pressure signs.

salmonchaser · Apr 10, 2014

Worked with my 338 Jarrett today having worked up to 84 grains 7828; 250 grain partitions. I'm still trying to better 1/2 moa. I started at COL of 3.600; 3.650; 3.700 and 3.718 touching the lands. Load one just a smidge over 1/2 moa. The others were stringing to about 1-1/4. I suspect operator error.
No pressure issues until the last load. The bolt was sticky enough to feel and a faint ejector mark on the back of the case. As Dr. Mike said I had tickled the tail of the Dragon.
My question is: will the load at 3.60 be a safe load as I had no obvious pressure sign until I touched the lands at 3.718?

DrMike · Apr 10, 2014

From your description, I'd be comfortable shooting the 3.600 OAL cartridge. From that point, you could play in 0.005 inch increments to see whether you can refine the load for accuracy. Velocities should change dramatically, but accuracy may tighten quite nicely.

nvbroncrider · Apr 10, 2014

You might be seeing pressure signs because you are having to overcome the resistance of the rifling before your pressure decreases. While with the 3.6" load the bullet moves and gives the gas a place to go before the pressure increases enough to show signs of pressure. Done it by accident with my 280AI.

Horsethief · Apr 11, 2014

Your 3.60" COL could be tickled up to 3.62 and 3.63 OR reduce the most accurate load by 0.005" at a time until you either are happy with what you have or frustrated beyond description and POed that you ever messed with something that was working. Keep us posted.

salmonchaser · Apr 11, 2014

H. T. You may have hit the nail on the head, not sure why I'm screwing around trying to beat 1/2 moa with partitions. I'll play around with +/- .005 increments.
One of my goals was to determine if I wanted to install a wyatt magazine so I can reach the lands. Not convinced I need to at this point. 3.67 is the longest round that will cycle through the mag.

CatskillCrawler · Apr 11, 2014

I would stop messing with it and load up a bunch of what already works. Surely there's another rifle you own that's begging for attention or better yet, another rifle/cartridge that needs to come into your stable. :wink:

sask boy · Apr 11, 2014

I strive to get all my rifles to shoot .5MOA when I am having a good day :wink:. I believe that is a great feat with a hunting type rifle :mrgreen:.

Blessings,
Dan

OU812 · Apr 11, 2014

I've never been a fan of keep fixing it until it's broke. 1/2 MOA, I would be done and very pleased at that.

woods · Apr 11, 2014

From my tests .010" DEEPER seating equates to about .2 gr REDUCTION in powder. So if you are seating approx. .070" off the lands it may be equivalent to reducing the load 1.4 grs or so. These calculations started at .015" off and went to .090" off.

Of course that was in my caliber with a different powder so there may be variables that increase or decrease that effect. There was also probably a drastic drop in pressure once you moved off the lands.

Personally I would back off 3 or 4 grains powder and do a seating depth test starting at least .015" off to stay away from the pressure spike loading into the lands creates