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Posted: 8/18/2010 8:24:55 AM EDT
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When using manuals, whatever - my loads all seem to run 200 FPS slower than what I expect.
Chronoed some factory M855 and it was 3000 FPS +/- so not the chrono. Used another member's Chrony - same thing - 200 FPS slower across the board. Sure - I know I can increase the charge, but . . . is that really a solution? ALL these were weighed on a RCBS chargemaster scale/dispenser and were very close in FPS 2623, 2613, 2631 etc. I'm stumped! TAC - Load data is for a 24" barrel, 1:7 to 1:9 twist and that's where it is I guess. BUT - how the hell can Privi make SS109 run 3,000 FPS out of my LMT Carbine, when I am only getting 2,700 tops on reloads? Another ? Loads are usually assigned a PSI, so for you experienced reloaders - what is an "acceptable" PSI with any given powder? I know to check brass for signs, but when loading - where do YOU draw the line on the barrel pressure? Thanks in advance. Good news is the loads were very consistent and also very accurate (at 25 yards - all I have to test loads). Bad news - I clipped the damned rod on my last batch of reloads that damaged the chrony cosmetically. The post test suggested the "eye" wasn't damaged. |
For your Chrony – I made wood rods that I can shot all day without hurting the Chrony 
Unless you can duplicate each and every factor that was used to test the loads in a manual you cannot possibly expect to duplicate the velocity… Velocity is essentially based on pressure. You have not been able to duplicate the pressure that they have… You do have accuracy and speaking from my experience, the fastest bullet in the world cannot compensate for missing a target 
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What is the length of the barrel you are shooting? You can estimate a loss of 25 fps for every inch of barrel loss, and the number could be even higher.
I'm certain you understand the notion that even though the peak pressure you develop with one of your loads may match that of different ammunition, the work developed may not, so even matching pressure is no guarantee that speed will be matched. One gunpowder may come down from the peak pressure more slowly than another; that gunpowder will generate more speed from the bullet. |
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Quoted:
When using manuals, whatever - my loads all seem to run 200 FPS slower than what I expect. Chronoed some factory M855 and it was 3000 FPS +/- so not the chrono. Used another member's Chrony - same thing - 200 FPS slower across the board. Sure - I know I can increase the charge, but . . . is that really a solution? ALL these were weighed on a RCBS chargemaster scale/dispenser and were very close in FPS 2623, 2613, 2631 etc. I'm stumped! TAC - Load data is for a 24" barrel, 1:7 to 1:9 twist and that's where it is I guess. BUT - how the hell can Privi make SS109 run 3,000 FPS out of my LMT Carbine, when I am only getting 2,700 tops on reloads? Another ? Loads are usually assigned a PSI, so for you experienced reloaders - what is an "acceptable" PSI with any given powder? I know to check brass for signs, but when loading - where do YOU draw the line on the barrel pressure? Thanks in advance. Good news is the loads were very consistent and also very accurate (at 25 yards - all I have to test loads). Bad news - I clipped the damned rod on my last batch of reloads that damaged the chrony cosmetically. The post test suggested the "eye" wasn't damaged. Sir, WADR I'm not sure what your question is. In my experience velocity expectations are based on published data from a manufacturer either in a loading table or on the side of a box of cartridges and were derived from testing done with a specific firearm. Actual chronograph testing with a firearm different from that used by the manufacturer will most often vary significantly from published data. That should come as no surprise to anyone. When I do load testing I consider the velocities published in the loading table as mere guides, the actual velocities I see on my chronograph are the only relavent numbers for my purposes. When I compare factory rated velocities on a factory loaded box of cartridges to actual chronograph velocities I normally dismiss the difference as manufacturers hype that they use to sell their product. In a society where nothing you can buy comes in the small size, only large, extra large, and giant size what else would you expect but the maker to exaggerate a bit! Most hobby reloaders have no actual means of measuring pressures in an internal ballistic sense. AFAIK the only way to actually do that involves the use of strain gages, and such expense usually discourages the hobby reloader. Like most other reloaders I rely on the existance or non-existant of certain indications that reveal that a given load may be approaching the limitations of pressure in my firearm. The usuall suspects such as difficult extraction, primer flattening or cratering, and distorted case rims are all signs that ignition pressures are to high and should be heeded by backing off on that particular volume of powder charge. There is no line in the sand, nor one size that fits all, but a prudent reloader will pay careful attention to detail regarding any indications of excessive pressures. HTH, 7zero1. |
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LMT Carbine 16"
They are using the mythical 1:7 24" barrel still. Mythical barrels must have a very long life I am guessing. 16" vs 24" would explain it. In my limited experience, I don't see how - given what I know - I can even come close to M855 running 3000 fps out of a 16" barrel. On the other hand, they were accurate at what I was able to test them at, and I need to test them at 100 yards. |
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Not uncommon to be off from published data.
