Bullet Seating Depth

[Calif. Hunter]

I finally got around to measuring the distance to the lands with various bullets today in my rifles with the Stoney Point guages, comparators, etc. I got from Midway a few weeks ago. I was amzed at how far out some of those bullets would have to be seated in order to just kiss the rifling. .270 and .30 Nosler partitions, in particular. Now I know you don't want them touching the rifling, but some people have said to seat them just a couple of thousandths off the rifling. If I do that, half the bullets I use would barely be seated in the case and may not fit in the magazine! (And this isn't even considering the .300 Weatherby, which appears to have well over 1/4 inch of freebore...which it is supposed to have in order to get the velocity without too much pressure.)
So just how far off the rifling do you seat your bullets?

 

[DGF]

I don't reload yet, but I say experment and see where you get the best accuracy. Once you find that experment with grains of powder till you esablish your pet load and have fun! I've heard it said on other boards that different guns like bullets seated different amounts off the lands (even same model guns) so what others do may not be the best thing for you. Just be sure you don't sacrafice safety for accuracy.

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~DAN~

 

[josh]

I discovered the same thing when I did this with my guns. I figure they got to at least fit in the magazine, no matter what accuracy you sacrafice, they still gotta function, so I seat those so they fit in the magazine and call it good. I did not find that it made much differnce wheather they were seated just off the rifeling or not.
I would be itnterested in the experiences of others on this?

 

[danr55]

Here I go shooting holes in another loading myth. The practice of seating bullets to the lands is one that was started by bench rest shooters a long time ago. I don't know why, but that's where it came from. When you seat bullets in contact with the lands, some interesting things happen to chamber pressures. I presume that most of you are familiar with Weatherby and their 1/4" freebore to provide extra relief for the overbore capacity loads that they build. When you seat bullets out far enough to touch the lands, you have exactly the opposite effect on the pressure capacity of the load. It is reduced considerably. In almost every loading manual, is listed a maximum overall cartidge length. It's usually listed as "MAX COL". Stick with this and you should optimize performance for any load. The trick to accurate loading is consistancy. If you keep the COL the same with all of your loads, then they should perform the same with every loading. That is to say that, unless something else changes, ....If you seat the bullets out far enough to touch the lands, the size of the expansion chamber is fixed and the bullet does not have the ability to start to move and flatten the pressure spike before it meets the resistance of the rifling. This can cause some dangerous rises in chamber pressure. As long as you start your load development in this fashion, you will do OK. You should get used to greatly reduced velocities and a greatly increased round to round sensitivity to pressure changes. All in all, it's more worry than I care to deal with. That is not to mention the need to lengthen most of you magazine boxes.

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Dan AZ www.huntandlodge.com

 

[Ken Howell]

You've just discovered a "little" matter of conflict between shooters' desire for good accuracy on one side, versus shooters' obsession with muzzle velocities and manufacturers' precautions on the other side.

The culprit is the throat. It's too long. Long throats let normally seated bullets get up some momentum before they hit the rifling. This helps keep pressures down and velocities higher, but makes for somewhat less than bench or varmint accuracy.

The best accuracy comes from bullets seated slightly into the lands. Bench-rest champs disagree about how far into the rifling to seat their bullets. One six-times world champ likes to see land marks on the ogive that are as long as they are wide. Others like land marks longer than they are wide. Either way, that seating aligns the bullet better and gets it started straighter when the action gets under way behind it, but that seating has two problems.

• In factory and many wildcat rifles, many bullets aren't long enough to reach from full seating in the neck to the rifling.

• Bullets seated into the lands raise pressures more abruptly, dangerously with loads that would be maximum with some amount of bullet jump to reach the rifling.

You've already identified the third frequent problem — bullets seated to span a long throat to get anywhere near the rifling often make those rounds too long for the magazine. The solution is a shorter throat, which means a minor overhaul of the rifle.

 

[danr55]

Hi Ken, Welcome to Moosies place. That was well written. Thanks for the backup.

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Dan AZ www.huntandlodge.com

 

[Deacon]

Dan and Ken, interesting and informative reading. Thanks.
I normally seat bullets .010 from the lands. That's for everything but Barnes X which needs to be seated approximately .050.

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[Nodak Hunter]

I work up a load using the recommended max c.o.l., and then, when I have the velocity I want, I make up a dummy round, "smoke the bullet" to determine max length before touching the rifling, split the difference between the two, and try out that length. I may try seating .01" deeper in a continuing step method until best accuracy is achieved.

I generally get slightly better accuracy without affecting velcocity.

Of course, the cartridge must easily fit into the magazine and feed smoothly every time. Also, if I get fine accuracy (.7 moa or better) with my first load at listed max c.o.l., I don't even monkey around with different seating depths.

