OAL Question

[Shoot&Ski]

I just started reloading for rifles, so my other experience is only with handgun ammo.
I have been experimenting with different bullet seating depths, starting at just off the lands, and going all of the way down to minimum OAL. As OAL is increased from the minimum OAL listed in load books, pressure will go down for a given powder load, right? So, am I right in thinking, that with a maximum powder load, a longer OAL ( say the bullet is just off the lands) will result in lower pressure than the same load with the bullet seated at Min OAL? I am not looking to increase my powder load over maximum, this is just something I have been wondering. I know that seating the bullet closer to the lands can increase accuracy, but I am wondering what other effects it has on pressure and velocity as well as consistency of powder burn.

 

[Gonzofam]

I know it will make the throat of the rifle very dirty. Lower pressure I imagine a little. But I would worry about the bullet not hitting the grooves right and causing problems in the rifleing catching extra copper. Not goof for the next rounds coming into the chamber accuracy wise and unwanted pressure buildup from what ever charge you throw into the cases. There is alot of variables there. Grey area question.

 

[gamestalker]

I've been seating my high powered rifle bullets just off the lands for over 2 1/2 deacdes with excellent results. It's rather important to try and not get into the lands as pressures can go up, so I've read and been told. But to load a maximum OAL when using slow burning powders has always produced excellent groups for me.
I've consulted with several experts at Hornady, Speer, and Sierra on this and the response was always pretty much the same, being that, accuracy can be better when seating like this, but keeping the bullet from touching the lands is necessary in preventing pressures from rising. The problem often encountered here is, most bullets have a wide spread regarding olgive location, .010" range or more in location isn't unusual. But my personal experience with every high power rifle I own, is even when I get some touching the lands nothing out of the ordinary has ever happened, and accuracy doesn't change either. I imagine if you had to jam the bullet into the lands pressures might show an unhealthy increase. I chamber each round after seating it to make sure it is where I want it. It's time consuming even with my competition die, but worth it to me. Even with a standard bullet or a light weight HP varmit bullet, groups have been consistently super tight.
I would suggest using slow burning powders if your wanting to really get what you can from this method of bullet seating. And regarding olgive consistency, Speer Hot Core has measured very consistent, unless you buy the really expensive bullets for $70 $80 a box.
What cartridge are you loading for? And what powder and bullet are you using?

 

[ranger335v]

"am I right in thinking, that with a maximum powder load, a longer OAL ( say the bullet is just off the lands) will result in lower pressure than the same load with the bullet seated at Min OAL?"

No, the reverse. Rifles and handguns are totally different animals and that's one of the ways it shows up. As a general rule, and given a fixed powder charge, a bullet that gets a decent running start before hitting the rifling will produce less pressure than one that is jammed into the lands.

 

[Shoot&Ski]

Gamestalker: I am starting off loading for my .270 win. I am using Hodgdon 4831sc and I am experimenting with 130 grain Remington corelokts and Hornady Interlock speer points. I found my maximum overall length by just barely seating a bullet, and then chambering it and closing the bolt. I used that length as my maximum and backed off from there.

Thank you for the detailed info, that is very helpful.

 

[gamestalker]

If it is into / touching the lands, yes, your pressurs can go up. But if you are back off the lands, and not toucing them your pressures are going to deffinitely be lower. A deeper seating depth will always create higher pressures unless the bullet is touching or into the lands. It's in the reloading books!! It's actually pretty simple to understand.
I'm quoting directly out of my Speer reloading manual as follows right from the beginning of the chapter titled:
BULLET SEATING
The way the bullet is seated in the case has a great deal to do with its accuracy. The idea is to have the bullet base even with the bottom of the case neck and the olgive of the bullet just short of touching the beginning of the rifling. This situation is hard to obtain because of the variety of bullet shapes and lengths handloaders use, and also because of variations in throating from chamber to chamber. For these reasons, it is impossible to list one given seating depth which will be absolutely correct for all rifles of that caliber and bullets of that specific weight.
The correct seating depth can be determined by using an empty, full resized, trimmed, unprimed case with the bullet your going to load seated out too far. Examine the bullet carefully before chambering it. Look on the bullet for the marks engraved by the rifling. Coloring the olgive of the bullet with a felt tip marker makes the rifling marks easier to see. Continue this process, seating the bullet a little deeper each time until the marks do not appear. The seating depth thus obtained, just short of touching the rifling, gives the best accuracy.
The above statements are directly from the Speer reloading manual and haven't been changed or taken out of context at all. All of the information is word for word, and should be used as the common standard for achieving proper seating depth in any firearm. Further into this chapter, it is reiterated as to accuracy being maintained in this way, and why it is such. When seating further away from the rifling than is necessary will increase harmonic distortion. This is easily explained and caused by the bullet slaming into the rifling, or lands. There are other factors associated with harmonic distortion, which is one of the reaosns why heavy barrels are prefered by competition shooters. Heavy barrels help to dampen harmonic distortion that can't be eliminated in the reloading process , barrel and action lapping, and so on. Browning made a design called the BOSS system that was quite effective in the dampening process. I've said enough for now and hope it has shed some light on the proper method for seating a bullet for accuracy, and to regulate pressures.
The longer the bullet remains in the case, the higher the pressure spike. Another angle on this is not trimming your brass. Reloading books tell us very clearly that by allowing your brass to go beyond maximum will cause pressures to go higher.

