Bullet stability and muzzle brakes

[Trap708]

Hey folks,
I'm new to the forem. I have two questions:

1). I have a question when measuring a bullets length for determining bullet stability it seems to me you would measure from bullet base to bullet tip irregardless of tip type (ie plastic tips versus non plastic tipped). I've heard some Discount the plastic tips in measuring the overall which to me seems to be cheating? Any comments?
Also related I have a muzzle loading bullet ( .50 cal - 300?grain all copper bullet with a pettled skirt ) the 300 grain Thor. How would you suggest measuring it to determine bullet stability.
The muzzle brake question I have is by having a brake on a rifle more detrimental to scope life. I guy I know mentioned he had read that brakes were hard on scopes. I have 3 guns with brakes 2 with the Vais one on 300 WM the other Vais on Tikka CTR in 308 Win and then my most recent a Kimber 7mm08 and yet to have any problems. In fact I've had more scope problems ( returns to manufacturers) in the past with guns that didn't have brakes. Any comments?

 

[elkaholic]

As far as the tip issue, the lighter weight plastic has less affect on how much twist is needed compared to a copper or lead combo clear to the tip. This equates to less value given to the same length.

 

[Trap708]

So, you do not or would not include the plastic tips length when plugging in the overall bullet length.

 

[lancetkenyon]

Every centerfire rifle I own (except a .223) has a brake. I have one scope that gets passed from rifle to rifle during load work that has to have a minimum of 8000 rounds shot under it, and 90% were with a brake. From 6.5CM to .300RUMs.

 

[elkaholic]

So, you do not or would not include the plastic tips length when plugging in the overall bullet length.

I think Litz wrote something about it if I'm not mistaken but I guess it depends on whose chart you're using. I know from making my own bullets that moving weight forward reduced stability.

 

[Trap708]

What about on that muzzle loading 300 grain Thor bullet. At hundred yards this bullet shoots very well. In fact the best consistently that I have ever fired. Anyhow that bullet has a plastic tip plus a real thin copper skirt at the base. This bullet is a Barnes style bullet all copper so it's long to begin with. Trying to see how stable it is on my applied ballistics app shows it to be unstable. I have yet to shoot it beyond 100 yds but at 100 it's again a good shoot consistently! Any comments or recommendations!

 

[elkaholic]

What about on that muzzle loading 300 grain Thor bullet. At hundred yards this bullet shoots very well. In fact the best consistently that I have ever fired. Anyhow that bullet has a plastic tip plus a real thin copper skirt at the base. This bullet is a Barnes style bullet all copper so it's long to begin with. Trying to see how stable it is on my applied ballistics app shows it to be unstable. I have yet to shoot it beyond 100 yds but at 100 it's again a good shoot consistently! Any comments or recommendations!

100 yards often won't tell you much about stability downrange. Many marginally stable bullets will group at 100 but fall apart at 1000.

 

[J E Custom]

The tip of the bullet is part of the overall length and has a bearing on the ballistic shape, so It counts as far as BCs go. The plastic Tip has very little to do/add to the weight.

A hollow point (Like the SMK) has lots of space between the tip and the core internally but the jacket from the point that the lead core stops, to the tip of the jacket performs the same function to improve ballistic shape just like the plastic tip.

So Yes, you measure the overall length to calculate the Ballistic coefficient . http://gundata.org/ballistic-coefficient-calculator/


Also a muzzle brake is easier on scopes equipped with a muzzle brake than one without. Scopes are designed for recoil, and when it is reduced it makes life better for the scope. The scope mass/weight has an effect the rings and bases because the more it weighs, the more inertia resist recoil. So if you have a heavy scope a muzzle brake makes it easier in the mounting system also.

The only instance that recoil can hurt a well made scope is to place it on a spring style air rifle that has recoil in both directions and the scope was not designed for recoil in both directions.

A properly installed Muzzle brake only improves the accuracy and life of the optics. They are not only easier on the scopes, rings and bases, and even the bedding, but also the shooter.

Fact, not fiction.

J E CUSTOM

 

[elkaholic]

I agree that you use the total length for b.c. but 2 bullets with the same b c do not necessarily have the same stability.

 

[whirlwindjml]

Muzzle brakes reduce recoil so thats healthyier on the scope. As was posted above. A lead sled i have found is hard on everything (ocular fell off one..a turret fell out another and split a stock). Yea muzzlebrakes and ear muffs.

The bullet stability calcs i think a nice rule of thumb but all the reading of done on peoples mileadge indicates testing gives the final/real answer.

 

[jebel]

I've heard some Discount the plastic tips in measuring the overall which to me seems to be cheating? Any comments?

The Miller Stability Formula is the one relied upon by most sources. It has a basic equation, then additional modifiers for velocity, atmospheric conditions, and polymer tips. With the tips, you both include the overall length and also the tip length, as an adjustment is made for the lower density of the tip. In general, a polymer tipped bullet will not require as much twist, all other things equal.

Some online twist calculators do not include the polymer tip adjustment (the one on Berger's site does not). Some do (e.g. JBM's calculator, linked below). If using a bullet with a polymer tip, use the correct calculator.

https://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi