I have always been of that assumption, namely since 16" .308 rifles have become "in vogue". You know, the SOCOM M1A, shorty FAL's, Saiga carbines, etc. I have always felt that 18" is about as low as you want to go with a .308 and still retain decent ballistic performance. My over-simplified assumption was that a 16" tube basically turned the .308 into a "heavy" 7.62x39. But is this true? A standard, mil-spec 147-150gr FMJ does what, ~2750fps from a full-sized M14/M1A? What would a similar round do out of a 16" barrel? Is there still enough "oomph", if you will, to make it a better (and in most cases a more expensive) choice than 7.63x39? I'm not talking about 800 meter kills here, say out to 300 meters. What say GlockTalk?
This is a good topic, and I myself never cared at all for short barreled rifles in the least... The .308 and it's case design will probably be affected less than other high powered rifles with long cases and sharp shoulders, but there will still inherently be some velocity loss... I guess we'd have to see some chronograph data to be sure, but I gonna take a guess and say that the velocity would be around 100 fps less than a typical hunting rifle... That's still strong enough for 300 yard kills with accurate bullet placement on deer size game, and still a good bit stronger than a 7.62x39...
When comparing to a standard M1A, keep one thing in mind...the M1A is still just a 22" barrel, as opposed to most hunting rifles which typically have 24" barrels. The 147gr/150gr bullet clocking 2750fps from the standard M1A barrel will most likely be moving at least 300fps slower when fired from the 16" tube. Still fairly potent performance, but I would still rather have a little more punch than that for a 300yd shot. The *general* rule of thumb ( there are exceptions ) is that you can expect to lose roughly 50fps per inch barrel length shortened.
In a case design like the .308 and it's typical velocity loss per inch will likely be around 15-20 fps... In a real agressive case design and extreme velocities loss may approach 50 fps, but usually in very high powder weight per caliber ratio's like the super screamer varmint rounds... It's unlikely to be that pronounced in a .308..
