Throat length question

[Doug Humbarger]

What affect does a long throat length have on velocity? Does it act to increase or decrease it or is there no affect? This is a group I shot with my 284 Win I just built with a long throat by mistake. As you see I am .250 off the lands. I had thought that accuracy was really going to suck but I was wrong.

 

[lpreddick]

the longer a bullet travels before impacting the lands the faster it goes. weatherby , i believe, has the longest freebore of factory guns for this reason. i have a .22-.250 chambered in the late 1960's with so much freebore a bullet seated to touch the lands will be barely in the neck! i jump the things .115 in and can occasionally get a cloverleaf group. one downside of long freebore is this problem and if the bullet has a lot of runout it may hit the lands a bit off center. only was to shorten excessive freebore os to rechamber, but your gun looks to be doing what it is designed to provide.

 

[RDavies]

My results have been different. In barrels which I have throated out, the velocity went down. If I either kept the bullets seated the same, with a lot more jump, or seated the bullets further out to contact the rifling (giving a larger internal volume), my velocity was lower than with the short throat. This has been with a few different 284s. With the same throat, I have found that when jumping bullets, I needed more powder to get the same speed than if it was jammed .015".
With my 284s, I have found I needed an extra .6-.8gns to get the same velocity as jammed if I ran with .015" jump.

On the other hand, If I wanted maximum velocity, I could throat the chamber out to either run more jump, or get more capacity by seating the bullets further out, then pump up the powder load, to get more speed. This is what Weatherby does, run a very long throat and run a load which would otherwise be very very high pressure in a standard chamber.

 

[robbor]

WOW 250 that some serious jumping. Glad it shoots good for you. I know wheatherbys have long throats but no idea how long. I have one of savage's 30" 6.5x284 target barrels new sitting in my safe and it has a long throat also. ive been tempeted to sell it but been on the fence since 30" extra heave barrels run a premium.

 

[amlevin]

I have a Remington .308 that has a long throat and shoots surprisingly well. I load to magazine length of 2.600 which gives me a jump of around .150" with a nosler custom comp 175 gr. Have had regular groups in the high "teens". For a factory barrel I'm pleased. It's a 5-R hammered rifling barrel and it has a lot of rounds through it with no sign of giving up.