Why I'm back to using Moly

[johnk]

I mentioned in a recent thread that I had ditched boron & reverted to moly. The turning point was my recent endeavours working up a load for my match rifle for Coonabarabran.

From 2001/2 until 2009 I had molied all my projectiles, my experience being that this, coupled with suitably long barrels minimised peak pressures somewhat without detriment to velocity. I guess the only reason, apart from the hype, that I converted to boron was that it only took a slight amount of generosity in the application process for moly to cause the dreaded blackfinger disease.

My epiphany came when I retrieved a half a dozen boron coated loaded rounds from a towel that I had sloppily tossed them into a year or so back when hurriedly unloading the small ammo box I use on the range. They'd stayed there for some time & admittedly would have been shaken around in my vehicle for a while before I unloaded the towel & stuck it on a shelf. Even cosseted by the towel, the projectiles had rubbed clean of boron to the extent that there was absolutely no slickness when I dragged them between two fingers. I'd always had some worries about how well the boron bonded (which is why I'd tried three separate application procedures) & these rounds seemed to bear that out.

So finally to my recent experience. With boron, my traditional "maximum" load, call it my working load (it's really just the load the case will hold & still pour back out if you later dismantle a round) consistently resulted in velocity spreads of between 25 & 47 fps with groups that seldom had shots touching when I was testing at 100 yards. SDs were inevitably double digits. More to the point, from one group to the next, their patterning was liable to change form from circular to horizontally strung to the same vertically, without rhyme or reason to this little black duck.

Once I took a deep breath & reverted to molybdenum, everything changed. Velocity spreads in three barrels I had tested were consistently under 25 fps with acceptable grouping both at 100 yards & on the club Saturday shoots, though admittedly they, unfortunately, were never more than 700 yards. The load & barrel I finally settled on & shot for a pair of 75s at 1000 & 1100 meters at Raglan on Tuesday's team practice (MR uses the obsolete 800m/900 yard centre) went over the chronograph today with a 12 fps spread & 4.2 SD (correct SD now, buggered if I know how I typoed the other) for 10 rounds, pretty much confirming why my open range results were so successful.

[6.5x55ai]

I have had a similar experience with HBN. In my 6.5 I have always shot moly but decided to go bare. (I have weaned all the guns I was using moly in off moly and the 6.5 was the only one left.) In the meantime I had the opportunity to have a few hundred projectiles coated in HBN so decided to give them a go before going bare. I was mightily disappointed - using same powder and similar grains to my moly load the ES was awful and groups crap. Velocity was less than moly load (HBN more slippery?). To get back to my moly velocities I will need to up my load but I cannot see this changing the ES and accuracy dramatically. The guy who coated them also warned about getting them damp, something I am unlikely to do, however.... So now I need to decide whether to go back to moly or go bare. Oh, and I gave the barrel a huge clean out before swapping to HBN and shot sufficient shots of HBN to "season" it.

[RDavies]

Have you tried different primers with BHN?
I was also getting 45 fps spreads in 3 different 7mm barrels. I tried different neck tensions and different case brands, but today when I tried different primers, I finally got each barrel down to around 20fps spread and an SD of 6 (still not GREAT, but a major improvement. I was using these same primers in my 6.5 WSSM which runs HBN and has VERY close velocity spreads.
Of course you caliber/barrel/firing pin/spring combo will likely have different preferences to mine.

[6.5x55ai]

I have always had very satisfactory performance using 6.5mm/142 MK moly coated, @ 3030fps. Low ES, single digit SD, excellent accuracy. It is only when I tried HBN that I upset the apple cart. Thanks for the suggestion but I cannot see the point in now experimenting with different primers and HBN. The only change I made was from moly to HBN. I am going to revert to moly (if it aint broken don't need to fix it) however I may try magnum primers (currently using BR2's) with my old combination just as an experiment as I use W760 powder which can be hard to ignite. But its good bye to HBN at this stage.