Re: So what .338LM Barrel Length
This discussion suggests that when you cut your barrel you lose about 100 fps per inch removed. <span style="font-style: italic">This is for Magnum rounds which 338LM is, 50-75 fps for 308 ilk, and 35-50 fps for slower bullets.</span> In practice (quoting from
here - based on 308) the loss of velocity would probably be less:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The 150-grain Sierra Game King, starting out at 2,905fps, generates 2,812ft/lb energy and only suffers a 157fps loss for a barrel reduction of 6in. That seems very efficient to me and certainly justifies reducing a .308 barrel to 18in, as there is little loss in velocity. Muzzle blast may increase, but a sound moderator will take care of that, replacing the length and weight of the rifle before it got the 'chop' and adding all the benefits of its inclusion.</div></div>
Lilja, discussing 50BMG barrel length, talks about 15-20 fps per inch (and mentions LeDuc's equations that could be used for precise calculations).
Clearly, the higher your muzzle velocity is - the longer your bullet will stay supersonic (longer reach). So if you want to squeeze every last fps - the longest barrel would be the answer. When practical considerations enter - by how much would the reach increase and whether it is worth the extra inconvenience of the longer and heavier barrel -
JBM online calculator is your friend: key in the velocity you expect to get from a given barrel (and load) and see whether you're happy with the trajectory.
Having said all that - most people would probably agree that 26" is a good enough compromise for 338LM ("good enough" reach with a "portable enough" platform).
