Big Bore Addiction Group

[tarbe]

I question the fast twist since all the Info Iv'e read points to a slow twist, but looking at CZ website it shows a factory twist at 1-10, I plan on staying with copper jacketed hunting bullets in the 400-450Gr range. Also this smith has done all the Custom shop work since 2004 using Mcgowan Barrels and has been in business for 20+ years.

Sounds like your 'smith has been around the block...hard to say not to follow his advice.

 

[Rob404]

Sounds like your 'smith has been around the block...hard to say not to follow his advice.

I guess, but why are these twist rates vary so much. Iv'e researched other calibers and twist rate seemed to vary depending on bullet weight, but heavy calibers don't have as many options in bullet weight, so why such a variance.
Would a bullet fired out of a 1-10 twist have better velocity and accuracy than the same bullet fired out of a 1-14 1-16 etc

 

[tarbe]

Twist required depends on the length of the bullet in relation to diameter, and velocity.

If guys are shooting 450gr boat tail match bullets, certainly a faster than normal twist is needed.

Twist rate has little measurable effect on velocity. The pressure curve can be different with different twist rates, but we will not notice the difference between rifles with a 2 inch change.

Primary effect is on bullet stability in flight. Secondary is effect on terminal ballistics due to different rotational speed.

Insufficient twist is much worse than too much. But I cannot imagine you benefitting from anything faster than 1 in 14.

 

[Velo Dog]

I'd like to see the same excerise with a large Caliber Bolt Gun

Have a look at: www.heymUSA.com.
Somewhere in that web site there is some fun video to watch, of people who obviously know how to run their rifles, including large bore bolt actions vs a "charging buffalo target".
My favorite sequence is the one with the Heym built Mauser in .404 Jeffery vs the above mentioned incoming target, fun stuff.

 

[tarbe]

/\

I have that 404 video saved on my computer...like porn!

 

[Velo Dog]

/\

I have that 404 video saved on my computer...like porn!

Great minds think alike.

 

[Rob404]

Twist required depends on the length of the bullet in relation to diameter, and velocity.

If guys are shooting 450gr boat tail match bullets, certainly a faster than normal twist is needed.

Twist rate has little measurable effect on velocity. The pressure curve can be different with different twist rates, but we will not notice the difference between rifles with a 2 inch change.

Primary effect is on bullet stability in flight. Secondary is effect on terminal ballistics due to different rotational speed.

Insufficient twist is much worse than too much. But I cannot imagine you benefitting from anything faster than 1 in 14.

I read on another site about a guy shooting a CZ 404 at the range and he claimed solid rounds key-holed but jacketed bullets produced some tight groups at 100, his error in loading or is there a big difference in solids Vs Jacketed other than just that

 

[tarbe]

I read on another site about a guy shooting a CZ 404 at the range and he claimed solid rounds key-holed but jacketed bullets produced some tight groups at 100, his error in loading or is there a big difference in solids Vs Jacketed other than just that

Solids are generally longer than softs, due to the higher ratio of less dense jacket material vs lead. That argues for a faster twist (longer bullet, faster twist).

BUT, the difference in minimal. Hard for me to imagine a rifle that would shoot a 400gr soft great, but keyhole with the same weight solids.

I'd have to see that one to believe it. Just doesn't add up in my simple mind.


Tim

 

[Rob404]

Solids are generally longer than softs, due to the higher ratio of less dense jacket material vs lead. That argues for a faster twist (longer bullet, faster twist).

BUT, the difference in minimal. Hard for me to imagine a rifle that would shoot a 400gr soft great, but keyhole with the same weight solids.

I'd have to see that one to believe it. Just doesn't add up in my simple mind.


Tim

Yes after looking at the length of different rounds I'm thinking user error or a target flapping in the wind

 

[Velo Dog]

Solids are generally longer than softs, due to the higher ratio of less dense jacket material vs lead. That argues for a faster twist (longer bullet, faster twist).

BUT, the difference in minimal. Hard for me to imagine a rifle that would shoot a 400gr soft great, but keyhole with the same weight solids.

