Precision or accuracy issues when

[308sako]

When allowing rounds to feed in the semi cycle accuracy suffers greatly. It appears that a cut or scratching on the bullet jacket is being made by contact to the barrel extension during clambering.

What or how can this problem be resolved?

Thank you.

[markm]

We get great results out of our gas guns. Is this a specific weapon issue that you've narrowed by single loading vs. semi auto feed?

Scratches shouldn't impact accuracy... but if the gun is knocking the bullet out of concentricity you might have a problem.

[308sako]

Yes this is a specific rifle which is showing this, and yes I have proven that the rifle shoots accurately(precisely) when being single loaded with the same ammunition which fails the magazine feed test.

[An Undocumented Worker]

Can we get pics of the feedramps and barrel extension?
And what ammo are you using to test this with, and is it factory ammo, or handloads. If handloads, tell us more about em.

[308sako]

Can't do pictures of the inner workings right now, but the ammunition is handloaded with Sierra 77 grain MK's a in new Winchester brass with Federal 205 Match primers, loaded length AVERAGE 2.257" COL

Firing at 400 yards this ammunition shot under 1/2 MOA in my Colt and just under 1 MOA with the questionable rifle (when single loaded) but near 3 MOA when magazine fed.

On the road now and will be a week before I can do the pictures.

[An Undocumented Worker]

Take a handfull of rounds and measure the overall length of them, load em into a mag. Fire off the first round under normal cycling. Pull the next round out of the chamber after it has cycled into the chamber, and set it aside do this with every other round untill you have five or so rounds set aside that have cycled into the chamber via the action cycling under gas pressure.

Then measure the overall length of these rounds and see how they compare to the previous measurments.

I think the feedramps may be hanging up on the open tips of the rounds and possibly setting them back. You may not have enough case neck tension on the rounds.

The other thing to check is take one of the rounds and drag the tip of one across the feedramps as though the rifle were cycling them in there and check to see if they try to hang up at any point.

[308sako]

Thanks, will try this approach ASAP, neck tension is .0025" as to sized with bushing versus loaded round neck diameter. Case is 102% + of powder according to QL.