Gas piston AR accuracy ... results from the range.

[MCMXI]

This is a continuation of sorts to THIS thread where I wanted to debunk the notion that gas piston (GP) ARs are significantly less accurate than DI ARs. I haven't seen a lot of accuracy data for ARs based on the .308 Winchester cartridge but my objective has been to show that my POF P-308 is capable of consistently shooting under 1 MOA under real-world conditions i.e. all rounds fed from the magazine (no single loading). I won't claim to be there yet but I'm definitely heading in the right direction. Today I shot four loads at the range at 100 yards prone with a bipod and rear bag. A shooting buddy made the interesting point that semi-autos require more "finesse" than bolt action rifles and I agree with him on this.

As for the loads, I'm trying to use up a box of SMK 168gr HPBT "moly" bullets. I bought them a couple of years ago and want to get rid of them. The brass is new and I didn't prep it (no sorting by weight either) other than make sure the case necks were round. I did measure the headspacing of the brass which was all around SAAMI - 0.002" and my POF chamber is SAAMI + 0.005" so there's quite a bit of case expansion going on. I shot 45 rounds today and the rifle and MAGPUL magazines performed flawlessly with zero issues ... this POF is a joy to shoot. The velocity data is disappointing so I plan on making up the next loads using once-fired cases. I'll neck size and bump the shoulder back 0.002" - 0.004". I'll also try sorting the cases by weight. Ultimately, I just want to see what the maximum potential of the rifle is. Once I know that, I may decide to give up some accuracy for the sake of reliability if it becomes an issue. Without further ado ... here are four targets shot "round-robin" this afternoon. Two groups are easily sub MOA.

 

[UT PROSIM]

how long is the barrel on your rifle? i shoot 44.0gr of varget with 168gr bergers and they average 2740 fps in my 24" barrel 308 savage.

great groups by the way, how much did your rifle cost? im thinking about a semi 308

 

[FlyinBryan]

VERY NICE SHOOTING!!! (as ive come to expect from you)

were you crunching that varget on those loads with 45.7g? does varget require compressing in any varget/308 combination?

i ask because the group size on that target appears to have responded the way my loads always seem to do once ive reached a bullet length that requires crunching it in. (my compressed loads always seem to tighten up (dont know why, but they always actually seem to head south as i go up in bullet weight, then when i finally have to compress, its like i flipped a switch)

 

[MCMXI]

how long is the barrel on your rifle? i shoot 44.0gr of varget with 168gr bergers and they average 2740 fps in my 24" barrel 308 savage. great groups by the way, how much did your rifle cost? im thinking about a semi 308

The barrel is 20", it's a semi-auto and the bullets are moly coated so those factors may help to explain the slower average velocities. The rifle was $2600 (see photo below - scope swapped for a FFP Mark 4 3.5-10x). What chronograph are you using? I'm using a CED M2 these days which reports my loads as being quite a bit slower than the Shooting Chrony I was using before. Not sure which is right though but the CED M2 sensors are much further apart so I would think (hope) that the CED M2 is more accurate.

I also shot 20 rounds of American Eagle 150gr FMJ BT out of a 16.25" barreled DSA SA58 FAL PARA yesterday. Ten rounds of that same ammunition had an average velocity of 2,799 fps out of my 25" Krieger barrel (bolt action) but wasn't much over 2,500 fps out of the 16.25" barrel. We can probably assume a 20 fps loss per inch.

were you crunching that varget on those loads with 45.7g? does varget require compressing in any varget/308 combination?

i ask because the group size on that target appears to have responded the way my loads always seem to do once ive reached a bullet length that requires crunching it in. (my compressed loads always seem to tighten up (dont know why, but they always actually seem to head south as i go up in bullet weight, then when i finally have to compress, its like i flipped a switch)

With new Winchester brass the powder is just starting to be compressed at 45.7gr ... but only very slightly and not consistently. Another 0.3gr and I bet every one would crunch. Like you I've found compressed loads to be very accurate.

 

[UT PROSIM]

1858, to be honest i dont know what type of crony it was, its my uncles but it seemed to match up well with what the reloading manuals were saying.

i didnt know compressed loads with varget were more accurate, might have to do some more load testing now. i have been able to get 2 different loads to shoot under .25" at 100 yards but i stopped cranking up the charge at 44.4gr because the groups were not getting any better, but i might have to load a few at 45.5 -46.0 (the max for my nosler manual) and see if they do any better.
But i think i am the weakest link in the accuracy chain for my rifle set up, so we'll see

 

[MCMXI]

i didnt know compressed loads with varget were more accurate, might have to do some more load testing now.

My favorite (most accurate) .223 load is 25.0gr of Varget and a 77gr SMK HPBT ... that load is compressed. I can't make a general statement about Varget and accuracy with compressed loads, but I know what works for me and my rifles. .308 semi-autos are a different animal compared to .223 ARs or .308 bolt guns, both in terms of what they like and how they shoot. I think they're less forgiving in many ways and that makes them harder to shoot accurately and consistently.

 

[FlyinBryan]

my relative success with crunching varget was also with .223.

it really gave me the heeby-jeebies to crunch it when i first started loading, even though i knew it was not uncommon to do it. LOL, it seemed louder when i first started, i would grimace and turn my head away at the top of the ram stroke!!! (im used to it now)

 

[Casefull]

My RRA 308 with 16 inch standard barrel groups like that with a 4x12 leupold rifleman scope and 150 g remington fmj rounds. I think your rifle is accurate and it is a lot prettier than my plane jane. Mine only cost $1175 though. Mine shoots best with full power loads as do my 223 rifles.