Ugh...Help me understand load data.

[Gato Montés]

Complete noob question here but I need to know. What I've been told (and subsequently been doing) is determine if the data is for jacketed or lead, then find your bullet weight and bingo, there's your data.

Alright, let's look at my Lyman 49th edition manual for 38 Special.

For 158 grain they list what looks like a flat point bullet, which gives a range for W231 3.6 to a max of 4.0 grains.

For 160 grain LRN my powder of choice now has a wide range, from 3.5 all the way to 5.2 for +P pressures.

In the comments section, they claim that the 160 grain bullet I listed closely represents the factory 158 grain LRN.

I'm using SWC as my first bullets, which as I understand can share data with LRN's.

So, my question is this; how much importance does bullet type have in determining load data? Can I use the 160 grain data, or am I restricted to 3.6 to 4.0 grains?

 

[MEHavey]

The difference is in the seating depth into the case -- as determined by both bullet design & OAL. This determines the internal ballistics/volume as the powder ignites.

Lyman's 160gr LRN data shows an OAL of 1.550" -- meaning it's seated 0.315" into the case when the crimping groove is aligned w/ the case mouth.

Before we can extrapolate to a different bullet design (even of the same weight), what is the distance from base-to-mid-crimp-groove for the SWC design you intend to use?

 

[ranger335v]

"how much importance does bullet type have in determining load data?"

In effect, none. No firearm cares what shape the bullet's nose is.


" Can I use the 160 grain data, or am I restricted to 3.6 to 4.0 grains?"

i'm not going to look up your data but there is no practical difference between bullets of virtually the same weight. So, the answer to your question depends on if you want to load standard .38s or +P. Personally, I would never load any +P simply because I don't believe the tiny increase in muzzle speed is meaningful and it does offer a potential for hazard to the shooter's revolver.

The oft mentioned concerns about touchy OAL/seating depth is mostly for small internal capacity/high pressure cartridges, neither of which has much application for the .38/.357. In fact, it mostly applies to the ballistically puny but hot loaded 9mm Parabellum and the .40 S&W auto cartridges.

 

[MEHavey]

Looking at that Lyman 160gr/W231/5.2gr/1.550"OAL +P load:

- There is almost a 30% increase in pressure from simply seating that same bullet deeper to an OAL of 1.445" (which is OAL of the 158gr SWC next up on Lyman's list.)

Again... what is the distance from base-to-mid-crimp-groove for the SWC design you [nasser] intend to use?

 

[Gato Montés]

Geez, what a day. Sorry to post and run, things came up.

Anyway, for right now I'm using swaged Hornady SWC that have no crimp groove, so there is no answer to that question. My decided overall length is now 1.480".

And to make clear, I really have no intention of cooking up +P loads, at least at the moment. I just found it highly suspect that my particular load would have a variable span of only .4 grains, while the 155 grain bullet and the 160 grain bullet would have a significantly larger (and almost similar) charge range.

 

[MEHavey]

This one, right?
http://www.natchezss.com/product.cfm?contentID=productDetail&prodID=HO10408

if so, and if seated to your suggested 1.480" OAL, Quickload tells me 5.0gr W231 with the Hornady 158SWC above would match the pressure it calculates for the other 160RN +P load you mentioned from Lyman#49.
Predicted velocity fr a 5" barrel would be 958fps

QL also tells me W231/4.6gr would generate Max/normal/non+P 38Special pressures for this HNDY 158SWC.
Predicted velocity fr a 5" barrel would be 904fps.

(FWIW, it doesn't appear you get all that much more velocity from going higher pressure.)

Now the Lawyers' Warnings: This is a theoretical calculation, based upon the differences between the internal case volumes generated by the two bullets. Approach w/ Caution and work up to where your gun performs to your satisfaction.

 

[Gato Montés]

Yep, those are the bullets I'm using.

So then I guess a better question would be why does the 158 grain listed in the Lyman 49th have such a small charge range while the two bullets that surround it, which are almost of the same weight, have a much larger range? Is it because of seating depth?

Again, not real interested in +P, just brought it up because of the dramatic variance between load charts. And thanks for looking all that stuff up (MEHavey), hate to burden anyone with all this.

 

[MEHavey]

Is it because of seating depth?

Exactly right. The deeper seating depth raises pressures for the Hornady bullet.

(Look on the bright side: You get the velocity you want for less powder ! )