458 Lott factory chamber vs a reamed from Win Mag chamber

Discussion in '.375 & Up' started by Nhoro, Apr 9, 2020.

  1. Nhoro

    Nhoro AH Veteran

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    Hi All, While doing some research, I noticed some differences between a factory chamber and a reamed from Win Mag chamber. This would impact developed hand loads and is something for hand loaders to be aware of and take extra care when using other peoples loads. If you look at the SAAMI picture of a Win Mag chamber, you will see it has a long 'weatherby ' throat as the chamber goes from cartridge diameter into the barrel/rifling diameter. This design helps the win mag get as much velocity as it can before the bullet is forced into the barrel/lands in a similar way to weatherby rifles. It also means that Win Mag handloads can have the bullet set out of the brass by a long way before it gets close to the rifling. The win mag throat would allow approx. 28 mm (1 1/10 in) of freebore before the rifling. You can pretty much match the length of the Lott cartridge with the right bullet (banded monolithics with lots of crimping grooves). Essentially the freebore extends to approx. 92 mm.

    458 win mag chamber.png

    The Lott chamber is longer but has a more conventional throat. You can see below that the chamber to rifling distance is about 8 mm (1/3 in). The freebore only extends to a total distance of 79.5 mm.

    458 lott.png

    That means if you ream out a Win Mag chamber to Lott, you will be left with almost 10 mm of the long Win Mag throat beyond a factory Lott chamber. This extra 10 mm of free bore is quite significant. I would expect higher velocities from a reamed chamber vs factory and also lower pressures. After all, that is why Weatherby allows so much freebore.Handloaders can also stretch the Lott OAL, seating bullets out for more powder capacity if your mag length allows in a reamed chamber.
     
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  2. bruce moulds

    bruce moulds AH Elite

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    longer freebore = less velocity with the same load, and needs more powder for the same velocity as a shorter throat, with same coal.
    the extra freebore actually allows more powder to be used to hopefully get more velocity.
    some cartridges have a leade angle of about 1/2 degree, while more modern ones seem to standardize on 1 1/2 degrees.
    the lower angle definitely gives less pressure with the same load, or vice versa.
    bruce.
     
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  3. fourfive8

    fourfive8 AH Elite

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    The 458 Win can have a longer throat because there is room for the extra length in standard long length actions/magazines and that allows for more powder capacity with a more shallow bullet seating depth. The extra powder capacity was or can then be used to attempt to reach the advertised marketing muzzle vels for the 500 gr bullet. You may notice many of the bullets designed for the 458 Win have the crimp groove well down the bullet shank indicating a purpose design for more powder capacity. The long freebore in the Weatherby design theoretically helps mitigate a front end pressure spike in the overbore, large powder capacity high vel cartridges. The OAL of the Lott is determined by the length of most common standard long length actions and is around 3.6". Extra freebore in the Lott would serve no useful purpose as the cartridge length, therefore powder capacity, is limited by the 3.6" action length. The exception would be the Lott in a long mag action length (3.75" +/-) allowing for a slightly longer than 3.6" overall cartridge length. A longer freebore in those actions chambered for the Lott then could be used for shallower bullet seating, more powder capacity and mitigate front end pressure spikes similar to the Weatherby theory- I guess? :)
     
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  4. crs

    crs AH Fanatic

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    This subject become a prime example of "beating a dead horse" on other forums a few years ago.
    So much so that the icon for the exercise is commonly seen. Ho Hum!
     

  5. fourfive8

    fourfive8 AH Elite

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    Kind of like the 45-70 vs 45-90 "discussions" :)
     
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  6. CoElkHunter

    CoElkHunter AH Elite

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    So a Lott cartridge in a Lott chambered action or a WM cartridge with bullet extended in the case in either a WM or Lott chambered action are pretty much equal or close in velocity with a given bullet weight? I now have both a CZ WM and Lott and am just about to reload the Lott so I’m trying to process this information in my feeble mind? Maybe some pressure differences? Maybe insignificant? I’ve reloaded some WMs but reloading these straight walled cartridges is still very new to me. Thanks!
     

  7. Forrest Halley

    Forrest Halley AH Enthusiast

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    You're trying to get a deaf horse to listen.

    Hehe I do enjoy the inside jokes.

    Well you've got a Lott so you don't need the WM because it can shoot both...hehe just kidding. Close the can of worms!

