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There may be more to the story than two grooves don't like boattails. Two groove barrels were wartime expedients that saved time and were found to have sufficient accuracy for the intended purpose. Flat base bullets are thought to "fit" better in barrels that may have some wear or just oversize dimensions. Boattail bullets were a post WW1 (for the USA) method to extend the range of 30 caliber weapons. The M1 30-06 round was the result. I do not have enough experience to refute or confirm the bullet type that a two groove barrel likes. I know there are plenty of M1903a3 sniper rifles that consistently shoot Sierra Matchkings quite well with their two groove barrels based on CMP scores. Only your rifle will tell you what it likes and if its accuracy is not up to par with a particular bullet, I would try another before I started looking for other reasons (stock fit, screw tightness, bedding etc.). I my experience, my as issued 5-groove barrel prefers a bullet that is more like 0.309-0.310" regardless of base type but it shoots OK with 0.308" bullets.
I stumbled upon the 2 groove / flat based VS 5 groove/ BT issue on my own. I was not satisfied with the way my BT were grouping so I tried FB & that was the ticket. It wasn't until years later that I had read posts from others with like experience. Dave, I think you are correct on the fit issue. My guess is the FB bullets obturate at the base better and thusly seal the gases better in a worn bore. My M1917 is extremely accurate w/ the FB Hornady's. That might be because my rifle has Elmer Keith's cartouche on it!
I had a OGEK M1903 Double Heat treat 1919 in my hands for a hot minute (gosh was it sweet). Guy decides to keep it when I show some interest. Tried for years to get it. He used to strap it to his ATV for Deer hunting. I went as far as $500 and a new Savage 30-06 with at scope to hunt with. Had some unusual bond with it. He passes and gives it to my ranch foreman, who again decides to safe queen it. Oh well, as they say: It was just another rifle...
I have found that after years of reloading for both my M1917 and P14 that they both perfer FB bullets. The '17 is an unissued 12/18 build that had an original pristine 5 groove barrel when I bought it 37 years ago and still is in excellent shape. The P14 not nearly as mint but a very serviceable original barrel. I saw my groups tighten up by about 1/8" in the '17 with the FB .308 bullets achieving sub moa. The P14 which doesn't shoot nearly as tightly still closed it up by a 1/4" with FB .312 diameter bullets now shooting nearly moa.
Most rifles of WW1 and WW2 shoot the Flat Based bullets much better. US, GB, German or Japan their rifles do better with the FB. Now a heavier BT will shoot well in many of these rifles but not all. I think it was the slower velocity allowed the BT time to stabile in the rifling. My Japanese type 38 would shoot 160 RN ok but not the BT
version as it would not group worth while. But my type 38 carbine will shoot 140 FB into 2 inches at 200 yards.
PM
Originally Posted by ArtPahl
