ERMA-WERKE Mod. EG 712 Kal .22 S.L.LR. (Part 2)

Delesoyby Dana Delesoy
Guns and Gunsmiths Contributor

(continued from Part 1)

Polishing the Chamber

The equipment I use for polishing a chamber is 400 grit sandpaper, spring steel stock for the mandrel (part that the sandpaper wraps around) and a rotary tool such as a Foredom Tool, hand drill, or Dremel.

 

The Sandpaper

The sandpaper is taped to one end of the mandrel and the other end of the mandrel inserted into a rotary tool. I wrap the sandpaper the opposite direction the mandrel spins. This ensures good polishing action and will prevent the sandpaper from wanting to unravel as the mandrel is spun in the chamber. The sandpaper needs to be of a length that when wrapped around the mandrel is large enough in diameter to fit slightly snug when inserted into the chamber. The photo “Mandrel and sandpaper used to polish the chamber” shows the first length of sandpaper too short (2 1/8″) to roll to a large enough diameter to effectively polish the chamber. I had to add (by taping) another length (1 1/2″) to the short length.

The sandpaper needs to be approximately three and a half inches (3 1/2″) long (based on the .068″ diameter mandrel I use). Since this gun is chambered for .22 Long Rifle I cut the width of sandpaper the same length as a .22 Long Rifle case (5/8″ or .610″) or slightly longer (3/4″ or .750″). In any situation the sandpaper width is the same width or slightly longer than the cartridge CASE length (the case is the brass portion only). You do not want to polish the rifling or the chamber throat, so cutting the sandpaper to the same length as a .22 long rifle case will serve as a depth indicator. If you can’t see the sandpaper during polishing then you have inserted the mandrel too far and will be close to or at the point of polishing the rifling.

The Mandrel

I use the spring stock from surveyor flag poles (compliments of “Dial before you dig”). They are .068″ diameter and work well as a polishing mandrel because they are thin enough in diameter to be flexible, which is beneficial for times you can’t get straight on into a chamber. I cut them to lengths suitable for the task at hand (I have various mandrels ranging from 2″ to 6″). For this gun I needed a mandrel length of 6″ to 6 1/2″ so that the rotary tool chuck would be clear of the receiver and to get the mandrel straight as possible in-line with the chamber. Having the polishing mandrel straight in line with the chamber is best. Polishing the chamber with the mandrel on an angle will oval the chamber (the greater the angle the greater the ovalling).

I was able to polish the chamber straight in line because the parts in the receiver were all removed for cleaning. If the parts were all assembled the hammer would be slightly in the way as you can see in the photo “Polishing the Chamber” in which the rotary tool end of the mandrel needed to be raised slightly above the receiver. The parts will more likely than not be assembled in this type of gun when the chamber is polished, thus the photos as such.

I polish the entire mandrel (in particular the end with the sandpaper on it that is inserted into the chamber). Then, if the tape unsticks from the mandrel the end of the mandrel will not damage the chamber. If the tip is sharp and contacts the chamber wall (or the rifling) things can get scratched, especially while it’s spinning around. Polishing the whole length of the mandrel removes any rough or sharp areas, removing the likelihood of scratching any part of the gun (the chamber in particular) it may come in contact with during the polishing process.

I basically make both ends of the mandrel hemispherical like a centerfire firing pin tip and then highly polish. To do this I clamp the mandrel in a vice, use a flat file to shape the ends. I chuck the other end into the rotary tool. As the rotary tool spins the mandrel I place a piece of 320 grit sandpaper over the tip (to polish it), then do the same with 400 grit to achieve the final polish. I perform the same process for the other end (tip) of the mandrel and then for the entire length of the shaft.

I chuck the mandrel into a Foredom Tool (a handheld drill also works well). Going slow and checking often when making adjustments to a gun is a key rule to adhere to, with chamber polishing being no different. I spin the sandpaper in the chamber for about 5 seconds, stop, clean out the chamber with a lightly oiled Q-Tip then test the chamber for smoothness (same way as done earlier).

When a cartridge is able to slip-seat freely into the chamber via gravity, polishing is complete.

Primary Extractor

With the chamber now polished smooth I assembled the gun, loaded a cartridge into the chamber, closed the bolt and slowly worked it open (using the lever) while carefully watching the cartridge case rim and the primary extractor. As the action opened I could see the primary extractor hook wasn’t able to grab the rim of the case and extract it from the chamber. I removed the bolt to inspect and test the extractor. I could have checked the extractor (for extraction, extraction hold, tension, etc.) before dealing with the chamber but since the chamber really needed a polishing anyhow I focused on the chamber first. Either way works so long as you test and inspect them both.

