OAL/charge

[nicknack2]

Few things I like to run thru the Boolits gurus...my short 6 month experience researching, casting and reloading Boolits tells me that OAL is directly responsible for cartridge pressure and bullet velocity, right??? what I have not yet understood is: do I want to go the shorter I can or do I want to go the longer I can??? I totally understand that each cartridge and Boolit weigh also play a role on all these as reloading manual tells you what your OAL should be; however each load has specific guidelines on these too...what happens when you are loading a bullet not listed on the manuals??? I guess my question is what chambers better short OALs or long OALs.

here is my specific on my loads and please your ideas...

.40 Cal140 grain
FP lead bullet(bought)
4.9 grains of Red Dot
1.300 OAL (most times), also tried 1.275 OAL

the above load has given me the accuracy results that I wanted at 25 yards with a velocity on high 1020s to 1100s.

Now, with my cast Boolits using the Lee 175 TC (non TL)...

.40 Cal ~175 grain
TC cast Boolit (by me)
4.7 grains of Red Dot
1.275 OAL

the above load has given me "OK" (not completely happy) accuracy results at 25 yards with velocities around 1020s to 1060s.

what is worrying me is the fact that little by little my 175 cast TC load is creping up in charge (4.7 grains) getting close to the 4.9 on the 140 FP load, the reason I been increasing the charge is because the 175 Boolit had no been as accurate as I would like (I started with 4.0 load and been increasing .10 of a grain gradually till the Boolit is starting to get accurate)...but a 40 grain bullet difference which is using almost the same amount of powder does not look right...

I know, long story...please your ideas comments and concerns...

Pistol used:

.40 P99 Walther
no problems locking back to the rear when magazine is empty
sporadic issues with feeding/locking the round in to battery maybe 3 out of 50 rounds (I know this needs to be good feeding 50 out of 50, reason for the OAL question)

[Tatume]

The more of your bullet you can keep out of the case, the more powder space is available. More powder space means more powder, for the same pressure. More powder means more burn time, for the same pressure. Extended pressure time means more velocity.

Deliberately reducing powder space (deeper seating of bullets) will usually not increase velocity without at the same time unacceptably increasing pressure.

Take care, Tom

[nicknack2]

Tatume thanks for the reply, I'm a little confused....I understand that keeping the boolit out of the case creates more room for more powder, but how is it that more powder does not create more pressure??? now, increasing the OAL of the case is helpful to proper feeding??? or the shorter the OAL is better?

[prs]

If your hand loads are dedicated to one pistol, then best practice should be to fit the COAL to the chamber of that arm; i.e. the "plunk test". Then work-up your charge for accuracy staying within the bounds of your reference source(s). If multiple pistols are fed the ammo, use a standard gauge to set the COAL. The COALs listed for specific boolits in the reference books will be close, but boolits with different designs will not chamber the same given the COAL for the specified design.

prs

[Tatume]

Tatume thanks for the reply, I'm a little confused. I understand that keeping the boolit out of the case creates more room for more powder, but how is it that more powder does not create more pressure?

If two case/bullet combinations are identical except that one has more powder space, and the same charge of powder is loaded into each, then the one with more space will generate less pressure. That means more powder can be added to the one with the greater space, to bring the pressure in each to the same level.

It is still possible to add too much powder, and raise the pressure still higher. But that is not the goal here. If you increase the powder space, pressure will be reduced. Increase the powder charge only enough to bring pressure back up to where it should be.

It will take more time to burn the additional powder, meaning that the pressure will act on the base of the bullet for a longer time. That is why there in an increase in velocity.

[nicknack2]

@ Tatume Nice!!! thanks for you explanation and patience... any input on what chambers better between a longer OAL or shorter OAL?

[Tatume]

The advice given by prs (post #4) is correct for auto-loading firearms.

[prs]

@ Tatume Nice!!! thanks for you explanation and patience... any input on what chambers better between a longer OAL or shorter OAL?


The advice given by prs (post #4) is correct for auto-loading firearms.

I figured he was working with semi-auto pistols that head space on cartridge mouth. Thus the best cartridge over all length is that one which fits with a given boolit. Given the same boolit design, there really is no opportunity to shorten or lengthen OAL for such pistol. A wad cutter will need to keep the forward limit of its edge short enough so that it does not lift the case away from the end of the chamber and the TC type boolit will need to be seated pretty much at the margin of the junction of the parallel sides of the boolit and the TC area to get that just right seating of the case mouth and level of the case head to the barrel hood.

Does that help or cloud the issue, NickNack2?

prs

[nicknack2]

it is confusing, but I guess given the type of cartridge the OAL don't matter(other than for pressure regulation per say) since the case length is what is going to stop the cartridge from going any further in the chamber as the bullet protrudes in to barrel(if that make any sense) so as long as my cartridge is not sticking out of the chamber OAL won't matter???

