Vihtavuori N140 for Use with 55gr 5.56 Handloads - Safety in Data Discrepancies?

[Gnash.Hyena]

Hey guys! I'm struggling with an issue I hope I can enlist some help in solving. I am using Vihtavuori N140 as my gunpowder of choice for doing load development for use in an 18" 1in7" twist heavy-barreled AR15. I performed test shooting today. The 75gr Hornady HPBTs did great. Less than 1MOA, right on target, and I suspect that group size will shrink with practice. I'm fine there, I think I've got good data for that. The question is with 55gr Hornady FMJ with cannelure. Which I know won't perform as well as the 75gr due to my barrel twist rate, but it is cheaper and I'd like to have it as a bulk option (mostly so I can shoot it out of my other ARs that's built for CQC and not feel as bad about not using benchrest techniques, but still have it do reasonably well in my benchrest AR should I choose to use it then).

The main question: Why does the load data in Vihtavuori's guide for handloading 55gr fmj .223 list a higher maximum load than the maximum load for the same powder in Hornady's handloading manual (9th edition)?

https://www.vihtavuori.com/reloading-data/rifle-reloading/?cartridge=7

Vihtavuori's maximum load for 55gr fmj Hornady bullets is 26.8 grains of N140 powder. That is a bit higher than Hornady's maximum load of 25.7 grains of N140 powder for the same bullet. Why is that discrepancy present? I safely shot 25.9 grains of N140 powder today - ten shots, five shots each at 100 and 200 yards. Is it safe to load an AR15 (5.56 chamber) to the maximum load of 26.8 grains of N140 powder that Vihtavuori suggests? Is it wise to do so?

I ask because I wasn't entirely pleased with any of my 55gr groups today at either range, and I've actually achieved better results with Frontier Hornady .223rem 55gr HP Match ammo, which has a velocity of 3240fps on the box. I estimate the aforementioned 25.9gr load to be most likely just under 3200fps, but I don't have a velocimeter to check. My results were "okay" in some places, but I want my handloads to meet or exceed the performance characteristics of the Frontier, and I'm hoping that the higher velocities might give me more precise results where the loads below Hornady's maximum velocity didn't. One, maybe two loads came close, but not quite a match, and I'm tempted to try the hotter loads to see if those work better. I'm just worried that Vihtavuori's table is made with a bolt action rifle in mind rather than a semiauto, and I don't want to damage my AR as a result of personal ignorance.

Thanks!

 

[Toprudder]

Load data from one source to another will vary - sometimes quite a bit. Welcome to reloading! I probably don't have to tell you this, but this is why you always start low and work up, in YOUR gun.

I usually find the Hornady data to be on the conservative side. When I see a discrepancy like this, I try to find load data from as many sources as possible, including Lyman, Speer, Sierra, etc. But, still, start low and work up. This is also where a Chrono can be a good thing, to let you know if you are in the ballpark as far as velocity goes.

As far as the 55 FMJ bullets, I have decided to stop using the FMJ and instead use the 55 SP bullets as I have found them to be more accurate, sometimes half the group size of the FMJ. Shop around and you can find them for only about a penny more than the FMJ. A bonus is that they can also be used for varmints.

Is it safe to load above the 223 data for ammo shot from an AR? Well, the common belief is that 5.56 is loaded hotter than 223, so one might say it can be done. I will say that I have gone slightly above published load data for some of my AR loads, but I started low, looked for pressure signs (no ejector or extractor swipe marks), and only went about 0.3gn above published.

 

[Gnash.Hyena]

Thanks Rudder!

That's fair. I think at this point, before I go any hotter with my 55gr loads, I should find a way to acquire or borrow (preferably borrow) a Chrono to see where that 25.9gr load is velocity-wise. Nothing felt particularly powerful, the case is still definitely not full, but I am going hotter than Hornady recommended (0.2 grains hotter than Hornady published, so that's roughly in line with your suggestion for only up to 0.3 over). Given I know for a fact that my AR does well with Frontier Hornady Match 5.56 55gr (though the 75gr is still much, much better performance-wise), and the Frontier claims to shoot at 3250fps, if the Chrono reads the 25.9gr load going equal or faster than that, I'll have no business going hotter.

Either way, I was also convinced by someone else to just accept that the 75gr is a better bullet all around for this gun. With the 1 in 7" twist that's to be expected, and there's just no real point in worrying about the 55gr load when I'm meaning to use it for another gun anyway. To keep this post simple, I was overthinking the 55gr load. They said that if I'm wanting to load the 55gr for another gun (which has a 1 in 8" twist barrel), then I really need to do the load development with that gun, rather than this one.

That is a really interesting point on the 55 SP. I would not have thought about trying those, but I'd be willing to buy a box to compare them to FMJ. Do you have a brand that you particularly prefer with SP, or do you find them to be about the same?

 

[Toprudder]

That is a really interesting point on the 55 SP. I would not have thought about trying those, but I'd be willing to buy a box to compare them to FMJ. Do you have a brand that you particularly prefer with SP, or do you find them to be about the same?

I'm using the Hornady 55 SP. They also make a 60 SP.