Neck tension

[scott>]

[Jake TN]

Or crimp and see if you have the same problem

[scott>]

[grayfox]

I can't speak to the mkz bullets, they have a cavity at the base right? But for a 100 gr ttsx 29.0 gr of xbr is an ok load, it's max is 29.5 by the book.
You don't say what OAL you are seating the mkz/cartridge to, is it 2.230? 2.250? 2.290? or what...
If a load is compressed but rather resistant to compression then yes the oal can grow, whether it is cycled or just sitting in the tray.
You don't say if the growth is from a bolt release, or following a fired round (bcg complete cycle) or what...
You also don't mention what type of lube/dry flake you might be using on the inner side of the neck, if any.
All these things can impact what you're doing.

But to address the general question of oal growth for ARs my solution was to get the Lee factory crimp die (fcd) - don't have to have all the brass trimmed to exact same length as you do for roll and die crimps and as for pistol loads. You set it once per instructions, lock in to that, then use. I don't have numbers but it has improved my oal shifts and also the groupings. Not an expensive die, the fcd, but worth it, it does cause an extra step in the reload process but I'm willing to do that for better shots.

Those who go all-out on neck tension do the neck bushing-thing... I just haven't brought myself to that level of ocd, lol.

by the way, imo the fcd die is the only die from Lee that I would recommend, I'd say throw out those LEE resizing/seating dies and get either hornady, forster, rcbs or some set that has better quality. I use hornady and they work well enough for me, but like I said the Lee factory crimp die is the only one of theirs I'm using. I have a mix of rcbs, hornady resizing, and those plus a couple forster seating, dies for all my calibers.

[scott>]

[Jake TN]

I have never had this problem. I would make a dummy round (no primer or powder) and test. That will tell you if die neck tension is out of spec, especially since you are crimping. Maybe even a bullet spec issue. At least that would rule out a potentially compressed load as the cause. I have never used Lee dies. I would also throw mighty armory dies into the mix, especially if loaded for different rifles. I would rule out Redding seating die if you are doing compressed loads and go with the forester seating die on the high end. Also when loading pause for a second at the top of your stroke to make sure the brass is not flexing. Only other thing I could think would be if your bullet is jamming into the lands and there is enough force upon extraction to pull the bullet slightly. I doubt that is the case, but you might want to check anyway-to rule it out.

[Old Bob]

I use the taper crimp die from a RCBS small base die set to put a light crimp my loads for my AR - You do have to be sure your cases are all the same length. I haven't noticed any bullet creep when cycling them through my AR. I don't crimp loads dedicated for my bolt gun.

[scott>]

2.250

[Koda]

I had to overcome this same problem. There are several variables I found added up I had to...

• clean the neck ID from any case lube from the sizing process before seating, I used ISO alcholol on a qtip, frustrating slow...
• I was only getting .001" neck tension.... Ordered another expander mandrel and turned it down .002 to give me .003" neck tension.
• Crimp with Lee Factory Crimp die
• Compressed loads.... Fill case with powder then vibrate it before seating to settle powder and prevent compression. Im using 32.2gn of A2520 so I'm not certain yours is compressed mine I think is 100% case fill (after vibration) though but measuring that is not an exact science but its surprising how much vibration will settle powder.

My litmus test was to chamber the round 5 times without any inertia drift over .003", after those steps they passed.

What I do to assure it wont happen after 5 times is slowly close the bolt and use the forward assist to chamber the round, doing that I had zero inertia drift after dozens of chamberings over 10 days of hunting. No need to slam it home to load it for a hunt.

[ported45]

I had the exact issue while trying to get BCA uppers to work out for me. I set the LFCD from light to tight enough to create a crimp ring in the bullet when crimping and the bullet still would slide forward in the cartridge when chambered. When I finally gave up on getting a "good enough" upper from BCA, I ordered a Hardened Arms upper as I had 5.56 and 300 Blackout uppers from them that shot bug holes. I had absolutely no bullet slip with the Hardened Arms upper even without using the LFCD at all. I don't know what it was about the BCA uppers, but they just sucked all the way around! Changing uppers solved my bullet slip problem.

[scott>]

[Klem]

Scott,

This happened to me when first shooting Grendel. Bullets would creep forward as they slammed into battery. Sometimes jamming in the lands which would give split vertical groups on the target. Not good for pressure spikes and a problem needing fixing.

Took the expander ball out of the Forster FL die and now the difference between OD of Lapua cases sized, and bullet seated is 0.004". Before, it was 0.001" which is fine for bolt guns, but not auto loaders. Bullets don't move now.

Lee crimp dies work brass way more than they should. Their crimp dies chew the mouth of cases to get the crimp; maybe they're designed for bullets with a cannelure. Redding makes a less severe taper crimp die if you want to solve it by crimping. As for Lee dies, I recommend getting better quality dies and the more you shoot, you'll end up doing this anyway.

As for compressed loads creeping forward. Yes, I've heard this happening with long-term storage of ammo. The longer you store, the more it creeps. Gripping bullets lightly is not going to help. Unlikely to be the problem here however.

Another possible cause is lack of bullet shank contact with the case. I am unfamiliar with the 105mkz but it is on the lighter side so might not have enough shank contact to provide a decent grip. Pushing bullets further in helps, as long as you account for the increase in peak pressure. Jump-to-lands becomes more severe but can't be helped, and might not make any difference to accuracy anyway.

What is the difference between the OD of a sized case at the neck, and the same spot after you've seated a bullet? This is the grip I am talking about above. What brand of case is it?

[Jake TN]

So you had the loaded cartridge increasing overall length and with the dummy round it decreased length. How much? Does it feed smooth. I would agree there is a tension problem. Measure the bullet area that contacts the case mouth. If it is consistent with the widest part of base section of the bullet, I would say that it is time for a new sizing die. I have never reloaded cavity back bullets. Also take a case that has been resized and measure the outer diameter of the case mouth. Do the same with seated bullet (dummy round would work). Should give you a good idea of what your neck tension is (the difference). It has been a long time, but I am pretty sure for my precision bolt guns I would shoot for .002 neck tension. I would expect more for an auto loader. I hope that all is articulate enough and makes sense. Holler if you need anything else, but still think a new sizing die is the answer. Sorry buddy. I haste wasting money

[scott>]

[MOW]

I have my resizing die primer pin set to 3/16" below the bottom of the die like the Hornady directions call for. What does raising or lower that do? I assume because it's connect to expander ball, it can change neck tension with the set height?