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Ruminations on N550

I've been out of the competition game for about 9 years but decided to get active again by shooting my first F-class match (600 yd). I dusted off my space gun (5.56x45) and reloading equipment; bought a bipod and rear bag, chronograph, etc. What I didn't buy was any reloading components since I have a lot in storage.

Previously, shooting 600 yards I had a standard load of 25.0 gn of V550 & RWS primer behind a Sierra 80 gn #9390M bullet, loaded to 2.490" LOA. Which produced around 2720 fps with a really good SD of 7.

Going through what I had in storage, I decided to work up loads using Rem 7 1/2 primers. I worked up from 25.0 to 26.5 gn of N550 and was not exactly thrilled with the results. I did get 2800 fps at the high end with no signs of excess pressure but my SDs were all around or above 20. (This is probably the worst SD I've ever loaded.) 26.5 gn fills the case to the shoulder. All the cases were the same Winchester lot, carefully prepped; primer pockets, flash holes, neck turned, etc. All the components are at least 10 years old. The n550 is from '95. The primers are probably about the same age. They've all been stored in air-tight containers in an air-conditioned room and show no signs of deterioration.

I've gone ahead and loaded 65 rounds with the 26.5 gn load for this match because I don't have time to start over and try something different. I won't be surprised if I see a lot of vertical stringing.

When the dust settles I plan to go back and try a bunch of new loads using various powders and primers. I'd like to pick the brains of folks who have more experience with N550 than I. Here are some theories:
1. The primers are old. Get new primers.
2. Remington 7 1/2 primers aren't suitable with N550. Use a different primer.
3. The powder is old. Fertilize the garden with it and buy new.
4. Your new CED M2 chronograph is giving you bad readings. Find out what's wrong and fix it.
5. Something else.

Of these I mostly suspect #1 & #2. Anyone care to share any thoughts? Thanks!
 
I won't even take a guess on 1 or 2 being the source of your problem, but I'll bet number 3 is not it. If your powder has been stored is the conditions you quote it is very unlikely that it's bad. I have powder that was manufactured in the 1960's that I bought in the late 70's that chronographs as good today as it did when I bought it. Powder is pretty stable stuff if treated nicely.
 
I's agree with STS - N550 is a VERY stable powder and won't go off quickly. Changing primers might help, but that's not guaranteed.

In a nutshell, N550 isn't an optimal powder for 80s in .223 Rem. It's far better suited to 90s, but even there I prefer either N150 or Reloder 15 both of which are faster burning. (2000MR and AR-COMP look suitable too for recent introductions.) N550 is too slow burning, so won't burn 100% efficiently with this bullet weight. The resulting pressure and velocity variations are worsened by the relatively long powder column in relation to the case's capacity, hence a primer change sometimes helping. My experience with Viht N500 series D-B powders in various grades and in various cartridges / bullet weight combinations is that they need to run at full or very nearly full pressures to perform well.

Running your combination through QuickLOAD, it works out at around 46-47,000 psi peak pressure with an estimated charge burn of 96% in a 26-inch barrel. You want to be getting on for 8,000 psi higher pressures and 100%. Varget, H4895, Viht N140/540, and Re15 will give you more consistent results.
 
Thanks everyone. I was actually wondering about the flash I was seeing through the scope and the possibility that I was not burning the charge in the barrel. My theory in using a triple-base powder is that it would give a longer burning curve giving higher velocities while keeping reasonable peak pressures. Maybe the N550 is just a bit too slow and I should try other powders.

P.S. The F-class match did not go real well. I did avoid having any misses but got my rear end handed to me by 14 year-old girl.
 
I was actually wondering about the flash I was seeing through the scope and the possibility that I was not burning the charge in the barrel.

Ah ... that wraps the issue up. I've found that the N500 powders produce an almighty muzzle flash if the application isn't working out / pressures are too low. I once tried N560 in .243 Win with some heavy bullet combination or other. The flash was clearly visible through the scope and near blinded my neighbours on the firing line. The results on the target and chronograph were dire too.
 
The nice thing about seeing the flash is that at least your concentrating on keeping your focus on the crosshairs of the reticle. And that is a good thing!
 
This conversation has opened my eyes. I now understand why the fired brass was so dirty. There was either not enough initial pressure or so much combustion still occurring when the bullet left the muzzle that considerable powder residue worked its way around the case neck. Live and learn.
 

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