Bullet seating issues

[Quicksilver]

I am currently working up a fresh load with a different powder than I normally use and did the usual ladder test, followed by another ladder test and finally, 3 loads in .1 increments (5 each) and had worse results.

I narrowed it down to 39, 39.1 and 39.2 grains and all worked GREAT. Were talking under 1/4 MOA groups!!!! The BEST I have ever shot-

This was with the bullet .005 INTO the lands and forcing the chamber closed-

I backed off the bullet .010 (so .005 from the lands) and fired another 5 shot group of 3 with the same loads and the results were terrible. Oddly enough, the entire group (of all 3) went from 1/4 moa to 1.5 moa, but 4 of the 5 bullets would "connect" in 2 bullet clusters. So I would have 2 bullets touching, an inch of space, 2 more bullets touching, and 1 bullet hole a inch or so away.

Am I missing something here? I have 2 double shot "touchers" and a stray, and the overall group size has gone huge now. I have .002 runout on the bullets, so I don't think its a runout issue?

Do I just need to keep it .005 in the lands? Or should I back it off more and more and see what happens?

I will post MV numbers up later- I had the magnetochrony on the barrel at all times to see how fast/extreme spread every group had.

 

[demolitionman]

If it's shooting 1/4" jammed, and your not seeing pressure signs, and your not worried about the possibility of the occassional bullet getting stuck in the lands when removing an unfired round from the chamber, I'd call it good and load up a mess of them!

 

[gvanhyning]

Keep in mind when you seat the bullet so it's no longer jammed the pressure has been reduced. I would stick with the jammed but if you are jumping because jammed won't fit in a magazine, then you may want to continue increasing charge weight to find another sweet spot.

 

[thrusty]

I'm interested in what caliber, powder and bullet you're using? Without that info, can't really say whether the load you have come up with is going to give you any issues.

Did you also record environment conditions when you tested? Only asking because this can play with pressure if you're using certain types of powder. A nice cool 70 degree day with no humidity may be ok, but shoot the same load on 95 degrees with high humidity and you could start seeing pressure signs.

As Demo mentioned, one of your potential issues will be getting a pill jammed into the lands if you have to open the bolt on a live round. Some styles of shooting this is not a big deal...tactical shooting where you're not carrying around a cleaning rod all the time, it can cause a stage DQ or you just run your time out.

 

[TRAAV]

I have stuck a bullet in the bore during a match and it is no fun. It's not only the bullet that's stuck in the bore but the powder that it dumps in the lug area that's the biggest pain in the ass.
I will no longer ever run a load that is kissing the lands for that reason. If it were me I would find something it shoots at least .005 off.

 

[Quicksilver]

Its a .308 gas gun and the bullet length jammed doesn't come close to fitting in the magazine- its nice and hot here in Texas, and temps were ranging from 99 to 102.

As for the charge, the book minimum is 39.0 and that's actually the best shooting one! Max book is 41.5, but I went to 42 (jammed against lands) before seeing pressure signs (primer & shiny brass end) so the charge is VERY safe. I followed the advice of the "powderin' it" thread when doing this, and the only SNAFU was backing the bullets OFF the lands. Go figure.

I will look at the MV numbers tonight or tomorrow to see how much of a change it was in MV from jammed to backed off .005 and see if I can make a charge that hits the same MV sweet spot with it backed off.

 

[oldfatguy]

You might want to load up some more test rounds with increasing jump distances. My rifles seem to like 0.020" jump and every rifle is different.

OFG

 

[Quicksilver]

Can I correlate the MV with the bullet exit times through the barrel to stay in the "node" or do I need to just do a completely new load test with bullets seated at the depth that I need them to fit in the magazine? I already know the MAX that I can shoot safely from loading powders in .5 increments with the bullet jammed in the lands. Would this be a safe assumption or would I be trying to make a mini pipe bomb?