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Discussion Starter · #1 ·
So I've read that shorter bullets can result in "bullet jump." To avoid this, desirable match ammo is long enough to touch or nearly touch the rifling.

That's what I think I understand anyways. What I have no concept of is how significant does the difference in the length of the round have to be before accuracy may be affected?

I bought some Federal Gold Medal 168gr at a gun show in the older white/black box. I had a bad day at the range with it. Today I was looking for something to use my new toy (calipers) on and started measuring cartridges. I noticed a difference of up to .018 between it and a newer design box of Federal Gold Medal.

I'm interested in knowing if any of you have noticed a difference the length of the round has on accuracy and how much difference it takes to matter. I'm listing the different cartridge lengths just because I measured them USN2

Federal Gold Medal 168 (white/black box)
2.797; 2.802; 2.792; 2.296; 2.797
Federal Gold Medal 168 (new box)
2.812; 2.814; 2.812; 2.812; 2.812
Remington Premier Match 168
2.793; 2.799; 2.793; 2.793; 2.788
American Eagle 168
2.787; 2.791; 2.792; 2.796; 2.797
Federal XM80C 149
2.787; 2.784; 2.787; 2.785; 2.785
 

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Although Hand loaders sometimes get real close to or even touch the Lands I do not believe any Commercial Ammo is long enough to do so.
In some Guns pressure can really spike with a round touching the Lands.
As for the M1A we are also limited by the Mag.

This being said the best Groups my BR 22-250 ever shot were with the shortest Bullets and the biggest jump.

As Mau stated above the only accurate way to measure a Bullet is from the Ogive.
 

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Bullet tips will vary slightly and as already stated, it's the consistency between the ogive of the bullet (the point at the bullet taper where it hits 0.308") and the base. What I found in measuring high quality bullets, like SMK's and Bergers, was that the ogive was always dead nuts on but the overall length of the bullet from base to tip would vary a few thousandths of an inch.

Here's a good illustration...
http://www.danpassaro.com/img/s9/v14/p369225741-4.jpg

Knowing that there's variations, I started adjusting my seater die so that the average total overall length of my cartridges were at my target length. Some will be longer or shorter and that's okay, as long as the window is spread evenly above and below your target length.

Here's what I use...

[ame]https://www.youtube.com/watch?v=u6P3GeLn2BA[/ame]

We are limited by magazine length so I don't think I'll ever be able to load a bullet "just off the lands" unless I'm single-feeding. Single feed is allowed in some competitions. My best groups were shot with 125 grain bullets and I seat to 2.700". Those bullets have to be jumping quite a bit so I'm not sure exactly how important bullet jump really is or if we're just over thinking it.

Tony.
 

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In most situations, having some bullet jump is not a big concern.

With 'some' barrels, having small bullet jump can help.
I think the reason for this is due to some misalignment of the chamber's centerline and the barrel's centerline, or perhaps because the throat / leade is a little large. These problems cause the bullet to tilt slightly as it enters the bore - so the bullet's axis is not exactly in line with the bore axis, resulting in some wobble as the bullet spins.

With good quality barrels and chambering, that problem is minimal.

Jay Kosta
Endwell NY USA
 

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Bullet jump

You might want to get a chamber gauge so you can measure the actual
chamber and then back off the bullet .010-.015.

You'll also need an ogive tool because that is the best way to keep the
jump fixed from bullet to bullet.

Now that I have said that I need to mention my Swedish M96 chambered for the wonderful 6.5x55 round. That chamber has a really LONG space for bullet jump and the rifle with the military ammo is truly accurate. So, that goes against all theories.

If I may add one piece of advice. Stop wasting big wads of cash on Federal GMM and other premium ammos.

Buy yourself a reloading set up and learn how to do it right.

I can match or exceed GMM accuracy at 1/2 the price per round.
 

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Way back when when I was shooting IHMSA handgun silhouette with a .357 maximum I always got my best accuracy using .357 mag. brass vs. the maximum brass with the same load. That would add a minimum of .250" bullet "jump" I don't know, never made sense.
After all these years it's still voo-doo
 

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I know you asked a philisophical question...but like Tonyben suggested, we may be over thinking this a bit.
I would just start to chart it out yourself. Then you will know the difference. Plus its kinda fun...if you like that sort of busy work.
Thousandths of an inch....very small.
Accuracy is relative and a very many variables are involved.

Mag size limits length.
I've tested this theory....maybe 1/2 m.o.a toward more accurate? Idk. Now, I think that it was the placebo deal. The increase had to do more with concentrating on sight picture and trigger control than the round being more accurate.
Like my pops says...."load the most accurate you can based on mag restrictions".


Deuces
 
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Discussion Starter · #10 ·
I think I get it. Now that I know what an ogive is, would my conclusion that the elimination of jump would actually require the ogive to reach the rifling not the tip be correct? I understand it's not practical with the M14 platform, just trying to be sure I get things mentally in the right places. I also would not have considered the magazine as a limiting factor, so thanks for that as well.

