Bullet/Cartridge comparisons: 7.62x51, 6.5G, 7.62x67

wigwamitus

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I'm trying to make some ammo decisions.

I've been shooting all six of these over the past several years and trying to pair down to one primary ammo for each gun. The actual cartridges are:

.308WIN
Double Tap 155gr (sierra bullet #2165)
FGMM 7.62 175gr

6.5G
Hornady 123 ELD-M
Federal 130gr Berger

.300WM
FGMM 190gr
Barnes 220gr

==
I used several of the formulae - ideas in Brian Litz's “Applied Ballistics for Long Range Shooting”, Third Edition, 2015 .

For those unfamiliar with these ideas, briefly:

Danger Space - a measure of the distance in front of and past a given size target at a given distance at which the in flight bullet "covers" the target in the vertical dimension. The larger the danger space the higher the probability of a hit.

Lag Time - The total flight time minus the flight time in a vacuum. We can control for this by selection bullets/cartridges which minimize the lag time. A smaller lag time results in less wind deflection.

Predicted MV. This is a handy lilttle formula that allows us to estimate the possible MV of a bullet/cartridge given a known MV for a known bullet and the weight of a second bullet. Since I had real MV numbers for all six of these, I ran the calculations in both directions. This gave me an idea about which cartridge was the "hotter" load. The prediction is based on the idea that predicted MV will have the same pressure as the known cartridge.
==

So the biggest surprise was the 155gr SMK versus the 175gr SMK. BL makes it clear that the heavier, higher BC bullet will usually "beat" the lighter faster lower BC bullet, unless the lower BC bullet is going at a much faster (possibly unsafe) velocity. Well, in this particular case, the 155gr wins on both danger space and lag time at the distances I compared (between 500yds and 1,050yds ... where I can get to on my land). And more surprisingly the MV predictions indicate the 175gr load is the hotter of the two. I have some HSM 155gr 7.62 load ammo inbound and the nominal MV for that cartridge is 2900. For the Double Tap load the nominal MV is 2850, though the observed MV is 2774 out of my 22 inch barrel. So we will see what the HSM load can do.

==
With the 123gr vs the 130gr ... I keep wanting the 130gr to be better ... the BC is higher ... but out of my gun anyway ... an 18 inch stoner in this case ... the observed MV over two 20 rd sessions has been 2252 and yesterday 2244. With that average MV of 2248 ... the 130gr is not worse, but it is not much better. And not worth the extra cost . BUT, the MV predictions indicate the 130gr could be loaded hotter. If I was going to continue with the 6.5G I would drill into this and possibly reload trhe 130gr if I could show that a load could exist which would beat that 123 by a sufficient margin. But right now, I'm thinking of putting the gun on the shelf, keeping the 1200rds of 130gr and 800rds of 123 I have and deactivating this line for my purposes.

==
As to the 190gr vs the 220gr ... well the MV prediction indicates the 190gr load could be hotter ... if I can find one, then the 190gr will win out to 1200yds. I was a bit surprised here. But the numbers are the numbers.
 

wigwamitus

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My main shooting buddy asked me if the 155gr would be stable in our 10 twist barrels. Per the "Miller Stabilization Formula" and including the adjustment for MV (2774/2800)^(1/3) the answer is yes as the SG = 2.17

That's a bit of a surprise also. I thought the 155gr would be borderline unstable, but per the Miller formula, it is fine.

So the only issues with adopting the HSM 155gr cartridge for me will be

01 - Will it group around my average with other ammo of 0.65 inches ?
02 - Availability ... only source is HSM
03 - Price .. buying in bulk will get the price down under $1.40 per round, close to $1.30 per round including shipping. The FGMM 7.62 175gr is $1.04 per round with shipping
04 - Erosion ... I presume the faster lighter cartridge will induce more erosion and reduce barrel life, but not sure how to measure that.

That said, if it passes 01, I will probably adopt the HSM 155gr load for one of my rifles, given the external ballistics numbers.
 

wigwamitus

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Per BL, another factor in erosion (04 above) is bearing surface length. So I found the bearing surface for the 155 SMK #2156

http://www.appliedballisticsllc.com/Articles/ABDOC107_2_Sierra155MK.pdf

and for the 175gr

https://rifleshooter.com/2015/06/si...elopment-and-review-308-winchester-and-varget

So bearing surface for the 155gr is .273 the bearing surface for the 175gr is .403 So the lighter faster bullet has a significantly shortly bearing surface than the heavier slower bullet. But I do not know the exact relationships between bearing surface, velocity and erosion. Just that BL says there is ... per this WEZ analysis.

]http://www.bergerbullets.com/images/articles/WEZ_300_Win_Mag.pdf


And the MV difference with cartridges I've currently tested is 2774 for the 155gr and 2652 for the 175gr.

So 4.5% more MV for the 155gr but 47.6% more bearing surface for the 175gr !
 
