Unstable 180 gr Bergers in 7mm Rem Mag

[bdpayne2000]

So here is my situation:

1-9 twist 26" Pacnor barrel in 7mm Rem Mag
Muzzle velocity of 2920
600 yards 5 shot 4" groups
Stretched it 750 and 3 of 10 landed sideways. ( they do make quite an impression in the steel sideways)

Thoughts and opinions? Thanks Brian.

 

[MudRunner2005]

You're approaching some ultra-hot velocites for the 180's in a 7mm RemMag...

Have you checked your crown? Could have a nick in it, or could be off-center causing funky gas expulsion to kick the boattail around as it leaves the bore...

Also, your barrel could just simply not like the 180's. I've got a sporter barreled 7mm RM that has a 1:9 barrel that just doesn't like 180gr bullets...VLD's or Hybrids. But it slings the 168's into a 1/2-5/8" groups all day long.

But my old Sendero SF 7mmSTW with a 9.25" twist barrel, loves all 180's I've shot through it.

Sometimes barrels can be picky. You just have to figure out what your's likes and stick with it.

 

[FearNoWind]

Wow!!! Now there's a head scratcher. I might have expected stability issues with something less than 1:9 but I don't see a clue in what's listed that readily sparks any ideas.

 

[Canadian Bushman]

Get a cleaning rod and a tight fitting jag and verify the twist. I always do this just to know.

It seems odd that at. 0-600 yds, stability is fine and then the bullet falls apart around 750.
Are you sure you didnt drop 3 and bounce them into the target, because ive done that a few times.

 

[Ingwe]

I would say that it's 100% your twist rate.

I was shooting 160gr Trophy Bonded Tipped Bear Claws with my 1:10 barrel and the bullets were unstable. I rebarreled to 1:9 and shoot 168gr Accubond LR's

 

[adam32]

I would say that it's 100% your twist rate.

I was shooting 160gr Trophy Bonded Tipped Bear Claws with my 1:10 barrel and the bullets were unstable. I rebarreled to 1:9 and shoot 168gr Accubond LR's

The odd thing is that they are stable out to 600...at 750 they were key-holing.

 

[bdpayne2000]

News from the OP, mystery solved and the lesson learned is trust but verify. Barrel is actually 1-9.5 twist not true 1-9. Looks like I will shooting 168's.

Thanks for the replays. Brian. lightbulb

 

[Canadian Bushman]

A 1:9.5 twist is still enough to stabilize berger's 180 gn bullet. I think your problem lies with something else.

 

[Dick Tinsley]

News from the OP, mystery solved and the lesson learned is trust but verify. Barrel is actually 1-9.5 twist not true 1-9. Looks like I will shooting 168's.

Thanks for the replays. Brian. lightbulb

I too had the same problem with a 1n9.25 twist 7 mag. It also would not stabilize the 180's. Had it rebarreled to a true 1n9 twist an now it shoots bug holes! I feel your pain!

DT

 

[deadidarren]

is .85 moa bad at 700y it's what i got the other day and thats with a 8mph

wofty breeze . i'm no expert shooter.

load was rem brass cci250 spark plug 69g of h1000 and 180g vld burger

sendero 7mm rem mag.. 9.25 twist.

i would be looking somewhere else


cheers Darren

 

[brentc]

You're approaching some ultra-hot velocites for the 180's in a 7mm RemMag...

Shhhh.. Don't tell my 7RM that 2920 fps is ultra hot with 180s, because it might just start believing it and drop 200 fps.

So here is my situation:

1-9 twist 26" Pacnor barrel in 7mm Rem Mag
Muzzle velocity of 2920
600 yards 5 shot 4" groups
Stretched it 750 and 3 of 10 landed sideways. ( they do make quite an impression in the steel sideways)

Thoughts and opinions? Thanks Brian.

All kidding aside, it's too bad you're experiencing this. It does appear that it's on the edge of stability. What are your load specs and environmental factors i.e. elevation. Pacnor does offer a 1 in 9.5 twist rate. Are you sure that yours was not supposed to be 1 in 9.5?

 

[Punisher]

Shhhh.. Don't tell my 7RM that 2920 fps is ultra hot with 180s, because it might just start believing it and drop 200 fps.



All kidding aside, it's too bad you're experiencing this. It does appear that it's on the edge of stability. What are your load specs and environmental factors i.e. elevation.

There is a ratio that you are completely out of. I honestly would tr slowing it down to about 2700 fps. I shoot a Remington 700 LR in 7mm mag with a 1/9.5 twos and have found that they need slower velocity to maintain their spin out to 1000 yards.

I shoot 168 gr VLD's better than 180's at 100 yards but I shoot 180's due to availability of 168's right now.

 

[brentc]

There is a ratio that you are completely out of. I honestly would tr slowing it down to about 2700 fps. I shoot a Remington 700 LR in 7mm mag with a 1/9.5 twos and have found that they need slower velocity to maintain their spin out to 1000 yards.

I shoot 168 gr VLD's better than 180's at 100 yards but I shoot 180's due to availability of 168's right now.

This reminds me of another point entirely. I always heard about bullets "going to sleep" so to speak, or Bergers need time to stabilize. With my current load of RL33 and 180s this plays out more than I've ever seen. My hunting load with this combo shoots a solid .6 out to 200 yards, however when I push it out past 400 yards the groups shrink to .3 MOA and sometimes smaller. I had my 7 RM out yesterday to verify my load prior to my bear hunt next week and the dang thing printed a nice triangle shaped 1.5" three shot group at 530 yards out of cold clean 28" 1 in 9 Pacnor barrel. Whatever the reason, I'll take it. Especially at 3140 fps.

I guess my main point is that sometimes rifle barrels do the unexpected. It seems weird to me that the OPs barrel is not stabilizing to 750 after printing solid groups at 600, but it is not beyond the realm of possibility in regards to dynamic stability.

 

[Canadian Bushman]

Typically bullets increase in stability as they fly.
A bullets spin decreases at a slower rate than it slows in linear fps. This typically increases its stability the longer it flies.
There are other things that can upset a bullet in flight or at its launch, but i dont see how they would apply to a 750 yd shot after it flew just fine at 600.
There is something amiss here.