Mauser Action Feeding Work - CZ 550

I wanted to put down my thoughts,opinions and actions that I used to tune a CZ 550 in 458 win mag, from what I understand, that caliber is particularly difficult being short and fat. I searched the internet and there was not much to be found. Duane Wiebe has posted a brief process on another forum and Von Gruff posted Proper Magazine Layout on africahunting forum and these were most helpful but don’t really tell you why you do something or what it affects. I found that as you feed the round, things are more complex than you first think and changing one thing invariably changes another. For what it is worth, here are my thoughts, use them at your peril! Some of you may have more experience than me and can add some bits that I got wrong or left out.

The bullet riding up the ramp initiates the process the feed action so I started there. As it lifts the front of the round, the cartridge case contacts the feed lips/side rails and pushes the round away from the side of the magazine and towards the center to align with the chamber. I expected the ramp to funnel the bullet into the chamber but found the cone shape does little for the left/right movement. See the diagram below for more clarity.


I carefully removed a bit of the feed ramp to create a flatter cone shape and lower the feed angle slightly.

If you alter the angle of the feed ramp by making the angle shallower, the feeding round will move away from the rail later in the feeding cycle. In addition, if you remove the feed rail from where it touches the case as you feed, the round will also be pushed away from the rail less and later in the feeding cycle. I tried to keep the round feeding to the center of the chamber. I removed material from the feeding ramp to aim the cartridge just below center of the chamber. I figured that I was using dummy rounds with the shortest bullet or head(480 gr hornady dgs) Other heads would be monolithics or 500 gr solids and longer so I left room.


I sloped the feed ramp to give a shallow angle of entry into the chamber but beware, the back of the feed ramp is the locking lug surface. A shallow angle of entry means that the camming of the bullet that slides it up the bolt face and out of the feed lips is easier. The bullet should enter the chamber just before the case leaves the magazine feed lips.After removing a bit of the feed ramp, I marked the feed lips with a marker where they pushed the case across too much and removed them with a file. I used small slips of paper to help, sliding the paper between the feed lip and cartridge to see where it was touching. The main problem I had was just as the bullet gets close to the chamber mouth, it is pushed wide and catches on the chamber mouth even after the feed lips are no longer touching the cartridge, apparently it is a common problem with CZ, especially when feeding from the left side. At this point I found that if I pushed the cartridge straighter, to line up with the chamber, it sprung back. It must be to do with the magazine and magazine spring because that is the only sprung part that is involved. I wracked my brains for a while and remembered Von Gruff’s post about Proper Magazine Layout. In that article, it states that if the magazine box is too narrow, it will cause crossover. That was what I was experiencing so I measured the box in the critical area where the bullet entered the chamber and it is 2 mm narrower than suggested by the formula in the article. So with much trepidation, I started removing material from the inside of the magazine box on the left and right. As I did so, the bullet slowly moved more central each time I tried it. I removed about ¼ mm on the left side. As the magazine box was widened, the cartridges stack more widely and this changes the tension on the bullet and the angles that are applied. Below is a photo with a matchbox to indicate the area and cover up irrelevant parts. The arrow indicates the width of the box. I used the rim diameter + diameter of the bottom round at that point to calculate proper width of 24 mm. I stopped removing material at 23 mm or there about because the round no longer sprung back and chambered every time for 100 + tests. What is interesting is that the article said that Mauser relieved his magazine boxes in the middle to reduce friction but I think that it may have been to solve this very problem. As the rim slides down, it is much wider than the cartridge and so needs about 1 mm extra width just as it reaches the chamber. The 458 win mag seems to be a perfect storm where a Lott will probably be fine because it is longer and has less steep angles as it feeds. Much thanks to Von Gruff and TokkieM for their answers to my Pm's

So after all this work can you fill your magazine with dummy rounds and rack all of them through the chamber numerous times without a hitch? I've given Von Gruff's article to a number of Gunsmiths. What I cannot figure out is how or why gun manufacturers don't make use of this information when designing their magazines and followers. After all the info has only been available for 120 years or more.

It has done about 250 feeds of dummy rounds without a problem.

I have been doing drills and trying every funny angle I can think of.....

That really bent my brain, running the bolt left handed and upside down !

Shootist43 said:

So after all this work can you fill your magazine with dummy rounds and rack all of them through the chamber numerous times without a hitch? I've given Von Gruff's article to a number of Gunsmiths. What I cannot figure out is how or why gun manufacturers don't make use of this information when designing their magazines and followers. After all the info has only been available for 120 years or more.