I placed a new, unfired cartridge rim under the primary extractor hook and saw that extractor spring-out was next to nothing, with cartridges always slipping right off the bolt face. No spring out means there is no extractor tension (spring-in) on the cartridge rim thus the extractor wasn’t able to hold cartridges snug onto the bolt face like it needs to do. This explains why the customer’s gun wasn’t able to remove fired cases from the chamber. The primary extractor failed to perform its functions.

Since the bolt was still dirty I wondered if there was enough debris between the body of the extractor and its slot in the bolt to limit the extractor from being able to move (spring in) closer toward the bolt face. I removed the primary extractor from the bolt and cleaned everything. I could see accumulation of debris (from lack of cleaning) between the primary extractor’s slot in the bolt body and the primary extractor’s “leg.”

After the gunk was removed I reassembled the extractor, slipped a cartridge under its hook and could see the extractor was showing spring-out. The debris removed from under the body of the primary extractor allowed its hook to move closer to the bolt face. This gave the required tension on the cartridge case rim.

A .22 rimfire cartridge rim is on average .040″ thick. If the extractor hook is more than the rim thickness (.040″) away from the bolt face, the hook is too far away to hold a case rim onto the bolt face.

I reassembled the gun, inserted a cartridge into the chamber and cycled the lever. The extractor was able to grab the cartridge rim and extract it from the chamber 100% of the time. But now another problem existed: every few rounds there was a failure to eject because the extractor lost hold of the cartridge before ejection could occur. It was dropping the cartridge as soon as it cleared the chamber.

I removed the bolt and performed the extractor hold test: I slipped a cartridge under the primary extractor hook and held the bolt still. The case rim was held snug onto the bolt face by the extractor tension (spring-in) but I could see the cartridge rim being forced in a downward angle from the primary extractor’s spring-in tension.

As I continued to lightly shake the bolt, the spring tension from the extractors (primary and secondary) further forced the cartridge case downward causing the primary extractor to lose its hold, resulting in the cartridge case falling off the bolt face. I reduced tension on the secondary extractor by limiting its spring-in (put a piece of masking tape in its slot in the bolt) but that didn’t help. I referred back to an Extractor lesson (instructed by Bob Dunlap) in an early issue of GunTech. One of his examples confirmed what I needed to do to the primary extractor hook.

Reshaping the Primary Extractor’s hook angle

I removed the primary extractor from the bolt. Using a fine polishing stone I applied three short strokes at an upward angle to the upper portion (upper half) of the hook, which removed a very small amount of metal.

Going slow and checking often is always a key rule to adhere to. Three short strokes of the stone on the edge of the hook, reassemble extractor, check extractor hold . . . much better, progress is moving in the right direction. The cartridge case was now being held upward but not quite snug enough into the rim cut in the bolt face (on the primary extractor side) for my liking.

I removed the extractor, two more short strokes of the stone (to the same area on hook), reassemble, check extractor hold . . . perfect!

I reassembled the gun, filled the mag tube with 14 cartridges and cycled the action slowly . . . 100% extraction and 100% ejection. I refilled the mag tube and cycled the action quickly . . . 100% extraction and 100% ejection. I repeated the process with each time confirming 100% extraction and 100% ejection. Success!!

 

“In summary”

Polishing the chamber, cleaning the slot in the bolt for the primary extractor and reshaping the primary extractor hook made the gun extract and eject perfectly every time. No parts were needed.

 


5 Responses to ERMA-WERKE Mod. EG 712 Kal .22 S.L.LR. (Part 2)

  1. Good points on the extractor, but I have some concerns on your rundown of Polishing the chamber and I offer a caution to others:

    Another way to do this is to use a soft annealed solid brass rod, rounded or tapered end with a narrow slot in the end cut lengthwise, parallel and center to the rod center. This allows you to quickly change the material you might be using for honing or polishing. We used this technique in our shop to precision port and polish both steel and aluminum heads on race bikes near valve seats (which we had to leave perfectly untouched or re-grind). The fact that the material being used is loosely adhered by lacing it through the dowel slot makes it less likely to gouge – it will fall off it it binds – that is irritating BUT it tells you that you may be being either too slow or too aggressive. The centrifugal force of the paper spinning at a chosen RPM gives you control over the aggressiveness of the bite. Use very narrow strips of material so as not to alter the chamber at it’s mouth where the cartridge must be snug and square (like a valve seat). A very narrow strip of media is recommended for our work, say 1/4″ or less. I start with 1,000 grit maximum, 1,500 may work better for light work.

