Home Forums Hunting & Shooting Ask The Gunwriters Question and thoughts about 35 Whelen A.I.

I have only fooled with about half a dozen "improved" cases, and all required little or no trimming at all, especially when compared to the parent cases. My guess is that the steeper shoulder does inhibit the flow of brass somewhat, but also PRECISELY headspaces the case in the chamber, thus preventing brass common among some rounds.

I know that I NEVER had to trim brass in my .257 Roberts AI, and do every 3-4 firings in standard Roberts rifles, even if the brass is only neck-sized. Also, I have yet to trim .280 AI brass, even when it is new from the factory Nosler stuff.

By the way, the .300 and .375 Weatherby rounds act just like AI rounds, preventing much stretch, especially when compared to the .300 and .375 H&H rounds they're based on.

I have heard this often enough that I can't really dispute it and it makes a certain amount of sense. I just have not verified it with a controlled test. I have had experiences with cases which are supposed to be "stretchers" and found them to be not so bad so I question the reason for the stretching.
For instance, the 303 British case stretches; not because it has lots of taper and a shallow shoulder angle but because the rifles it is most commonly chambered in are stretchy. The 270 Winchester is purported to stretch pretty badly but mine does not.
One fellow came into the shop with a 6MM Remington which stretched cases badly. It turned out the boltface was badly off from perpendicular (about .004"!) and the brass was stretching to fit the bolt. Each time it was fired it had to do this and the brass ended up stretching rapidly.
I suspect the more precise headspacing afforded by the sharper shoulder may well have more to do with any reduction in stretching than anything else does. After all, it makes little sense that the rounded corners of the Weatherby shoulder would inhibit brass flow. It does make sense that the case is more positively headspaced.
If one was to test a standard 30/06, for instance, and keep track of the amount of stretching; then rechamber the same rifle to 30/06 AI and repeat the test; the results would have some validity. One would have to be sure and just partially size the cases to insure the shoulders were not touched and load similar loads in each. I've got a bunch of old 06 barrels just taking up space. Maybe I'll try it sometime. The rimmed 303 or 30/40 could be used to test the precise headspacing theory. If closely fitted, the rim would take the shoulder angle out of the equation as far as precise headspacing was concerned. I'm too busy now but maybe this summer sometime.GD

I am with you on the .303--and that there are other causes of case stretch.

In fact, there are two common causes of case stretch even without considering the design of the rifle itself. One is the lengthwise stretching caused by sizing. The other is actual forward flow of the brass.

The first is exacerbated by a mismatch in sizing die and chamber. Unless cut by very carefully made custom reamers, both vary somewhat. If you combine a relatively small sizing die and a large chamber, brass will stretch noticeably with each sizing. This is purely a matter of forcing the larger case into a smaller space: The brass has to go somewhere. I have experienced this with several rifles, most notably a .270 that I eventually had rebarreled to 6.5x55 partly because of that problem.

But some cases do have a tendency to stretch more than others, due to brass flow. Those with longer, sloping shoulders tend to do so. And it is indeed a matter of brass flow. This is proven by the thickening of necks, especially at the base. This is normaly diagnosed by sticking a bullet in the necks of fired cases. If the bullet doesn't want to slide in, the necks are thickening somewhere, and it WILL cause problems.

Whatever the reason, I have indeed seen much less need to trim cases in the "improved" rifles I've owned, as well as some factory rounds with sharper shoulders.