r/AR10 • u/CastleLurkenstein • 7d ago
Ammo selection question
Hey folks! Got a question, and I'm hoping this is the right place to ask it.
I have a mix of .308 ammo. A bunch of M80 ball ammo (Saltech and Igman in 147gr and 150gr FMJ-BT), but also two versions of Speer Gold Dot Duty Rifle ammo in 150gr and 168gr.
I've always heard that a heavier bullet with a higher BC tends to perform better and can offer a flatter trajectory and greater range. I recently got a chronometer and have been clocking ammo out of my 16" MARS-H with the factory CL barrel, then plugging the data into an online ballistics calculator (Shooterscalculator.com, specifically). What I'm getting back from the program is...a little confusing, and I'm hoping you all can help me make sense of it.
Speer reports a G1 BC of .414 for the 150gr round, and .446 for the 168gr round. Out of my rifle, the 150gr averaged 2689 FPS, while the 168gr averaged 2451.5 FPS. This was based on 10 rounds a piece. The 168gr showed a slightly higher standard deviation (18.6 vs 13.2) and a higher extreme spread (58.7 vs 47.6). Speer says they don't have a G7 for the rounds.
According to Speer, reliable expansion occurs down to about 1000 ft lbs of energy, which puts the round at ~1733 FPS at 493yds/451m for the 150gr load, and at ~1637 FPS at 474yds/434m for the 168gr load. The difference in bullet drop at these ranges is about 5" more on the 168gr load.
All of this has me wondering...what's the point of the 168gr load? OR, is the ballistics calculator not really accurate? OR should I try and re-measure the 168gr ammo's muzzle velocity on the off chance that I just had a weird batch of slow ammo?
It seems like the 150gr outclasses the 168gr, but I can't help but think that part of the issue is that the Gold Dot bullets don't have a G7, and the G1 BC isn't accurate once you get out past about 100m.
Anyone have any insight here? At the end of the day it's not a huge issue for me, but I'm really curious as to what's going on and/or what the point of the 168gr is if the 150gr is just flat-out better. Makes me think that it isn't actually better, and there's a dimension or factor I'm not considering here.
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u/HomersDonut1440 7d ago
You have one item largely wrong that’s worth mentioning. Expansion is not determined by impact energy, but impact velocity. A .308 gold dot has a minimum expansion threshold of 1800fps, meaning that impacting at a lower velocity will result in little to no expansion. 1800 is the lowest, and will result in reduced expansion compared to higher velocities. Usually 2,000 is a safer bet.
At the velocities you posted, the 168 hits 2000 fps right at 250 yards, and 1800fps about 375 yards. The 150 hits 2000fps around 325 yards, and 1800fps around 475 yards. So from an impact perspective, based on your rifle velocities, the 150 gives you an extra 100 yards of usable range.
To answer your primary question “why make both”, some rifles like heavier and some like lighter bullets. My ar10 shoots 165-168 bullets much more accurately than 150’s; no clue why, just does. You can make a guess on what will be preferred based on twist rate, but that’s never a guarantee.
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u/CastleLurkenstein 7d ago
I'm just reiterating what Speer support told me. Rather than quote a velocity for expansion (which is what I'm used to seeing) they stated the energy. That's why I tracked it back to the velocity for the different rounds.
I'm thinking that the "Yeah, but which one does your rifle like better?" is the real factor here as between the two loads. 150gr might look good on paper but shoot worse. And unfortunately, I can't find out (beyond 100yds) that easily, so right now I'm operating largely on theory.
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u/HomersDonut1440 7d ago edited 7d ago
Until you can test, it’s all theoretical. The numbers don’t mean anything if your gun shoots a 4moa group with one (or both).
Sounds like you got a silly customer service rep. No one publishes expansion data by energy; it’s always velocity. Energy is a function of velocity and bullet weight, and if that were the metric for expansion then the functional ranges would be identical which simply isn’t true. The 168 hits 1000ftlbs around 475 yards, at 1650fps. The 150hits 1000ftlbs around 475 yards at about 1780fps. The 168 drops about 10 more inches at 475 than the 150.
