How much can you push a shoulder forward?

It should still add powder capacity since I'll be using a short bullet that won't protrude into the case.
That has nothing to do with the shoulder.
And a shorter bullet can protrude into the case as much or more, depending on your freebore.
Do you have a plan to setup a false shoulder for fire forming?
Are you filling out the reamer print?
 
I see what you are saying.
It should still add powder capacity since I'll be using a short bullet that won't protrude into the case.

Kris
While you have not communicated it as clearly as others would like, I understand. Moving the shoulder forward (shortening the neck dimension) and increasing the shoulder angle does increase the H20 capacity (not to be confused with the "actual" powder capacity). Below is the H20 gain chart per the first picture in #3.

1697407929836.png


I also have a .30 Gibbs that shows a similar result.

.30-06 IMPROVED INSIDE VOLUME.JPG
.30 GIBBS fire-forming progress1.jpg

L-R:
1- .35 Whelen virgin brass
2- After establishing a false shoulder
3 - After running .30 Gibbs sizing die
4 - After COW method
5 - .30-06 brass

.30 Gibbs 75.80 H20 after fireforming off the chamber..jpg

The .30-06 H20 capacity is ~68g, depending on the source document (https://en.wikipedia.org/wiki/.30-06_Springfield) and brass manufacturer/brand.
 
I want to run a little Hammer bullet but keep the OAL the same so bring the brass up and use that powder capacity. I've got a 26" new factory take off barrel I will try it with.
I'm following you just fine. You're using a light-weight Hammer so you're using a much shorter bullet than is typical for the RUM case, and you want to bring the shoulders forward until the bullet base it at the bottom of the neck relative to your current COL. Since the base of the bullet almost certainly doesn't extend past the neck/shoulder junction in a standard RUM with a .306" long neck, you want to turn ~0.089" of empty neck space into full-diameter space. Same exact concept as the Dasher vs the parent BR case.

I don't know exactly which one you want to use, but one of their bullets (the 101 Hammer Blackout) is 0.852" long and the total length of the bearing surface and base is 0.245". That's just about the shortest bullet I know of that could be shot from a 300 RUM and hold together, unless you did something like a 16 twist.

My assumption that you're looking at the super-light Hammers is what drove my comment about the Gibbs being the shortest neck I'm aware of that actually holds up under decent recoil, at .217". If you made the neck Gibbs-length then their shortest bullets (Hammer 100 Shock Hammer, 101 Blackout Hammer, and 103 Power Hammer) will all seat their base to the neck/shoulder junction, but not protrude too much out the front to not fit in a standard 300 RUM throat. If anything I'd still be nervous about the throat being too long, but Hammers have shown themselves to be jump tolerant if you don't want to mess with that geometry.

So 0.217" neck, blow it out to 40* and take a little taper out of it, and we can call it the 300 ROCKY after Mr Gibbs 🤣 👍 You've made me want one now. I'm going to go waste a lot of time in QuickDesign now.

Viola: Projected 113gn of H20 Capacity.
300 ROCKY.jpg
 
Last edited:
I'm following you just fine. You're using a light-weight Hammer so you're using a much shorter bullet than is typical for the RUM case, and you want to bring the shoulders forward until the bullet base it at the bottom of the neck relative to your current COL. Since the base of the bullet almost certainly doesn't extend past the neck/shoulder junction in a standard RUM with a .306" long neck, you want to turn ~0.089" of empty neck space into full-diameter space. Same exact concept as the Dasher vs the parent BR case.

I don't know exactly which one you want to use, but one of their bullets (the 101 Hammer Blackout) is 0.852" long and the total length of the bearing surface and base is 0.245". That's just about the shortest bullet I know of that could be shot from a 300 RUM and hold together, unless you did something like a 16 twist.

My assumption that you're looking at the super-light Hammers is what drove my comment about the Gibbs being the shortest neck I'm aware of that actually holds up under decent recoil, at .217". If you made the neck Gibbs-length then their shortest bullets (Hammer 100 Shock Hammer, 101 Blackout Hammer, and 103 Power Hammer) will all seat their base to the neck/shoulder junction, but not protrude too much out the front to not fit in a standard 300 RUM throat. If anything I'd still be nervous about the throat being too long, but Hammers have shown themselves to be jump tolerant if you don't want to mess with that geometry.

So 0.217" neck, blow it out to 40* and take a little taper out of it, and we can call it the 300 ROCKY after Mr Gibbs 🤣 👍 You've made me want one now. I'm going to go waste a lot of time in QuickDesign now.

