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Old 02-14-2014, 12:00   #1
wdchk
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COAL and Rifle accuracy

How much impact does COAL have on rifle accuracy? My reloading manual lists 3.25" for 165 gr. soft point .30-06 (deer loads.) I have some factory bullets at 3.175" (Remington) and 3.2" (Hornady). My manual indicates that seating the bullet at slightly short of the bullet touching the rifling will help accuracy, but it doesn't give a figure as to how much gap there should be. For my Remington 700 the bullet hits rifling at 3.4", which means with boattail bullets there isn't a lot of contact between the case neck and the bullet. At what point is this an issue?
Is the impact on accuracy significant, and is there a safety factor that I need to be mindful of in any of this?
Any help is greatly appreciated.


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Old 02-14-2014, 12:24   #2
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You will find that some Remington 700 as extremely long throated, to rectify the problem you having with COAL and those 165s you would have to have the barrel set back. MAX COAL for a 30-06 is 3.34 I believe.
Generally the longing the COAL within the chamber the more accurate the round. However NOT in all cases. Some bullets actually like the jump to the lands. I've tested my own loads starting at MAX COAL for my rifle and then setting back the COAL 0.010 at a time and noticed that the groups actually tighten up depending on the bullet powder combo of course.
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Old 02-14-2014, 12:24   #3
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Originally Posted by wdchk View Post
How much impact does COAL have on rifle accuracy? My reloading manual lists 3.25" for 165 gr. soft point .30-06 (deer loads.) I have some factory bullets at 3.175" (Remington) and 3.2" (Hornady). My manual indicates that seating the bullet at slightly short of the bullet touching the rifling will help accuracy, but it doesn't give a figure as to how much gap there should be. For my Remington 700 the bullet hits rifling at 3.4", which means with boattail bullets there isn't a lot of contact between the case neck and the bullet. At what point is this an issue?
Is the impact on accuracy significant, and is there a safety factor that I need to be mindful of in any of this?
Any help is greatly appreciated.


Wdchk

If you are loading for hunting, just load them to magazine length, find the velocity that works for your specific bullet you want to load and be done with it.

For bench rest shooting, the jump (how far from the lands the bullet is seated to) will affect your groups.

Each bullet (even within a given weight) will have a different jump at a given seating depth (OAL). The shape of the ogive will affect it.

To make matters even more complicated, some bullets like (or tolerate) more jump than others. If you are bench rest shooting, experimentation is required.

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Old 02-14-2014, 13:15   #4
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It will impact accuracy, but the best place to start is the OAL they list in the bullet manufacturer's data. If it has a cannelure, line it up with the case mouth and try crimp vs. no crimp. That will likely have a larger impact on your groups. Some BR folks jam the bullet into the lands (this will raise pressure - if you're going to do it, start load development over).

As mentioned, other considerations are magazine length and the variation you'll inevitably get with the ogive in a given batch of bullets. Some will hit the lands before others do. Guys that really try to get .00x" off the lands will sort bullets so they're all the same. Leave a little wiggle room.
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Old 02-14-2014, 13:16   #5
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Every rifle is diff & every bullet has a preference, so yes, it can make a diff. There is no magic distance off the lands & some bullets prefer a shorter or longer jump to the rifling. So I load to max mag length for those rifles, backing off the OAL 0.010" to see if things get better or worse. Often, no accuracy change. For a couple single shots, I can play with the OAL as much as I like, results then are more easily seen. NO ONE can tell you what OAL works best, it's a trial & error endeavor.
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Old 02-15-2014, 04:10   #6
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Thanks, I appreciate your replies. I'll play around a little, and see what happens. These are hunting rounds, my interest is in getting as much accuracy as I reasonably can.
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Old 02-15-2014, 08:40   #7
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Quote:
Originally Posted by wdchk
For my Remington 700 the bullet hits rifling at 3.4", which means with boattail bullets there isn't a lot of contact between the case neck and the bullet. At what point is this an issue?
Is the impact on accuracy significant, and is there a safety factor that I need to be mindful of in any of this?
The general rule of thumb is that you should have at least one bullet diameter seated into the case. In your 30-06 that would be about .308 inches of bullet seated into the case. Only a guide, not written in stone.

Safety factor, can mean many things, but if you are talking pressure, then you should be aware that the longer the round the closer the bullet is to the lands, the closer the bullet is to the lands the Higher the pressure.

This means that if you work up a max load that is say .050 off the lands and you decide to increase the OAL to .010 off the lands, chances are you will be over Max pressure.

The best way to avoid this is to start your load development as long as possible, then with each decrease in OAL the pressures will not rise. This of course is for Rifle rounds and not straight walled pistol rounds.
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Old 02-15-2014, 09:59   #8
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Thanks, I appreciate your replies. I'll play around a little, and see what happens. These are hunting rounds, my interest is in getting as much accuracy as I reasonably can.

I care a lot about accuracy, but with all my hunting rounds, I load to magazine length which in your 700 (if it is a factory barrel) is going to be roughly .150" off the lands for a nominal bullet. Although I have never needed a second shot (that was sarcastic humor), having it reliably there is far more important than squeezing another .5 MOA out of the groups.

