30-30AI data with Leverevolution powder

[Unclenick]

So you are saying you get stretching at the web and you have the primer backing out? That's interesting. Are you sure it isn't just the shoulder blowing forward rather than the web stretching back?

What is the copper bullet you are using and what COL are you loading to? Also, what is the water overflow capacity of one of your fired (but not yet resized) cases? (To find case water "overflow" capacity, you leave the spent primer in the fired case and weigh it and measure the case length and then fill with water level with the mouth and with no meniscus and weigh it again. The difference in the two weights is the case water overflow capacity in grains).

In QuickLOAD with a Barnes Flat nose seated out to 2.782", I couldn't get past about 2200 fps without raising pressure (adjusting case capacity) to 62,000 psi. GRT's powder model is a bit different and it let me reach 2380 at about 54,000 psi.

 

[BeeKay]

Unclenick
Yes - this is baffling
I had Mike Bellm chamber this barrel for me and he likes to remove some material from the back of the barrel to make it simple to check the consistency of the headspacing by using a feeler gauge between the back of the case and the breech and what I'm getting with the cases headspaced off the shoulder is .002" gap.
I fired about 20 loads and they were sized at 2.015" to 2.016" when i loaded them.
Now I'm measuring them and they're in the area of 2.024" and the primer is proud after firing, when it was inset before firing.
So somehow these cases are stretching - But where and how?
This almost sounds like it has to be a hoax - LOL
But I'm seeing it with my own eyes - All of the cases, from the starting loads - Which is 39 gr (.5 gr above the max load for a .30/30 case before fireforming) up to 41 gr which is about 95% to 98% filled.

Either the cases are stretching at the neck, or the frame is deforming that far with each shot.

It's really difficult to try to look for excess pressure indications when this is taking place.

It's difficult to measure stretching of the neck because I don't have a tool that rests on the shoulder to provide a square surface to measure from.

If they're stretching at the neck... which Is possible, apparently, then maybe that isn't such a bad thing.
Maybe I should make some more cases that have a longer neck that rests against the front edge.
But my concern is that I might be somehow stretching my frame.

I haven't fired any of my Barnes bullets yet.
I've been firing some Sierra and Nosler bullets of 125 and 150 gr
OAL of 2.863" leaves them about .002" behind the rifling.
They're seated pretty far out and the base of the bullet doesn't extend below the shoulder, adding a bit to the capacity.

I'm thinking I may add a .002" shim begind the breech to close the gap between the breech face and the case to 0" such as what is done with Herret cases, back when I had one of those.

 

[Unclenick]

Yes, that's within normal neck stretch, though stretching mostly occurs during resizing. The shoulder location changing would explain it though. If the shoulder is shortening during firing, that would both elongate the neck and make more room for primer protrusion if the stretch is not in the usual pressure ring location. There's a discussion in another thread currently about whether firing pins and primer force can shorten a case before the powder gets burning, and you may have proof of that happening in your case.

If you don't have the commercial case comparator tool, you can improvise. Just take a case to the hardware with you and find a spacer whose hold lands in the middle of the neck slope somewhere and that is longer than the neck. That means the hole should be about 3/8". Just be aware that because a spacer is labeled 3/8" doesn't mean it actually is. The one in the photo below was more like 0.41" inside. If you have a hardware store that sells replacement bonze bearing bushings, one of those in 3/8" will be pretty accurate.

If our theory in the first paragraph is right, the head-to-shoulder dimension will actually be shorter after firing.

 

[BeeKay]

On a couple of cases I was seeing a crack just below the shoulder.
I'm going to do a chamber cast and see how far the neck goes up before it steps down to the throat and if I can, I'll size the cases to that length, so they headspace from the shoulder, but won't allow neck to stretch.

I remember sizing my .357 Herret cases so there was a slight interference fit when the action was closed.
If I do it that way, then it ought to eliminate the primer backing out.

Thanks for your thoughts on this.
It helps out to write stuff down sometimes, to get off the hamster wheel of thought processing, when trying to problem-solve.

 

[BeeKay]

Shown is a (grainy, but I think it will suffice) pic of a chamber cast next to a case and another pic of a case with the bullet seated to the point where it touches the lands.

There is no step in the chamber where the case mouth fits in before the throat.
I thought there should be a step there but there isn't.
It's .335" dia between the shoulder and a short tapered area then about .030" of cylindrical throat before the rifling lands.

When I had this done I wasn't familiar enough with the AI chambering to ask for anything specific. So I left it up to the gunsmith.

But the target shows a 15 shot string @ 30 yd.
I pulled one shot because I was having a hard time believing they were all going through one hole.
At 100 ys it widened out and I was shooting 5 different loads so 100 yd consistency wasn't impressive.

it seems like it's accurate, but the necks stretching like they do bugs me.
I probably won't get more that 3 firings per case if they're stretching .010" each time I shoot and I hoped for better.
But maybe I should just learn to live with it

 

[BeeKay]

I spent some time pondering what might be the sequence of events taking place that would cause case stretch to happen at the neck, and i got an idea.

On Friday i put together some loads for the Contender, to try out over the weekend.
I measured brass and chose pieces that were sized 2.015" to 2.016"
When i seated the bullet, instead of seating it away from the rifling, I put a bullet in partially seated but long enough to touch the rifling, when chambered.

Before final seating die adjustment or crimping, I chambered the round and closed the action to press the bullet against the rifling when the action is closed.
I then measured the length and adjusted the seating/crimping die to that length, minus .001" just to be sure the shoulder was contacting the chamber before the bullet.

Problem solved - no case stretch
Fired all of the tests samples and case stretch was un-measurable or minimized to the extent that it could be attributable to measurement error. ... Like .0015" +or-

Time to proceed to the next step.

I'll still seat my loads using Barnes bullets away from the lands, as recommended.
But those are for hunting only, not range practice, so I'll write off a case to stretch when I use those.