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Well, spent a few hours this morning to play with my 375 Allen Xpress. This is not a new wildcat, I have had it in the stable for several years but just set up to form brass for customers so decided it was time to start to release some actual load data.
This specific rifle one of my Raptor Stalker for a customers rifle that I am getting ready to ship. Its intended use is heavy and dangerous game, as such, it has a Swaro 1-6x in the saddles. A quick scope change to something like a NF NXS 3.5-15x 50mm would turn it into a zero to 1K rifle pretty easily.
The rifle has a 26" Lilja barrel made to my Raptor Stalker specs, 1-10 twist. Bare rifle weight is 10.3 lbs. Again, this is NOT a heavy, long range style rifle but a medium weight, dual purpose rifle with the ability to hammer a cape buff at 50 yards or a Kudu at 700 yards on the same day easily.
Anyway, to the testing. This morning was quite nice, 60-70 degrees during velocity testing. Again, this was velocity testing and load development done at my shop, no accuracy testing yet.
The customer wanted loads developed using the Barnes 250 gr TTSX and 350 gr TSX bullets. First up the 250 gr TTSX. I had four powders I felt would be possible good choices, IMR-4350, IMR-7828, Magpro and Ramshot Magnum. Figured the last two would be pretty slow for the 250 gr TTSX but would give them a try anyway.
First up was IMR-7828. Figured it would give me a bit of a pressure cushion being a pretty slow burner and relatively bulky stick powder. To get started, I looked up some load data for the 375 RUM with 250 gr bullet weight and then took a couple grains off that listed max charge and started there.
250 gr TTSX
Fed-215 primer
3.575" OAL (0.070" off the lands)
100.0 gr..........................3058 fps
101.0 gr..........................3079 fps
102.0 gr..........................3108 fps
103.0 gr..........................3146 fps
104.0 gr..........................3182 fps (out of capacity)
Ran out of case capacity long before pressuring out with IMR-7828. Pressures even with the 104.0 gr load level were EXTREMELY mild.
Needed a bit faster burn rate so next up was IMR-4350. H-4350 could be substituted for these numbers as well. From what I have seen, H-4350 is either identical or very slightly slower burning then IMR-4350. Its also a bit better for wide temp changes but with our current powder shortages, did not have any H-4350 on the shelf to test so stuck with the old standard IMR-4350. Same load specs as the first test but with new powder, since IMR-4350 is significantly faster burning I started at 96.0 gr and worked up from there.
96.0 gr..........................3100 fps
97.0 gr..........................3147 fps
98.0 gr..........................3182 fps
99.0 gr..........................3221 fps
100.0 gr........................3252 fps 100% load density
101.0 gr........................3273 fps
102.0 gr........................3308 fps (FAINT ejector ring)
You can really tell when you get the right match of burn rate with case capacity and bullet weight. The velocity gains really jump quick with the right combination and the burn rate of IMR-4350 seems to be nearly perfect for the 375 Allen Xpress with the 250 gr bullet weights. I would suspect it may be even better with the 300 gr bullet weight. At 102.0 gr, there was a bit more powder crunching then I like to see. With a bit longer throat, I am sure this bullet could be easily driven to 3350 fps with no real problems at all with max working loads With this combo however, I feel 3300 fps is max. What an elk hammer this will be for anything from close in timber hunting to reaching out to 1/2 mile easily.
I did try Ramshot Magnum with the 250 gr TTSX but it was far to slow. I started with 100.0 gr which only clocked just over 2700 fps. Just to slow for this lighter bullet weight.
I feel that another Ramshot powder, HUNTER, may be nearly perfect for this combo as its burn rate is slightly slower then IMR-4350 but being a ball powder, you can get much more powder into the same capacity so it should be a very good match. Will be trying that next. The Ramshot powders are also pretty decent at staying stable over temp changes, something most ball powders have problems with. They are not quite as good as the Extreme stick powders at this but pretty good in my testing.
For the powders I had on the shelf, IMR-4350 seems to be a very impressive powder for the 250 gr TTSX easily pushing 3300 fps, again remember out of a relatively short, 26" barrel length and with very reasonable chamber pressures.
