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Old October 10, 2013, 06:44 PM   #1
tangolima
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Bullet jump optimization. Practical?

Bullet jump is the distance between the bullet's ogive and the starting of rifling. I read that one can adjust bullet jump to improve accuracy. I tried that and found it is mostly a rather impractical proposition.

In order to shorten the bullet jump to between 0 to 0.1", I will have to seat the bullet so high that either max. COL is exceeded or the neck has little purchase on the bullet. Is this only for custom made rifles with short leade? Granted I don't own any custom rifles. I have a whole bunch of military rifles from the great wars. Non of them can do it, even though they shoot exceptional well. The only one that comes close is a 25 year-old Rem 700 BDL in .30-06. Even with that I will have to use heavy bullet (> 174gr) to get into the range.

Do I understand it correctly? Thanks for your comments.

-TL
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Old October 10, 2013, 07:40 PM   #2
Bart B.
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TL, you can seat bullets to any depth that you want. Note that they should not be so deep as to crush the powder in the case. As long as the rounds are reasonably straight, the bullets can jump 1/10th inch to the rifling and still shoot very accurate. And as you've seen, there has to be enough bullet held by the case neck for keeping the round intact in normal handling as well as loading.

For loading from a rifle's box magazine, the overall cartridge length should be about 1/16th inch shorter than the magazine's length. For single round loading they can be seated long enough to gently push into the rifling; a method that some bullets shoot most accurate with.
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Old October 10, 2013, 07:51 PM   #3
tangolima
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Quote:
And as you've seen, there has to be enough bullet held by the case neck for keeping the round intact in normal handling as well as loading.
That's the problem. If I want to minimize the bullet jump, there will be little neck holding the bullet. Rule of thumb is to have at least as much as the bullet diameter. I will have not even half of that if I'm using light bullet (<150gr).

-TL
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Old October 10, 2013, 08:00 PM   #4
Brian Pfleuger
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Bullet jump optimization. Practical?

That rule of thumb really has no basis in fact. Some cartridges don't even have necks as long as a caliber. I've seated bullets as little as 0.10
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Old October 10, 2013, 08:02 PM   #5
firewrench044
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for most shooting it is impractical
mostly used in competition at long range (600 yards or more )
these longer rounds are usualy too long to fit into the magazine and
must be loaded one at a time through the ejection port

yes it helps ( but you will only see the difference at ranges more than
300 yards )
I use the Sierra 30 cal. 175 MK in my US military rifles, they like to be
10 to 15 thou. off the lands
My 223 Bushmaster likes the 80 gr Sierras at 25 to 30 thou. off lands

the distance off lands will vary as to the bullet - barrel combination

the only bullet I have tried that likes a jump of 1 to 5 thou. off is Berger
and I found that Sierra did just as good and were less expensive
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Old October 10, 2013, 08:28 PM   #6
603Country
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What rifle and caliber are you having the problem with? I don't presently have a rifle that won't let me seat the bullet close to the lands. That said, my 223 with 40 gr Noslers are seated out to that one caliber seating depth and are a bit further off the lands than I'd usually want.
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Old October 11, 2013, 03:22 AM   #7
tangolima
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Quote:
for most shooting it is impractical
mostly used in competition at long range (600 yards or more )
these longer rounds are usualy too long to fit into the magazine and
must be loaded one at a time through the ejection port
That is exactly what my conclusion is. I should have defined practicality more precisely. A round must fit in the rifle's magazine and be fed reliably without babying. Without enough bearing area between the neck and the bullet, should it be more or less than the bullet diameter, the round may get banged up when it is being handled in the field. Loading a round one at a time in single-shot manner is not practical.

Quote:
What rifle and caliber are you having the problem with?
I tried it on Mauser K98K, a couple of SMLEs, a 1903, and a Mosin. They are all from WWII or even WWI. They all shoot no worse than 2 MOA with iron sights and normal handload ammunition.

-TL
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Old October 11, 2013, 07:30 AM   #8
F. Guffey
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tangolima, I am the fan of the running start, I want my bullet to have the jump, if I have a rifle that insist on seating the bullet to the lands, it does not get shot.

I have tested rifles for maximum overall length, in some of the test I have shoved the bullet out of the case and in to the throat, past every thing else and finally to the rifling.

