Rifle accuracy with different bullets

[Ammo Junky]

I know it is no shock to see difference perfromance in a rifle with different bullets wts, but I found this interesting, so Ill share it. I am working up a load for a rem sps 308. I an using x1 fl rem brass, wlr primers, varget powder and sierra game king bullets, loaded to 2.790" both 150 and 165gr. The 165 shot consistant moa groups over a range of powder charges. The 150gr consistantly shot 2moa over a range of charges with a singel 1" group. I was suprised to see the groups grow to double with only a change in bullet wt. The bullet was the same brand type and loaded with the same powder and cases. You just never know what variable is gona make a difference in a particular gun / load. I have found the 165gk to shoot better than many in 308 and 3006 most of the time. It shoots as good as a 168mk at 100 and seems to only give up 1/8 or 1/4moa at longer ranges and is much more felxable in its use. I had a box of hornaday 165spbt that wouldnt shoot under 21/2" from any gun. I would like to hear the accuracy changes you guys have seen between bullets.
AJ

[30Cal]

I've found that accuracy is 95% bullet choice and the rest only makes a small difference.

[Unclenick]

The shorter bullets can tip more easily in the bore, making it more important that you hold their cartridge runout down. They also get tipped more easily when you run them up a loading ramp because they don't have as much neck gripping them. Try sorting your reloads with a runout gauge, marking the high point with a Sharpie. Only shoot those with 0.002" runout or less in your test. I find the Redding Competition Bullet Seating die ensures this level of precision if your case necks are no more tha 0.002" thicker on one side than the other. Test the loads singly and give the high spot the same orientation (top, bottom, whatever) each time, and see what happens? Once you've established the loading and sorting method, you still have to work your powder charge up to a best accuracy sweet spot.

[Wildalaska]

Easiest way to control runout for the lazy among us is to use Lapua brass

WildhelpiminKaliforniaAlaska

[Unclenick]

Lapua and Norma both keep very uniform neck thickness, but that does not control runout by itself. A standard seating die can still introduce a good bit of it. Back when I first started reloading I had one of the old Lyman umbrella type turret presses. That was probably a good worst-case for die alignment setup for a rifle cartridge. Seating 168 grain SMK's in .30-06 with a standard Redding seating die resulted in runout up to 0.008" in LC cases I'd sorted to have no more than 0.002" neck wall thickness variation. After switching to the Redding Competition Bullet Seating die, the runnout reduced to that caused by the case wall thickness. In a perfectly even case neck, I am hard put to measure even a half thousandth runout in bullets seated with that die.

The problem with runout is it causes the bullet to go down the bore tipped at a slight angle. The out-of-print NRA Handloading book includes the results of a study of M72 match ammunition done in 1960. This cartridge fired a 173 grain boattail FMJ match bullet. Not as good as the 175 grain SMK made now, but not a bad bullet, either. The guys doing the test measured runout and marked the high spots as I mentioned above. They would have been firing from a national match accurized M1 Garand. They sorted and fired 829 rounds in 0.001" runout increments. They found that each 0.001" of runout caused about 0.25 m.o.a. of group size increase on the target with that bullet. Above 0.004" runout, nor further group deterioration occurred because the bullet would straghten out any greater runout as it fired. A shorter version of that same bullet presumably could tip more in the bore without straightening out.

[MrGee]

[ loaded to 2.790" both 150 and 165gr. ]
the ogive measurement is different on both bullets, possibly one is making a smoother jump from neck to rifling, also your building more area into the case with the shorter bullet ~ at a guess

[Unclenick]

Volume in the case should be fixed by adjusting the powder charge. The ogive difference is a good point. To get best accuracy you have to find both a powder charge and a seating depth sweet spot. Often the seating depth sweet spot is too far out to fit a magazine, but you may find a second sweet spot for a given load, that isn't quite as good but better than most and is closer in. If you are going to use a magazine, you want to find the greatest OAL it will tolerate, and then make sure this is safe with your bullet (not jammed onto the lands), then experiment with seating below that point to see if you identify an accuracy increase.

I would also experiment with the Lee Factory Crimp die. It slightly indents the bullets, but improves start pressure consistency and immunity to feed ramp bumping. You find a similar crimp in most military ammunition. It may or may not improve accuracy with a particular bullet, so you need to try it to find out if it will in your particular case?

I would also investigate Dan Newberry’s optimum charge weight concept and ladder shooting.

[Ammo Junky]

UN, you could be on to something on bullet tip and bearing surface. This gun being a rem 308 has the lawyer throat :barf: . As such it is jumping well over .100" at mag length. The longer bearing surface may be a factor. I was not too sad as I really like the 165gk and use it in several other rifles.

+1 on the redding comp seaters.

How offten do you guys find that your gun shoots x number of bullets fairly well, but one or two much better or much worse? I had an 223 adl (first rifle I ever loaded for) that shot most anything into 11/4" consistantly. I tested a LOT of different powders and bullets in that rifle. In part becaus I had no system or prejudice for bullets etc. I found it liked short bullets best, probably becaus of the 1/12" twist. It shot 50gr tnt well and 55 hornady sxsp into 5 shot 3/4" groups. My win stelth 223 which has shot many 1/2" 5 shot groups with vmax of varied wt and varied powders, wont put tnt's under 2". Agian probably do to twist 9" in this case.