You should be able to get sub-MOA accuracy at magazine length OAL's by just finding a nice wide node for the bullet and powder combination you are are using.

Heck, I even full length size the brass and crimp my hunting rounds. Horror of horror to the bench rest side of my personality.

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Old 02-16-2014, 12:00   #9
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You can get stupid about bullet OAL...

but I've had best results by seating bullets against the lands, using said round to set up my seating die(s) to reflect that length, withdrawing the round slightly from the die, turning the seating die stem down 1 full turn, then reseating the bullet. Most of the time this extended length will fit the magazine if a bolt gun. If not, adjustments must be made unless you want to use the gun as a single shot and not a repeater.

A rough rule-of-thumb but one that's worked very well in my BG rifles and most of my walk-around varminters as well.
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Old 02-16-2014, 15:40   #10
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It's probably is not worth any time or effort trying to get the optimal distance off the lands on a Remington rifle. I have a 5R and can't seat anywhere near the lands and have the bullet inside the case (!). Guess that's what you get when lawyers build guns instead of gunsmiths.

But, in broader terms, you really need a Hornady Comparitor to gain control of seating distances of bullets from lands. The comparitor allows you to precisely measure the position of the bullet from the lands for a given bullet with a given ogive.

Remember, it is not the tip of the bullet that contacts the lands, but the ogive -- somewhere further down from the tip. The Comparitor allows you to find this measurement and work back from it to the stand-off you feel is optimal.

Now, in very broad strokes, I start developing loads with the ogive .015 off the lands. This is pretty tight, so there are definite pressure consequences of choosing this starting point. Therefore, I start very low on the charge data recommendations from reputable laboritories (usually Speer and/or Hornady). If you go to one of the precision rifle sites, like Sniper's Hide, you'll get a pretty good idea of how far most guys are jumping their bullets. There is some robust, pragmatic data (experience) out there about how far people are jumping bullets of different types and consequent accuracy. VLDs, in particular, seem to like a shorter jump, while standard bullet configurations seem to be less affected by the ogive to lands distance.

O.A.L. -- again -- tells you nothing about the relationship of a bullet to the lands of a rifle. It is only useful when you're feeding cartridges from a magazine and are willing to compromise ballistic optimization for mechanical function.

Finally, back to where I began, all of this is esoteric and impractical if a Remington factory barrel is what you're flying bullets out of.
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Old 02-17-2014, 04:25   #11
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Yeah, after making some measurements with my rifle, and reading all the replies, I see that COAL is one rabbit I don't need to chase.
Thanks all!
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Old 02-17-2014, 12:35   #12
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My buddy who shoot Long Range Rifle says this.

Start at about .010" off the rifling,

Get the most accurate load.

Then load to .005" off and test, then .015" off and test.

You can watch the group change easily at that point.
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Old 02-17-2014, 12:54   #13
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Here's my CRB method for bolt rifles to find your COL when the bullet actually engages the rifling. You most likely will end up with a COL that will not fit your magazine, so these will be individually loaded rounds. Not so good for hunting purposes, where you may need a follow-up shot.


Using a Dremel cutoff wheel (or maybe a thin hacksaw blade) and a resized case, cut two slits in the neck, 180 degrees opposite each other. Now, just barely start a bullet into this case. The neck should hold it in place, but allow it to slide into the neck when the bullet engages the rifling.


Slowly chamber this round in the bolt gun, then very carefully extract the round being sure not to let the bullet hit any part of the chamber or extraction slot. Measure the COL. Pull the bullet back out, maybe use another bullet from the same box, and repeat and remeasure. Do this several times and record each COL measurement.


The minimum COL you recorded should be your MAX COL (to not engage the rifling with that specific bullet in that specific rifle). Remember that bullet makers often use multi-cavities and/or multiple machines to make bullets, so you can have variances within the same box for the exact same type of bullet.
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Old 02-17-2014, 13:32   #14
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My buddy who shoot Long Range Rifle says this.

Start at about .010" off the rifling,

Get the most accurate load.

Then load to .005" off and test, then .015" off and test.

You can watch the group change easily at that point.
That's not what I say...

Wait... when did you get another buddy?

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Old 02-17-2014, 13:56   #15
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It's probably is not worth any time or effort trying to get the optimal distance off the lands on a Remington rifle. I have a 5R and can't seat anywhere near the lands and have the bullet inside the case (!). Guess that's what you get when lawyers build guns instead of gunsmiths.
So, is it worth the effort to have the barrel cut down and the chamber recut?

It would be a little more complex on my 5R due to the indexing of the muzzle brake. There's no crush washer involved with my setup.

Might as well have the action trued at the same time, I suppose.

On a good day I can shoot < 1/2 MOA the way the gun came out of the box. A bad day has a much different result...

I just shoot for giggles so maybe it just isn't worth the effort.