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j-huskey

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Historically, erosion is caused by heat and friction, the hotter the load, the hotter the barrel, the hotter the course of fire, the more erosion.
In former competition, "rattle battle" ate barrels.
The NRA 200 and 300 yard 20 round rapid fire strings ate 762 barrels pretty fast, not uncommon to lose M1A's at 3500-4000 rounds and get 8000 out of a slow fire bolt gun.
The 155's generally run hotter than 175's in my Palma shooting days. Luckily Palma was all slow fire.

The 300 magnums eat barrels in any rapid fire situations. 1000-1200 rounds and I've lost several barrels there.
6.5-06 and 6.5-284 ate them at 1800ish.
6.5 grendel still running, havent killed the first one yet.

Jmhe
vr
 
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Snuby642

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@wigwamitus
So could I get a conformation you have ran the 130gr berger hybrid in 6.5 grendel gas gun?

I was thinking of it but started figuring length and powder capacity would kill the deal.


Getting board of hornadys not preforming that good at mag lenght for me.
 

Snuby642

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I will recalculate lengths in the morning.
I have a 20 inch stoner to work with.

Thank you
 
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wigwamitus

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Since starting this thread 14 months ago, I started reloading Oct 2019.
Also I sold the Grendel upper in summer 2019.
Shooting buddy #1 and I are now down to two calibers for center fire rifles and carbines.
For 556 I am reloading 77gr SMK and for 762 the 175 SMK.
However, working on a load for 155 SMK.

The problem with the Federal/Berger 130gr cartridge was the MV was less than desirable (under 2300 in my 18 inch no-name barrel) and hence the performance was roughly equivalent to the Hornady ELD-M, which cost less and was more highly available.
However, if reloading, this could change. With the right powder and 2 more inches of barrel to work with, the goal of 2400+ might be attainable.

If I were doing this now, I would include CFE123 in the list of powders to try. That's the powder I'm currently trying with the 155gr. I tried Varget (which I'm using for the 175gr) and IMR 4064 and now trying the CFE123. Out of a GOOD barrel (Criterion 22 inch) I've gotten 2917 MV with no sign of pressure, with a standard length (with fit in SR-25 mag) cartridge. And that's better than the HSM 2891 I got though not as good as the Berger/Berger 155.5 "fullbore" (aka palma) I got. Though the berger/berger is a long coal cartridge, whereas the HSM is standard length.

So, CFE might work for the 130gr as well.

I have learned that "the barrel matters" ... and I don't just mean its different, I mean I have two REM700 SA actions. One has a factory REM barrel, the other a criterion heavy barrel. The criterion barrel is much faster and strangely seems to show less pressure signs with the same load. I just bought tools to rebarrel the factory barrel over to another criterion. It will be my first rebarrel, but I think it is do-able with the right tools and the right patience.
So, again, barrel matters, at least in my experience, in terms of ability to get the results you are after.
 

j-huskey

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Barrel matters !!!!!!!!!!

I'm having a similar thing on slower higher pressure barrel vs faster no pressure barrel. Both are custom built guns by big name smiths. Absolutely zero problems with the smithing.

Friends are running 2900fps with a certain bullet with retumbo powder, several friends, and none of them have had any problem. None.
My 3 groove fast barrel, will run their loads all day long, as fast as them. And factory ammo, zero pressure sign.

Custom barrel #2 has proved to be a tighter bore, cut with the same reamer and throat. It doesnt eat the 2900fps load and wont eat some factory loads. It has annoyed me now three years to get to this understanding.
It shoots unbelievably well, so well, I choose to keep it as is.

Now, for Grendel...
Both mine have Alexander Arms barrels, 18 and 20. I have considered rebarrelling both with custom barrels because these two rifles confound me beyond belief.
As long as I shoot factory hornady 123's, both shoot 2400-2450 all day long.
Reloading both once fired and new brass I find 2400-2450 with 123's almost as good and equal to factory.

ANY bullet outside that, doesnt matter whose or what load, both rifles become different animals.

If I were Snuby, I would test a couple of boxes if Fed Gold medal premium with the Berger b4 I tried any reloading of it.
If Snubys grendel are like mine, it might save some frustration.
It seems the Alexander Arms barrels were optimized to run the original 123 hornady, and do so pretty well. The 18" barrel has an 8 twist, the 22, a 9 twist.
I think this is because the bullets are running so close to minimum ballistic coefficient speeds, AA put different twist rates to hold rotational velocity to gain the longer range performance and these barrels perform right on, barely, the edge of the envelope.
And this is why my factory bullet performance outside of the 123's has been edge of bizarre and my reloading attempts outside the "factory 123 copy" with different weight bullets has been insane enough that I am buying case lots of hornady 123s and staying with that.
No more reloading grendel for me.
Best to you Snuby.
 

Snuby642

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You guys have hit it on the head.

Its a 1/8 20 inch and the factory 123's preform but I am a stubborn old guy.

Out doing that factory load has now officially made my bucket list.

The Berger bullets may be the trick if I can shove them fast enough.

I think Hornady ay be pushing a proprietary powder or blend of some type.

Blending powders is above my pay grade.
 

Snuby642

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Your comments are spooky on point.

