Bullets moving out (longer OAL) when chambered

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azrocks

azrocks

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I'm pretty new to hand-loading bottleneck rifle cartridges, in this case, 300AAC. What I have done so far has worked great, but that was with bullets with a cannelure (& some measure of crimp). I'm now working w/ 135g bullets w/o a cannelure, and have a problem.

I assembled a few dummy rounds (no primer/powder) with various levels of crimp, using a Lee FCD. The bullets are seated so that the entire neck of the cartridge is in contact with the bullet for maximum friction / holding power. Brass is brand new, trimmed just a few thousandths below the trim-to spec, & re-sized for consistency. I am belling the case mouth a tiny bit - without doing so these flat-base bullets simply fall right off no matter how well you try to balance them - but I emphasize tiny... just a hair. Crimp runs from just enough to take the bell out to as far as the Lee will go.

Thing is - no matter what - when I chamber a round aggressively by hand (AR platform) - the bullet walks a little bit out towards the lands. The more crimp the less pronounced, but even at full crimp they're walking anywhere from .002" to .005" each time the round is chambered, increasing the COAL each time. Zero setback, which I find surprising, as the bullets have an aggressive HP design. No matter how hard you slam them into the feed ramp, they don't set back. But they do come forward, each & every time.

These will be used exclusively in semi-autos. Where should I go from here?
 
You mentioned that you were using new brass, and that you had sized the cases. Did you measure neck OD and ID and compare these readings to spec?

Regardless, the decision tree here is pretty simple. It looks like this:

Are you planning on chambering these rounds repeatedly? Yes: continue your investigation. No: this isn't a problem.

Option 2 is a really good course to choose.
 
Hornady seat dies with the sliding alignment sleeve are a god send for seating flat base bullets. The need to flare will go away.

Your flare die is probably expanding also.
 
Alright, gonna try to get them to seat w/o flaring at all & see if that fixes the problem. The only way I see this happening, though, is putting a pretty aggressive chamfer inside the case mouth. I had already chamfered the case mouth after trimming an amount that seemed reasonable, but it was not sufficient alone. Will also check neck specs, as I did not yet do so.

Regarding chambering rounds repeatedly - no - that's not the plan, but it could happen. I might be fretting over nothing. But I'd really rather they didn't move at all in this platform. At least they're moving the less dangerous direction!
 
Just tried a couple more dummy rounds. Put just enough additional chamfer inside the case neck to avoid using any bell, which made for a balancing act... pretty much as tight as possible. One round I didn't crimp at all, the other I used the FCD at full crimp. I then chambered & ejected each round by hand aggressively 5 times, measuring in-between. The walk-out (still present) for each is as follows, relative to OAL before chambering once (cumulative figures):

Non-crimped: .001", .003", .005", .007", .009" (each time chambered, walked out .001 - .002").
Crimped: .002", .005", .008", .009", .012". (each time chambered, walked out .001-.003").

This is pretty much identical to where I was with the belling. Better not crimping than crimping, but no complete fix.

Outside diameter of case necks are ~.329 after sizing, and ~.331 after bullet seating (max spec .334). So the bullet is stretching the case neck by ~.002". This was taken from measuring a significant number of cases & completed rounds, not just the two above.

cross-section of brass at case neck is ~.013". Again, from a number of cases. They're pretty darned consistent.
 
Two suggestions:

1) Turn your expander ball down in increments of less than 0.001" (0.0005" if you have a micrometer capable of this level of accuracy) and test again after each step.

2) Degrease the inside of case neck and bullet to increase friction coefficient.

Interference fits (the engineering term for the condition that creates what reloaders call neck tension) are highly sensitive to diameter differences and friction between the two components.

Also, consider shooting some of these rounds you've made and then resizing and reloading them. This will work the case necks a bit, and will make them a little stiffer, increasing "neck tension".
 
