Lathe? Drilling and tapping a cartridge case.

ENTERKO

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This might be a long shot, but can’t hurt to ask. I’m attempting to modify one of my fired cases by drilling out the primer pocket and tapping with 3/16 x 36 threads. The goal is to use this case to measure against while sizing my brass. This way I would be able to consistently measure when setting up my sizing die so that I bumping the shoulders down by .002”. As far as I can tell using a fired case is the only way to do this, so purchasing a Hornady modified case isn’t very helpful in this case.

I can’t find a way to fixture the brass so that I can drill the necessary hole (bit size L) without deforming the case. If anyone has suggestions, I am eager to try. My thought is chucking up in a lathe, equal pressure could be applied to the case outer surface such that minimal deformation occurs.

Anyone have similar experience? If so, what did you do? I also wouldn’t mind paying a member who is close that has access to a lathe. I have the drill but and tap already.
 
I use a headspace gauge to set up my size die. Insert the gauge in the shell holder, lower the ram and screw the size die down to touch the shoulder of the gauge. That will be your constant, from there use the die threads TIP to adjust the amount of crush or clearance.
 
Chuck the case up in a drill and hold the bit with a vice. It doesnt sound like you gotta be all that precise
 
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I use a headspace gauge to set up my size die. Insert the gauge in the shell holder, lower the ram and screw the size die down to touch the shoulder of the gauge. That will be your constant, from there use the die threads TIP to adjust the amount of crush or clearance.

I appreciate the reply. What I’m going for here is to know my chamber”s dimensions rather than the SAAMI minimum sizing that the headspace gauge indicates.
 
Put a bullet in the case and hold the case in a drill chuck. That will keep the case from deforming.
 
I’d put it in a collet chuck, but given what you’ve got maybe fill the case with epoxy and let it cure before working on it.
 
I’d put it in a collet chuck, but given what you’ve got maybe fill the case with epoxy and let it cure before working on it.
I use a QR collet in a lathe to hold 5.56 cases while cutting off the shoulder prior to forming them into 300BO cases. Should work for the OP if he can find someone with a similar setup.
 
I'm curious now - what's the reason for threading the primer hole? I've been trying to imaging how that could be useful and I got nothing.
Fits the case onto the stem of the Hornady thing-a-ma-jig.

Not entirely why the OP wants to do this, sounds like he has to change settings on his sizing die from time to time. I don’t use that hornady tool, so not sure.
 
I'm curious now - what's the reason for threading the primer hole? I've been trying to imaging how that could be useful and I got nothing.

I want to be able to consistently measure seating depth of different bullet choices. Hornady make a OAL guage and a bullet comparator that threads into a cartridge using a 3/16" x 36tpi thread. If I were to use a fired case that has this thread pitch in the case head I would be able to use that case as a measuring tool using a variety of bullets. The goal is to know a relative depth of the chamber and use that when setting up the seating dies of different bullets.
 
The comparator allows me to accurately seat bullets such that they are a certain size away from the lands. For example, if I know the distance that the bullet is just touching the lands, I would be able to use that and subtract say .015" to allow for a .015" jump to the lands for example.
 
If I want to measure how far to bump the shoulders, based on a fired case, I use a case head space gauge. I use calipers to measure the length of the fired case while it is inside the gauge - basically how far the head sticks out of the gauge.



I can use this to compare to a sized case to see how to adjust the die. I have started using the Redding competition shell holders since I feel I get a more reliable bump using those.
 
If I want to measure how far to bump the shoulders, based on a fired case, I use a case head space gauge. I use calipers to measure the length of the fired case while it is inside the gauge - basically how far the head sticks out of the gauge.



I can use this to compare to a sized case to see how to adjust the die. I have started using the Redding competition shell holders since I feel I get a more reliable bump using those.


Ah, I see. That looks like a great idea to measure how much to bump down the shoulder. Thanks.

Do you use a bullet comparator to determine seating depth, or do you use a different method?
 
The goal is to use this case to measure against while sizing my brass. This way I would be able to consistently measure when setting up my sizing die so that I bumping the shoulders down by .002”. As far as I can tell using a fired case is the only way to do this, so purchasing a Hornady modified case isn’t very helpful in this case.

