Question on hand feed versus mag feed accuracy issue

[Luke2236]

probably a newb question but I'm a bolt guy just learning the AR platform so need a little help please

AR10-308. Gas gun. Experiencing the issue with my loads as well as Fed Premium.

My loads are consistently under .70 assuming decent conditions when I single feed with a mag in then release the bolt. If I load the mag then shoot a group from it, the groups double in size. I ran several through manually and checked COL, there was .000 to .001 growth in COL so I don't think that's it. I am noticing 2-3 light-medium scratches on the projectile, could that cause the groups to grow that much?

I also loaded the mag and watched as I slowly let the bolt go forward, does not appear to be catching any lugs when you do it slowly by hand, might not mean diddle versus full speed though I guess.

FYI, I also tried it with multiple mags and two different loads in each mag. It never changes. The only consistent change in group size is mag load versus single feed by hand.

Would appreciate any suggestions gentleman

 

[zulu1delta]

One reason is the jump from the magazine... My LR308 has about .195 jump to the rifling.. Not best for accuracy. I single loaded the same rounds seated .010 off and the groups were very good... I'm getting a barrel made with a short chamber so when seated in the mag the bullets will be about .010 off when chambered. Hopefully, it will be best accuracy and mag fed. We will see.

 

[Tangodown911]

I've often thought the same thing. Perhaps it does something to the concentricity of the round itself. When it's loaded roughly by the bolt versus by hand, said force could be the issue. This would cause an issue in accuracy if the round leaves the case crooked it'll shoot crooked. Not saying this is the case but it's worth a thought. Obviously this doesn't happen in all gas guns because plenty shoot .5" groups from the mag.

 

[mtrmn]

I haven't SEEN it but one of my buddies swears his Armalite AR10 shoots 2 separate groups from the same magazine. One group strips from the left side of the mag and the rounds stripped from the right side form their own group in a different POI. So as he goes through a mag his shots would alternate between 2 different groups on paper.

I know this doesn't help, but it has got me wondering about a couple of my AR's and I will have to do more research into them.