You asked the same question over at Field and Stream Antlers, and here is what DakotaMan had to say in response to your question and in response to the comments of others on the thread you started:
"Those were my experiences and observations and they came from my first antelope hunt with my new Weatherby Mark V Ultralight. I was excited about using this beautiful new rifle but encountered a few issues with its design on my first hunt. I loved the light weight, the look and feel and most of all the 60 degree bolt throw. Those attributes are top notch. I was also told by numerous people that its ability to fire without blowing up is an important feature too but personally I have had this feature on all my rifles. I've never been blown up by any of them and the Weatherby did NOT blow up either. I just don't get as excited about that feature as some others do because I consider it a constant across all my rifles.
I'm sorry to see WAM feels my comments are "BS" but can assure you this factually happened to me. The three Mark V design issues I've been exposed to are not of my making and are part of EVERY Mark V action. You need only look at one to discern for yourself. I don't think of these issues as show stoppers and recognize that I seemed to get hit by multiple problems at once which seems to be quite rare.
Although I observed and experienced design issues in my Mark V receiver, that doesn't mean a Weatherby Mark V is useless, and the Weatherby Vanguard has none of these issues. Not many rifles are perfect and each model has its positives and negatives. You just have to be aware of their issues and guard against any risk that they might expose you to. Like any rifle, if you keep them in the safe or walk out back to sit in a tree stand for your hunt, your exposure to risk is much less than if you are hiking miles from home for days at a time in rugged weather.
I'd like hear from others to know who factually disagrees with these design observations:
FACT #1 - Firing Pin Design. The firing pin screws into the bolt shroud with a small retaining ball that holds it in place. The protrusion of the firing pin from the bolt face is dependent on being on exactly the right firing pin thread as measured by pin protrusion of a few thousandths of an inch. A "short protrusion" of the firing pin is possible causing the bullet primer to dent but not detonate. I've been respectfully told by F&S members that I have no business cleaning or adjusting it. FACTUALLY, (no BS) this is what Weatherby Customer Support advised me to do. NO BS... If you feel this observation is BS, please open it up and LOOK for yourself or at least look at a schematic! Note I am not recommending you open it up because of the risk but if you feel this design is BS go ahead and please look for yourself. Once it is tightened to the appropriate screw thread, it works fine. If it is not adjusted right it fails to fire randomly based on what thread it is ON. If yours fires as expected, leave it alone and don't clean it EVER and it should keep working until it gums up completely. Another alternative is to bring it in to a gunsmith to have it cleaned and hope they know how to do it. If your gunsmith is Weatherby certified (I found one between Atlanta and Montana in Sioux Falls South Dakota), they will know how to do it. Mine came from the factory that way and the very kind and helpful Weatherby Customer Support rep said that it happens occasionally and walked me through the process, recommending extreme caution against losing the retaining ball. I had to wait until I got home from the hunt to do this though because I needed a micrometer and a relatively clean room to catch the BB-sized retaining ball. Please make up your own mind how great a risk losing the retaining ball is for emergency repairs or cleaning. I don't want to mislead anyone... take it out and put it back a few times and see what YOU think. My guess is that this is a rare issue unless you clean your bolt interior or disassemble it for any reason. Then, if you don't know what you are doing, there is a pretty high probability you will mess it up. Just to be completely open, my field failure involved the use of #34 primers because that is all I could get at the time. These are by design the most difficult to detonate with a poor pin strike but I did have failures with other types of primers too since my pin protrusion was measured at only .021.
FACT #2. The trigger can and apparently DOES fail to engage the sear (mine is set at a legal 3 pounds as tested with my fish scale) with the combination of factory lubrication and dust. Mine DID FAIL twice in one hunt on two different antelope (NO BS). It got worse as time went on until I had to stop hunting with it. The Weatherby Customer Support rep was most helpful and stepped me through this as well. They offered to repair it for me but of course it would take weeks during hunting season and they felt I could easily do it myself with the correct solvent. I agreed to try it myself and only send it in to them if absolutely necessary. After cleaning with the regimen recommended by Weatherby Customer Support, it fired with only one failure in 300 tries. I've used it that way since. Weatherby advised that if that wasn't satisfactory I could adjust the trigger to more than 4 pounds and move pull weight up until it worked. It's OK with me for now. With the 60 degree bolt throw, I can re-cycle it real fast if needed. If it happens again, I will put an Timney trigger in it. I won't use it for dangerous game. You may not encounter this but I'd heartily suggest that if you intend to hunt in high wind and blowing dirt/sand where you are walking miles daily in rough conditions, bring some alcohol to dip your trigger group in at least nightly. Remove all lubrication, factory or otherwise... NO BS. Make up your own mind on this. It can and DOES happen, NO BS. Note that after about 50 years of such hunts, this was the first rifle I've ever carried that reacted this way to common prairie hunting conditions. I thought the weather was relatively nice but dust WAS blowing almost constantly for three days... NO BS.