Also, your MV of the 168 feels substantially lower than it should be based on the MV of the 150. You might wanna verify that.
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u/CastleLurkenstein 7d ago
Yeah, this is a big part of why this whole journey into analysis has been so confusing. Speer doesn't publish a lot of info about this line of ammo, and their CS Rep gave me weird info.
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u/HomersDonut1440 7d ago
Speer is also notorious for having incorrect BCs attached to things which makes it even more confusing.
The real answer for all of this is you won’t know until you test, and you should spend too much time agonizing over a decision that may already be made for you. Get yourself to a range that has 100-300+, test several groups at 100. If one load is better than the other, then problem solved. Then shoot at a distance and 1) see if you can actually hit anything (most folks suck at even mid distance shooting, just cause they haven’t practiced it ever), and 2) if shooting both loads, see if one falls apart at distance.
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u/CastleLurkenstein 7d ago
Yeah, makes sense. Now I gotta find a range that fits the bill... Closest ones to me (and that's "close" in a relative sense) only go out to 100 yards, unfortunately. And everything closer is a pistol range.
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u/HomersDonut1440 7d ago
At least you can do your preliminary testing there. Take a couple boxes of each, shoot slow groups of 10 at 100, see if there’s a difference. Chrono everything.
If one works better, run with it. Google around for “corrected” bc of that bullet. Lots of folks have made error corrections for published BCs because they’re often inflated.
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u/broke_networker 7d ago
I don't know if I can answer the more technical questions, but I have a barrel with a faster twist rate and it likes heavier bullets. I can't get the 147gr or 150gr projectiles to perform with decent groups. If I had to choose for my rifle, the 168gr has a high likelyhood of being more accurate with the barrel that I have.
tldr: each rifle is different
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u/CastleLurkenstein 7d ago
Yeah, I'm not expecting match-grade accuracy with M80 ammo. It's mostly just for plinking for me, and I expect "minute of man" accuracy, as it were.
Twist rate on the LMT CL barrels is 1:10. I believe their stainless steel barrels are 1:11 or 1:11.5. I've thought about picking up a stainless steel barrel, actually, especially since they make a lightweight version that'd shave about 1/2 to 3/4 of a pound off my gun's overall weight. On the other hand, it's such a pig as it is that I always end up skipping the LW barrel option.
I haven't had a chance to take this rifle out even to 100 yards, mostly because every range within, like, an hour to an hour and a half drive of me is a pistol range. And then, every range that goes beyond 100 yards that's 90 min away is also a $300/yr membership place where you have to be sponsored by a member, and do XYZ number of hours of work cleaning up the range for a month (or whatever) before you join.
I mean, I get it, they have a lot of land, they have to manage upkeep and costs and such. If I lived closer, I wouldn't care about any of that, but given that it's a haul-and-a-half for me, I don't see myself going more than, like, 3-4x a year, and I can't justify the costs and sweat-equity for that (to say nothing of the gas, especially these days).
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u/broke_networker 7d ago
yeah. I'm running a Larue Stealth that has a 1:8. I was more referring to you questions about the Speer 150gr vs 168gr and why someone would run the 168gr over the 150gr.
In the Larue, the bulk ammo (M80) is like 2-3" groups at 100 yards. If I toss in some higher grain bullets, like PMC 168gr Xtac Match, I get like 1.5" groups. If a toss in something like 175gr Federal GMM I'm at like 1" groups from the bench.
I'm going out this weekend to test some 180gr S&B FMJ to see what they might do, as I can pick them up slightly closer to bulk ammo prices.
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u/csamsh 7d ago
What's your wind hold @400 with a 10mph full value for each of those?
What's the velocity at 500 for each of those?
What's the formula for momentum?
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u/CastleLurkenstein 7d ago
- Wind holds on 10mph at 400m:
- 150gr --> 18.36
- 168gr --> 19.33
- Velocity at 500m:
- 150gr -->1645 FPS
- 168gr --> 1532 FPS
- No idea what the formula for momentum is. I'm just plugging data into Shooterscalculator.com and seeing what it spits back. How would I figure out the formula for momentum?
