Is OAL too long?

[ColWhitecakes]

I just received my order of 75gr A-max' today and proceeded to make a "dummy" round for both of my .223s (actually, one is chambered for 5.56 NATO) by seating a bullet, fitted in the loosely sized neck of unprimed brass, by chambering it each rifle to have a base for working up seating depth on my die. The 5.56 chambered round is seated considerably longer than the one in my .223. Of course, it goes without saying why this is; but, my question is, how long is too long. Or, what I mean might better be asked is, how shallow can a bullet be seated in to the neck of a cartridge before it is simply not seated enough? Every thing I have read about the A-max, and most seceant ogive bullets in general, indicates that they prefer to be seated near the lands, if not jammed. The chamber of my model 12 ( the .223 in this case) has the bullet seated at a depth that is plenty sufficient when jammed to the lands for this round. However, the 5.56 is seated so that the bearing surface above the boattail is only seated about halfway down the neck. I was planning on trying these seated about .015off the land to start with for load development; but, seating another .015 is still not gonna seat it to a point where the bt/bearing surface junction is to the bottom of the neck.
What problems, if any, will this create? Should I even attempt to develope this load given the circumstances, or seat it in further?

 

[Killshot]

The 5.56 NATO chamber has a loooong throat and you may not be able to reach the lands with a 75gr bullet.

Are you single-loading? Nothing longer than 2.650" is going to feed from the magazine. I'd load the Amax for the 5.56 at magazine-length and see what you get.

Pick up a Hornady OAL gauge to measure the distance to lands. AR chambers are difficult to accurately measure using the slip-case method.

 

[ColWhitecakes]

Yes, I am single loading, and the 5.56 rifle is a Mossberg MVP. I have a bullet seated touching the lands in a case. I used this same method to measure off the lands for a 77gr smk load, but since it is a tangent ogive, it seats much deeper into the case, and at .015 off the lands, it performs pretty good. I decided to try the 75gr Amax to work up a load that will still a little higher above mach at 1000yrds than the 77 smk. I just dont want to create a dangerous situation, mainly. Also, I fear that I may have run-out problems with it seated so shallow. I may just start backed up a lil more than planned and see how it does.

 

[Tango51]

I would think if the bullet is seated reasonably deep in the case neck and was done that way via chambering a dummy round and jamming it into the lands to seat it it would be ok. If the bullet stayed in the dummy case without sticking in the barrel it must be seated well enough. Plus you said you would single feed right? So no rough handling to affect runout? Right

 

[ColWhitecakes]

I would think if the bullet is seated reasonably deep in the case neck and was done that way via chambering a dummy round and jamming it into the lands to seat it it would be ok. If the bullet stayed in the dummy case without sticking in the barrel it must be seated well enough. Plus you said you would single feed right? So no rough handling to affect runout? Right

Yes, the bullet stayed in the case fine on extraction, and in reality, the case was already neck sized, I just seat a FMJ full depth then pulled the bullet to open up the case neck. Also, I am pretty easy on my loaded ammo, i.e. always careful not to shake the box up and such.
I guess its at least worth a try seated as I planned, and go from there

 

[Laurie]

Traditionally, the rule of thumb is half the calibre, ie 1/10" or just above here, is enough. In practice, I've found that 1/10", even slightly less works fine in larger calibres too as long as you're not feeding from a magazine or otherwise treating the cartridge roughly. For instance, trying short 55gn varmint bullets in a long-throated 6mm BR Norma chamber saw some models group really well despite their being barely gripped by the case neck.

The 75gn A-Max doesn't seem to be overly jump sensitive in my experience despite the secant ogive. It's not as aggressive a body to shoulder section junction as you find in a full-blown VLD design. In my last AR type rifle with a Wylde form chamber, the various makes of 77s didn't care how much jump they took and loading them to magazine length gave no disadvantage in group size over seating them out and single-loading.

 

[ColWhitecakes]

That's comforting, and useful, info to learn. I'm only several months into precision reloading (or as precision as I can manage) for competition use. There is definitely much I have to learn. I couldn't imagine doing all this without access to info and help from good folks on sites like this, and the web in general. In the past (pre-internet), learning the ropes must have been a much slower process, lol.

 

[steve4102]

The rule of thumb for Min seating depth is One bullet diameter seated into the case.
Hornady warns against loading the 75gr A-Max to Mag length, #7 recommends a min of 2.390.

 

[ColWhitecakes]

I sure appreciate everyone's help with this. I had decided to load some up for the 5.56 and give it a try. The COAL at .015 off the lands ended up at 2.565. I choose to start with Alliant's listed load for AR Comp at 23.3gr. I loaded ten in neck-sized previously fired cases with BR2 primers. My son was able to obtain a pretty dang decent group on the second string of five rounds (intitial five were shot to check POI and adjust for zero). These shoot 1.5 MOA higher at 300yrds than the 77gr SMK load with 23.7gr Varget that he shot in his first match. The pic below shows the results. OnTarget program measures all five at .771 MOA and the four tightest at .384 MOA Not too bad for a 15yo shooting an intitial, untuned load from a Mossberg MVP at 300yrds, I think. I cant wait to tweek it out some.