Im trying to figure out what chamber is in my new to me win71 450 alaskan , the gun was rebarreled by ssk industries as it is scribed on the barrel “ssk 450 alaskan” i purchased some ammo from reeds ammunition’s that were straight taper no shoulder and fired them and what came out looks like a 450/348 alaskan Ackley Improved,any help would be greatly appreciated, i have a set of rcbs dies that came with the gun but when i form 50 alaskan brass in them they will not go in , the shoulder is to far forward on the formed brass to fully close the chamber.

Reed's had 450 Alaskan ammo with no shoulder?

The Johnson case is the one in the GMDR drawing for 450 Alaskan (2.145" case) ... just google it. The 450 Fuller has the longer neck. But there are others ... 450/348 Ackley you mentioned. Though you'd think the barrel would have been marked as 450/348 Ackley if that's what they reamed the chamber with.

I've always bought the QualCart 450 Alaskan brass or fireformed from 348 WCF. I've never tried to size down something like 50AK.

OK, I went to Reed's site and what they call 450AK has almost no visible shoulder. I can't tell you what that is, but it's not what I know as 450 Alaskan. Their 450AK "Improved" looks to me more like actual 450 Alaskan with the small but easily discernable shoulder.

What it the length of the case on the Reeds stuff before you fire it? Is it 2.145"? If it's 2.260"-ish, then it's Fuller. They don't seem to have a case drawing on their site for their "improved" stuff.

Did your dies come in the RCBS box marked 450 Alaskan? That's what my box says.

In the image, the 450 Alaskan is at the far right loaded with the 350 grain Speer HotCore. Just to the left is a factory 348 WCF.

Your issue is the barrel chamber.
I have 2 450s on pre-war Model 71 Winchesters. The original .450 Alaskan and 450 Fuller, as outlined in PO Ackley's VOL 1 book shows
pronounced angled shoulders 16-25 degrees. The Ackley version can have a shoulder angle of 30-45 degrees. Even Ackley stated that the
the Fuller/Alaskans fed better without internal action modification.

If you did NOT get the work done, i.e.-it was bought used by yourself- you will probably not get much help from SSK-- on your 450 Alaskan. You
have to remember that these 450 wildcat cartridges are not SAAMI certified. Start by determining your chamber dimensions.
A straight case may help by fire forming. That and/or a chamber cast. My estimation is that you might have one of the "accepted" 450 Alaskan chambers which means a decided shoulder angle.

I use 348 brass with a set of RCBS 450 Alaskan re-form dies. I do Not use 50 Alaskan brass as you have not enough body taper to assist the reform process
in getting the empty brass closer to chamber dimensions. The Winchester/Browning Model 71s are the most satisfactory.

Use some medium or light loads in your Reed brass. THEN, try reloading the fire-formed brass using your RCBS dies. IF they work-you have your answer. Stick withe fire-formed brass. Look up "450 Alaskan by John Kronfeld in Handloader magazine or get HM/Rifle Magazine Big Bore book. You have some work and study ahead of you.

From the post in the other section, I think the OP has identified it as the PTG 450/348 AI instead of the PTG 450 Alaskan. I wish PTG had the drawings on their site.

Thanks guys , if i measure from the bottom of the rim to the shoulder where it meets the neck my fireformed cases measure 1.760 , across the neck 0.535 , case is almost straight about 10 thou taper, when i form50 alaskan in my rcbs “450alaskan “ die the same bottom to top of shoulder is like 1.820 ish so they will not chamber due to neck being out to far , indeed a deep dark rabbit hole , looking like custom dies , ouch ! Rcbs are on ebay right now, the shoulder is pretty sharp angle , and yes spoke to ssk , no help whatsoever, bought out in19 and burned every record prior

Thanks guys , if i measure from the bottom of the rim to the shoulder where it meets the neck my fireformed cases measure 1.760 , across the neck 0.535 , case is almost straight about 10 thou taper, when i form50 alaskan in my rcbs “450alaskan “ die the same bottom to top of shoulder is like 1.820 ish so they will not chamber due to neck being out to far , indeed a deep dark rabbit hole , looking like custom dies , ouch ! Rcbs are on ebay right now, the shoulder is pretty sharp angle , and yes spoke to ssk , no help whatsoever, bought out in19 and burned every record prior , my chamber is definitely 2.255 ish, the formed 50 alaskan bras s is 2.145 ,

I have several ptg reamer drawings i can share , cant post them on here though , maybe email

It probably would help to stick to non-50 AK brass, as you may be making more work for yourself.
The Johnson/Fuller wildcats have more taper and are easier to work with. It might be possible to alter your
FL re size die, but the real problem is the minimum taper on the Ackley case. In short, it is maxxed out compared to the Johnson/Fuller 450s. Minimum taper.

Also-look closely at your M-71 rifle. If there have been stronger magazine tube screw and internal action mods to the carrier and other tolerances,
that is definite evidence it is the Ackley Improved 450/348version.
Be very careful about buying any "new" dies without a chamber cast. RCBS usually requires 3 fired cases for custom dies. If the shoulder is sharp
and very little or .00010 taper-it is an Ackley 450/348: not good news for reloading, as it must have a 100% correct F/L sizing die. As an example, I can use my Johnson dies to load my 450 Fuller-AND-the 450 Fuller cartridges shoot well in the 450 AK Johnson chamber, but NOT vice versa. The AK shoulder angle is sharper. That's how close they are... I would be willing to bet either one of my 450s would chamber in your rifle, but once fired-would be Ackleys...
Try RCBS and Huntington Die Specialties near Oroville, CA. Ask them for an Ackley 458/348 set of dimensions. Wish I had better news, but RCBS & Huntington have scaled back on their custom die production. And they
are $$$$. A 50 AK seating die or 450 AK seating die...but for F/L resizing, a custom die will be necessary.

PM me if you get frustrated to the point of giving up.

NRA-LIFE

thanks again for the help ,talked to ben over at hornady custom die shop ,great guy ,very knowledgeable,sending the fire formed cases and he said he can fix me right up,200-230 ish ,not cheap but not outrages , now to find 50-110 brass so i can get to 2.255 oal .

Bear in mind in case you’re using Starline brass for case forming, their brass is not annealed. They state this on their website. If you’re case forming using their brass annealing will make it easier and result in a better outcome.

Yup , i anneal everything , the short steep shoulder on the ackley version of this is going to be the weak point , not going to shoot it alot , just want everything to be right when i hand it down to the grand son one day,

Thanks again fuller , all good info, rcbs is done with custom dies , alot of custom guys will build them but they are in the 600-900 dollar range , ouch! . Hornady ,lee, Redding are more reasonable , 200-300 range