Next bullet up was the 350 gr TSX. This is a massively long bullet in 375 cal. It has a very long body length and relatively short ogive. That adds up to taking up a lot of case capacity!!! The throat on my 375 Allen Xpress reamer is set up for use with the 350 gr SMK seated to the base of the neck. Its not set up for the 350 gr TSX but it can certainly be used with this throat length. Were I setting a rifle up specifically for the 350 gr TSX, I would cut the throat length 0.150" longer which would increase case capacity noticeably.
In this chamber, with the 350 gr TSX seated 0.070" off the lands, the OAL of the loaded rounds is 3.570". Seeing the impressive results that IMR-4350 chalked up with the 250 gr TTSX, I decided to try that bullet first. I did however believe that it would be a bit fast in burn rate with this very heavy bullet weight. Still, wanted to see what it would do. Did some quick figuring and started at 83.0 gr and worked up 1 grain at a time until I got 100% load density.
83.0 gr..................2460 fps
84.0 gr..................2483 fps
85.0 gr..................2517 fps
86.0 gr..................2539 fps
87.0 gr..................2561 fps
88.0 gr..................2578 fps
89.0 gr..................2608 fps 100% load density
90.0 gr..................2640 fps Very mild pressures
I really did not know what to expect with this powder and bullet but was pretty happy but this is where I really found that I needed a denser powder. Burn rate was a pretty good match but powder just took up to much room, again, a better throat length for this specific bullet would have made a huge difference.
I then decided to try MagPro with it being a ball powder which is quite a bit slower burning then IMR-4350. Because of that, I started at 90.0 gr, where I left off with IMR-4350.
90 grains of 4350, there was slight powder crunching. With 90 gr of MagPro, there was plenty of case capacity left, good old ball powders!!!
90.0 gr................2424 fps VERY low pressure, jumped 5 grains
95.0 gr................2530 fps Still very low pressure, increased 3 grains
98.0 gr................2569 fps
99.0 gr................2598 fps
100.0 gr..............2647 fps
101.0 gr..............2672 fps
102.0 gr..............2684 fps
103.0 gr..............2702 fps 100% load density
104.0 gr..............2733 fps
105.0 gr..............2760 fps Just ran out of case capacity
it was clear that Magpro was so slow in burn rate for this bullet and throat length but it is very clear that with the correct powder, 2800 fps is easily possible with a 350 gr bullet weight and in a relatively short 26" barrel length. Very happy with those results.
With a 24" barrel length, The Barnes loading manual lists this same 350 gr TSX at the same exact velocity but using 10 grains more velocity then the 375 Allen Xpress has to use. Exactly what all the other Lapua based AX and AM chamberings have proven. Again, with the proper powder, perhaps Ramshot Hunter, I fully believe that 2800 fps is realistic with this combo as it sits now. Very happy.
Finally, I wanted to test the bullet that the 375 Allen Xpress was really designed to shoot. The 350 gr SMK. With the low pressures I had just seen with MagPro and the 350 gr TSX, I decided to start off where I has stopped with that bullet. Where 105.0 gr was heavily compressed with the very long bodied 350 gr TSX, there was plenty of case capacity left using the 350 gr SMK seated to 3.820" OAL which is roughly 20 thou off the lands.
105.0 gr.......................2802 fps
106.0 gr.......................2818 fps
107.0 gr.......................2830 fps
108.0 gr.......................2857 fps
109.0 gr.......................2886 fps 100% load density
110.0 gr.......................2932 fps faint ejector ring (good working max load)
In this test it was clear that MagPro was a very good match for the 350 gr SMK and the throat length. Just started to see the earliest signs of top pressures at a grain over 100% load density, about as good as it gets. 2932 fps from a 350 gr SMK with a BC of roughly .800 and out of a 26" barrel length. Now, I am very excited to see what this combo will do in something like my Raptor LRSS with its full length 30" or 32" barrel length.
Left to right, 250 gr TTSX, 350 gr TSX and 350 gr SMK. In this picture its easy to see the difference in bullet body length between the three. The 250 gr TTSX has very similar bullet body length as the 350 gr SMK. The 350 gr TSX is dramatically longer then the 350 gr SMK and has a much shorter ogive. This is why the 350 gr SMK can be loaded to significantly higher velocities with same powder.
