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Posted: 10/5/2009 5:33:55 AM EDT
| For some of you guys on here that have tons of experience, what is your ballpark guess on much accuracy can suffer as a result of seating bullets too far off the lands? For the sake of argument, lets say you were loading a 70 grain .224 bullet .15" off the lands in a 5.56 gun. What would the impact most likely be in terms of MOA lost? |
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There is no answer to that question.
If you're shooting a quality bullet through a good barrel on an AR, it's really nothing to fret over. The improvements by moving close to or into the lands are small increments, and the rifle must have inherent accuracy first. Fooling around with seating depth is mostly a waste of time with off the rack rifles chambered with long throats. You're not going to cause a rifle with poor baseline accuracy to suddenly start shooting brilliantly with handloads. The one thing that might be worthwhile in a rifle with a long throat that shows promise is to find bullets that are insensitive to a long jump to the lands. The problem is, it's hard to predict, although the manufacturers give some guidance on their web sites (take a look at the recommendation for Berger bullets, for example). I would look for a bullet with a long bearing surface, then load it with as little runout as possible. |
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Quoted:
There is no answer to that question. If you're shooting a quality bullet through a good barrel on an AR, it's really nothing to fret over. The improvements by moving close to or into the lands are small increments, and the rifle must have inherent accuracy first. Fooling around with seating depth is mostly a waste of time with off the rack rifles chambered with long throats. You're not going to cause a rifle with poor baseline accuracy to suddenly start shooting brilliantly with handloads. The one thing that might be worthwhile in a rifle with a long throat that shows promise is to find bullets that are insensitive to a long jump to the lands. The problem is, it's hard to predict, although the manufacturers give some guidance on their web sites (take a look at the recommendation for Berger bullets, for example). I would look for a bullet with a long bearing surface, then load it with as little runout as possible. Sounds like good recommendations. Thanks much. As a follow-up, would you guess that a harder bullet (a copper solid) would be more or less tolorant of a long jump to the lands? |
| Nose shape would have much more of an effect than hardness of the bullet. Metal jacketed bullets do not deform upon firing, thus hardness will not matter. However the shape of the nose will have an effect on how much the bullet can tip before centering on the bore. A chamber which has a larger diameter throat and a bullet which allows for more tip will be influenced more by seating depth than a tight throat and better bullet shape. |
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Quoted:
For some of you guys on here that have tons of experience, what is your ballpark guess on much accuracy can suffer as a result of seating bullets too far off the lands? For the sake of argument, lets say you were loading a 70 grain .224 bullet .15" off the lands in a 5.56 gun. What would the impact most likely be in terms of MOA lost? The only 70 grain bullet I know of is Speers and it must be seated deep to avoid contact with the lands. You will even get jamming if loaded to magazine length in an AR-15. All the other "match bullets" in this weight class (68/69) are designed to jump and very little if anything can be gained because of their bullet style. In most AR based rifles the 68/69 will just about fall out of the case if you try to load them close to the lands (NATO 5.56mm). Custom chambers (Wylde or SAAMI) may or may not allow this, but is a waste of effort and makes those rounds unuseable from a magazine. I leave the long loading to the bullets that need or benefit from it, 80 Sierra MK's, Hornady 75 A-MAX and any VLD. .15" off the rifling isn't considered close to the lands, .015" is. |
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Quoted:
Quoted:
For some of you guys on here that have tons of experience, what is your ballpark guess on much accuracy can suffer as a result of seating bullets too far off the lands? For the sake of argument, lets say you were loading a 70 grain .224 bullet .15" off the lands in a 5.56 gun. What would the impact most likely be in terms of MOA lost? The only 70 grain bullet I know of is Speers and it must be seated deep to avoid contact with the lands. You will even get jamming if loaded to magazine length in an AR-15. All the other "match bullets" in this weight class (68/69) are designed to jump and very little if anything can be gained because of their bullet style. In most AR based rifles the 68/69 will just about fall out of the case if you try to load them close to the lands (NATO 5.56mm). Custom chambers (Wylde or SAAMI) may or may not allow this, but is a waste of effort and makes those rounds unuseable from a magazine. I leave the long loading to the bullets that need or benefit from it, 80 Sierra MK's, Hornady 75 A-MAX and any VLD. .15" off the rifling isn't considered close to the lands, .015" is. Berger sells a 70 grain bullet. They recommend seating close to the lands. Well, they did at one time - For years we have relayed that it is best to jam the VLD into the lands for best performance. This works for many rifles however there are many rifles that do not shoot the VLD well when the bullet is jammed. We have learned that the VLD can shoot best as much as .150 jump off the rifling. VLD bullets can be sensitive to seating depth and it has been found that these bullets shoot best in a COAL “sweet spot”. This sweet spot is a COAL range that is usually .030 to .040 wide.
The quickest way to find this sweet spot is to load ammo at four different COAL. Start with a COAL that allows the bullet to touch the rifling. The next COAL needs to be .040 off the lands. The third COAL needs to be .080 off the lands. The last COAL needs to be .120 off the lands. One of these COAL will outperform the other three by a considerable margin. It has been reported that the VLD bullets don’t group as well at 100 yards but get better as the bullet “goes to sleep” at further ranges. We have learned that by doing the four COAL test you will find a COAL where the VLD bullets will group well at 100 yards. Once the COAL that shoots best is established you can tweak +/- .005 or .010 to increase precision or you can adjust powder charges and other load variables. Frankly, those who do the four COAL test usually are happy with the results they get from this test alone. Pretty pitchers: http://www.bergerbullets.com/Products/All%20Bullets.html |
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Thanks AeroE. I found that blurb from Berger after you made the earlier post. Very interesting.
Barnes makes a 70 grain bullet too, and it is actually the source of my current problem. Interestingly, Barnes recommends seating a little farther off the lands than most companies do (except the qualfied recommendation that Berger gives). Barnes recommends somewhere between .03-.07" off the lands. I can't even get anywhere near that close with magazine length constraints though. |
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My Colt rifle has such a long throat that none of the long heavy bullets will touch the lands. I've never tried in my 16 inch carbine, but I do know there's enough room to clear an 80 grain Berger seated to about 0.005 off in my match rifle. I don't really care in the carbine.
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