I am surprised to learn that high end rounds such as Sierra MatchKing are not more consistent in overall length. Do the variances in length not result in variances in weight?
 

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Hopefully a picture really is worth 1000 words.

What this picture doesn't show too well is the fit of the throat (space around bullet) and how it will affect accuracy. If it is close fitting, a jump to the rifling is okay (Weatherby rifles were known to have a long freebore to help reduce pressure for the given powder charge.) IF the whole chamber is sloppy, resting the ogive on the lands will help center the cartridge.


Then there is the whole extra case capacity vs no running start before rifling engraving resistance
 

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There is a guide on here about how to load into the lands and grooves.

I believe all the ar15 across the coarse shooters load Em so long they won't fit in the mag.
 

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This is going to be a drawn out anwser and hopefully reloaders with more experience will chime in but here goes:

All rifles are going to be different and some prefer jam vs. jump to the lands and it also comes down to bullet design, if you are talking about loading for the M14 you need to realize you are going to be limited by mag length, the first thing you need to do is get a way to measure the HS in said rifle and trust me if your reloading for the M1A/M14 platform it will exceed mag length, I believe my max length is somewhere around 2.850 (don't hold me to this my notes are home) anyway the ideal starting point is to initally load .010"-.020" off the lands, also understand the the point you want to use is off the "ogive" not the "OAL" but the OAL is going to be what stops you due to mag length.

Most guys just load to 2.800" and call it done and play with the load but I don't do that I currently load to 2.235 off the ogive and this puts the OAL pretty much past the 2.800" but clear the mag without issue.

Another thing to consider while your looking at this if you reload is controlling how far you bump the shoulder on your brass, my M1A is HS at 1.631" so I bump the shoulder back to 1.628" and this reduces over working the brass and also helps in the waytowards accuracy.

So in conclusion my suggestion would be get a good match bullet (SMK, Nosler CC etc..) say in the 168g prep your brass (I use milsurp) look for a good powder (4895, RL-15 TAC etc..) work up a good load and trust me their are a ton out there and some are known standards and start shooting.

Hope this helps and sorry if I covered things you may already know but consider reloading if you don't already, it's not rocket science and you will always be able to tune a load to a firearm better than over the counter ammo.
 
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Not in any significant way. But of course someone makes a tool to cut the tips to a uniform length.
________________________________________________________________

That tool is called a MEPLAT.

One thing I've learned in some 52 years of shooting for accuracy and fun is something a Marine told me.

"Theres the right gun for the right job"

Many M1A lovers who are stuck having to shoot at 100yd. get anal about every little thing.
But, the M1A was designed as a battle weapon, not a sniper rifle.

At ranges out to 200yds. You can come up with a decent load using a decent bullet and forget about EXACT jump or powder measured to .001gr. precision and the rifle will perform very well.

If your lucky enough to be able to shoot long range (600yds+) then EVERYTHING counts.

So, before you make yourself crazy about little details , look at what you need
to do to satisfy your distance requirements.

If I remember the M1A was designed to be able to shoot an 18"wide by 24" tall target at 300yds as a benchmark and it does that pretty well with any decent ammo.

If you want to spend a lot of time on small details, spend that time trying to keep your wife happy. Wives are more dangerous than any M1A.
 

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________________________________________________________________

That tool is called a MEPLAT.

One thing I've learned in some 52 years of shooting for accuracy and fun is something a Marine told me.

"Theres the right gun for the right job"

Many M1A lovers who are stuck having to shoot at 100yd. get anal about every little thing.
But, the M1A was designed as a battle weapon, not a sniper rifle.

At ranges out to 200yds. You can come up with a decent load using a decent bullet and forget about EXACT jump or powder measured to .001gr. precision and the rifle will perform very well.

If your lucky enough to be able to shoot long range (600yds+) then EVERYTHING counts.

So, before you make yourself crazy about little details , look at what you need
to do to satisfy your distance requirements.

If I remember the M1A was designed to be able to shoot an 18"wide by 24" tall target at 300yds as a benchmark and it does that pretty well with any decent ammo.

If you want to spend a lot of time on small details, spend that time trying to keep your wife happy. Wives are more dangerous than any M1A.

I agree with pretty much everything you've got here. Except the statement about everything counting at 600yds--some stuff does; some stuff, not so much.
 

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every barrel/bullet/load combo is an entity unto itself. with a semi auto, i myself never, and advise to never seat the bullet out far enough to jam into the lands. for a bolt gun, whole nother story, some rifles respond very well to jamming a bullet into the lands. one of my varmint rigs likes the bullets jammed in so tight, that you almost have to fire the rifle to unload it, as once it gets hot , it makes an excellent bullet puller(very very messy), but that rifle will remove a prarie dogs head at 500yds with boring regularity. some rifles like to have some jump to the lands too, thats why we do load developement, to see what works best for each rifle.
 
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