grains of Unique powder for the .40 S & W in the 165 gr Speer GDHP bullet using CCI 500 primers. The 49th edition (2008) of the Lyman Reloading Handbook states a maximum load of 6.0 grains of Unique for the 165 TMJ bullet using Winchester WSP primers. That much powder discrepancy makes me wonder why. The 47th edition of Lyman provided the same data as the 49th edition, so I do not believe the Lyman data is a misprint. Would/could the primer brand difference account for that much difference in the powder load? I would appreciate any ideas. Thanks in advance.

[Gearheadpyro]

Maybe differences in barrel length are at fault here? Possibly different bore diameters by a coupls of thousandths? Might be the primers.
Only other thing I could think of was different bearing surfaces on the different bullets.

I usually take an average of an abundance of loading manuals as my max load.

[Terry_P]

That is why we start low and work up while checking for pressure. I have found the Speer manual to be conservative enough to avoid pressure issues but the Sierra manual can be over the top. Speer lists 6.2-7.2 gr of Unique with a 165 gr JHP or TMJ.

On a side note my favorite powder for the 40 S&W is Power Pistol as it gives me excellent accuracy in my P94.

[res45]

Both the Speer GD and the Win. TMJ both have about the same BC and SD but they are slightly different but not enough to make that much of a difference. I think probably the difference comes in what was used to do the test with. I don't know what Alliant uses to or where they get there data from.

Lyman uses a 4" barreled Universal receiver so a call to Alliant might be in order and if someone has a new Speer manual to verify Alliants data agents. Other wise start at the bottom and work your way up watching for pressure signs a Chrony would be very valuable to verify your load vs. the data your loading to.

[woolleyworm]

165 gr Speer GDHP bullet vice 165 TMJ bullet

Originally Posted by smlake

Would/could the primer brand difference account for that much difference in the powder load? I would appreciate any ideas. Thanks in advance.

HUGE difference in bullets here that you must understand; a HP vice a TMJ is very different. if you take all that weight out of the nose of the bullet, it has to go somewhere, so it goes to the base. Compare it to a FMJ or TMJ that is of the same weight; you will find that in most cases CASE VOLUME is different when seated to the same OAL. You can never assume that is it ok to interchange data between bullet types. You must compare apples to apples; this is like a apples to cannon ball situation.

Win primers - I do find to be a slight bit hotter and get better powder burn from slower burning powders.

Testing barrel lengths and temps can vary between manufacturers also.

I'll always tend to start off at the min load between those that differ and work my way up until I find my sweet spot load.

[smlake]

The manuals do not have the same types of bullets and that is likely a problem. I just find the difference is powder loads, given the same bullet weights, somewhat alarming. The difference in bullet design may matter that much. I appreciate the opinions expressed here in explaining the differences.

[GMFWoodchuck]

Originally Posted by Terry_P

That is why we start low and work up while checking for pressure. I have found the Speer manual to be conservative enough to avoid pressure issues but the Sierra manual can be over the top. Speer lists 6.2-7.2 gr of Unique with a 165 gr JHP or TMJ.

On a side note my favorite powder for the 40 S&W is Power Pistol as it gives me excellent accuracy in my P94.

I don't know if "over the top" is the right term, but Sierra sure does have higher powder charges than any of the other manuals I have seen.

[38 special]

Originally Posted by smlake

The manuals do not have the same types of bullets and that is likely a problem. I just find the difference is powder loads, given the same bullet weights, somewhat alarming. The difference in bullet design may matter that much. I appreciate the opinions expressed here in explaining the differences.

You observations and conclusion are correct. Loading data IS all over the place. I load alot of 38 specials and with 1 manual I am loading a HOT +P load and in another I am loading a MILD 38 special load all with same bullet type exact same powder and charge and exact same primer.I too thought perhaps the hardness of the different jacketed bullets may account for descrepancy but there is just way too much difference for this to be the reason.I took the Sierra,Lyman,Hornady,Speer,AlLiant,Hodgdens,Winchester and other manuals and wrote down all the listed mins. and max loads for a given powder,bullet and primer and compared them. There are Huge differences.
I gave up trying to figure out what +P load was. From the manuals there simply is no way to know. And +P factory loads? Maybe just a marketing gimmick for people who want to think they bought the "hottest" load there is
when maybe they are just getting a stout 38 special load.

[Terry_P]

GMF thats why I said "can be over the top". It was kind of a load specific comment. I have pulled bullets from their loads before just because I was showing pressure with lighter charges and they were scaring the hell out of me.

[GMFWoodchuck]

Originally Posted by Terry_P

GMF thats why I said "can be over the top". It was kind of a load specific comment. I have pulled bullets from their loads before just because I was showing pressure with lighter charges and they were scaring the hell out of me.

Naaww.....That's how you grow hair on your chest.

But on a serious note, I was thinking I had the Sierra manual when it's the Speer manual that I have. My bad.