Warning, for non techie people this will be similar to a white paper. Long and lots of information.
After reading about people trying to blow their faces up attempting to make a civilian variant of Mk 262 with varying levels of success (one guy was talking about 28 gr of Varget, wtf). Add to that varied loading charts (even the Sierra loading manual version 5) disagrees with other versions of sierra's loading for their and other ar bullets.I thought I would take some time between classes and come up with a combination which you can use commercially available components on the cheap to replicate the velocity and or bullet trace of the Mk 262 Mod 0 match long range ammunition.
This will start with working smarter, not harder. The US Military is limited, Hague convention and Geneva conventions regarding combatants and the munitions you can use by laws of land warfare. Short version is using fleshetes, or other non full metal jacket ammo isn't allowed. Since I joined the First Civ Div I figured I would share some info. First, we don't have to use the SMK 77gr round. There are better bullets for long range shooting as civilians like the Hornady 75 grain A-Max. Second, Make sure your uber experimental loads are checked for signs of pressure. Flattened primers are the first clue. Unlike bolt guns you don't have the ability to feel the stiff bolt lift from an over pressured round in an AR platform rifle. Third chambering reamer used has a large effect on what cartridges will have more pressure. Longer throats allow you to generally run hotter rounds due to more "jump".
This approach will be more trying to mimic the trajectory of a Mk 262 mod 0, I will call my attempts Mk 262 Mod M1n3 (mine). So the bullet I am choosing to use is the Hornady 75 grain A-Max bullet. Why? Because it is less expensive than 77gr SMK, and has a higher BC. Today I was at the sporting goods store and grabbed a box of 100 bullets for 20 bucks. The Ballistic Coefficient is also higher with this round making it shrug the wind better and not requiring as high of muzzle velocity. Some algebra and trig will be used to make the calculated plots for bullet drop and wind drift (10 mph full value wind). The A-Max bullet has a BC of 0.435, vs 0.362 for a SMK (contacted Hornady for clarification on what velocities that BC is valid for). <span style="color: #FFFF00">EDIT- The Amax 75 gr doesn't load to mag length. </span> Swapping the Hornady 75 gr bthp 0.396 G1 BC. Not quite where I wanted to be but still better than the SMK 77gr in terminal performance in theory.
I will save you the calculations. More or less the A-Max can have a muzzle velocity of 2650 for a 600 yard drop of 101.97 inches. The SMK needs an initial velocity of 2746.xx to have similar point of aim / point of impact (within 0.1 inch). Less pressure will make your barrel last longer and sometimes decrease copper fouling. In my experience ramshot tac also burns cleaner than other powders I have used. The bonus is that with the higher BC the A-Max has win drift of 33.xx inches, the SMK has 40.xx inch wind drift at the same wind speed/ direction. Another added bonus is that the Meplat of the A max changes minimally round to round. The SMK round for competition is often trimmed to make the BC more consistent (trimming off the deformed tips).
My expectations, try to see if I can create a round which attempts to favor jumping the lands as the SMK rounds do. (traditionally Berger, lapua and similar target rounds like minimal jump or being jammed into the lands) SMK's seem to not mind jumping over 0.015 into the lands and still maintaining exceptional accuracy. It will be critical for this trait to be mimiced due to the overall length limits imposed by the magazine dimensions.
Bullets tend to have several nodes that they are more accurate at. Finding the velocity node is key to getting good accuracy AND long range ballistics which don't have your bullets tumbling at 800 meters.
The final stage will be tests on a hand full of AR's. 16 inch Noveske N4 (my three gun/ recce rifle), 24 inch DPMS and a 16 inch DPMS(later to be followed by 18 inch woa)The thought behind this is simple. If I can match the trajectory with a 16 inch barrel with less powder it's a win for me. Most testing will be done with cronograph and at ranges from 100-600 meters (my gunclubs max range of 600 isn't always available since it shoots OVER the 200/300 yard lines. So the 600 yard evaluations may take a while). I will do my best to add accuracy notes as shot from my light weight benchrest rig when I get some fixtures machined for adapting an ar to benchrest for repeatable accuracy (I am a scientist, I need to establish controls leave me alone lol) For practical competition you can also load them hotter for even less wind drift at your own risk.
*** By using my loading data you are doing so at your own risk in your rifle. As with all loading start 10% lower and work up***
Components:
-Lake City Once/ twice fired brass with full benchrest prep.
