Range Report What the monkey duece..? (Something I'm kinda picking up)

[TallShot]

So the past couple shooting sessions, from 300-795yds, I've been noticing some change in my zero, as it's been showing at longer ranges. Haven't checked 100yd zero on paper since the spring, since I mostly shoot smaller steel at distance.


Well, today, I load up my not so awesome home-made target stand, some home made 1" square tagets on paper, my roller of 100ft tape measure, a shit load of shooting essentials, some 45% ipsc targets from ole jcvibby, rifle, my 4 & 6 yr old boys, and left my pride at the house.

Here's what I think I found....

I'm shooting a 700 AAC 20" 308. Bushy DMR, G2 ret., AICS stock. I put a YHM flash suppressor on it when I bought it. It's shot pretty well in the 800+ rds through it. However, I've NEVER got it to shoot 175 HPBT's worth a damn. Ever. This fact, plus the change in zero brought me to today.....

I shot the first group with the FS on, 5rds, 168 FGMM. I listed the rest of the groups.... The "Oops..." was a correction I meant to make -.2mil down, but went +.2 up, as I was turning check on the boys making sure they were not flailing each other with gravel, and they still had their ears on.....

I'm curious as to why this rifle will not shoot the 175's. And I've tried FGMM 7.62, FGMM .308 175's, and Southwest Ammo 175's (which were the worst). All I can say is " WTF "...?

But I did learn that the rifle shoots damn good without the FS, but almost as well with a well torqued FS

Oh, with the corrected zero, I was nailing the 620yd 45% ipsc target regularly It was still slight right, but I'm thinking I need more time with that slight wind.....

Pics:

Spider-Man approves

 

[TallShot]

Gosh it's slow around here.

For the "too long, didn't read" crowd; Why is my 10tw AAC 308 not shooting 175's worth a hoot? And what's the deal with it shooting better without the flash suppressor?

 

[gstaylorg]

You know it shoots well with FGMM168s, so it's not likely the rifle. You know it shoots well with FGMM 168s, so it's not likely the shooter either. What does that leave? My guess would be that your chamber/barrel harmonics simply aren't optimal for the FGMM 175 load. I'd be willing to bet you could get it to shoot the 175 SMK well with a properly tuned handload.

If you don't reload and are limited to factory ammo, this is one of the inherent downsides you'll encounter. You're at the mercy of someone else's load and the best you can do is try a variety of different loads and find what works well, and what doesn't work well. It's entirely possible you could try SMK 175 match loads from other manufacturers, such as Black Hills, CorBon, SW Ammo, Copper Creek, etc., and find one that does shoot well in your rifle. They will all have slightly different load specs, one of which may be more optimal for your rifle.

 

[TallShot]

I get the harmonics.

Just not sure how it could from what it shoots with 168's to that bad...... I'm sitting on 500rds of the FGMM 7.62 175's

Might have to attempt to locate some Black hills.

 

[KATLarsen]

Maybe the 175s you're shooting just don't like the twist rate or the harmonics are slightly off. Is there really that huge of a difference in BC between a 168 and 175? I know the military just switched, but those R700 barrels are custom contours and custom rifling (twist and type).

 

[DocB]

TS,

Hey, look at it this way: You've got 500 rnds. someone else would love to have. Take advantage of the situation.

HTH,
DocB

 

[Temp9]

Maybe the 175s you're shooting just don't like the twist rate or the harmonics are slightly off. Is there really that huge of a difference in BC between a 168 and 175? I know the military just switched, but those R700 barrels are custom contours and custom rifling (twist and type).

The BC isn't the entire problem with the 168's. Those bullets destabilize very quickly in transonic flight due to the angle of the boat tail. As such, they're not much use past 900 yards or so.

 

[TallShot]

Maybe the 175s you're shooting just don't like the twist rate or the harmonics are slightly off. Is there really that huge of a difference in BC between a 168 and 175? I know the military just switched, but those R700 barrels are custom contours and custom rifling (twist and type).

I've witnessed and read so many reports that 10tw is the beans for 175's and up, so it's had me scratching my head.

And not too concerned with what the mil goes with. I just wanted to standardize one factory match load for my 308's. And 168's have been becoming a little harder to find compared to 175's, in the last 8-9 months.

Used to reload, but no time anymore. Would rather pay a little extra for the convenience of just grabbing some boxes of ammo and going...

 

[TallShot]

The BC isn't the entire problem with the 168's. Those bullets destabilize very quickly in transonic flight due to the angle of the boat tail. As such, they're not much use past 900 yards or so.

Not that I've shot that far, yet, but I'm getting there.

I do like the little extra wind bucking of the 175's.

Anyone have suggestions of torquing the FS? Such as how many inch lbs

 

[Tomcat088]

Gosh it's slow around here.

For the "too long, didn't read" crowd; Why is my 10tw AAC 308 not shooting 175's worth a hoot? And what's the deal with it shooting better without the flash suppressor?

I'm in agreement with some others that the rifle just must not like the particular loads that have been fed to it, and that you could probably get it to shoot the 175's fine with handloads. I'm definitely not an expert, but I have some input on some possibilities on why it may shoot better without the flash hider.

