Benchmark burns hot it seems

[watson556]

First, hello everyone. What an incredible site. I love the "entrance exam". This-here post is evidence I passed

Okay, so I'm toying w/ some powders in a 223 wylde gas gun and the new Nosler 64gr BSB bullets. I have learned, observed, realized or dispelled many, many, many things in the course of this endeavor. One thing that has occured to me was by unintentional consequence rather than by design of experiment.

As I developed a course of loads to shoot I had formed the habit after each shot of safing the rifle, sliding the rifle back forward in the rests, recording the velocity, recording the impact, then grabbing the brass and observing it and placing it back in its order in the box.

All was unremarkable in this rote repetition until recovering the first case loaded with Hodgdon Benchmark - "Ouch, that's hot!" Mind you, I had been very methodical in shot intermission so as not to overly heat the barrel up and skew the grouping progression. "Odd", I thought, "let's see if that happens again. "Bang",... (OCD steps noted above)... Ouch!" Yup. And thusly was the experience for every round I fired loaded w/ BM, that day, every other day, cold/hot barrel, light/heavy load, or otherwise.

So, to boil down where I am at with the powder and what has begiled me and driven me to join a site where the ballistically lucid hang out - I have a chance to buy an 8lb jug of it from a buddy. It shot respectable groups, functioned the action fine, had decent SD/velocity, and so on. What has me on the fence is that if I load it for this or any other bullet and decide to go 3-gunning, a civilian CQB-TTP course of instruction, or just have an ammo dumping frame of mind one day, I can't imagine that having BM driven loads regurgitate all that heat into the direct impingement action is conducive to anything good. Other powders I have tried so far have resulted in cases much, much cooler to the touch w/ better velocity but less accurate and/or more sensitivity to barrel temp.

Does anyone have anything of technical, anecdotal, experience to share w/ me to help me see something more clearly in the vein of thought as it pertains to BM and gas guns and/or flame-temp or what have-you?

 

[fredhorace77]

imo benchmark is too fast of a powder for 64gr. bullets ...go to Varget.
Benchmark for bullets weighing 35-50gr.
H4895 for bullets weighing 50-60gr.
Varget for bullets weighing 55-75gr.

 

[KMart]

In gas guns, especially AR's, I have found that all empty fired cases are smoking hot when they leave the chamber weather it is Benchmark, Varget, 4895 or whatever. I think it has to do with the design of a semi auto where the bolt is opening to some degree as the bullet leaves the barrel, forcing hot gases onto the fired cases.

 

[CatShooter]

imo benchmark is too fast of a powder for 64gr. bullets ...go to Varget.
Benchmark for bullets weighing 35-50gr.
H4895 for bullets weighing 50-60gr.
Varget for bullets weighing 55-75gr.

What he said...

 

[markm87]

Never noticed Benchmark heating up any ARs out the the norm in the past. I use if for 55 gr blaster ammo, and it seems to group better towards published max loads.

 

[vtmarmot]

I have been shooting H-4350 in my .260 F-Open rifle. Another shooter said I should try H-XXXX because it burned a lot cooler than other powders. I didn't particularly want to change loads, but I called Hodgdon just to see if there was any truth to it. The tech guy said that the difference in burning temperature of all of their powders is insignificant. I have shot a lot of Benchmark in my 30 BR and now shoot H-4198. I remove fired cases with my fingers and I find that with both powders they are equally mildly warm. I would find something else to worry about that is significant, such as the intensity of various brands/types of primers.

 

[JamesnTN]

Last weekend at the Top Gun Shoot in Ky while I was shooting my AR with 24 grns Varget and a 69 grn Sierra Mk I was told the brass coming out of the chamber on each shot was cherry red. I knew they were hot but never knew just how hot until he told me.

 

[MrMajestic]

Does anyone have anything of technical, anecdotal, experience to share w/ me to help me see something more clearly in the vein of thought as it pertains to BM and gas......

I have many stories and words of wisdom but this just doesn't seem to be the correct portal! ;D

 

[markm87]

Check out this tidbit I found over on TheFiringLine.com

Now I wouldn't put benchmark in the SLOW burn category... but some interesting variances observed in this guy's test.

http://thefiringline.com/forums/showthread.php?t=532039

The faster the twist, the higher the burn rate temperature and the faster the bullet is pushed are the factors that really "cook" barrels. Chrome-lined, 1/7 twist, hot and slower powders (such as Varget) with light bullets has been a problematic recipe for heat related barrel damage.

When I ran some tests for a manufacturer in such a barrel with 50 grain bullets pushed at 3300 fps, the surface temp of the barrel after 100 round beta mag dump was about 105 degrees hotter than a sister barrel shooting 77 grain slugs at 2800 fps with a cooler powder. The peak temp on the hotter load occurred 75 seconds after the last round was fired and just 12 seconds after the last round on the cooler load. Those 100 round mag dumps were just over 14 seconds, or just under 7 rounds per second. It was slower than the FA rate the barrels were intended to be used at, but the hassle of a FA lower was not worth it. When the barrels were examined with digital x-ray, I was able to see gas port erosion on the barrel that was run hotter around the 1400 round mark. The one that was run cooler, not until just past 11,000 rounds was I able to detect any gas port erosion. In the 1/9 barrels, pretty much all else equal, gas port erosion was first detected at about 7,000 rounds.

If you have fast twist barrels, light bullets, especially with hot slow powders, should be avoided. I avoid anything under 55g in 1/7 and 1/8 barrels and anything lighter than 50g in 1/9 barrels. The new VDC coatings (what I was actually testing) do perform much better than chrome lined when exposed to high heat cycles. Lengthening gas systems also helps.

 

[watson556]

Thanks for the replies. So much to say, so little time. I’ll start the process and try to get back later tonight…

Regarding the optimum/light bullet weight niche of BM in 223 (BTW, MrMajestic , that was damn funny to re-read that – I assure you, any inferences were flatulently unintentional ) I got this from Hodgdon’s website for 77gr SMK's:

Hodgdon CFE 223 22.5 2627 45,400 PSI 24.3 2811 53,500 PSI
Hodgdon BL-C(2) 23.0 2640 42,500 CUP 24.9 2804 50,700 CUP
IMR IMR 8208 XBR 20.5 2535 41,800 PSI 23.2 2792 55,000 PSI
Hodgdon Benchmark 20.5 2523 27,400 CUP 22.8 2763 50,000 CUP

Granted Hodgdon’s data is for 223 chambers, and on the conservative side at that, it appears to be only 48 FPS off the fastest powder for the 77gr SMK, and 2 of the 4 are “new wonder powders”. I am not making a case from this one data reference that BM is ideally suited for heavier bullets, I honestly have a very low mileage ride so far w/ the powder, but I do find this data to be a curious thing at the moment.

I have also scanned some references in the last couple days regarding the physical chemistry involved in the flame temps of various powder types. From what I have gathered so far, there are distinct differences in flame temps between single and double base powders as a general correlative relative to pressure, and that the faster the burn rate of a particular powder relative to the particular bore ratio of the cartridge it’s in, the hotter it burns as well. Granted there is a lot of room in what I just said for my interpretation and that I haven’t seen/read all there is on the subject.

I can say for certain though, that the cases that were coming out of my rifle w/ BM were significantly hotter (as in it was on the brink of outright burning me) than the ones coming out with TAC, Varget, and IMR-8208XBR (as in they were very easy to handle). I can say it also seemed that TAC cases might have been the coolest, but I wasn’t observing as much for that… yet.

It seems what marm87 referenced is barking up that same sort of tree too.

Check in later I hope…
w-