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I think there are a couple of reasons:

1. Money- I probably have 16 to 24 hrs in this work including research and sketching. Any rifle company that adds $500 of gunsmithing to their rifle ?? arent going to sell many.
2. CZ did leave extra steel in all the right places ie a gunsmith can remove material in order to custom fit the feeding. If they removed more material, you may end up with a problem. Also with regards to the magazine width, I have a theory. The case tapers and so as the rim slides forward, the case diameter on the bottom is reducing while the rim of the upper case remains the same.At the critical point (as the bullet nose feeds into the chamber) The case rim and belt(13.51 mm) is supported by the lower case diameter of 12.3 mm. So the magazine should actually have a 1-2 mm bulge/bowing to allow for the rim being wider than the case. CZ magazine has straight walls with no bowing. I believe Mauser created this in his design (as sighted by Von Gruff) It may have been for friction reduction or Mauser probably figured it was needed for the rim or belt.

Something I didn't mention but that I kept at the forefront of my mind when I did this:
Controlled round feed- For true controlled round feeding, the case must be held under the feed lip of the magazine until the bullet nose enters the chamber (Duane Wiebe). Then the rim is cammed up and out of the magazine and into the extractor/boltface by the bullet nose and feed ramp lifting the back end of the case. Maybe a really good gunsmith gets the magazine to release exactly as the case cams up but in my action, it could see the leverage(gentle as it is).This ensures that if you pull the bolt back at any time in the feed process(or jiggle it around as if you tripped/fell/were run in to by a tracker), the round is either still held in the magazine OR the extractor pulls it back and ejects it. The round cannot fall out. You can 'fix' the feed problems by simply getting the round to pop out of the magazine before the bullet nose enters the chamber. This method in effect turns the CRF action into a push feed action. I experimented with masking tape to pop the round out earlier in the feed cycle and, from the left rail, the round is not in the magazine OR chamber mouth OR extractor claw.It jumps up with speed, sometimes engaging the extractor, sometimes hooking under the side rim of the bolt and sometimes jumping ahead of the bolt. It is not controlled or predicatble. In a couple of cases, if the rifle was angled downwards, the round slid down into the chamber. With a Mauser extractor, you will struggle to snap it over the rim of a chambered round. In effect it is a push feed and it feeds smoothly-all the awkward angles are gone because the round back end is lifted. So unscrupulous people can 'fix' your feeding problems by turning your CRF into a Push feed. You should also check second hand rifles because someone could have removed too much metal from the feed lips for a gunsmith to fix this problem.

Shootist43 said:

So after all this work can you fill your magazine with dummy rounds and rack all of them through the chamber numerous times without a hitch? I've given Von Gruff's article to a number of Gunsmiths. What I cannot figure out is how or why gun manufacturers don't make use of this information when designing their magazines and followers. After all the info has only been available for 120 years or more.

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And another thought, I think that this problem goes away with spitzers.only blunt solids/flat meplats show up the issue. So we can say .375, 416 Rigby, 458 wm and 458 Lott are the only cz models affected. Lott and Rigby are longer, 375 is slimmer and longer. I think the angles are easier and so they are more tolerant of dimensions. My experience watching Zimbabwe ph and pg shooting exams suggests that feeding problems occur across all calibers and manufacturers and in an alarming %. My rifle fed about 100 % when absolutely vertical and the bolt was rammed home with force. Ease up on it or not be able to apply enough force and it dropped to about 80%. My wife was not able to force it, and it jammed often. Rotate the rifle on 45 degrees to the right and it jammed every time. It chewed up the case rim and the bullet at the edge of the meplat. After my work, my kids (10 and 8)can run the bolt without jamming. At any angle,0 jams out of 250. I think that all manufacturers could set up their machines to fix magazine width at no extra cost,if that is a problem.I saw that Duane Wiebe set up magazine width first thing in his write up. Feed ramp and magazine feed lips might be a little better but perhaps they would rather leave extra steel, err on the side of caution.

Nhoro, sounds like you've got it licked. That bad boy is ready for a DG hunt. Only four questions need to be answered. When, where, what and with whom. One final thought, don't give out your name and address or a lot of guys will be asking you for a favor.

I live in Zimbabwe. Probably a little far for people to come see me for favors it is also the reason that I tackled it myself- no gunsmiths around here. I have had my learner PH licence for 21 years and decided to finally finish it off( university and life intervened). Before I can can get a full guided/ hunters licence, I will need 2 elephant and a buffalo or 3. So I will be working my contacts for some problem animal control in the near future. And I have the shooting exam, 3 scenarios against the clock that I have to pass as well before I go for interviews and proficiency exam.

