Questions about crimping a projectile


#1

Hi all,

I was asked a pretty basic question about crimping and realized that I really know very little of the history and purpose of crimping a projectile into a case (other than that they make it more difficult to pull a projectile for sectioning).

I’d thought that the primary purpose was to retain the projectile during shipment and in magazines/belt so that when the weapon is being fired that the unfired projectiles in upcoming rounds aren’t shaken loose. Is this true? I know that projectiles can have a cannelure into which a crimp can index (and that sometimes the projectile does not have a cannelure but is still crimped). I know that most match/accuracy loads are not crimped as this affects accuracy.

So, what is the history and purpose of the cannelure & crimp? Why the different styles of crimps? Is it as simple as above, or are there other reasons?

Thanks,
Paul

crimps


#2

You correct there are many reasons for crimping.

Recoil in double rifles would loosen the projectile in the other barrel & when it was needed - OH DRAT, the Elophant is going to make a mud pie out of me.

It could jam a revolver cylinder from turning.

the reasons of shipping, handling & storage effecting the integrity of the round.

It also helps control the case pressure (& other factors) with a consistent bullet / case release

Before reloading companies started selling segmented crimping tools for the home handloader a company could easily tell if ammunition that came back to them with a problem was original or…
.
I’m sure there are many more reasons & hope that others contribute, a very interesting question, Paul.


#3

One further reason for “crimping” was to prevent soldiers from “improving” their ammo, by augmenting the charge by robbing Powder from one cartridge, to augment several others (Ref: Introduced by Italy for M91 cartridge, as this was found to occur with the initially uncramped M91 cartridge. By the time of the M95 case improvements, the large stab crimps had been introduced, and the Italian cartridge became “un-tamperable” for all but the most well equipped ; as to preventing Bullet Movement under recoil or handling, the Italian cartridge had a Machined “stop shoulder” in the neck, to positively seat the bullet.( Push in).

DocAV


#4

Thanks Pete & Doc.

When composing the question, I wasn’t even thinking about revolvers, but it’s so obvious. So, did crimping occur on pistol cartridges before rifle?

Doc - I’ve seen the machined shoulder on the 6.5 M95 and always wondered about that - thanks.

Can anyone else comment on how it controls case pressure? Between crimps and sealant, so projectiles are very difficult to remove using a kinetic puller. Can crimping be so accurate that pressures can be regulated?

Paul


#5

Another reason for crimping is that most modern powders need pressure to build quickly to achieve the intended burn rate. Ball powders, even the fast burn rate formulas need the crimp to get them up to speed. Whether a metallic or shot shell cartridge the crimp is important if you want the round to properly go bang. Successive reloading of shot shell cases and the repeated wear and fatigue of the crimp results in drastically reduced pressure and velocity.


#6

I recall mention of “pull tests” in HWS, I think in context of different neck sealants, and I think it may have mentioned the reason for seeking uniformity of the results.


#7

With black powder cartridges crimps serve primarily to prevent bullets from working forward, especially, as Pete said, in revolvers. Since black powder loads almost invariably are compressed charges recession of the bullet into the case isn’t a problem. Jack


#8

Paul, which came first, I don’t know for sure but as double rifles were becoming common(?) for dangerous game ca. late 1860’s as a rough guess, revolvers would predate them. However most of the BP Colt & other cartridges had a slight taper or friction fit, not the sort of segmented or slash crimps.

Shot shells were being crimped, I’d think, after the first guy firing one, fired his third shot because the shot dribbled out of the barrel when he tipped the muzzle down & he got nothing out of his 2nd shot.

Now the case-mouth sealant also functions somewhat as a crimp. Although on some revolvers and some auto pistol case types you see a taper crimp

Now with the .45 M-1911 & the 9mm Luger, which I believe both headspace on the case mouth, crimping to almost any degree is not feasible. However being in a magazine helps control bullet movement, and your most likely aware that in using half-moon clips for the .45 M-1911 ACP in a revolver the cases show three small punch crimps to secure the bullet.

You right about match not needing them, some shooters even have jigs which they use to seat the bullet perfectly concentric to the case mouth, which has also been turned to be concentric and of uniform thickness. Nothing to tug it one way or the other before it hits the rifling.


#9

The German S bullet (1903) originally was smooth, because it was already known that grooves increased air drag.
But around 1915 the number of loose bullets in the field became a problem. So the bullet reveived a crimping groove (Kneifrille in German) to ensure a good case grip.

In my humble opinion crimping as such is not detrimental to accuracy. The difficult trick is to do the crimping in a very unifomr way from cartridge to cartridge. I believe it was found to be easier to drop the crimp on match cartridges.


