Pros/Cons of 30 vs 40 degree shoulder?

[Andy4600]

What are the advantages/disadvantages of a 30 vs 40 degree shoulder in a round, if all else is equal?

I've read there is a slight accuracy advantage in a 30 degree shoulder. Any truth to this?

I've also read somehing about less throat erosion and longer barrel life in a 30 degree shoulder...but the proof on this was vague.

Other items I am fairly sure of:
30 degree should feed better (but this matters little in a bolt gun).
40 degree has better case life due to less expansion.

Anything else?

 

[just_jon]

Pros: More powder capacity, more speed, better case life, reduced trimming.
Cons: None that I've found.

I hear the barrel life argument, but I've not noticed a significant difference in barrel life. I get around 1800 rounds out of a 22-250 barrel running 3800 fps and 1500 rounds out of my 22-250AI barrel running 4500+ fps. Barrels are an expendable commodity just like powder, primers, bullets and brass.

 

[Buckleman]

Cons would be with me. Fire forming the improved version

 

[elkaholic]

Some assumptions are being made that all 40 degree shoulders need fire forming, which is not true. If thats the case, then fire forming is a minus. The only other downside is potential feeding issues which are not often a problem with the new magazines, especially DBM's.
Pros are many, including more capacity in the same body length (to shoulder/neck jct) which equals more velocity.
Better burning efficiency within the case. (changes pressure curve and facilitates burning of slower powders). Less case stretching which equals better case life with less trimming.
Better throat life especially when combined with a longer neck, when all else is equal. (pressure and vo;ume)

 

[josip89]

Tag

 

[Andy4600]

Some assumptions are being made that all 40 degree shoulders need fire forming, which is not true. If thats the case, then fire forming is a minus. The only other downside is potential feeding issues which are not often a problem with the new magazines, especially DBM's.
Pros are many, including more capacity in the same body length (to shoulder/neck jct) which equals more velocity.
Better burning efficiency within the case. (changes pressure curve and facilitates burning of slower powders). Less case stretching which equals better case life with less trimming.
Better throat life especially when combined with a longer neck, when all else is equal. (pressure and vo;ume)

Yes, but is this as compared to a standard cartridge...20ish degree shoulder...or a 30 degree? Does a 40 degree perform better than a 30 degree in the catagories you described?

 

[elkaholic]

Some assumptions are being made that all 40 degree shoulders need fire forming, which is not true. If thats the case, then fire forming is a minus. The only other downside is potential feeding issues which are not often a problem with the new magazines, especially DBM's.
Pros are many, including more capacity in the same body length (to shoulder/neck jct) which equals more velocity.
Better burning efficiency within the case. (changes pressure curve and facilitates burning of slower powders). Less case stretching which equals better case life with less trimming.
Better throat life especially when combined with a longer neck, when all else is equal. (pressure and vo;ume)

Yes, but is this as compared to a standard cartridge...20ish degree shoulder...or a 30 degree? Does a 40 degree perform better than a 30 degree in the catagories you described?

Yes, I just realized that I misread your post. I described the advantages of 40 over 30 but the same rules would apply to 30 over 20 to some degree

 

[Varmint Hunter]

Barrels are an expendable commodity just like powder, primers, bullets and brass.

I read this all the time but let's put it into perspective.

I recently shipped out a rifle to get rebarreled. It cost:

$125 to ship it out
$950 to get it back including the gunsmith work and return shipping
Total cost for a new SS barrel - $1,075

That makes barrel life an important issue when cartridge selection and load development are being considered.

 

[cabelasken]

I used to think that a gentle case slope helped with throat erosion, but now I believe the length of the neck contributes more to minimizing erosion. As the powder kernals (extruded) exit the case, the ones near the bullet are unburned and for a few inches down the barrel act as sandpaper against the throat causing erosion. I think those cases with gentler shoulders keep the kernals traveling more straight and the cases with longer necks will help even more and could help with throat erosion. However, cases like the 280 AI with the 40 degree shoulder seem to deform very little and brass lasts a very long time.

 

[elkaholic]

I used to think that a gentle case slope helped with throat erosion, but now I believe the length of the neck contributes more to minimizing erosion. As the powder kernals (extruded) exit the case, the ones near the bullet are unburned and for a few inches down the barrel act as sandpaper against the throat causing erosion. I think those cases with gentler shoulders keep the kernals traveling more straight and the cases with longer necks will help even more and could help with throat erosion. However, cases like the 280 AI with the 40 degree shoulder seem to deform very little and brass lasts a very long time.

I agree with the long neck helping but I think a short burn column coupled with a 40 degree shoulder burns more powder inside the case BEFORE it travels through the throat which alleviates the problem you described. Also, the hottest part of the flame is deflected more into the neck with a sharper shoulder. Much like adjusting the flame tip on your cutting torch.

 

[Philward]

30° shoulder more forgiving during the resizing process compared to 35° and 40°, and better alignment in chamber that steeper shoulder angles like 20° and 17°. At least that is what I just heard in a Backfire video interview with Hornady tech. No personal experience either way, just what I heard. I didn't stay in a Holiday Inn Express either, at least not lately.

 

[Mike Matteson]

The only thing here is they must have seen you coming for the cost of the barrel work costing. the other is I am become a believer in purchasing the reamer to start with. They about $250.00 and you have it for life.

 

[coop2564]

According to Hornady the case is weaker with a 40 degree shoulder and more susceptible to case crush/set back (shoulder hunch) when sizing and loading in tight necks.

 

[sable tireur]

Let's face it, 20° and 17° shoulders were created for those cartridges selected for use by the military. This is to guarantee absolute feeding and functioning, no failures from magazine to chamber. The belt on 'magnum' cartridges guaranteed safe, repeatable headspace when the H&H cartridge case use shoulders with very mild 15° shoulders in order to accept the strands of Cordite easily.

Unfortunately, this thinking has continued throughout earlier case designs without any additional thinking about what might be an improvement. Ackley gave us the largest angular change with the 40° shoulders (AI). But the 7x61 S&H uses a 42.25° shoulder straight from the factory.

Now even the grandly supported .243 and .260 have been designed properly with the advent of the Creedmoor cases. What once was readily acceptable (mild shoulders) is now making headway with the 30° shoulder. And the Dasher cases come from the factory with 40° shoulders.