7mm Allen Magnum load testing 160 gr Accubond

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Fiftydriver, Oct 31, 2007.

  1. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

    Messages:
    6,848
    Joined:
    Jun 12, 2004
    TO all, Was just catching up on some load development testing in my 7mm AM. The test rifle I was using was my lightweight 7mm AM with a 27" #3 contour Lilja 6 groove 1-9 barrel.

    I have not really given the 160 gr Accubond a good load development so I wanted to test the bullet with some differnt powders to see what she could do. The wind was so bad today that I just did some velocity testing at the shop.

    Honestly, I figured Retumbo was to fast in burn rate but wanted to test it as its a standby for rounds such as the 7mm RUM, 300 RUM and 30-378.

    The Hodgdon manual lists a top load of 94.0 gr under a 160 gr Partition. With the capacity increase over the RUM, I figured this would certainly be a comfortable load. This RUM load by the way is listed to have a velocity of 3212 fps in a 24" barrel just for reference.

    I started at 95.0 gr and worked up to 99.0 grains in 1/2 grain steps, here are the velocity results:

    95.0.......................3378 fps
    95.5.......................3419 fps
    96.0.......................3465 fps
    96.5.......................3499 fps
    97.0.......................3534 fps Max working load
    97.5.......................3555 fps slight ejector mark, easy bolt lift
    98.0.......................3580 fps slight ejector mark, easy bolt lift
    98.5.......................3601 fps heavier ejector mark, increase bolt lift
    99.0.......................3622 fps Heavy ejector mark, snug bolt lift

    Velocities are averages of three shots with each load. Iwas really susprise how much velocity increase was seen with each 1/2 grain increase in powder. This is not common with what I have seen with this chambering using the slow ball powders.

    I consider 97.0 grains to be the max working load in my Rem 700 based rifle. This load showed very little if any ejector marks, bolt lift is effortless as well and fired cases can be rechambered with only slight increase in effort to close the bolt on a fired case compared to the loaded round.

    Primer pockets were tight on every load tested, still, I feel 97.0 grains is max for this combination of componants in this rifle.

    I was also suprised at the amount of velocity generated with the powder charges. The 7mm RUM is said to get 3212 fps in a 26" barrel with 94.0 grains. My 7mm AM with its 8-9 grains capacity advantage over the RUM is generating nearly 160 fps more velocity with only one more gain of powder. This does not make alot of sense to me butI am sure its due to the tight Lilja bore, very tight fitted throat and shorter, fatter case design of the AM compared to the RUM.

    Top working loads of 3534 fps are roughtly 320 fps more then what Hodgdons lists for the RUM. In reality, the RUM will easily get 3300 fps with this bullet but that is still +230 fps over what the RUM will get. Frankly more then I expected to see with this powder and more of a velocity advantage then I see when using WC872, US869 or AA8700 which does not make alot of sense for the size of the case capacity of this wildcat.

    The slower powders should offer the most velocity advantage but that is not the case here.

    We have all seen this, one powder, just happens to seem magical with a certain chambering, perhaps combining Retumbo with the 7mm AM and the 160 gr Accubond is one of these combinations.

    Now I am not saying this load is superior to my standard 200 gr ULD RBBT load because at long range that is simply not the case. Still, for a 1/2 mile rifle/load combo, this load will be hard to beat, that is if accuracy is up to the job. That still has to be proven, supposed to be windy as heck tomorrow so we will have to see. Will report my accuracy results when I get them.

    This rifle will be limited to 1/2 mile shooting so as long as I can hold 3/4 moa out to that range or better, I will be happy, to be honest, 1 moa at 800 yards would still be more then usible for long range big game hunting out of this 9 lbs sporter rifle.

    Those of you with 7mm AM rifles, if you want to try this load, start at 93.0 gr and work up watching for ejector marks or any sign of pressure. In a 27" barrel I would not recommend pushing over this 3530 fps level. In a 30" barrel, upper 3500 fps or even lower 3600 fps levels maybe realistic but approach these levels with great care.

