dupin' a factory load...

[JD338]

So you're sighted at 100 and there is no drop at 300 yards?

Or did I misunderstand?

Yes :wink: no drop.

Every bullet drops as soon as it leaves the barrel due to garvity. You would have to sight in your rifle to have bullets impacting high at 100 yds to drop into a zreo at 300 yds. You have bullet drop, you are just compensating for it. :wink:

JD338

 

[boolit]

You just ruined all the fun JD!!! :wink:

Anyhoo.... I didn't zero the ammo 3 1/2 inches high at 100, it shot that way. Probobly from another time I zeroed other ammo. So you are right, if the ammo shot dead center....at 100, the 300 yard shot would have dropped. :mrgreen:

 

[FOTIS]

Thought so.

 

[elkeater2]

I worked for a great but gullible fella in the 70's who bought a Sako .308 from a real salesman. The guy told him that it had special rifling that caused the bullet to accelerate when it left the muzzle, and he believed it. Since he believed it, he had huge confidence in that rifle, and harvested all manner of Wyo critters with it, from antelope to moose. Confidence, even misguided, is a wonderful thing!

On the technical side, isn't there a brief instant when the bullet goes from barrel friction to zero friction when it does speed up slightly? Isn't this why a decent crown is so important? Just asking, my chrono tells me what I need to know in practical terms.
Elkeater2

 

[FOTIS]

The key to the crown is it must be concentric even in all places. If not accuracy will suffer. If such is the case a recrowning tool from Brownells will fix that easily.

 

[elkeater2]

The key to the crown is it must be concentric even in all places. If not accuracy will suffer. If such is the case a recrowning tool from Brownells will fix that easily.

Well, sure. I guess I was speculating that the reason it must be concentric and if not accuracy will suffer is: At that instant the expanding gas is freed from behind the bullet and the bullet base jumps clear of the rifling, the gas will start to blow by the the bullet base. If it has unequal places to get by because of dings or lack of squareness and concentricity, the gas will push the base off to one side. I've often been told to look at the residue pattern on the crown after firing a few rounds. If the pattern for any land/groove area looks even slightly different from the others, there is something wrong.

I know I'm preaching to the choir here, and wrote the above tutorial because I want to know if I have the right perception of what's going on :grin:

My other assumption is that this might be a little more critical in smaller diam. bullets with large case capacity, vs. 45/70's and 338's. If the same degree of crown problem is present in a .257 Bee as in that 45/70, won't the blow-by introduce morre yaw in that skinny lighter weight bullet? Especially if everything is moving faster, the gas will have more 'momentum'. Maybe? Fun to ponder, my crowns are all checked and good...
Elkeater2

 

[DrMike]

elkeater2,

The bullet does not speed up as it exits the barrel. Because of gravity and because the pressure is already beginning to subside, the velocity begins to drop immediately.

 

[elkeater2]

So it's not like popping a reluctant cork out of a wine bottle? Dang!!! :grin:
There are good reasons I am not a physics grad....

 

[boolit]

The key to the crown is it must be concentric even in all places. If not accuracy will suffer. If such is the case a recrowning tool from Brownells will fix that easily.

I like zis.....
http://www.youtube.com/watch?v=b23lfzpZrJ4

 

[FOTIS]

yes correct

 

[boolit]

The key to the crown is it must be concentric even in all places. If not accuracy will suffer. If such is the case a recrowning tool from Brownells will fix that easily.

Well, sure. I guess I was speculating that the reason it must be concentric and if not accuracy will suffer is: At that instant the expanding gas is freed from behind the bullet and the bullet base jumps clear of the rifling, the gas will start to blow by the the bullet base. If it has unequal places to get by because of dings or lack of squareness and concentricity, the gas will push the base off to one side. I've often been told to look at the residue pattern on the crown after firing a few rounds. If the pattern for any land/groove area looks even slightly different from the others, there is something wrong.

I know I'm preaching to the choir here, and wrote the above tutorial because I want to know if I have the right perception of what's going on :grin:

My other assumption is that this might be a little more critical in smaller diam. bullets with large case capacity, vs. 45/70's and 338's. If the same degree of crown problem is present in a .257 Bee as in that 45/70, won't the blow-by introduce morre yaw in that skinny lighter weight bullet? Especially if everything is moving faster, the gas will have more 'momentum'. Maybe? Fun to ponder, my crowns are all checked and good...
Elkeater2

So what crown is the best? 11 degree, round, or recessed? I have a 11 degree on my varmint rifle.... What do you all have?

 

[FOTIS]

I prefer 11 degrees, however many do work well.

 

[boolit]

I prefer 11 degrees, however many do work well.

Why do you prefer 11 degree?

 

[FOTIS]

Just had great luck with it in my customs. Certainly not to say other would not work.

 

[boolit]

Why the different crowns? They all have a purpose for different applications?

 

[FOTIS]

Different ways to accomplish the same goal. Accuracy.