Reducing rim thickness on rimmed centerfire brass?

[arakboss]

I would like to remove just a bit of the rim thickness on the inside surface of some 444 Marlin cases. Any thoughts on an easy way to do that with out damaging the sidewall of the case? I might have a 100 or more to do this to.

The area where the pen is pointing to is the area I want to remove the material from.

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[edzz]

I'm curios why you want to thin the rim.
FWIW I'd use my little lathe.

 

[arakboss]

I'm curios why you want to thin the rim.
FWIW I'd use my little lathe.

I want to use these in place of 410 Brass Hulls. The rim thickness of the 444 Marlin brass doesn't allow the case to sit completely flush in the chamber of my break action shotgun. It will close on the case but only about half of the time will it allow the trigger to engage in full cock. It is very close and only needs a minimum of material removed. I don't own a lathe.

 

[Bon Sauvage]

These guys built a lathe in 5 minutes. You can't spare 5 minutes?

 

[arakboss]

These guys built a lathe in 5 minutes. You can't spare 5 minutes?

Man they worked fast.

 

[DizzyJ]

I assume you've scrubbed the shotgun chamber of any crud that may have built up in that area?

 

[arakboss]

I assume you've scrubbed the shotgun chamber of any crud that may have built up in that area?

I haven't but 410 shells sit in perfectly flush and the trigger cocks back fine on shells. If you compare the rim thickness of the 444 case to the rim thickness on a 410 hull, it's close to double the thickness on the 444 case. There is no visible crud where the rim rest inside the chamber.

 

[DizzyJ]

I don't have any expertise whatsoever with either platform so I can't definitively say it's safe to make that modification.

I personally would steer clear of that, but, again I really don't have the experience to know if anything would be dangerous in doing so.

 

[whitney]

Make a hand held cutter/grinder from a wooden closet dowel or broom handle.
Cut off an inch or so of the dowel and drill a close fitting hole the brass will pass through. Glue on 100 grit garnet paper and trim out the hole. Use garnet because it does not embed in the material but you can use aluminum oxide if you want. Inspect the brass for abrasive material.

If you can not get the hole quite right cut your tool in half long ways so it is a "split shell" and use a rubber band to hold the two halves together around the brass. You can trim the half shells if the hole was too big or start again with a blank pair.

Work slow and methodical, take your time. Most folks likely have everything or can scrounge it pretty easily.

~Whitney

 

[arakboss]

Make a hand held cutter/grinder from a wooden closet dowel or broom handle.
Cut off an inch or so of the dowel and drill a close fitting hole the brass will pass through. Glue on 100 grit garnet paper and trim out the hole. Use garnet because it does not embed in the material but you can use aluminum oxide if you want. Inspect the brass for abrasive material.

If you can not get the hole quite right cut your tool in half long ways so it is a "split shell" and use a rubber band to hold the two halves together around the brass. You can trim the half shells if the hole was too big or start again with a blank pair.

Work slow and methodical, take your time. Most folks likely have everything or can scrounge it pretty easily.

~Whitney

Great suggestion! I will give that a try. Where do you find garnet?

 

[whitney]

Garnet paper sources:

https://www.mscdirect.com/browse/tn/?searchterm=garnet+sandpaper&hdrsrh=true

3M Garnet 3.7 in. x 9 in. Medium 100-Grit Sheet Sandpaper (6-Sheets/Pack) 19037-20-CC - The Home Depot

3M Garnet Sandpaper 19037-20-CC, 3-2/3 in. x 9 in. (9.29 cm x 22.8 cm), Open Stock. 3M Garnet Sandpaper is the choice of professional woodworkers for sanding a wide variety of bare and unfinished goods.

www.homedepot.com

~Whitney

 

[arakboss]

Garnet paper sources:

https://www.mscdirect.com/browse/tn/?searchterm=garnet+sandpaper&hdrsrh=true

3M Garnet 3.7 in. x 9 in. Medium 100-Grit Sheet Sandpaper (6-Sheets/Pack) 19037-20-CC - The Home Depot

3M Garnet Sandpaper 19037-20-CC, 3-2/3 in. x 9 in. (9.29 cm x 22.8 cm), Open Stock. 3M Garnet Sandpaper is the choice of professional woodworkers for sanding a wide variety of bare and unfinished goods.

www.homedepot.com

~Whitney

That is fantastic, I will report back to this thread and let you know how it turns out. I might be able to get the British 303 brass to work in the 410 using this method too.

Thank you.

 

[CLT65]

I use my little drill press as a simple lathe all the time. I've modified brass many times for odd-ball calibers. It's a time-consuming hassle without a real lathe when you have a bunch to do. I'd love to have a lathe. One of these days...

What I do to thin the rims is this: get a fine, single-cut, hand file, and grind one side smooth so that it cuts on the edge but not the flat. Chuck your brass in your drill press and carefully use the edge of the file to thin the rim. The smooth flat will run along the body of the case without damaging it. Getting the rims precise and uniform will take some practice, and 100 will take quite a while, since you'll need to stop and measure regularly.

 

[gmerkt]

What I do to thin the rims is this: get a fine, single-cut, hand file, and grind one side smooth so that it cuts on the edge but not the flat. Chuck your brass in your drill press and carefully use the edge of the file to thin the rim. The smooth flat will run along the body of the case without damaging it.

I like this idea with a little fine-tuning. Instead of placing the cartridge case itself into the drill press chuck, get some dowel for a mandrel and insert that into the cartridge case, made for a snug fit. Then chuck the wood dowel into the drill press. The .444 case has some taper, so you would need to make a pilot on the bottom end of the dowel that would fit through the primer flash hole to keep it centered. Use a small nail with the head cut off for the pilot.

Files with a smooth flat on one side can be purchased. It's called a safe edge file.

You'll probably have to turn down the dowel mandrel to fit. As you use it repeatedly, the snug fit will wear down. You may need to build it back up with masking tape from time to time for the snug fit. Snug enough so that light pressure from the file won't cause the brass case to spin. Keep a file card handy for cleaning out the file.

This is what I would try. The weak point is keeping any eccentric movement out of the case at the head. So getting the wooden mandrel and pilot right is critical. The other critical issue is keeping the case from spinning on the mandrel, hence a snug fit. Brass is soft, has enough spring-back for this to work well.

 

[CLT65]

I like this idea with a little fine-tuning. Instead of placing the cartridge case itself into the drill press chuck, get some dowel for a mandrel and insert that into the cartridge case, made for a snug fit. Then chuck the wood dowel into the drill press. The .444 case has some taper, so you would need to make a pilot on the bottom end of the dowel that would fit through the primer flash hole to keep it centered. Use a small nail with the head cut off for the pilot.

Files with a smooth flat on one side can be purchased. It's called a safe edge file.

You'll probably have to turn down the dowel mandrel to fit. As you use it repeatedly, the snug fit will wear down. You may need to build it back up with masking tape from time to time for the snug fit. Snug enough so that light pressure from the file won't cause the brass case to spin. Keep a file card handy for cleaning out the file.

This is what I would try. The weak point is keeping any eccentric movement out of the case at the head. So getting the wooden mandrel and pilot right is critical. The other critical issue is keeping the case from spinning on the mandrel, hence a snug fit. Brass is soft, has enough spring-back for this to work well.

Absolutely, that is an option, and I have done that before. I've found for what I've done though, that simply chucking the brass right in the drill press chuck works as well or better.

The trick is in tightening it enough so it doesn't come loose, but not so much as to crush the brass. I've found that even with tapered brass it works pretty well and is less likely to come loose in the chuck than on a mandrel. I've done it many times.