Kind of got two threads going here, guys, on the same subject. But to everyone touching on neck tension, many thanks. I've learned a lot. Still need to make the changes to correct this issue, but right now I'm only getting between .001-.002" difference between the neck OD after sizing and the neck OD after bullet seating. Hopefully another .001 does the trick. Unfortunately do not have a mic capable of .0001 level precision.

Does carbide make a difference in turning it down? Are all expander balls carbide?

To tell the truth, I'm a little nervous about trying to reduce a precision-machined item like this with a drill.
 
Perhaps a silly question; have you measured the OD of your bullets and the ID of your sized case necks? "Normally" a .002"-.003" interference fit is a good neck tension (closes thing I have to your guns/ammo is a Garand and with some cheap brass I only am getting .001" interference, not quite enough)...
 
mdi said:
Perhaps a silly question; have you measured the OD of your bullets and the ID of your sized case necks? "Normally" a .002"-.003" interference fit is a good neck tension (closes thing I have to your guns/ammo is a Garand and with some cheap brass I only am getting .001" interference, not quite enough)...
Click to expand...

Yep, sure have. Those numbers agree with the results I got measuring case mouth OD. I'm at .001-.002", so as y'all have suggested, most likely my main issue. Now my issue is figuring out how to reduce the diameter of the expander ball without jacking it up.
 
murf said:
try cleaning the inside of the case necks.

luck,

murf
Click to expand...

Just did that. Pulled expander ball / decapper assembly & cleaned everything w/ alcohol (wasn't oily or dirty before cleaning). Did the same to the inside of the case mouth as well as the bullet. Carefully lubed by hand to only touch outside of case, resized, went through (dry) powder funnel. Checked neck dimension to make sure powder funnel didn't change anything (it didn't), and cleaned inside of case mouth again w/ alcohol to make sure powder funnel didn't contaminate it. Seated cleaned bullet. Difference in neck OD before/after seating bullet was (estimated) .0015 (mic only goes to 1000s). Ran it through a few cycles chambering & it's doing the same thing. Pretty much 100% it's neck tension now as mentioned by many. I've eliminated every other variable I can think of.
 
Do you have a heavier buffer that you could try? A heavier buffer will slow down the motion so it doesn't slam into the chamber as fast.

luzyfuerza said:
Are you planning on chambering these rounds repeatedly? Yes: continue your investigation. No: this isn't a problem.

Option 2 is a really good course to choose.
Click to expand...

I agree with option 2.
 
Sorry, but I'm on a rampage now. Option 2 is not an option for me. I'm going to get this fixed or die trying.

As far as turning down that carbide expander, though.... I very might well die trying. That simply isn't happening with what I've got. Just spent a couple hours going absolutely nowhere.

Have an inquiry into Dillon, but if anyone knows: How precise are the manufacturing tolerances of something like this? If I go down to Dillon & ask them to let me pick through a handful of expander buttons, what are the odds I'll find one .001 smaller than the one I've got?
 
azrocks said:
Sorry, but I'm on a rampage now. Option 2 is not an option for me. I'm going to get this fixed or die trying.

As far as turning down that carbide expander, though.... I very might well die trying. That simply isn't happening with what I've got. Just spent a couple hours going absolutely nowhere.

Have an inquiry into Dillon, but if anyone knows: How precise are the manufacturing tolerances of something like this? If I go down to Dillon & ask them to let me pick through a handful of expander buttons, what are the odds I'll find one .001 smaller than the one I've got?
Click to expand...
Idk about Dillon but Lee happily sets folks up with under sized mandrels. Could always call and explain the issue and ask for a smaller expander? I mean what are they gonna do, take your press away?
 
Your not jamming the bullets into the rifling when chambering then pulling the bullet back out when ejecting the round are you?

Not sure why your having a balancing act when seating flat base bullets? Hold the bullet on top of the case mouth until the bullet and case mouth enter the die then seat away. Go slow until you get the feel so you don't pinch your fingers, you'll only pinch them a couple times before you get it down. If your using a progressive and bullet feeder then a little bell doesn't hurt and from your description on your process I don't think the belling is causing your issue.
 
