375 Allen Xpress load development with velocity results

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Fiftydriver, Sep 1, 2013.

  1. Fiftydriver

    Fiftydriver Official LRH Sponsor

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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.

    [​IMG]
    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.

    [​IMG]
    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.
     
  2. catskinner

    catskinner Active Member

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    Did you get a chance to stretch these out to 1800-2000 yet?
     
  3. Fiftydriver

    Fiftydriver Official LRH Sponsor

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    The rifle I have to accuracy test is one of my Raptor Stalkers which is a 10 lb mid weight rifle. Not designed for 1800-2000 yard shooting. When I test it, it will likely be at 800 to 1000 yards max. Hope to do that this week.

    The customer is wanting load development for the 250 gr TTSX and 350 gr TSX, neither of which are 1800 yard bullets.
     
  4. catskinner

    catskinner Active Member

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    My bad, I thought you mainly built extra long range rifles
     
  5. Fiftydriver

    Fiftydriver Official LRH Sponsor

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    I build big game rifles that will cover everything from 0 to 3000 yards but not all models of my rifles will cover that entire range.
     
  6. Fiftydriver

    Fiftydriver Official LRH Sponsor

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    Got some Ramshot Hunter powder in to try with the 350 gr TSX. Was pretty happy with the results, was hoping to break 2800 fps. Here are the specs:

    375 Allen Xpress once fired brass
    350 gr TSX
    3.565" OAL
    Fed-215
    Ramshot Hunter

    85.0 gr...................2455 fps
    90.0 gr...................2569 fps
    93.0 gr...................2656 fps
    95.0 gr...................2685 fps
    97.0 gr...................2737 fps 100% load density
    98.0 gr...................2772 fps
    99.0 gr...................2805 fps Max working load, very faint ejector ring

    If I were hunting here I would be 100% confortable using the 99.0 gr load and even 100.0 gr would be very practical pressure wise. Still, this customer is heading to Africa where it may be a lot hotter so for this use, I would recommend dropping down to the 95.0 gr load which is basically at the 2700 fps level and have a HUGE margin of safety pressure wise for 100% reliable function in possible hot temps.

    This powder is a great match for this chambering and bullet and the short throat design. We ran into 100% load density about the same time that the round started to show faint ejector rings. About perfect.

    Again, at 99.0 gr, primer pockets are virgin tight, bolt life is effortless so this is no way near a red line load, no reason to push things that hard, reached my desired goal and that was plenty and a great comfortable place to stop testing at.
     
  7. catskinner

    catskinner Active Member

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    I checked out your website, and that raptor is one hell for stout looking design.
     
  8. Fiftydriver

    Fiftydriver Official LRH Sponsor

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    Wanted the Raptor receiver to be the strongest receiver in its class and I believe it is pretty easily. The Raptor rifles are also designed with a bit of overkill in mind!! :D
     
  9. catskinner

    catskinner Active Member

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    I also liked the barrel profile you spec'd. With the diameter going 5" before changing. Any other calibers you been coming up with
     
  10. Fiftydriver

    Fiftydriver Official LRH Sponsor

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    Have to do R&D on the following new wildcats this fall and winter:

    300 Raptor
    458 Allen Magnum
    510 Maximus
     
  11. 300whisper

    300whisper Well-Known Member

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    Kirby, I read your article and very awesome work. I cant believe that one of your chamberings only has 20.9 MOA drop at 1K! But on the topic of barrels, I went to your website and you have several barrels in the 30+ inch catergory with straight tapers. With your large capacity rounds and the heaviness of the barrel, do you experince crazy harmonics or barrel droop? Also, you said that you tested your AX in a 24 inch barrel? Was that for test purposes or do customers order your rifles with that short of a barrel?
     
  12. Fiftydriver

    Fiftydriver Official LRH Sponsor

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    Are you getting this information off www.apsrifles.com?

    Some of the information your listing does not sound like it came from me....

    I rarely use straight taper barrels. I use some straight cylinder barrels from time to time but generally only on my 50 cal class weapon systems.

    All of my Raptor barrels, including the Raptor Hunter contour, Raptor Stalker contour and Raptor LRSS contour are custom made for me by Lilja barrels. None of them are straight taper barrels, they are all contoured.
     
  13. 300whisper

    300whisper Well-Known Member

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    You're right just went back saw that I was looking at the .50 cal class rifles. Thanks for clearing that up.