For one thing, it definitely changes the barrel harmonics of the barrel for a lot of reasons, whether that's differences in material, length, torque (value it's tensioned at), etc. etc. As you're aware of, all of those things can have some effect on the way the barrel shoots. Something else to keep in mind is that there is a column of gas preceding the bullet before it exits. The flash hider is definitely affecting that column as the bullet exits, and because you are shooting a precision rifle with tight accuracy requirements, it may be something that has enough affect on the bullet, yaw, etc. that the difference is measurable because of the inconsistencies; although I don't think it's really the culprit.

The other thing that I noticed, and where I think variation could be introduced is related to the flash hider's slots and the indexing of their position. From what I could tell, you don't have a level on your rifle. That's fine, and most people would say that it's probably not going to be a big deal for your groups at 100 yards. I think it's possible that you may be canting the rifle slightly from one shot to the next, and it's affecting the position of the ports on the brake (where they're indexed). Because there is gas that precedes the bullet, I think that it starts to pass through the flash hider and will slightly move the barrel while the bullet is exiting. If the rifle is canted, then the ports aren't at exactly the same place every time, and this would make the barrel move in a slightly different direction due to the gases venting on slightly different angles. I can't prove that, but that's what I think is happening, and from what I've seen happens with high speed cameras and rifles being fired.

Personally, I think having a flash hider on a precision rifle is a bit silly, especially if it's not there to use to attach a suppressor to. Muzzle brakes definitely have their place and purpose, but they're still different from a flash hider. If it was me, I'd take the flash hider off and put the thread protector back on it.

 

[Greg Langelius *]

I agree completely with the suggestion that the flash hider could be messing with the barrel harmonics. While it is possible that a flash hider may provide a muzzle mass that just exactly produces barrel harmonics which are in tune with a factory load, that's highly unlikely. Loose parts attached to the barrel are also less than optimal.

Besides, using a flash hider in a long distance application may or may not make tactical sense, even in a combat environment.

Often, it's a lot less accidental that a production barrel and a factory match loading are pretty compatible. Altering barrel harmonics by adding random sized masses to the muzzle is a whole lot less likely to produce such compatibilities.

I say all this after having recently engaged in a year-plus-long project looking into barrel tuners. They work, but just when they start working really well, they also start getting really sensitive to changes in the environment. I abandoned them in favor of developing more forgiving handloads.

As for the 168 FGMM's, unless you are shooting significantly over 800yd with a really shorter barrel, they may just be a better load than the 175's.

I found that the .30-'06 168 FGMM load works fine at 1000yd in a 24" barrel, which is probably why Federal doesn't appear to make a 175gr .30-'06 loading.

I am also not in favor of attempting maximum distances with a shorter barrel, i.e. under 24". My own 1000yd barrel is 28" long, chambered in .260 Rem. The added length is not about achieving extra velocity; rather, it is about achieving reasonably adequate velocities with tamer loads. This preserves throat life. No matter what your velocity, you are still a slave to the winds; and going faster doesn't really make enough of this go away to make the added throat wear such a great bargain.

At 800 rounds, the throat may be getting a bit longer. This is one specific area where being a handloader can be especially helpful.

Also, with a flash hider on the muzzle, there may be carbon accumulation of the face of the barrel, itself. This accumulation is seldom symmetrical, and can have accuracy consequences very similar to crown damage.

Greg

 

[TallShot]

@ Tomcat; that's a very interesting thought. Thanks for the insight. And I might put back on a level, and see if I'm canting a bit. I had a USO level on it for while, but found it distracting and I didn't trust it anyhow.

 

[TallShot]

[MENTION=79378]greg[/MENTION]; thanks for chiming in man. No carbon build up at muzzle. I put the hider on there primarily for protecting the crown/muzzle, and it does a great job of directing the blast away from me.

Reloading just isn't an option for me right now. Used to do it, but no time with shift work, kids, and trying to chase a load.

I agree with the longer barrel for longer distances. I want 24" 5r, but this is what I have to work with for now. And over the last year or so, I've definitely been shooting at 400-800 yds regularly. Gonna have to step up and get a longer/better barrel I suppose.

 

[Joop]

While I can't really add too much to what has been said, already, I will say that my Savage 10FP is the same way. I can't get it to shoot the 175 SMK or Nosler CC worth a darn. The Hornady 168 BTHP will actually shoot better, even at 800 yards in this rifle (as far as I have compared them). Now, the 178 A-Max is a different story, altogether. My rifle loves 'em.

 

[TallShot]

While I can't really add too much to what has been said, already, I will say that my Savage 10FP is the same way. I can't get it to shoot the 175 SMK or Nosler CC worth a darn. The Hornady 168 BTHP will actually shoot better, even at 800 yards in this rifle (as far as I have compared them). Now, the 178 A-Max is a different story, altogether. My rifle loves 'em.

What twist?

 

[Joop]

What twist?

1 in 10 twist on a 24" barrel.

 

[calling4life]

My old savage 10fcp 10twist 26" barrel shot fgm 168's in that .4-.6 range at 100, the 175's were .6-.8. I had gap cut the barrel to 18" and throw a badger fte on, the fgm 168's went to .6-.8 and the fgm 175's were now .2-.4.

Buy a different muzzle device, you'll see different results yet again, I'll say, that 308 with the brake removed went to .9-1.2" groups at 100.

 

[Ring]

Not that I've shot that far, yet, but I'm getting there.

I do like the little extra wind bucking of the 175's.

Anyone have suggestions of torquing the FS? Such as how many inch lbs

if pillar bedded, chassis or block, 50 to 60in p

 

[Ring]

for 10$ u can give this a try... it may not look cool... but they sure as shit work...

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