Crimp Jumping : how to solve?

[Short Barrel]

A tight crimp on heavy loads I guess is number one.I like all my big bore single actions free wheeling for just this reason.You can turn the cylinder either direction to remove the offending round-if it should happen.It is more likely to happen with lighter revolvers due to snappier recoil.

 

[Lost Sheep]

A question about the test's validity:

How does the use of a Ransom Rest affect the number of firings needed to cause measurable crimp jump?

I don't own a Ransom, but simple physics will give you the answer.

It has been reported that lighter guns experience crimp jump worst than heavier guns. That is because the lighter the gun, the more it recoils back from the forces exerted by the round being fired. The other cartridges' cases get pulled back by the recoil while the slugs (by their inertia) want to remain stationary. Let me repeat: The cases pull back from the stationary slugs.

Now, clamp the gun in a Ransom Rest, bolt the rest to the shooting bench and lock all movement of the gun.

It should be obvious. The gun, the cylinder, the unfired cases in the cylinder do not get pulled back by recoil. Less tendency (down to near zero) to jump crimp. Suspend the gun in a cradle that can swing free and you will maximize the tendency to jump crimp (for that gun and ammunition).

On another note. I have experienced crimp jump in my SP101 firing moderate loads, 158 grain bullets and light crimp (very light). I have even tied up the gun a couple of times. But I have also been able to push the bullets back in the case/cylinder with my finger. I have no idea if a heavily crimped slug (that jumped crimp) could be pushed back into the case by finger pressure, but if faced with a bear and a tied-up revolver, I would certainly try.

Lost Sheep

 

[WESHOOT2]

It's easy to turn down an expander, but considerably more difficult to increase the ID of a carbide sizing die.

I can crimp an 'autoloader' cartridge so hard the bullet breaks off at the crimp, but IME crimp will NOT secure a bullet from setback. I use other mechanical means.

I use Lyman 'M' dies for virtually all single-staged ammo. I modify some Dillon expanders (used in my XL650 powder measure stations) to mimic the Lyman.

 

[tek4260]

Here is the reason I turned my 44 dies all the way down. Relatively light loads of 22gr of 4227 with a 300gr and a 240gr.

And the puller

 

[PO2Hammer]

One of the writers in Handloader magazine recommended using a medium roll crimp with the seating die, then finishing the crimp with a Redding profile crimp. This was with .454 Casull loads.

 

[Lost Sheep]

It's easy to turn down an expander, but considerably more difficult to increase the ID of a carbide sizing die.

(edited for focus).

But not impossible. Decreasing the inside diameter of the carbide ring in the Lee FCD is impossible.

1- You can remove the ring entirely.

2- You can ream it out (conceptually, much as one sizes chamber throats, but using a different tool), but being Tungsten Carbide, this is a lot of trouble and takes time.

3- Specify to the manufacturer what size you want it (the sizing ring) to be.

4- Use a second Seat-crimp die (one to seat the bullet, with the body of the die backed out so no crimp is applied and the other with the seating stem out to apply the crimp).

Respectfully,

Lost Sheep

 

[WESHOOT2]

".....sizing die....."

 

[seasterl]

I use the RCBS die with my 500WE mainly because that's the only die made for the cartridge. I'm pleased with it. Preventing the jump happended to me a few times with this cartridge in a 6" SA revolver, and it was a learning curve to get the right crimp for the loads I was using. I have thought about also doing a taper crimp step just before my roll crimp step, though, to increase neck tension because I use a good amount of mouth expansion in order to get the big cast slugs seated nicely. I like the suggestion of turning the expander plugs down, though. That sounds like a great idea. For now, though, my crimp and expander dies are set and locked down because they now work for my loads.

I also agree that the lighter guns move more and experience crimp jump more. This would be my biggest concern with those that pack the smaller, lightweight revolvers in big bore calibers loaded for bear. The owners really (really) need to spend a lot of painful and unpleasant shooting experiences firing those loads to gain confidence and use their calipers to measure bullet movement of the unfired rounds. And, if possible, I would still opt for a free-spin pawl.

I have also had to learn a good crimp for loading for the 416 Rigby in a Ruger Magnum Mark II rifle with magazine.

 

[G-30]

Forgive me if this has already been asked, but I've wondered for years: Is this a problem with factory ammo (stnd. or custom?) Or is this only with home reloads?

Yes it can happen with factory ammo as well, I just went out with my Ruger Alaskan and it jammed on me. I had it loaded with Magtech 260gr. FMC-FLAT and my own loads of 300gr. XTP Mags over 31.4gr. of H-110 and figured I would shoot the mixed cylinder and then switch to my reloads, two shots and it was jammed. the Magtech had jumped. I will now just use my reloads as I have never had a problem with them.

 

[tek4260]

Look at those cases. Doesn't appear to have any tension due to the lack of a bulge at the bullet. Is the left case as it came from the factory or has it pulled some too? If it is as it came from the box, they missed the seating depth and didn't crimp into the cannelure.

 

[G-30]

Both cases came out of my .454 Alaskan after it jammed, all the new ones are seated to the top of the cannelure.