Testing different powders in the 338 Kahn...
Was able to find a short break in the rain this weekend to fire some test loads down range in my 338 Kahn.
I wanted to try some Retumbo in my loads as it was recommended to try some faster burning powders in my rifle as they would offer higher velocity potential with the 300 gr SMK.
Let me give you the base line for this particular rifle. It is a 34" Lilja 1.350" straight cylinder barrel, Rem 700 receiver and McMillan MBR Tooley stock. 28lb rifle.
My standard load has been 105.0 gr H-50BMG which will run from 2850 to 2875 fps depending on lot of powder. I have run things up to 2950 fps with this rifle but pressures were a bit higher then I liked. No loosening of primer pockets but with the soft Norma 338-378 brass I do not want to burn cases up prematurely, Spendy!!
This rifle is not what I would call a fast rifle, in fact it is relatively slow for a 338 Kahn with this bullet weight. The reason is because I used the same throat design that Kenny Jarrett originally used. That included a very steep 3 degree throat angle and a VERY tight diameter throat. even tight on the SMK 300 gr bullets. These combine to top out in pressures much quicker then normally would be.
An example of this is a rifle I built for my brother, same barrel, chamber and everything except I throated it with a 1-30-00 degree throat angle and a slightly larger diameter throat. Added a full 150 fps over what I can get in my Kahn at what seems to be similiar pressures.
My rifle is EXTREMELY accurate and consistant with this load even out to the one mile range where it will hold under 1 moa easily. At 1000 yards, 1/2 to 3/4 moa is not a problem in good shooting conditions with this load and rifle.
Last weekend my brother and I were shooting at chucks at +2000 yards and ran into some severe consistancy issues. The reason was found to be that we were dropping out of super sonic velocity which was causing this inconsistancy.
This is what led me to want to try to get some more FPS in the 338 Kahn.
Back to the Retumbo tests. I started with 98.0 gr and loaded up to 106.0 gr.
The first load at 98.0 gr produced 2910 fps. A solid increase over H-50BMG but there was a noticable extractor mark on the case head. The 99.0 gr load averaged 2935 fps and there was a significant extractor mark! Again, common with the soft Norma brass but more pressure then I wanted so I stopped the testing there.
Accuracy was also not that great, running around 1/2 to 3/4" at 100 yards which for this rifle is a BAD group. Just to check things out, I shot three of my standard H-50BMG loads, cut a perfect sub 3/8" cloverleaf!!
Retumbo no good.
I headed back to the bench to pull the remaining loads and then loaded up a new batch of test loads using Hodgdons new US869. I started at 100.0 gr and loaded up to 110.0 gr. Here are the velocity averages for these loads:
101.0..........2743 fps ??
All loads showed no more pressure sign then my standard H-50BMG load and with the top 110 gr load I was getting a full 60 fps more velocity then my current lot of H-50BMG with what seems to be lower pressures as far as the extractor mark was concerned.
Accuracy was also running very well with all loads. Sub 1/2" groups were the norm with all loads and many were identical to the BMG loads.
I ran back and loaded up five more levels, one grain increases at a time figuring I would top out in this range. Here are those results:
113.0............2968 fps Very slight extractor mark
114.0............3014 fps brighter extractor mark
115.0............3027 fps To hot, bright extractor mark
Again accuracy was very good and with the loads above 108.0 gr consistancy was also very good, generally running well below 10 fps per load.
At 113.0 gr the extractor mark appears identical to the 105.0 gr H-50BMG load but with an extra 120 fps of velocity, same accuracy and what seems to be the same consistancy level.
The 114 and 115 gr loads produced a heavier extractor mark then I like and at 115, the bolt lift was just slightly heavier then I like to feel on a Rem 700 chambered for a case of this size.
When I got back to the loading bench I checked the primer pockets on all cases. None had loosened at all, not even the 115 gr load but still it was more then I wanted in my Rem 700 based rifle.
I am totally happy with the 113.0 gr load with its 2970 fps velocity potential and accuracy and consistancy. Its very easy on brass and the rifle as well.
Again, I am not unhappy with the H-50BMG loads, I was just looking to get another 100 fps without alot more pressure and it looks like US869 will get me even more then that.
To be honest, the real cure would be to pull the barrel and recut my throat with my better designed throating reamer but the rifle shoots so darn well right now its hard to justify.
I do suspect though that with the new throat design, this rifle would comfortably be in the 3150 fps range with top end loads seeing what my brothers Kahn is getting with his top end H-50BMG loads.
Will have to test US869 in his rifle and see how it works.
So for those shooting the 338-378 Wby or the 338 Kahn or 338-416 Rigby and using 300 gr bullets, US869 seems to be a serious powder to consider!!
For lighter bullets its to slow burning but for the big 300 gr pills it seems about right for high performance and relatively low pressure.
Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.
Farther, Faster and Flatter then ever before.
Web Page: www.apsrifles.com