Roll Crimping

Crimps, whether folded in the classic six or eight point "pie" shape – so named for the visible triangular segments – or rolled serve the same purpose for a shotshell: Crimps are to

1. Contain the load within the confines of the shell.
2. Assist the powder burn to create adequate combustion pressure during the early stages by not allowing a premature movement.
3. As pressure builds, release at a predictable moment – minimizing pressure variables.
4. Protect the contents of the load from contamination.

Fold crimps did not become popular for performance reasons. Fold crimps started out as "a cheaper way to produce more shells quickly." Fold crimps require less material, in that they do not require overshot cards and the entire process is speedier and easier for mass-production equipment.

Shotshell reloaders were adapted to the quickly standardized fold crimps not because they worked better, but once-fired hulls already had the fold memory and again, the process is faster and easier for production.

Functionally, roll crimps do many things better than fold crimps. Roll crimps can compress the shotshell closure in a far more controlled manner than fold crimps since each shell will be adjusted exactly to its requirement. Roll crimps, with typical, treated overshot cards or plastic overshot cards provide a tighter, more water-resistant seal than fold crimps. Finally, as a clear benefit to slug and large pellet users, roll crimps use less hull area for a quality closure.

Whether applying a fold or roll crimp, reloading a previously crimped hull may require a little reshaping by the Spin Doctor tool. This tool restores hulls by rolling back the shrunken plastic area and smoothing rippled plastic via heat and slight pressure.

Heat, in the form of very hot propellant gases generated by the burning powder, gradually "cooks" hulls and after repeated firings will render the hull unusable. The crimp area is subject to the greatest amount of damage and therefore the origin of most hull failures.

The use of thick plastic overshot spreading devices can reduce the life of a roll-crimped hull. After powder ignition, the hard plastic cards or spreader devices punch at rolled edges of the hull and can increase the conditions of cracking it.

Roll Crimping Tool break-in

Often times, the first few times that the roller head is used the resulting crimps will not be attractive. Several reasons: user inexperience with the tool and bumps or unevenness on the surface and top edges of the crimp. This is normal and to be expected.

Progressive use of the new roll crimping tool gradually begins to "cure" the specially formulated alloys. The tool builds and retains heat from shell to shell. Microscopic pores in the finish fill with lubricating particles of plastic, and practice will show you the small techniques and movements that will create perfect-looking roll crimps. Additionally, you will notice that roll crimping works much more easily if heat is retained – a roll crimping tool kept near 100 degrees F is perfect.

For purposes of practice and for curing the roller head, try out your new roll crimping tool on your oldest, cheapest "throw-away" hulls for a little while. Just a short practice session will improve the look of finished products.

Working with certain types of hull resins, it is beneficial to utilize a single drop of high-grade lubricant (anti-seize) placed on the contact area of the crimper – an old manufacturer’s trick for leaving a factory-finish on roll-crimped shells. Only one drop is required and this should last for many crimps (the pores in the crimper alloy will absorb small amounts of the lube and distribute it evenly.

Overshot Card Wads

Unless you are loading broad-faced non-conical slugs, it is necessary to use an overshot card (also known as "top" or "closure" cards) on which the crimp edges will be rolled. One of our favorite products for this purpose is the Instant ID Clear Overshot Disk. It is clear and allows one to identify contents of a shell. Additionally, it provides a very rigid base of support for the crimp – essential for a proper crimp. Although it is thicker than standard overshot cards (.080" versus .030"), it is made of a special frangible material that will break up into small pieces during the firing cycle - it does not interfere with patterns or shotshell performance. Manufactured of plastic, it is also water-resistant – a big plus for field loads.

Other products utilized for roll crimped closures are  standard Overshot (#OS) cards (.030") thick.

 
(Clear overshot Disk)            (Standard Overshot Card)

Hull Trimming for Roll Crimps

Roll crimping does not require a specific-length hull for adjustment. If you have a stash of hulls with fold crimps, or even some with damaged fold crimps, you can still use them to make shortened load hulls.

Hull trimming is easy once a Trim Doctor tool has been setup for the job. The tool has a stop-cut feature that will make exacting shell length cuts easy and uniform. Generally, between ¼" and 3/8" of material is removed from the top of the hull. ¼" leaves you with a European standard 2-1/2 inch case, for which we have many load recipes, including slugs.

Applying Roll Crimps

1. During the roll crimping process, the hull should be firmly cinched into a Hull Vise in an upright position. You can also hold onto the shell with your fingers, but your hand will get really tired if you are doing a number of shells.
2. An overshot card is placed on top of the shot or slug.
3. The roll crimping tool, chucked into a drill bit, should be held squarely on the hull mouth.
4. The drill or drill press should begin a clockwise spin at low to medium speed while apply little pressure.
5. Engage the top of the shell with the roll crimping tool for a full five seconds before increasing downward pressure. When the shell is ready to accept the crimp, you will feel a slight movement downward – finish the crimp in a steady effort.

 Perform a quality control check of the shell.

1. Is the crimp round when view from the top (chambering)
2. Is the crimp functionally even when viewed from the side?
3. Are there any noticeable imperfections or opening that could cause a load failure?
4. Is the load, within a few grains, the identical weight of shells loaded in the same batch with same components?

Roll Crimp Notes:

Never try to roll crimp a hull that previously had a fold crimp. The resulting roll crimp will not be satisfactory.

Slowly lower the crimper head down on top of the shell mouth. At first, you will feel the plastic yield to the roll. It needs just a couple seconds for the spinning crimper to heat the plastic edges of the hull. The particular timing of this heating process depends upon the heat retained in the metal of the roll crimping tool from previous use. If you have been crimping for a while, the crimper will be warm and it will transfer heat to the hull’s plastic.

Although many loaders prefer the precision and power of a drill press, it does not allow the reloader the sense of "feel" that a hand drill provides. An experienced handloader will gain a distinct feel for that moment when the plastic first begins to yield to the spin.

The exact speed (rpm) of the spin is not the essential part of a good crimp. In fact, a modest spin speed seems to work the best. A fast spin may cause plastic to heat up too quickly and control of the downward movement may be lost. Like any other talent, technique is very individual in nature and you will develop your own style of roll crimping; composing your own particular combinations of pressure and rpm.

Excessive downward force is not an essential component of a good roll crimp. The particular combination of heat and the timing of the yielding plastic (guided by the roll crimping tool head) is key. Immediately remove the crimping head once the roll crimp had been fully turned down. If the tool lingers on a fully turned crimp too long the top edge will "smear". If inspection reveals the crimp is not deep enough go ahead and spin the rolled edge a bit deeper.

Ballistic Products Inc.

20015 75^th Avenue North · Corcoran, MN 55340-9456
Technical (612) 494-9237 · Fax (612) 494-9236
www.ballisticproducts.com

WARNING: Ballistic Products, Inc. disclaims all possible liability for damages, including actual, incidental and consequential, resulting from usage of information or advice contained in this and other publications, labels, catalogs and booklets. Use data and advice at your own risk and with caution. Where data list specific components, no changes or substitutions for these components can be made without risking significant changes in the level of ballistic performance and/or safety of the loads shown. Follow loading data exactly and do not substitute components. We make no warranties express or implied, limited or full. Failure to comply with these and other standards of reloading may result in accidents with serious injury and/or death to the shooter and/or bystanders. All product sold as is.

 

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