Best Velocity for Precision?

Discussion in 'The Ammo & Reloading Forum' started by Josh Smith, Dec 3, 2011.

  1. Josh Smith

    Josh Smith Member

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    Hi Folks,

    I'm wondering if there's a general rule of thumb with regard to accuracy from certain weight (or length) bullets from a certain twist.

    For example, if I load a .30 caliber 150 grain round for a 1:10 twist, I might be able to adjust the load to anywhere from 2200fps to 3000fps. But would the highest precision be found in around 2400fps to 2600fps?

    How exactly does this work? I'm mostly into milsurps and I don't suppose the militaries of the world pay particular attention to precision except in certain specialized applications.

    I do like to experiment, but is there a velocity range in which I should look for the best precision?

    I do always start at the starting loads and work up.

    Thanks!

    Josh
  2. reynolds357

    reynolds357 Former Guest

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    Your factors that are most important to accuracy are velocity consistency and barrel harmonics. Many of my rifles accuracy load is actually above max. My heavy barrel bench rest rifles (in which harmonics play only a miniscule role) seem to be most accurate wherever velocity is most consistent.
  3. Caneman

    Caneman Active Member

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    at ignition the powder generates pressure, and this pressure moves as a wave down the barrel and back... it starts at the breech and moves to the muzzle then back again, doing this back and forth until in dampens to nothing... this happens very fast, of course...

    wherever the pressure wave is on your barrel it alters the original design diameter, if the pressure wave is at the muzzle at the same time your bullet is then you will have maximum variance in accuracy... however, if your bullet exits the muzzle when the pressure wave is at the breech then the barrel will retain the design diameter and you will have maximum accuracy...

    here is a simulation of what happens (not exactly but close):

    [​IMG]

    there are two ways to find what load is needed with your choice of powder, bullet, and rifle, to achieve maximum accuracy: the ladder test, and quick load.

    there was a good thread on here a week or so ago for doing the ladder test... the ladder test won't tell you which powder to use but it will help you find the most accurate load with that powder...

    if you want to use quick load then read this link and it explains the whole process: Optimal Barrel Time QL is great at finding powders that work well with your gun, and does a pretty good job of suggesting which load is needed, although you need a chrony with QL to use the OBT method...

    i really like using quick load, it has not let me down with three different rifle calibers to find accurate powders and loads for my bullet of choice...

    have fun!
    Last edited: Dec 3, 2011
  4. cpttango30

    cpttango30 Guest

    I always start in the middle of the load range and work a few grains up and down. If I get nothing I like I will work up a little.

    It really depends on the harmonics of your barrel and gun.
  5. JLA

    JLA Well-Known Member

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    As a general rule, if the barrel has a twist rate thats more than the bullet being used requires, then yu will find better accuracy at lower velocities.

    Bullets require a certian RPM to stabilize. rifling pitch and velocity are the vehicles that impart those RPMs. so if you have a 10 twist .30 cal barrel, and 10 twist will stabilize up to 220 gr .30 cal bullets, but you want to shoot 150 gr .30 cals, then you will most likely find your best accuracy at a lower velocity, where if you wanted to shoot the 220s, then youd most likely have to run your loads as hot as they can safely be ran to get the bullets to stabilize.

    Of course this is all dependent on the barreled actions ability to consistently absorb recoil forces and settle back intot he same position everytime.

    And also greatly dependent upon the loads consistency as well.

    So as the others have said, there are far more important things to rifle accuracy. ;)
  6. Josh Smith

    Josh Smith Member

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    Thanks folks.

    Here's the deal: I'm actually above max according to Hornady on the 7.62x54R loads. I use 47 grains of Varget. This is Hodgdon starting load, but 0.5grns above max according to Hornady. I did call Hodgdon and they assured me the pressure was safe. That load is pushing around 2700FPS from their test barrel.

    The 7.92x57J gets loaded with 46.5 grains of Varget, which, according to Hornady's test barrel works out to something around 2550FPS. Hornady's shows a bit faster. Additionally, Hornady's loads show this as mid-range while Hodgdon shows it as 1grn over starting.

    Now, I'm not sure that pushing the 7.62x54R as fast as I am is accomplishing anything. I'd sort of like to start working backwards on that cartridge, but especially on the 7.92x57J load using Hornady's data, as I'm not real comfortable pushing the old Gew88 quite that fast.

    I'd like to shoot for around 2500fps in both, bumping velocity up or down a few feet per second to stabilize the bullet as needed.

    The longest shot I can foresee ever taking would be 200 meters or so. Certainly no more than that, and probably not that far as there are only a couple places where I could take a shot that far, don't know why I would, and would have trouble seeing much past it with my 20/40 vision which I feel is a bad habit to correct when shooting if one carries a firearm for defense.

    I'll be saving powder, brass, and undue wear on the rifles, especially the old German gal. I'm still in pressure specs for Gooey's action, but not by a whole heck of a lot. No reason to stress it.

    The Mosinka I don't think could care less about how much stress I put the action under, but because of the primitive gas venting system (it does have one; you can see it if you smoke the action with the bolt closed, but it's certainly not up to, say, Remington 700 standards), I'd rather not push it too high, either.

    Looking back on performance, I really sort of like the old .30-40 Krag, which ran around 2500fps. Heck, the .30-30 runs less and gets used plenty!

    Does anyone see any practical disadvantages to loading the old working gals down to 2500FPS give or take a few feet per second? I started low and worked up, and now would like to fall back a bit.

    Any and all thoughts are welcome.

    Thank you!

