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I have a new MGM 6.5 Rem. Mag barrel with a 1 in 8 twist I had the throat cut long enough to seat a 140 grain Sierra Gameking bullet and not encroach into the useful powder space. I would like some load data for the 1 in 8 twist. all the reload data I have seen use a 1 in 9 twist for their data. Does anyone have any suggestions? Thanks in advance and keep it nice please. | ||
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You can use the data for the 9 twist, just be careful as you approach the maximum- your 8 twist might develop a little more pressure than a 9 twist, but then barrels are a rule onto themselves and not having the bullet intruding into the powder space changes things. | |||
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Develop your loads with a chronograph. Pressure and speed tend to be much closer in relationship than pressure and load. Whatever bullet weight you choose, do not exceed the maximum speed given by the various recipes for your barrel length and forget about the maximum charge given in these recipes. | |||
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I appreciate the advice rendered from DuaneinND and Gerard. I do have a chronograph and shall put it to use. The problem I see many manuals discount the 6.5 mag as a cartridge just in short action rifles and the I suspect the published velocities are low for this round. In fact one of the ballisticians at Sierra said they discounted the round beyond 120 grains. I thought this odd but I guess I can see their point. Thanks again,  | |||
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The problem with this philosophy is that the same load will give different velocities in different guns and sometimes the slower guns will show signs of pressure long before reaching the maximum load in the books. Minute differences in bore size and finish and chamber size can produce faster/slower bullets at higher/lower pressures. You always have to work up your load while watching for signs of excessive pressure. I look for accuracy and pressure signs and leave the chronograph at home until I have worked up the load. I have never been able to safely achieve the velocities listed in the Sierra manuals as they are typically 200 - 250 fps higher than I get with the same load in my guns. The Speer manual seems to be a lot closer to what my guns actually produce. My guns have 24" barrels for small and medium bores and I have given up the fantasy of getting Sierra velocities from them. Your guns may be able to safely reach those velocities - that is fine but you should remember to warn folks to watch for signs of excessive pressure when trying to get that last 200 fps from a gun that you are not familiar with. A chronograph only measures velocity and the pressure in any gun can be very different from one rifle to another at the same velocity. There are just too many variables to say that a chronograph is a good tool to determine maximum loads. Speer, Sierra, Lyman, Hornady, Hodgdon have reliable reloading data. You won't find it on so and so's web page. | |||
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That is what I said: Load is not a good indication of pressure and speed and pressure go together. Speed goes up, pressure goes up. Speed comes down, pressure comes down. Chronographs do not read pressure. Neither does the eye and pressure signs are deceptive because you may be looking at signs of headspace. The symptoms of headspace and the symptoms of pressure are almost identical The only way to tell what you are looking at, pressure signs or headspace signs, is by measuring the speed of the bullet. If you see pressure/headspace signs and the speed is way under the speed where pressure can be expected, you are looking at headspace. Point is that very few people have access to pressure measuring and just about everyone has access to a chronograph. Pressure/headspace signs are, at best, an indication that you should be measuring rather than looking and feeling. It is possible to have no visible pressure signs and be over pressure. In a lab where pressure as well as speed is measured, both instruments will tell you that the load is too high. The load may not be at maximum but speed and pressure indicates that it is too high. By the same token, I have seen pressure and speed readings that are under maximum where the powder charge is over maximum. So, a chronograph does not measure pressure but it will tell you that the speed is under/at/over what the pressure is likely to be. | |||
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| One of Us |
True It cannot account for the burn rate of the powder selected.
