Can excessive neck clearance cause over pressure??

[ar10ar15man]

if your neck sizing...with a neck sizing die, and you have it set up to short..the case can bulge...get fat...

try with a fired case..no sizing

 

[Toby Bradshaw]

Assuming that your once-fired brass chambers easily without being neck sized, you will have to set up your neck sizer correctly so that ONLY the neck is touched.

Once that is sorted out, the simple experiment is to start at 56gr and 2.860 OAL, then increase OAL by 0.010 or 0.020 at a time and see if you get higher pressures as you get closer to the lands (which will also produce higher velocities). Personally, I doubt that shortening the OAL by 0.050 explains the difference between a hard bolt lift at 54.5gr and no problem at 56gr, but it's easy enough to check for yourself. I certainly would (generally) expect less pressure if the bullet has a little more jump, but not as much difference as you're reporting.

 

[AKShooter]

Pretty sure what I'm feeling is simply the "tightness" of fire formed brass. If new brass chambered like that I'd be alarmed. I can see on the brass I'm only contacting neck.

The brass that showed signs of pressure won't rechamber at all. Fired or neck sized. I'll run that through a FL and see

That's a good thought for a OAL test. I'll get that test loaded up too. I'll have some time again this weekend to spend more time on it.

 

[Toby Bradshaw]

If your neck die is pushing down on the neck/shoulder junction it won't show on the body of the case but it will bulge the shoulder, making it hard to chamber.

Does the fireformed but unsized brass chamber any easier than fireformed + neck sized? If it does, then your neck die is out of spec.

You have to hit brass with quite a bit of pressure to make it tight after just one firing.

 

[ljhsniper1]

One would have to wonder if this is a possible die problem as Toby mentioned. Had a .280 Rem die that was out of spec once. Wound up replacing die and problem went away. Just another variable to look at. ..... Semper FI!

 

[AKShooter]

Okay, I have some light to shed on the subject.

Went out today, clean rifle, worked 55-59.5 up over the chrono. 59.5 is listed as max in Noslers book. Not a single pressure sign! Groups started to tighted up right around 59.0, going to focus another panel plus minus .2 around here. For velocities, all were par with data, hit around 59 and 2890, 59.5 only saw about a 20 FPS increase vs 80 or so, so was hitting around max for the rifle too. These rounds OAL was 2.870, my to land measurement is 2.910

So pretty much on par with everyother rifle I've shot, things went great.

So, somewhat interesting and maybe my whole issue,,,. Decided to run with a group of H4350. Ran some cleaner through, mainly wanted to hit powder fouling. I forgot some things in the cleaning kit, so had a pretty loose fitting patch, and was using patches to dry out chamber.

Well, first round showed my pressure signs, and a starting load. So, I really believe I never really had the bore as "Dry" as I should have. For velocity, printed a low 2750 FPS. But had hard bolt and extractor mark. I was done, wanted to clean properly and dry the rifle. Wondering if this may not have been some of my past issues, just started using wipeout, wondeirng if I was not "drying" the bore. I was running a lightly oiled patch?? Not positive

Not done experimenting by any means, but sure going to make sure I'm completely clean and dry before shooting,,,,,,,,going to play with the OAL very carefully with a mid charge of H4831SC.

Fianlly, run the H4350 run again, clean and dry bore. I really wish I had the chrono with the first experiments, would have loved to know the velocity,,,,,,and I have zero plan to re-create it.

H4831SC loads looked promising, put one 1/2moa up, and two 3/4 on either side of 59 grains, all three shot groups.

I'll certainly keep proceeding with caution!