my loads do not approach reloading book velocities?

Discussion in 'Reloading' started by skeeterboud, Mar 1, 2014.

  1. skeeterboud

    skeeterboud Well-Known Member

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    i know there must be dozens of variables, but nary a load, in any grain weight, rivals that of published reloading books???? my cheapo 130$ chrony mirrors a friends high end readings, so i checked my chrono. Any powder/grain/primer etc combo. i try is 60-180 fps slower than what nosler/hornday reloading books publish for the same grain load. Velocities are slower regardless of ambient temps, although not as slow the wamer it is.. is this commom?
     
  2. jmason

    jmason Well-Known Member

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    how long is your barrel compared to what they used in the book? how are you comparing? by weight of powder charge?

    If your barrel is shorter it won't produce top end speeds. You lot of powder could also be on the slow end.
     
  3. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    Many variables including bore/ throat condition and loosness, chamber dimensions, barrel length, component lots, temp., and shooter (yes shooter- how much you roll with the recoil and the clothing you wear makes some difference).

    I usually land rather close to specs but I've seen up to 300 fps difference from book spec's to what I actually get in the real world. I've got one rifle with a sub moa load performing 200+ fps under right now; trouble is my chrono was on the fritz when I developed the load and I have 450 loaded at present. I think I'll shoot up the ammo and rework the load afterward.
     
  4. dah605

    dah605 Well-Known Member

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    Also compare the brand of case and primer to the published load data. Different brands of cases have different capacities, which directly relates to the pressure. Seating depth can also have an impact on the pressure curve.

    I haven't done any direct comparisons of the various primers, so I can't speak to that as something that would be a big impact on velocity, however, I know to work up a load after changing the primer. This tells me that they can have an impact on the overall pressure.

    As far as chronographs go, the placement of the chronograph can also show a difference, but I would think that the published data would be using something like an Oehler out in front of the barrel. I've seen higher readings from my Magnetospeed because it is right on the muzzle when compared to my CE chrono.

    -David
     
  5. 556

    556 Well-Known Member

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    I have the same problem with my sons Ruger M77 MKII 257 Roberts. No matter what load I try I am always 150 - 250 FPS slow with majority of the loads are closer to 250 FPS slower. My barrel is a 22" barrel; 2" shorter than what the loading manuals use and realize I will be somewhat slower. This has been very frustrating. At first I thought it was my chronograph. I recently purchased a Magneto Speed and still the same results. I come to the conclusion it is probably the chamber, throat, or just the barrel in general. At some point I would like to put another barrel on it.
     
  6. LoneTraveler

    LoneTraveler Well-Known Member

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    There is so many variables it could take some checking to find the problem. My old 222 Rem, usually comes up short on book posted speed. My 300 WSM shoots faster than posted velocities. Usually 100 to 150 ft. faster. Primer, powder even bullets could change from one lot to the other. Some barrels can be fast or slow. Barrel length can effect speed. I have a Pac Model 1 chronograph. It seems to work best about 20 feet from the muzzle. To close it becomes unpredictable. Good luck in getting the problem you are having.
     
  7. Michael Courtney

    Michael Courtney Silver Member

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    In my experience, most factory barrels are a bit on the slow side, especially the less expensive ones. A gun that's not built to tight tolerances can possibly create high pressure situations, so manufacturers tend to adjust the dimensions so the tolerances produce guns unlikely to produce overpressures. The combinations of loose chambers, long throats, and bore sizes on the large side tend to produce less than peak chamber pressures which in turn produce lower velocities.
     
  8. Engineering101

    Engineering101 Well-Known Member

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    skeeterboud

    The comments about chamber size, powder burn rate, etc. are right on. However there is one thing not mentioned that will help a little. You won't get all of the velocity accounted for but some of it if you align your chrono with a laser bore sighter. This is because any misalignment results in reduced velocity readings. For example, ten degrees of misalignment in both pitch and yaw will make 3,000 fps true velocity read near 2,900 fps. (That is why the magnetospeeds are nice because they are automatically aligned with the bore.)

    Anyway to do this with a normal chrono, aim the rifle at the target, put the laser bore sighter in the bore and then put marked (with a grid) see through plastic targets on each chrono sky screens to catch the laser. When the laser hits the same spot on the plastic targets on both sky screens, it is perfectly aligned.
     