    Remember we are cleaning up a snag, not re-cambering. The rod must be exactly parallel and centered with the bore (top view picture shown in the article is incorrect – it is angled – do not do this. Use a bore guide if you have to. Use tiny overlapping short stokes in and out quickly to create a very light, almost imperceptible cross hatch pattern that reduces friction by reducing metal to metal surface area and allowing microscopic lubricant to have a place to hide. This operation should only require ten to twenty seconds of total spinning time – in short bursts unless you intend to increase the chamber diameter. Same as honing a cylinder in a race engine, you can easily overdo the job and create more tolerance than you want between the chamber wall and cartridge.

    This is a very, very exacting thing to do at such small bore diameters. It is better done by hand if you aren’t familiar with honing a cylinder of any type. It is very easy to erase metal at the breach face where it should be square, if not very slightly chamfer. I’m not saying the author is wrong, I’m just saying that the force of what is being suggested can very quickly ruin a chamber unless you really, really have a light touch and know what the heck you are doing.

    • Hey John, regarding with what you stated here: “Remember we are cleaning up a snag, not re-cambering. The rod must be exactly parallel and centered with the bore (top view picture shown in the article is incorrect – it is angled – do not do this. Use a bore guide if you have to.”.

      I agree with you that the polishing mandrel (or rod as you referred to it) should be parallel and centered with the bore.

      I would like to clarify with you that in my article here in the paragraph above the photo titled “Polishing the Chamber (side view)” I stated:
      “I was able to polish the chamber straight in line because the parts in the receiver were all removed for cleaning. If the parts were all assembled the hammer would be slightly in the way as you can see in the photo “Polishing the Chamber” in which the rotary tool end of the mandrel needed to be raised slightly above the receiver. The parts will more likely than not be assembled in this type of gun when the chamber is polished, thus the photos as such.”. The photos of those two chamber polishing photos are of a friends gun in which is illustrating how to get by with polishing the chamber if you do not know how to remove the receiver components/parts in order to get straight in line with the chamber/bore OR if it is not a viable option to remove the barrel (in which with this gun it is not viable). The barrel is pinned into a soft, alloy receiver and it is not advisable to remove barrels as such because when driving the pins out the pins have grooves that shave away material from the pin holes and thus eventually the pins won’t have enough alloy for the pins to fit tight in their holes, thus the barrel becomes loose and accuracy is negatively affected. Therefor the best way to get at polishing the chamber in this type of gun is to remove the internals of the receiver components (in this gun it is all of them) that block direct alignment of the polishing mandrel to the bore.

      Back to the paragraph when I stated: “I was able to polish the chamber straight in line because the parts in the receiver were all removed for cleaning.”. This pertains to the actual customer’s gun the article is based on, in which the receiver components/parts were completely removed/stripped for cleaning and thus I made it possible to get the polishing mandrel straight in line with the chamber/bore. Unfortunately I did not take any photos of the customer’s gun’s stripped receiver with the polishing mandrel straight in line with the chamber/bore. Since I do know how to disassemble/reassemble all of the receiver’s internal components I would personally always remove the receiver’s components to polish chambers for every gun like the one here.

      Apologies to anyone for any confusion regarding the polishing photos and rationale around it.

      Thanks for the good/constructive comments John.
      Cheers

  2. An excellent article. I intend to make use of the many suggestions and tips.
    I have a STI AR15 in .223 that stops working when it gets hot.
    I am sure that the brass stuck in the chamber is due to tighter .223 tolerance than 5.56 Nato. I am sure that a polish of the chamber will lessen the chances of the cartridge case getting stuck due to the tight tolerances in this very accurate rifle.
    Please keep up the good work.

    • Great to hear you like the article, thank-you Graham!

      Interesting issue with your AR15. I’m curious of the cure for it’s stated condition. Perhaps you could write us an article for Guns and Gunsmiths regarding your gun’s issue/condition and the remedy for it to satisfy our curiosities?

      Best wishes for your AR’s outcome! Thanks for the comments!
      Cheers

  3. No parts needed, enough said. It’s amazing how easy it is to fix things and also how well they work when you understand how all the parts function. Thanks for another job well done, sir.

    Cheers

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.