AR 10 gas gun seating depth?

[Mark611]

I have a question about seating depth, I'm loading for a 6.5cm AR10 upper, trying the 120 and 123gn pills, I look at the manuals Hornady and Sierra Nosler {ect} I am also looking at the Hodgen reload center, I'm seeing some info That is different, for example, the Hornady manual says to seat the 120gn ELDM at 2.710 Hogden says 2.670, what I have noticed is 2.710 doesn't push the bullet all the way into the bottom of the neck , I'm running 38.3gn of VARGET {Test} which only has about 85% case fill to begin with, according to Nosler and is close to a max powder charge, I'm also loading the Sierra 120gn MK's Sierra shows this bullet seated at 2.750 again the bullet is about 3/4 of the way into the neck, Nosler shows there 123gn CC seated at 2.650 which I have loaded some of those as well at that seating depth, any suggestions, or you thoughts please.

 

[Steve Donlon]

If it's a Hornady bullet, start with what the Hornady manual says. Same with Sierra. Use the bullets manual to start. Sometimes it's the minimum length and sometimes it's the maximum length.

 

[ebb]

In all my Ars ive always seated them to max magazine length, and they are still way too short.

 

[The boogalorian]

I have been working on a 6.5 creed ar10 that likes 140gn Eldm. Turns out it likes 2.740” oal better than mag length.
Start with the bullet manufacturer’s recommendations as stated above. Once you know it is safe in your gun don’t be afraid to experiment a little.

 

[divingin]

Unless you're single loading, you're length limited by the mag.

 

[Mark611]

I'm going to run these at the bullet manufacture suggested C.O.A.L. to start, my concerns are these 2 things, 1 is the case volume with the 85% case fill with the 120and 123gn bullets, 2 is the bullets not being supported fully by the neck, I'm not going to single load once I find a load that shoots well, I'm planning to mag load and run like it should, I'm working with the powders I have right now, VARGET, H4895, RL16, 6.5 StaBall, VARGET and H4895 only give about 85% case fill, I have 30 test rounds loaded with RL16, with the 140gn Hornady HPBTM, and the 120gn ELDM's and 120gn SMK's, I know the 140gn pills are longer, they seat way deeper into the case, than the 120 or 123gn pills, before you say just use the 140's VARGET and H4985 won't produce the velocities I'm looking for, and I'm trying to save my RL16 for my bolt gun, RL16 is to expensive anymore just to burn through in a gas gun, I don't have any H4350, Just sayin,

 

[Coyotefurharvester]

I saw a box of the Horn 120 eldm(white match box ammo) on the shelf. Asked if I could measure a few,coal was 2.713-2.716. Digital caliper.

 

[10XSHOOTER]

That's a problem with the Needmoors!
Not long enough to feed from a magazine gun

 

[Steve Donlon]

I'm going to run these at the bullet manufacture suggested C.O.A.L. to start, my concerns are these 2 things, 1 is the case volume with the 85% case fill with the 120and 123gn bullets, 2 is the bullets not being supported fully by the neck, I'm not going to single load once I find a load that shoots well, I'm planning to mag load and run like it should, I'm working with the powders I have right now, VARGET, H4895, RL16, 6.5 StaBall, VARGET and H4895 only give about 85% case fill, I have 30 test rounds loaded with RL16, with the 140gn Hornady HPBTM, and the 120gn ELDM's and 120gn SMK's, I know the 140gn pills are longer, they seat way deeper into the case, than the 120 or 123gn pills, before you say just use the 140's VARGET and H4985 won't produce the velocities I'm looking for, and I'm trying to save my RL16 for my bolt gun, RL16 is to expensive anymore just to burn through in a gas gun, I don't have any H4350, Just sayin,

Your two concerns are why most people don't bother with 120 and 123 gr. bullets. You don't gain enough positives to use them IMO if maximum accuracy is what you are after.

 

[Mark611]

Accuracy is what I'm after, not spray and pray bullets, I guess I'm going to have to buy some different powder, I would prefer to run the 140 or 147gn weight pills, due to much higher BC bullets, and powder suggestions?

 

[ebb]

I started running 140s and after reading some on the subject and looking at the battered brass I went to 123-130 weight bullets. On the JP rifles site, he writes a page on why to use the lighter weight bullets in an ar10. I tried several and my rifle seemed to like Nosler custom comp 123s the best, and brass didn't look so beat up. YMMV

 

[mgunderson]

You need to run a seating depth test with the bullet you want to shoot. Start at magazine length and push the bullets in 0.005 inch each step. You will find a length that shoots good.

For fun. Seat a dummy round at mag length. Use a fired case that is cleaned in your process. Feed the round from the mag dropping the bolt. Eject and measure the base to ogive again. Do this a few times and see if the bullet moves. I typically increase neck tension till the bullet stays in place. Seating depth tests are useless if the bullet moves.

I really like the 123s and 130s in the Creedmoor, but i shoot them with a 30 inch barrel. The 140+ bullets end up in a bigger case for me. Just my opinion.

 

[Steve Donlon]

I started running 140s and after reading some on the subject and looking at the battered brass I went to 123-130 weight bullets. On the JP rifles site, he writes a page on why to use the lighter weight bullets in an ar10. I tried several and my rifle seemed to like Nosler custom comp 123s the best, and brass didn't look so beat up. YMMV

You are right about that. The lighter bullets are a lot easier on the brass. For me, that was the reason I lost interest in AR 10's in 6.5, To many compromises. But that's just me and my loss.