#10

The effect of crimping on accuracy has been argued for years, especially
among those interested in precision rifle shooting, commonly called “Bench
Rest.” I did that for awhile, although not in competition. My own opinion is
that crimping can affect the accuracy of cartridges when you are speaking
of shooting 5 shots into basically one slight enlarge hole at 100 yards with
a rifle. I have tried it both ways in both the .222 Remington (Varmint or Light-
caliber class) and .308 Winchester (Heavy varmint or caliber class). I always
got better results with no crimp, where every other factor, including case-neck
turning, were the same.

That said, for any field use, and most certainly in ammunition designed for the
rigors of military combat, including shipping, handling, loading feeding devices with
or without loading machines, carry in ammunition pouches and even rough handling
of the loaded weapon, I would demand crimped-bullet ammunition. Proper crimping
can produce very accurate ammunition in every sense of the word, including normal
match position target shooting, but I still believe that when the ammo and the rifle
can be handled with extreme care, with no problem, a proper bullet fit in the case
neck, with no other bullet crimp is slightly better. That is just my own opinion based
on my own shooting experiences.

Regarding crimping and “bullet pull,” testing is often done for weight of pull with crimps
or lack of crimps in mind, mating of inside case-neck diameter and bullet diameter, and, yes,
even for external and internal neck seals. Bullet pull is very important to not only accuracy,
but also to maintaining safe and proper pressures. That is even true in extreme circumstances
of hunting and combat. A loose bullet pushed back into the case reduces the size of the
powder chamber and raise pressures.

As already said, in revolvers the crimp is necessary to keep the forces of inertia from recoil
forcing the bullet partially out of the case in the unfired chambers, causing a lockup of the
cylinder. In an auto pistol, crimping is still important (I always favor a taper-crimp over a roll
crimp due to the aforementioned headspacing considerations). Even in a magazine, a hot
enough load can force a bullet, and even the whole loaded cartridge to move forward in the
magazine with sufficient force to dent the front of the magazine box from within. I have witnessed
this on Luger magazines and even on Colt/Browning style .45 magazines when fired a lot with
FMJ ammunition in full loads.

As any ammo factory guy knows, and most reloaders now, it is never just a matter of sticking
a primer in a case, putting in the powder, and seating a bullet with not other considerations.
Crimp or no crimp can be very important either way.

Again, JMHO.

John Moss


#11

Thanks everyone. I sure appreciate the responses thus far.

Paul


#12

Another aspect that was significant in the black powder period in particular was helping to provide a thoroughly waterproof seal for the interior of the cartridge case. Black powder is intensely hygroscopic and will pull humidity out of the air to the extent of damaging the powder itself, along with the priming. A good strong crimp and plenty of grease on the bullet helped keep the interior dry at least for a period of several years. Jack


#13

A couple of years after the introduction from the M88 round they found out that the bullets were loose in the case mouth from the stored cartridges. The reasons were small cracks.
The cartridges were reworked with two rows of tree crimps, from June 1894 with one row of four case mouth crimps.
In 1895 DWM found a solution by glowing of the case mouth.
It is very hard to find a M88 round from these day’s without any crimps on the case mouth.

Rgds


#14

Dutch: The German word for making metal less brittle by applying heat is best rendered in this context by the word “annealing,” a word that will be pretty universally understood by handloaders in the U.S. Jack


#15

Paul,
proper crimp is a must especially on pistol bottleneck cartridges where any millimeter of pushing the bullet inside the case means bye-bye to your pistol - I have developed 6 segment crimp to several calibers I reload (.32 ZVI, 7.62 TT, 357 Sig, .357 AMP, 400 Cor Bon…) in 90’s. Such a crimp can hold the bullet even if the neck is spit.
Approached several times LEE factory to introduce this die for bottleneck pistol calibers…usual answer was - “you’re the only one who needs that”…few years after it came from them as a revolutionary idea…funny. The only problem on LEE crimp die is that material used for collet - it’s not heat threated and can’t be used for steel cases nor long time on brass.

Crimp

Another chapter are the powerful revolver cartridges loaded either with light bullets or slow powders (or combination). Should you load 460 SW with 200grs Hornady XTP and not profile crimp, after first shot you’re not able to turn the cylinder. Same with airlight SW’s in 357Mag with light bullets. Friends are bringing me the factory loads to crimp that stuff properly.
Rifle calibers it would be the long long story… :-)


#16

Sry - forgot to post steel case crimp.

Crimp steel case


#17

Jack, many thanks for the correction.

Best regards


#18

most semi and auto weapons would push the bullet back inside of the case if not crimped when feeding from a mag or belt. when i was a trainer for the army M60, i would encounter a jam due a bullet being smashed at the mouth of the receiver

if these were not crimped, you would encounter lots of feed problems. joe gatz