Optimal shoulder angle for ELR cartridge design

E

ELR researcher

Sergeant
Full Member
Minuteman
Mar 30, 2011
982
253
www.elr-resources.com
#1
If someone wanted to design a cartridge for ELR, using a .375 projectile, is there a way to calculate the optimal shoulder angle for such a cartridge? This question assumes a limit of 50” for the associated barrel length.

I am spec-ing a .375 caliber as there are the most projectiles currently available for this caliber above .338 and below .510. I note the barrel length at 50” because I know of at least one excellent barrel maker that will produce barrels up to that length (RFour/Feddersen).

I'm also assuming powder capacity is not an issue – cartridge based (at least in base dimensions) on 50 BMG.

Again, the question is, “is there any way to calculate the optimal shoulder angle for such a cartridge?"

Thank you and God Bless!
 
#2
Re: Optimal shoulder angle for ELR cartridge design

When Jon Barness designed the B-29, (29 caliber) he tried different shoulder angles, when he got the most velocity, most efficient, case life, they stopped. But as far as formula, I don`t know. Some of the worlds most accurate shoulder angles are around 30.
 
  • Like
Reactions: lash
#3
Re: Optimal shoulder angle for ELR cartridge design

There was an article in Precision Shooting Magazine a few years back that discussed this and specifically the effects of a sharper shoulder angle reflecting the "fire" back down into the case to effect a more complete and efficient burn. IIRC it was 41 - 45* as optimal which tracks right along w/ P.O. Ackley.

I would hypothesize that there should be more investigation as to the relationship between not only the shoulder angle but the upper vs lower case diameter as being a vital component. The WSM cases certainly have big performance jumps via the "short - fat" powder column. If you were basing a cartridge off the 50 BMG round it would be interesting to see if you could blow out the upper case diameter and give it an "AI" shoulder after squeezing the neck down to .375. It's not like your going to link a bunch of this together and run it through an M2.

Cheers,

Doc
 
#4
Re: Optimal shoulder angle for ELR cartridge design

Take the 416 Barret and neck it down to 375. The 50 case necked down would probably require cannon powder, which is very dirty, and also would it be hard to get?
 
#5
Re: Optimal shoulder angle for ELR cartridge design

Doc:

Thanks for the reminder about "reflection".

What I did not specifically state is that a barrel as long as 50" should be able to allow for the burn of all the powder in a 50BMG-based cartridge (necked down to .375) before the end of the barrel. Point being, I probably don't need more capacity, just to use it quite efficiently (most velocity for the energy produced).

Unless a sharp corner (like the classical 40 degree AI chambering) buys me something, I'm tending toward the 20s - simple logic (simple-minded logic) that the more direct the forward push the more efficient. But, at some point, I need to get down to .375, so I can't just go straight-sided like a 45 ACP.

The 14.5×114 mm has a 22 degree 15 minute angle - and reports are it is certainly a very effective ELR cartridge. I realize that the shallow shoulder of that cartridge, and the 50BMG, is at least partially for feeding purposes, just thinking shallow. Again assuming going forward that I'll have plenty of length to burn the powder.

Then again, I think more consideration might be warranted on more of (higher volume of) a faster powder - then the 50" might not be sufficient to burn all the powder. Moves the question back and forth.

Other thoughts?
 
#7
Re: Optimal shoulder angle for ELR cartridge design

I have been down this road. What you will run into is difficulty in powder selection. Necking down either the. 416 or. 50 (same case minus length etc.) Will result in a horribly inefficient cartridge. Shoulder angles at this point are a moot point. What you are referring to as "reflection" is actually called "convection". The steeper the shoulder angle the more powder granules are caught at the neck shoulder junctio n resulting in a more efficient burn and less ejecta mass traveling behind the projectile. The ideal cartridge shape would be a sphere, but that's not what you asked. If you are set on the. 50 case and the. 50" barrel, I would go with a 45* shoulder minimal body taper, and look at ADI 2218 or around there.
 
#8
Re: Optimal shoulder angle for ELR cartridge design

saojao:

The 50BMG base is simply a matter of brass and reloading equipment availability with plenty of case capacity to work a lot of options.

