Crimping questions

M

Micro man

New member
I’ve been reloading off and on for many years and now have more time available since I retired. I have mostly reloaded pistol calibers, 38/357, 9mm and 45ACP.
I have always had questions about proper crimping . I know you typically roll crimp for revolvers and taper crimp for semi-autos, but that’s about the extent of my knowledge. I’m hoping someone on the forum could point me to some good reference material or articles or internet source to help me increase my knowledge about light,medium,or heavy crimps etc. I have no idea about crimping for rifle calibers either.

Thanks for any information you can provide.
 
This is interesting. I setup semiauto crimp to be enough to stop bullet movement for 5 feedings. Revolver I set by the eye test and confirm the 6th round hasn’t moved…..

Not sure about further study.
 
How to zero point calibrate crimp:

1)After seating the bullets into the cartridges, back out the seating stem. 2)Raise the ram all the way up then spin the crimper portion of the reloading die in until it interferes with the case mouth. 3) with the ram still raised finger tighten as hard as you can the crimper, then slightly lower the ram adjust the crimper die one quarter turn tighter, crimp the cartridge then check for proper feeding and chamber fitment aka the plunk test.

Usually this works just fine I'm using Lee dies for 9 mm and RCBS dies for 38 and 357 Magnum. For centerfire rifle I use the lee collet crimp dies they are activated from pressure against the shell holder. Set up is pretty much the same
 
Some reloading data will suggest a measurement at the case mouth for rimless semi auto ammo.
 
Crimping is done as an extra step to keep the bullet from moving/being moved in the case. In some situations, this is a needed, necessary step. In others, not so much.

Cases that headspace on the case mouth should be taper crimped. Cases that don't can be either taper or roll crimped. For some applications one works better than the other.

With straight wall cases, where the case mouth is flared to allow bullet seating, the seater die should return the case mouth back to straight. Any amount of squeezing or bending the case mouth in, from straight is referred to as crimping.

The amount of inward bend or compression is described as "light, medium, or heavy" but those are relative terms.

Taper crimp (done right) still leaves a sharp edge at the case mouth that the round can use to headspace on. A roll crimp is just that, the case mouth is "rolled inwards" and the rounded mouth is not considered positive for headspace use.

There is a huge amount of variations possible, so blanket statements are of rather limited use. It is entirely possible to need a certain amount/type of crimp for a round to function properly in one design of gun, and the exact same round with no crimp may function properly in a different design of gun.

For just one example, rounds used in tube magazine rifles should be crimped. The same round in a box magazine fed rifle may not need to be crimped. And does not need to be crimped in a single shot rifle.

Bullets can be pushed into the case by striking the feed ramp, or from recoil slamming them into the magazine wall or even spring tension and the weight of other rounds in some designs.

Bullets can be "pulled" by inertia during recoil in revolvers, due to the way they are held in the cylinder.

How much crimp is enough is situational depending on the load, and the gun it is being fired from.

Too much crimp, or crimp applied in the wrong place can damage the ammo and in extreme cases render it unable to be chambered, and so, useless.

I've been loading my own ammo for a bit over 50 years now, learned mostly from loading manuals, books and gun magazine articles, decades before the internet existed. If there's a way to do it wrong, I've probably done it. But along the way, I've learned how to do it right, for the equipment and components I use.

A couple of important points, not often mentioned with enough emphasis, to get uniform crimps from a single die adjustment position, you NEED uniform case lengths. That means inspection and trimming for uniformity of length.

This is more important with roll crimps, less so with taper crimps, but does matter with both as extreme variations in case length leads to short cases not getting the proper amount of crimp and over long ones getting too much crimp,

Ask any thing you are wondering about, I'm happy to share my experience and can give you specific answers to many specific questions.

If I don't know the answers odd are good someone else here on TFL does. Just watch out for information overload, :D:rolleyes:
 
I'll add one point to Post #5...

Over crimping plated, powder coated or varmint bullets can strip off the coating/jacket and result in poor accuracy.
 
Post #5 is good information. The only experience I would add is that in testing heavier taper crimps over what are needed result in less holding force. Too light and there is still some flare. Even a micro flare will have negative feeding impact. Trust me 3 feed issues in 100 are too many! They always happen shooting IDPA or bowling pins! Light crimps also hold less than needed too.

With roll crimps, a moderate crimp….visibly rolled fully into the groove is all I’ve ever need except on heavy 45 Colt rounds where the just a bit more from the Redding Profile crimp die helped.

For plated bullets, just fully closing the cased to bullet gap is all I’ve needed.
 
I don't use the Lee collet dies, and so will not comment on them, other than I never found a need for anything like them.

A couple points about taper vs roll crimp. With a taper crimp (and I assume a collet crimp, collet crimpers correct me if I'm wrong), you are squeezing more than just the case mouth. You are squeezing a portion of the case "neck" and the bullet, as well.

This has the potential to create problems when done wrong. (of course, what doesn't? :D) The brass case, and the bullet are dissimilar metals, and while both will spring back a bit after being compressed, the amount will differ. Generally speaking the bullet will not "spring back" as much as the brass case, and when this situation is extreme, can actually loosen the fit of the bullet in the case (reduction of case neck tension) and that frequently is an unsatisfactory result.

