How long is to long? Prioritise OAL or bearing surface contact with case neck?

[TQB]

Hi,



How long is to long?

Let me explain. When one uses a factory rifle with a long freebore/throat, when does it become detrimental to keep extending the OAL to have the smallest jump?

I’ve read that the bearing surface of the bullet shouldn’t be seated further than the neck/shoulder junction. But when does seating depth become too shallow? I’ve loaded some rounds that the seating depth was just a few thousands bellow the case mouth, with little to no contact of the case neck with the bearing surface of the neck.

I know that the answer to my question is testing, but range time is precious around here.

Should I keep extending the OAL to be close to the lands, or should I prioritise contact between the case neck and the bearing surface of the bullet?



Thank You.

Best regards,

Tiago

 

[INTJ]

Many years ago a Sierra Bullet tech rep told me 1/2 caliber was a good minimum. I prefer to have a full caliber of length in the neck, but I have used less.

 

[JEFFPPC]

If it doesn't fall out of the case it works but my require delicate handling if you have minimal engagement with the bullet. If you have a long free bore and it's a hunting rifle with a magazine your limited by the length of the magazine. Ideally it's best to have the pressure ring of the bullet above the case neck junction. But unless you develope a donut it causes no harm if it's deeper.. The relationship between the ogive of the bullet and the lands in your barrel is a method of tuning your load. Every barrel and bullet combo along with powder charge and neck tension will likely be different. It is how and why you tune the bullet to your barrel. The downside of seating a bullet to engage the rifeling in a hunting rifle is pulling a bullet when unloading during a hunt and ending up with powder everywhere.

 

[Dave M.]

Hi,



How long is to long?

Let me explain. When one uses a factory rifle with a long freebore/throat, when does it become detrimental to keep extending the OAL to have the smallest jump?

I’ve read that the bearing surface of the bullet shouldn’t be seated further than the neck/shoulder junction. But when does seating depth become too shallow? I’ve loaded some rounds that the seating depth was just a few thousands bellow the case mouth, with little to no contact of the case neck with the bearing surface of the neck.

I know that the answer to my question is testing, but range time is precious around here.

Should I keep extending the OAL to be close to the lands, or should I prioritise contact between the case neck and the bearing surface of the bullet?



Thank You.

Best regards,

Tiago

I always use 1/2 of the caliber as my minimum. For benchrest or F class work I’m certain you could go even less, but for hunting rounds I wouldn’t consider ever going less than that. For hunting rifles with long freebore, try several different factory ammos and/or different Bullets. One will likely stand out above the rest as the most accurate. Find a hunting bullet that is jump tolerant because it’s unlikely you can ever get to the lands.
dave

 

[mikecr]

when does it become detrimental to keep extending the OAL to have the smallest jump?

When that doesn't test as best.
The object is not to get the smallest jump, but the best bullet-bore interface as shown on target.
This could be hard into lands or back so far as to worry you about bullet bearing into donut area.

No matter where the bullet ends up (as tested best CBTO), you set the neck sizing length.
IMO this should stop above donut thickness of necks, and definitely within seated bearing.
I think it's a bad move to FL size necks.
You can use neck sizing length as a tension tuning tweak. It's a very fine adjustment.

 

[mgunderson]

Don't be afraid to use more jump.

 

[D-4297]

I ran into this situation . My newest barrel for my TR rifle was only cut to .160 Freebore , and using 185 Juggs wasn't feasible , let alone 200.20x , or 208's . Barrel was re-throated to accommodate 200.20x , but that stretched it for the 185's . I had to move the bullet around till I found the sweet-spot , but it shoots very tight now . With only about .125 of the bearing surface in the neck . The amount of "Jump" would be considered excessive for most TR rifles , but if you have a original COAL or BTO number for length , start from there and go in and out with the bullet in the cases neck , as long as there isn't a magazine length requirement , or it doesn't fall out .