The 45 degree shoulder is to promote convection, correct? Or are you also looking at adding capacity - minimal body taper - (what I was assuming I did not need - to burn all the powder beofre the projectile leaves the muzzle)?

Thanks.
 
#9
Re: Optimal shoulder angle for ELR cartridge design

It will improve the efficiency of the case.depending on the projectile used, I would probably take a .5 inch to 1 inch off the case. What are your goals velocity wise? Projectile weight?
 
#10
Re: Optimal shoulder angle for ELR cartridge design

As far as body taper im thinking about primer blast deflection etc. There is alot of taper in a .50 case if you remove length you can gain some capacity back by removing some taper. It may be nominal though.
 
#11
Re: Optimal shoulder angle for ELR cartridge design

saojao:

I've learned (hopefully) not to be too specific, else I generate a lot of micro-management pushback (seems you've experienced same). Suffice to say, the initial idea is 460 Steyr-based (hopefully I can find a source so I don't have to work down from 50 BMG) and about a 400 gr projectile.

I wonder that I'm making an assumption that I might be able to calculate. That's regarding burning the entire powder load in a given barrel length. [A shorter barrel has a number of advantages, the 50" was simply to suggest I could go that long if needed.] As I look at the powder sites I can find relative burn rate rankings but no specifics (energy/powder volume). Do you have some suggestions as to how I might calculate the amount of powder burned for a given case and barrel "capacity"? Other thoughts in this regard?

Thanks.
 
#12
Re: Optimal shoulder angle for ELR cartridge design

With the known and tested .375 projectiles on the market, what is your plan for the cartridge. Do you have a target speed or a target distance in which to maintain supersonic.

My thoughts on this may be way off but I would try to come close to mimicking the bore to case capacity ratio and shape of the 7/300 WSM only formed from the .50 BMG brass in order to keep the circumference. Doubt you'd need 50" at that point, maybe 34" to 36".
 
#13
Re: Optimal shoulder angle for ELR cartridge design

Look at your displacement ratio, that will tell you alot. As far as burn rates etc. They are relevant to the application. Burn rates will really not tell you what you are looking for. Start looking at powders that are typically used in your parent case and work from there. Maintai as close to possible a 100% fill rate. Anything
Less than 80% or so, and secondary detonation is a concern. Looking at surface area of a given propellant as well as density within a set of given parameters will yield your best results. Dave Viers has an excellent case design,and was/is doing something very similar. I believe his issue was with powder column ignition, with such a large amount of slow burning propellant. His case design with a .50 big primer pocket may remedy that.
 
#14
Re: Optimal shoulder angle for ELR cartridge design

Thinking out loud here but why not use a radius type shoulder like on a weatherby. I amjust throwing that out there, Im not any type of expert
 
#15
Re: Optimal shoulder angle for ELR cartridge design

There are 2 radius on a weatherby. The neck shoulder junction as well as the shoulder body junction. The one on the neck is useless, and actually defeats the purpose of the shoulder body junction radius. Forming brass is where the problem lies...
 
#16
Re: Optimal shoulder angle for ELR cartridge design

Your problem here is that you've picked probably the most "over bored" calibre/case combination which is unlikely to give good results at ELR because of slow dirty powder forming carbon deposits in the barrel at the start of the lands and causing a difficulty in getting low ES's needed for accuracy. You're also running the risk of very poor barrel life with rapid throat errosion. Essentially your 50 BMG case is likely to have too much powder for the bore diameter of the rifle to work with.

The shoulder angle to benefit this type of arrangement is likely to be best off being very long and shallow giving as much reduction in capacity as you can and anabling a funnelling of the charge to the base of the case neck. Otherwise the risk of case neck/shoulder seperation is high.

Why not go with a .375 CT case though ? This is a better bore to case volume option.
 
#17
Re: Optimal shoulder angle for ELR cartridge design

There is at least one manufacturer that produces hemispherical shoulder angles for rifle cartridges. I'll find the link and post it here. If memory serves he may have it patented.

