Moving away from double base powders.

[WhizzyBill]

With all of these questions, it depends on the circumstances.

If you are a Target Rifle or F/TR shooter, i.e. .308, 155gr or less bullet, out to 1000x, there is no need to consider a double base powder, with the inevitable increase in barrel wear that comes with it.

If, on the other hand, you are unable to get the necessary velocity out of your round, (for the required degree of consistent accuracy at the target end that you desire), without some over-pressuring, then a double base powder will enable you to achieve this, but you will lose some barrel life.

I am just about to start loading for Match Rifle and Nick Tremlett has told me that yes, I can be entirely competitive with N140, but N540 will give me some extra velocity and that this is "important" at 1200x.

One comment I would also make to anyone thinking... "ok, I'll use N140 for short range and a double base powder for the longs", bear in mind that a change of powder can cause significant group issues, unless you clean out first.

[scoobydoo]

One comment I would also make to anyone thinking... "ok, I'll use N140 for short range and a double base powder for the longs", bear in mind that a change of powder can cause significant group issues, unless you clean out first.

I did notice the first time I shot rounds with N550 how much dirtier the barrel was than with N140. But it does give me higher velocity without increasing chamber pressure which is what I'm looking for.

[AFA82]

Honestly, the only reason why you might get faster barrel wear is because of increased velocity. I for one did not notice that my barrel was any dirtier.

[RDavies]

I havent tried any of the double based powders in 308, only H4895 and Varget . How much velocity do you lose by sticking with either Varget or N140 in a 308 with 155s compared to N540? Any thoughts on the new Alliant AR-Comp powder?

[Laurie]

I havent tried any of the double based powders in 308, only H4895 and Varget . How much velocity do you lose by sticking with either Varget or N140 in a 308 with 155s compared to N540? Any thoughts on the new Alliant AR-Comp powder?

It depends on the barrel, not just length, but internal dimensions too. From 30", you can find that N140 and VarGet simply won't get above around 2,970 fps. Heavier charges don't initially give higher pressure signs, the MVs simply plateau. Other barrels keep on producing velocity to a bit over 3,000 fps.

N540 will easily produce 3,050-3,075 fps, and 3,100 fps + is on with some barrels.

At the end of the day, barrel life in this instance is less affected by single v double-base powder forms than by the peak chamber pressure being produced and its duration. The higher the pressure, the longer it lasts, the quicker the barrel becomes scrap. That's why Re17 is getting the barrel burner reputation. These characters say: "Wow! I'm getting 200 fps more with Re17 than I did with H4350 or whatever and think they'll get the same barrel life. An extra 100 fps at the peak margin probably halves barrel life with most cartridges, obtaining another 150-250 fps on the peak end of the scale likely reduces it by 50-75%.

Remember, all ball powders are double-base, yet the US armed forces have used nothing but WCC / Olin / St. Marks Powder Co. ball in their basic 5.56 and 7.62 ammo loadings for around 40-50 years now. Armies are very cost conscious indeed and if WCC-whatever from St Marks reduced an M16A2's barrel life by say 1,000 rounds over a single-base extruded form for the same performance, you can be damned sure the US Army would switch to the latter.

AR-Comp is another double-base powder of course (like all Alliant-ATK products). When I spoke to Derek Edgar the importer's MD re this powder, he said the odds are we'll never see it here. Getting CE product certification is an onerous and expensive job for propellants and with this one targeted largely at AR15 shooters, the manufacturer will likely take the view that it's not worth the effort involved to be able to sell it in Europe to a very small market segment.