powder weight vs. OAL ?

[Pauliedad]

I've been working up some various loads for .40 with several different powders and as a result am making lists of what I can put together based on what components I have.
My Walther P99 4.2" barrel
is fine with OAL of 1.135
so all the loads I'm working up are using that length.
If I reach the maximum powder weight but am using a longer OAL does that buy me any wiggle room? Or do I just need to start shortening my OAL? I'm not at velocities listed so I'm wanting to see if I can step it up.
Each load seems to show a different OAL and I get that a shorter length adds pressure so am I on the right track here?
I'm trying to have a standard OAL that can cross over to several powders.

I hope this makes sense and thanks for input.

[ar15barrels]

Shorter overall length changes the effective case volume.
If you are loading longer than a published load spec, you would usually need to increase your charge to reach the same performance.

[rcschummers]

I would be extremely carful reducing you OAL with the listed maximum loads. If you decide to go that route, make sure you're tediously checking spent cases for signs of over pressure.

Spend some time looking over all the load data you can find on your components, you will quickly see a large variation in the data, some data is significantly "hotter" than others, most new stuff is on the safe side.

In my opinion, unless you are loading up hot self defense loads, there is absolutely no reason to put unnecessary wear and tear on the brass or more importantly, your firearm. If its plinking your doing, load to whatever is reliable and accurate.

[Dark Mod]

A lot of the velocity I find listed is from longer test barrels, kind of a dirty trick, but I've resigned myself to coming up a little short on velocity.

I wouldn't play too much with seating depth at max load, but if you know what your doing and take it slow, watching for pressure signs every step of the way it's safe enough.

[Pauliedad]

I'm wondering about taking powder up 0.1 grain at a time INSTEAD of shortening OAL.
I'm confident in my abilities for proper procedure, accuracy and ability to spot signs of excessive pressure.
I've chrono ed factory rounds and I'm trying to get my loads up to that.
Agreed that I dont want to stress firearms unnecessarily. Just more of a let's see what I can do safely and dublicate what factory feels like.
Thanks for the thoughts on this.

[XDRoX]

OAL should be about function, not velocity.
If you want more velocity the safest way to get it is to add more powder or switch powders. Not to shorten the OAL.

Shortening AOL's to achieve more velocity is a dangerous practice IMO. Bullet setback could result in catastrophic failure.

There are plenty of powders out there that will get you well past factory velocities. What are you using now?

[Pauliedad]

Good to hear. I haven't felt a need to go shorter but wanted some validation.
I do want to try a tad more powder but again, want to be sure.
I have power pistol, tight group, bullseye, unique, WST, 231, blue dot.
I've worked mostly with power pistol so far and WST is headed in the right direction too.
On a side note, when I start low sometimes I get a halfway predictable load in that it may shoot low and slow but minimal recoil and function is fine. Mostly on lower work ups I have next to no clue where the bullet is going. So what's the deal? Spinning so far out of control it ends up in a alternate universe?
Thanks.

[stilly]

Shorter overall length changes the effective case volume.
If you are loading longer than a published load spec, you would usually need to increase your charge to reach the same performance.

+1

Sounds good to me.

When I make all of my 45 ACP 1.150 or whatever, I know that I am WAY over the minimum length and I expect the velocity to be a bit slower, so to compensate I will add more powder if I want faster velocity.

[rsrocket1]

Charge vs SD effect on Pmax and MV

I ran a few Quickload calculations and entered them into an Excel spreadsheet so that I could plot the effect of increased charge weight vs Pmax and muzzle velocity. I then did the same, but kept the charge weight the same and varied the seating depth to see the effect of Pmax and MV. I hope it makes sense to you.

Disclaimer: Quickload is not the final authority on velocities and pressures but with this particular combination using Unique powder, a 4.25" S&W M&P 40 shooting 175g lead TC bullets, my measured velocities are very close to the predicted velocities.

Here is the plot of increasing powder vs MV vs Pmax using a 1.135" COL or a .258" seating depth:

Notice the fairly linear effect of velocity and pressure vs increased charge weight
The velocities between 5.0g and 6.0g are extremely close to my chronographed measurements. I typically shoot 5.0g for target practice. Remember 35 kpsi is the SAAMI max and you don't want to be close to that number.

This graph is a plot showing the effect of seating depth vs. Pmax and MV with a constant charge of 6.0g Unique. 0.258" is the nominal seat depth.


Notice the rapid increase in pressure vs seating depth, but the linear increase in velocity. As seating depth increases, the pressures go way up. Conversely, as seating depth decreases (COL increases), pressures drop considerably when you are @ near max pressures.

So yes, an increase in COL can buy you some room for more powder to get a higher muzzle velocity. This is obviously demonstrated when you jump from 40 S&W to 10mm.

I personally wouldn't try to push it. What are you trying to gain with an extra fps? Reliable expansion? Can you guarantee equal accuracy with the added recoil?

[Pauliedad]

"I personally wouldn't try to push it."
"What are you trying to gain with an extra fps?"
"Reliable expansion?"
"Can you guarantee equal accuracy with the added recoil?"

First off rsrocket1, a big thanks for your response on this. Interesting data.

#1, #2, and #4 answers:
I don't really want to push to the edge either. I've been shooting longer than I've been reloading so I'm very comfortable with factory ammo. As I've been working up various loads for .40, .45acp, and .38 I've periodically gone back to factory to see if the accuracy issues are me,firearm,or ammo. What I've concluded is that I tend to do well with a faster load right off. I have landed on a powderpuff load with Power Pistol that after a few shots with it I can hold almost the best groupings I've done before. Very cool.
My main goal is to work up loads so that I have an accurate "light" load and one like a factory round. Just to be greedy, I want to be able to do this in several different powders. Over the last year in my travels I've been able to get a hold of a pound at a time of various powders so if things keep up the way they are I will have more options for my reloads. As of now I have Bullseye, Unique, WST, W231, Power Pistol,Tightgroup, Blue Dot, Accurate#7.
With the three calibers I'm working with the .40 seems the one that will be the most fussy so I'm working out that one first.
#3. Not at all thinking about this.

As I've been working up loads and chrono ing them I'm getting really close to published data and really don't want to have to re adjust the OAL each time. My Walther P99 eats any and everything so working with a OAL around 1.135 seems easy. A flip of the Dillon die from round point to flat point keeps OAL really simmilar.

Again, thanks for the insight on this and I welcome any other experience out there.

[rsrocket1]

That's a good reply and a good description of what you want.
You probably already know that for a full house load, a slow burning powder such as Power Pistol will get you the max velocity in 40 S&W. The downside of course is more powder needed per case, bigger muzzle flash and blast (which can be fun too).

For light loads, you want both low (but sufficient) velocity and high enough pressure to expand the case to seal off the gases and as complete a burn as possible. A fast powder such as Hodgdon's Clays is ideal because it gets the pressure up to where it likes to burn well before it gets the bullet moving very fast. 3.0g under a 180g Lee 401-175-TC gets me about 770 fps and feels just like a 120g 9mm bullet at 1100 fps (what I shoot when I put the 9mm barrel in my M&P 40). It generates about 20 kpsi which is more than enough to burn cleanly. I've used and equal weight of Titewad (not Titegroup) and successfully shot that with the same velocity.

With the powders you list, W231 would be the best candidate for a low recoil load with 4g giving you about the same velocity. But that load generates only 14 kpsi which may burn cleanly, but also may be a little more sooty than the Clays load. The other powders are better candidates for higher powered loads than for low recoil loads.

Hope that helps.