To all interested,
I was shooting my new lightweight 338 AM Xtreme Heavy Sporter(XHS) a bit more this weekend finishing up the barrel break in and ran into some interesting things that I wanted to pass onto those interested in this wildcat.
Here is a pic of the rifle. I gave a review of it on the Long Range Hunting section but I feel this is a more appropriate area to post about it.
I was using some of my original cases that I have been using since I have started shooting the 338 Allen Magnum in my heavy rifle. Some of these cases have well over 10 firings on them. To be honest, lost count on the firings per case.
Most have pretty loose primer pockets but still have enough to hold a primer in place.
I started working loads up while doing the barrel break in and quickly ran into a problem. Once I reached aroung 140 to 142.0 gr H-50BMG under the 300 gr SMK, I was getting sticky extraction. The bolt lift was very smooth and easy on the BAT receiver, but when the mechanical cam on the bolt contacted the cam surface on the receiver, I needed to pop the bolt handle with the palm of my hand, pretty stoutly to open the bolt. Once it opened, the cases extracted effortlessly.
When I increased to 144.0 gr the bolt had to be tapped open at the top of its stroke with a non marring mallet to open the bolt. NO GOOD!!!
I decided there were several things that may have been causing this problem but the easiest to test was that the cases were simply to old and that I should try some new freshly formed cases and see how they performed.
Yesterday I formed up a small batch of cases, only five of them, just got this test. I loaded them all up over 144.0 gr H-50BMG with the 300 gr SMK. Again, remember this load needed the bolt handle tapped open with a mallet with the old cases.
I took the rifle out with some customer rifles to range accuracy test and shot three of the round. The group below was the result of the 100 yard three shot group. I think this little rifle will be a decent shooter!!!
As listed on the target the average velocity was 3344 fps with an extreme spread well under 10 fps. If I recall correctly it was 8 fps.
Just as importantly, the bolt opened like there was no case in the chamber at all!!!
I wanted to test this farther and find out at what point in the case life did this start to be a problem with extraction characteristics?
This morning I took one of those new formed case that had one high pressure firing on them. After sizing the case was reduced in size roughly 0.0006" at the expansion
ring just ahead of the solid case head. I loaded up the case again with 144.0 gr H-50BMG and fired the round again, extraction was picture perfect, just like the first high pressure firing. I then repeated the loadings and firing.
3rd high pressure loading and firing
diameter reduced 0.0005" after FL sizing
Extraction again perfect
4th high pressure loading and firing
Diameter reduced 0.0005" afer FL sizing
Extraction again perfect
5th high pressure loading and firing
Diameter reduced 0.0003" after sizing
Extraction had just the slightest resistance at the top of the bolt travel, hardly noticable however.
6th high pressure loading and firing
Diameter reduced 0.0002" after FL sizing
Extraction had a noticable resistance at top of bolt stroke, roughly twice that of the 5th firing. Still fully acceptable but noticable
7th high pressure loading and firing
Diameter reduced only 0.00015 after FL sizing
Extraction had heavier resistance at top of bolt stroke. Had to pop with the palm of my hand to open the bolt all the way. Excessive in my opinion.
After seeing this, I believe this is simply a case issue. The cases simply seem to become heat tempered as the case is fired a certain amount of time and once this happens, there is really no way to move the heavy case wall
just ahead of the solid case head, it simply springs back after it is released by the FL sizing die.
I also wanted to see if the number of rounds that each case would handle with good extraction was effected by the level at which the round was loaded to. I had tested my 7mm AM and it really did not make a significant difference how hard I loaded the round, in about 6-7 firings, I was seeing
the same thing and it was time for new brass.
As such, I took another freshly formed case and repeated the entire test using 135.0 gr of H-50BMG, a very mild load producing roughly 3150 fps with the 300 gr SMK.
I was able to get only one more firing with this low pressure level loading before extraction resistance got to the point where I felt it was excessive needing me to pop the bolt handle with the palm of my hand.
