Looking for a general idea of velocity with Benchmark

[CXRs]

Hey all, so I've been playing with my PSA 20" Grendel lately, and found a load that is giving me insane accuracy, but I dont have a chrono to check it, and I've got no idea what kind of velocity to expect.

I've been loading 27.2 grains of Benchmark behind a 123 SST, and according to Hodgdon's website and my Lee manual I should be getting around 2400fps, but factory ammo like the Black and Custom come in around 2550-2600fps. Is factory ammo that hot, or are the numbers wrong on my reloading manuals?

[grayfox]

Hornady's factory ammo doesn't come close to those numbers in real-life barrels. Maybe in their 24" test barrels.
The SST for a 20" very nice barrel should be around 2500 ft/sec, the Hdy Black more like 2440. Less MV for a cheaper barrel or for one that has lots of internal friction.
There are some benchmark users on here, maybe they will chime in, but bear in mind that every barrel is unique from the rest. Your MV, to coin a phrase, will vary.

[CXRs]

Thank you! I wasn't sure, I know some factory ammo is labeled a little liberally.
I'm saving up for a chrono, but in the meantime I'm going to try to work the numbers backwards using drop from 200 and 300 yards.

[Mitdr774]

Howa Mini 22", 123 SST, Starline brass, Federal GM205M, and 27.4 Benchmark gave me about 2475 FPS (I may be off a little on the velocity, but thats the approximate number I recall). Keep in mind this is 0.2gr above Hornady book max, but it works well in my gun and does not show any indication of pressure. I know the 6.5 Grendel is held to a lower pressure than a lot of cartridges not designed around the AR platform limitations, and as such doesnt show pressure signs until above the SAAMI rated pressure. I also know that just about every piece of factory load brass comes out with a tiny ejector mark on it, where the loads I have been using do not. Different brass, but the factory stuff shouldnt be showing pressure signs like that.

[greaseywater]

Since you said general idea: 120 SMK, Hornady brass, cci450, and 27.1 grains of benchmark gets 2385 fps from my 18" barrel.

[LRRPF52]

Benchmark is on the faster end for shooting lighter weight projectiles in the 85-100gr range, so we normally don't use it much for 120gr and higher.

It can spike on you and it's common to see very tight accuracy nodes when going over max loads.

Approach 27.0gr carefully under 123gr cup and core bullets, using .3gr increments from a start load over a chronograph.

When Bill A. did his initial load testing with 6.5 Grendel, he left Benchmark only for the 90gr TNT and nothing heavier/longer.

Hodgdon's has a lot of data for it for everything from 85gr to 123gr Sierras.

These handbooks are your friends:

[Klem]

CXR,

I agree with 52, BENCHMARK is fast. Arguably too fast for the Grendel and therefore inefficient relative to other powders when loading safely. It is not a popular powder because you can get higher muzzle velocities using slower powders. This is no doubt why your factory loads are faster than Lee's tables for BENCHMARK, not because they are hotter but because they use more efficient powders.

Be also aware as Greyfox was saying that powder tables come from 24" test barrels with strain gauges. You can add another 100fps to the same load if you swapped your 20" barrel for 24" - roughly 25fps/inch.

BENCHMARK is a single-based powder made by Australian Defence Industries (ADI). In Australia it is called BM2, to delineate it from BM1, which is even faster. BM was developed to be a fine grain single-based powder that meters similar to ball powders for the civilian Bench-rest market; hence the name. Hodgdon imports BM2 and re-badges it for the US market calling it BENCHMARK. Hodgdon and ADI's load tables give a clumsy range of powders for the Grendel. It is unclear whether ADI or Hodgdon did the testing but as they both display exactly the same data they are both equally misguided in recommending fast powders for the Grendel. By tabling particular powders it implies they are the most efficient and we seem to have eclipsed them over the years with our community testing.

For single-based/temperature stable powders like H4198 and BENCHMARK are, according to this forum too fast and therefore too inefficient. I would only recommend them for SBR's. Your 20" barrel is better suited for slower powders like 8208 and H4895. For the avoidance of doubt a 'slow' powder refers to burn rate, not muzzle velocity. In the Grendel, faster powders can reach their max safe load with volume to spare that is unusable.

What is 'Safe' depends on the gun you are shooting - how strong it is, and of course your attitude to safety. SAAMI is a good benchmark however you can exceed it if you know what you are doing. Be careful of hot loads in an AR. AR's are not as strong as bolt guns. Your bolt will crack and this is the canary in the coal mine that your loads have exceeded SAAMI and are unsafe in that gun.

