.200" line on a reamer print

[Alex Wheeler]

This number has caused a lot of confusion. When you are designing a reamer and a die you are concerned with the brass just above the solid web. This is where it expands to fit the chamber and where clickers usually come from if the design is not right. This is not always at the .200 line. The .200 line is just a spot on the print. They could have made it a .250 or .300 line. It doenst mean anything. In some cases the .200 line is still solid brass and doesnt expand so if your measuring it you will get into trouble. In other cases if you measure the widest part of the case and you want to compare it to the chamber you need to do the math to know what the chamber measures in that spot. Just some thing to consider for those playing with this stuff.

 

[338 Mollett]

The wild cats I fooled around with , I just cut the bottom off the existing die until I got what I wanted. This made the base a tiny bit smaller but most of the time I don't like the diameter of the die at the base anyway.

 

[Brians356]

Good post. I'd pondered it. Simple geometry to extrapolate the actual expansion at the observed ring, given the slope of the unfired case body.
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[whatwind?]

Can you show this on a case, like the PRC for example, that you fixed and shared with all?

 

[riflewoman]

The purpose of the .200 line on the chamber drawing is to define the taper of the body of the case. The .200 has a diameter specified. At some distance ahead of this dimension (varies per cartridge) there is another transverse line and diameter specified. These are “Basic” dimensions and are therefore not subject to tolerancing.

The purpose of these is to define the taper to be ground on The reamer and to define the forming die for the case. Otherwise you would have to define the taper either by “theoretical intersections of two lines” (shoulder and body). These dimensions are now “Reference” dimensions due to the radius on the shoulder to body area.

 

[SweaterDood]

The purpose of the .200 line on the chamber drawing is to define the taper of the body of the case. The .200 has a diameter specified. At some distance ahead of this dimension (varies per cartridge) there is another transverse line and diameter specified. These are “Basic” dimensions and are therefore not subject to tolerancing.

The purpose of these is to define the taper to be ground on The reamer and to define the forming die for the case. Otherwise you would have to define the taper either by “theoretical intersections of two lines” (shoulder and body). These dimensions are now “Reference” dimensions due to the radius on the shoulder to body area.

Unfortunately this doesn’t translate well to improved cases and changing the body taper on wildcats. This is something I wish I would have known more about when I drew up my first wildcat 3 years ago. It was a good learning experience and I know much more now that if everything would have worked out perfectly. Moving forward, and into the next iteration of the venture, I will definitely use a cross section of the chosen parent case to define the exact geometry desired. Note: Custom dies are also cheaper than buying tons of brass that commercial dies won’t resize correctly.

I’m sure many members here know all of this, but I wish I’d have had more resources and information than I did. I read a lot on here and other forums, spoke with the best people that I could find, etc. These threads are my favorite to come across on the forum, because I generally find something to learn from or analyze further.

In the end you can’t know what you don’t know, and you can’t have all the answers without first the questions to ask.

 

[riflewoman]

Unfortunately this doesn’t translate well to improved cases and changing the body taper on wildcats. This is something I wish I would have known more about when I drew up my first wildcat 3 years ago. It was a good learning experience and I know much more now that if everything would have worked out perfectly. Moving forward, and into the next iteration of the venture, I will definitely use a cross section of the chosen parent case to define the exact geometry desired. Note: Custom dies are also cheaper than buying tons of brass that commercial dies won’t resize correctly.

I’m sure many members here know all of this, but I wish I’d have had more resources and information than I did. I read a lot on here and other forums, spoke with the best people that I could find, etc. These threads are my favorite to come across on the forum, because I generally find something to learn from or analyze further.

In the end you can’t know what you don’t know, and you can’t have all the answers without first the questions to ask.

There IS a limit on how much you can “improve” a cartridge. You will still need some body taper and shoulders steeper than 40degrees are problematic. Not to say that Ackley was omniscient, but his alterations are about optimal. Most likely an educated guess….

 

[DaveTooley]

In the early to late 90's I did a lot of wildcatting. There was a learning curve to alleviating the clicker problem. I/we settled on .010" taper per inch. We could have gone to .008" TPI but we wanted a solution not another learning exercise. .010" worked well with properly matched FL dies with enough chamber/brass clearance.

 

[Alex Wheeler]

Can you show this on a case, like the PRC for example, that you fixed and shared with all?

The PRC case has a unique problem. Not that its a problem with the original design and the brass used at that time. But now we have ADG and Lapua making tough brass for it. Tough brass has to be squeezed more to make it work without clickers. When working with the ADG brass, I found you needed a minimum of .0045" of sizing at the base. A virgin case is .530 or so, the original chamber is .533 at the .2 line. You really dont want to make a die smaller than the solid web of a case or you run the risk of cracking the die. You can a little bit but with the lager magnums the dies start getting thin so I avoid doing that. So you can see we can only get .003 of squeeze on the case. You could make the brass smaller which would allow you to go smaller on the die, but the easier way is to increase the chamber to allow you to get about .005 of squeeze on that case. Now the point of this post is that in the case of the PRC with ADG brass for example the .2" line doesnt even expand. The brass expands to fit the chamber about .275" from the bolt face. So if you just measure a case and compare it to the .2 line on the print you will not be comparing the same spots in the chamber. Probably the worst offender is anything based off the 338 Lapua or 300 Norma cases. Guys have more clicker problems with that one than any. One reason is they tighten up the chamber creating the same problem the PRC case has. The other is they expand more like .350 from the bolt face, so you may think your getting a lot more sizing than you are because the chamber is smaller there. The 338 Lapua and 300 Norma is so tough you have to squeeze it really hard and you can not tighten up that chamber. I was told once by a die maker my chambers were undersized. This is because he measured the case at the fattest part .350 or so from the bolt face and compared it to the .128 line (cip).

 

[Alex Wheeler]

In the early to late 90's I did a lot of wildcatting. There was a learning curve to alleviating the clicker problem. I/we settled on .010" taper per inch. We could have gone to .008" TPI but we wanted a solution not another learning exercise. .010" worked well with properly matched FL dies with enough chamber/brass clearance.

My most aggressive case is .009" and its working well, but I wont push it past that. Mostly I stick to .010" as well.

 

[SweaterDood]

There IS a limit on how much you can “improve” a cartridge. You will still need some body taper and shoulders steeper than 40degrees are problematic. Not to say that Ackley was omniscient, but his alterations are about optimal. Most likely an educated guess….

Ackley put in a large amount of iterative testing before he arrived at .008”/1” and 40* from everything I have read.

My experience seems to match perfectly with Alex’s posts, as the area where the brass thins enough to be sized correctly can firmly dictate a few factors. My assumption was to use the .200” as the first reference for taper and then figure the shoulder diameter by extrapolating at .008”/1”. Turns out the particular brass I had purchased was still solid at that point and a small bulge exists a bit further forward.

I believe this contributes to my primer pockets opening up early and yielding poor brass life. But decapping force seems to give a reliable indication of when to toss cases. I have recently started gauging them as well as an empirical verification. I have enough brass to last out the barrel and the learning experience is half (or more) of the fun for me.