View Single Post
Old September 30, 2008, 02:37 PM   #8
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 21,022
TargetTerror,

I ran your load in QuickLOAD. It predicts a peak pressure of 36,280 and muzzle velocity of 2,409 fps in a 24" barrel using a COL of 3.250”. As the COL goes out toward the SAAMI magazine maximum of 3.340”, the pressure peak drops about 500 PSI and the velocity drops to 2,398 fps. I used 3.25” initially because many bullets not seated out near the lands, will then shoot best when their bearing surface is about 1 caliber into the case neck. 3.25” COL creates that condition for the 168 grain Sierra MatchKing (SMK).

The main problem with that load will be the fact the space in the case is only 78% filled by the powder. If you tip the cartridge forward before firing, the muzzle velocity will be lower than if the powder is back over the primer. Even Lake City’s M72 match ammunition would show muzzle velocity variation of 80 fps depending whether the muzzle was tipped up or down just before coming horizontal to fire. It used a 172 grain (actual weight spec. 174 grains +0, -3 grains) FMJ bullet over 46.5 grains of IMR 4895, which filled the empty case space 83%, and was fired by a military primer (magnum equivalent), While I would not put polyester fiber in a load as high as the one you are you are using, you might consider a single disc of newspaper or packaging tissue cut just fractionally over the case’s diameter at the powder column height, and pressed into place with a wood dowel to help keep the powder positioned over the primer. Transport all such ammo nose-up and keep it that way until you are given the command to load.

The other downside of 4064 in this application is the powder can't burn as completely at that low chamber pressure as it would in a full load. It will burn about 96% in the bore and have not quite 27% ballistic efficiency (BE). Making the switch to 41 grains of IMR 3031 increases the % burned in the barrel to 100% and the BE to 29.4% to produce the same barrel time (assuming you've found a good accuracy sweet spot whose barrel time should be maintained). It increases bullet velocity by 52 fps, but does not increase the recoil impulse. That remains a calculated 11.94 ft-lbs for both loads in the 9 lb, 3 oz 1917. You would expect more recoil because you are pushing the bullet faster, but that recoil neutrality occurs partly because there is less powder mass accelerated with the 3031 load. It is also because the muzzle pressure is slightly lower and then has less propellant gas mass to blow out. So, the IMR 3031 load produces less rocket effect after the bullet clears the muzzle. Case filling for the IMR 3031 load is 75%, so the paper disc suggestion still applies.

All that said, you will find that most rifles achieve peak accuracy at closer to maximum loads. You don't need that much precision or wind immunity for the 200 yard offhand or sitting rapid phases of a match. Indeed, for reduced recoil, I would recommend you develop a load using the 150 grain SMK at that shorter range. My records show 40.4 grains of 3031 to be a good reduced recoil load with the 150 grain SMK seated to 3.145” COL. This is in Lake City or Remington brass. Where 41.0 grains of 3031 under the 168 grain bullet produces 11.94 ft-lbs of total recoil impulse in the 1917, the 40.4 grain load under the 150 grain SMK drops that to 10.26 ft-bs, a 14 % reduction. That is enough so you will be able to feel the difference (as a rule of thumb, you only clearly feel 10% or more difference). The predicted velocity is 2498. These loads assume a mild primer. If you like what you're using now, stay with it. I used the Federal 210M for the 40.4 grain load.

When you go out to 300 yards, the wind will start knocking the bullet around more. Try again with the 150 grain bullet, but up the charge to 44.1 grains of 3031. The total recoil impulse goes up to 12.01 ft-lbs, barely different from your current load, and in the prone position with the sling tightly in place, will not move you around much. I actually use 47.5 grains of IMR 4064 in the Garand at that range, but your recoil impulse would be up to 15.55 ft-lbs with that load, and you might not like it as much. Velocity is predicted to be 2678 fps, and chamber pressure to be 39,592 psi with 44.1 grains of IMR 3031. Only your experience will tell you whether the 150 or 168 grain bullets work best for you at this range?

600 yards is another animal. The 168 grain SMK does well, but that 1959 design is overshadowed by the 175 grain SMK designed in cooperation with the military. I don’t recall seeing the 175’s at Camp Perry until the late 1990’s, but I don’t know what their military design cycle history was? I believe it started in the late 80’s. The point is, they have higher ballistic coefficients and don’t become unstable in the transonic region, so they may shoot better for you, especially if you use reduced loads. I don’t do that at 600 yards. My records show I last IMR 4064 load I used with the 175 grain SMK’s for the Garand was 48.8 grains with a COL of 3.230. That produces a predicted 2682 fps, though in my gun it ran more like 2650 fps. The pressure is predicted to be 53,000, PSI, which is below maximum, but that is with a fired case water capacity of 69.2 grains. It is a high enough pressure load that prudence suggests reducing it to 44 grains and working up in 0.3 grain increments in your gun until you see an accuracy peak. If you see pressure signs at any time during the work-up or after, then, obviously, you need to back the load down. I don’t expect you will. 48.7 grains of Varget produces similar results, and seems to be slightly more temperature immune. Recoil impulses with these loads are 15.71 and 15.63 ft-lbs, respectively.

By the way, I would recommend you buy and use a sliding-sleeve type competition bullet seating die for these loads. I use the Redding, but have heard good things about the Forster, too. I just haven’t personally measured the latter’s effectiveness, while the Redding works essentially perfectly for me. In the early 60’s the NRA published results from firing about 830 rounds of M72 in match rifles after first measuring bullet runout. They found that 0.004” of runout opened groups about 1 moa. Greater runout than that had no additional effect because the bullet could line itself up to correct greater runout. It just could not correct the first four thousandths.

I hope this is helpful?

Nick
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is offline  
 
Page generated in 0.03889 seconds with 8 queries