I want to be able to consistently measure seating depth of different bullet choices. Hornady make a OAL guage and a bullet comparator that threads into a cartridge using a 3/16" x 36tpi thread. If I were to use a fired case that has this thread pitch in the case head I would be able to use that case as a measuring tool using a variety of bullets. The goal is to know a relative depth of the chamber and use that when setting up the seating dies of different bullets.

Two entirely different things you are asking for there - sizing (bumping) and seating (distance from lands). My reply was regarding the sizing operation.
 
Ok that helps. Now I understand why you need a fired case. I use an ad-hoc tool that uses measures from the bolt face.
 
Ah, I see. That looks like a great idea to measure how much to bump down the shoulder. Thanks.

Do you use a bullet comparator to determine seating depth, or do you use a different method?
No, I don't use a comparator, though I probably should. I have used modified cases (slotted) so that I can simply push the brass into the chamber, which pushes the bullet into the brass (slip fit). Not as good as a comparator, but works for me.
 
Two entirely different things you are asking for there - sizing (bumping) and seating (distance from lands). My reply was regarding the sizing operation.

Yep, you are right. I wrote the wrong original post.

Basically I want to be able to measure both, but the threaded cartridge is only needed for bullet seating, not shoulder bump. I am still learning, so there are a ton of concepts to wrap my head around. I'm glad I joined here and getting advise from those that have experience.
 
Use a l drill bit will make starting the tap much easier.
Tom
 
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Yep, you are right. I wrote the wrong original post.

Basically I want to be able to measure both, but the threaded cartridge is only needed for bullet seating, not shoulder bump. I am still learning, so there are a ton of concepts to wrap my head around. I'm glad I joined here and getting advise from those that have experience.
No problem, been there myself. Just wanted to make sure I understood what you really wanted.
 
You guys are over thinking this. Just chuck it in a lathe, you don’t have to crush it. Drill, tap and move on.
Brass is soft and easy to work on.

Where are you in Iredell county?


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You guys are over thinking this. Just chuck it in a lathe, you don’t have to crush it. Drill, tap and move on.
Brass is soft and easy to work on.

Where are you in Iredell county?


Sent from my iPhone using Tapatalk

I split my time between Cool Springs and exit 31. So Eastern portion and southern portion. My house is on the extreme southern end.
 
This might be a long shot, but can’t hurt to ask. I’m attempting to modify one of my fired cases by drilling out the primer pocket and tapping with 3/16 x 36 threads. The goal is to use this case to measure against while sizing my brass. This way I would be able to consistently measure when setting up my sizing die so that I bumping the shoulders down by .002”. As far as I can tell using a fired case is the only way to do this, so purchasing a Hornady modified case isn’t very helpful in this case.

I can’t find a way to fixture the brass so that I can drill the necessary hole (bit size L) without deforming the case. If anyone has suggestions, I am eager to try. My thought is chucking up in a lathe, equal pressure could be applied to the case outer surface such that minimal deformation occurs.

Anyone have similar experience? If so, what did you do? I also wouldn’t mind paying a member who is close that has access to a lathe. I have the drill but and tap already.
I appreciate the reply. What I’m going for here is to know my chamber”s dimensions rather than the SAAMI minimum sizing that the headspace gauge indicates.
The reason for the use of a headspace gauge is that it is uncompressable and can be used as a constant for measuring. That said, the two fold plan you have would be better served by the usage of a RCBC Precision Mic if they make it in the cartridge you're using. Again, reason being the Mic measures with a steel on steel method rather than using a brass device that is easily compressed and more subject to temperatures. Either way, good luck.
 
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The reason for the use of a headspace gauge is that it is uncompressable and can be used as a constant for measuring. That said, the two fold plan you have would be better served by the usage of a RCBC Precision Mic if they make it in the cartridge you're using. Again, reason being the Mic measures with a steel on steel method rather than using a brass device that is easily compressed and more subject to temperatures. Either way, good luck.

Gotcha. That looks like a good method as well.

This is a link to a good video of both the RCBS and the Hornady comparator.

 
I split my time between Cool Springs and exit 31. So Eastern portion and southern portion. My house is on the extreme southern end.

OK. I have access to a lathe in Mooresville. Next time I’m that way I can let you know and if you still need it done maybe we can work something out.


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