Ammunition

To Crimp or Not to Crimp — That Is the Question

Reloading bench with cartridges and shell casings

Recently, a student (who is new to reloading) asked me about crimping handgun cartridges. To be honest, I have been reloading for almost longer than I can remember and all of my procedures and dies are set. That made answering his questions somewhat difficult. Difficult because his questions jumped around, and I could not put my answers in a logical teachable order.

I quickly realized that answering random questions would not work and decided to start at the beginning to make everything — as to the how and why — logical and understandable. Admittedly, one area that most shooters could use a better understanding of is the subject of crimps. So, let me try to add my two cents to the subject and get the hate mail started.

A slight roll crimp on a light-recoiling .38 Special practice round.
A slight roll crimp on a light-recoiling .38 Special practice round.

To begin with, I believe we all understand that when the cartridge is fired it expands, releasing its hold on the bullet and allowing it to begin its journey to ‘who knows’ where. When the reloading process starts, the first procedure is to return the case to its original size by resizing the case. The next step is to expand (bell or flare) the mouth of the case, so it will allow you to seat a new bullet.

Once the new bullet is seated, the case must be squeezed to its original dimension. That way, it holds the new bullet in place and can be once again chambered properly in the firearm. The process of returning the flared case mouth to the size that will hold the bullet in place is referred to as ‘crimping.’

Questions that invariably arise concern which type of crimp to use and how much crimp is correct. It is of course possible to ‘over crimp’ when your crimp die is set incorrectly. That is something you most definitely want to avoid.

Roll Crimp

There are basically two common handgun crimps that we will discuss. The first is the roll crimp. With the roll crimp, the case mouth rolls in at the top to securely grip the bullet. The roll crimp is what we see most often on revolver cartridges, especially those revolver cartridges with excessively heavy recoil.

The roll crimp is necessary to prevent the bullets from moving forward in the case under recoil. If that happens, they could protrude from the front of the cylinder and jam the ability of the gun to function. Most bullets — designed to be fired in revolvers — will have a crimp groove formed into the bullet body. You’ll see this at some point along the bullet’s length for the roll-crimped case mouth to curl into, without damaging the bullet.

Brass cartridge cases collected from a shooting range
All cartridge casings are not created equal! Just because the caliber matches, does not mean the casings have the same case mouth thickness.

Almost all manufacturers offer seating dies with a built-in roll crimper — especially for revolver cartridges that utilize a roll crimp. To adjust the die to properly roll crimp, raise the seating die body so the case is not crimped when the press is at the top of the stroke. With several prepared dummy cartridges (no primer or powder), adjust the seating stem so it seats the bullet at the proper OAL, and seat a bullet in each of the 6 cartridges without any crimp.

Remove the seating stem. With the ram at the top of its stroke and a dummy cartridge in the shell holder, lower the die down until you feel contact with the case mouth. Next, lower the ram, and adjust the die body down approximately 1/4 of a turn.

Run the cartridge back through the die and examine the crimp. If more crimp is called for, adjust, and repeat until the crimp is correct. Then, tighten the lock ring and have at it.

Headspace infographic

You will then be good until you switch bullets. A different bullet will probably have a different seating depth, and you will have to adjust the seater itself until you get the cannelure centered correctly on the case mouth.

Tapered Crimp

The second type of crimp found on handgun cartridges, specifically those intended for pistols, is the tapered crimp. With the tapered crimp, the flare of the case mouth is straightened, so the round will chamber. This allows friction alone to hold the bullet in place.

When discussing pistol-cartridge crimping, we must remember headspace. Headspace, on a straight-walled cartridge, is defined as the distance between the face of the bolt and a point in the chamber that prevents further forward movement of a cartridge. All straight-walled, rimless pistol cartridges, headspace off the case mouth. That makes the tapered crimp essential. Remember, pistol cartridges have a case diameter that is slightly larger than the bullet, and the chamber has a shoulder for that case mouth to rest against as in the illustration of the .45 ACP.

Infographic of an exaggerated Illustration of the “shelf” that is formed to prevent set back.
An exaggerated Illustration of the “shelf” that is formed to prevent setback.

When crimping for auto pistols, one common mistake is over crimping — especially on the larger calibers. Most believe applying a heavy crimp to the cartridge prevents bullet setback during feeding. That is not correct.

Bullet setback — during feeding — is prevented by friction, between the sides of the bullet and the interior of the case. When the bullet is seated, its diameter is greater than the interior diameter of the resized case. This difference causes the bullet to slightly expand the case (as far down as that bullet is seated).

