improved case question

[ishootkittens]

Do smaller calibers gain more velocity from an improved case as opposed to larger calibers? For example will a 6.5-300win improved gain more of an advantage (in terms of a velocity jump over the "standard" clambering) over a 300win improved (if compared to a 300win). I do not have either of these chamberings nor do I plan on building a rifle in either clambering. They are simply examples.

In other words, if a 338lapua improved gains 200 fps over the standard lapua, would a 7-338 lapua improved gain more than 200fps because of the smaller bullet?

Kind of a strange question, yes, but If you guys could help I'd appreciate it.

 

[dkhunt14]

I believe that would be a hard question to answer. You can build one and it is a slow barrel and build another and it is a fast barrel. I have seen over a hundred feet a second difference with the same chambering. Matt

 

[65WSM]

I theory, and that is what we are discussing here, the scale of the cartridge should have the same increase in capacity and performance with the "Improvement" regardless of size of the bullet. In use, some body and shoulders are tapered more than others. The 6.5-300 WSM you speak of starts with a 30 degree shoulder and less body taper than most cartridges. (I own a reamer and two rifles). It would gain very little through "improvement" Less than 3 percent. The .338 Lapua would gain a lot from "Improvement" whether it were kept .338 or necked down. The .338 Remington Ultra Mag is close to an Improved .338 Lapua in capacity. The Lapua case is built for possible use in full auto (machine guns) military weapons with very hot barrels and chambers. The Lapua has lots of taper and "Improving" it would push out the front of the shoulder and gain about 8 to 10 percent (My guess) in volume.

I own 6.5-06 improved, .22-6.5X47 Lapua Improved 40 degrees, .22-250 Ackley Improved,

 

[WildRose]

Basically all of or at least the vast majority of the "improved" cases have some increase in case capacity over the parent case.

All else being equal, more powder equals an increase in velocity.

There is not always a 1:1 gain but theoretically if you increase powder volume you are going to increase velocity.

One of the reasons though for the AI cases isn't increasing powder capacity but lowering pressures and changing the way the ejecta from the case affects the throat so as to increase barrel life.

Humans and particularly wildcatters are always trying to find ways to increase performance, barrel life etch. It's what we do.

 

[65WSM]

I would bet on a one third gain in velocity compared to increase in powder charge at best. Using my 6.5-06 Ackley 26 inch barrel. I gain 9 percent in powder charge to get about 3 percent more velocity 90 fps.

I like the looks of the Ackley 40 degree shoulder.

The cases tend to stretch less than the factory parent cartridges.

Break action rifles like the G2 or Encore will headspace much more consistently and shoot better with Ackley shoulders.

Powder burns in the case more and is not blown out the barrel as much with Improved shoulders.

 

[WildRose]

I would bet on a one third gain in velocity compared to increase in powder charge at best. Using my 6.5-06 Ackley 26 inch barrel. I gain 9 percent in powder charge to get about 3 percent more velocity 90 fps.

I like the looks of the Ackley 40 degree shoulder.

The cases tend to stretch less than the factory parent cartridges.

Break action rifles like the G2 or Encore will headspace much more consistently and shoot better with Ackley shoulders.

Powder burns in the case more and is not blown out the barrel as much with Improved shoulders.

That's probably not real far off. Look at the difference in the 7 Rem and 7STW Around 10% more case capacity each for a net gain of around 200fps.

 

[ishootkittens]

Well that makes sense I guess! I guess I was just thinking that a 3% improvement on a case's capacity would push say a 6.5 bullet marginally faster than a .338 bullet if the same case was used (maybe like the Lapua case).

 

[Bravo 4]

My guess is that it would depend on how overbore the chambering was to begin with. Maybe I'm wrong but isn't the more it is overbore the more you contend with that whole law of dimenishing returns thing?

 

[WildRose]

My guess is that it would depend on how overbore the chambering was to begin with. Maybe I'm wrong but isn't the more it is overbore the more you contend with that whole law of dimenishing returns thing?

Yep.