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Old November 2, 2012, 11:55 AM   #1
Eppie
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Replicating Federal GMM 308 ammo

Hi Guys,
I'm new to reloading so, now that I've worked out the mechanics, I'm starting to focus on powder and loads. The best ammo I've used is the Federal GMM .308 168HPBT. I'd like to use that as my reference point.

I've taken a couple of rounds of it apart to look at the powder and weighed it. The Varget powder is on the left and the powder from the Federal GMM on the right. I measured both of the federal and they came out to 43.9 and 43.8 grains.



I'm well aware that "looks" mean nothing in chemistry. I assume that Federal probably uses a propriatary gun powder.

So my question is really this: Has anyone here ever actually measured the velocity of a FGMM 308 168grain HPBT bullet? Or do you know where I could find that info?
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Old November 2, 2012, 12:27 PM   #2
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The one on the right sure looks like RL-15. Which is very popular in 308 loads
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Old November 2, 2012, 12:32 PM   #3
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GMM has been loaded with IMR4064 and Reloader15. The current Navy version of M118LR (Mk316 developed for SOCOM) uses a 41.75 gr charge of IMR4064 with a Fed GMM primer, 175 SMK. Standard M118LR brass.

The 4064 charge is supposedly more temp stable than the Re15 load, according to NSWC Crane.

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Old November 2, 2012, 01:38 PM   #4
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I just have a question, why would you want to replicate an ammo, when you could make better with all the qualities your want...like just as accurate, as fast but with less kick, or whatever else you may want.

Just wondering.
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Old November 2, 2012, 02:04 PM   #5
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jwrowland77,

A lot of guys I know are issued Fed GMM for their duty ammunition, and want to duplicate its ballistics for training beyond what they are authorized by their department.

Other times it just shoots so well in someone's rifle that they want to duplicate that performance.

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Old November 2, 2012, 02:05 PM   #6
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Ah ok...thank you for the reply. I was wondering.
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Old November 2, 2012, 03:15 PM   #7
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Jimro,

The Alliant website boasts RL15 was selected for M118 LR. Has something changed? I just figured that since ATK is the current LC contract manager and they also own Alliant, that they'd probably pushed to get that powder accepted.


Eppie,

I once pulled a box of the old GMM 168 load, and it had 43.5 grains of IMR 4064 under the 168 grain SMK. The claimed velocity was 2650 fps from a 24" velocity test barrel, same as it is for the RL15 version today (ATK also owns Federal now). QuickLOAD predicts 2648 fps, which is so close that the difference is utterly insignificant. So I know the IMR 4064 used in the rounds I pulled was very close to what's in the QuickLOAD powder model. That good agreement means that even if Federal was using a bulk grade IMR 4064 with a wider burn rate standard deviation, that the particular lot I weighed happened to fall right into the same burn rate range sold to reloaders as canister grade IMR 4064. The charge weights were ±0.2 grains, for a span of 0.4 grains variance, which is very good for a volumetric throw of IMR 4064's long grains. The loads were very slightly compressed. They were in Federal .308 Match cases with Federal 210M primers, obviously.

If I wanted to duplicate that load I would start by firing a whole box of purchased Federal ammunition over the chronograph. Then, starting at 41 grains, in no greater than half grain steps, I would work up toward the same velocity average using the same brass to see what the charge weight was with my lot of powder. Then I would switch to tougher brass for longer reloading life. Remington for every day shooting and Lapua for match critical loads. With both I'd be starting back at 41 grains of charge weight and working up just as before, checking to be sure the different cases didn't show any pressure signs reaching the same velocity, either.

I would also be double-checking to be sure accuracy stayed as good as with the commercial ammo. Sometimes when you roll your own you get worse before you get better. Search the sight for load work up and seating depth workup and other factors.
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Old November 2, 2012, 03:20 PM   #8
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jimro, jwrowland77

jimro,
I appreviate the info on the powder. As soon as I use what I have I will try IMR4064 or Reloader15.

jwroland77,
My reason for wanting to replicate the FGMM is that it has worked so well for me in the past.