If you prefer single-based powders I advise using 8208 for bullet weights up to 120gn and 4895 for 120 and above, in a 20" barrel. You also need a chronograph so you know what's happening in your gun and not someone else's.

If you want a good source of load data across a wide range of powders the manuals 52' is recommending is a neat, comprehensive reference. Plus the Search function of this forum. A ballistics program like Quickload is also very helpful. Most helpful is a combination of all of these and of course, experience. Manufacturers may have the fancy strain gauges but we have the 'broken-bolt gauges' and a community of shared experience. This includes years of constant engagement/interest with the calibre whereas manufacturers have to dilute theirs across many other calibres.

Here's a picture of Hogdon's powders in a range from fast on the left to slower on the right. Note how the kernels get bigger and longer the slower the powder. Your BENCHMARK will meter well but I wouldn't use it.

[tdbru]

this load was for a 22" mini howa. trying to find some load combo that groups 100gr. Barnes TTSX out of my mini howa i tried 29gr. of benchmark today. averaged 2683, with SD of 11.4 but didn't group worth a hoot. but neither did any other powder i tried with the 100gr. TTSX. so far. but they've got a LOT of jump. which is what Barnes says to do. so next rounds will be seat out further, back down the powder and start over. i was trying benchmark because i was trying a 100gr. bullet. as Klem and LRRPF52 have both said, for heavier bullets, chose a slower burning powder. i have also used benchmark with the Sierra 85gr. Varmint bullet. and it works pretty well for that light bullet, short bearing length. with the 85gr. Sierra varmint bullet i was loading 31 gr. of benchmark for the same rifle. avg speed = 2943 and SD of 7.4
these group much better than the barnes 100gr. TTSX even so the 85gr. weren't grouping like a match rifle either. probably my poor shooting ability. but i am determined to find a decent load for the barnes 100gr. TTSX for my little howa. so to repeat good advice from previous posters, Benchmark works ok for light weight bullets for the grendel, but for the normal 120-130 gr bullets, it not as good for purpose as other ones are.
-tdbru

[Code4]

BM2 2,421 fps Howa 20" barrel

[sbowhuntr]

Never ran benchmark with anything heavier than 95g vmax, mostly use it with the 90g tnt's. I have had awesome results with it in my grendel and a handful of other small bores. Cant remember the velocities with the tnt but im running 30.2g benchmark and cci 450's at 2.20 oal.

[caleb90]

i use benchmark for my 100gr nosler cc. 28.5 gr yields 2650fps out of my 20in tube

[Klem]

Caleb,

Have you tried using 8208 with the 100NCC?

[CXRs]

Ok so I'm at the range now, and just got some bullets on paper at 1, 2, and 300 yards. I've got about 6" of drop at 2, and almost 20" at 3. Using Strelok this has me in the low 2200s, which is much lower than I'd like to be.

I now realize that benchmark is a bit fast, and the only reason I went with it was because it was the only powder I could find locally for a reasonable price(local store wanted $45 for 1lb 8208). My only issue is that I'm getting insane groups, routinely under .5" at 100, and I'm not sure i wanna give that up for an extra 100-200fps. If 8208 or some other powder will get me up to 2500+ and keep the accuracy, then I will gladly pick up whatever I can of it.

[CXRs]

I just realized that part of the reason I picked up Benchmark, aside from the price, was this video:

https://youtu.be/LCTpO38Ew54

I came across it while looking for powders to start with, so I grabbed it the next time I saw it.

And thank you everyone for your help! I will be picking up some IMR 4198 the next time I'm at my local reloader's shop. Right now the slowest powders I have are IMR4895, AR Comp, and CFE223, but I can't really find anything on those for 123gr, but I'm seriously considering picking up those manuals to see if thethey have anything on it.

[A5BLASTER]

I just realized that part of the reason I picked up Benchmark, aside from the price, was this video:

https://youtu.be/LCTpO38Ew54

I came across it while looking for powders to start with, so I grabbed it the next time I saw it.

And thank you everyone for your help! I will be picking up some IMR 4198 the next time I'm at my local reloader's shop. Right now the slowest powders I have are IMR4895, AR Comp, and CFE223, but I can't really find anything on those for 123gr, but I'm seriously considering picking up those manuals to see if thethey have anything on it.

No need to pick up powder. You have ar-comp, it will give you the speed, the accuracy is up to you and the barrel.