Richard
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Old 02-17-2014, 16:28   #16
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I think it depends on the smiths you know. Most of the guys I know that specialize in precision rifle will just say, "get a new barrel, it will cost you the same whether we start with a quality new one versus screwing with the old one." This is from guys that don't care if you buy your barrel and bring it to them, or they buy it for you. YMMV.
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Old 02-17-2014, 17:03   #17
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I don't know any 'smiths and I don't know anything about barrels. I know I like the 11.25" twist and the 5R rifling. I have been told that other manufacturers sell the same type of barrel but I haven't really gone looking.

Then I would have to tell the 'smith where I wanted the chamber to wind up. I don't think I know that. I suppose I could start with the idea that the nominal .308 OAL is 2.8" and that I wanted the rifling within about 0.020" for a 175 gr HPBT. I could probably verify that a 2.820" round would fit in the magazine.

Something like that...

This stuff is really above my paygrade. I need to do some more research.

Richard
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Old 02-17-2014, 17:34   #18
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Maybe the best way to find a local smith that knows what he is doing is start attending some local matches. Get to know the high power and bench guys and after you listen patiently to their sales pitches about that "perfect for you" gun that just happen to have for sale, ask them who they use to do their builds. A consensus may emerge and that probably will be a good place to start.


After you find the right smith, just tell them what you want, they will be able to accommodate it. They might have a favorite barrel mfg like Kreiger, Shilen or Lilja (to name a few), or they may want you to go decide yourself.


Be prepared to be talked out of some ideas, if they don't agree that your ideas make sense in their experience. They are usually a wealth of practical experience.


Or just keep what you have, practice, experiment, practice experiment, repeat, and when you are down to .2 MOA resolve yourself to calling it good.
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Old 02-17-2014, 17:48   #19
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Only you can determine if a new bbl is worth it. For most of us, it's not. If you are just plinking & getting 1/2MOA, a new bbl might get you into the 0.3s, maybe, depending on who chambers it & refits it. So if I had a rifle shooting 1/2MOA, I would look to just tweek the load. Again, there are no magic numbers, so 0.010" off the lands is as good a spot to start as any. Most rifles have more lead/throat than that for most bullets set to clear the mag dims.
IF I were changing bbls anyway, as I did when I went form a 308 to a 260AI, then you might as well make up a dummy round for your chosen bullet & have the smith set the chamber up for that bullet. Mine was setup for 0.010" off the lands with the COAL as 2.810", to guarantee it fed in the mag all the way down. Now this rifle will shoot into the 0.3s on good days with that bullet but still shoots 1/2moa with other bullets that are well off the lands.
A good bbl, properly chambered & bedded, is a good bbl. The distance to the lands is an after thought IMO. If the chamber & bore are as perfectly aligned as possible, then the round will enter the bore straight, which is why many will like to wedge the bullet into the rifling, to hold it straight.
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Old 02-17-2014, 18:01   #20
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On one VERY exceptional day, I was able to shoot a single group of 0.2"x0.050". That may never happen again. But I have the target that shows it happened once. So the rifle and load are capable even if the shooter is marginal. Mostly I get sub MOA and usually around 1/2 MOA. Not always, but usually.

Right now, there is more than 0.100" of jump with the 175 gr BTHP. The BT really constrains how long I can load the rounds. Even if the magazine didn't.

If I ever manage to shoot the barrel out, I'll give some consideration to having it accurized. For now, I'll just shoot what I have and call it good.

I like .308 and probably the best thing to do is buy a custom rifle. The problem is my short attention span. When people start talking 6+ months to get a stock and who knows how long to get a barrel, I lose interest real quick.

Richard
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Old 02-17-2014, 18:13   #21
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On one VERY exceptional day, I was able to shoot a single group of 0.2"x0.050". That may never happen again. But I have the target that shows it happened once. So the rifle and load are capable even if the shooter is marginal. Mostly I get sub MOA and usually around 1/2 MOA. Not always, but usually.

Right now, there is more than 0.100" of jump with the 175 gr BTHP. The BT really constrains how long I can load the rounds. Even if the magazine didn't.

If I ever manage to shoot the barrel out, I'll give some consideration to having it accurized. For now, I'll just shoot what I have and call it good.

I like .308 and probably the best thing to do is buy a custom rifle. The problem is my short attention span. When people start talking 6+ months to get a stock and who knows how long to get a barrel, I lose interest real quick.

Richard

I think I recall you saying you shoot from a bi-pod, right?

If so, I think .5 MOA is pretty good. When I speak of my little homebuilt 308 shooting sub .2 MOA, I am talking from a heavy three point front rest on a concrete bench, a rear bag on a custom height platform, stock marked so it is in the exact same place on the bags each shot, bags dusted, lately using a dryer sheet on the front rest, etc. etc. etc.

Frankly, if I was shooting that same gun and load from a bi-pod and it delivered .5 MOA, I would be pretty happy.

PS - Reading Fred's post jogged my memory, your action is bedded and barrel free floated, right? If not, that is something to do first. It is pretty easy to accomplish yourself, lots of good advice on how on youtube.

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