Nhoro said:

I live in Zimbabwe. Probably a little far for people to come see me for favors it is also the reason that I tackled it myself- no gunsmiths around here. I have had my learner PH licence for 21 years and decided to finally finish it off( university and life intervened). Before I can can get a full guided/ hunters licence, I will need 2 elephant and a buffalo or 3. So I will be working my contacts for some problem animal control in the near future. And I have the shooting exam, 3 scenarios against the clock that I have to pass as well before I go for interviews and proficiency exam.

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With your perseverance, you shouldn't have any trouble with the test. Good luck and good hunting!

Nhoro, from your writing style and ability you certainly fooled me. Although I guess you could have English or American ancestry and live in Zim.

Excellent result Darryl. Expect you to tackle the remaining steps to your PH Licence with the same positive outcome.

Nhoro said:

I live in Zimbabwe. Probably a little far for people to come see me for favors it is also the reason that I tackled it myself- no gunsmiths around here. I have had my learner PH licence for 21 years and decided to finally finish it off( university and life intervened). Before I can can get a full guided/ hunters licence, I will need 2 elephant and a buffalo or 3. So I will be working my contacts for some problem animal control in the near future. And I have the shooting exam, 3 scenarios against the clock that I have to pass as well before I go for interviews and proficiency exam.

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Good luck with finishing it off. The rifle and the license.

BRICKBURN said:

Good luck with finishing it off. The rifle and the license.

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My wife's 550 in .404j had the same exact problem. I worked on the left feed rail, removing metal until a "short" round would line up with the chamber, while maintaining controlled feed. She has already taken 4 elephant and 11 buff, 6 hippo + backup on lion. As you know on the shooting test 10 points are deducted for shooting less than .40 caliber. She would have passed every time (except once due to a injury) if she would have been using the .404j. Looking forward to seeing you in Feb.

Thank you for this very interesting write-up! I really enjoyed reading this. And, good luck with your remaining tests.

I am visiting my brother and he has 416 rigby on the same cz 550 action. His rifle was setup by a good ( now deceased) local gunsmith. He solved the problem in a different way. He made the left rail release the round 5 mm before the chamber. The case engages the bolt face and extractor and feeds the round. Essentially the difficult angle is solved because the back end lifts. What does everyone think, is this still cfr? The bullet is inside the receiver ring and is controlled throughout. It also feeds smoother than mine by releasing earlier from both rails because the round goes straighter into the chamber. Does the nose of the bullet have to be in the chamber before the rail releases ?

Is there a good gunsmithing book on Mauser action feeding?

lockingblock said:

Is there a good gunsmithing book on Mauser action feeding?

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Quite a few, but not that I can access. Online, JBelk does a good mauser extractor article on another forum (not allowed to post a link). I am sure a search will turn it up. Von Gruff posted on this site about proper magazine layout and lists these books : Ludwig Olsen's Mauser Bolt Rifles and De Haas' Bolt Action Rifles.

Shootist43 said:

What I cannot figure out is how or why gun manufacturers don't make use of this information when designing their magazines and followers. After all the info has only been available for 120 years or more.

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Over Christmas, I had some time to think about why manufacturers don't use the info that's been around forever. With .458 win mag, there is a load of space in the front of the magazine (or the back depending on how you load) So do the engineers design the magazine box to fit the belted rim when the round is at the back or at the front of the magazine ? My measurement suggest that they fit the back of the magazine correctly but the front is too narrow. When you cycle the bolt, the rounds naturally push to the front. I did find some people that claimed fitting a block in the front of the magazine solved the problem, maybe by keeping the rounds in the wider magazine box at the back ?The magazine box is also correctly dimensioned but the receiver just under the rail (where the feeding round and supporting round sit) is narrower. The receiver is narrower than the magazine by about 1.1 mm. So the feeding round and supporting round stack steeper and tend to crossover and the supporting round dives down at an angle as you feed the top round.

I realise why so many PH's carry a double rifle. I watched the PH and Guides shooting exams last year, failure to feed and jamming of bolt rifles is more common than we would like to believe (I would guess 65 %). I have been amazed how drills that put pressure on me highlighted my technique and the rifles shortcomings. The smoother and straighter I run the bolt, the faster I am and the less force I need. Slow rough bolt movement often causes the round to move rough and be more resistant.

I am very impressed at your methodical approach to getting it right.

Many is the gunsmith who appears to squeals with sadistic joy when they give the," you should have brought it to me first" speech.

Von S. said:

I am very impressed at your methodical approach to getting it right.

Many is the gunsmith who appears to squeals with sadistic joy when they give the," you should have brought it to me first" speech.

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I would have taken it to a gunsmith but there are none around ! I am amazed that there is very little info online and what there is available is posted by the grey heads amongst us. I have to say that I enjoy doing things myself but it did cause a fair amount of marital friction.