ZKK-602 feeding problem

Tawporn

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First I have to tell all of you that I newbie in big bore rifle . I just got my brno zkk-602 in .375 h&h from my cousin last few weeks with all of his old cartridge (all factory load) most of them feed and work fine except PMP solid . anyone ever have problem with this cartridge ? and what should I do?
 

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I do not want to sound sarcastic, but my recommendation is do not use PMP solids. Seriously I am not familiar with PMP solids. Are they a round point or flat point. Many DG rifles do not like flat nose bullets.

Before you do that hunt of a lifetime find out what cartridges will NOT properly feed. Also find out if your ZKK-602 will single feed!

After a very dangerous situation we found that a certain brand with a round plastic tipped
solid would not feed 100% reliably thru our CZ-550s. Slow yes, fast no!

Cheers, Lon
 

Tawporn

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I do not want to sound sarcastic, but my recommendation is do not use PMP solids. Seriously I am not familiar with PMP solids. Are they a round point or flat point. Many DG rifles do not like flat nose bullets.

Before you do that hunt of a lifetime find out what cartridges will NOT properly feed. Also find out if your ZKK-602 will single feed!

After a very dangerous situation we found that a certain brand with a round plastic tipped
solid would not feed 100% reliably thru our CZ-550s. Slow yes, fast no!

Cheers, Lon
This is one of cartridge that have problem. Look like they not fully seat in chamber that why I cannot close a bolt

58A4EFEC-0721-4FD6-976E-C738D082E554.jpeg
 
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fourfive8

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I have some experience with the BRNO 602 in 375HH with various bullet designs. I haven’t noted any specific problem feeding into the chamber with a variety of bullets. BUT, I do note that in the BRNO, and I assume the 550, the angle the cartridge transitions from magazine into chamber is steeper than in other bolt guns I have experience with namely CRF Win 70s. With the BRNO 375, I can feel an ever so slight zone of resistance (friction) as the round chambers likely because of that angle of entry into the chamber.

Having said that, your issue sounds more like slightly oversized ammo in some dimension possibly coupled with a “minimum” chamber. Those dimensions can include- total length, throat length and various diameters. I’ve also noted the chamber in my BRNO 375 to be close to “minimum”spec. I reload exclusively so can only guess about any particular brand of ammo.

And as others have posted- make sure of reliable function of any ammo for DG purposes. Important to determine the SPECIFIC cause of the issue and correct it.
 

fourfive8

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The most important part may be positively identifying the cause- then correcting it (or avoiding it). With a single shot or double rifle, it is very easy to either eliminate or ID some causes for failure to fully chamber or resistance to chambering. It can also be done with a bolt gun. Open the bolt, hold the rifle vertically with muzzle down. Drop a round as directly as possible into the chamber. If you hear a solid "plunk", chances are the round has been stopped by the headspace control... in this case the belt. If the round simply "slides" to a stop in the chamber without a solid "plunk" sound, chances are there is some dimension of the cartridge that is over spec for the chamber, throat or leade. If that happens you may smoke (or mark with a felt tip) the surface of the case and bullet, drop it into the chamber and apply force with your finger then inspect the cartridge for interference markings on the cartridge or bullet. If there is abnormal chambering resistance, you may have to lightly tap the cartridge out of the chamber with a cleaning rod inserted from the muzzle.

After careful study of the loaded round you pictured, it may be that particular bullet is simply too long for easy cycling. The round nose is sticking out too far... for lack of better wording. So when the cartridge makes the "turn" so to speak as it aligns itself into the chamber, the end of the nose is contacting the side of the chamber in such a way that prevents chambering or resistance free chambering. You'll have to investigate more to pin that down. Also, marking or smoking the bullet may help ID that issue. Good luck with resolution!
 

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So is it not feeding properly from the magazine or is not chambering properly?
 

Tawporn

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So is it not feeding properly from the magazine or is not chambering properly?
Both sir . Hard to feed from magazine(have to force) and cannot seat in chamber properly . Having a gap nearly 1 mm when I compare with normal one.
 

fourfive8

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@Tawporn,
Not sure what you mean by gap? No matter. Give me a day or so to put together some extra long roundnose cartridges for my 602 and do a little experimenting to see if I can cause the same feeding problems. I don't think I have any exact copy of that roundness profile in your picture but I do have some older WW 300 gr FMJ roundnose "solids" I can play with.

If I can cause the same issue on purpose, I'll report the specs of the cartridge, describe the issue and maybe it will help isolate the problem. Especially so if our rifles are near the same DOM. Mine was made in about 1994.
 

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I had a BRNO 375, the bolt would not close on the “Go” gauge. It would load and fire The ammo I fed it. (Reloads with federal brass)
 

Neil Molendyk

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I had a similar problem with my CZ550 in 416 Rigby. With handloads of identical cartridge overall length, Hornady both DGS and DGX did not want to ramp from the magazine into the chamber easily. With Swift A Frame and Breakaway solids the feeding and chambering was smooth as butter. I examined the angle and contour from both Hornady and Swift and there was quite a significant difference. Needless to say I went with the Swift bullets and only used the Hornadys for practice. Better to know what works best before going on your hunt.
 

Tawporn

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After read all of your advice . I just test test one of problem cartridge with fit checker agent from my dental office and found metal exposed as picture . After I polish the metal exposed point , It’s feed from magazine more easier and the bolt close properly .The question is this scratch is normal ?(I decide to avoid all of my pmp stamp cartridge and will use these test round as dummy)

image.jpg
0FAA5635-A875-411C-A1A9-78D00E8F24D1.jpeg
BAEC620E-7186-4752-8BEA-D05980219FA4.jpeg
 
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fourfive8

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OK I can't quite make out scuffs on case body in your photo but do see the scuffs on the bullet's nose. That looks like typical ramp contact scuff mark as the nose hits the ramp to begin the process of angling up and out of the magazine.