 

[concerned hunter]

Why can't you just seat the bullet just enough until the bolt closes on your rifle? If you can close your bolt smoothly then is there a problem or no?

 

[concerned hunter]

I loaded up some 150's today and seated them about 1/4 inch longer and my groups tightened from about an inch at 100 yds. to less than 1/2 inch. That is 1/4 inch longer than the COL listed in Speer's book.

 

[Nodak Hunter]

Bullet jackets are soft enough that you may be sliding them right into the lands and not even realize it. As mentioned earlier, this could cause dangerously high pressures at near max velocities. That's why I always check what the max length is when the bullet touches the lands, (the "smoking" method) and back off teh length a bit from there.

 

[danr55]

CH, Don't forget to try the rounds in your magazine before you take them hunting. Hell of a note to turn your bolt gun into a single shot.

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Dan AZ www.huntandlodge.com

 

[Slamfire]

I've got a couple of guns chambered for the .260 Remington. The carbine likes the bullets seated out so far I'm afraid the bullets will fall out of the cases. The rifle on the other hand prefers the 129 grain Hornady seated to the cannalure. Some time back Rick Jamison wrote that varying the seating depth can have a bigger effect on accuracy than any other single factor in your load. While it is true that maximum loads will be too much with bullet in the land seating, you can develop a load with good velocity and complete safety. That is the whole point of handloading, customize the load to the gun. Far too many folks are just looking for "pet loads" from others, that may or may not suit their rifles.

 

[concerned hunter]

Danr55, Isn't these COL listings a little short because the book loads are to fit in just the gun testing the ammo? I tried the sooting the bullet technique and it came out without a mark around it so I think I am still safe. My load is between the minimum and maximum.I just started handloading so I am still learning.

 

[Calif. Hunter]

I wasn't sure if my .300 Weatherby had the freebore or not, as it was a custom barrel. It has a good 1/4 inch of freebore in it. My old .30-06 MK1 '03 Springfield had a good bit of throat in it, too, but maybe some of that could be erosion. I don't think so, as the bore is pretty bright and smooth. What was most surprising was my brand new .270. Some popular bullets would have to be seated out so far that they would either be too long for the magazine or would not have enough bullet in the neck to give a good grip! My Savage .223 also would be tough to seat out far enough with Sierra 60 gr HP's. I found it interesting to see the diffrent throat lengths in my various guns.

 

[danr55]

Slamfire, I don't recall that article, I'll have to write to see if I can get a copy of it.

ConcernedHunter, The answer to your question is NO. The COL listed in most manuals is a SAAMI specification lenght for a particular load. By having a standard specification, you can be assured that your .270 round from Hornady and your 270 load from Winchester will both fit in your 270 rifle from Savage or Remington or whoever. Without industries standards, everyone would be doing things their own way and you would never be certain of anything. If you will notice, most of the listings say "Max. COL".

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Dan AZ www.huntandlodge.com

 

[concerned hunter]

Right,Danr55,but some are talking about having their cartridges so long that the bullet is about to fall out. This might be a little questionable but wouldn't that be way over their COL if that is the case? I guess what I am trying to say is in my 7Mag the max.COL is 3.290 but what if I have another 1/4 of inch before my rifling or a 1/2 inch? I guess that is kind of what I am getting from different posters is you can go clear up till you are almost touching your rifling, right? Then this could be over 3.290?

 

[danr55]

That is precisely what you are hearing from other posters. Let's start at the beginning. SAAMI is responsible for maintaining the specifications for all standard chambers. These provide min-max dimensions for these standard chambers including all of the relative dimensions. Now, that being said, there isn't anything short of legal liability that says that those specifications have to be maintained. So you do occassionally by accident wind up with nonstandard chambers. There are also several gunsmiths that wish to improve on the design standard by one of several methods. One of the favorite improvements is the adding of a little freebore to increase velocity. Freebore allows the bullet to jump for a ways without any appreciable increase in chamber pressure. Weatherby made it famous and you will hear all kinds of arguements both ways. Anyway, freebore is one of the things that can effect the clearence between a bullet and the rifling. Another thing that can effect this distance is the type of bullet you're loading. It can be a one caliber ogive up to a five caliber ogive. The higher that caliber number the longer the distance to the rifling because of the slope of the nose. So there are all kinds of different results. I have found that consistancy is the best supplement to accuracy and velocity. Experiment with the load combinations until you find one that will work for you. Then stick with it. I have experimented with seating depths and have never found anything that improved the accuracy enough to make me change to original recipe.

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Dan AZ www.huntandlodge.com

 

[josh]

Well said, Dan....You certainly cleared this up for me.