Having said that, I consider that a starting point. As I gain experience I will look to improve it's accuracy. More accuracy is why I decided to get into reloading in the first place.
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Old November 2, 2012, 03:36 PM   #9
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WOW Unclenick YOU are the MAN!!!!!

That was more than I had ever hoped for. I am very grateful to you. I will print your response and refer to it as I proceed.

You have laid out before me a road map with clear path of action. Thanks for sharing the wealth.
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Old November 2, 2012, 03:40 PM   #10
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Unclenick,

The Army is still buying M118LR with a charge of Reloader15. It currently exists side by side in the inventory with M118LR Mk316 which has the IMR4064 charge and Fed GMM primer.

Currently the Army is looking at a PIP (Product Improvement Package) for M118LR and the Navy (Mk316 was developed by NSWC Crane for SOCOM) is shaking their heads and asking "why?"

They exist with the same DODIC in the inventory and are being issued side by side in theater (regular units get M118LR, SOCOM units get Mk316).

They are ballistically identical at 70 degrees F, but Mk316 shows less variation with temperature extremes than the older version. The Leupold Mk4 scope has a BDC turret that is calibrated for M118 under "standard atmospherics" so removing temperature from the equation lets snipers in Afghanistan focus solely on elevation as the major factor in ballistic change.

I don't know why Re15 is considered less temp stable than IMR4064, as it is advertised as a temp stable powder, but the math I was taught for MOA shift was 1 MOA difference per 20 degrees with M118LR and 1 MOA for every thousand feet above sea level, IIRC.

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Old November 2, 2012, 07:23 PM   #11
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Keep in mind that even if Federal uses RL15 for their GMM, or if Lake City uses it for M118LR that it is not the same RL15 you get at your local retailer.

They use non-canister grade powders that can vary from lot to lot, and adjust the recipe to get the specified performance.

Canister grade powders that you and I can buy are remarkably consistent, and a can you get today will most likely be close enough to one you bought a couple years ago that you couldn't tell them apart.

If you really want to duplicate the load, shoot a box across a chrono and get the average velocity. Then load Gold Medal brass, with Gold Medal Match LR primers, and a Sierra Matchking and tweak your load to get the same average velocity.

Honestly though, unless there is a really specific reason to duplicate it, you are almost certainly better off working up a load on your own.

For .308 sized cases, I have always had excellent luck with IMR4064.
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Old November 2, 2012, 09:04 PM   #12
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The thing is that the FC cases are very thick, and soft... not really good for repeated reloading... loose primer pockets will be the norm. And you'd of course have to be using FC cases if you're planning on duplicating their load. In winchester brass, you'll need more than 44 grains of RL15 for a good match load that will fly like the Federal load does (the FC cases are tighter on the inside, so less powder will make more pressure).

So whatever the powder is (and yes, it's almost certainly RL-15, we're here next to the Radford Army Ammunition plant, and all sorts of ATK components are spoken... and revealed...

...but, you won't simply be able to put that amount of RL-15 into any other case other than the FC cases (working up from published data, of course... watching for pressure signs of course... and realizing that your lot of RL-15 may not be just like Federal's lot)...

If you want to blow the doors off the Federal ammo, get some Winchester brass and work up to 43.6 grains of IMR 4895, using any good 168 grain match bullet. You won't be looking back...

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Old November 2, 2012, 09:41 PM   #13
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Eppie, you asked for some velocity info.

I have a Winchester model 70 .308 with a factory 26" heavy barrel.

Federal GMM 168gr ammo averages 2700 fps from this rifle.

Following Unclenick's methods I arrived at 45.0gr of Varget with the same bullet which is at or near max in most manuals. This load is a bit faster at 2750 fps. It betters the accuracy of the GMM ammo by a small but repeatable margin. Experimentation continues...

