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Yesterday I completed the additional psi work up in the 6.5×55 Swede with IMR 4350 as and the Hornady 129 gr SP. Cases were Winchester and the primers were WLRs. Charges were weighed on a Redding balance scale that has been checked for accuracy with verified weights. The AOL of the loaded cartridge was 3.041″. Test rifle for this test was My M38 Carl Gustaf “scout”. The rear sight had been removed and a Redfield style base modified to fit so the Leupold 2X Scout scope could be correctly mounted. The bolt was converted to cock on opening and the bolt handle forged. It was then pillar bedded in a composite stock making for a nice handling lightweight “scout”. The rear of the base has a Redfield flip up aperture for emergency use and I replaced the barleycorn front sight with a blade front sight.
The strain gauge for the M43 Oehler was positioned over the chamber as per SAAMI location specifications. Winchester Factory 140 gr SP ammunition was used as “reference ammunition”.
After setting up the equipment at the range it was 48 degrees with 40% humidity and a barometric pressure of 30.13. I had tests made up of 5 rounds of each increment from 42 gr to 49 gr in 1 gr increments of IMR 4350. The initial 5 shot tests, while not as definitive as 10 shot tests, will give us a good idea of what to expect. Again, let us remember; as with velocity, averages of different tests of the same load vary, so will pressure averages vary test string to test string. Not by a lot usually but they do vary. And different lots of the same powder will also give some variation in velocity and pressure lot to lot.
My initial test yesterday was a 10 shot test of this “reference” ammunition to confirm the M43 System was “calibrated” and working correctly with this rifle. The factory measured psi was 37,900 and should give 2400 – 2475 fps in 24” barrels. Yesterdays test gave pretty much that with 37,900 psi at 2454 fps (muzzle). The 10 shot group at 100 yards (remember it’s only a 2X scope) was just under 2 moa.
I then shot a 10 shot test of my “big game” load which is the 140 gr Hornady SP over 49 gr H4831SC in the Winchester cases with WLR primers to an OAL of 3.112”. The muzzle velocity was 2745 fps at 54,500 psi….just under the C.I.P. PMAP. Those 10 shots went into less than 1.5 moa at 100 yards.
Results of yesterday’s test of IMR4350 under the 129 gr Hornady SP;
Load FPS (muzzle) psi(M43)
42 2514 41,000
43 2611 44,400
44 2642 45,500
45 2697 47,800
46 2747 50,100
47 2810 54,000
I did not test the 48 and 49 gr loads as the psi would have probably been in the high 58+k and 60+k range which is over the C.I.P. PMAP. The 5 shots of the 47 gr load went into 1.1” at 100 yards. It is a very good load as as the 10 fps SD and 22 fps ES indicates.
As a final test I shot a 10 shot test of my previously developed 129 gr Hornady SP using IMR4831. It hovers right around the 55,000 psi C.I.P. PMAP +/- and today’s was a tudge on the plus side which was expected given I had not cleaned the barrel after the previous 80 shots had been fired. The velocity was 2927 fps at 55,700 psi and the 10 shots went into 1.4” at 100 yards centered exactly 1.6” above point of aim for a 200 yard zero. The 300, 400 and 500 yard drop is 7, 21 and 42” with 1960+ fps remaining at 500 yards. It makes for an excellent coyote, deer.and antelope load.
Hope you find this information useful as I have with an added powder (IMR 4350) to use in my own 6.5x55s.
Hold hard, shoot straight…..