Developing Load for 168 Berger New Brass vs Once Fired

Discussion in 'Reloading' started by happyhunter, May 16, 2012.

  1. happyhunter

    happyhunter Member

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    I am new to reloading and want to know how to develop a load for my 7mm Remington Mag, with an emphasis on how to deal with virgin brass. I have determined that I have safe pressures in once fired Remington brass with H1000 from 66 to 69 grains using Berger 168’s. I have a Redding Instant Indicator and have determined that my longest twice fired case is right at SAMMI min specs (chamber). Most of my fired cases are around .002” less than SAMMI min as a point of reference, but they range from .004” to .000” less than the min. I am assuming at this point that my chamber is close to the SAMMI min. My new Nosler brass is .015” less than SAMMI min.
    Should I continue straight to seating depth using the method described in Getting the Best Precision and Accuracy from Berger VLD bullets in Your Rifle or should I fire form my cases first? My understanding is that pressures will be different between new brass and once fired brass.
    If I do fire form my cases, what is the best method?
    What difference in accuracy should I expect comparing new brass to once fired brass?
    I am still getting variation in head space for once and twice fired brass. How do you get the most consistent headspace without having to bump the shoulders back excessively?
    I am using Redding S bushing full length sizing die and competition seating die.
    Factory Remington 700 7mm Mag, 24” barrel.
    Thank you everyone for all of your postings. I was able to get a .6” (edge to edge) 3 shot group with my 66 grain load .010” off the lands on my first reload, which is my best group so far.
     
  2. rscott5028

    rscott5028 Well-Known Member

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    New/virgin brass can/does give exellent results. There's no need to fireform just for the sake of it.

    Just develop your load as described in the article. Make note of any difference in velocity/accuracy between your new brass and once/twice fired. You may need to experiment and possibly add a half grain of powder to the once fired brass to keep velocity consistent.

    I'm usually on my second or third firing before I'm done with my load development.

    The rest comes down to a lot of variables with respect to your methods. e.g. neck size vs full length

    Good Luck and Be safe!
    -- richard
     

  3. Trnelson

    Trnelson Well-Known Member

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    I have to agree. "Fire formed" and neck sized may or may not be "better" than full length sized brass. I take detailed notes on each load so I can exactly replicate it if I want to. I also keep track of the conditions I shoot in during load development so that can be taken into account as well. In a factory chambered hunting gun these things aren't terribly important but are nice things to know. Maybe the POI is half MOA different using full length sized and once fired... Maybe a particular load tends to print a half to three quarters MOA different from 40* to 90*, which is an exaggeration but you get the picture. I like having as much data as I can, some guys not so much. Have fun with it and be safe. YMMV
     
  4. happyhunter

    happyhunter Member

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    Thank you for your replies. I made it back to the range and want to report back and ask another question. It looks like you guys were right and it was not necessary for me to be overly concerned about the need to fire-form my brass. Groups were measured edge to edge and then I subtracted 0.284".

    Groups for once fired Rem brass were as follows: 66gr = 0.31", 68gr = 0.66", 69gr = 0.54”
    Groups for virgin Nosler brass were as follows: 66gr = 0.32", 68gr = 0.70", 69gr = 0.57”
    I am using a 7mm Mag with a 24 inch barrel, Nosler brass, H1000 , Winchester WLR primers, and 168 Berger VLD’s.
    I measured the velocity with my ProChrono for the following powder loads: 66gr at 2,637 ft/sec, 68gr at 2,700 ft/sec, and 70gr at 2797 ft/sec.
    I am showing no signs of pressure with any of my powder charges between 66 and 70 gr. The expected load data that I got from Berger is as follows: with 69.5 grains H1000 in a 26" barrel I should get 2987 ft/sec and with 66g I should get 2826 ft/sec.
    Why am I getting almost 200 ft/sec less?
    Why am I not seeing signs of pressure because I am 0.5gr past the max load data published?
    Should I try to go to higher powder loads until I see signs of pressure?
    Should I switch powders to Retumbo or H4831? I saw that someone on this forum was having a hard time getting the H1000 to work in a 24in barrel even though it worked great in a 26in barrel in their hands and they had better results with H4831.
    Thanks again for all your help.
     
  5. Bart B

    Bart B Well-Known Member

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    First, the appearance, shape and other visible things on a fired case are typically a poor indicator of actual peak pressures developed. Most folks loading their own belted cases end up with pressures higher than SAAMI specs suggest. If ones load data matches what was published someplace, there's no guarantee its pressure and muzzle velocity listed will be the same as your rifle gets because your barrel's different as well as the components are from different lots and the neck tension is probably different. Barrels with oversize bore and groove dimensions will easily get 200 or so less fps with a given load; there's less resistance to the bullet entering and going down the bore to put pressure and velocity high enough.

    It's normal to have as much as 100 fps difference between two people shooting the same rifle and ammo from a bench. Us humans don't hold rifles with the exact same force against our shoulders; the harder it's held the higher the muzzle velocity will be. Ammo factorys often use test barrels clamped in a solid, non-recoiling rest to test for pressure and velocity; they typically get higher velocities with the same ammo as consumers do with hand held rifles with barrels having the same internal dimensions.