Muddydogs said:
Your not jamming the bullets into the rifling when chambering then pulling the bullet back out when ejecting the round are you?

Not sure why your having a balancing act when seating flat base bullets? Hold the bullet on top of the case mouth until the bullet and case mouth enter the die then seat away. Go slow until you get the feel so you don't pinch your fingers, you'll only pinch them a couple times before you get it down. If your using a progressive and bullet feeder then a little bell doesn't hurt and from your description on your process I don't think the belling is causing your issue.
Click to expand...

Am using a progressive, and correct... the belling wasn't the issue. There was no difference in 'set-forward' (or whatever you call the opposite of set-back lol) between a very-mildly-belled case crimped just enough to remove the bell, and one never belled nor ever crimped, all else being equal.

Regarding flat-base balancing, maybe it's just inexperience. I've also been (perhaps unnecessarily) concerned that if the case mouth was tight enough to prevent balancing the bullet, it might cut into / sheer the bullet jacket & cause issues. Not a problem?

And working backwards, no... I'm way back from the lands.
 
azrocks said:
Yep, sure have. Those numbers agree with the results I got measuring case mouth OD. I'm at .001-.002", so as y'all have suggested, most likely my main issue. Now my issue is figuring out how to reduce the diameter of the expander ball without jacking it up.
Click to expand...
Just for grins size a case without the expander ball in place then measure the neck ID...
 
mdi said:
Just for grins size a case without the expander ball in place then measure the neck ID...
Click to expand...

I'll do that later today - can't at the moment - but the brass before being resized is ~ .001-.002 smaller (case mouth OD). So the expander button is definitely working it out. Gonna drop by Dillon to see if they have an expander .001 smaller. Also need to have them look at this one. When I went to grind what I thought would be a precision part it wasn't quite as precision as I had hoped. Don't know if this is part for the course or if I got a bad part.
 
azrocks said:
Gonna drop by Dillon
Click to expand...

You're fortunate that you live close enough to the "blue temple" to just drive over there. I only get down there a couple times a year, but every time I do, I head over to Scottsdale to see what's new.

Just a note, as good as they are, Dillon has been known to let an off-spec die set or two out the door. I had a 9mm carbide sizing die that just wouldn't produce enough neck tension, and when I took it back, they told me that the inside diameter of the carbide ring in that die was correct...for 38 super.

I'd suggest that you take your bullets and brass to help them troubleshoot the problem.
 
@luzyfuerza It worked out well this time, but the bennies of living nearby are definitely a double-edged sword ;) I look forward to the day when I live somewhere less convenient.

Well, I got this problem figured out. The expander button was defective. Dillon hooked me up w/ a new one, no questions asked.

At first, I didn't think it would work. Despite the obvious problem (you could see the flat on the original button not machined evenly all the way around it's circumference), the dimensions measured at multiple points were the same as the new one. But it worked like a charm. I tried bullets w/ both no belling/no crimp, as well as mild bell / mild crimp (just enough to remove bell). No more bullet movement from chambering! Only thing I can think is it was pulling the neck off center, or introducing an inconsistency in neck tension.

Rep @ Dillon also suggested i tried running w/o the expander ball at all if the new one didn't work. But that didn't work. W/o the expander the neck OD shrank to .323 (from .329 w/ the ball), which would be ~.008" neck tension. I then absolutely had to bell the mouth to get the bullet to seat, and once you did seat it, the case mouth just below the base of the bullet was visually reduced in diameter. You'd think with that amount of tension - there's no way the bullet would go anywhere. Wrong. It was like pushing toothpaste by rolling up the bottom of the tube. The one round like this I tried chambering almost spit the bullet out the first time (.006" movement in one shot - worst of all my experiments).

Thanks for everyone's help!
 
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