(primer pockets uniformed, Neck sized, neck turned, weight matched etc)
Primers: Rem 7 1/2, CCI BR4, <span style="text-decoration: underline">CCI 450 Mag</span>
Powder: <span style="text-decoration: underline">Ramshot tac</span>, compared to varget
Bullet:hornady 75 gr hpbt
Oal: 2.250
Crimp 0, +
Primary rifle to be used Noveske N4 recce (my build)
After reading about people trying to blow their faces up attempting to make a civilian variant of Mk 262 with varying levels of success (one guy was talking about 28 gr of Varget, wtf). Add to that varied loading charts (even the Sierra loading manual version 5) disagrees with other versions of sierra's loading for their and other ar bullets.I thought I would take some time between classes and come up with a combination which you can use commercially available components on the cheap to replicate the velocity and or bullet trace of the Mk 262 Mod 0 match long range ammunition.
This will start with working smarter, not harder. The US Military is limited, Hague convention and Geneva conventions regarding combatants and the munitions you can use by laws of land warfare. Short version is using fleshetes, or other non full metal jacket ammo isn't allowed. Since I joined the First Civ Div I figured I would share some info. First, we don't have to use the SMK 77gr round. There are better bullets for long range shooting as civilians like the Hornady 75 grain A-Max. Second, Make sure your uber experimental loads are checked for signs of pressure. Flattened primers are the first clue. Unlike bolt guns you don't have the ability to feel the stiff bolt lift from an over pressured round in an AR platform rifle. Third chambering reamer used has a large effect on what cartridges will have more pressure. Longer throats allow you to generally run hotter rounds due to more "jump".
This approach will be more trying to mimic the trajectory of a Mk 262 mod 0, I will call my attempts Mk 262 Mod M1n3 (mine). So the bullet I am choosing to use is the Hornady 75 grain A-Max bullet. Why? Because it is less expensive than 77gr SMK, and has a higher BC. Today I was at the sporting goods store and grabbed a box of 100 bullets for 20 bucks. The Ballistic Coefficient is also higher with this round making it shrug the wind better and not requiring as high of muzzle velocity. Some algebra and trig will be used to make the calculated plots for bullet drop and wind drift (10 mph full value wind). The A-Max bullet has a BC of 0.435, vs 0.362 for a SMK (contacted Hornady for clarification on what velocities that BC is valid for). <span style="color: #FFFF00">EDIT- The Amax 75 gr doesn't load to mag length. </span> Swapping the Hornady 75 gr bthp 0.396 G1 BC. Not quite where I wanted to be but still better than the SMK 77gr in terminal performance in theory.
I will save you the calculations. More or less the A-Max can have a muzzle velocity of 2650 for a 600 yard drop of 101.97 inches. The SMK needs an initial velocity of 2746.xx to have similar point of aim / point of impact (within 0.1 inch). Less pressure will make your barrel last longer and sometimes decrease copper fouling. In my experience ramshot tac also burns cleaner than other powders I have used. The bonus is that with the higher BC the A-Max has win drift of 33.xx inches, the SMK has 40.xx inch wind drift at the same wind speed/ direction. Another added bonus is that the Meplat of the A max changes minimally round to round. The SMK round for competition is often trimmed to make the BC more consistent (trimming off the deformed tips).
My expectations, try to see if I can create a round which attempts to favor jumping the lands as the SMK rounds do. (traditionally Berger, lapua and similar target rounds like minimal jump or being jammed into the lands) SMK's seem to not mind jumping over 0.015 into the lands and still maintaining exceptional accuracy. It will be critical for this trait to be mimiced due to the overall length limits imposed by the magazine dimensions.
Bullets tend to have several nodes that they are more accurate at. Finding the velocity node is key to getting good accuracy AND long range ballistics which don't have your bullets tumbling at 800 meters.
The final stage will be tests on a hand full of AR's. 16 inch Noveske N4 (my three gun/ recce rifle), 24 inch DPMS and a 16 inch DPMS(later to be followed by 18 inch woa)The thought behind this is simple. If I can match the trajectory with a 16 inch barrel with less powder it's a win for me. Most testing will be done with cronograph and at ranges from 100-600 meters (my gunclubs max range of 600 isn't always available since it shoots OVER the 200/300 yard lines. So the 600 yard evaluations may take a while). I will do my best to add accuracy notes as shot from my light weight benchrest rig when I get some fixtures machined for adapting an ar to benchrest for repeatable accuracy (I am a scientist, I need to establish controls leave me alone lol) For practical competition you can also load them hotter for even less wind drift at your own risk.
*** By using my loading data you are doing so at your own risk in your rifle. As with all loading start 10% lower and work up***
Components:
-Lake City Once/ twice fired brass with full benchrest prep.
(primer pockets uniformed, Neck sized, neck turned, weight matched etc)
Primers: Rem 7 1/2, CCI BR4, <span style="text-decoration: underline">CCI 450 Mag</span>
Powder: <span style="text-decoration: underline">Ramshot tac</span>, compared to varget
Bullet:hornady 75 gr hpbt
Oal: 2.250
Crimp 0, +
Primary rifle to be used Noveske N4 recce (my build)