 

[noylj]

If one jams the bullet in the leade/rifling, there is either going to be a wedged bullet or bullet set-back.
Neither seems like something that would improve accuracy and would increase pressure.

 

[gamestalker]

You are very welcome Shoot&Ski.
As long as the bullet is not touching your good to go.

 

[ghostwriter]

I have experimented with my handloads in my 300 win mag and if I take a particular load and just change the COA then I find the accuracy suffers if I back off more than .030" from the rifling. If I touch I find a slight bit of difference in accuracy as opposed to the best loads I shoot which are just .012-.018" off the rifling.
I too take the empty fireformed case, remove the primer, take a little squeeze in the die to hold the bullet and using the particular bullet paint it on the OGIVE black so it'll show the rifling marks as it touches. Then chamber it easy and then remove it just as carefully. Measure it overall and that's the zero length with that particular bullet. If you change bullets you have to do this all over again with another case and bullet.
I measure and reduce that by the clearance I want... (.012 to .018") and that's the length I "shoot for" with the bullet seater die. It takes a few rounds to get it perfect so don't rush. Your patience will be greatly rewarded with tighter groups.

 

[918v]

I see a change in accuracy with a change in OAL, but it does not necessarily mean it gets worse the further the bullet is away from the rifling. Sometimes it gets better. I'd rather have an accurate load that fits in the magazine than a 10% more accurate load that has to be single loaded. The difference in accuracy is not linear and is not predictable. You can adjust the powder charge or change primers to tweak the load further.

 

[ghostwriter]

Yes, you are absolutely right. Some average rifles like to jump and there's plenty of examples and threads that highlight this aspect. There's an article about the Houston warehouse and Virgil wrote this:
==============================
One thing that IS important is that the bullet be precisely seated against the
lands. T.J. Jackson reported this fact in the May 1987 issue of Precision
Shooting. In a letter to the Editor, T.J. wrote, “...in all our testing in that
Houston warehouse... and the dozens and dozens of groups that Virgil King
shot in there ‘in the zeroes’... he NEVER fired a single official screamer group
when he was ‘jumping’ bullets. All his best groups were always seated into the
lands, or at the very least... touching the lands.”
Virgil said his practice was to seat the bullets so the engraving was half as long
as the width of the lands. He noticed an interesting phenomenon with rifles that
could really shoot: if the bullets were seated a little short and the powder charge
was a bit on the light side, the groups formed vertically. As he seated the
bullets farther out and increased the powder charge, the groups finally became
horizontal. If he went still farther, the groups formed big globs. He said the
trick is to find the midway point between vertical and horizontal. That point
should be a small hole.
================================
He also found that primers had little if no effect on accuracy and this came from guys who shot groups so small you need a "floater" card moving behind the target to actually prove you put 5 rounds downrange thru the target! Incredible.

For us average shooters, probably doesn't matter and I have the whole article about the warehouse if anyone wants it. I was going to post it but you can google it and download the pdf yourself fairly easy.

http://www.angelfire.com/ma3/max357/houston.html

http://bulletin.accurateshooter.com...-houston-warehouse-read-this-classic-article/

The biggest thing in accuracy is case preparation, way more than bullet selection or sorting or powder weighing or primer selection. It's quite an art and I admire those who can put round after round thru the same hole.