Shoulder angle

[Grimstod]

So how does shoulder angle affect the cartridge. Was reading about he 6.5x55 and they said it had the ideal 30degree angle. Are there pros and cons to having a sharper shoulder angle vs less shoulder angle? Will it affect barrel life? Or efficiency? How about extraction and head spacing? Does one head space more consistently then the other?

 

[LHSmith]

The Swede shoulder is 25 degree. Less angle = better feeding, more angle = less case stretch.....since 30 degree is somewhere in- between, perhaps it is true. After-all the 6 BR, 30 BR and 6 PPC are 30'.

 

[Grimstod]

Good answer Smith. Just what I wanted to know. What about barrel life? Will steeper angle burn be more prone to a throat burner?

 

[mikecr]

+1 LHSmith
And you'll never prove an affect to barrel life from only shoulder angle.

 

[Scott Harris]

+1 to LHsmith. The "consensus" is that longer necks and sharper shoulder angles results in a less intense burning of the throat, thereby enhancing barrel life. It makes sense to me, but I too have no proof of that idea.

 

[22BRGUY]

+1 to LHsmith. The "consensus" is that longer necks and sharper shoulder angles results in a less intense burning of the throat, thereby enhancing barrel life. It makes sense to me, but I too have no proof of that idea.

Good answer....It SEEMS that if you take a cartridge diagram and extend the line of the shoulder angle to the neck area, if the line extends past the end of the neck, it POSSIBLY will burn the throat area more as the hot burning gases would theoretically be directed beyond the protection of the case neck.........if that makes sense???

 

[dannyjbiggs]

You might Google the term "convergence angle" to get the low down on advantages of keeping the convergence of the case shoulder angles within the cartridge case neck. The theory has been around for a long time.

Danny Biggs

 

[cdparker]

However, Two lines from anywhere on Earth to a Star are considered Parallel.
That is just a thought.

 

[lpreddick]

i saw the term "turbulence point" to describe the point where the burning propellant/pressure vectors converges due to shoulder angle...the shoulder from the inside of a case is a funnel. the idea is if this point is outside the neck, the barrel at this point gets really torched...the .243 is one excellant example. if the turbulence point is in the neck...less barrel burning. if the point converges EXACTLY at the bullet's base...accuracy, accuracy, accuracy. this latter idea is interesting. my one hole shooting 6 MMBR and 22 BRS bullet's seat with their bases very close to this majic point...i'v not seen a lot regarding this as possibly a real thing, but it is interesting.

 

[22BRGUY]

i saw the term "turbulence point" to describe the point where the burning propellant/pressure vectors converges due to shoulder angle...the shoulder from the inside of a case is a funnel. the idea is if this point is outside the neck, the barrel at this point gets really torched...the .243 is one excellant example. if the turbulence point is in the neck...less barrel burning. if the point converges EXACTLY at the bullet's base...accuracy, accuracy, accuracy. this latter idea is interesting. my one hole shooting 6 MMBR and 22 BRS bullet's seat with their bases very close to this majic point...i'v not seen a lot regarding this as possibly a real thing, but it is interesting.

Excellent thinking IMHO...that's why it's important to sort bullets with the bullet base length from the front beginning bearing surface.

 

[maxpower]

Then there is the theory to which the SMc cases subscribe which has the rounded shoulder reflecting the turbulence point back towards the base of the case.

 

[mikecr]

The SMc internal ballistic advantage isn't about turbulence point, and neither is shoulder angle with most cartridges.
It's about containing more of the powder burn(not flamepoint) inside the chamber, instead of somwhere down the bore.
This bottlenecking improves efficiency, much as Gibb's front ignition did.
Bottlenecking comes down to a ratio of case diameter to bore & shoulder angle & powder speed & starting pressure.

Wildcats, which tend to be fat for bore, and holding high shoulder angles, are very efficient.
But barrel life is another matter completely. While affected by powder burned further down the bore -vs- near case mouth, the usable life itself is more complicated as it usually comes down to carbon restriction management.

 

[Grimstod]

But barrel life is another matter completely. While affected by powder burned further down the bore -vs- near case mouth, the usable life itself is more complicated as it usually comes down to carbon restriction management.

What's carbon restriction management?

 

[CatShooter]

But barrel life is another matter completely. While affected by powder burned further down the bore -vs- near case mouth, the usable life itself is more complicated as it usually comes down to carbon restriction management.

What's carbon restriction management?

You heard it here first..

Brand new.

 

[mikecr]

I mean't constriction
The ultimate ender of barrel performance follows bore constrictions due to carbon. You can set back barrels to extend life, but eventually constrictions downstream of the throat will still end it. Otherwise we could shoot barrels forever.