    Remember that if you are loosening the primer pockets on a Lapua case, your into serious pressure levels, back off.

    More to come with the accuracy results. Velocity means nothing without accuracy.

    Kirby Allen(50)
     
  2. gamedog

    gamedog Well-Known Member

    Messages:
    591
    Joined:
    Aug 16, 2007
    Keep us posted on how they group for you Kirby. That's one hell of a caliber:D
     

  3. Ridge Runner

    Ridge Runner Well-Known Member

    Messages:
    987
    Joined:
    Dec 13, 2002
    accubonds at 3500 shoot great in my 1/9 4 groove lilja, with wc872 in cool weather accuracy runs 1/3 moa or better, may give retumbo a try when the supply's of 872 dry up.
    James Staggs
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

    Messages:
    6,848
    Joined:
    Jun 12, 2004
    Wind was blowing 20 mph today but I had a couple customer rifles that I HAD to range test to get shipped ASAP.

    So I ran out and took the lightweight 7mm AM along(also threw in my lightweight 338 AM to resight in as well).

    First group was not that great, 1.2" at 100 yards. Made a scope adjustment and next three cut a 0.744" ctc group with most of the group variation was horizontal from the wind slapping the side of the rifle.

    Let the barrel cool and shot three more, they landed exactly where I wanted them, 2.4" high, first two landed basically in the same hole, had to actually measure the bullet hole to make sure there were two in there. The third shot landed .4" straight up from that. I figure if I can get a .4 moa group in a 20 mph wind in a lightweight rifle things are shooting pretty well!!!

    Running the numbers, with a +2.4" impact at 100 yards you need only 4 1/4 mils to be able to reach out to 1000 yards. Basically the same as the 200 gr ULD loaded to 3150 fps. Wind drift is more then the 200 gr by around 1/2 mil and energy is off a fair amount as well but more then enough to still take game at long range.

    Nosler lists you should have a minimum impact velocity of 1800 fps for proper bullet performance, this load should arrive at 1000 yards with over 2000 fps and nearly 1500 ft/lbs of energy. Certainly not what the 200 gr ULD offers but still very impressive. In fact you can reach out to 1200 yards and you should still see full bullet expansion.

    only thing you have to do is watch the wind closer and tighten up the limits of wind speed you will shoot in.

    So far I am happy with the results. How the 160 gr would handle a close range impact at this velocity is yet to be seen but I amsure it would easily get through any big deer and through the vitals of any elk with a clean chest shot.

    Kirby Allen(50)
     
  5. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

    Messages:
    6,848
    Joined:
    Jun 12, 2004
    Tested this load at longer ranges today, was a bit windy and was shooting up through a deep canyon so the wind did get to the bullets a bit. At 665 yards, the first two landed 2" apart, third shot dropped 6"??? Think it was me.

    At 1005 yards first three shots went into 9" with two only 3" apart. Four shot opened things up to 11" and fifth shot dropped well out of the group, about 8" low of rest of shots.

    I am sure barrel heat was the problem here. Still first three were very impressive. I did not let the barrel cool, just shot five as quickly as possible.

    Under 1 moa for the first three at 1000 yards is plenty with a 9 lb rifle in my opinion. Wind is a kicker, not used to holding that far into the wind.

    Also shot the 338 AM with 265 gr AT RBBT. At 750 yards, put three in a 3" group. At 1005, four shots measured 12" horizontal by 5" vertical. Wind was 15 to 25 mph from my 8 o'clock position, very variable so I am pretty happy with that. In calm conditions I am sure that 1/2 moa would not be much challange for those first three.

    Got to get some calm time to get them fine tuned for hunting!!! They are pretty darn close right now but just need one good calm morning to varify horizontal zero and their ready for field work. Horizontally, they are right on the money.

    Kirby Allen(50)