I am trying to load a round for my 20" Steyr Mannlicher Pro Hunter and am confused by what I am experiencing. I am trying to use the Yew Tree 6.5mm 112gr bullet with N150, CCI LR primers and new Lapua cases.
Starting advice was to use load data for 120gr Barnes TTSX and a jump of 50 thou, unfortunately after a few weeks searching I can't find any load data for Barnes TTSX that uses Vhit powders. So I started with Vhits data for N150 with 120gr Scenars which, gives a max load of 40.9gr, I originally started at 38.2gr and worked up in 0.3 gr steps. After seeing issues at 38.8gr, I stopped, pulled the rounds and started another ladder at 36.1gr, I am still seeing pressure signs at almost 5grs under the suggested max load. Using Gordon's Reloading Tool, as a guide, a 38.2gr load only produces peak pressure of 2722 bar, and a MV of 2541ft/s which gives a ME of 1606ftlb which is not enough to be deer legal.
From 37.3grs I started to intermittently get very faint markings that look like ejector rings and swipe, the rings do not feel raised at all. I then saw primer cratering at 38.5 and 38.8gr. Pictures attached are of 38.2 gr and 38.8gr cases. The two without any writing in the background are both the same case that had a 38.2gr powder charge.
I have rechecked the point at which the bullets jam in the rifling 3 times now and have got the same readings of COAL of 3.047" which gives a COL of 2.548" at jam, which gives a COAL for 50 thou jump of 2.997". I weighed every charge using a new RCBS mechanical scale and a tickler, the scales give me reliable and repeatable readings when I weigh the bullets.
Comparing base to shoulder length using a hornady comparator shows that the once fired cases are 8 thou longer than the new cases, the fired cases still chamber without any additional force on the bolt, but will not chamber if I add 2 thou of masking tape to the base.
What confuses me is that these pressure signs seem to happen at such a low powder charge. Having scoured the internet there seems to be a suggestion that excessive headspace could cause this. Is it likely that by having 9thou of headspace that the case is being forced into the bolt face hard enough to generate pressure signs and that if I was to bump the fired case shoulders 2thou and reload that I wouldn't see the same pressure signs until a higher charge? Is there anything else that would be worthwhile checking or should I just try a different powder?
Thanks
Starting advice was to use load data for 120gr Barnes TTSX and a jump of 50 thou, unfortunately after a few weeks searching I can't find any load data for Barnes TTSX that uses Vhit powders. So I started with Vhits data for N150 with 120gr Scenars which, gives a max load of 40.9gr, I originally started at 38.2gr and worked up in 0.3 gr steps. After seeing issues at 38.8gr, I stopped, pulled the rounds and started another ladder at 36.1gr, I am still seeing pressure signs at almost 5grs under the suggested max load. Using Gordon's Reloading Tool, as a guide, a 38.2gr load only produces peak pressure of 2722 bar, and a MV of 2541ft/s which gives a ME of 1606ftlb which is not enough to be deer legal.
From 37.3grs I started to intermittently get very faint markings that look like ejector rings and swipe, the rings do not feel raised at all. I then saw primer cratering at 38.5 and 38.8gr. Pictures attached are of 38.2 gr and 38.8gr cases. The two without any writing in the background are both the same case that had a 38.2gr powder charge.
I have rechecked the point at which the bullets jam in the rifling 3 times now and have got the same readings of COAL of 3.047" which gives a COL of 2.548" at jam, which gives a COAL for 50 thou jump of 2.997". I weighed every charge using a new RCBS mechanical scale and a tickler, the scales give me reliable and repeatable readings when I weigh the bullets.
Comparing base to shoulder length using a hornady comparator shows that the once fired cases are 8 thou longer than the new cases, the fired cases still chamber without any additional force on the bolt, but will not chamber if I add 2 thou of masking tape to the base.
What confuses me is that these pressure signs seem to happen at such a low powder charge. Having scoured the internet there seems to be a suggestion that excessive headspace could cause this. Is it likely that by having 9thou of headspace that the case is being forced into the bolt face hard enough to generate pressure signs and that if I was to bump the fired case shoulders 2thou and reload that I wouldn't see the same pressure signs until a higher charge? Is there anything else that would be worthwhile checking or should I just try a different powder?
Thanks
but I think I got there in the end.