The case then angles in — underneath the bottom of the bullet — giving the bullet a little “shelf” around its circumference to sit on, preventing setback. The main problems encountered with over crimping:

  • Over crimping can cause the rim to cut into the bullet, deforming it and degrading accuracy.
  • With plated bullets, it can press through the plating. This will cause pieces of the plating to fall away and foul the chamber.
  • Pressing the case mouth too much — at the top — will cause the lower shelf (mentioned earlier) to disappear. Therefore, the lower shelf will stop supporting the bullet, making setback during feeding more likely to occur.

So, how do we determine the correct amount, of tapered crimp to apply, so the cartridge will feed and not cut into the bullet or compromise the shelf?

Dillon Precision 9mm headspace gauge
Just drop this 9mm Luger cartridge in the case gauge to determine whether it is correctly sized and crimped.

We need to remember some of the realities of reloading. Anything mass-produced will have variances. Proceed with the understanding that different brands of cases have different dimensions — including case mouth thickness. That means that any mathematical formula calculated using one brand of case might not apply to another brand. Likewise, if you reload mixed brass, the problem is compounded.

The Case Gauge

The simplest, or most elegant solution, is to use a case gauge. A case gauge is a cylindrical piece of metal that is machined with a tight, match chamber that is equivalent to the caliber it’s made for. After reloading a cartridge, insert it into the case gauge to check its overall dimensions. If it fits into the gauge, it will fit into a chamber.

By the way, all experienced reloaders have case gauges for all the cartridges they reload. The correct way to use a case gauge — to check crimp — is to first install the crimp die on your reloading machine, with it backed out to the point it will not completely eliminate the case-mouth flare. Then, run a round into the crimp die. Remove that cartridge from the machine and insert it into the case gauge.

Brass 9mm case fully seated in a case gauge
If it fully seats, it is good to go!

Does it drop easily into place? Does it fall free, smoothly, when you turn the case gauge over? If not, tighten the crimp down a quarter-turn. Repeat those steps until the round drops easily into the case gauge and drops free — easily — when the gauge is inverted.

Conclusion

That easy procedure will allow you to taper crimp your auto pistol rounds with the least amount of work. It will also allow smooth feeding, without cutting into/deforming the bullet, or compromising the “shelf” — regardless of the thickness of the case mouth or variance between shells.

I hope this eliminates some of the confusion and helps your understanding of the fine art of crimping. Stay safe, train often, and practice, practice, practice!

Do you have any reloading tips? How do you prefer crimping? Share your thoughts in the Comment section.

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (24)

  1. I agree with what Rockit wrote…

    Good article. I knew there was a different in crimp type between revolvers, and semi-auto, but wasn’t really sure why. This all makes sense to me now.

    Thanks!

  2. Oh yes and I forgot to mention -so if the casings are not trimmed and you have inconsistent crimping you will have inconsistent pressures in your bullets which will effect accuracy consistency and could even create unsafe pressures

  3. This article is very helpful buuuuut it leaves out one very important step- the first one.all your brass needs to be trimmed to a uniform length or the crimp will very from bullet to bullet resulting in some bullets being over crimped and some under crimped in the same batch. I have been reloading for over 20 years and only crimp bullets with crimp markings. 9ns and 45s etc.I only barely flare the mouth so the bullet will slide in and still fit in the bullet checker and do not crimp or unflare the casing.I have never had an issue and have done this on thousands of rounds.

  4. Actually tumbling your cases and cleaning with an ultrasonic device is the first thing you do so you don’t scratch your dies!! Use the crimp grove on all your revolver cartridges that call for it. (I know, someone will snivel about the barrels on a TC Contender) Read your Bible,(Lyman book of any century). Otherwise a good article.

  5. I’ve been reloading about twenty years. I used to shoot silhouette with .38/.357. Used a Ruger Blackhawh 61/2″ barrel. Never crimped except with what came with the Lee 3 die set. When my wife got her Ruger LCR, the bullets would come out of the case so the cylinder wouldn’t turn. Bought the Lee Factory Crimp Die, problem solved. I say Crimp and don’t take chances

  6. MAC brings up an interesting point, Lee collet dies. So is this a third type crimp, Collet crimp?

    I do believe they do a great job on rifle rounds, especially for accuracy, and keeping bullets in place (in the magazine) during recoil.

  7. Few years ago I tried taper crimping 270 loads, It did not give me any more consistent velocity or accuracy. But I was pretty tight to begin with, 5 shot groups were within 10 FPS always and some were less than 5. accuracy was less than 1/2 MOA. I really found the sweet spot for that post 94 Winchester. Turning the necks did not yield anything either. I attribute the Lee collet dies and a technique in seating that gave me run outs less than .002. Again you have to find the sweet spot for the bullet and barrel.

  8. Another good article. Thanks Ed and CTD for taking the time and effort.
    I have a tiny shrine to an old feller from my former club. He has long passed but i keep two of his 9mm reloads and a small photo of him on the wall of my loading bench… They are hands down the worst 9mm reloads i ever have seen. To say ‘over crimped’ would be understatement of the year. Absolutely deformed would be closer to accurate. Was fun helping him set up his dies properly.

