Date: Jul 30 2006
You hear a lot of talk about “improved” cartridges, which are standard factory cartridges that have been “blown out” and had their shoulders “sharpened” or flattened, usually to 35 or 40 degrees. Headspace usually remains the same but is sometimes reduced to prevent chambering standard loads in an improved chamber for perceived safety factors. If increased significantly, you’re creating a wildcat cartridge, and that’s beyond the scope of this short article.
What’s the point of this? Does it gain anything? How hard is it to do?
Because the cartridge increases in volume, powder capacity increases slightly and so does velocity. My Holland-built .22-250 Improved with 40-degree shoulder burns 1 to 2 grains more powder than a standard .22-250 and churns up 50 to 150 fps more velocity. My .280 Improved bests a standard .280 by 100 to 150 fps with most bullets. Big deal. Some ammunition gains or loses that much shot-to-shot due to inconsistency in loading. You can gain or lose 100 fps with extreme heat or cold. I wouldn’t fall in love with an improved cartridge for its velocity gain. Call it a nice side benefit.
The real benefit seems to be in brass longevity. The sharper shoulder appears to reduce neck stretching and subsequent trimming. You may resize an improved case half as often as a standard, perhaps even less often. All depends on how hot you load ’em and how minimally or maximally you resize them. Some Improved fans claim sharper shoulder angles provide more positive headspacing, though I haven’t had problems with standard cartridges in that regard. Detractors say minimal body taper and sharp shoulders interfere with smooth loading from magazine to chamber. I haven’t noticed that either.
Creating an improved chamber requires reaming it to the new dimensions. Any competent gunsmith should be able to do it for $50 to $100. Then you must buy the appropriate resizing die. Be aware that there may be more than one size of a “given” improved cartridge. The Nosler Reloading Guide #4, for instance, lists dimensions for a .22- 250 Remington Ackley Improved that are 1.524 inches from base to start of shoulder, 1.892 inches total length while the Barnes Reloading Manual #3 depicts a .22-250 Improved that’s 1.539 inches base to start of shoulder, 1.910 total length. Both have 40-degree shoulders. Consult carefully with your gunsmith to match chamber to the die you’ll need to load for it.
Making Improved brass is easily done by fireforming. If the new chamber was cut with the same headspace (length from face of locked bolt to shoulder “wall” in the chamber, correlating to base-to shoulder length of the cartridge at the start of the neck), as it should have been, just shoot standard ammunition in the new chamber, i.e. .22-250 in a .22-250 Improved chamber, .25-06 in a .25-06 Improved chamber, .257 Roberts in a .257 Robert’s Improved, etc. Many gunsmiths recommend seating bullets to firmly touch the lands during fireforming as this forces the cartridge base firmly against the bolt face, minimizing case stretch just ahead of the webbing in the base. Target shooters like to seat bullets to touch rifling lands lightly just to center the bullet/cartridge with the bore, believing this creates straighter, more evenly balanced cases. Maybe it does.
After fireforming, check for excessive case stretch with a small wire bent at a 90-degree angle and inserted to the base of the web. Push the angled tip against the inner wall and slide up, feeling for any gaps or grooves, which indicate thinning of the wall. If you detect none, nor any cracks along the shoulder edges or necks, you’ve got a good fireformed case that you may subsequently size, trim and load like any other. Avoid excessive pressure in your handloads and each case should last a long, long time.
Consult with an experienced gunsmith before electing to Improve any rifle. Oh, there’s one more argument for having an Improved: just to be different.