7mm Rem mag 168gr or even 180Gr tumble and inaccuracy with 8 twist barrel?

[Deleted member 25294]

It doesnt matter what you agree with.
You know what they call people who insist on remaining ignorant ?
Go study "Principles of Artillery 101"
If what you said is true, there would be no need for grooves in barrels, they
would all be smooth bore. In fact some projectiles do adhere to your explanation
and they are or can be shot from smooth bores. Tanks and Shotgun slugs as examples........ NOT modern BULLETS. If fact... you got it backwards. When impacting gel for instance, why do you think bullets swap ends ? Because the center of gravity is behind the center of friction/drag. And for the other expert who doesnt like 15 degrees, have him study english for the understanding of the expression "for clarity"
And hey, yes some bullets are/were shaped like footballs. In the 30's there were experiments showing pointed on both ends outperformed all others but
later testing revealed that truncating the rear point into "boattail" shape provided 90ish percent of the improvement with major improvements in practicality.
I would not have said anything but I hate to see know-it-alls to profess they
know it all when they dont. Here is the lesson for the expert who only thinks there
is stabilized or not stabilized. There in fact us under stabilized, stabilized and over stabilized. That's all.

Holy crap dude.. speaking of English consider using paragraphs

I was in the process of getting a 8 twist barrel for my new to shoot the berger 180 or eld 175 and was going to test the 195 bergers but then I read an article the other day in Terminal Ballistics that using the 8 twist barrel will cause accuracy issues and bullet tumbling with 168 gr bullets as well as the 180 grain bullets at longer distances, say over 500 yrds. I dont want to just have a single use barrel for the 195 as this is a hunting rig and need to shoot different bullets for different purposes although main use for this 7mm is potentially long range elk hunting, hence also testing the 195 gr as well,,,,

Anyone have this experience using an 8 twist barrel and 7mm mag?

Thanks for any hel

Elkdeerhunter

I've had extremely good accuracy with 180 ELDM's and 195's beyond 1100 yards with several 8 twist barrels.
I can't comment on 168's, with 180's there's absolutely no reason to shoot them.

 

[Capt RB]

The only issies you may run into arre throat wear related. The 8tw will work for the 168 and up bullets till you you have excessive fire cracking then the shorter bullets will lose accuracy much sooner than the long et r 180eldm 183 195 197's. The big monos should still shoot well. The 177 hammer would be great in yhe 8tw btw

 

[HobieH3]

In really small bullets like .223 and under that are super light with very light jackets you can see bullets turn to grey puffs of smoke about 15 yards out from the barrel when they're spun exceedingly hard

 

[HobieH3]

I'd like to see that. I've got a 26" 9 twist, maybe I can find somebody shooting a hot 40g varmint load from an AR...

 

[coop2564]

I am surprised at how WRONG the supposed "experts" are here with their "nonsense".
Yes indeed there are consequences of over spinning a bullet other than
spinning the jacket off. The decrease in accuracy significance increases with distance.
For illustration, lets assume an extreme situation. Long shot at 2500
yards. Lets assume for simplicity you aim fifteen degrees above target.
IF your bullet is over spun, when the bullet arrived and hits the target
the bullet will be aiming or pointed 15 degrees off of the direction of
travel. ie flying sideways a bit compared to the light path and still
pointing in the original direction of aim instead of following the path of flight.
THIS IS OVER-STABILIZATION.
When the bullet flies sideways like this accuracy goes all to heck
as you would imagine... especially as the bullet is spinning rapidly
and an effect much like a curve baseball occurs causing a veer sideways
as if there was a slight wind.
This is the reason every barrel does not come from the factory with
crazy fast twist. You cannot get good accuracy with a light short bullet
in a fast twist barrel nor vice versa.
You know where I learned all this ? I was a punter in football.
Too much spin and the spiraling ball will not "turn over" as it comes
down at the other end.

He is not talking about light short bullets here! The bullets he speaks of should work very well with that twist!

 

[taly01]

The idea of overspinning a bullet was explained to me as in throwing a football with spin, too much spin it will not follow the trajectory on the downwards path on its axis, but be pointed up a bit in the same orientation as it left the barrel.

So this is why the long range overspun bullet gets a bit weird, mostly trajectory is a bit off as the BC of the bullet changes as its travelling nose up *minutely* off axis.

Hope that makes sense.

 

[clemens]

View attachment 132058

This picture is simple yet makes me laugh everytime.

 

[Canhunter35]

Why in the world would an 8tw overspin a 168?
A 8tw 6.5 doesn't overspin a 120.

 

[HARPERC]

......Yes indeed there are consequences of over spinning a bullet other than spinning the jacket off. The decrease in accuracy significance increases with distance.For illustration, lets assume an extreme situation. Long shot at 2500 yards. Lets assume for simplicity you aim fifteen degrees above target.IF your bullet is over spun, when the bullet arrived and hits the targetthe bullet will be aiming or pointed 15 degrees off of the direction of
travel. ie flying sideways a bit compared to the light path and still pointing in the original direction of aim instead of following the path of flight........

For simplicity 2500 yards is irrelevant to elk hunting.

 

[HobieH3]

Does a bullet "nose over" during flight?

 

[Silly_Ghillie]

Well, if it counts for anything- I have been using 198 grain flatline out of a 29" bbl. with a 1:9 RHT (.300 WM) and everything seems to stabilize just fine considering the aggressive twist for that weight and caliber. I get a bit more spin drift but nothing that makes me want to hack my barrel in half and pick up stamp collecting instead. I think a 1:8 for a 7mm mag is fine.

I think gyroscopic stability is relative to the bearing surface of the bullet, its overall center of gravity comparative to its center of air resistance, and the aerodynamic character of the bullet as it decelerates. I have noticed that the bigger bore players like the .375 up to .416 typically work very well with insanely tight twist rates.
Its popular to have super long bullets and the like (2+ inch bullets) in twist rates as tight as 1:7 leaving at 3000+ FPS. I mean these people are the leading edge in ballistic science and I don't think over-stabilization is an issue considering they are blasting steel at 3000+ yards with wildcats with names I cant pronounce.
Needless to say, I never bought into that argument of over stabilizing, however I never thought I would go bald or have ED- so I could be wrong.

 

[CMDR Kibo]

OP - As others have already stated, this instability and lack of accuracy you refer to in the article is counterintuitive and counterfactual. Here's the link to Berger's twist rate stability calculator for you to use: https://bergerbullets.com/twist-rate-calculator/.

I put in the bullet weights you mentioned and none of them produced an unstable result. I used very conservative muzzle velocities also. Go ahead and try for yourself.

Also, if you look at manufacturers like Browning for example, they are producing their long range versions of the X-Bolt Pro and X-Bolt Hell's Canyon with 1:8 twists specifically for the heavier/longer and better BC bullets available now. You can see this on pages 49, 51 and 52 of their 2019 catalog.

Personally, I shoot the 7mm RM a lot and I have no problem stabilizing the bullets you mention. I have both a 1:9.5 twist barrel and a 1:8 twist barrel for the heavier/longer bullets past 160 gr.