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Thread: Bullet lube gluing bullets in case necks

  1. #41
    Boolit Buddy
    Join Date
    Apr 2021
    Posts
    214
    Lubricated Cast Bullets Bonding to Case Necks – Results of Investigation

    Previous post:

    https://castboolits.gunloads.com/sho...-in-case-necks

    Thanks to everyone for helping me conceptualise this issue better, and for suggesting lines of enquiry. References to contributions to the previous post are in square brackets [ ].

    Originally stated as “ lubes gluing bullets in case necks”, the observation as described [1] could better be termed “lubricated cast bullets bonding to case necks”.

    This occurrence is demonstrated in aged versus freshly loaded ammunition. Symptoms include elevated velocities, POI shift, and bullets being very stubborn to pull. Bullets put up a fight if an increase in seating depth is attempted, and there is a noticeable auditory crack as the seal is broken by seating pressure [1, 28].

    Bonding where it exists must be between the band of the bullet and the case neck. In sizing the bullet the bands remain unlubed. If tumble or pan lubing, everything is lubed including the bands, but the lube on the bands may still be wiped off or squeezed off in seating the bullets.

    It looks as if this bonding occurs from lack of lube between the surfaces, rather than from any adhesive properties of the lubes, although it IS affected by type of lube. It has been suggested that neck tension [5, 18, 20] may also be involved.

    It appears that bonding can begin within a day of loading, that it re-establishes after being broken, but perhaps not after multiple breaks, and that it can be variable. I have two instances where type of lube has apparently precluded bonding.

    Here are some things I have tested. Initial tests were with BAC lube, bullets sized .312”, and neck tension .004” (Lyman M31 expander die).

    1. Seating an unlubed bullet and testing after one week [24]. Result: Bullet really held out against being seated deeper and gave a resounding crack when it went. Tested again four days later (same dummy) gave the same result. Bare lead bonds to case neck, and bond re-establishes after having been broken.

    2. Loading lubed bullets in dummy cartridges and testing deeper seating, one dummy at a time, from one day after loading to five days. The test continued, retesting the same dummies to achieve six days seven day etc intervals. It was demonstrated that bonding could occur in as little as one day. Test cases were individually identified [31, 35]. Over a few weeks, dummies that bonded kept on bonding with repeat testing, and dummies that reseated smoothly kept on doing so.

    3. Neck tension [5, 18, 20] was tested with another group – test bullets were .312”, used with Lyman M Dies 30 and 31 (neck tension .004” and .006” approx.). There was no clear pattern related to neck tension or time after loading (one to three weeks). Overall 11 of the 26 dummies “clicked”. Lack of equipment precluded testing .001” or .002” neck tension.

    4. In an unintended test, five cartridges were loaded but incompletely seated, and were the following day finish seated then pulled. These were .310” bullets at .003” neck tension, with a different lube (mix of scraps). Two seated cleanly and three gave small cracks, highlighting the variabilty of the condition. Reducing neck tension to .003” had not eliminated bonding [5, 18, 20].

    5. A fortuitous lube comparison was made with two groups of six cartridges each, 27 gns BM2, #311041 .310” hard alloy partially seated, .003” neck tension, lubed with Lyman Orange Magic and my scraps mix respectively. After nine days, being the day before I was to fire them, the LOM group all reseated smoothly, while 3/6 of the scraps group clicked. Again, the .003” tension had not fixed the problem.

    6. Six cartridges with bullets lubed LOM, neck tension .004”, were loaded and partially seated, then finish seated four days later – they reseated smoothly.

    7. Some subsonic .30-30 and .32-40 ammo, with bullets lubed with beeswax : synthetic two stroke oil 4:1, reseated smoothly after months of ageing. Cases for this and the next test had been prepared without any inside neck cleaning or lubing.

    8. Subsonic .30-30 ammo, lubed with BAC, that had been loaded a couple of months, had bonded firmly. This was shot for velocity, group, and POI, five shot groups following one fouler for each group. Load was 163 gn PB bullets and 5.5 gns Unique. With only one five shot group for each treatment, the small differences are no more than suggestive.

    Velocity x SD Group POI
    Bonded 1022 x 16 1.91” -1.55”
    Cracked 1000 x 7 1.19” -2.16”

    Bonding could interfere with intended bullet pull, and could do so unevenly. Remedial options might include: Lube inside case necks before neck expanding; lube bullets in a die that is bigger than the bullet, e.g. .310” bullet in .311” die; find a lube that obviates bonding; long seat, then finish seat just before use; or find a powder that is not sensitive to bonding. The first three, combined with long seating, can be tested by “cracking” at intervals after loading.

    I acknowledge that some means of pulling bullets [31, 35] that does not involve slipping collets may be superior to the “Crack Test”. This would be particularly so if the object was to quantify the effect of bonding versus just confirming its existence.

    The significance for ammo to be used in .30-30 lever action rifles, is that velocity variation equals vertical stringing. My own calculation is that for high teen velocities, in tests with Varget/2208 and BM2/Benchmark, 100 fps change in velocity equates with approximately 2” and 2.2” difference in POI at 50 meters. Thus the difference between an SD of 10 (40 fps spread) and an SD of 35 (140 fps spread), could be an addition of 2” to vertical shot dispersion. This is against a backdrop of loads giving less than 1” lateral dispersion.

    Type of lube does appear to have some bearing on bonding. Bonding has been observed with BAC, Lyman Super Moly and LBT Blue. Non-bonding was observed with Lyman Orange Magic and my mix of synthetic two-stroke oil and beeswax. Alox was not tested, though it is in the BAC mix.

    Bonding effect may depend on the load. I have observed what I believe to be a substantial effect in .30-30 with BM2/Benchmark powder, but a lesser or perhaps non-effect with subsonic Unique loads.

    The initial test for some degree of bonding on aged ammo is to take some spare cartridges and reseat the bullets .010” deeper (1/8 turn on a 7/8x14 die). Do they resist? How pronounced is the “crack” when they let go?

    What have I done about it? For a start I have abandoned BM2 (Benchmark) as a sub 2000 fps cast bullet powder and gone instead to 2208/Varget, and I am now lubing with Lyman Orange Magic.
    It'll be handy if I never need it.

    Insomniac, agnostic, dyslectic - awake all night wondering if there is a Dog.

  2. #42
    Boolit Master
    Join Date
    Jan 2016
    Posts
    995
    GONRA knows this is NOT exactly wots being discussed here, but ya'll might be interested:

    (From looong ago memory, so be sure to double check !)

    In 1920's (?) Frankford Arsenal loaded Tin Plated Bullets in National Match ammo.
    Not sure how long it took (not much?) but the tin diffused into the brass case neck.

    HIGH PRESSURES! Bullet was soldered to the case neck!

  3. #43
    Boolit Master
    Join Date
    Apr 2016
    Location
    NC
    Posts
    2,862
    Quote Originally Posted by GONRA View Post
    GONRA knows this is NOT exactly wots being discussed here, but ya'll might be interested:

    (From looong ago memory, so be sure to double check !)

    In 1920's (?) Frankford Arsenal loaded Tin Plated Bullets in National Match ammo.
    Not sure how long it took (not much?) but the tin diffused into the brass case neck.

    HIGH PRESSURES! Bullet was soldered to the case neck!
    Maybe tin-brass galvanic corrosion. Interesting story, short read https://www.ssusa.org/articles/2016/...l-matches-1921

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check