Question about the AI's

[handirifle]

At the range today I spoke with an elderly gent that has a lot more years of handloading than I'll ever have.  He was telling me of his thoughts on AI rounds.  He was referring specifically to the 22-250.  It seems he is on his second and soon to be third barrel for his Ruger #1.  

He has shot out the other two.

he says his next rebarrel will be for the 22-250 AI.  He claims the more forward shoulder , in addition to the greater case capacity, straighter walls, less back thrust, also causes the powder to burn slower, or at least more evenly.  His theory was the sharp shoulder angle seemed to keep the powder from "blowing" out and causing a "fireball" (my words, not his) in the throat of the chamber.  Kinda like the new short magnums.  His theory seemed to make sense to me.  Any thoughts from you guys?

[onesonek]

Hmmm,posted reply earlier,musta got ate up up in the cyber world,
Anyhow, yes, straighter body tapers reduce back thust.  There are many theory's as to shoulder angles, but I have seen no hard evidence or data on the effect on "powder burn". I do believe, shoulder angles can and do affect accuracy to some degree, but there are no set "rules"  for that theory either.  Some claim sharper shoulders reduce throat erosion. But heat is is more the culprit on that issue. Sharp(er) shoulder's do reduce case trimming.
Originally shoulder angle, was and is a feeding issue first, and had very little to do with case capacity, other than first designs of bottle neck cartridge's. Which in a sense, like today's wildcatters, using exsisting brass for "new" designs. Shortly, came totally new designs, all revolving around the advent of "smokeless powder"
Dave

[SteveAZ]

If efficiency is defined as fps of muzzle velocity per grain of powder then yes, AI's in specific and sharper shoulders (30 deg and up) in general do seem to be more efficient.
 
I can give you general information about a wildcat I used to shoot. The case began life as a 308. It was necked down to .277 and neck turned to .008. The shoulder, measured on an optical comparator was 43 deg 25 sec. The sidewall was almost straight, just enough that the fired case could be extracted.

I don't remember the load, probably VihtaVuori N 560 and Sierra bullets. I chronographed the results, the muzzle velocity exceeded the published MV for Factory 270 loads for the same bullet weight. And this is from a 308 length case. Granted the case capacitywas greater than a 308 , but it was less than the capacity of a 270 case.  
 
It could be something else, but I attribute the greater efficiency to the sharper shoulder.
 
Steve

[Shoot!]

It could be something else, but I attribute the greater efficiency to the sharper shoulder.

Most skeptics (myself included) would attribute it to higher chamber pressure. Did you have any means of quntifying your pressure?

[Catfish]

At present I load 2 different wildcats in .17 cal., 2 in .25 cal. and 1 in .411 cal. I load more for efficentcy than velosity. I also believe that the straighter the case wall and the sharper the shoulder the better the pontical accuracy of the round is. BUT That means very little unless you are going for bench rest size groups and there are many other things that effect gorup size more.
   I also believe that there are alot of cases that are a total waist of time to improve. When you make a case larger your increase in velosity will be 1/2 of the percentage increase in volume. A good example of what I`m talking about is the .25-06. With that round you can push a 75 grn. bullet to 3,600 fps with 59.7 grns. of h-4831. With a .25-06 imp. you can push that same bullet to 3,900 fps., but it takes 75 grns of H-4831 to do it. You shorten you barrel life a bunch and you only gain 20 yrds. on max. point blank range. With the .257 Roberts cas, on the other hand, you can push an 87 grn. bullet to 3200 fps. with 45.9 grns. of H-380. If you imp. that case you can push that same bullet to 3500 fps. with 49.7 grns. of H-380. and increase your point blank range by 25 yrds. and use alot less powder doing it. I personally feel that improveing the .22-250 is a total waist of time for that same reason, but there are those that don`t care how much more powder it takes, they want every last fps they can get, even iif it will eat barrels. Just my thoughts on wildcat.

[SteveAZ]

It could be something else, but I attribute the greater efficiency to the sharper shoulder.

Most skeptics (myself included) would attribute it to higher chamber pressure. Did you have any means of quntifying your pressure?

I did not have a way of measuring the pressure if that's what you mean. I look the primers over carefully, they were not flattened, pierced, cratered, none of the usual signs of excessive pressure. In other instances where there have not been signs on the primers of undue pressure I have noticed that the primer pockets became loose after 3 or 4 re-loadings. This was not the case here. Also, I usually only neck size so I tend to notice 'over pressure' loads as they usually require a full length resizing. Again, no evidence here, neck sizing was sufficient for at least 5 re-loadings of the cases.