FACT #3. The little screw might come loose. Take a look behind the bolt handle and see if you observe a little slotted screw (the bolt sleeve lock screw). It should be there... NO BS. You may think that there is NO WAY this little screw can come loose. You are welcome to your own opinion on that. However, I highly recommend that you get a small screw driver and check this little screw as part of your routine maintenance. If you are going to be away from home and hiking miles every day in rough conditions (like some of us hunters do NO BS), I suggest you check it periodically. If you don't believe that this screw being loose will stop your shot, please check it out yourself... loosen this screw and take a shot... see if this is BS. I didn't have this happen to me personally (but I now check mine with regular maintenance) but it happened to my buddy. I know him well enough to believe him without doubt. It happened to him in Alaska and like me, he was quite disappointed when it PREVENTED his trophy Dahl sheep shot of a lifetime. I also believe him when he said his guide saw that he had a Mark V and took a small screw driver just in case it would be needed some time during their hunt. It seemed unfortunate that his guide waited until it failed to discuss it with him rather than checking it periodically. My advising you of this design issue is certainly hearsay but I would suggest you not consider it "BS"... check out your screw or hope for the best... your choice. Several on F&S have stated that their screw has NEVER come loose so I guess that means for them at least, it can't.
My accuracy issue is a little different. The lack of accuracy I experienced is an exception for Weatherby rifles. The Ultralight has a very small contour fluted barrel... NO BS... it wanders... NO BS. There is a lump in the forend of the Ultralight to stop it from wandering too far. It is NOT free floated because of this heat distortion issue. Mine shoots like crap... NO BS. That doesn't mean yours will. I talked to a Weatherby Customer Support rep and they said that's the way it is with such a light barrel. The only solution is to put a heavier barrel on it at my cost. I also communicated via email on this issue with someone whose last name was Weatherby. He was sympathetic but concurred. There is NO replacement rifle in the cards for me. I also communicated the three design issues above to him. He didn't seem too happy to hear of these and didn't want to discuss them.
WAM, I realize that since I only shoot accurate rifles, I'm probably one of the few that dusts off my pre-hunt rustiness by shooting lots of prairie dogs way out there before most prairie hunts. I've never had a "short range" or "inaccurate" 25-06 before but could understand that some shooters may be content with that. I don't judge them and hope they don't judge me for choosing accurate firearms, given the choice.
I understand that ultralight barrels may have issues but I've shot plenty of light weight 25-06 barrels that were highly accurate. As a matter of fact (no BS) another buddy has the same rifle in .270 Wby and his is very accurate (although yet another buddy has a .257 Wby that shoots like crap too). My only request is that Weatherby make potential customers aware that it could be quite inaccurate and what they get is all they will get. If anyone knows of anyone at Weatherby who will replace my rifle with one that shoots, I'm all ears! My exchange with Mr. Weatherby didn't go that way.
WAM, perhaps you misunderstood, I was referring to the Mark V itself in the African hunting comment; not the 25-06 cartridge. Even the .416 Weatherby Magnum has the 3 design issues highlighted in items 1 through 3 above. They are not exclusive to the lighter version of this receiver. You certainly did offer to buy the rifle but since it was a gift I have kept it because of the sentimental value. I would love to have Weatherby replace it but I can live with it. I now understand its limitations and won't be caught by surprise. I can watch for these issues and prepare to maintain my rifle during relatively extreme hunting conditions. I'm still fiddling with the barrel trying to squeeze as much out of it as possible by varying barrel pressure. I'll use the rifle for hunting deer and antelope sized game inside 250 yards and that is not a severe limitation for most of us. I really like the 60 degree bolt throw. Even where I had five consecutive miss-fires (four firing pin and one sear slip) on the same running antelope, I never missed an antelope because of these issues... mainly because of the exceptionally fast re-cycle time. My nephew even commented that he thought he saw four unfired cartridges in the air at the same time on one. NOW that could be BS... I think he was just ribbing me.
In closing, let me say to antlers and anyone watching... The Weatherby rifles are a work of art and fine rifles. You will be hard pressed to find a more attractive rifle. Most of them are highly accurate too. The buddy that had the screw problem has nailed lots of game world wide with his 30-378 in the 400 to 700 yards plus range. My comments are not intended to discredit Weatherby rifles; just to make users of those fine rifles aware of a few issues that could catch them off guard at the worst moment. None of us want that to happen and I will openly admit, these failures made my friend and me quite unhappy for a while. I would not want you to have that experience and all it takes is a little preventative maintenance.
jhjimbo - I'm a little surprised by your comment to stay the h#ll away from the poor hunter who experienced these issues. That's a little bit like shooting the messenger which seems beneath you. This happened on my first three day antelope hunt with this new rifle of which I was very proud. I was 50 miles out on the prairie 1,500 miles from home. I did have a back up rifle but I persevered with this rifle because of the challenge and because of the friend who gave it to me (it's not nice to look a gift horse in the mouth). I always appreciate your well thought out comments and hope you will forgive me for telling it like I see it; even it if involved a beloved Weatherby. I only put down my OPINIONS and realize others may unceremoniously call them BS. My best to all and good luck with choosing your rifle. I'd buy another Weatherby, but if it is an ultralight I'd get a written guarantee of full replacement if it couldn't maintain 1.5 MOA."