The 28-20?

[Elric]

Folks, I love my 285448 so much, but I find the 7-30 case size is a bit overkill. 8gr of you-neek barely fills 1/3d of the case. In spite of which the 7-30 and 285448 is an accurate combo.

Think of the 270 REN, a blown-out 22 Hornet. Straight walled case.

Hows about taking a 25-20 case and necking it up to take a .285 diameter cast bullet. The neck walls will be @.010 on a side, so the total width of a 28-20 case neck will be .305 minus a skosh.

The 25-20 case is @ .349 at the head. So the case will taper @ .030 over .900 inch. A nice small cast bullet case for small game, target, and plinking. Frugal source of brass. Just love me the 7mm action.

Looks like the 25-20 chamber has a .005 allowance for the neck, so maybe we would have a .310 diameter neck. Chamber appears to have a .001 clearance (.350) at the head...

http://www.saami.org/pubresources/cc_drawings/Rifle/25-20 Winchester.pdf

 

[RBHarter]

If your going tiny and necking up why not a 256 Win Mag ? 7x357 . The brass is cheap and available .....some places have it laying everywhere . The case will be both stronger and more durable.

Just throwing it out there . I like the 7mm myself . I built ,or rather hired out , a 7x6.8 Rem . Sweet little rifle . 2300 fps with a paper patched 140 gr , 2100 with a naked 130 , and 2500 with a 120 Sierra SP .
Talk about wasted space , I had to take a 285-150 hunter down to 3.7 gr of Unique to get it subsonic . The 7mm-168 SIL takes the same load .

Wicked fun little scout rifle to shoot .

 

[Elric]

The parent 357 case needs to be necked down. I looked for an available case where the head is just a wee bit over the OD of the loaded neck. The 25-20 and related 32-20 have a case head of .349

Once you go straight (walled), you never want to go back.

 

[RBHarter]

.0394 isn't much of a shoulder. Based on 9mm down to 7mm . You might even be able to buy actual 256 brass .

Look at me all acting like I have a clue . I too have fallen in to the fat and slow shooting class too . All I want to do is take a perfectly good rimless straight wall hot rod based on rimmed super mag pistol cartridge ,it even runs the data , and turn it down to pistol performance in a rifle ...,....

I don't remember the shoulder diameter of a 222 or 223 but there is a 7mm cat on that also and that wouldn't have much shoulder either .
Went and looked . 378 rim ,376 head , .357 shoulder for the 222 . Lots of production rifles to put it in . .

As far as straight wall goes , a 327 mag would make just about a 1/3 scale 45-70 in 7mm .
For rimless how about a 5.7 ?

 

[Elric]

http://saami.org/PubResources/CC_Drawings/Pistol/327 Federal Magnum.pdf

Hmm, .336 head. BUT, look at the drawing, -.006, so as far as the case goes, .330 minimum.

Though a straight wall case would be nice, some taper will most likely be present.

Let me czech on the 32-40...
http://www.saami.org/pubresources/cc_drawings/Rifle/32-40 Winchester.pdf

Hmm, .424 head, .3455 at end of taper, .0785 total taper over... oh god, math with no alcohol... 1.645 length, (1.7080- .063 rim thickness). Makes it .04742 taper per inch.

327 Mag, 1.145 total case length (minus .055 rim). 54.3 thousandths. Oops, let's not forget the straight segment on the 32-40... Straight segment is .422, which is about 1.31x bullet diameter. So if following this proportion, that is .285 x 1.31, or about .373 length.

More mathification... Tapered case length of .772, at 47.42 thousandths per inch... .0366 thousandths taper... Nope, needs less taper than the 32-40 (yay!).

Let's look at the 28 neck, I'm using a size-to of .285, slap on .010 a side for neck thickness, that would be @ .305, so at the base of the neck is .305... math! Looks to be .031 over .772 inches. .040 taper an inch. Not bad.

Using the lower side of the SAAMI spec of a .330 case head, the taper over length drops to .025 per inch, or .032 of taper.

Doing some quick mathification, the 45-70 has about .012 taper per inch.
http://www.saami.org/PubResources/CC_Drawings/Rifle/45-70 Government.pdf

25-20 case length, minus rim, is 1.265, minus .373 for the neck, leaves .892, with a .349 head minus .305.... .044 or so. Mybe .049 taper per inch.

Maybe the 25-21 case for a basis?

 

[Elric]

Boy-o-boy. Yes, the 25-21 has a case head of .300 (nominal) so it _could_ be considered. BUT... for all the poodle faking, these 25-21 cases are not widely available. A shorter 28-30 case? $$$$, but at least folks are used to it. 28-30 has a case head of .305, which is right on for a .285 bullet width.

 

[Elric]

As far as straight wall goes , a 327 mag would make just about a 1/3 scale 45-70 in 7mm .

Or... a 45-70 scaled down (.285/.458 = .622), so scaled down 45-70 case of 2.105 x .622 = 1.31 length, compared to the full 28-30 2.51"

28-30 head is .357, neck is .309, rim thickness is .060, so 2.51 - .060 = 2.45

.357 - .309 is .048, so... .048 / 2.45, .0196 taper per inch. .0196 x 1.31 = .0257 taper.

Argh. More mathification. So a 28-30 cut down to 1.31 long.. oops, is this supposed to be half the taper per side? Yup, the 357 minus 309 is 48 thou reduction across BOTH sides. Each side would taper 24 thou