Left to right, 300 Win Mag (for scale), 375 AX w/ 250 gr TTSX, 375 AX w/ 350 gr TSX and 375 AX w/ 350 gr SMK.
The 375 cal is not overly barrel length dependant so its likely that you will not see much improvement in a 32" barrel compared to a 30" barrel length. Still, it is clear that the 375 Allen Xpress with the 350 gr SMK will easily be able to reach 3000 fps in my Raptor LRSS.
Compared to the 338 Allen Xpress and other similar 338 wildcats based on the 338 Lapua Improved design, using a 300 gr SMK, Bullet drops and drifts will pretty much be identical as both bullets have basically the same BC.
...........................1000yards......1500.......2000......2500
Drop numbers......-20.9 moa......-39.0......-64.0......-98.8
Drift numbers.........3.6 moa.........6.1..........9.1........12.5
So is there any real advantage to go with the 375 Allen Xpress over the 338 Allen Xpress, well, there are two main advantages, retained kenetic energy and terminal performance on heavy game where the larger 375 caliber bullet simply smacks harder.
If you look at the retained energy levels between the two, here is the comparision
................... 500yards......1000........1500.......2000.......2500
338 AX.........4129 ft/lbs....2747........1766.......1127.......780
375 AX.........4817.............3205........2060.......1315.......910
Will these two even reach 2500 yards with supersonic velocity, turns out at my elevation of 3400 ft, they both hit the supersonic velocity barrier exactly at 2500 yards.
Second advantage, barrel life, I estimate that barrel life on the 375 Allen Xpress will be 15-20% longer then the 338 Allen Xpress. Again, remember these numbers are all from throats of conventional design so they will offer good long barrel life.
So is the 375 AX a better choice, Not for every situation. There is more recoil with the 375 AX, not a lot more but its noticeable compared to the 338s. There are also better bullets out there for ballistic performance then what is available for the 375. Still there are good selections in both, just more for the 338s.
Powder choices are about the same numbers for each.
This is just another great chambering for a slightly different design goal then the 338s which helps the APS line of wildcats cover an even wider range of field uses and goals.
Accuracy testing next and then I also plan on testing the 260 gr Accubond and 300 gr Accbond which I feel IMR-4350 will be pretty hard to beat with these two.
This specific rifle one of my Raptor Stalker for a customers rifle that I am getting ready to ship. Its intended use is heavy and dangerous game, as such, it has a Swaro 1-6x in the saddles. A quick scope change to something like a NF NXS 3.5-15x 50mm would turn it into a zero to 1K rifle pretty easily.
The rifle has a 26" Lilja barrel made to my Raptor Stalker specs, 1-10 twist. Bare rifle weight is 10.3 lbs. Again, this is NOT a heavy, long range style rifle but a medium weight, dual purpose rifle with the ability to hammer a cape buff at 50 yards or a Kudu at 700 yards on the same day easily.
Anyway, to the testing. This morning was quite nice, 60-70 degrees during velocity testing. Again, this was velocity testing and load development done at my shop, no accuracy testing yet.
The customer wanted loads developed using the Barnes 250 gr TTSX and 350 gr TSX bullets. First up the 250 gr TTSX. I had four powders I felt would be possible good choices, IMR-4350, IMR-7828, Magpro and Ramshot Magnum. Figured the last two would be pretty slow for the 250 gr TTSX but would give them a try anyway.
First up was IMR-7828. Figured it would give me a bit of a pressure cushion being a pretty slow burner and relatively bulky stick powder. To get started, I looked up some load data for the 375 RUM with 250 gr bullet weight and then took a couple grains off that listed max charge and started there.
250 gr TTSX
Fed-215 primer
3.575" OAL (0.070" off the lands)
100.0 gr..........................3058 fps
101.0 gr..........................3079 fps
102.0 gr..........................3108 fps
103.0 gr..........................3146 fps
104.0 gr..........................3182 fps (out of capacity)
Ran out of case capacity long before pressuring out with IMR-7828. Pressures even with the 104.0 gr load level were EXTREMELY mild.
