Berger .223 70gr VLD bullet setback-what am I doing wrong?

[Amanda4461]

Hello folks,
I took a fresh batch of ammo to the range today, to adjust the ACOG on my 7.5” Sig AR. My normal load is Sierra’s 77gr MatchKing with 21gr of Vihtavouri N135 and CCI #41 primer, coal 2.250”. When I ran out of my first box of these, I tried an identical load that used the Berger 70gr VLD, instead of the SMK. I load a 20-round Colt mag that has the green follower, with 19 rounds. I load the first round by releasing the bolt catch. Today, I had to eject my first round due to a fellow shooter asking to go down range. When I went to place the ejected round back in the magazine, I noticed that the bullet had set back in the case, to the degree that I could see inside the case neck. I duplicated this situation six times, then tried the loads with the SMK. The SMK bullets did not move. The cases were the same in both instances, Remington Nickel once-fired. All were full-length sized in the same Redding Competition die, run through a Small Base sizer body, and seated with the same Redding Micrometer die. The only thing that I noticed when loading, is the length of the SMK was longer than the Berger. The SMK had excess full-diameter bullet body available if I had desired to seat the bullet deeper. The Berger had zero room to be seated deeper. Any ideas what I did wrong?
Thanks!
Amanda

 

[spife7980]

Case Grip on Bullet — There’s More to Neck Tension Than Just Bushing Size « Daily Bulletin

Many novice hand-loaders believe that neck bushing Inside Diameter (ID) size is the only important factor in neck tension. In fact, many different things will influence the grip on your bullet and its ability to release from the case neck.

bulletin.accurateshooter.com

Could be a smaller bearing surface simply doesn’t offer enough friction to hold the bullet. Could be the bullet is half a thou smaller and that’s the difference. Could be the lengths and geometry of the bullets and seating the Berger that deep may start it mostly down past the neck.

Could be lots. Measurements and pictures tell all.

 

[whatsupdoc]

Typically 77SMK's are loaded to 2.260 so you are loading them .060 short why?
A Berger 70gr VLD when it is loaded to AR mag length, the bullets ogive is "almost" pushed into the case, this is normal.
That chamber is a 5.56 nato so a 70 vld bullet cannot not be pushed back by hitting the rifling. So something else is pushing it back. Catching between the barrel extension and upper possibly.

Load some dummy rounds (no primer no powder ) with the bergers and put them in the mag like you normally do then pull the charging handle back and slowly "ride" it foreward watching the bath of the bullet.

 

[Doom]

2.200” COAL with the SMK is awfully short for that bullet. I suspect with the Berger at this length the ogive my be in the neck and you have less bearing surface in the neck.

 

[supercorndogs]

Do most shoot such heavy bullets in their pistols and SBRs? I would think something 50-60g would be better.

 

[Amanda4461]

Well, if I didn’t fat finger my iPad, my coal should have said 2.250”, so I edited the op. I am expecting another shipment of Berger’s, so I’ll be able to take measurements and compare to some Hornady, SMK and Nosler bullets. I believe that the Berger bullet will provide a much shorter bearing surface, and the ar15 magazine oal restriction will keep me from seating the bullet out where it needs to be. A dummy round or two will probably prove that assumption. My sbr is a Sig 7.5” piston upper. With heavy bullets, it will group under one MOA out to 300 yards if I mount a decent scope. As currently set up, it has an acog with piggyback red dot. With this setup, I keep it loaded with Nosler 55gr Varmegeddons for pest control. I used the heavyweight bullets this week while waiting on my resupply of Nosler. Ball powder with the Nosler makes for a nasty muzzle flash. Just the thing to scare off those toilet paper bandits at night?