Bullet Jump

BCBRAD

BCBRAD

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I have one rifle that has a long free bore. (Tikka Tac 300wm and a 185 Jugg)

With the bullet seated to the base of the neck there is 0.103" to the rifling.

Question is: Is there any benefit doing bullet seating depth trials with a long jump?
 
That depends on how tight the throat is.

Every Tikka T3 I've had has had lots of freebore.

Every one of the rifles shot consistently like lazers and all had tight throats.

In a 6.5x55 that I still have, it will shoot everything from 95 grain flat base, hollow points to 160 grain round nose and Berger ELDs into sub moa groups, seated over .100 from the leade.

It's all about how well your reloads fit the chamber and how straight everything is in relation to the axis of the bore.

Loose, sloppy cartridges in a chamber usually don't shoot well and getting them a few thou off the leade will often help to alleviate the problem. You shouldn't have this problem with your Tikka, unless you're using a small base die, etc.

Even at .103 in of jump, the base of your bullet is likely still being held in the neck before it enters the leade

The reason folks try to get close to the leade is to keep their cartridges aligned with the axis of the bore and ensure a straight feed into the bore, with minimal cant.
 
I had some luck playing with COL on the Weatherby cartridges. One in particular is a custom 270 'Bee with a short throat and long magbox making it a rare case of actually being able to touch the lands. I wanted to use Swift Scirrocos 11s but seated to the lands they weren't doing so great. Not real bad but not what you build a rifle for. I found a decent working maximum and loaded sequences moving back 30 thou at a time. At .180" it came to life. Go figure.

Barnes has a decent write-up on tuning by jump.
 
Jump tuning is interesting work, for sure. FWIW, my much more limited experience agrees with bearhunter: Your Tikka probably won't care about jump for its own sake.

But if you haven't done it already, I think it might care about COAL tuning. Just in terms of effective case volume and pressure curve.
 
been playing with bullet jump last couple of days.it seems that if you lenthen your oal you need to up the charge a bit to compensate.had to lenthen oal by .050 over factory lenth to bring it to .020 from the lands.savage model 10 in 22-250 with a shilen barrel
 
In my limited experience loading for minimum bullet "jump" is an American thing because of sloppy and imprecise USA chamber specifications. Many European cartridges like the 7x64 and 9.3x62 are designed with very long throats. In all four of the 7x64 rifles I have owned, the throat is so long that the bullet is almost completely out of the case before engaging the rifling. But they shot well. Same thing with my 9.3x62. I just can't get very enthusiastic about compensating for a sloppy chamber by tweaking reloaded cartridge over all length. If it doesn't shoot well at standard length, it goes down the road. My prediction is that your Tikka will shoot well, regardless. Tikka knows how to build a proper chamber and throat.
 
Lead hammer said:
Bullet seating depth test is huge. Don’t skip out on that.
Click to expand...

That really depends on the rifle.

I have several that could care less where the bullets are seated and others that need the bullet jammed right into the leade to be accurate.

Tight chambers and throats, reamed to perfectly align with the axis of the bore are always the least sensitive and the most accurate.
 
BCBRAD said:
I have one rifle that has a long free bore. (Tikka Tac 300wm and a 185 Jugg)

With the bullet seated to the base of the neck there is 0.103" to the rifling.

Question is: Is there any benefit doing bullet seating depth trials with a long jump?
Click to expand...

I have a custom heavy barreled Browning BBR 7/08 that shoots it's best at .120 off touch so I believe testing is worthwhile. Got to this by doing the Berger seating depth test.
 
Lead hammer said:
Bullet seating depth test is huge. Don’t skip out on that.
Click to expand...

I agree. 100% worth it, if you are looking for your best precision. That’s why every bench/Fclass/precision shooters do seating depth tests. I like to seat mine so the bearing surface of the bullet is just above the the neck/shoulder junction. So if you form a donut you don’t get inconsistent neck tension. Only an issue if you resize your brass multiple times.
 
I agree that bullet seating depth tests are very worthwhile, even if the jump is long-ish. I watch many videos on YouTube made by benchrest and f-class shooters who win matches, or same who are being interviewed by another pro shooter. The consistent message I get from them is that seating depth experiments tune the load, and are essential for winning matches.
 
I have played with seating depths since day 1 of my reloading for accuracy quest... 0-10-15-20 were what most articles/people claimed gave the best accuracy. Any bullet that didn't group with 0-20 jump got shelved.
Then I got a rifle that wouldn't seem to shoot Bergers - so I did the Berger test - 30-60-90-120.....
I would say, based on my personal evidence, that most rifles I have shot seem to like 55-65 thou jump. I couldn't believe it, but trial after trial showed the same results.
Even bullets that shot 1.5-2moa with 10-20 jump, were shrinking to half that or more with further jump. The most dramatic diffs in my rifles were with Berger elites and Nosler ABLR - Berger likes 60 or 110 off, ABLR liked 55 off.

Never know till you try.
 
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