Needed a bit faster burn rate so next up was IMR-4350. H-4350 could be substituted for these numbers as well. From what I have seen, H-4350 is either identical or very slightly slower burning then IMR-4350. Its also a bit better for wide temp changes but with our current powder shortages, did not have any H-4350 on the shelf to test so stuck with the old standard IMR-4350. Same load specs as the first test but with new powder, since IMR-4350 is significantly faster burning I started at 96.0 gr and worked up from there.
96.0 gr..........................3100 fps
97.0 gr..........................3147 fps
98.0 gr..........................3182 fps
99.0 gr..........................3221 fps
100.0 gr........................3252 fps 100% load density
101.0 gr........................3273 fps
102.0 gr........................3308 fps (FAINT ejector ring)
You can really tell when you get the right match of burn rate with case capacity and bullet weight. The velocity gains really jump quick with the right combination and the burn rate of IMR-4350 seems to be nearly perfect for the 375 Allen Xpress with the 250 gr bullet weights. I would suspect it may be even better with the 300 gr bullet weight. At 102.0 gr, there was a bit more powder crunching then I like to see. With a bit longer throat, I am sure this bullet could be easily driven to 3350 fps with no real problems at all with max working loads With this combo however, I feel 3300 fps is max. What an elk hammer this will be for anything from close in timber hunting to reaching out to 1/2 mile easily.
I did try Ramshot Magnum with the 250 gr TTSX but it was far to slow. I started with 100.0 gr which only clocked just over 2700 fps. Just to slow for this lighter bullet weight.
I feel that another Ramshot powder, HUNTER, may be nearly perfect for this combo as its burn rate is slightly slower then IMR-4350 but being a ball powder, you can get much more powder into the same capacity so it should be a very good match. Will be trying that next. The Ramshot powders are also pretty decent at staying stable over temp changes, something most ball powders have problems with. They are not quite as good as the Extreme stick powders at this but pretty good in my testing.
For the powders I had on the shelf, IMR-4350 seems to be a very impressive powder for the 250 gr TTSX easily pushing 3300 fps, again remember out of a relatively short, 26" barrel length and with very reasonable chamber pressures.
Next bullet up was the 350 gr TSX. This is a massively long bullet in 375 cal. It has a very long body length and relatively short ogive. That adds up to taking up a lot of case capacity!!! The throat on my 375 Allen Xpress reamer is set up for use with the 350 gr SMK seated to the base of the neck. Its not set up for the 350 gr TSX but it can certainly be used with this throat length. Were I setting a rifle up specifically for the 350 gr TSX, I would cut the throat length 0.150" longer which would increase case capacity noticeably.
In this chamber, with the 350 gr TSX seated 0.070" off the lands, the OAL of the loaded rounds is 3.570". Seeing the impressive results that IMR-4350 chalked up with the 250 gr TTSX, I decided to try that bullet first. I did however believe that it would be a bit fast in burn rate with this very heavy bullet weight. Still, wanted to see what it would do. Did some quick figuring and started at 83.0 gr and worked up 1 grain at a time until I got 100% load density.
83.0 gr..................2460 fps
84.0 gr..................2483 fps
85.0 gr..................2517 fps
86.0 gr..................2539 fps
87.0 gr..................2561 fps
88.0 gr..................2578 fps
89.0 gr..................2608 fps 100% load density
90.0 gr..................2640 fps Very mild pressures
I really did not know what to expect with this powder and bullet but was pretty happy but this is where I really found that I needed a denser powder. Burn rate was a pretty good match but powder just took up to much room, again, a better throat length for this specific bullet would have made a huge difference.
I then decided to try MagPro with it being a ball powder which is quite a bit slower burning then IMR-4350. Because of that, I started at 90.0 gr, where I left off with IMR-4350.
90 grains of 4350, there was slight powder crunching. With 90 gr of MagPro, there was plenty of case capacity left, good old ball powders!!!
90.0 gr................2424 fps VERY low pressure, jumped 5 grains
95.0 gr................2530 fps Still very low pressure, increased 3 grains
98.0 gr................2569 fps
99.0 gr................2598 fps
100.0 gr..............2647 fps
101.0 gr..............2672 fps
102.0 gr..............2684 fps
103.0 gr..............2702 fps 100% load density
104.0 gr..............2733 fps
105.0 gr..............2760 fps Just ran out of case capacity
it was clear that Magpro was so slow in burn rate for this bullet and throat length but it is very clear that with the correct powder, 2800 fps is easily possible with a 350 gr bullet weight and in a relatively short 26" barrel length. Very happy with those results.