Different barrels, different weather conditions/environments, etc. Not an issue for me... I'm off a little all the time from "published" data. I look for low spreads, no signs of high pressure, and good groups. If I get all that within a couple hundred FPS of the "published" data, I'm more than pleased. |
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Quoted:
Quoted:
When using manuals, whatever - my loads all seem to run 200 FPS slower than what I expect. Chronoed some factory M855 and it was 3000 FPS +/- so not the chrono. Used another member's Chrony - same thing - 200 FPS slower across the board. Sure - I know I can increase the charge, but . . . is that really a solution? ALL these were weighed on a RCBS chargemaster scale/dispenser and were very close in FPS 2623, 2613, 2631 etc. I'm stumped! TAC - Load data is for a 24" barrel, 1:7 to 1:9 twist and that's where it is I guess. BUT - how the hell can Privi make SS109 run 3,000 FPS out of my LMT Carbine, when I am only getting 2,700 tops on reloads? Another ? Loads are usually assigned a PSI, so for you experienced reloaders - what is an "acceptable" PSI with any given powder? I know to check brass for signs, but when loading - where do YOU draw the line on the barrel pressure? Thanks in advance. Good news is the loads were very consistent and also very accurate (at 25 yards - all I have to test loads). Bad news - I clipped the damned rod on my last batch of reloads that damaged the chrony cosmetically. The post test suggested the "eye" wasn't damaged. Sir, WADR I'm not sure what your question is. In my experience velocity expectations are based on published data from a manufacturer either in a loading table or on the side of a box of cartridges and were derived from testing done with a specific firearm. Actual chronograph testing with a firearm different from that used by the manufacturer will most often vary significantly from published data. That should come as no surprise to anyone. When I do load testing I consider the velocities published in the loading table as mere guides, the actual velocities I see on my chronograph are the only relavent numbers for my purposes. When I compare factory rated velocities on a factory loaded box of cartridges to actual chronograph velocities I normally dismiss the difference as manufacturers hype that they use to sell their product. In a society where nothing you can buy comes in the small size, only large, extra large, and giant size what else would you expect but the maker to exaggerate a bit! Most hobby reloaders have no actual means of measuring pressures in an internal ballistic sense. AFAIK the only way to actually do that involves the use of strain gages, and such expense usually discourages the hobby reloader. Like most other reloaders I rely on the existance or non-existant of certain indications that reveal that a given load may be approaching the limitations of pressure in my firearm. The usuall suspects such as difficult extraction, primer flattening or cratering, and distorted case rims are all signs that ignition pressures are to high and should be heeded by backing off on that particular volume of powder charge. There is no line in the sand, nor one size that fits all, but a prudent reloader will pay careful attention to detail regarding any indications of excessive pressures. HTH, 7zero1. WADR>?? HTH??? |
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I own several 24" and 26", 1/7 and 1/8 twist, spaceguns (NRA match rifles) they routinely post velocities 100 fps faster than anything I get from a 20" barrel.
I own several 16" and 14.5" barrels with pinned and welded flash hiders, 1/7, 1/8 and 1/9 and they routinely get 200 fps less than my 20" barrels. The match ammo I shoot the most often generates 2550 fps from the 16", 2730 to 2750 from a 20" and 2850 fps from a 24" barrel. All AR's. The load is 24.5 grains of Varget, 69 grain Sierra Match Kings seated @ 2.250", Winchester brass and CCI-BR4 primers. M855 is loaded hot, over SAAMI and about as fast as physics will safely allow. It can't make up for the time in barrel that comes from 24" or 26" tube. The longer the bullet and gasses are trapped, the faster it's going to fly. |
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Quoted:
Some powders will allow higher velocicities. You could always try to get some WC-844, whic hiswhat I believe the military loads M855 with. To get max velocity you have to work up the loads until you see high pressure signs I can see I will have a lot of powder stock soon 
Pressure signs - yep - I got that message loud and clear - about 50x |
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