With a roll crimp, the case mouth hits a "hard stop" on the crimp shoulder of the die, and since you are still pushing the case up into the die the case mouth gets bent into the bullet. BUT, only if it has someplace to go. A crimp groove and correct alignment of the case mouth in the groove are necessary.
(you can, usually get a light crimp on a soft lead bullet without a groove, but if the bullet is a harder material such as an alloy or jacketed, no groove is a problem)

IF there is no crimp groove (or the bullet is not seated correctly for the case to crimp into the groove), what will happen is that, as pressure is applied, the case will bulge somewhere below the case mouth. This can result in the case bulging away from the bullet, leaving little or no tension on the bullet, except at the actual crimp point. In bottlenecked cases, such as the .30-30, the bulge can be at the case shoulder, and can even bulge it so much it will not chamber. (yes, I've done both :o)

Uncle Nick has some excellent illustrations showing this clearly. Hopefully, he will be along soon and share them again in this thread.

One of the commonly asked questions is "how much crimp do I need to use?" and that is very dependent on the load and the gun firing it. You will hear that you should only use enough crimp to keep the bullet from moving, and using more simply works the brass more than needed, leading to it failing sooner. This is true, however, the minimum needed varies with the specifics of your gun and load.

Some slow pistol powders need a firm crimp for reliable consistent ignition. Many do not. If the powder maker recommends it, do it.

You will hear the term "crimp jump" referring to revolvers, where the inertia of the bullet and the recoil of the revolver work to "pull" the bullet, so it appears to have moved forward, "jumping" the crimp.

This is absolutely a real thing, but again, its a variable thing, depending on many factors.

The usual check is firing 5 from a fully loaded cylinder, then checking the unfired round for bullet movement. Then doing it again with keeping the same round unfired. If there's no movement, you good to go.

HOWEVER, doing that in one gun does not mean its good for every gun.

Some years back I did a test, using uncrimped .38 Special rounds, (standard 158gr@850fps).

Fired through my S&W M28 6" they passed the jump test, the bullets did not move. Same (uncrimped) rounds fired through a J frame, the bullets DID "jump" (moved forward).

The difference here was the weight of the gun. The light gun recoiled more, and that "pulled harder", enough to overcome the case neck tension. The big Smith did not recoil as much, and the bullets stayed where they were seated, without any crimp.

In my test a light crimp provided the minimum needed for the light gun, and, of course, the heavy gun results didn't change at all.

A different load (heavier) would require more crimp to provide the minimum needed hold.

The standard factory crimp is done heavy enough so the ammo will work properly no matter what gun it is shot from.

IF you are looking for the minimum crimp needed, only testing with your stuff will show you that, and again, it will be gun/load specific.

Done right, more crimp than the minimum needed usually hurts nothing. Done wrong, results can be severely ...suboptimal. :D
 
I am surprised that no one has mentioned the Lee Factory Crimp (FCD) dies.
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On semi-auto rifle, I’m having good success. On pistol, I had mixed results. Hard to explain, but they seemed to weaken crimps compared to standard crimp dies. Maybe they were squeezing the bullet, but I never really proved that to myself either. I ended up selling mine off to people who wanted that “feature”.
 
For magnum revolvers I use the Lee Collet Crimp die, for semi auto calibers the Lee FCD, and for rifles I use two options, either the Lee Collet Crimp die or when I neck size with the Lee Collet Neck die if I feel the need for more hold I’ll get an undersized anvil for the Collet sizing die. But, in my specific case using the Neck sizing die I get plenty of hold with the standard size anvil, even in my gas guns.
 
I expect the bulged case profiles you see in this illustration is what 44 AMP was referring to:

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The common bulge problem is the roll crimp one, exaggerated in the third from left cartridge. What happens is the act of rolling the case mouth inward is making the brass turn the corner so sharply that it pries the sides of the case away from the bullet. This eliminates friction between the bullet and the case walls, so it can actually be weaker than a less dramatic crimp that does not do that.

The taper crimp bulge is much less common because it takes much more force, and that force is trying to accordion the case below the taper, and usually does so with the slightly longer cases in the batch while bulging the shorter ones, so you know pretty quickly when you get close to going that much too far. Indeed, one of the strategies for avoiding the more common bulge in the third type of roll crimp is the Redding Profile Crimp die approach. That is to start the crimp shoulder out as a taper crimp to hold the sides of the case flat and then have that taper terminate in a roll crimp profile at the top. This lets you make a more extreme roll crimp than you could do with a conventional roll crimp die. If you have heavy bullets in a very light revolver, you may well need that.

The Lee Carbide Factory Crimp Die with roll crimp ring makes the bulge and then irons it out. Because brass is more springy than lead, this most often does not restore side friction between the bullet and case walls but does ensure the round will chamber.

The Lee Collet Style Crimp Die for long revolver cartridges is less prone to bulge creation, though you can damage some bullets with it if you take it too far, as MarkCO pointed out.