  9. Garycrow

    Garycrow Well-Known Member

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    It's pretty standard for handloads to not make book velocity. When they work up loads for the manuals they usually use pressure barrels that have minimum dimension bores and have the chamber cut to minimum SAAMI dimensions. They do this so the data they get and publish will be for a worst case scenario as far as pressure goes. By using minimum spec equipment they guarantee that they will be generating the highest pressure that round is capable of with that powder/bullet combination. Any factory rifle out there is going to be looser so will generate less pressure than their test barrel. Less pressure also means less velocity so that's why your velocities are lower than theirs.

    You didn't hear me say it, but a judicious handloader can usually match the book velocity assuming the same length barrel as the test rig and the pressures will still be within limits. However, this means going over book max loads sometimes and working up to it with a chronograph. Since pressure and velocity are correlated, if you match the book velocity then you've matched the book pressure pretty closely, at least close enough that you're not going to damage your rifle or hurt yourself.

    I'll get howls of protest of how you should never go over book max, that's just the lawyer driven society we live in. Reloading manuals are a guide, not a bible. They're only completely accurate for the particular circumstances they were developed under. Your rifle isn't an exact copy of theirs so loads have to be tuned to your rifle. Sometimes that means you have to stop below what's published and sometimes it's conservative. You have to let your rifle tell you what works.
     
  10. woods

    woods Well-Known Member

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    Also the deeper you seat the lower your pressure will be and the lower your velocity will be (within the normal range of jump to lands of against the lands to ~.250" off). If you have a restrictive magazine and have a large jump then your velocity will suffer.

    Yes I know Weatherby's have a long jump but they make up for it with added powder to bring the larger combustion chamber up to pressure.

    Just another one of the many variables
     
  11. Kennibear

    Kennibear Well-Known Member

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    If you reload pistol ammo you will find an even greater disparity between published velocity and the speed your gun generates. I find Hornady and Sierra to be closer to published and Nosler to be pretty off. The data listed on the posts here are backed up with field velocity data and so is pretty good.

    Too many variables to simplify this but oversize chambers and bores along with shorter barrels are probably the leading causes. I had a Form 1 M16 and a Frankenstein AR that both had 20" barrels. The AR had a match chamber that I cut myself as well as a tight bore and the F1/M16 had a Colt factory average barrel. The Frankenstein was a good 100 fps faster with everything and developed pressure signs sooner too. My middle son had a Remington 700 in 30/06 w/ 24" barrel and I have a custom Mauser 30/06 with a 27" barrel and they both posted identical velocities. His was a "fast" gun, the only one I have actually found as other 30/06's posted slower velocities with the same ammo. I have no clue as to why his 700 was so fast. Could've kicked him into next week when he sold it....

    I don't chase down that "lost" velocity anymore. The loading manuals are strangled by the lawsuits and you need only read some of the 70's manuals to see how far the loads have been cut back. If you think your gun may not be cranking out the speed it should, sell it and get another. Works on cars too....

    KB
     
  12. LaHunter

    LaHunter Well-Known Member

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    I see the same results with my rifle: Slower mv in real life than what is published in the manual, by about 100 fps. I have a M700 action with Krieger 26" barrel 7mm rem mag.
     
  13. SidecarFlip

    SidecarFlip Well-Known Member

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    With magnum caliber handgun loads, if you can't see the bullet traveling, it's moving fast enough.....:D

    I'm hard pressed to get 900 fps with my 44 Mag/240 SSM loads with Unique....
     
  14. skeeterboud

    skeeterboud Well-Known Member

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    yes, i'm comparing same length barrels, and switching primers doesn't really alter the results. i shoot alot of weatherby stuff, and i find that their published velocities are spot on.... as a matter of fact, when i shot the 150gr sp 270wb, the 3 shot average was exactly 3245, the published vel!!
    i definitely agree on the barrel specs, as i can shoot my 300 winmag sendero 180gr vortex factory ammo and it's is always 30-50fps faster that what my xcr tact l/r is.

    but the fact remains, not ONE load that i have fired has met or exceeded the published velocities. not for a 22-250 nosler or hornady loads, 300 win mag nosler loads(two rifles), 222 remington hornady or nosler, 257 hornady loads, 7mmRem nosler, etc. most of them fall 150-200fps shy

    does crimping increase velocity? seems like it could, but i have yet to crimp anything