    IMR4350 or IMR4831 gave the best accuracy in the 7 RM in its competition heyday and I don't think it's any different today. And in standard SAAMI spec dimensioned chambers; no tight necks often believed to be best for accuracy. While slower powders typically shot the same bullet out faster, they didn't end up as close together on target down range. So one has to make a compromise deciding what's most important; bullet speed or bullet accuracy. And shoot at least 10 shots per group testing for accuracy; anything less ain't very indicative of what accuracy will be all the time.

    For what its worth, when the 7mm Rem Mag was first used in 1000 yard matches back in the early 1970's, best accuracy happened with brand new cases or fired ones correctly full length sized back to virtual new case dimensions. The best ones for accuracy got only 800 to 900 rounds of sub MOA results at long range so fire forming cases took away a lot of that barrel life.
     
  6. happyhunter

    happyhunter Member

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    What is the best way to determine safe pressures then?

    If I am not reaching velocities in the SAAMI specs for a give bullet weight does that mean that I am also not reaching pressures?

    Can I at least load to a suggested SAAMI velocity for a given bullet weight and still be safe, assuming I am seeing no bolt sticking or other indicators?
     
  7. Bart B

    Bart B Well-Known Member

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    Use either a CUP or PSI measuring system as that's the best and most accurate way but it comes at a high price. Looking at primers and cases for expansion or deforming issues is not all that good as both have different hardness numbers and won't show the same indications for a given amount of pressure. Primer and case indicators read by a trained eye are just a rough guess, but work well if one's conservative and not power and velocity hungry.

    Second best is to get SAAMI spec reference ammunition from ammo companies; SAAMI's web site lists companys that make them.

    http://www.saami.org/specifications_and_information/publications/download/206.pdf

    They're precision loaded to give SAAMI spec pressure in a standard SAAMI spec pressure test barrel. When fired in a consumer's rifle, the case and primer indications will show what those two specific items indicate the pressure is. That pressure may be lower in your barrel that a SAAMI spec test barrel, but at least it's a very good indicator to use the same make of primer and case to load your own ammo.

    Yes, but the pressure is pretty close. I don't think it's worth that barrel's life to find a load that matches SAAMI (or some other) specs. If you're 50 fps off, that's going to mean only a 10 to 15 inch drop difference at 1000 yards.

    Yes, but the peak pressure may still be higher that SAAMI spec depending on the powder charge used, bullet to bore fit, case neck tension and primer used. There's a bunch of variables at hand.

    No competitor cares if muzzle velocity is off some cartridge "specification" by 50 (or for the most part, even 100) fps. They don't care about winning the race to the target. They just want their bullets to land close together. No hunter nor game animal will tell the difference at any range with a bullet leaving the barrel with the same difference from "specifications" say. Even the best wildlife forensic expert would be hard pressed to tell the difference.

    At least, this is my opinion. Others can set their own standards depending on what they must have.
     
  8. Joe King

    Joe King Well-Known Member

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    Observe your bolt lift, look at your case head for deformation, primer getting squared off, measure just in front of your case head. If it increases in dia more than (I think) 0.0005
    Nope just means your not getting those velocities

    Depends. Some barrels produce high velocities some don't, every rifle every barrel are all different. If getting close to or above list velocities is a big deal for you then about the best bet is to get a custom barrel from a top manufacturer, and have a damned good gunsmith install it.:)
     
  9. rscott5028

    rscott5028 Well-Known Member

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    All of the load data that I ever got from Berger was based on quick load.

    200 fps seems like a big difference. But, a lot of things can make a little difference and sometimes they stack up to a lot of difference.

    - different barrel/chamber/freebore, lands/grooves/twist/length
    - different brass.. case volume.. seating depth
    - chrony usage/calibration/precision
    - different powder/primer lots
    - environmentatl conditions including temp/pressure/altitude
    - powder scale calibration

    I'm sure there's plenty more reasons.

    Get a good reloading manual and read it. They go into great length about pressure signs.

    -- richard
     
  10. Bart B

    Bart B Well-Known Member

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    I don't think that's a good way. How much the case expands at that point depends a lot on two critical things. One's the ductile properties of the cartridge brass as well as how thick it is at that point. The other's the difference in diameters between the chamber at that point and that point on a new unfired cases.

    I've taken Federal .308 Win. match ammo from the same lot then fired it in a minimum spec SAAMI chamber Hart barrel and a mil spec 7.62 NATO chamber in a match grade arsenal barrel in a Garand. Both had identical bore and groove diameters but the mil spec chamber was a couple thousandths larger at the pressure ring point than the SAAMI chamber. Same ammo had almost 1/1000th difference in pressure ring diameter; the one from the mil spec chamber was bigger. Peak pressure was pretty close to the same amount in each one at least by how the primers were flattened and muzzle velocity was only 40 fps slower in the 24 inch Garand barrel compared to the 26 inch Hart barrel in a bolt gun.