Sunday, December 27, 2009

Rimfire Magazines - Part 3

In addition to a "Magazine Lipper" tool, as previously described, another extremely handy tool to have along when tuning rimfire magazines is a full set of number and letter size drill bits. The difference in size from one bit to the next is too great with a fractional drill bit set, but with a number and letter sized set the increments between sizes are small.

You can pick up a cheap set of these drill bits for around twenty bucks, and as gauges, they work just fine. As drill bits, however, they pretty much suck. If you can swing it, for somewhere around a hundred dollars you can get a pretty decent set of drill bits that will last you a very long time, at least, if you take care of them and don't break any!


A letter and number sized drill bit set. This set came from W.W. Granger's and the quality if very good.


Trying to measure the gap between the lips of a rimfire magazine with dial calipers is difficult due to the odd shape of the lips, but using a drill bit shank makes it a lot easier.


Using a drill bit shank to gauge the distance between magazine lips.

Hopefully when you get to the range to dial in your magazines you will find one or more magazines that seem to work just fine, and some that have problems. If that's the case, use a drill bit shank to determine the gap between the magazine lips of the working magazines and then carefully bend the magazine lips of the magazines that aren't feeding properly to match. If luck is with you, this may be all you need to do to get your magazines feeding properly. In the real world, however, there always seems to be at least one "Problem Child" of a magazine in every bunch. For these, you need to determine exactly what it's doing and then bend it accordingly.

There are a number of different types of failure to feed situations. If you can't get the rounds smoothly out f the magazine, no amount of magazine lip adjusting is going to help. When you load your magazines, do the rounds slide freely up and down with the follower, or do they tend to hang up a bit? If there is a bit of a tight spot perhaps the magazine has been slightly squeezed narrower, and a little careful spreading of the magazine from the inside is in order.

One of the more common FTF's is "Feeding Too High". Usually the bullet is jammed against the top edge of the chamber. There is usually a big dent in the nose of the bullet, and often times the bullet is actually partially dislodged so that it is no longer straight with the case. These situations are also just about the worst to clear in a hurry since the slide has usually hammered the cartridge into a solidly wedged position. Feeding too high is usually caused by the magazine lips being to far apart, or too high in the gun relative to the chamber.


A classic case of feeding too high.


Find the drill bit that just fits between the magazine lips. Now pick out the next smaller bit. Using the magazine lipper, carefully bend the lips inward until the smaller bit just fits between the lips. Keep in mind that the change will be approximately the thickness of a sheet of paper, so it doesn't take much bending to close the lips to the smaller gap. Once you have narrowed the magazine lips to the new dimension, give it a try and see if you have made any improvement. If it's still feeding high, try going down another step. If you go too far you will end up with the bullet hitting too low, and it will then usually kick up and look like a case of feeding too high, or it may not get out of the magazine at all.

When I stated that feeding too high was usually caused by the magazine lips being too far apart, this is the exception. If the magazine is feeding too low the bullet may hit the ramp leading up to the chamber and bounce past the opening into the chamber, ending up either jammed up like a regular case of feeding too high, or sometimes it will caught between the slide and the breech face, pointed almost straight up. This is a fairly rare situation, and if you look carefully at the bottom side of the nose of the bullet you will often see the beveled flat spot caused by hitting the ramp. A regular case of feeding too high will not have the dent.


When the magazine lips are to close together they won't let the rim end of the cartridge rise enough for the round to enter the chamber.


If the round is feeding too low it will often hang up with the cartridge rim still held under the magazine lips and the bullet partially in the chamber. The top of the bullet is jammed against the top of the chamber, the bottom of the bullet is jammed against the lower edge of the chamber at the breech face, and the rim is still under the magazine lips.


Notice the cartridge rim is still below the extractor.


Another view of a failure to feed caused by the magazine lips being too close together.


Keep in mind that this as also what you get with a dirty chamber, so before you get carried away bending up your magazines, make sure your chamber is really clean. In fact, polishing the chamber can resolve a lot of problems that appear to be caused by the magazines. Really close tolerance "Match" chambers are especially vulnerable.

There is also another failure to feed that can easily be blamed on the magazines, and unless you look closely, it would appear to be a case of the magazine lips being too close together. However, in this case it's the extractor being a bit too tight to the face of the slide, not allowing the rim to slide up between the hook of the extractor and the slide face.


The bottom corner of the extractor has snagged on the side of the cartridge just in front of the rim, keeping the cartridge from sliding all the way up the face of the slide.


In the above picture you can see that the rim of the cartridge is fully out from under the magazine lips. The cure to this failure to feed is simple. Lightly stone off just the tiniest amount of the bottom corner of the extractor. When I say a tiny amount, that's exactly what I mean, as anything more will create a whole new batch of problems related to failure to extract. It's really closer to de-burring, rather than actually removing any metal.

When you are at the range and you get a FTF, the natural reaction is to clear it as quickly as you can and get to the next shot. However, if you take a moment to look closely at the situation, then carefully remove the round and look closely at the nose of the bullet, you'll have a much better chance to correctly identifying the exact cause of the FTF, and you'll have a lot easier time of resolving it. All magazines have a "Sweet Spot" where they are extremely reliable. If you are at one end or the other of the envelope the magazine will work really well almost always. Tuning your magazines, sometimes only an extremely small amount, will make them significantly better.
I should mention, though, that I have seen the occasional after-market magazine that absolutely refused to feed reliably. I attribute it to the after-market magazines sometimes not being quite as accurately made as the factory originals.

Rimfire magazine tuning can be something of a black art, but with a bit of patience, and trial and error, you should be able to get the results you are looking for. Failing that, you may want to consider a different pistol, or possibly a revolver..............


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2 Comments:

At Monday, December 28, 2009 3:52:00 PM, Anonymous Anonymous said...

I tried bending the lips on my Colt Single Action Army but to no avail. I can't seem to get more than six rounds to feed reliably then I have to start over and reload the magazine. Any suggestions he asks with some fear that you might have one.

Seriously, nicely done. I've got a couple of Ruger Mags that are only so-so reliable, I'll try your fix.

Damiphino

 
At Friday, January 01, 2010 8:30:00 PM, Blogger TrueBlueSam said...

Happy New Year, Mr. C and KeeWee! We are cold in Southern IL, and are bringing in firewood while the ground is frozen. EJ cut short his holiday visit and is in Singapore now. In a few days he will be in Dubai, then the UK. He will be doing some tuning work for Bea on her Mk III after he returns. She is planning on going to GBR with EJ again next Sept.

 

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