  9. Another lesson from the master.

    The only thing I might clarify is that crimping rifle ammunition is ANOTHER “voodoo science,” and deserves an article all to itself- especially when loading both straight walled and bottle neck cartridges.

    “Someday, master, I will take the stone from your hand, and I, too, will be called “Master.”
    (Bows)

  10. Craig, Some military ammo does have the primers crimped, primarily if the ammo can be fired in full automatic firearms. Typically these days you will find 5.56 MM ammo and some .223 Rem ammo with crimped primers. The purpose for this is to ensure that the primer does not become unseated during full auto fire scenarios. Ammo that has crimped primers is more difficult to reload because there is another step involved. After the primer is punched out there is a ridge left in the base of the cartridge that prevents new primers from being inserted. Before a primer can be inserted into the primer pocket has to be swagged to remove the ridge. RCBS as well as the other reloading tool manufacturers all have tools available for this procedure.

  11. Things i knew nothing about for $1000 pls alex…
    I thought crimping was referrant to the primer.
    Whered i get that from? Or do you do it for that too?
    Brain hurts.

  12. The answer is simple. Roll crimp revolver cartridges and taper crime any semi-auto cartridges. Just be sure that you don’t over crimp.

  13. @DALE. “Putting your own ammo together is a science within itself. Maybe one day!” It can be as simple or complex as you want to make it, although I highly suggest starting out with simple. It can be as simple as a single powder for all of your handgun rounds, and a different single powder for all your long gun rounds, provided you are reloading very common calibers. If you are just going to punch holes in paper with them, you don’t need to use the hottest load possible. I suggest starting with a re-load manual, see if you can find loads in the calibers you plan on reloading, which would all use the same powder, and start with that powder. I believe revolver calibers are the simplest to reload.

    I suggest starting with a single station press, loading in lots of 50 = a box, as a single stage press lets you get more comfortable with each process, and you can always transfer your dies and stuff to a progressive press later. I also suggest using something like Lee disk power measure, making labels for each load showing the powder name and load in grains, bullet style and weight, and the disk(s) used for that load, so you can refer to it lot after lot, for excellent consistency. Follow the instruction for setting up each individual die correctly, using locking collars for future repeat, as modern dies have considered the information in the above article. Begin with the lightest recommend powder charge per load, to relieve the stress of thinking you may blow your gun up.

    The one part that tends to muddy the water is: When throwing a powder charge, with a disk, or an adjustable powder thrower, it is being “thrown” by VOLUME, but CHECKED, by WEIGHT, on a scale. So a little confusing, but eventually will become comfortable. FYI: A pound of powder is 7,000 grains. So lets say you are loading 5.5 grains of powder into say a 9 mm round, you can expect to be able to load 1,272 rounds from a single pound of powder, or about 25 and a half boxes. @ say $49 per pound = $0.0385 per round, plus the cost of bullets, and primers.

    Obviously a few tools besides a press, dies, and case preparation tools, are handy. I suggest shell holder, a digital powder scale, which can be found for around $30, and digital caliper set to measure ($20 Harbor Freight?), for occasionally checking overall loaded length (so it will fit a standard chamber)

    So why wait another day? 🙂

  14. Great artice, thank you again Ed. I’ve been reloading for over 4 decades now, and I continue to make mistakes, and learn from them. I kept getting jams and FTF in all of my 1911 pistols with a batch of bullets I was using, sized at .452″. Well, I finally broke down and spent a few dollars on a case gauge, and sure enough, none of my reloads dropped in. After re-reading my several reloading manuals I saw that the proper diameter for my .45 ACP was .451″, not .452″. OOPS! I was able to salvage everything by running everything through a sizing die just enough to drop into the gauge, Worked like a charm. A case gauge is inexpensive, and well worth the investment if you reload cartridges that headspace on the case rim.

  15. I have no idea why you would receive negative emails. That’s a great article. You just helped me to understand what my 87 year old Marine Korean war vet Dad has been trying to teach me for 47 years! I just never got it. He doesn’t have any case gauges but I already have 3 in my wishlist. Thanks for a great explanation.

  16. Good article. I knew there was a different in crimp type between revolvers, and semi-auto, but wasn’t really sure why. This all makes sense to me. My thinking is: Anything that is expected to generate any recoil, should probably be crimped. Possibly, for precision purposes, maybe a single shot would be fine without crimping?

  17. My son who shot expert in the US Army didn’t crimp when shooting competition & won a lot. I personally feel I get more consistent groups crimping. Let us not forget the Wayne of the NRA had help with his money grubbing like his wife. We need to expose them all & jail them in a court of law. I know thank you!

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