Does 'best' jump vary with different bullets?

Jaysee · 11-27-2015, 11:59 AM

apologies if this has been asked previously.. I understand the principles of having the ideal seating depth for loads in my rifle, and have worked out, by testing various seating depths, that the best for my rifle using a particular bullet (75gr A-Max) is 0.012" off the lands.

My question is - If my rifle likes 0.012" jump with these particular bullets, would the same distance from the lands apply to, for example, an 80gr A-Max.. or a 77gr SMK?, or do I have to go through the same testing of various seating depths for each and every bullet I want to shoot. I realise that c.o.a.l. varies with different brands/sizes as the ogive varies.. but just wondered if the jump also varied bullet to bullet, or if that would be a constant with my particular throat/chamber?.

LongRange · 11-27-2015, 12:38 PM

yes each bullet is different.

**mudpig** · 11-27-2015, 04:15 PM

each bullet is very different and will like different jumps. I have seen it myself and I have read from many that the most common place to find accuracy is about .010 jump.

**Texas10** · 11-30-2015, 11:00 AM

Yes, each bullet design may be sensitive to a particular jump. The VLD bullets come to mind as being a source of much controversy regarding seating into the lands or off by some distance. Finally the manufacturer went public with a big change in their advise on how to seat, going against seating into the lands and instead towards seating for a jump.

Last week when loading a pet round I inadvertently seated .080 deeper than usual ( .040 off) . The bullets (53gr. V-Max) shot three 5 round groups that averaged .368 which was about .020 better than previous best.

Tomorrow I'm off to the range to repeat that load and see what the buck is happening. I keep reading that it's not supposed to go like that.

**Mozella** · 11-30-2015, 11:44 AM

Originally Posted by Texas10

Yes, each bullet design may be sensitive to a particular jump. The VLD bullets come to mind as being a source of much controversy regarding seating into the lands or off by some distance. Finally the manufacturer went public with a big change in their advise on how to seat, going against seating into the lands and instead towards seating for a jump.

........... snip............

I think you're characterizing what Berger said about their VLD bullets. The way I read the article is that conventional wisdom used to say that the unusually long skinny VLD bullets should be seated very long, usually longer than just touching the lands; i.e. "jaming" by .010" more or less. This is because many target shooters do just that and get excellent performance from the VLDs.

However, those who must extract a loaded round can find themselves disassembling the cartridge and spilling powder all over the place if they jam their rounds. Others found that they couldn't fit these long rounds into a magazine. The answer for those folks used to be, "Tough luck. Use an alternative bullet". For a long time most VLD shooters and indeed the Berger company itself believed that if you can't touch the rifling or jam the bullet to some degree, you wouldn't enjoy good performance from the VLDs; this in spite of getting some reports that some folks had good results jumping these bullets.

But, Berger took another look and decided that many rifles can be made to shoot the VLDs well even with what most target shooters would characterize as miles of jump, up to .130" or even more. The current recommendation is to do a seating depth test, but conduct that test over what most of us would say is a VERY wide range, from .130" jump to .010" jam depending on if you're a hunter or a target shooter. After finding a depth producing good groups, then retest over a narrow range of CBTO measurements to zero in on the very best performance.

In other words, Berger has not changed their view (a view held by many others) that jaming the VLDs provides the best results in SOME rifles. They've simply added the belief that other rifles which either don't shoot accurately with very long CBTO measurements or must be seated short because of magazine length issues or possible round extraction worries may find Nirvana by using rather long jump distances. Berger no longer says forget the VLDs if you can't reach the rifling. The article gives specific recommendations on how to find the "sweet spot" for your particular rifle.

**Fotheringill** · 12-01-2015, 10:47 AM

I am new to reloading but have made the following observation for a Savage 12 F/TR in .223 that was driving me nuts.

In my rifle, Sierra Match Kings 77 gr needed to be set MUCH deeper to get off the lands. I just got 200 rounds of Hornady A-Max in 75 grain and because of the contour of the bullet, the lands don't hit until very close to the case mouth, allowing a much higher seating.