First hundred rounds, and what's the opposite of set-back?

[boing]

I loaded my first 100 rounds last night, .45ACP on my 550B:

5.1gr - 5.8 gr of 231
West Coast 230 gr RN
Federal primers
Once fired Winchester brass
1.255 OAL.

Fired them this afternoon through my 5" Springfield parts gun, with good results. No malfunctions, no over-pressure signs, no incidents.

The lower loads seemed dirtier, throwing some soot back in my face (inefficient powder burn?). The 5.6 and 5.8 were okay, with the 5.6 showing the best accuracy of all. I didn't really shoot for groups, though, so much as function/pressure signs. I'll bench the next batch of loads and see what they do.

Set-back: As I loaded last night, I chambered several rounds from slide lock multiple times to check for set-back. None of the rounds got any shorter. They got longer. Just a thou or two, and only on the first one or two chamberings. After that OAL remained unchanged over several more chamberings.

What's going on there?

Oh, and--->

 

[HSMITH]

What is going on there is that you have enough crimp to keep the bullet where it belongs, that is a good thing. Congrats on your fine start!!!!!!!!

 

[Mike Irwin]

"I chambered several rounds from slide lock multiple times to check for set-back. None of the rounds got any shorter. They got longer...What's going on there?"

It's called inertia.

I'm assuming that you're chamering the rounds by letting the slide fly forward and strip a round from the magazine.

When the slide slams home and the cartridge stops against the barrel lip, the bullet has a lot of built up inertia. It weighs 230 grains, after all.

As Newton taught us, a body at rest tends to stay at rest, a body in motion tends to stay in motion.

The bullet is trying to stay in motion. Because of the crimp tension it doesnt' stay in motion for very long, but it does manage to move forward just a little bit.

Let that particular round run home often enough, and you'll eventually see some substantial bullet jump.

 

[boing]

I thought the crimp being tight enough to prevent set-back would hold the bullet against inertia. The bullets get a pretty good whack making their way into my 1911. I guess the edge of the case mouth provides some mechanical resistance to set-back, over and above just friction.

 

[Mike Irwin]

Not all crimps are created equal, and a taper crimp isn't as secure as a roll crimp or stab crimp, which actually make a physical lock between the bullet and the case.

A taper crimp holds the bullet in place with friction only, meaning that if you can overcome that frictional bond, the bullet will move.

During chambering the impact on the bullet normally isn't square, meaning that the bullet isn't pushed directly back into the case, so the effect is greatly reduced.

But the force of slamming home into the chamber, which is attempting to move the bullet parallel to the case, is often enough to move the bullet slightly.

A good experiment is to use an impact bullet puller.

Take a roll-crimped revolver round and a taper crimped semi-auto round, and see which one pulls first, and with less effort.

 

[Sunray]

Sounds like the die has jiggled loose. Make sure it's tight. Then test the loaded round for chamber fit by remocving the barrel and dropping your loaded ammo into the chamber. Load 4 or 5 and test 'em. If they don't drop in then you can adjust your dies.
Mike, roll crimps don't work on cases designed to head space on the rim.

 

[Mike Irwin]

Sunray,

"Roll crimps don't work on cases designed to headspace on the rim."


Hence my comment "Not all crimps are created equal, and a taper crimp isn't as secure as a roll or stab crimp."

 

[tex_n_cal]

It will also help you if you turn down the expander plug in your dies. It should be at least .005" smaller than bullet diameter to get a tight fit of the bullet in the case. A crimp by itself cannot correct loose bullet fit!

 

[winwun]

You didn't mention whether or not your brass had been trimmed. Different lengths of brass will get different crimps from the same setting of a crimp die, whether it is roll, taper, or stab.

Beware of people selling "once fired brass". In a Clinton-esque fashion, their definition of "once" is similar to the "once" in "Once upon a time". It means simply that the brass at one time comprised a fully loaded cartridge and was subsequently fired.

It does not necessarily at all mean ONE TIME ONLY.

The more its fired, the longer it gets.

Caveat Emptor.

 

[Clark]

There are guys who have their act together and seat and crimp at the same time, but I don't.

I make the seating and crimping a seperate step.

I make a couple dummy rounds with no primer or powder every time I load.

I drop the rounding into the chamber of the barrel and see if they go all the way in without being pushed. I know from experience that the slide can chamber a round that is difficult to chamber and I will not know it. Those rounds may be innaccurate or over pressure.

Sometimes, to get the rounds to chamber nicely, I have to add the step of partial resizing the loaded round in a sizing die with the decapping stem removed.

I cylcle the dummies through the magazine and gun and see if they feed.

Lee factory crimp dies for pistols make a superior roll crimp. The carbide ring [integral to the factory crimp die] also resizes the loaded ammo. This ring is ~.010" larger than the resizing die and should be the first resort.

When I am working up hot loads [that's all I do with pistols anyway] I get to the situation where the powder is compressing and the bullet is springing back out. Each incremental increase in powder requires the seating die be adjusted that much further down to maintain the same over all length.

Finnaly over roll crimping can actually make the bullets loose. The copper and lead cannot spring back as much as the brass case. So carefull with that crimping.

 

[Gewehr98]

That doesn't make sense.

Mike, roll crimps don't work on cases designed to head space on the rim.

If taper crimps are designed for rounds that headspace on the case mouth, ie. .45 ACP, then why aren't roll crimps designed to work on rimmed rounds? Granted, you can taper crimp a rimmed round like a .357 Magnum, but I find the roll crimp secures that bullet a lot better, especially in a light alloy J-frame.

And I sure wouldn't roll crimp a .45 ACP round for an autoloader, then you're relying on just the extractor and bullet shoulder to keep the round positioned in the chamber.