Lubricated Cast Bullets Bonding to .30-30 Case Necks – Results of Investigation
This post is by way of acknowledging responses to a post I made some months ago on what I described as lubes gluing cast bullets in case necks. This post also documents what I have done to get to the bottom of the issue. A couple of days ago I tried posting this as a reply to the original post, however it has not come up, so I'll go down this path instead.
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 Post# 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 .3125”, 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 at 50 meters 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” for determining bullet pull. 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 for a Marlin 336A is that for high teen velocities, in tests with Varget/2208 and BM2/Benchmark, 100 fps change in velocity equates with approximately 2” 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.
Thanks to all for your suggestions.
|
   
   
|
|
Reply With Quote
Originally Posted by Hick
