Accuracy question?

[Shooter212]

My rifle I built throws the first shot out of the magazine two inches give or take low at fifty yards every time. I can shoot good groups there after. I just don't know what I am missing. The rifle is one I put together out of some salvaged parts and some new. Barrel is a ballistic advantage 18" rifle length gas, the bcg and upper are out of an m&p rifle I bought for my first ar. 

[caspian guy]

How are you loading the first round?

[Shooter212]

Dropping the bolt off the catch. 

[Nathan]

If it is truly your first shot out of every magazine, not you first shot of a session, I’m stumped.  Maybe the extra weight is pulling your rifle down? (Joking).

If it is the first shot of a session or string after a cool-down, my old varmint rig had a similar “tic” to it, albeit not as drastic.  I always wrote it off as the cold bore shot barrel temp vs warm, it was a 24” bull barrel and I figured the heat eliminated some sag or something.  It would shoot .25 moa after the first shot, but my first shot usually looked like a “flyer.”  I eventually learned the hold for cold bore shot.

Just a thought...  I wonder if this could be a fuction of the face of the receiver to barrel connection?  Like possibke contacting more on one side (bottom?) so when the system heats, the expansion is pushing the barrel up?  Maybe true-ing the face would settle this down?

One other thought...  In load development I try not to let my rounds sit in my chamber because many powders will give higher velocity with the warmer temps...  Hard to imagine 2” difference, but higher velocity would shoot higher...

 

Hope you get her figured out!

[DesertTortoise]

If it’s the first shot of the session only, it’s the cold bore shot and that’s the way it goes... 4 MOA is a lot though

If it’s the first shot of every magazine, I have no idea

[Balwolley]

A little more info maybe would be good, optics, rest, ammo. Is the out of a FULL magazine, or just the round that you chamber from an open bolt.  I have noticed a small, very small difference in POI at 100 yds.  I'm talking less than 1/2" difference.  I let that be thought of as how the bolt locks up. I'm not really sure how it's different then letting the bolt pickup the round by using bolt catch vs a fired round.  The bolt travels the same distance, and is being pushed forward by the same spring.  Give us a bit more infor and if we can't help then it sounds like you should just send that rifle to me and just forget you owned it .  

[Shooter212]

Hey guys figured out the problem my scope had let loose on me. Dropping it off the bolt must of threw the scope different. It would group good then move I was chasing zero. Tried the box drill  and it was all over the place. I have a strike eagle and it was in a Burris pepr mount. This is just pure speculation but I talked to a couple other guys with strike eagles and pepr mounts at a match last weekend, and they had to send there's back too. I know a bunch of guys that run these scopes so I don't think that's it. On the pepr there in not that much space between rings. I don't know if that has something to do with it. I ordered a warne mount to try that. 

[Balwolley]

Well, as for vortex..  I've had 5 including the strike eagle.  2 viper PST'  and 2 viper HS-t's.. all were mil mil.  All of them except the eagle have been back to vortex......twice.  Go figure, the one that gets abused the most I guess you could say, has been the most reliable.  I currently only own the strike eagle 1-6 and a HS-T 6-24 ( it's at vortex right now !) I've sold the others at a reasonable loss.  I might be doing the same for the HS-T when it gets back.