The results from your rifle will probably be different.
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Old November 3, 2012, 09:39 AM   #14
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While duplicating a given load's muzzle velocity is oft times the "objective" of lots of folks believing that it's the sure way to get its accuracy, nothing could be further from the truth. Best example's when Federal GMM .308 ammo's been chronographed in several rifles all shooting it well under 5/8 MOA at 600 yards, muzzle velocity spread across those barrels was over 60 fps. This is what some of us learned chronographing it in several M1 and M14 barrels. One lot of that ammo shot at least that accurate in three of my .308Win. bolt gun barrels and there was a 45 fps spread in its average muzzle velocity.

I used the same load across nine or ten .308 Win. barrels with the lot numbers of powder, bullet, powder and primer all being diffefrent. They all shot about 1/3 MOA with 168's through 300 yards, about 1/2 MOA at 600 with 180's, 190's and 200's and sub 3/4 MOA at 1000 with 190's and 200's. The same lot number and charge weight of IMR4320 across different lots of 7.62 NATO M118 primed cases was used in my handloads for Sierra 190 HPMK's across four barrels in Garand M1's; they all shot about 2/3 MOA at 600 yards and about 1 MOA at 1000.

Dan Newberry, I wish I still had the Federal brass .308 Win. case I reloaded 47 times with 42 grains of IMR4895 under a Sierra 165 SBT atop Federal 210 primers that was fired in a tight bore Hart barrel; definitely a maximum load. Primer pocket didn't open up and never annealed the neck once. Muzzle velocity spread was about 30 fps across all shots that went into 3/4ths inch at 100 yards. Friend of mine got 56 loads on his .308 Win. Federal brass case using the same load under Sierra 168's; they all went into 1/3 MOA fired in his machine rested match rifle at 100 yards.

I'm convinced that with new, unprepped .308 Win. cases of reasonable quality, 44 grains of IMR4064 under a Sierra 168 or 43 grains of it under a Sierra 175 or 180 using any decent primer and assembled decently, one will easily get sub 1/2 MOA accuracy from a decent rifle properly tested at 100 yards. If not, check out the rifle or the shooter's technique. Sierra does not work up loads for testing their bullets when changing lots of powder, primers or cases; their best 30 caliber match bullets go into 1/4 MOA at 200 yards.

Last edited by Bart B.; November 4, 2012 at 07:08 AM.
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Old November 4, 2012, 12:48 PM   #15
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Dan,

Unless I totally misunderstood your OCW load development system, replicating the velocity of an "accurate" factory load is pretty much irrelevant, no?

An almost infinite combination of powders and charge weights can deliver that end result- but it's the barrel harmonics/burn rate that's determines whether that MV duplicates the accuracy of the factory load (??)

So, if FGGM is a proprietary powder blend, the results could only be duplicated by trying to duplicate pressure curves with a strain gauge or similar?
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Old November 4, 2012, 02:14 PM   #16
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I'll go on record and say that FGMM .308 168gr SMK (GM308M) is the standard by which all others are compared to by.

Or to quote Federal:

Quote:
The Yardstick that all others are measured with! The FGMM 308 168 (and 175gr) is literally the "golden ruler" to which all others are measured.


I personally think Black Hills and Remington premium match ammo comes in a close second
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Old November 4, 2012, 06:11 PM   #17
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tobpnr, the barrel's gonna whip and vibrate the same for every shot; it's got the same "harmonics" which are multiples of its resonant frequency for every shot. It's metalurgy doesn't change 'cause it's shape is the same for every shot. But the amplitude the muzzle axis swings through will vary with the amount of powder used.

But the pressure curve for best accuracy has to be the same (within reasonably tolerances) for each shot. It doesn't have to produce the same muzzle velocity of a given lot of other ammo that shoots great. As long as that pressure curve's the same size and shape for every round, the bullet's going to leave at the same place in the barrel's vertical whip and vibration cycle. That pressure curve may well be a slightly different shape and size than the reference ammo' bullet produces, but as long as its repeatable for that same bullet, good accuracy will happen.