I hope no one gets the ideal I am anti-against the rifling, I think it is cute, as you suggested, loading a magazine type rifle in a single shot manner is at best annoying, I am the fan of 'fix the rifle'.



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Old October 11, 2013, 07:39 AM   #9
F. Guffey
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Seating depth, I built a 30 Gibbs, the neck length was .217" (I fixed that).

The 300 Winchester Magnum neck length? Not much better at .264".

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Old October 11, 2013, 12:44 PM   #10
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The one gun I have come across that seems to need that is the older Sako (Finnbear 270/30-06)

Those had deep reach to the rifling. Not sure why. Deeper than military chambers I have for sure.

The 270 I reload for needed it for accuracy desired, did not play with the 06 enough before I sold it to tell for sure, but it was also seriously deep (or long)

One possible answer to getting some better grip is the non lead bullets as they are long for the weight they are missing.

Some guns it makes a measurable difference on and fine without tuning the COAL.

I would try the gun first for accuracy with normal of a bit extended depth and if not satisfactory then experiment.

Keeping in mind getting to long can interfere withe the gun function, not fit the magazine or if too far to fragile for anything but single shot bench shooting (which is ok but even bench shooting rounds get knocked around at times). Personally I would draw the line at a reasonable solid rounds but nothing to say you can't do it if you want.
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Old October 11, 2013, 12:48 PM   #11
tangolima
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Thanks guys for your inputs. I got the idea.

-TL
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Old October 12, 2013, 12:54 AM   #12
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I could not get anywhere near the rifling in either of my stock Remingtons, 30-06 and 308. It didn't matter how long or short bullets were loaded. Only thing that made a difference was powder and powder charge. In my CZ Varmint .223 I can load touching the lands with plenty bullet seated in the case neck. It likes bullets either 0.002 or 0.040 off the lands. Anywhere in-between or longer and groups open up. Both of my custom barreled Remington 308s like bullets 0.002 to 0.005 off the lands. Any farther off the lands and groups start opening up. All fall within magazine length.

In my experience rifles with long necks bullet seating depth doesn't seem to make much difference. In rifles with shorter necks it can make a big difference in group size.
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Old October 12, 2013, 07:07 PM   #13
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I accually just posted in another thread regarding this. Let me start by stating the specifics...

I shoot a Ruger .308 markII bolt action with a built in mag well. I have taken an empty case, barely started the seating in my press and then put the round in my rifle and closed the bolt to finish seating the round to ensure that the round is touching the rifling so there is zero jump. I then used that dud round as my template for reloading EVERY .308 round ive reloaded over the years. Now, i dont chrono anything, i dont measure groups, and i really dont load specifically for top notch accuracy, but, if i shoot three factory rounds and three of my reloads, that grouping is extremely different. Ive also used this process for my AR....BUT im only using 50-55gr bullets so i dont have an issue of not fitting my mags. I was informed that heavier rounds, 70+gr, would be an issue in the mags.

Anyway, i feel like it has a significant effect on accuracy.
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Old October 12, 2013, 07:40 PM   #14
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In reading "Secrets of the Houston Warehouse", they determined that accuracy was usually best with no jump- seated touching the lands. Some of my loads are set with the boolits "kissing" the rifling (in theory, anyway...)

Like anything else, every combination of bullet weight/type and barrel is unique so I can't see a hard/fast rule here.
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Old October 13, 2013, 01:44 PM   #15
Bart B.
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Jeff2131, do you change the seating depth as the barrel's leade erodes away? If not, it will allow bullet jump of about .010" for every 300 to 500 rounds fired when all rounds have the bullets seated to the same depth/over-all-cartridge-length.
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Old October 13, 2013, 06:06 PM   #16
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Hmmmmm, good info. Didnt realize the.barrel "erroded" away. Maybe ill have to make myself a new dummy round and change my seating...over two years ive probably put about 1500 rounds through that rifle. Ill make a new dummy round and gauge it with the original and see the difference, if any.
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Old October 13, 2013, 06:18 PM   #17
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depends on your application. For long range target shooting, there is really no reason you can't load rounds one at a time (if they exceed magazine length).

Calibers such as 30-06 and 300 win mag can be difficult to touch the lands on, due to the wide variety of bullets you can shoot through them, For example, pretty much any bullet lighter than 180 or 190 grains will be too short to load like this in my 06.
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