Jeffvn
 
#19
Re: Optimal shoulder angle for ELR cartridge design

For what its worth I have a friend that used the 50bmg spotter case and reduced it down to the.375,it took almost 20 more grains to match the velocity of my ,375 chey-tac along with doughnuts bieng created in the neck,a hassle trying to get full burn on powder charges,forming the brass down to .375,he did stay with the 50bmg primer.Next step I belive he was going to try a duplex load for a complete burn. I will say cases look extremly sexy and efficient.
 
#22
Re: Optimal shoulder angle for ELR cartridge design

Keep in mind that case geometry is irrelevant If powder column ignition occurs directly behind the projectile. This opens the door to endless possibilities.
 
#23
Re: Optimal shoulder angle for ELR cartridge design

ELR, Have a email sent to friend asking if I can share data with you,as soon as he replies I will post the information.He is good about sharing.
 
#25
Re: Optimal shoulder angle for ELR cartridge design

ELR,the barrel length is 32",1:10,he has tried US-869,WC-872,H-50bmg,when he gets back in town he will try the new RL-50 along with the Rocky Mountain bullets in the 375,400,425 grns.Also we will be trying the spotter cases that have a flash tube ingniting from the top for a better burn.I might add that this project is a switch barrel set up on the Armalite 50bmg we are trying to meet or surpass the 375 chey-tac. he gave me the okay to share his info if your interested let me know.
 
#27
Re: Optimal shoulder angle for ELR cartridge design

Paul:

Thanks for the scoop.

I finally focused on your "spotter" case part of the spec and, since I was not familiar with it, I did some Googling.

Is the "M48 Spotter" shown here (http://www.daplane.com/50bmg/50dtc/cart_comp_00.jpg) what he is using?

If so, I'm going to "thanks but no thanks" as I am looking for a much larger case for my project. Something around a 460 Steyr - for which forming dies are already available (to go from 50BMG to 460 Steyr) - going from there to .375 - OR if I could actually find 460 Steyr factory brass - would be acceptable.

Please advise about the "spotter".

If anyone has a source for FACTORY 460 Steyr brass or brass that was built from scratch as 460 Steyr, please jump on this thread or PM me - please! FYI, I have no interest in the Winchester 50BMG-based 460 Steyr that AAA is producing.
 
#28
Re: Optimal shoulder angle for ELR cartridge design

ELR here is some info,

Apparently I can log in and read SnipersHide posts, but cannot post myself. Do see errors on page message in lower left corner.

Please post whatever you would like. Feel free to copy-paste any of our correspondence.

I kept the shoulder angle at original, that is about 16.7 degrees to make case forming easy. Form, FL, & seater Dies I had Dave at CH4D make. Long lead time but am happy. Am not happy at all with WC-872 as I find it very erratic in both the 50BMG and in the 375Libert. I find it a bit faster than H50BMG. It is the erratic that truly bothers me. Data and pressures are measured. US869 has been OK so far but testing limited. H50BMG good for lighter bullets as load density closer to 98% to keep pressures in the 58-61K range. Utilizing loading with the flashtube, will change direction of burn and reduce case capacity a little bit and maybe get back to using H50BMG with the heavier bullets, as want to stay with the more consistent canister as opposed to Bulk powders.. Want to try with standard ignition first with RL-50 and the heavy bullets. Like the big primer as plenty of hot to get these charges set off in nice as well as cold weather. Still a lot of experimenting to do. Want to utilize heavier bullets, more mass and higher BC, wanting to maximize supersonic range. Faster we push bullets means the faster we have to push the powder to do that, which means less efficiency and diminishing returns on powder use.



Be home in a little over a week, will connectivity is good.



Libert
 
  • Like
Reactions: lash
#30
Re: Optimal shoulder angle for ELR cartridge design

Paul:

Pictures are fun to deal with. JPGs seem to be the smallest. Use Microsoft Paint (in Windows OS for many years). Open in Paint and then save to jpg. You may need to make separate posts.

BTW, you didn't mention, does your cartridge case match the "M48 Spotter" shown here (http://www.daplane.com/50bmg/50dtc/cart_comp_00.jpg)?

Thanks much for taking the time to respond!
 