    Straight walled cases are not difficult. Easier to save if you minorly booger one up. Google a die set up video and you'll have no trouble. I am also of the school of using your last loaded cartridge to reset your die to that bullet weight or OAL if you have been fooling around with different bullets/weights.
    I am trying to find one .375 bullet weight and one .458 bullet weight for simplicity of powders and components.
     
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  8. fourfive8

    fourfive8 AH Elite

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    Yes, theoretically you can just about duplicate Lott ballistics with the 458 WM if the throat is long enough and is a true freebore and the pressures are kept within parameters with the correct powders. The issue is primarily one of practicality! You'd end up with a cartridge with far too shallow bullet seating to be practical. Pic below shows the seating depth dilemma. 458 Win Mag left and 458 Lott right

    The issue with the 45-70 vs the 45-90 is one of action length limitations particularly in the Win 86 ever gun. I have owned, cast for, swaged for, loaded for and shot MANY rifles (levers and single shots) from 45-70 to 45-110. I have sold off all except for one 45-70 Trapdoor that I've kept for fun. The original 500 gr cast bullet loaded 45-70 at about 2.8" was the longest practical cartridge to fit in the Win 86 lever action. I always got a kick out of "talking shop" at the local gun store or even gunshows about Win lever guns. Almost without exception if I was discussing loads or bullets for the Win 86 and the 45-70 cartridge someone would play the "ya-but I know a guy who has a 45-90" game with a tone of one-up-manship in the statement :) Hah! OK me too. But the truth is that the 45-90 in the 86 action was considered an express cartridge. No advantage with heavier bullets because the case capacity was all used up. The only thing the 45-90 could do in an 86 length action with original loads was to fire a lighter (therefore shorter) bullet, 300-330 gr, faster than the 45-70. Because of that many of the Win 86s in 45-90 have a slower twist... which is a detriment if shooting a heavier bullets in the 45-90. The only real advantage the 45-90 may have shooting a 500 gr bullet with original type loads would be in a single shot because the action is not length limiting (powder capacity limiting) to the cartridge length. Currently for modern ammo and loads with strong actions and modern smokeless powders and modern bullets the 45-70 makes even more sense than the 45-90.

    458 WM and Lott.jpg
     

  9. crs

    crs AH Fanatic

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    No live horses left to ride these days.

    Time for a nap.
     
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  10. Forrest Halley

    Forrest Halley AH Enthusiast

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    @fourfive8 , your truth bombs are ruining story time. The revelation of the American definition of express rifle may well break some hearts. The revelation of the case capacity issue may well cause a great deal more heartbreak. I guess it's okay to shoot a 450 grain bullet as fast as a 500 grain in a longer case. I sit typing this in the company of a .243 loaded with heavy boat tails and cool burning powder under no illusion of its full capabilities. I can only wonder why others cannot do the same.
     
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  11. CoElkHunter

    CoElkHunter AH Elite

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    Great illustrated comparison! As soon as I get some REAL time off from work, I’m going to load some 450 and 500gr Barnes TSXs behind a bunch of 748W and light em off in both my WM and new to me Lott!
     

  12. CoElkHunter

    CoElkHunter AH Elite

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    Yeah, well get up from your nap, go the range with a rifle in .458 something, and wake yourself up! Ha! Ha!
     

  13. CoElkHunter

    CoElkHunter AH Elite

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    Well, I couldn’t find someone here on AH who lives in Colorado who would let me shoot or even has a Lott, so I bought a CZ off GB for a good price. I bought a couple of boxes of 500gr Nosler partitions during their last sale and have fired ten rounds through the Lott. I love it! I love my WM too, and in particular just love the straight walled cases and .458 caliber for reloading. I guess I’m just a “simpleton “, but one has to enjoy something in life with regards to shooting and reloading large bore rifles!
     
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  14. Forrest Halley

    Forrest Halley AH Enthusiast

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    The Nosler ammo feels good shooting. It must not be worth a darn as far as velocity. No Chrono for me yet. My reloads are not as enjoyable. I'm a simple man too.
     
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  15. fourfive8

    fourfive8 AH Elite

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    A chronograph is certainly an asset for any reloader. It took me years to realize it and get one. I don't use one every time I shoot of course or even every time I try a new load. But for serious load work up for hunting loads that absolutely must work reliably and consistently- yes a most valuable asset. I've been using mine a lot lately in working and playing with 375 HH loads. A target by itself will not tell the whole story but coupled with a chronograph, together they will tell a much more complete story. Good record keeping, knowledge of pressure signs, a chronograph and a target is about the best most of us can do sans full blown and PITA pressure testing equipment.

