Originally Posted by Hookturnr
Well, I have run this gun from 89.0 gr. of retumbo at .010 off the lands up to 94.0 gr. and didn't see any pressure signs until 93.5. At 94 the bolt lift was sticky.
I attained my fired case dimension by averaging 12 fired cases from the first batch of 30 rounds that had no extraction issues.
I'm loading it at 90 grains currently and still having issues.
My numbers on the fired cases haven't changed over several setups of my caliper with the hornady gauges and repeated measurements so i think I'm good there.
When I took the .002 off the shellholder I also removed the firing pin from the bolt and chambered about 15 pieces of brass with the new sizing spec and had no resistance when closing the bolt. Seems to me that headspace shouldn't be a possible issue at this point, I'm measuring .004 shorter than fired with my resized brass.
I'm going to take a shot in the dark and put a new extractor in it and see if that alleviates the issue. The current extractor has around 1800 rounds on it and looks like it may have a slight twist to it.
Two more things that may also be the problem, The RUM was designed with .309 free bore and the
.010 may be a little close for that much powder. I would recomend at least .020 to .025 to start
with and pressures should drop off.
Also Retumbo is one of those powders that can go critical from one load to the next with just
a small increase. 95 to 96 grains seem to be about max with bullets seated to magazine length.
So with the bullets seated close you powder charge may be over max.
I use between 102 and 104 grains of 50BMG to get top velocities without any pressure signs
and 95.2 grains of Retumbo with 200 grain ABs for just over 3120 ft/sec.(Also no extraction
While working up the Retumbo loads I found that 95.4 grains showed signs of pressure and 95.6
was over the top and bolt lift was stiff so I backed off to 95.2 and everything was good.
There are ways to get accuracy without seating the bullet close but the rifle and ammo has to be
set up for it to yield great accuracy. (Below .200 hundred Thousandths MOA).
Just a thought. I hope it helps.
J E CUSTOM