I have a question for those of you who not only design cartridges but also use these cartridges in rifles you’ve built for them.

My question, when you design your cartridge(s) do you also design the relating chamber reamer specifications? And if so do you design the chamber such that a maximum cartridge dimension will chamber into a minimum chamber dimension? And if not have you compared your maximum cartridge dimension to the minimum chamber reamer specification to assure a lack of collision points?

I’m a new user of Hartmut Broemel’s QuickLOAD and QuickDESIGN software. I’ve notice that virtually all CIP and SAAMI approved cartridges contained within these two program’s cartridge drawing window indicates the entire shoulder-angle from the shoulder to the shoulder-neck intersection is a collision area with an Error message indicating the cartridge will not chamber with less than _____ mm/inch headspace. There are no other collision points between cartridge and chamber dimensions. The exception this statement is the .404 Rimless N.E. which indicates no collision points.

Here is a link to a similar question posted on another forum with a reply from Mr. Broemel:
http://www.24hourcampfire.com/...1/page/1#Post3067131

Thanks for your consideration, time and comments.

Jim

I have built several long-range Benchrest rifles chambered for my own cartridges. Maybe I do it different than others but, there's no such thing as max cartridge and min chamber (or the other way around). After I've decided on the bullet I want to use and the velocity I'm after, I determine the case capacity necessary. I then design a cartridge around that capacity goal and finally select a parent case to make the brass. I then buy a barrels-worth of the brass I will be using. By barrels-worth, I mean enough brass to last the accuracy life of the barrel. I then carefully measure the critical points of the brass and use those dimensions to design a reamer. My reamers are all ground with a minimum allowance for expansion and minimum neck and free-bore clearances. Once fire-formed, my cases require only minimum neck sizing and an occasional shoulder bump.

I also make my own dies unless there are factory dies already available that meet my criteria.

Others may do it differently but it has worked for me over the years.

Ray

Don't know if this the the correct way. When I designed my 280PDK I had elected to use only 280Rem brass made by Norma. I took the head and outside neck measurements of the Norma brass. Then my shoulder location, dia and angle. Then sent this drawing to the reamer manufacturer and ask that the reamer be cut to yield minimum clearances.

I design the cases.. Dave Manson takes the case drawing, makes a reamer drawing, and is very patient explaining WHY to me.

quote:

I design the cases.. Dave Manson takes the case drawing, makes a reamer drawing, and is very patient explaining WHY to me.

+1! I design, but I send to Brian and JD at SSK, they send to Dave and work out any bugs I may have introduced, Dave makes the reamers and sends to SSK. There are many things in life that I am ignorant of, and many of those I choose to be so! I don't want to hear about all the labor pains, just show me the baby!

Michael

Thanks Ray, Paul, Jeffe, and Michael.

Ray and Paul…you both state that you request reamers to be manufactured giving minimal clearances to your cartridge designs. I presume this to mean that the reamer is cut such that a cartridge of your design specification will chamber and bolt close without forcing the closure? Perhaps a reamer designated for benchrest shooting vis-à-vis hunting would be slightly tighter in clearance?

Jeffe and Michael…do either of you discuss or provide clearance specifications for the production of your reamers? And if so are the specifications designated for hunting vis-à-vis benchrest shooting?

Thanks again to you all for your comments and clarification to my second set of questions.

Regards,

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Ray and Paul…you both state that you request reamers to be manufactured giving minimal clearances to your cartridge designs. I presume this to mean that the reamer is cut such that a cartridge of your design specification will chamber and bolt close without forcing the closure

Holy crap Batman that was 25+ years ago. I know I have paper work from Clymer but sure can't find it. I know we talked and it isn't as tight in the neck as a benchrest. If my swiss cheese memeory is working it is more on the line of my case drawing being like a maximum Saami and the reamer set to cut a minimum. McGowen cut the first chamber for me to be on the order of .002" clearence from the shoulder cut to my dimensions. Since I had dies made to my cases the exact headspace for the first chamber was not the most critical. My worry area was the neck and the base. I didn't want a reamer to cut .473 with slop and have brass with .467 heads since I was going with a minimum taper.

First dies were RCBS later calibers were Hornady. If I hit the shell holder I have no feel of the brass on closing the bolt. However if I take a new case and form a false shoulder to fireform a piece of paper gives me a crush fit. I think the paper is around .0025-.003.

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Originally posted by ramrod340:
Holy crap Batman that was 25+ years ago.

Good one Paul…Looks like the memory cells are perking just fine.

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Jeffe and Michael…do either of you discuss or provide clearance specifications for the production of your reamers? And if so are the specifications designated for hunting vis-à-vis benchrest shooting?

Capoward

No I do not specify however mine would be for hunting, and function, and not too tight, but fortunately I have not had that issue at all. Dave is pretty sharp on this stuff and I am sure Brian told him what I am most interested in. For my rifles the last thing I want is anything that might be an issue in the field.
Sorry, I know I am not much help to you in your endeavor.
Michael

quote:

. . . Ray and Paul…you both state that you request reamers to be manufactured giving minimal clearances to your cartridge designs. I presume this to mean that the reamer is cut such that a cartridge of your design specification will chamber and bolt close without forcing the closure? Perhaps a reamer designated for benchrest shooting vis-à-vis hunting would be slightly tighter in clearance?. . .

I have my reamers ground by Dave Kiff. He knows reamers, and chambers, and rifles, and bullets, better than most shooters do. I let him know the intended purpose of the rifle and he seldom questions any of my dimensions.

For my Benchrest rifles I do use very close fitting chambers. By close fitting I mean very little expansion of the case. For hunting or plain old shooting I loosen up a little but not very much.

Ray

and I tell Dave Manson -
DGR round or bench gun ...
my 257 WSM was a "bench" deal .. bascially tight

all the ARs and others have been big bores, and therefore NOT tight

but Dave tells me what it should be

quote:

Originally posted by jeffeosso:
I design the cases.. Dave Manson takes the case drawing, makes a reamer drawing, and is very patient explaining WHY to me.

+1
Dave has always been helpful and knowledgeable

Ok. From everyone’s comments care is taken via their reamer manufacturer to assure proper clearance between the cartridge and chamber.

Anyway the reason for my original post is the lack of clearance between the SAAMI cartridge design (CIP maximum cartridge dimensions) and the SAAMI chamber design/reamer specification (CIP minimum chamber dimensions) for the .375 Ruger:
Bolt face/Base to shoulder: cartridge – 2.1797” and reamer – 2.1749”
Bolt face/Base to shoulder/neck junction: cartridge – 2.2750” and reamer – 2.2693”

As can be seen, the bolt wouldn't close on a cartridge of design dimension and a chamber using a specification reamer - in this case both SAAMI specifications.

I can't post pictures else I'd post a copy of the .375 Ruger cartridge design as well as a reamer schematic from McGowen Precision Barrel, very similar to PTGs’ schematic (spec’s provided by Hornady/Ruger) and the QuickDESIGN’ chamber minimum dimensions for the .375 Ruger. That's where I drew the above data from.