model 85 low wall breach block

  • Last Post 10 March 2018
loophole posted this 03 March 2018

I am converting my mod 85 low wall from 32 rimfire to 32wcf.  Larry Potterfield of Midway has a video showing how this is done and I once converted a 22wcf to 22 lr.  I had no trouble drilling the 22wcf breach block with a hss bit, and Potterfield does not specify a carbide bit for the 32 rimfire block.    My 32 rimfire was made in 1901.  I tried using a new hss bit to drill out the rimfire pin hole to plug it and it was very hard to do.  A new drill bit would not even start a hole for the new center fire pin.  It appears that the breach block is made of very hard steel or has a thick surface hardening.  I have a couple of carbide bits ordered which I hope solve the problem.  

Does anyone know if Winchester made the breach blocks harder after a while? Did they use harder steel to make the rifle stronger for smokeless powder loads?

Steve K



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corerftech posted this 04 March 2018

You got lucky the first time. They are case hardened and you simply got lucky on the wcf/Lr conversion. If you have a dremel maybe chuck up the finest little pointy grinding bit you have and just poke at the skin at you mark and take .002/.003 off the spot. That might get you through enough case to be able to center drill with a number 2 and move forward. The other option is that you should have used a transfer punch to mark the block with a modified case. Modify the case further, put a meaner hardened punch in it or through hardened steel and make it sharp. Hit it like you mean it with a bore guide and a steel rod driver. Ala throat pound cast. That will drive the mark punch throug the .020 thick case and yet leave you a small/tiny center punch to drill. It “should” bite with a tip of a new HSS USA made center drill and then follow with the rest of the process. Lastly you can use your current transfer punch mark and in a padded and tight vise or better yet a steel or alum pseudo fixture, use another more fortified punch to Re strike the existing transfer mark. If you go .010 to .020 you’ll be in the clear and have success.

It’s HARD like a Mauser boltface. Sometimes really sharp carbides just glance off of it.

Lastly, anneal it and send it out for Re-case and it will be easy!

Pick your poison.

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loophole posted this 04 March 2018

Thanks for the info.  I will try a center punch and carbide drill bit.  Potterfield's video is a bit misleading.

Steve k

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loophole posted this 08 March 2018

Very useful information, Corerftech.  I am using a centerfire pin,  so the hole has to be drilled from the back side, using a homemade fixture to keep the bit centered in the big part of the hole in the breach block.  If I had broken  the bit drilling from the back side of the block, it would have been real problem getting the broken bit out.

I got a couple of Carbide bits; I used a very sharp center punch on the back side of the block.  I decided to drill the vent hole in the top of the breachblock to see how the carbide bit would work.  Centerpunch, then carbide bit, which broke off as it tried to punch thru the case hardened, but it was easy to get the broken piece out with a 1/16" punch, since I had access to both sides of the hole.

I carefully drilled through the case hardened part of the block with the carbide bit, then used a new American HSS number bit a little smaller than 5/64 and backed the exit with a flat piece of aluminum.  It drilled thru the second layer of case hardening.  I enlarged the hole with a HSS 5/64th bit.  That part of the project is done.

I have relearned to be suspicious of anything i see on the net.  Potterfield's video made this look like a simple project, but you really need a milling machine to use these little carbide bits.

Steve K 


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corerftech posted this 09 March 2018

I didn't know you weren't attempting w/o use of a mill.

You had a drill press, yes?

A center drill would have helped, even with the bushing issue form backside. As I mentioned in my post, #2 Center drill but a #1 may have been deployed and been helpful. W/O a center drill with its inherent rigidity and thick shank, Id be fearful of any drilling.

I do believe they make carbide centers. You may have to make a new bushing. I think the vent hole bit broke due to lack of support. There again the center drill wool have helped, as long as US made and SHARP. Chinese are OK, ground accurately but typically no SHARP. And for HSS to cut at all on cased material (post center punch), it will need to be sharp right at first penetration.


Glad you got one hole done successfully w/o any loss.


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loophole posted this 10 March 2018

An old drill press with a very good Jacobs chuck.  I realize I should have used by brother's mill.  I'd rather be lucky than good.  I appreciate your good advice.

Steve K

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