Crimping comparison question


#1

Hello guys,

I was wondering what’s the difference between these old types of crimping, stake and stab, since today the most used are roll and taper crimp, and their domain of applicability.
And regarding these two, roll and taper, if I understood correctly, the roll crimp is mostly used on revolvers and those cartridges which headspace off the case shoulder, belt or rim, while the taper crimp is used for semi and full automatic weapons, semi-automatic pistols and all the military rifles (semi and full auto), right?

With appreciation,
Bogdan


#2

As pistol cartridges make up the headspace by being seated with the case mouth the crimp there should not be rolled.
And roll crimps are often used with revolver cartridges when these have lead bullets. Less often (or not at all) seen with jacketed types then.


#3

From left to right:
No crimp
Factory crimp
Taper crimp
Roll crimp

crimps


#4

The crimp on a cartridge is used to retain the bullet in the case, as we all know, however, this can sometimes be done by friction fit between case and bullet. Military ammunition will normally have a specification calling for the amount of force required to have the bullet leave the case, referred to as bullet pull. If the friction fit is not up to specs, either a stab or stake can be used to increase the bullet pull to acceptable levels. So we can see ammunition of the same type from a single factory with no or either stab or stake crimp.


#5

So, you are saying that even today the military cartridges are stab or stake crimped?


#6

Hey EOD, what troubles me is regarding this picture showing that for the rimmed cartridges used in automatic weapons the headspace goes up to the soulder of the case.
image
So, I picked up some examples. For instance, the 7.62x54 mmR for a SVD rifle or the Romanian variant PSL rifle. The gauges aren’t as usual - long, they are some tiny coins. And I’m wondering for an automatic weapon, like an PKM, how they would be.

And this problem with headspace extends to my recent crimping question: I’ve seen that on all military ammo the taper crimp is used and I know that this type of crimping should be used on rimless cartridges. And since those cartridges I spoke above (7.62x54R) headspace off the case shoulder or rim, a roll crimp should be applied. This is what this guy says here: http://www.massreloading.com/Handgun_Cartridge_Crimping.html


#7

There are different crimping methods used on at least Russian x54R ammo. 1908 L-Type has a radial grooved cannelure and a crimp. The crimp is also done with 2/3 clear stakes. See this post:


ShKAS ammunition for the ShKAS aircraft guns has its own crimping made to resist bullets being pushed in/pulled out during the firing cycle (delinking and chambering) of the very high RPM ShKAS. There might be pictures here on the forum if you search.

Not “all” rimless military ammo has a taper crimp, look up 7,5x55, 8x59 Breda, or older 6,5x55 (which has 3-point staking).

Lastly - I want to point out that the PSL is not a variant of the SVD! They have very little in common.
The PSL, like the Yugoslavian M76, it is “only” an upscaled and modified AK mechanism. It has the long-stroke one-piece piston, same hammer/trigger system as the AK, and different magazines.
The SVD utilizes a multiple-piece short-stroke piston, an entirely different trigger module, different magazines, and the profile of the barrel is different. Bolt carrier is similar but not identical.
They have some shared elements but technically they’re not very closely related.

You need to keep in mind, your linked website, is for civilian handgun reloaders, and his views don’t really reflect how military ammo is made - to be easily mass produced and work without problems in rifles, MGs, and precision guns alike - or in pistols, SMGs, and carbines alike.

Ole


#8

Thank you Ole for your answer! On SVD and PSL it was my mistake, I admit. Concerning military cartridges, if I understood correctly, the “nowadays” ammunition like 9x19 Parabellum and 7.62x51 NATO is tapered crimp, while the still used 7.62x54R is taper crimped taking into account that bullet groove. The same can be said about .303 British and .30-06 Springfield. Am I right?


#9

The image where it says “exception” for automatic weapons with rimmed cartridges is something that contradicts common knowledge.
One always needs to observe the source for such info.

Ole, not all ShKAS had the distinctive double crimp. Actually it was the minority.
Also other crimp styles are known from Russia but that would consume too much time (for me) to treat here.


#10

Well, it’s actually from Wikipedia. Just wondering about it if it’s right or not.


#11

The 7.62 x 54 R headspace gauges of the East German army had the dimensions 1.625 mm, 1.778 mm and 1.905 mm and were used for machine guns as well as rifles.
These dimensions obviously refer to headspacing on the rim.


#12

I never saw a Russian gauge in 7.62x54R which even had shoulders.
So much for this.


#13

So, my guessings were right. Thanks man for support!


#14

Thanks for the correction Alex. I was sure I had read that ShKAS rounds had crimps ranging from normal roll to double crimp to another I cannot recall.

Ole


#15

There is one additional type of headspace. For bottleneck cartridges it is correct that the older system used to headspace at the base of the neck. However, for quite a few years now, headspace is gauged to a “datum point”. If you look at a cartridge that does have a datum point included, this is how its headspace is measured. Say, just for the sake of discussion, that a bottleneck cartridge has a datum point of 0.350". Take a (short) cylinder, the inside diameter of which measures 0.350". Insert the cartridge in the cylinder and measure from the base of the cartridge to the bottom of the cylinder. That length is your headspace. Here’s a drawing.