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| one of us |
You are right, a chrono cannot tell what the burn rate of a particular powder might be. The problem is that it is often the only means many reloaders have to ensure safety and reasonableness. Intelligent measurement of a known parameter is always better than intelligent thumbsucking. If one reads the SAAMI specifications and methods for producing ammunition, it is clear that they correlate speed to pressure and set a standard whereby manufacturers must use a powder of the correct burn rate to achieve the standard. Not once does SAAMI or CIP state that one must watch for signs of pressure. They do warn that one must ensure proper headspace. Example: Take a 30-06 and any 165gr jacketed lead core or mono grooved bullet. The maximum pressure that SAAMI allows is 60000psi The Western Powder reloading manual which is available on line lists: Ramshot TAC ----- Nosler Partition - Max speed 2725fps - Pressure 59003 Accurate 2520 ---- Nosler Partition - Max speed 2741fps - Pressure 59664 Accurate 4064 ---- Nosler Partition - Max speed 2836fps - Pressure 59357 Accurate 4064 ---- Barnes MRX ---- Max speed 2855fps - Pressure 59441 Ramshot Big Game - Nosler Partition - Max speed 2900fps - Pressure 59819 Ramshot Big Game - Barnes MRX ---- Max speed 2910fps - Pressure 59731 Accurate 2700 ---- Nosler Partition - Max speed 2890fps - Pressure 59338 Accurate 2700 ---- Barnes MRX ---- Max speed 2913fps - Pressure 59612 Accurate 4350 ---- Nosler Partition - Max speed 2908fps - Pressure 59309 Ramshot Hunter --- Nosler Partition - Max speed 2991fps - Pressure 59840 It would be foolishness for a reloader to use Accurate No. 2 to try and get to 2900fps. The case fill will be way too low and maximum pressure will be seen at around 2100fps. The manufacturer knows this and that is why they do not list it. Any reloader who uses Ramshot TAC and tries to get to the Ramshot Hunter speed of 2991fps is on thin ice. A small amount of intelligent thought is required when a powder is chosen. That is why the manufacturers recommendation should be followed. Manufacturers follow guidelines and measure their products to ensure that they stay within safe parameters. Following their recommendation and using a chronograph in an intelligent way, is the best tools that the average reloader has in order to stay safe. | |||
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One of Us |
I have a 6.5 rem mag that has a Douglas XX 26" #4 contour 1 in 8 twist. It is a rebarrel of a 300 win mag so there is plenty of room in the magazine, not being a short action. I sent a dummy round to the gunsmith when rebarreling that set the long 130 gr Accubond way out there and out of the powder column   I shot 130 AB, 140 GK, 140 Horn Interlocks, 130 TSX, 140 NPT, 125 NPT and 140 TBBC with RL19, RL22, RL25 and H1000 - all with good accuracy and velocities. The gun is not too particular. Loaded for hunting a set of 140 Sierra Game King as they shot well and consistently  DAMN THOSE FLYERS!  First deer I shot with the 140 SGK at about 90 yds ran for about 50 yards with no exit. Where I hunt that is not what you need as you could hunt for a tank within 50 yards of the sendero and have a hard time finding it Went looking for a better bullet and now my load is 130 gr Scirrocco II in front of a stiff load of RL17 with a velocity of 3175 fps. Very consistent and all subsequent game shot have been DRT with full pass thru's and 50 cent size exits. Haven't recovered a bullet yet. Once you find the right seating depth (in my case .060" off) that has the lowest extreme spread and standard deviation in velocity and gives a decent group, load a bunch and go hunting and don't worry about further load development. I haven't worked on that gun in 3 or 4 years  But each gun is different and you should work up to these pictured loads like I did ____________________________________ There are those who would misteach us that to stick in a rut is consistency - and a virtue, and that to climb out of the rut is inconsistency - and a vice. - Mark Twain | Chinese Proverb: When someone shares something of value with you and you benefit from it, you have a moral obligation to share it with others. ___________________________________ | |||
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It makes no difference what the velocity is if the primers are falling out of the case. In addition shooters compare one source with another. When multiple sources are compared there are also many other variables introduced yet the velocity goal may remain the same. There are only 3 criteria you can resonably judge. The load is safe. The load is marginal The load is excessive. None of that comes from a chronograph. It comes by understanding the damage done to the brass when the load is fired.
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Primers could fall out of the case after firing for more reasons than being over pressure. There could be excessive headspace and it may be a rifle fault or a reloading fault. How would you tell whether it is pressure or headspace?
If you do not use a chrono, how would you tell if a load is safe, marginal or excessive? | |||
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