Viola: Projected 113gn of H20 Capacity.
View attachment 502121
I'm pretty new to designing my own case but yes I'm looking to add as much capacity to it as possible. I think we are both on the same trail.
I'm thinking the 124 Hammer or something in the 135 range. Don't have the exact bullet in front of me at the moment.
You come up with a good reamer and I'll split the cost with you.

Kris
 
I'm following you just fine. You're using a light-weight Hammer so you're using a much shorter bullet than is typical for the RUM case, and you want to bring the shoulders forward until the bullet base it at the bottom of the neck relative to your current COL. Since the base of the bullet almost certainly doesn't extend past the neck/shoulder junction in a standard RUM with a .306" long neck, you want to turn ~0.089" of empty neck space into full-diameter space. Same exact concept as the Dasher vs the parent BR case.

I don't know exactly which one you want to use, but one of their bullets (the 101 Hammer Blackout) is 0.852" long and the total length of the bearing surface and base is 0.245". That's just about the shortest bullet I know of that could be shot from a 300 RUM and hold together, unless you did something like a 16 twist.

My assumption that you're looking at the super-light Hammers is what drove my comment about the Gibbs being the shortest neck I'm aware of that actually holds up under decent recoil, at .217". If you made the neck Gibbs-length then their shortest bullets (Hammer 100 Shock Hammer, 101 Blackout Hammer, and 103 Power Hammer) will all seat their base to the neck/shoulder junction, but not protrude too much out the front to not fit in a standard 300 RUM throat. If anything I'd still be nervous about the throat being too long, but Hammers have shown themselves to be jump tolerant if you don't want to mess with that geometry.

So 0.217" neck, blow it out to 40* and take a little taper out of it, and we can call it the 300 ROCKY after Mr Gibbs 🤣 👍 You've made me want one now. I'm going to go waste a lot of time in QuickDesign now.

Viola: Projected 113gn of H20 Capacity.
View attachment 502121
Do you have quick load? Curious what it shows for potential velocity with that case design as well as optimum powder. I'm thinking H4350

Kris
 
I'm looking to add as much capacity to it as possible.
If you had said this,, just this, you would have direct answers.
This portion of design really needs no consideration of a bullet.

You should have all components on-hand, put a dummy round together, measure it, fill out a blank reamer print for what you want, order a reamer set (or at least a finish reamer).
Choosing an already existing wildcat/cartridge as discussed would be even easier.

You could do a 6Dasher to it, as QuietTexan mentioned. Ackley improve. Or leave shoulder angle the same.
If your action is fairly precise, and designed well for the parent cartridge, you should not have feeding issues.

I would never begin something like this without pre-designing/estimating results with cartridge design software and QuickLoad -first.
That's where you could find out if your notion here is good or horrible.
 
Do you have quick load? Curious what it shows for potential velocity with that case design as well as optimum powder. I'm thinking H4350

Kris
Yes, you can cross-deck from QD to QL and get rough load data. It really takes loading and shooting to true up some of the details, but it's always given me good starting points.
 
Probably get 3400++ fps with that one. If it is custom cartridge do you get to give it a name?
300 RUM AI is boring so I'd suggest 300 RUMBLE
Well it's a Rat Rod biuld with extra parts so either 300 RatRod or 30 RUMRat. I'm hoping for 4300 fps.
I'd be happy with that. I'm thinking others have got 4300 with a 124 hammer from a standard RUM and H4350.
 
Probably get 3400++ fps with that one.
More like 4500 FPS with the bullet I did that case for:
 
When I designed my Rigby based cartridges, I used percentages to base dimensions from, first was neck length dimension basing calibre plus 10% for 30 cal through 338 and 15% for 375 and 408.
Then shoulder angle in relation to calibre, steeper 45° for 30 and 33, shallower 40° for 37 and 40.
Case taper was .005" per inch, all other dimensions came about from the neck length and shoulder datum.
Hope this helps.
To make a false shoulder, you neck up in steps until a case chambers hard when closing the bolt. If 33, neck up to 35, and so on…

Cheers.
 
When I designed my Rigby based cartridges, I used percentages to base dimensions from, first was neck length dimension basing calibre plus 10% for 30 cal through 338 and 15% for 375 and 408.
Then shoulder angle in relation to calibre, steeper 45° for 30 and 33, shallower 40° for 37 and 40.
Case taper was .005" per inch, all other dimensions came about from the neck length and shoulder datum.
Hope this helps.
To make a false shoulder, you neck up in steps until a case chambers hard when closing the bolt. If 33, neck up to 35, and so on…

Cheers.
I spent a few minutes looking at pics and that is how I figured I'd do it. Thanks for the info. That is a big help.

Kris
 
What do you guys think is the best way to make that false shoulder for fire forming? That's a new one to me.

Kris
Neck up with a mandrel, neck down with a neck die.


 

Recent Posts

Top