I'd have to see that one to believe it. Just doesn't add up in my simple mind.


Tim

Hi again Tim/tarbe,

+1 with your opinion here again (as usual.)
And, I can't help but wonder if the solids that were "key holing", (in other words, severely wobbling or even tumbling, prior to impact,) were too long for the twist rate in the shooter's rifle barrel.
If for instance the accurate softs were 400 grains each and the wobbling solids were 450 grains each, perhaps therein lurks the problem.

This "too long of bullet for the rifling twist rate" problem would also be worsened if the solids were monolithic, such as Barnes or Stewart or whatever brand monolithic solid.
Because, these are longer yet than lead core solids.

One of these years I will find the right deal on a .404 Jeffery or my screen name isn't Velo Dog.
At the moment, I have a .416 Rigby that I am very fond of but, there's just something about a .404 by dang.

Cheers,
Paul/Velo Dog.

 

[Rob404]

I sent an e-mail to the smith telling him I may shoot solids with the 404 I want to see what he has to say, The fact that CZ doesn't take this into consideration has me wondering

 

[matt85]

while i havent tried their 404 Jeffery, ive never had a CZ factory twist rate give me trouble.

-matt

 

[Pheroze]

Hi Rob44

My recent experience with trying to reload for a short barrelled rifle has lead me to believe that the faster twist rate is important when you want to use long projectiles through a shortened barrel. My 20" stabilized the Rn 160gr but not the 160 gr PP and there was not a lot of difference in length there. I had many other problems loading for that rifle but the fellow at Woodleigh suspected the issue with stabilization may be related to barrel length. Just my two cents. Good luck with the project!

 

[tarbe]

Hi Rob44

My recent experience with trying to reload for a short barrelled rifle has lead me to believe that the faster twist rate is important when you want to use long projectiles through a shortened barrel. My 20" stabilized the Rn 160gr but not the 160 gr PP and there was not a lot of difference in length there. I had many other problems loading for that rifle but the fellow at Woodleigh suspected the issue with stabilization may be related to barrel length. Just my two cents. Good luck with the project!

You are seeing the effects of lower velocity.

A given bullet needs a faster twist at a lower velocity.

3000 fps with a 1 in 12 twist imparts 180,000 rpm to the bullet, whereas a 300 Blackout firing the same bullet at 1,050 fps in a sub-sonic load only gives 63,000 rpm.

A one inch long .308 bullet at 3000 fps can live with a 1 in 18, but that same bullet at 1000 fps needs 1 in 10.

 

[tarbe]

Of course, I am talking muzzle velocities, above.

The bullet launched at 3000 and spinning at 180,000 rpm is still turning pretty darn close to 180,000 rpm when it hits 1000 fps down range.

Not much resistance to rotational velocity!

 

[Pheroze]

You are seeing the effects of lower velocity.

A given bullet needs a faster twist at a lower velocity.

3000 fps with a 1 in 12 twist imparts 180,000 rpm to the bullet, whereas a 300 Blackout firing the same bullet at 1,050 fps in a sub-sonic load only gives 63,000 rpm.

A one inch long .308 bullet at 3000 fps can live with a 1 in 18, but that same bullet at 1000 fps needs 1 in 10.

With a large bore rifle I was wondering if the combination of a long projectile, reduced loads (early load development, accuracy, recoil or whatever) and shorter barrel would potentially pose an issue for stabalization? In which case the 1:10 would help to compensate?

 

[KMG Hunting Safaris]

With a large bore rifle I was wondering if the combination of a long projectile, reduced loads (early load development, accuracy, recoil or whatever) and shorter barrel would potentially pose an issue for stabalization? In which case the 1:10 would help to compensate?

Shoot GS Customs. That will end your troubles.

 

[Pheroze]

Shoot GS Customs. That will end your troubles.

Off to the range now to shoot my first load of GS in the 375! Holy powder charge batman

 

[KMG Hunting Safaris]

Off to the range now to shoot my first load of GS in the 375! Holy powder charge batman

What caliber and bullet weight did you go for?

 

[KMG Hunting Safaris]

Sorry, I see now you mentioned the 375.