Seating Depth and Magazine Length
 

Is it unreasonable to want a rifle to have a seating length to the lands that with a particular bullet will still fit in the magazine?

A friend says it's a dangerous idea.

Would love to hear some thoughts on this subject.

Just to provide some additional info going to be buying a rifle soon in .308 and would like to have the rifle smithed to achieve the above.

Would love to hear some opinions.

Tom

Sometimes this just isn't possible depending on a number of factors. Generally speaking, a rifles magazine is designed to at the least accommodate a cartridge loaded to the max cartridge overall length as per SAAMI specs (i.e. 2.80" for the 308 family, or 3.34" for most "long action" cartridges). Conveniently, most of the "typical for caliber" bullets will be under the max COL when loaded within this spec. Most rifle mass producers will cut their chambers so that the leade/freebore is sufficient to safely accommodate all bullet weights that are considered typical for the cartridge. In other words, when they design the reamer to chamber rifles for, say, 30-06, they have to consider that the owner might shoot factory loads up to 200 or even 220 grains, so they design the chamber to ensure that a long 220 grainer will chamber without hitting the rifling. They also cut a generous freebore because the greater freebore then lower peak pressures will be, giving an additional safety margin.

So with a factory cut chamber, you may have a difficult time seating out close to the lands unless you use a heavy for caliber bullet, and then you can easily run into the problem of not enough space in the magazine. In addition is may be impossible to reach the rifling with a mid to lightweight bullet because the bullet won't be seated far enough into the neck to hold it securely.

Depending on you rifle's chamber, you may or may not be able to reach the rifling and still fit the magazine, or maybe not at all with your chosen bullet. I lot of the competition AR shooters shoot the long 75-80 grain .224 cal bullets, and they have to single load the rifle through the ejection port because there is just no way to fit them into the magazine. If this is the case you might be left with two options, either just load the heavy for caliber bullets out and be satisfied with a single shot rifle, or you could have the barrel turned in and the chamber recut with a custom reamer with less freebore suited to the type and weight of bullet that you want to use. The problem with option 2 is that this might cause you to have problems chambering longer bullets and might cause pressure problems if you use factory ammo.

Mike

I have a browning BAR in 30-06 the clip restricts the length of cartridge I can use, I get it about 30 thou off the lands and still fit in the clip. same story for my mod 70 in 300 WM I can get a little closer with it at 20 thou off the lands. My rem 700 in 223 I can get to the lands. I did have one problem. I was out hunting and had loaded out to the lands. It was a hot day and I think my shells grew a bit. I chambered a round and went after some ground hogs. Shot a few no problems. I came to a fence so I unloaded my gun. The bullet stuck in the lands and pulled out of the case. I was done hunting for the day. I poked it out with a cleaning rod easily. I now keep it at least 10 thou off the lands.

Tom.... driftrider has given you some things to be concerned about. What I might recommend is a long action with the barrel of your choice to shoot the bullets you wish (read "twist"). Mag length should be a non-issue. Followers can be adapted to what you need. Find what shoots best that you want at the distance it likes on or off the lands, and it should work..... Just something to think about.....

Lots of good info here. Thanks guys.

I'm trying to understand what PA said with the long action and barrel of choice. Wouldn't a standard cut barrel still have to much freebore in it to seat the bullets in the brass to a good depth?

I'm thinking the bullets would fit the mag but they would be sticking way out.

Big Guy,

How far off the lands were you seating? I'm not trying to do .005. I just want to get to .001. That would suck if that had happened to you on a big game hunt. Wow.

Other than the risks of factory ammo I'm still feeling like this is something that I want to do. I may even consider shelling out some bucks to have the barrel stamped or engraves with .308 Custom or something like that. Just in case it ends up in someone else's hands.

My buddy says it would be tough to find a smith that would actually do this for me.

I would love to hear some more thoughts.

Tom

I seat the bullets as far off the lands as necessary to make the rifle shoot well, or to the length of the magazine, whichever is shorter. Seating depth is another controllable factor when handloading for accuracy and can make a difference, but loading very close to the lands doesn't always yield better accuracy. Also, if you do seat them very close to the rifling, make sure you back the charge down at 5-10% and work up slowly. Pressure signs can come on pretty suddenly when the bullet doesn't have far to move before engaging the rifling.

I generally seat my bullets to the recommended COL in the load manual for the initial load workup. Once I find a powder charge that the shows promise, I will then load up another batch with different seating depths to see if I can shrink the groups more.

Mike

I'm not sure what part of it they think is dangerous, perhaps I'm not reading enough into your post.

You are correct, if you build a custom gun throated for a specific type of load that may be short and jam a factory cartridge into the lands on someone, that could be dangerous. Though factory ammo is also loaded soft to add safety margin for such things.

My 300WM, even with 200gr bullets, must be loaded out well beyond SAAMI to get close enough to the lands for optimal accuracy with these bullets. Since I can do this and squeak the shells into the magazine still, I do it. My load was worked up from low charge so there is no issue. I burn a bit more powder than a SAAMI shell to get the same velocity due to the increased case capacity, but there's no problem with that for me.

My friend has a factory .308 and he cannot reach the lands with a 165gr bullet and still have it in the brass. It's still accurate, so the jump distance is not an issue in all guns.

If I were having a custom gun built, I'd have it throated for the specific bullet and load I planned to use most frequently. Since I favor long bullets it'd probably still be perfectly safe for factory loads.

spaniel pretty much got the jist of what I wanted to say.

I can't remember what the actual measurement was .I think I loaded them to just touch the lands, 10 thou off the lands didn't hurt or inprove the accuracy.

Tom...Tried to PM you with reply. Didn't work....Would give you my e-mail ???