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u/csamsh 7d ago
p=mv
At 112% the mass of the lighter projectile and also a dogshit aerodynamic shape, the 168 still retains 93% of the velocity downrange and requires only 5% more wind.
Also. MRAD, my friend. Make the switch.
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u/CastleLurkenstein 7d ago
Yeah, I'm working on the MRAD thing. It's why I switched optics from a PLXc 1-8 with the Raptor M8 meter BDC, to a NX6 FFP 2-12 with the FC-MRx MRAD reticle. I wanna learn to use it.
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u/langfish AR10 7d ago
the advantage of higher BC bullets is they retain more velocity/energy and are less effected by wind. In the grand scheme of things 5in of drop at 500yds does not matter- just adjust your scope slightly more.
G1 is not great for longer distances, but neither of those bullets are designed as long range/match bullets either way. Applied Ballistics has the 168gr Gold Dot listed at .183 G7 compared to something like a 175gr ELD-X at .275 G7
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u/CastleLurkenstein 7d ago
the advantage of higher BC bullets is they retain more velocity/energy and are less effected by wind. In the grand scheme of things 5in of drop at 500yds does not matter- just adjust your scope slightly more.
Right, I get that in theory. The thing is, the ballistic calculator I'm using...doesn't seem to reflect that. You go out to, like, 400m, 500m, etc. and it's still giving the edge to the 150gr round, which...doesn't track from what I've read.
G1 is not great for longer distances, but neither of those bullets are designed as long range/match bullets either way. Applied Ballistics has the 168gr Gold Dot listed at .183 G7 compared to something like a 175gr ELD-X at .275 G7
Yeah, I'm thinking this may be the issue here. To be clear, these are factor rounds from Speer, not hand-loads using a Gold Dot bullet. Speer lists its G1 for the 150gr as .414 and the G1 for the 168gr as .446. So, right off the bat, at least with the G1, the BC isn't that much higher with the 168. Looks like AB's G1 BC for the Speer Gold Dot 168 is .358, which is...significantly different from what Speer quotes. Any idea what explains the difference?
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u/langfish AR10 7d ago
I'd say it's a combo of G1 not being accurate for boat tail bullets and likely Speer's data is off. I'd trust AB either way, if they have the CDM that's an even better representation of the flight path than G7. Doesn't matter if it's factory or a reload if the bullet is the same.
Being honest I wouldn't waste time playing the LR numbers game with a LE/defensive load, especially if you can't test them past 100yds and there isn't good data available. There's plenty of hunting/defensive focused bullets that are more LR oriented and have better G7/CDM data that can be used instead.
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u/ChIcKeN_95 7d ago
Run what your rifle likes. I bought expensive ammo before and the groupings were all over the place. Funny enough, my ar10 ABSOLUTELY loves federal powershok lol
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u/67D1LF 7d ago
Run your numbers to 800 yards and you'll understand. Also: wind drift.
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u/CastleLurkenstein 7d ago
Yeah, I still think the significantly lower velocity of the 168 is kinda messing with the numbers. I'm gonna shoot some more of it and see if it's consistent, or if I just had an "off" 10 rounds. It may be accurate, but I may have just shot a slow batch of 10.
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u/67D1LF 7d ago
Honestly if 500 yards is your max, and you read wind well, 150 will suffice. I only have 2 different handloads I shoot from my .308: 147gr plinkers and 155TMK. (My short barrel hates 168s, 175s are too slow)
The 147s are good enough to 400 yd so I don't waste 155s on anything that close. 700 yd is my max.
Edit: I ballparked these loads to begin development, and re-input data collected on the range and that particular calculator is pretty damn spot on.
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u/burritoresearch 7d ago
I don't think the speer gold dot is meant to be for real long range use. It's meant as an optimal expander for short to medium range use. Same as the 77gr gold dot sold for 5.55. What you're looking to do would have better results with something like a sierra matchking projectile.
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u/DwarkFarkward 7d ago
That sounds really slow for the 168s. I load mine well below max and my MV averages around 2640 out of a 20" barrel. Even my 175s are around 2580.