#31
Re: Optimal shoulder angle for ELR cartridge design

ELR, Sorry for the delay in pics, it is the 50 spotter case you saw previously. However, I must say that the 375 diameter and the 50 spotter case are comming together thru more experimentation and calcualtions, I feel that Libert and I will reach our goal before long.
untitled5.png

untitled4.png

untitled1.png

4.png


PS, I have more data if your are interested.
 
#32
Re: Optimal shoulder angle for ELR cartridge design

Is it hard to find Spotter cases? Why not use the 416 Barrett case, I would think the Spotter cases would be alot cheaper.That is mean looking!
 
#33
Most precision rifle cartridges developed in modern times (since the 2000s) are 30(60) degrees. The 6mmcreedmoor, 6.5creedmoor,6.5prc, 300prc, 7mmprc, and countless other cartridges all have a shoulder angle of 30 degrees, the 28nosler is 35 degrees, and the 416barrett is also 25 degrees. In fact, 90% of cartridges are within 25 to 35 degrees.

Perhaps half a century ago when metallurgy was inferior, the low shoulder angle was set to prevent the cartridge from being pressed out of the barrel, but today we don't have to worry about that.
 
#35
Shrimptempura said:
Most precision rifle cartridges developed in modern times (since the 2000s) are 30(60) degrees. The 6mmcreedmoor, 6.5creedmoor,6.5prc, 300prc, 7mmprc, and countless other cartridges all have a shoulder angle of 30 degrees, the 28nosler is 35 degrees, and the 416barrett is also 25 degrees. In fact, 90% of cartridges are within 25 to 35 degrees.

Perhaps half a century ago when metallurgy was inferior, the low shoulder angle was set to prevent the cartridge from being pressed out of the barrel, but today we don't have to worry about that.
Click to expand...
Perhaps.

Perhaps not.


1722470392430.png
 
#36
saojao said:
Re: Optimal shoulder angle for ELR cartridge design

Look at your displacement ratio, that will tell you alot. As far as burn rates etc. They are relevant to the application. Burn rates will really not tell you what you are looking for. Start looking at powders that are typically used in your parent case and work from there. Maintai as close to possible a 100% fill rate. Anything
Less than 80% or so, and secondary detonation is a concern. Looking at surface area of a given propellant as well as density within a set of given parameters will yield your best results. Dave Viers has an excellent case design,and was/is doing something very similar. I believe his issue was with powder column ignition, with such a large amount of slow burning propellant. His case design with a .50 big primer pocket may remedy that.
Click to expand...
The issue with the viers case was never about to great of case capacity or primer size . We currently ignite well over 285 grains of powder with no delay with a standard magnum primer. The issue that dave experanced was a combination of several issues. First problem the Lawton actions were too small of tennon and suffered from not enough primary extraction. When you combine that with a reduced taper case you end up with extraction issues
Dave would back the loads down to solve the extraction issue and that caused ignition issues. Due to low case fill. The fix was simple he just did not know how to fix it. On a case that size you need aprox. .011 of case taper per inch excluding shoulder neck and the .200 mark. (Case body leingth ) the viers case was to straight. The other issue was bertram made the brass and like typical bertram flash holes were to big. Fuse timming is controlled by cfm. Or flow
 
#37
Oscar, My suggestion for guys like you. Stay away from your non typical untried and Proven Wild cat work. It's guys like you that lose fingers and eyes doing stuff that they should not be doing, and don't know what they're doing.
 
You must log in or register to reply here.

Similar threads

R
SOLD ELR rig: BAT EXS action, jewel trigger, Mirage ULR 18" rail, in a Manners ELR stock.
Replies
3
Views
337
Mj1995
Mj1995
FimRire RongLifle
Firearms ELR Heavy 375CT gain twist WTC built Rifle Setup w bullets/brass/dies
Replies
1
Views
194
FimRire RongLifle
FimRire RongLifle
J
.223 Rem Manson Fullbore T.15 reamer
Replies
21
Views
771
just browsing
just browsing
A
Bullets with shortest jump to lands, AR 308 gas guns
Replies
10
Views
387
nn8734
nn8734
Texian Liberty
375 Raptor vs 308 Winchester
Replies
52
Views
8K
SAUMuvabitch
SAUMuvabitch
Top Bottom
Back
Home
Forums
Merch
Alerts