o.a.l. --vs.---pressure to get accuracy...???

[mozeppa]

okay ...i'm trying to learn as much as i can.

i have 4 pistols that i'd like to cast/load for.

.380
9mm
40 s&w
45 acp

and i've heard that you do the plunk test to get the case to properly headspace in the chamber.
should i adjust my o.a.l. to get the bullet to just barely touch the lands in the bore?

barely not touch?

here's my question:

lets say i've achieved a o.a.l. that suits the cartridge fit in the chamber...BUT the cartridge o.a.l. is significantly longer that that bullets book listed o.a.l....is there an adjustment to the powder load i should do now because the volume of the case has increased?

will pressures be higher?...lower? ....due to the volume increase?

and if it gets flipped the other way? as in: the cartridge is significantly shorter than the book listed o.a.l.?
now the case volume is much less ...how do i adjust powders for smaller case volumes?

or am i all wet?

[mozeppa]

42 views? ....and nobody has an idea?:holysheep:-|

[Paul Tummers]

When your COAL is longer than the one listed in your reloading data source, you will have to increase the powder load to maintain the same velocity/pressure, when your COAL is shorter, the opposite will be the case. Work up in 0.1 grain steps, when your round is shorter, go down by 1 grain and work up again. shooting over a chrono would be a good thing because speed gives you a rough indication about pressure.

[tazman]

What Paul said is correct. The 380 and 9mm particularly can be touchy about how much boolit is inside the case.
Rule of thumb is
Less volume available(shorter oal)= more pressure
More volume available(longer oal)= less pressure

The chronograph is your friend. If you see a sudden disproportionate increase in velocity you have probably gone too far(pressure spike) and need to reduce your powder charge.

We aren't ignoring you. It's not uncommon to get over 100 views before you get a reply.

[Larry Gibson]

Given the other variable and having measured the psi of numerous loads in numerous handgun cartridges the subtle (that's what it really is when seating longer) will probably not be outside the normal load to load variations. In layman's terms you'll be hard pressed to measure the difference let alone tell it on target with either of those cartridges and the handguns they're chambered in.

Larry Gibson

[TomAM]

As for the boolit contacting barrel steel upon chambering, you'll likely find that fouling eventually interferes with that fit and prevents the slide from closing fully. Your pistols will quickly tell you how close you can get to the lands and still retain reliability.

[gpidaho]

+ one for both Larry and Tom GP

[375RUGER]

I think you should be loading all those cartridges to function if they are all autoloaders. Just tweaking the powder charge and experimenting with different powders all of those can be made to shoot very accurately, if the respective gun is up to the task.

[srd]

I would also slug your barrel and get the size. Not all 9 mm like the same bullet diameter. Example..MY Beretta likes .358...Hi Power likes .356...Tanfo likes .357. Bullet weight is another issue. Some brands like the heavyweights [ 160 gr ] and some like the lightweights. If you have not purchased your mold yet....order sample packs of cast bullets from one of the commercial casters in various weights and find out what it wants AFTER you slug your barrel.Now you can work on length and accuracy. Personally I load to the length of what my mags will feed the best. Then I let the chronograph and target tell me what i need.

[jhalcott]

Just so I know. What IF the col "plunk" test gives a length too long to fit into the magazine!? Do I shorten the cartridge to BOOK max, or to fit the magazine? This is ONE reason I do not like 9MM

[Scharfschuetze]

SRD and 375Ruger allude to it above, but to elucidate further, your overall length needs to be within the limits of your magazine. You can seat a boolit out to touch the leade and still pass the plunk test, but if it doesn't fit in the magazine, all will be for naught.

I generally load my 9mm and 45 ACP rounds so that a dummy round first functions in the magazine, then I see if it passes the plunk test and then I develop my loads once those two factors are in sync. Doing so usually results in both accurate and reliable ammo.

As Larry notes above, the pistols and calibres referenced here, while potentially very accurate, are not bench rest rounds.