    Josh
  7. LDBennett

    LDBennett Well-Known Member

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    Why are rifles sensitive to different load levels when it comes to best accuracy? Here's why (and it is similar to what was presented above but not quite):

    When the cartridge goes off it starts the barrel moving in a whipping action. If the muzzle ends up in the whipping action near the original center any changes in the load impacts the accuracy the most because the barrel is moving the fastest there. But it the bullet exits when the barrel is turning around to go the other way the muzzle is stopped or nearly so and slight reloading variations have the least effect on accuracy.

    By trying different combos of primers, bullets, powder and powder weights you are searching out that point where the barrel has whipped to its extreme and is nearly stopped. That point could be anywhere in the load level (faster, slower, ???). You must step through all load levels to find that magic point.

    Now, if your barrel is touched by the stock and you hold the gun differently between shots or the weather changes from the last time you shot the gun then not only might the zero change but the whipping might also be effected by the change in the harmonics of the barrel and rate at which the barrel whips. That is why we free float barrels.

    As JLA points out the stability of the bullet in flight (think "bullet pass" in football) is effected by how fast the bullet is spinning. Get the twist too slow for the length (not weight) of the bullet and it wobbles in flight causing drag and the groups spread. Get it too fast and the bullet may fly apart (yes, it happens!). Velocity affects the RPM's the bullet spins at so sometimes the day can be saved by reducing the velocity. The rule of thumb is the Greenhill formula for twist rates as a function of the bullet diameter and its length (heavy bullets are typically longer).

    Hope this helps.

    LDBennett
  8. Josh Smith

    Josh Smith Member

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    Hi Guys,

    I'm trying to keep the bullets on the lighter side because, in the case of the 7.92J and the Gooey rifle, I don't want to be any harder on that old action than I have to be.

    The 7.62x54R gets 147 to 150 grain bullets too, because I bought (five hundred, maybe?) years back for like $50, which seemed like a good price at the time for pulled bullets when stuff was hard to find, powder, primers, etc.

    So you're saying that I will probably find best precision up around 2800fps with the Mosinka? I have plenty of room to work either which way.

    The original 7.92x57J load used a 220 grain bullet. Loading 200 grain jacketed round nose gets me very, very good precision, but I'm not 100% sure that the heavier bullets aren't stressing the action, even with a relatively sedate 2200fps (or so).

    Plus, those 0.318" bullets are expensive! About 37 cents apiece for the 150 grain, the cheapest, all the way up to about 75 cents apiece for the 200 grainers.

    I really need to call Lee about a custom sizer...

    I'm going to call the 47 grains of Varget a middle-of-the-road load for the 147 to 150 grain bullets in the 7.62x54R. Might bump it up to 47.2 grains as I found some notes and recall that as being my accuracy load. A 47 grain load is published at a mean of 2800fps, and only one surplus load I can find pushes it into the realm of 3000fps. We'll see what happens there, I guess!

    As for the 7.92x57J, I only came off the minimum of 45.5 grains (around 2500fps) because I was backing primers out. Turns out that was a bad run of R-P cases; Winchester cases haven't done that (formed them from .30-06).

    I'm not really sure where I need to set my max for the J load at, but I'm likely very near it. These Gew88 rifles are known to hold up to surplus ammo which uses a higher velocity and larger bullet than is recommended, but this definitely shortens life and Turkish armorers noted catastrophic failures in WWI and II with the new JS ammo an the Gew88's action.

    So, I'm going to work backwards on that one until I find optimum precision in the other direction. According to Hornady, I can go all the way down to 43.5 grains, their starting load, for a published 2400fps. Plenty of room to play there.

    I need to actually buy a chronograph now as the guy I used to borrow one from passed back in Feb, but I just only found out about it recently! Life is strange like that sometimes. Might ask for one for Christmas.

    I'm concerned about wearing out brass but have yet to find any signs of anything. I just keep them trimmed and run a wire to check for case head separation. I only neck size so as not to overwork the brass in generously proportioned chambers. How many loadings is brass usually good for?

    But anyway, does all this sound like a sane, safe plan gents?

    Thanks!

    Josh
  9. warriflefan

    warriflefan New Member

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    I have been trying 185 gn cast lead loads over 43 gn of varget for a starter load. It is nowhere near as accurate as the 180 gn winchester sp factory loads. Does anyone know what kind of components winchester uses for their 7.62x54r?
  10. JLA

    JLA Well-Known Member

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    The bullets themselves wont stress the actions. Pressures used to drive the bullet will though. If the 200 grainers shoot good then use em. Even at 2200 fps they are probably only running about 45-50K psi.. Thats about .30-40 Krag pressure or .303 brit. pressure. I think youre more than OK, especially since the mauser action, even the '88, is leagues stronger than the krag or the brit enfield running similar weight bullets at similar velocities.
  11. LDBennett

    LDBennett Well-Known Member

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    For 7.62x54R you need to slug the barrel to find out what the Russians made the barrel. But most are much larger than the .308 that the "7.62" indicates. The bullet I found (as did many others) that works best in Mosin Nagants is the 303 british bullet at around .312 inches. Most of the guns are from about there to as much as .314 or even more for some. DO NOT use Mauser bullets. I believe they are at .323.

    LDBennett
  12. JLA

    JLA Well-Known Member

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    Yes, the 8mm (7.92X57 or 7.9MM) mauser JS bore is .323, the older pre WW2 J bores ran .318 and the russian 7.62X54R is .310" but i have seen examples of these run from .307 (a lucky bore 1928 finn) to .316 (a shot out corroded tula I had once). Do slug your bores to determine the diameter. its a relatively simple procedure accomplished by hammering a soft lead muzzle loader ball down the first inch or so of bore. A little case lube on the ball ensures it wont stick. Some folks like to slug the entire length of the bore to get the tightest dimension, but i find the only dimension that matters is at the muzzle, as this is where its usually loosest.
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