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> External Ballistic Performance of Fresh or Fireformed Brass
External Ballistic Performance of Fresh or Fireformed Brass
@ 10:19 pm (GMT) |
deerndingoNathan,In my last question about the use FL resized brass and its ability to take heavier loads due to absorbing the peak of the pressure curve, do reloading manuals use fresh brass or fireformed brass. As I have found with both my 22-250 and the 270-308 that there can be a difference in performance between fresh and fireformed loads, do ammunition manufacturers take advantage of the same and get more out of their fresh rounds than reloaders do out of typically fireformed brass. Is an example of this the performance of factory loaded compared to handloaded 270WSM. Thanks for your input. |
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@ 10:26 am (GMT) |
Nathan FosterRe: External Ballistic Performance of Fresh or Fireformed BrassHi deerndingo, no, the powder manufacturers do not take this into account. When developing loads, you will see that for one cartridge, lets say .308 Winchester, there will have been atleast 160 variations tried though the test barrel. Considering that the cases must be hand loaded to perform these tests, resizing is a natural part of the operation.A few things to bare in mind. Some manufacturers have no data of their own. For example, Hodgdon rely solely on ADI/Thales (Australia defense industries) for data on powders supplied to Hodgdon. The reloading manuals for Hodgdon and ADI are interchangeable. That said, Hodgdon have data developed for their own spherical powder range. Manufacturers will often try to utilize tight chamber dimensioned test barrels. This is very important as occasionally, a user will come across a sporting rifle of tight chamber/throat dimensions and will reach maximum pressures with mid point loads. Brass brand is another factor. For example, while discussing factory load development for the .308 Win with an ammo manufacturer recently, the manager described how their powder supplier ADI were very much against using what is traditionally an accurate yet mild load in the .308 Win- a 165-168gr bullet driven with 43.5 grains of 2206H (H4895). While this load is usually mild in sporting rifles with the upper sweet spot being 44.5 grains, ADI call the normally mild 43.5 grain load a max load that should be approached with great caution and not utilized by factory ammo makers. This is due to variations in brass thickness from brand to brand, not just chamber dimensions. Quite right too as the manufacturer I was working with, utilized a heavy walled brass that achieved optimum velocities 1.5 grains below the max listed charge. A good example of heavy walled brass would be Hirtenberger or RWS. I think Nick Harvey deserves some special mention. His collection of data from testing rifles for the Australian gun magazines has helped ADI immensely. I noted that there was a time when the ADI manual and Nick Harvey's own published reloading manual were much the same (ADI really owe Nick a public thank you). But in recent years, I have seen ADI drop powder charges (just slightly and with reason), more in line with what I assume is Hodgdon expectations / litigation factors but also with regard to the brass variations mentioned. lastly, I think that more recently there has been a move towards software such as or duplicating quick load which has proven to be safe. This is just an assumption on my part, based on some loads which I think are a bit mismatched. For U.S readers, Nick harvey was a bit like Vernon Speer. Speer really put his sporting rifles through their paces, the Speer No. 11 manual being the 'hottest' manual on the market. But over the years, Nick backed off the loads a bit, just like Vernon. These days, when Nick wants a fast load, he shoots a magnum. |
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@ 07:15 pm (GMT) |
deerndingoRe: External Ballistic Performance of Fresh or Fireformed BrassNathan,Your points are valid and accepted. Manufacturers may not be taking advantage of this phenomenon, but I might. There is still the issue that for a 22-250 a load of 36.8gr of RL15 in Lapua brass topped with so far either a Sierra 1365 or a Hornady SP gives rediculous FPS in fresh brass. The same load in neck sized is too hot. That leaves me wondering if I should just FL resize or even shoulder bump to give the brass some capacity to buffer the peak pressure curve. I'd be left with a load that is more accurate than I can shoot (very thick reticle x 10x Bushnell Firefly) and in a 22 5/8" barrel gives 3650fps. In the Savage it gives 3820fps and groups touch (when I get it right). Given I have only shot about 15 rounds in the T3 rig and maybe 5 in the 12BVSS this year I have a long way to go to shoot either barrell out. Next time I'm going to the range I'm going to photograpgh the chrono readout. |
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