Moly shooters report better barrel life, and this is because moly's latent heat of vaporization cools the burn early. But when those shooters don't manage the constricting overlaps of moly downstream, they shorten barrel life.
When you run a cartridge with reduced bottlenecking, a powder slug forms & travels & burns differently down the bore, adding to bullet mass. Some of it burns further down the barrel, and some of it ignites just beyond the muzzle. None good for efficiency, accuracy, or barrel life. This is where you're at with a 243, 270, 30-06 case design.

 

[wboggs]

Some interesting discussions on this thread. How does the shoulder angle and configuration affect velocity with cases of the same capacity, same seating, same throat, same barrel, etc. Only difference being the shoulder. Roy Weatherby claimed it increased velocity and P.O. Ackley said it didn't.

 

[Laurie]

Some interesting discussions on this thread. How does the shoulder angle and configuration affect velocity with cases of the same capacity, same seating, same throat, same barrel, etc. Only difference being the shoulder. Roy Weatherby claimed it increased velocity and P.O. Ackley said it didn't.

It doesn't, period! While it can be argued that sharp shoulders and minimum case body taper with a short charge column may improve ignition consistency and likewise charge burn consistency, if all of the powder charge is consumed within the barrel, the sole relevant factors are the charge's energy content (specific energy x charge weight) and maximum pressure produced in relation to the bore size and bullet weight.

Roy Weatherby used his case forms as unique selling propositions and marketed his designs very cleverly, but in practice the additional performance was obtained by maximising both case volume / charge weight allied to loading his ammo to some seriously high pressures.

As an example of how case shape has relatively little effect on performance, compare the archaic .300 H&H Magnum against the modern .300 Winchester Short Magnum. The WSM has most things 'right' (30-deg shoulder angle, short fat case-body with minimal taper); the H&H has everything '100% wrong' - long skinny shallow taper case and hardly any shoulder at all. However, as luck would have it, they share a near identical case capacity and are both rated at 65,000 psi PMax by SAAMI using the Piezo measurement system. In practice, they produce near identical MVs with any particular charge weight of suitable powder under any given bullet in any reasonable barrel length. Those who love modern short fat designs and hate old tapered, shallow shoulder types might be surprised to discover that the antediluvian H&H model produces extremely small ES and SD values and will group extremely well with carefully loaded handoads in a good quality rifle.

The WSM is superior for precision shooting in that a rimless case provides better headspace control than a belted magnum which in the .300 H&H's case must use the belt for headspacing because of its shallow shoulders. It's easier to make very uniform cases too the shorter the case body. Otherwise, the sole provable internal ballistics benefit from the short WSM over the long H&H is that the latter's noticeably shorter case and COAL extend the usable (rifled) section of the barrel by around 0.4-0.5 inch in any given length of chamber blank once it's chambered.

 

[CatShooter]

"... The WSM is superior for precision shooting in that a rimless case provides better headspace control than a belted magnum which in the .300 H&H's case must use the belt for headspacing because of its shallow shoulders. It's easier to make very uniform cases too the shorter the case body. Otherwise, the sole provable internal ballistics benefit from the short WSM over the long H&H is that the latter's noticeably shorter case and COAL extend the usable (rifled) section of the barrel by around 0.4-0.5 inch in any given length of chamber blank once it's chambered."

Comparing the 300 WSM to the 300 H&H is comparing apples to oranges - or maybe apples to watermelons.

Compare it to the 300 Win Mag, shot by someone that shoots it in competition or other long range sport, and who adjusts the dies to seat on the shoulder - then there is no difference. In fact, I would take the 300 WM over the 300 WSM any day of the week.

And many that shoot rimless cases do NOT adjust their dies properly, and don't understand why they have to keep trimming their cases... until the heads fall off.

 

[Laurie]

The reason for comparing .300WSM and .300H&H is not about their suitability or otherwise for match applications compared to other .30 magnums rather their internal ballistics which are so close as to be indistinguisable despite their very different case shapes. The topic is about shoulder angles after all - and you can't get much further apart than this pair, the WSM at 30-degrees, the H&H at 8-deg 30 minutes angle.

That's also why I said the H&H is inferior in this department as the shallow shoulder angle means that the belt must be used for its original purpose unlike most other belted designs. That is a secondary consideration / issue though when we're discussing whether a steep shoulder angle affects a cartridge's thermal efficiency.

 

[CatShooter]

The reason for comparing .300WSM and .300H&H is not about their suitability or otherwise for match applications compared to other .30 magnums rather their internal ballistics which are so close as to be indistinguisable despite their very different case shapes. The topic is about shoulder angles after all - and you can't get much further apart than this pair, the WSM at 30-degrees, the H&H at 8-deg 30 minutes angle.

That's also why I said the H&H is inferior in this department as the shallow shoulder angle means that the belt must be used for its original purpose unlike most other belted designs. That is a secondary consideration / issue though when we're discussing whether a steep shoulder angle affects a cartridge's thermal efficiency.

Ok... that's fair comparison...