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Bullet jump

skeetlee

Lee Gardner Precision
Keep in mind my shooting roots are benchrest. Everything I do here in my shop for my customers is done just like I do for my personal benchrest guns. From chambering to reloading.
While shooting short range and mid range I never heard anyone say they were jumping their bullets. Maybe they were but everyone I personally knew where setting their bullets into the lands.

I do a lot of rifle work for all kinds of shooters. Benchrest to rimfire to hunting. I do it all, all the time I’m always surprised when a customer ask me how much they should jump their bullets. In my mind and my responders always is. Why would you want to jump a bullet that you know probably has a min of .002 runout. Maybe more. Why would you jump this into a perfectly straight chamber that I just spent a lot of time making perfect. The bullet sitting in your brass is not perfectly straight', hopefully it is but probably isn’t. Wouldn’t it make more sense to jam that bullet a bit into the rifling in hope that it will at least start straight. I don’t know why but I’m always surprised at this question.
Am I just thinking about this wrong? Eric Cortina’s podcast with Lou Merdics. Eric asked a question to Lou about jumping bullets. He didn’t even know what to say or how to answer. I think for the same reasons I think the way I do? I just find it interesting. I guess at the end of the day, if your rifle is shooting well that’s all that matters. Myself, I can’t bring myself to even try it. I know I’ll find something that works with my bullet into the rifling! Your thoughts?
 
Once that bullet is jammed, you have no choice but to pull the trigger. Not a wise choice when you have other options. If your bullet has no run out and went in straight, it will come out straight. You don't have to jam them but it is more work to get them in straight than just jamming them in. For me it's a safety issue.
 
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skeetlee said:
Keep in mind my shooting roots are benchrest. Everything I do here in my shop for my customers is done just like I do for my personal benchrest guns. From chambering to reloading.
While shooting short range and mid range I never heard anyone say they were jumping their bullets. Maybe they were but everyone I personally knew where setting their bullets into the lands.

I do a lot of rifle work for all kinds of shooters. Benchrest to rimfire to hunting. I do it all, all the time I’m always surprised when a customer ask me how much they should jump their bullets. In my mind and my responders always is. Why would you want to jump a bullet that you know probably has a min of .002 runout. Maybe more. Why would you jump this into a perfectly straight chamber that I just spent a lot of time making perfect. The bullet sitting in your brass is not perfectly straight', hopefully it is but probably isn’t. Wouldn’t it make more sense to jam that bullet a bit into the rifling in hope that it will at least start straight. I don’t know why but I’m always surprised at this question.
Am I just thinking about this wrong? Eric Cortina’s podcast with Lou Merdics. Eric asked a question to Lou about jumping bullets. He didn’t even know what to say or how to answer. I think for the same reasons I think the way I do? I just find it interesting. I guess at the end of the day, if your rifle is shooting well that’s all that matters. Myself, I can’t bring myself to even try it. I know I’ll find something that works with my bullet into the rifling! Your thoughts?
Click to expand...
I think it depends on the bullet and the angle of the lead. It's my understanding that high quality barrels used in Benchrest guns tend to have leads that are 1 - 1.5°. Such an angle tends to straighten out the bullet's entry into the lands with little or no damage to the surface of the bullet as it makes contact with the lead and and begins it's deformation into the barrel. Barrels with leads of 3-4° tends to be a problem getting the bullet into the lands without first straightening out well and even inducing a little of it's own deformation from impact with the lead before being engraved as it's entering the lands. Anyway, right or wrong, this has become my current understanding of what's gong on as the bullet moves onto the lead and into the bore.

The big advantage for seating into the lands can be as you say, better for straitening the bullet out before it's fired, but much more so, I see it's the consistency in pressure one gets by almost eliminating the blowby that one gets when jumping their bullets. The way I see it, you get more consistent pressure on the bullet into the bore and you have much less blowby interfering with the bullet's exiting the muzzle. IMHO, from an internal ballistics POV, jamming a bullet is the best way to go for the consistency that Benchrest shooters are after.
 
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skeetlee said:
Wouldn’t it make more sense to jam that bullet a bit into the rifling
Click to expand...
Extracting a loaded round may leave the bullet in the barrel & powder in the action. Light bullet hold/neck tension may allow this. Happens when a emergency ceasefire is called.

Hunting guns like Weatherby produce less pressure, with a jump.

VLD Bergers A Berger bullet has been said to shoot better with a jump. Was it .030" ?

To center rounds in the chamber-
Jam
Size 1/2 of neck with bushing. - my method.
Crush fit. when chambering a round.

Only the target knows what works.
 
So I assume that if a guy wanted to try jamming with an established load, he'd better scale back the powder charge to account for extra pressure?? Pretty much start all over again. :confused:

Also, it's not to hard to establish a seating depth that is "at" or touching the lands without being jammed to the point of pulling the bullet. Seems that would serve to center the cartridge about as well as jamming. jd
 
Just about every single shot competition rifle (benchrest & F-class) I have had, has shot best when the bullet was seated touching the lands. Just because the bullet is touching the lands doesn’t mean the bullet is automatically going to “stick” in the lands if it has to be ejected without firing. A brand new barrel with a really sharp throat will easily “stick” bullets but after 50 to 100 rounds the throat wears in and generally I can seat the bullets up to about +0.015 or slightly more into the lands before I have to worry about sticking. Granted, on a short range benchrest gun with a “heavy” jam you can stick a bullet but since you get unlimited sighters it normally isn’t a problem. As far as high pressure, when I start my powder testing I usually start with a mild load seated 0.005 to 0.008 into the lands and work up. I have never had pressure problems doing this. Overpressure is overpressure, the gun doesn’t care if the bullet is jammed or jumping. Granted if you want to use the highest charge possible or drive the bullet as fast as possible you would probably do better with a long jump, BUT maximum velocity doesn’t necessarily equate to accuracy.
The one thing I have found when shooting in the lands is that you have to keep track of throat wear and do more frequent tuning. The gun will tend to go out of tune faster as the throat wears than when jumping the bullets. All this considered I still have found better accuracy and had more success jammed than jumping.
 
Cease fires due to boats in the impact area at Camp Perry have caused innumerable occasions for competitors to unload on the line. Those who jammed their bullets learn the hard way when X-grains of powder gets dumped into their trigger group. "Armorer to firing point ..........."
 
Steve Donlon said:
Once that bullet is jammed, you have no choice but to pull the trigger. Not a wise choice when you have other options. If your bullet has no run out and went in straight, it will come out straight. You don't have to jam them but is is more work to get them in straight than just jamming them in. For me it's a safety issue.
Click to expand...
I agree, but you do have a choice and it means powder everywhere. I’ve always assumed that jamming would give me better precision. But in F-Class we often have the range go cold for different reasons and the chamber must be cleared. Also we have to wait for the target to come back up and sometimes (often) pull the cartridge out of the chamber waiting for the right condition. we cant “run and gun“ like BR shooters.
 
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jelenko said:
Wait. Does that graph say that there was a range of seating depth where pressure decreased with increasing seating depth?
Click to expand...
Yes. This is what was contrary to my thinking about effects of reduced case volume but was in line with what I was seeing from my chronograph data. It took a little while to realize it has to do with the blowby and how it escapes as the neck expands before the bullet is fully engraved into the bore.
 
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