On the other end of the performance scale, I wanted to test with higher Pressure loads as well. I loaded up 146.0 gr and repeated the entire test. The results were extremely similiar to the original 144.0 gr load test. On the
6th firing however, there was slightly more force needed to open the bolt but not excessive in my opinion. On the 7th firing it was definately excessive force needed to open the bolt. By the way. 146.0 gr averaged 3371 fps.
I took things one step farther. I loaded up 148.0 gr and repeated the test with the last freshly formed case. This load was cooking along at an average 3395 fps with a couple firings over 3400 fps!!
First firing extracted perfectly. There was a noticable and well defined ejector mark however. Second firing extracted fine but there was definate resistance on
the bolt at the top of the stroke, not excessive however. Third firing was stiff on the upper end of the bolt stroke and on the four firing I would call it definately excessive force needed to open the bolt.
Keep in mind however, this load showed well defined ejector mark on all firings so it is certainly a higher pressure load then I would ever recommend should be used.
As far as primer pocket tightness, the 144.0 gr load maintained a very snug primer pocket fit to the 5th firing. Firings #6 and #7 were noticably looser but still perfectly usible with no chance of any gas leakage.
The 146.0 gr load held snug primer pockets to the 3rd firing but again remained adiquate to prevent any gas leakage until the 7th firing although the 6th and 7th loading did have a noticably looser primer pocket.
The 148.0 gr load had noticable primer pocket loosening right from the get go. It remained adiquate to prevent any gas leakage until the 3rd firing
but the 4th was looser then I like to see and there was a hint of gas leakage on that 4th firing but again, this load is hotter then I would ever recommend.
From looking at all the results, it seems pretty clear that the cases simply heat temper at a certain point and with loads in the comfortable working ranges of the round, it really is not effected much but the level at which you load to resulting in only a difference of two firings from very low end pressure to top working load pressures.
It is my opinion from this test that cases should be used to a max of 7 firings. In most cases I believe that 6 firings will be about max with upper end loadings and that once you start feeling the slight resistance on the top of the bolt stroke, its time to retire the brass and start with a fresh batch.
I was frankly suprised at the level of performance that was possible with this barrel length, nearly 3400 fps!!
Personally, if one can get at least 6 firings per case, thats fully acceptable to me. With 100 cases, thats 600 rounds and well over 1/2 the accuracy life of a barrel with this chambering and even if we pay $2.50 per case. That comes out to just shy of 42 cents per firing for case cost.
More then acceptable in my opinion for this type of rifle and this level of performance.
If we were talking about a chambering that would offer 2000 rounds of accuracy barrel life, my opinion may be a bit different but still getting 6 full pressure loadings with each given piece or brass is as good as you will see with any case other then perhaps the 338 Lapua and the wildcats based on it depending on the amount of case taper in their design.
I know for a fact if you load a RUM case up to 65,000 psi, your primer pockets will be loose by the time you hit 5 to 6 firings on a given case. My numbers are based on studies representing velocity for givien tested pressure ranges and I feel that 65,000 psi is about max for the RUM case.
For the 338 AM, I would estimate that 68,000 psi is about max and I would imagine these 146.0 gr loads are in that range from the length of the case life.
Just wanted to offer this information to those that already have the 338 AM or those that may be interested in it.
Basically, if you buy 200 cases, you will get enough shooting out of those cases to cover the projected accuracy life of the barrel even if you take EXTREMELY good care of that barrel.
I do not feel this should be a detractor of the 338 Allen Magnum in any way. I just wanted to offer the information to you so that you can gain even more knowledge about the round in the event you decide you want to play with one of the highest performing rounds out there today. Knowing the limits of a wildcat are just as important and anything else.
I am very happy with the results I have tested and found with my wildcat.
Now if I could just get some 265 gr Aluminum tipped Wildcat Bullets, we may be able to push near 3500 fps with even higher BC numbers then the 300 gr SMK!!!! [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]
Have a good memorial day weekend to all,