Incidentally, just to make some trouble: The taper crimp is a later development than the roll crimp, at least in reloading tools. My old 45 Auto dies by Lyman had a roll crimp, and you just had to adjust the die until it flattened the flare and brought the case mouth inside the 0.467-0.473" case mouth diameter spec in the SAAMI drawings (specified on the drawing as 0.473" with the note that all cartridge diameters have a -0.006" tolerance). However, many target shooters in bygone eras did not do this. Instead, they seated their lead bullets out so the cartridge headspace on the bullet by it making contact with the throat before the case mouth reached the part of the chamber John Browning wanted it to headspace on. They then roll-crimped fairly firmly, knowing the bullet/throat headspace contact would prevent the rolled case mouth from reaching into the throat and raising pressure by being unable to release the bullet normally. They swore this made the most accurate ammunition. It also wears your cases out by starting mouth splits a lot sooner.

In experimentation with headspacing on the throat of a 1911 barrel, I have found it does, indeed, shoot significantly smaller groups and produces less lead fouling. However, I wasn't roll crimping, just taper crimping to get that result (groups almost 40% smaller with good cast bullets). I have played with the roll crimp a little since I have dies old enough to have a roll crimp shoulder, but I didn't immediately see a statistically significant difference with a small sample and opted for a longer case life instead.

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jetinteriorguy said:
For magnum revolvers I use the Lee Collet Crimp die, for semi auto calibers the Lee FCD, and for rifles I use two options, either the Lee Collet Crimp die or when I neck size with the Lee Collet Neck die if I feel the need for more hold I’ll get an undersized anvil for the Collet sizing die. But, in my specific case using the Neck sizing die I get plenty of hold with the standard size anvil, even in my gas guns.
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Only had 1 cartridge where the Lee collet crimp die was not enough. The .450BM (and the .450 Corvette of course). I ended up modifying the Lee die and basically did a light double ring crimp. We had called it a "stab crimp" but it was not a point, nor a rectangle, so stake crimp and stab crimp it technically was not. But in the same relative location one would place a stab, or stake crimp. The collet portion was machined shorter so that the crimp would be placed under the case mouth in the actual neck. It took three steps, first take out any flare, then the first crimp about 0.15" below the case mouth, then the second about 0.3" below the case mouth. We found two lighter crimps to be superior to one heavier crimp in terms of accuracy.

I have always said I was going to do the same thing with my .41 Magnums, but have still not gotten around to it.
 
Lots of good information here! It gives me even more to think about, such as what gun am I loading for, a 6 inch S&W 586 or a Ruger LCR.
I have heard that many shooters don’t crimp when loading for bolt guns, it that the general consensus? I have also heard that when loading for AR style rifles that you do need to apply a crimp.
 
Semi-auto pistol 9mm, 40SW, 45ACP

I have started using expander dies like Lyman M and Redding. IMO the bullet grab of properly expanded new brass seems fully adequate. I cycle that rounds and the COAL does not change. No crimping step.
 
Micro man said:
I have heard that many shooters don’t crimp when loading for bolt guns, it that the general consensus? I have also heard that when loading for AR style rifles that you do need to apply a crimp.
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Generally, I don't crimp for bolt guns. If sized properly, you will have enough case neck tension. This is where you have some discussion though. Case neck tension has factors, anneal, and when, how often, to maintain consistent case neck tension. That is for accuracy more than for reliability. I know hunters that do not have an annealing process and thus, don't crimp their hunting rounds. Where is your acceptable SD...accuracy for your ammo should dictate the processes you use.

Auto-loaders (AR or other) generally should have a crimp. The action is more violent and you don't want the bullet to jump forward upon chambering. And if you have a misfeed, you don't want the bullet jammed further into the case.
 
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I know hunters that do not have an annealing process and thus, do crimp their hunting rounds. Where is your acceptable SD...accuracy for your ammo should dictate the processes you use.
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I know hunters who don't anneal, don't crimp and don't give a rodent's posterior about SD as they don't even measure it. Their accuracy standard is "minute of deer" (or elk) and when they get that, they're happy. Different folks have different standards.

I don't crimp for box magazine fed bolt guns, with one exception, .458 Win Mag.

Right now, I'm down to 3 calibers in semi auto rifles, .223, .308, and 9mm Luger. I don't bother with crimp for the .223 or .308 and have never had any issues. I do taper crimp 9mm Luger, to be sure of the best feeding.
 
44 AMP said:
I know hunters who don't anneal, don't crimp and don't give a rodent's posterior about SD as they don't even measure it. Their accuracy standard is "minute of deer" (or elk) and when they get that, they're happy.
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Dang typo got me. I'll fix it. I am in agreement though.
 
I use the collet crimp die on .44-40, it socks the thin case mouth into the groove better than a roll crimp.

I have a collet crimp die modified to put a cannelure at the base of the bullet in .45 ACPs with short slick bullets subject to setback.

9mm gets the carbide factory crimp but I only use it on .45 ACP to salvage gauge failures.
 
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