After getting some enlightenment on this subject [and my question] I thought this would be worth sharing with other readers with Vera’s blessing, (I think.)
Hey Veral,
I am seeking your opinion on the subject of bullets "creeping" under recoil.
I have been shooting the 454, the 475, the 45 Colt and in recent times the 44 Mag.
The guns are; RSR 454 w 7.5" barrel, the Ruger Alaskan 454 w 2.5" barrel, the Mag Research BFR 475 w 5.5" barrel, and Ruger Blackhawks in 45 Colt w 5.5" and 44 w 7.5" barrel.
I am in the habit of loading these cartridges to push bullets not much faster than the upper 1200s of fps because its a lot easier [for me] to control where the bullet goes and there seems to be plenty of power for our eastern big game, (Deer, Black Bear & Hogs.)
I have nothing "bad" to say about full power. I just don't feel a need for it.
I use the cases many, many times over as a direct result [I think] of these gentler levels of power.
I use them until they split.
Every now and then I run experiments of new [to me] powders and these always include going into the full power range of the named cartridges.
In most of these experiments there also comes an attendant likelihood of the bullets creeping out of their crimp under the recoil. The Alaskan revolver is particularly unforgiving whenever the velocity of any load goes faster than about 1050+fps.
I know the wicked recoil of that gun is a large part of that picture.
The BFR-475 is next most unforgiving as loads get faster than 1100+fps.
The RSR loads will begin to creep as they get faster than 1300+fps.
Both 454s and the 475 creep readily anytime the velocity climbs out of the "comfortable to shoot" category.
The bullets are all 300gr or more, as might be guessed.
The 45 Colt only begins to creep [a little] when loads push the limits (in every way.)
The 44 seems immune to this phenomenon so far, (I haven't gotten involved with heavier bullets yet.)
I have and use Dillon equipment but also have and use single stage Lee and RCBS presses when it seems expedient for smaller batches.
Expander Plugs: I understand that much of this subject can revolve around the grip of the case on the surface of the bullet, (that part that is inside in the case,) which might be effected by the size of the expander plug.
To avoid a long explanation I'll just say that I am using expanders of the next-smaller caliber for the 45 and 475 caliber cartridges. The cases are not being expanded at all. Only the case mouth is flared a bit [as little as reliably possible] to get the heel of the bullet started into the case.
I cannot think of a stronger "grip" the case might be able to achieve.
Crimping: I have and use the Lee "Factory Crimp" die and the Redding "Profile Crimp" Die. I think the Redding die is the better of the two but I also think the Lee followed by the Redding is the better crimping program. The carbide ring of the Lee die has not been touching the cases so I think that’s a non-issue...so far.
The Redding die is a taper-crimp with a roll-crimp at the end of the taper. This helps eliminate the bulging effect of applying the roll crimp, (the magnifying glass and caliper seems to bear this out.)
Seating depth: Controlling exactly how much of the crimp-groove is seated into the case-mouth and thus how much of the case is actually crimped into the groove seems to matter a lot too.
I get my least-creeping when the case mouth is laying snug against the slope of the crimp-groove [after crimping] leaving no room for movement.
If the bullet is too deep the crimp seems to be well forward of the slope of the crimp-groove leaving a small bit of "room" for the bullet to move before encountering the crimped brass of the case mouth.
If the bullet can move it develops more momentum [than from just the recoil and muzzle-whip] which can easily overcome any crimp. Once I got this under control I had an attendant reduction in creeping incidents.
Now to the subject of this note.
I re-use all these cases many, many times before they begin to split.
In the matter of the 475 I have been using the same 50 pieces of brass for 3+ years.
I am now getting one or two split cases with each re-sizing process.
(Might be time for more new cases.)
I suspect that the portion of the case that is getting worked the most, (that portion where the crimp is applied,) has become weak from all the bending back and forth.
I am beginning to suspect that the case mouths are made significantly weaker this way, becoming less capable of withstanding the inertia of the bullet under recoil with each reloading process.
My mechanical mind tells me this is likely to be a significant part of my situation, especially since we are talking about loads that are much less powerful than full power.
I guess my question is whether or not you agree that the higher amount of work applied to the case-mouth will/can/does cause it to lose much of its ability to do the job I ask of it?
I note that full-power Factory-made ammunition does not move under recoil...ever.
Only reloaded ammo does this.
I am beginning to suspect that the re-worked case mouth simply cannot hold as well as a first-ever, "virgin" factory applied crimp.
What say you?
Tim
Veral’s patient and thoughtful answer:
Tim,
I've found two things to be important in getting maximum case neck grip for revolvers.
The expander plug should be only slightly smaller than sized bullet diameter.
As close as a half thousandths is fine, and preferably not more than about .003 smaller than bullet diameter. It should also expand the case a little deeper than the bullet will be seated. Reason for this being that when cast bullets have to expand brass cases too much, the bullets tend to round at the base a little and become tapered, which is a setup to provide some push forward, which helps recoil to move them.
Second. Crimps must NEVER be forced hard at the bottom of the stroke, or it will bulge the case neck slightly and loosen the case neck grip. My preferred method of crimping for heavy loads is to set the seating die about a turn deeper than needed then carefully feeling when the crimp gives a slight bump as it hits the bottom of the crimp groove. This method does create ammo with OAL's that match whatever case length happens to be, which I haven't found to be a problem with either pressure or accuracy.
I absolutely detest the Lee factory crimp dies for straight wall cases, however, if the carbide ring doesn't change diameter of your rounds at all, I wouldn't hate it. If it does size the brass at all, (and it will if the bullets are much over standard diameter,) case neck grip is lost except for the little provided by the crimp, and this is the reason I hate the dies.
I have experienced no change in case neck grip with old brass until it actually starts to crack, which is often not detected without careful inspection. Brass hardens with working, so case neck grip should actually increase as the work hardening makes the cases stiffer.
I'm quite sure the reason factory ammo never has a bullet slip problem is that the dry jacketed bullets against a dry case creates strong friction. Greased lead is another matter, and simply can't be held against slippage as a dry bullet/case neck.
Veral