There's probably 2 or 3 different powders that could produce the same accuracy as Federal's .308 match ammo. The charge weigh won't be the same and neither will the pressure curves or muzzle velocity be. But as long as everything's repeatable and the bullet leaves the barrel at the right time, excellent accuracy will happen.
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Old November 4, 2012, 09:33 PM   #18
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Pretty much any powder in the IMR4896, IMR4064, Varget, Re15 burn range works just fine. Stick powders are preferred because they light easier, so you can use a primer with smaller amounts of compound, which causes less initial pressure variation.

I'm pretty happy with Alliant PowerPro 2000-MR in my heavy 223 loads, so when I use up my last 8 lbs of IMR4064 I might transition to it if it does as well with 308.

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Old November 5, 2012, 12:40 PM   #19
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Quote:
But as long as everything's repeatable and the bullet leaves the barrel at the right time, excellent accuracy will happen.
OK, I get that, it's the "heart" of the OCW principle.

Now, from what is being said here, FGMM's powder is not proprietary...I assumed it was...

But IF we're talking about a proprietary mix- say, Hornady Superformance (which is available in their loaded ammunition in .308, but not as a powder through Hodgdon), how could one "replicate" the powder's results- getting the bullet to exit the muzzle at it's most consistent point in space?
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Old November 5, 2012, 01:06 PM   #20
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What superformance load do you want to replicate?

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Old November 5, 2012, 04:10 PM   #21
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Looking at Hornady 308 Win Superformance GMX, we see 2940 fps. 24 inch barrel.

Looking at Alliant's data, we see AR-Comp max charge 2929 fps, 24 inch barrel. 11fps difference is close enough for "duplication" to me. Hogdon lists CFE 223 and a 150gr Nosler to 2974, which isn't the same bullet, but sure as heck is a higher velocity.

Moving up to the 165 GMX, Hornady Superformance lists velocity as 2750. Alliant lists both AR Comp and 2000-MR in excess of 2,800 with a 165gr Speer BTSP, not the same bullet unfortunately. Hogdon lists CFE and a 165gr Hornady BTSP to over 2,800 fps as well.

I really don't think that Hornady's Superformance line is really all that special. Pawpaw took apart some Superormance ammo a while back and commented that it sure looked like 2000-MR but with some weird green grains mixed in.

I dissassembled some of my 75gr BTHP 223 loads that I loaded this spring with 2000-MR, and guess what I found, some weird green grains that weren't there when I loaded the ammo. I don't know what that means for powder longevity, but it seems to me that handloaders can easily reproduce Superformance performance by picking appropriate powders.

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Old November 5, 2012, 04:20 PM   #22
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tobpnr:
Quote:
OK, I get that, it's the "heart" of the OCW principle.
Well, sort of, regarding when bullet leaves the barrel at the right time.

The OCW theory's based on the assumption that best accuracy's when the shock wave from the round firing has gone forward to the muzzle and is back at the breech end when the bullet leaves the barrel. As nobody's ever hooked up test equipment to verify this is reality, it's still just a theory. Meanwhile, consider the following facts; yes, facts.

The speed sound waves propagate in steel is stated somewhere between 13,000 and 19,000 fps depending on the source one looks it up in. Whichever speed you choose to use, it means that shock/sound wave from the cartridge will take from .000222 to .000308 seconds for one round trip back and forth in a 24 inch barrel. Typical barrel times for a .308 Win. bullet to exit a 24 inch barrel's about .002500 seconds. That shock/sound wave will make about 8.1 to 11.2 round trips from breech to muzzle while the bullet's going down the barrel. So when the bullet exits, one of those sound/shock waves will be no more than a few inches back from the muzzle. Until it's defined as to where that shock/sound wave starts at, there's a 2 to 3 inch range of barrel length at the back end one has to start its timing from; who knows where that's at? And nobody's published any inof on how long the bulged area of the barrel is where that shock wave is at. Nor how much does it enlarge the muzzle.

