Well, the weather this weekend finally got dry enough and light enough to do a little range testing. I wanted to test the big 350 gr ULD RBBTs from Wildcat in my 338 AM so I decided to use the new US869 and see what they would do in the big girl.
These 350 gr ULD RBBTs are moly coated. I seated them to 0.010" off the lands which is shorter then I normally go. Generally I seat at least 5 thou into the lands but for the first range test I figured this would give a slight pressure cushion to start from.
The load specs were as follows:
TTI 408 CT brass(cornmeal formed)
350 gr ULD RBBT (moly)
I started at 143.0 gr and stopped at 146.0 gr. Three shots for each except at 146.0 gr which I only loaded two at this level
The wind was not perfect, about 15 mph from my 5:00 position and the light was not good either for chrono testing but still I wanted to see what this big girl would do on paper. I decided to set up at 200 yards to shoot groups for the first time with this rifle.
I got everything set up and lined the big girl up and bore sighted her and then lined up on the center 1" black square aiming point.
At the break of the trigger, the big rifle lazily rolled back into my shoulder. I was a bit suprised at the distance it actually moved me rearward but it was like someone put their hand on your shoulder and gentely pushed you back 3 to 4".
I looked up on the target and there was a hole roughly 3" high and pretty much dead center. Velocity was pretty much where I was expecting it to be 3174 fps.
Lined up for shot two and after the trigger break there was a hole just about 1/2" to the left of the first. I was happy. Lined up for shot three and was very happy to see that shot land right between the first two. Here is a pic of that first group on paper at 200 yards from the big 338 AM. Not a bad start.
Velocity averge for this first three shot string was 3171 fps. Bolt lift and case extraction was effortless, could not even tell there was a case in the chamber. That said, the primer cratering was present as it was with my earlier velocity testing with the 300 gr bullets. No pressure signs at all with the load but cratered primers??? More on this later.
This barrel is not fully broke in yet, I am still cleaning after every three shot group so I went to cleaning the bore again which took a bit of time but not much. When there is 40" of barrel theres alot of area for fouling. Got her clean and then made a scope adjustment. The first group was at the top of the target paper so I took 3" off the elevation and gave her 1/2" to the right. Mainly to test the adjustment of the USS Xotic scope more then anything. I then lined up for another three shot group with the next load.
First shot landed perfectly 3" lower but the horizontal adjustment did not take. On the next two shots however, they cut the same hole right where they should have been from the total scope adjustment.
Including the first shot the group measured 1.205" ctc which would prove to be the largest group fired during this range test. Just over 1/2 moa, I was not unhappy. Especially having the second two shots cut the same hole measuring 0.113" ctc.
TO my suprise though, velocity did not increase much at all averaging 3179 fps for these three shots. Extreme spread tightened up going from 22 fps for the first three shots down to 5 fps for the second three.
Cleaned her down again and left the scope adjustments alone for the third group. This one was with 145.0 gr and I was very happy to see another near 1/2" group form on the target. Seems to be pretty much the same size as the first group shot.
Again, I was suprised as the average velocity did not change at all, stayed 3179 fps with an extreme spread still in single digits at 8 fps.
Also to my suprise one of the primers pierced with this load level but the other two looked just like the first two loads. Primer cratering but no other pressure signs. Bolt lift and extraction were effortless as before.
I looked at the firing pin head and sure enough there was a bit of brass chip on the head of the firing pin which I was sure caused the primer pierce.
I decided I would try the 146.0 gr load and see what they would do. The group from these two shots measured 0.744" ctc. Muzzle velocity was 3212 fps and 3205 fps and primer cratering was the same as the other groups but there was just a slight extractor mark on these case heads.
Still not bad at all for 200 yards but noticably larger then the previous groups.
I packed everything up and headed back to the bench to evaluate the cases and see what we had for expansion on the case heads and primer pocket tightness.
For case head expansion I use a case head diameter of 0.6359" which is the case head diameter on a once fired case with a fireforming load using a 300 gr SMK. I figure this is a very safe, mild pressure load and a good standard to use from the cases I have measured and averaged with this TTI brass.
Case head diameters were as follows for the different loads, these are averages for the cases. all were within 0.0002" of the other cases with the same load:
Primer tightness with the 143.0 gr load was virgin tight still. At 144.0 gr I could just tell that there was slightly less pressure needed to seat a primer but still VERY snug. The primer pocket tightness stayed consistant from there up to the 146.0 gr load.
From this testing I have come to some conclusions on this new wildcat. First off, I feel pressure wise 3200 fps is practical with a 350 gr ULD RBBT. That said, it seems that 40" of barrel length is more then needed for even a +140 gr capacity in a 338 bore length. The reason I say this is because BD408 is getting similiar velocity in a shorter barrel.
But, I am also using a Lilja barrel which are extremely tight in bore diameter. In fact I had to order in custom made pilot diameters to fit in this bore for chambering. They are very tight bores. A full 0.0006" smaller then what is typically the low end diameter for a 338 bushing. this I am sure contributes to alot of the velocity limits.
A looser barrel will certainly produce more velocity as will a faster twist but I think the twist is dead on for this bullet weight and I will take the accuracy of the Lilja barrel so far, very happy.
I was a bit suprised at the relatively unchanged velocity from 143.0 gr up to 146.0 gr as well, again telling me that 40" of barrel is really far more then needed for even this case capacity in a 338 bore at least with the 350 gr bullet weights.
Currently the only problem I am having with this rifle is the primer cratering at what seem to be totally safe pressures from case head expansion measurements, primer pocket tightness, bolt lift and extraction of cases. Hell, even fired cases rechamber easily so I know pressures are safe with these loads.
Just have to do some more playing around to figure out what is causing the primer cratering.
I also believe these bullets have a heavy jacket on them as well. I will have to talk with Richard to see what jacket they are bult with but I think they are the 0.040" jacket. A 0.030" jacket or thinner will really free up this tigh bore pressure wise and produce higher velocities.
After the first test I will admit I was a bit suprised with the velocity level of this round. I was expecting near 3300 fps but to be honest, I will take 3200 fps anyday with a 1/2" grouping rifle at 200 yards.
This is all playing right now though. Need to test H-50BMG as well to see how they compare burn rate wise. Seems US869 is a bit quick as there is quite a bit of air in the case even at the 146.0 gr load level. I will test some H-50BMG and see how it does. May also test some of the ultra slow Vhita Vouri powders for the 50 BMG and see how they do.
SO far a good outing for the first time, a couple 1/4 moa groups at 200 yards is not a bad start. Longer range should be fun to say the least!!!