What started all this was my sons ruger tactical 20 inch. The magazine is mag lenght 2.800000 with about .020 clearance at best. The chamber is short and lands close.

I belive they hammer forged it using fgmm 168 as a mandrell. It doesn't like much else at all.
 

j-huskey

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Grendel is a hog killing piece of machinery. Not to bad on deer either. I've killed hogs dead right there at 350 yards several times. Made one 450 yard kill.
Reason I suggested a couple boxes of factory, if the rifle shoots the factory load, you can make it shoot the same bullet. Chronograph them and try to match the factory velocity. I didnt have any trouble matching hornadys load with me using AA2520.

I really do want to do a custom barrel grendel like a 3 groove benchmark, that I know is stress free. My AA barrels are NOT stress free, and I can tell this very easy using two different suppressors.

Right now, I'm working out Warner solids in both 338 lapua and 375 cheytac for elr, and just dont have time to mess with rebuilding the grendel right now. It's on the bucket list. One of the 338's is referenced above.. problem child with a tight barrel.

I'm always interested in hearing how grendel loading goes. I really do like that caliber.
 
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wigwamitus

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Ok, but what we meant about "the barrel matters" ... is like .. my two REM700 barrels ... shoot sub 0.5 inch groups with my varget 44gr and 175gr SMK ... I want to switch to 155gr SMK because on paper the ballistics are better out to 900yds, which is how far out I shoot, officially (actually I go out to 1050yds).

But both my barrels were apparently reamed for 175s ... so the 155s don't group up as well ...0.75 inch ... hence rebarrelling required ... the new barrel will be reamed for 155s ... so hoping to reverse the current state and get sub 0.5 with 155 but retain 0.75 with the 175.

If your barrel was reamed for the 123 .. it might not group as well with the 130 .. you'll have to try it and see.

==
Now given that ... yes my challenge is to push the 155 fast enuff to replicate what the factory HSM 155 and Berger/berger 155.5 can do ... which is blow away the 175 on lagtime, danger space and even energy ... and yes I suspect both the HSM and berger/berger are using "magic dust" powder ... but so far, it seems the CFE223 is promising ...
 

Snuby642

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I think I will do some side by side testing with the Berger's and 123's.

And may as well do the 8208 and cfe at the same time.
Hornady lists cfe223 at 2500 fps maxgr is 31.2 . Wow
 

j-huskey

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I think I will do some side by side testing with the Berger's and 123's.

And may as well do the 8208 and cfe at the same time.
Hornady lists cfe223 at 2500 fps maxgr is 31.2 . Wow
Couple of my guys are getting right at 2500 with 30.5 cfe223 with 123's in 20" guns.
 
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deersniper

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Since starting this thread 14 months ago, I started reloading Oct 2019.
Also I sold the Grendel upper in summer 2019.
Shooting buddy #1 and I are now down to two calibers for center fire rifles and carbines.
For 556 I am reloading 77gr SMK and for 762 the 175 SMK.
However, working on a load for 155 SMK.

The problem with the Federal/Berger 130gr cartridge was the MV was less than desirable (under 2300 in my 18 inch no-name barrel) and hence the performance was roughly equivalent to the Hornady ELD-M, which cost less and was more highly available.
However, if reloading, this could change. With the right powder and 2 more inches of barrel to work with, the goal of 2400+ might be attainable.

If I were doing this now, I would include CFE123 in the list of powders to try. That's the powder I'm currently trying with the 155gr. I tried Varget (which I'm using for the 175gr) and IMR 4064 and now trying the CFE123. Out of a GOOD barrel (Criterion 22 inch) I've gotten 2917 MV with no sign of pressure, with a standard length (with fit in SR-25 mag) cartridge. And that's better than the HSM 2891 I got though not as good as the Berger/Berger 155.5 "fullbore" (aka palma) I got. Though the berger/berger is a long coal cartridge, whereas the HSM is standard length.

So, CFE might work for the 130gr as well.

I have learned that "the barrel matters" ... and I don't just mean its different, I mean I have two REM700 SA actions. One has a factory REM barrel, the other a criterion heavy barrel. The criterion barrel is much faster and strangely seems to show less pressure signs with the same load. I just bought tools to rebarrel the factory barrel over to another criterion. It will be my first rebarrel, but I think it is do-able with the right tools and the right patience.
So, again, barrel matters, at least in my experience, in terms of ability to get the results you are after.
Have you considered the TMK for 556? Reading about it seems like it is very slightly less accurate than SMK but has much better effect on living things
 

wigwamitus

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For me for the 77gr, I am shooting it out of a pair of mk12 ... and the key requirement is 12 inch steel at 750yds, day or night, rain or shine, etc. So sub 0.5 inch groups is not a requirement. Nor is enhanced terminal ballistics. Velocity and ballistic coefficient are the keys for the 77gr for my use cases. With sub 1.0 being fine for 100yd groups.

And at least Bryan Litz doesn't seem to rate the TMK any differently than the SMK for ballistic coefficient, so for now, I'm going with that idea. I might use the TMK to make it easier to tell it apart from SMK, unless I get up the nerve to paint the tips. That would cost less !
 
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