OCW believers championing the theory that the shock/sound wave makes the muzzle larger and that's a bad time for the bullet to exit might consider the following. Folks have tested top quality match conditioned M1 service rifles whose bore's been rubbed bigger by steel cleaning rods slid back and forth in their muzzle. The lands and grooves are enough larger that no copper wash from jacketed bullets exists for the last 3/4" of the bore. Yet they still shoot under 2/3 MOA with good lots of both Federal GMM .308 ammo as well as good lots of National Match lots of M118 or M852 arsenal ammo. That's as good as they shot 2000 rounds earlier when the barrel was new. Many very accurate barrels will have a groove diameter .0001" larger at the muzzle than a point a few inches back from it; that's normal best-qualty barrel making.

Yet in barrels from 22 to 28 inches long with a variety of bore and groove diameters shoot Federal GMM .308 ammo very accurate in spite of having that shock/sound wave all over the place in them as well as lots to cycle times for that wave to round-trip in those barrels along with lots of barrel times for each.

OCW theory, in my opinion is far too much UWAG-ing for me to believe. I'm still waiting for someone to prove it's reality. But it's a good competitor for Browning's BOSS system the makers thereof claim it makes the barrel shoot best (again, no testing's been done to prove it) when the bore straight out in the middle of its whip cycle; no mention of when its on the down or up swing when that happens.

Quote:
getting the bullet to exit the muzzle at it's most consistent point in space?
I don't think either of those two places where the barrel's most consistant point are best for accuracy. Here's why. But first note that most barrel's whip frequency at their muzzle is 3 or 4 times their resonant frequency or a few hundred cycles per second. They'll go through one cycle in about .002 to .004 seconds or something like that.

There's two of them; one at the top of the muzzle axis whip arc and the other's at the bottom. Barrels are bent the most in the wiggling whipping cycle at that point. But how much that angle changes in a few millionths of a second is the least at those places. Note that the barrel time from case mouth to muzzle will have a small spread which causes a small spread in muzzle velocity. Getting bullets to leave at either the top or bottom one brings up the following situations...

If the bullet's leave about the high point, faster ones will leave sooner as the angle gets bigger just before the muzzle axis is at its highest angle. Slower ones will leave after the axis is at its highest angle while it's on the way down. Some slower ones will exit at the same angle as some faster ones.

If the bullet's leave about the low point, faster ones will leave sooner as the muzzle angle gets lower just before reaching its lowest angle. Slower ones will leave after the axis is at its lowest angle while it's on the way back up. Some slower ones will exit at the same angle as some faster ones.

Both of the above will cause too much elevation shot stringing; each bullet's muzzle velocity's not compensated for. However, if all the bullets left just before the muzzle axis reached its top, they all would have good compensation to correct for bullet drop. Faster ones leaving sooner at lower muzzle axis angles would have about the same impact point as slower ones leaving later at higher muzzle axis angles.

Last edited by Bart B.; November 5, 2012 at 05:17 PM.
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Old November 5, 2012, 07:52 PM   #23
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I agree with Bart B. about not buying into the "shockwave in steel" theory.

I do however believe in barrel harmonics (in the sonic range, just like a church bell) and timing to coincide with that frequency.

How I understand harmonics: round steel rifle barrels vibrates in a "figure 8 pattern" with one major orbit and one minor orbit (in a perfect system the orbits would be equal, but normally we fire rifles relatively horizontal to the gravity well). The "shockwave" in the steel itself is traveling 90 degrees through the steel from this figure 8 vibration has very little to do with this other than providing the intial "hammer strike" that "rings the bell"

The muzzle whipping around in that figure 8 pattern will spend some amount of time in each orbit (if I remember physics correctly the velocity changes with the radius of orbit), so obviously you want the bullet to exit in the minor orbit (less movement because of a smaller distance to travel, so the actual velocity of the muzzle it as its smallest) even if the barrel spends a smaller amount of time in that "node."

