Why crimp when reloading

The important thing to remember is that crimping is not a corrective technique for sloppy seating. Even though they are not parallel the walls are all straight. That flair has to be pressed flat or it wont fit all the way into the chamber. Wowsers, stirred up a lot of opinions and facts too!. Nearly all Factory ammunition has a crimp according to the type of ammunition that it is by design.

I never questioned weather to crimp or not to crimp. Crimp to a cartridge is like water to a duck, you crimp. There is so much difference with the way wood reacts to expansion and contraction and the way brass metal works that the two are apples and oranges.

The case mouth has to be expanded to get the bullet to seat without damaging it. Once it is seated to the proper depth it then needs to be case crimped back to the proper state to hold the bullet in place and chamber properly without hanging up on the case mouth. The key to crimping the case mouth is to NOT over crimp it. Over crimping will cause too much case pressure.

Under crimping, well, you explained that right. The bullet can move around causing unexpected pressures or even catastrophic results including squib rounds. I use the Lee dies and quick change bushings. Once the dies are set up, put the bushing on and tighten it to the die. You never have to change it after that. Lee offers pretty good videos on setting them up but the crimp dies are not explained very well for rifle loading.

The pistol crimp dies are simple and adjustable. Rifle crimp dies are not as easy for some reason different design engineer. FTX bullet. And as always with a taper crimp, only crimp enough to remove the mouth flare. Do not over crimp. Do not attempt to roll crimp, as this will cause headspacing issues that may result in ignition problems light primer strikes. First of all, the analogy was incorrect … pistol case reloading use an expander die on the case mouth, opening the case mouth slightly which allows the bullet to be seated with its axis correctly oriented , thus must be crimped back down to hold the bullet in place.

Secondly, forward movement of a cartrdge into a firearm chamber is always, ALWAYS, controlled by the extractor assembly, and a simple review of SAAMI specs shows that pistol cases are shorter than chamber head space rimmed cases, aka virtually all revolvers headspace on the rim, but case length is still shorter than chamber length. A similiar review of bottleneck cartridge dimensions also show that cartridge headspace is shorter than the corresponding chamber dimension.

If the cartridge is to be used in a bolt-action rifle, and the cartridge was properly loaded, then crimping is not required. If, on the other hand, the cartridge is to be used in a semi-automatic firearm, then crimping is almost certainly required. The reason for the difference is inertia Newtons First Law ; a cartridge being loaded into a bolt-action firearm imparts almost no inertia into the projectile as the cartridge comes to a stop into the chamber.

That same cartridge being loaded into a semi- imparts an enormous amount of inertia into the projectile and, when the cartridge comes to a sudden stop, the projectile — in accordance with Newtons First Law — wants to keep moving and will almost certainly unseat or loosen from the case this lossening is not only highly unsafe, but has a drastic, i. Sure no problem. Point 1- The function of the expander die. The article above attempted to explain neck tension with a dowel in a block of wood…we could debate whether this was an effective analogy or not, but the article failed to explain is that neck tension is always the most important factor for keeping a bullet in place.

When brass is sized, the neck ID is purposely squeezed down smaller than the OD of the bullet to be seated, by several thousandths of an inch. This is to create a press-fit between the bullet and the case.

Most straight wall cartridges come with an expander die primarily because the design of the bullets that are to be seated are usually flat based, usually with a pretty sharply squared bottom edge. The case mouth needs opened up to allow easy entry of the bullet, and prevent mashing the case. The plug inside an expander die has a rounded bottom to guide it into the undersized case mouth, a somewhat short cylindrical shank, and then tapers up to a larger OD.

The taper provides the mouth flare. The short cylindrical shank below the taper is still several thousandths smaller than the bullet OD to preserve the desired press fit and neck tension. Most all of the bullet shank is seated down in the undersized, tight neck of the brass below the flare and is providing all the force needed to hold the bullet in place. The only reason to taper crimp is to bring the very short section of expanded mouth back to spec by removing the flare.

Not to hold the bullet in place. There are several styles of crimp, and it is difficult to discuss them independently of the different shapes of cannelures and crimping grooves. Technically, a cannelure is a knurled band around the bullet. It is easy to apply, does not weaken the case appreciably, and accepts any kind of crimp.

Its one drawback is that the crimp is not as solid as with a crimping groove, and attempting to apply a tighter crimp can easily bulge the case neck. Crimping grooves are actual grooves, made either by impressing the jacket or cutting a groove. Cutting removes stock and creates a band of thinner metal, and this can lead to bullet break-up on impact.

An impressed groove is usually a radius, where a cut crimping groove is generally square. The ideal crimping groove is one that in cross-section appears to be a shallow triangle, with its deepest point near the tip of the bullet. It presents a solid wall for the crimped mouth of the case to brace against, effectively preventing the bullet from being pushed into the case. This was a common design on cast bullets and had the added benefit of distinguishing the crimping groove from the lubrication grooves.

The most common rifle crimp is the "roll. Inside the die, the diameter is reduced, and there is an angled transition like a forcing cone. The steepness of this forcing cone determines the shape of the crimp. This style of crimp has the advantage of working with virtually any style of cannelure or crimping groove. Redding makes a special die that applies a "profile" crimp. This forms a taper, ending in a tight, uniform roll crimp.

It is intended for blackpowder target shooters, where ignition and consistency depend largely on uniformity of crimping. However, it is also ideal for cartridges used in a tubular magazine. Another style of crimp, rare in civilian circles, is the parallel crimp. This prevents the bullet from moving either forward or back and gives the case an iron grip.

It was the standard approach for machine-gun ammunition, where cartridges take a terrific pounding whether in belt or box, and where durability is critical. For the average handloader, even one loading powerful dangerous-game cartridges, such a crimp is not necessary. Finally, there is a style of crimp that is almost completely forgotten, in rifle ammunition at least: the neck crease.

When the bullet is seated, the cannelure is hidden inside the neck. A special tool is used to imprint a crease in the neck, pressing it down into the hidden cannelure.

This was common with Kynoch cartridges loaded with jacketed bullets. We still see such crimps on handgun cartridges, both semiauto and revolver. Handloaders view them with a jaundiced eye because they mar the brass and can weaken it, but they are effective crimps.

Applying a crimp is not difficult, but it does require attention to detail. We will assume you have chosen the correct bullet, and you know the crimping groove is in the right place to give you the desired overall cartridge length. Next, you need brass sized and trimmed to the exact same length. Show more. Inline Feedbacks. Load More Comments. Submit Video. Contact Form 7 or GravityForms plugin is required!

You are going to send email to. Revolvers that produce noticeable recoil can cause uncrimped ammunition to lengthen. The effects of inertia during recoil can cause poorly secured bullets to slide forward, possibly causing a malfunction in revolvers. Cartridges can also elongate under heavy recoil in box magazine rifles. In repeating rifles, feeding can force an unsecured uncrimped bullet to move too deeply into the case to continue feeding properly.

Roll crimping is common for revolver ammunition; a different system is used for many rifle cartridges, including military cartridges. A roll crimped case is assembled with a crimp shoulder to reinforce placement of the bullet in the mouth of the cartridge case.