Reloading: A selection of products

‘Well, I’ve read about it but what can it do for me?’ That’s the popular response to the question of moly coating. The idea is simple; carefully tumble your bullets in a molybdenum disulphide (English spelling) talcum. The claimed results? Reduced bore friction and pressure giving better throat/barrel life, potentially improved accuracy and more shots between cleaning. Some of the top branded bullet-smiths, such as Norma and Hornady offer ranges of coated designs… the Hornady 168gn .30 cal BTHP Moly having an impressive ballistic coefficient. The claimed downside being the inability to remove all traces of moly once it has been used in a barrel. Moly coating kits are offered by several UK suppliers, usually comprising a budget tumbler and coating powder. Add to that a box of disposable nitrile gloves, detergent, cleaning cloths and a location that will not be unduly damaged by the presence of a coating of moly dust! I’ve experimented with the process but not drawn any conclusions from the results.

A Bit at a Time

Mentioned a couple of times before, powder trickling is the simplest and cheapest form of ammo ‘tuning’ you can get. However, I remember being surprised by the number of students on our NRA reloading courses that did not own one. Using a mechanical powder measure can get you to a consistent 1 to 3/10- grain accuracy. However you’re weighing scale should be capable of detecting variations of less than half 1/10-grain - even better from some of the electronics. Enter the manual trickler. If you can spare the time to twiddle a knob you can add powder one kernel at a time. Indeed, the changes in the pan of your mechanical scale are almost too subtle for it to register accurately - gently tapping the beam often being the best way to prompt a reaction. Tricklers can be prone to sliding around on a shiny work bench - the fix on some models is to drill the lower skirt, wind a couple of self tappers into the inside and then carefully fill with molten lead. Remember to remove all the plastic bits beforehand! From £12 to £20 the mechanical trickler is a no brainer.

Same Calibre, Different Performance?

Many of us load the same calibre for a number of different applications. If we use a different bullet design then the cartridges may be fairly easy to identify. But if the changes are just to the primer or powder charge, or just a marginal change in bullet weight then the cartridges may be hard to segregate. Yes, the obvious solutions are to use different colour ammo boxes, keep loading data labels with each batch and even store them in different locations. All good ideas but they’re not the best. Colour coding works… a dab of a chosen colour from a felt-tip on the rim of each round can mark the vertical position of the cartridge in the chamber as well as the recipe it contains. For reference, just note each colour/ recipe combination in your database.

A Turn of Speed?

Worrying about the speed of your bullets’ rotation hardly seems worthy of consideration… but it is. Alright, for a given rate of barrel twist it is just a direct function of muzzle velocity (MV), but there’s more to it than that. Let’s get the maths out of the way before we explore the arguments. Take your MV in feet per second and multiply by sixty to give feet per minute. (e.g. 1000 fps would give 60,000 fpm). Now divide your barrel twist, in inches, by twelve and then divide the result into one to get the reciprocal in turns per foot. (e.g. 1 in 14 would become 1.1667 divided into 1(one) to give 0.857142 recurring). To get your bullet rotational speed we now simply multiply the two figures, in this case obtaining a rounded figure of 51429 rpm. We can simplify this calculation to: - MV (fps) x 720 divided by twist (in inches).

Free Calculator

Stability, accuracy, stopping power and structural integrity are all bound up with the rate of spin. So what does spin do? Well, imagine a simple gyroscope such as a kid’s top. Set it spinning and, despite being balanced on a tiny point, it remains upright and resistant to changes of attitude. So spin keeps the bullet pointing in the direction in which it was fired… ‘ish. In practice there are upper and lower limits to this rate of spin and these in turn change with velocity, bullet length and calibre. At this point the arguments and maths get too heavy for this column - suffice it to say that a clever chap called Don Miller has produced a downloadable rate calculator that can be found at several sites on the web.

Twisted Logic

With regard to accuracy, it is partly a function of stability. If the impact of external forces such as air pressure and gravity are reduced then improved accuracy must follow. This is best demonstrated at the lowest practical rate of spin, below which the bullet does not stabilise. As an example, I once had a .44 Mag revolver re-barrelled. The gunsmith inadvertently fitted a length of Douglas bull barrel designed for use with a .444 Marlin. At 1:38 it was almost half of the desired rate for my Ruger. At first I was unable to explain why my previously high scoring 200 yard round was often failing to hit the Army 6’, or tumbling through it sideways whenever it did make contact!

Noticing that the cleaning rod failed to rotate was the first indication of the disastrous error. Doing the maths indicated that I needed at least 31,000 rpm for bullet stability. By calculation and experimentation I discovered that the Sierra 180gn JHP set out to the max COL and carefully loaded beyond book limits would give almost 1700 fps AND accuracy. It was an interesting lesson. At the other end of the rotational spectrum - stopping power (in hunting terms a function of the energy imparted from the projectile into the quarry) is considered to be improved by higher rates of spin. However, if the centrifugal force of the spinning bullet exceeds its centripetal force then the bullet will fly apart, a ‘blow-up’.