[Tatume]

If OAL is too long the cartridge won't chamber. The bullet will touch the rifling. You should adjust the seating depth until the loaded cartridge drops freely into the chamber. This test should be performed with the barrel removed from the gun (or, if a fixed barrel then with the slide removed). If the cartridge drops in and the base is even with or a few thousandths below the hood (breech extension), and falls in with a satisfying "plunk," then the cartridge passes the plunk test.

If the cartridge passes the plunk test it is possible that it is still too long to feed through the mechanism correctly, but I've seen this only on very rare occasions. Usually the plunk test is conclusive.

[prs]

Yes, indeed it does matter! Consider the dimensions of chamber diameter, the ridge at the end of the chamber and transition from that ridge to the full size of the lands. The modern trend seems to be to make that transition (leade) very abrupt where as some new guns and many older ones have a nice tapered leade. I can tell Ya first hand that the abrupt transition is not very cast boolit friendly. Anyway, if you set your boolit out too far, the lead will contact the leade before the case mouth seats resulting in anything from occasional failure to go into batter to an overall stubborn failure to cycle and with extremes a failure to fit the magazine. So, let us consider going shorter than a good fit. With your TC type boolit, you surely do not want to try to crimp on the actual cone, same thing with a RN, crimp on the full diameter. WC and SWC are typically crimped close to the end of the full diameter but not on the edge. If you do go a bit too short you again get occasional failures to feed or feeding that bashes your boolets a bit. Going back to the cartridge OALs printed in reliable sources, the stated length should fit abut any pistol that meets standards, except over time the mold makers tend to vary their designs which throws off the designs a bit. So, unless you change volume by selecting a different boolit design, or loading it backward, there is not much wiggle room. Try it and see.

prs

[fredj338]

Tatume thanks for the reply, I'm a little confused....I understand that keeping the boolit out of the case creates more room for more powder, but how is it that more powder does not create more pressure??? now, increasing the OAL of the case is helpful to proper feeding??? or the shorter the OAL is better?
Yes adding powder always increases pressures, regardless of oal. It does not always increase vel though. Vel increases are linear with powder increases. When you hit a flat spot, it often means you are at or approaching max & should back off, especially with fast pistol powders like RD.

[Tatume]

Yes adding powder always increases pressures, regardless of oal. It does not always increase vel though.

This statement is not true without qualification. Adding powder increases pressure if combustion volume stays the same. Increasing combustion volume decreases pressure if powder charge stays the same. Therefore it is possible to add powder and increase volume at the same time, and pressure will not change.


Vel increases are linear with powder increases. When you hit a flat spot, it often means you are at or approaching max & should back off, especially with fast pistol powders like RD.

This statement makes the case that velocity increases as a function of powder charge are distinctly non-linear. In parts of the charge/velocity curve the changes in velocity can be viewed as approximately linear, but in other areas the changes cannot be approximated by a straight line. Nowhere is the relationship actually linear.

[rsrocket1]

Think of it this way when it comes to case volume, pressure and powder charge.

If you start out with a fixed powder charge, as you increase the available volume, the pressure goes down as well as the velocity. Think about your 40 charge in a volume that starts out with a 40 case, then a .308 case, then a 50 BMG case, then a 105mm case with a .40 neck. Now think of increasing the powder charge with a much larger but slower powder. You will be able to drive that bullet much faster with a big charge of slower powder and not exceed 35,000 psi right?

I tried fooling around with cast hot melt glue bullets in 38 special and 40 S&W shot with just a primer, no powder. When seated normally, they sometimes shot out, sometimes got stuck in the barrel. When I seated the bullets all the way against the primer (essentially zero case volume), they shot out nicely and punched through the wall of a cardboard box.

Here is a Quickload run I did a while back showing the relationship between MV, Pmax and seating depth with a fixed charge. This was with a 180g bullet and 5.0g Unique in a 4.25" barrel
123248

You can see that the MV increases with the Pmax for a while as you increase the seating depth, but at some point, the Pmax starts to climb faster than the MV.

I use Quickload with lots of different powders to see what the relative effects are of using more slower powder versus less faster powder for a given cartridge as well as the effects of seating depth and bullet types. The predictions are pretty accurate, but most importantly, I can see relative differences between one type of powder versus another.

Red Dot works well in 40, but peaks out a little sooner than a slower powder like Unique and Power Pistol. Not enough to worry about for plinking and probably not enough to make much difference anywhere. The differences are more pronounced as the case volume decreases like when you make the comparison in a 9mm or 380 load. For low recoil loads like 10g in a .308, the differences are almost negligible, any of the fast to medium powders perform about the same.

Hope that helps.