With a 24" barrel length, The Barnes loading manual lists this same 350 gr TSX at the same exact velocity but using 10 grains more velocity then the 375 Allen Xpress has to use. Exactly what all the other Lapua based AX and AM chamberings have proven. Again, with the proper powder, perhaps Ramshot Hunter, I fully believe that 2800 fps is realistic with this combo as it sits now. Very happy.
Finally, I wanted to test the bullet that the 375 Allen Xpress was really designed to shoot. The 350 gr SMK. With the low pressures I had just seen with MagPro and the 350 gr TSX, I decided to start off where I has stopped with that bullet. Where 105.0 gr was heavily compressed with the very long bodied 350 gr TSX, there was plenty of case capacity left using the 350 gr SMK seated to 3.820" OAL which is roughly 20 thou off the lands.
105.0 gr.......................2802 fps
106.0 gr.......................2818 fps
107.0 gr.......................2830 fps
108.0 gr.......................2857 fps
109.0 gr.......................2886 fps 100% load density
110.0 gr.......................2932 fps faint ejector ring (good working max load)
In this test it was clear that MagPro was a very good match for the 350 gr SMK and the throat length. Just started to see the earliest signs of top pressures at a grain over 100% load density, about as good as it gets. 2932 fps from a 350 gr SMK with a BC of roughly .800 and out of a 26" barrel length. Now, I am very excited to see what this combo will do in something like my Raptor LRSS with its full length 30" or 32" barrel length.
Left to right, 250 gr TTSX, 350 gr TSX and 350 gr SMK. In this picture its easy to see the difference in bullet body length between the three. The 250 gr TTSX has very similar bullet body length as the 350 gr SMK. The 350 gr TSX is dramatically longer then the 350 gr SMK and has a much shorter ogive. This is why the 350 gr SMK can be loaded to significantly higher velocities with same powder.
Left to right, 300 Win Mag (for scale), 375 AX w/ 250 gr TTSX, 375 AX w/ 350 gr TSX and 375 AX w/ 350 gr SMK.
The 375 cal is not overly barrel length dependant so its likely that you will not see much improvement in a 32" barrel compared to a 30" barrel length. Still, it is clear that the 375 Allen Xpress with the 350 gr SMK will easily be able to reach 3000 fps in my Raptor LRSS.
Compared to the 338 Allen Xpress and other similar 338 wildcats based on the 338 Lapua Improved design, using a 300 gr SMK, Bullet drops and drifts will pretty much be identical as both bullets have basically the same BC.
...........................1000yards......1500.......2000......2500
Drop numbers......-20.9 moa......-39.0......-64.0......-98.8
Drift numbers.........3.6 moa.........6.1..........9.1........12.5
So is there any real advantage to go with the 375 Allen Xpress over the 338 Allen Xpress, well, there are two main advantages, retained kenetic energy and terminal performance on heavy game where the larger 375 caliber bullet simply smacks harder.
If you look at the retained energy levels between the two, here is the comparision
................... 500yards......1000........1500.......2000.......2500
338 AX.........4129 ft/lbs....2747........1766.......1127.......780
375 AX.........4817.............3205........2060.......1315.......910
Will these two even reach 2500 yards with supersonic velocity, turns out at my elevation of 3400 ft, they both hit the supersonic velocity barrier exactly at 2500 yards.
Second advantage, barrel life, I estimate that barrel life on the 375 Allen Xpress will be 15-20% longer then the 338 Allen Xpress. Again, remember these numbers are all from throats of conventional design so they will offer good long barrel life.
So is the 375 AX a better choice, Not for every situation. There is more recoil with the 375 AX, not a lot more but its noticeable compared to the 338s. There are also better bullets out there for ballistic performance then what is available for the 375. Still there are good selections in both, just more for the 338s.
Powder choices are about the same numbers for each.
This is just another great chambering for a slightly different design goal then the 338s which helps the APS line of wildcats cover an even wider range of field uses and goals.
Accuracy testing next and then I also plan on testing the 260 gr Accubond and 300 gr Accbond which I feel IMR-4350 will be pretty hard to beat with these two.
