Author Topic: Bullet Jump (Read 834 times)

Tn Jim · « **on:** January 15, 2005, 06:00:09 AM »

I have a new Encore in 7mm-08 that I finally got to shoot yesterday with my handloads. This rifle hasn't had a factory round fired through it so I can't say what the accuracy is with them. All loads were R-P cases, 140 grain Nosler BT's, WLR primers and 45 grains of IMR 4350. Only the bullet to lands distance changed. I loaded 5 rounds of each load starting 60 thousandths off and moved 10 thousandths at a time until I was 10 thousandths off. The closer I got the more the groups opened up. I was waiting a timed 4 minutes between shots in 44 degree weather so barrel heating wasn't an issue. Also, the barrel is free floated. At 60 off I was getting a little under a inch at 100 yards and progressively opening to 3 1/4" at 10 off. Is it normal for a single shot to prefer this big a jump? My 700 BDL 30-06 shoots best at 20 thousandths off. I'm sure if I start tweaking the powder charges .2 grains at a time and using neck sized brass my groups will shrink. I've just never seen a rifle that liked bullets seated that far off before.

Dusty Miller · « **Reply #1 on:** January 15, 2005, 07:17:41 AM »

In my limited experience this sure sounds strange to me. In my '06 the bullet is about .001 off the lands and is much better than "hunter accurate".

Catfish · « **Reply #2 on:** January 15, 2005, 01:49:47 PM »

Most gun do prefer ammo with a shorter jump, but I have seen afew over the years that just plain liked alot of free bore. It really doesn`t matter what your gun likes best as long as you know what it like and feed it that.

Bullseye · « **Reply #3 on:** January 15, 2005, 05:58:34 PM »

I load all of my Encore and Contender rounds to the book OAL, and that is off the rifling way more than you are talking about. All my calibers that should be MOA shooters are. They might shoot better if seated closer to the rifling, but my point is that they can shoot great without it.

Duffy · « **Reply #4 on:** January 15, 2005, 06:45:46 PM »

My Encore 708 is best at .040-.045 so don't feel bad. I found that it's not written in stone that they HAVE to be .010 off the lands. One thing you didn't mention but have to remember is that as you get closer to the lands the psi goes up. In that last .020 the pressure jumps up darn quick and that could be enough to throw your load off of the curve. Try backing down about 1 to 1.5 grains and trying it at .020 or so. If it's still crummy just think, it should shoot factory stuff great! :grin:

Darrell Davis · « **Reply #5 on:** January 17, 2005, 03:23:46 PM »

Hey there Tn Jim,

This may not be as unusual we once thought.

Rick Jamison wrote in one of his magazine articals that he felt changes in bullet seating depth had an effect on groups in about the same way the changes made with a "Boss" do.

According to his writings, just as the position of the Boss changes the barrel vibs. so also does the seating depth of the bullet.

My personal tests seem to bare this out on a .300 Win Mag. A-Bolt.

Keep em coming! :wink:

Tn Jim · « **Reply #6 on:** January 20, 2005, 05:53:34 AM »

OK,here's another question. If I change to another bullet, say a 160 Partition, would the seating depth stay the same? Or would the heavier bullet and slower velocity change the barrel vibrations? I've never tried two totally different bullets in the same gun before.

Vern Humphrey · « **Reply #7 on:** January 20, 2005, 06:00:17 AM »

Sad to say, when you change components, you have to start from scratch in working up a load.

If the key is barrel harmonics, changing bullet weight can change the harmonics -- so start as before and experiment to find the best load.

Duffy · « **Reply #8 on:** January 22, 2005, 08:19:58 AM »

I start where my gun shoots best with a given bullet and work from there. Sometimes you hit it on the first go round, sometimes not. You have to check your seating depth with EVERY bullet. That is check max OAL in the bbl with every bullet you plan to use. The ojives are all a bit different even with the same brand. eg, A 150g Nosler Partiton has a different seating depth than a 160g par, and all 140g bullets are a bit differen too. In mine I have to seat a 140 Accubond deeper than the 140 BT, but the Accubond is a longer bullet with a bit different ojive too! Just leaving your seating die at one setting doesnt work..........that takes the fun and excitement out of reloading.

Leftoverdj · « **Reply #9 on:** January 22, 2005, 12:13:31 PM »

We've had several similar reports on the H&R Centerfire Board. Handies generally have ridiculously long throats, and several shooters have found that loading to book length has given better accuracy than seating out.

Lotta mysteries in handloading.