    I shot a pretty nice target a couple of days ago with the 375 and a certain hunting bullet and a powder I hadn't tried yet. The recoil seemed stiff, the target showed a good group but the mean velocity was much too high, higher than average max and the SD was well beyond what I am comfortable with and there was one velocity outlier. The load was at least 3 grains less than a published mid level load- go figure. The velocity data provided by the chronograph plainly showed me that load was a NO GO!

    I've found that the very simple F1 Shooting Chrony does everything I need. I've used some fancy ones belonging to friends and there are all manner out there and while some calculate everything including the futures price of pork bellies, IMO, simple is good. I learned how to set up my simple little unit pretty quickly when others are shooting and how to do it consistently for best data. Shoot, record vel with a pencil and paper after each shot. Take the shot string raw data home and use a simple SD calculator for the SD and mean velocity- then enter it into my load log.
     
    Last edited: Apr 13, 2020
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  16. Nhoro

    Nhoro AH Veteran

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    I would appreciate if you READ the topic and make a meaningful contribution. It is a discussion of two different LOTT chambers- factory reamed and gunsmith reamed-and how that will have different characteristics because of the parent of one of those chambers.
     
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  17. Nhoro

    Nhoro AH Veteran

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    Thanks for this. I always thought Weatherby allowed there bullets to get up to speed before engraving the rifling and slowing down but of course that is when pressure spikes. So the long throat is really to stop pressure going through the roof. The Win Mag doesnt have that problem so what do you think the designers had planned ? There is over an inch of freebore, there is no way that any bullet could be set out that far. It seems like a waste of time to me.

    Secondly, with the pressure stabilizing effect, doesnt that mean Lott from Win Mag chambers would take high pressure loads and cope with them much better than a factory chamber ? Or is this likely to be a minor difference because a Lott is not as extreme as a 460 Weatherby or 378 Weatherby.
     

  18. fourfive8

    fourfive8 AH Elite

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    Good questions Nhoro. After looking at quite a few sources over the years, this is as I close as I can come to understanding it.

    These exact questions have been asked on other boards and forums for a few years now. And there seems to be really no concrete absolutes because of all the variations of reamers and throaters available. According to SAAMI and CIP, I think it is a given that most factory WM chambers will have a fairly long, shallow angled tapered throat with no true parallel throat section. So in the sense of a conventional freebore throat- no the WM doesn't have one, but the long tapered throat will have the same effect of reducing the front end pressure spike. There are more variations among Lott chambers (reamers). SAAMI shows one and CIP shows another. But I think the best guess would be that a 458 Lott reamer would "clean up" an entire 458 WM chamber including the throat. If the zigs met with the zags between a particular Lott reamer and a particular WM chamber there may be a small chance for some untouched area left in the WM chamber. The obvious solution to prevent that, prior to reaming, would be to cut off a thread or two of the WM. But cutting off then clocking a barrel is much, much! easier said than done. And I think a long freebore and/or throat will mitigate some of the high pressure problems that occur early in the burn cycle for most if not all cartridges. But there may be trade offs to some long throat designs. Some may allow for partially unsupported bullet travel before full land engagement and the area in many chambers, just in front of the case mouth, is prone to carbon build up. :(

    I would think that during the R&D of the WM until its introduction in 1956, both the rifle manufacturing and ammo sections of Winchester worked closely together in attempting to achieve that pre-conceived marketing target velocity for the 510 gr bullet of 2150 fps. One fudge was doing some testing with a 26" barrel. Because of case capacity limits they also had to use extremely compressed powder charges of double based powder- so much so in the earlier ammo, bullets had to be glued into the case to prevent future movement because of that compression. As part of that development, during pressure testing, I would bet the long throat was purpose designed to allow for both maximum powder capacity by shallow bullet seating and to allow "pushing the envelope" with the pressures required in the attempt to get a 510 gr bullet (or even a 500 gr bullet) to 2150 fps. Slightly modifying the shape of the pressure curve using a long throat design would have been obvious to the ballisticians at the time working on the WM and its marketing objectives.
     
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  19. Forrest Halley

    Forrest Halley AH Enthusiast

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    .458 WM, because you glued bullets in to make a stated velocity, I'm out.
     

  20. fourfive8

    fourfive8 AH Elite

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    :) That much compression of a heavily coated ball powder... add a little heat and voila! Not hard to understand why there was at least a potential problem for the earliest of the WM ammo. I think that was recognized and corrected not long after the first reports started to filter back from the field. But even as early as Winchester made the corrections to that ammo... the perception was cast and the "damage" had been done.
     
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