As I understand it, OCW is about timing your load to always have the bullet leave the barrel on the minor node of the figure 8 (which is the physical vibration of the barrel itself, nothing much to do with the shockwave that started it).

This is why loads that have the same barrel time and different velocities can both group well, or you find distinct "accuracy nodes" during a load workup (For a 308 normally around 2,400 fps, again at 2550 fps, and again at 2650 fps, and 2750 fps (with a 168 or 175 bullet), and again at 2900 to 3000 fps for long barrels with 155 gr bullets).

This can also explain why the load with the lowest SD and ES may not be the tightest grouping in your rifle all the time (though generally it is).

But I don't have the experimental equipment to actually run the tests I'd need to confirm or deny my understanding of the whole process.

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Old November 5, 2012, 10:58 PM   #24
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Jimro, here's a link to the theory behind OCW:

http://www.the-long-family.com/OBT_paper.htm

It's all about the shock wave making the muzzle bigger and that's believed to not be a good time for the bullet to leave.

He's listed the speed of sound in steel at over 18,000 fps but others say its about 13,000 in 416R stainless steel used in rifle barrels. He also states that shock wave makes 4 or 5 round trips before the bullet leaves the barrel; his math ain't so good.

Rifle barrels, when screwed into a receiver bolted in a stock, whip and vibrate much like a fishing pole held in ones hand when it's flexed. Its back end doesn't move much at all but its front end does. Only when the barrel's free at both ends does it wiggle in somewhat of a figure 8 pattern. Best on-line examples of exactly how it whips are at:

http://www.varmintal.com/amode.htm.

A barrel's resonant frequency it vibrates at will be different when screwed into a receiver (one end fixed) than when free at both ends. It's higher when free, lower when one end's fixed.

While Varmint Al's numbers for the bullet's barrel time are not correct, his barrel whipping wave shapes are very accurate. Other links on that page show how bullets leaving as the muzzle axis swings up and is close to the top are at a good place for the bullets to leave at.

But I don't understand your comment
Quote:
that loads that have the same barrel time and different velocities can both group well, or you find distinct "accuracy nodes" during a load workup (For a 308 normally around 2,400 fps, again at 2550 fps, and again at 2650 fps, and 2750 fps (with a 168 or 175 bullet), and again at 2900 to 3000 fps for long barrels with 155 gr bullets).

Last edited by Bart B.; November 5, 2012 at 11:10 PM.
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Old November 6, 2012, 03:58 PM   #25
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Bart B.

To explain my comment.

Two powders that have the same barrel time may produce equally good groups with different muzzle velocities. Or they might not, but it is worth looking into.

During a load workup (Audette ladder, OCW, etc) you expect to find "accuracy nodes" with a given powder/bullet combination. I listed a few of the common ones.

Varmint Al should probably have a talk with Bill Calfee about how barrels actually vibrate. http://www.ozfclass.com/articles/1/psm_2005_03.html Because either one or both of them is wrong.

As far as the OBT paper goes, the author did not eliminate pressure variation timing as a cause of the variation that he proscribed to harmonics. He makes a good case for his idea, but when the shockwave traveling through steel is 5 to 8 times faster than the accellerating bullet, the "traveling wave" will have functionally traveled 8 to 10 barrel lengths by the time the bullet gets to the muzzle.

"Free Space Loss" of a traveling wave comes into play (the authors epiphany of guy wires transmitting a wave is stupid, there is no fixed point at the muzzle to reflect energy back towards the action), so the chart showing muzzle diameter verses time is misleading because each "expansion" must by less than the one before it (unless you get a secondary spike from the powder, as outlined here: http://www.shootingsoftware.com/barrel.htm).

Now if the OBT method produces accurate ammo, by all means use it :-) Whether it is actually modeling the truth is another matter (one that makes me wish I had a few laser measuring devices to accurately map barrel movement during firing).

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