I did some testing using my BRNO 375 to see, in detail, the mechanics of the feeding/chambering process. As I posted earlier the only thing I notice different with the rifle is the angle of transition between magazine and chamber is greater in the BRNO than in the Win M70.

I experimented with 300 gr WW FMJ round nose bullets seated to different depths to see if I could cause a jam or unusual chambering resistance. I could not. I tried the bullet seated out to a cartridge OAL of maximum magazine capacity length of approximately 3.800" and it fed out of the magazine fine and entered the chamber fine. That shallow bullet seating depth for the 3.8" OAL exceeded the throat/leade length of the chamber and the bullet contacted the lands before the cartridge fully chambered. I seated that bullet deeper for an OAL of 3.750". That is the "jam" length for a cartridge with that bullet in my chamber. Any longer and and there is definite, hard resistance caused by land contact. I cycled/chambered/extracted the 3.750" length cartridge without issue. I seated a bullet very deep for an OAL of 3.375". It cycled/chambered/exracted without issue.

To reload /resize these test cartridges I used a standard RCBS FL 375 HH die. The loaded cartridge measurements are: case trim length- 2.845". Neck diameter- .398". Upper body diameter- .450". Lower body at web diameter- .510".

The land contact area for this WW FMJ bullet in my chamber is just forward of the cannelure. When checking for OAL jam length, you should see land marks around the circumference of the bullet at the area of contact- one mark for each land. The location of these marks on the bullet will vary depending upon dimensions and shape of chamber's leade and profile of bullet.

I examined the bolt head and tested in hand, by feel, to judge how smooth the entry of the rimmed case head was into the CRF position on the bolt face as it is captured by the extractor. You may check this to see if there is any bur or obstruction to full engagement as the bolt picks up and pushes the case forward while encountering that transition angle when the bullet nose slides up the feed ramp. There has to be some clearance, sloppiness of fit or flex of the extractor for the case head to slightly pivot during that angled transition while being held by the extractor. The cartridge starts parallel to the chamber as it sits in the magazine, the bolt head contacts the case base and starts pushing forward, the cartridge angles up as the bullet's nose slides up the feed ramp toward the chamber, then as the body clears the magazine and slides over the ramp it again returns to parallel with the chamber as it enters for full chambering. That's two angled "turns" for a rigid cartridge while the extractor maintains control of the cartridge during the feed cycle. :)

I've attached photos showing most of this. It may very well be an oversized ammo issue with either wrong bullet profile, too great a diameter of the bullet's nose section, too great a diameter at one of the key points of the case itself, too long a case or neck where the cartridge case is too long for the chamber (BTW, that is an especially dangerous condition because if forced into the chamber in effect locking the bullet in place at the end of the chamber neck. This can and usually does casue pressure to sky rocket pressure). Be sure to check case trim length- should be between 2.840" and 2.845".

Hope you can find the problem and solve it or avoid it.

375 brno ramp contact.JPG

375 brno feed mag max.jpeg


375 brno test round.JPG


375 brno bolt head capture.JPG
 
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baxterb

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I'm going to take a few guesses here...

Are the remaining cartridges you are using pointed? Or are some also round nosed solids? Are the PMPs 300 grains or 286?


I'm not that familiar with the PMP, so have looked them up. It looks like they carry the diameter of the bullet farther forward than most bullets. To the point, I found a picture that shows rifling marks well ahead of the cannelure. In your picture above, it even looks as though the bullet actually sightly increases in diameter just ahead of the case mouth - this would cause the rifling to engrave in that swelled area. So, where am I going with this...??

I think what's happening is that the fuller diameter bullet toward the tip is pushing the cartridge left (or right depending on which side you are feeding from) too soon - before the case is ready to be released from the rails of the action. This is essentially locking the cartridge between the bolt face, the action rails, and the bullet nose on the feed ramp.

The 375, due to that soft, sloping shoulder, is known for very slick feeding. My guess is a little work on the feed ramp and/or rails will solve this.

BUT... if I were you, I'd try several brands of solids to see if there were one that worked perfect and stick with it.

Feeding can be tricky - there are many things going on at once, usually a matter of working to isolate a single issue, but solving one can cause another.

CAn you video the feeding?
 

Tawporn

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I'm going to take a few guesses here...

Are the remaining cartridges you are using pointed? Or are some also round nosed solids? Are the PMPs 300 grains or 286?


I'm not that familiar with the PMP, so have looked them up. It looks like they carry the diameter of the bullet farther forward than most bullets. To the point, I found a picture that shows rifling marks well ahead of the cannelure. In your picture above, it even looks as though the bullet actually sightly increases in diameter just ahead of the case mouth - this would cause the rifling to engrave in that swelled area. So, where am I going with this...??

I think what's happening is that the fuller diameter bullet toward the tip is pushing the cartridge left (or right depending on which side you are feeding from) too soon - before the case is ready to be released from the rails of the action. This is essentially locking the cartridge between the bolt face, the action rails, and the bullet nose on the feed ramp.

The 375, due to that soft, sloping shoulder, is known for very slick feeding. My guess is a little work on the feed ramp and/or rails will solve this.

BUT... if I were you, I'd try several brands of solids to see if there were one that worked perfect and stick with it.

Feeding can be tricky - there are many things going on at once, usually a matter of working to isolate a single issue, but solving one can cause another.

CAn you video the feeding?
Other round nose (all with WW super stamp) feed fine sir .
 

baxterb

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Describe what's happening as the round feeds. Can you take pics of it as you feed the round and show how/where it fails?
 

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