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Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
Posted: 7/27/2014 11:34:33 AM EDT
Moving this here in hopes of help:

I have a 300 BLK pistol I just put together. Free float rail.

My first shot is 3-4" high then the rest settle into nice groups. Wait for 15 minutes to shoot another group and 1st shot is high again.

This is an 8" WASP barrel. It was on the very low end of the torque scale so I went to the next hole on the barrel nut-same issue.

I don't ease the first round in- I use the carrier release.

I know about cold bore but this is a stubby little barrel and 3-4" seems like a lot. Scope is tight and using a Larue SPR mount.

Any ideas?
Link Posted: 7/27/2014 1:23:10 PM EDT
[#1]
What distance?  

I have a 20" SAPR that a CCB shot is about 1" high left.   My Savage CCB is about an inch high centered. Both at 100 yards.

If it's repeatable every time you left the barrel cool down then I would lean toward it being a cold bore issue althoug 4" at 100 yards sounds a little much?

Have you tried having someone else shoot it?  Not saying you're doing anything wrong, I just know that personally my first group of a string is usually my worst group of a string.
Link Posted: 7/28/2014 1:22:50 PM EDT
[#2]
I shot my other AR first when I went out again. All in a tight group.

I may pull the barrel and get one of those lapping tools to see if that is part of the problem.
Link Posted: 7/28/2014 1:33:13 PM EDT
[#3]
My guess is it's just a cold bore issue, with the very short barrel length making it more severe on first shot. It sounds like you're a good shot and the fact that it's only on the first shot of a cold bore pretty much eliminates everything else that I can think of. Unless you accidentally align your sight picture differently on first shot lol
Link Posted: 7/28/2014 1:42:53 PM EDT
[#4]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
I shot my other AR first when I went out again. All in a tight group.

I may pull the barrel and get one of those lapping tools to see if that is part of the problem.
View Quote


This is the issue. It is cold bore / sort of related, but either the barrel / extension isn't seated completely, or the receiver isn't squared. Either way, the first shot is warming it up and expanding the metal resulting in a better fit and better groups when warm.


Link Posted: 7/28/2014 8:57:57 PM EDT
[#5]
Link Posted: 7/29/2014 6:15:25 AM EDT
[#6]
Different ammo.  Same issue-first shot high then settle into better groups.  Some loads group better than others once it settles.

Link Posted: 7/29/2014 10:45:10 AM EDT
[#7]
Link Posted: 7/29/2014 10:55:03 AM EDT
[#8]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
You have a tension problem, hence either a barrel bent, or something going on with the upper receiver/barrel install.


Chuck the barrel in a lathe and spin it to see if the barrel is bent.

As for the barrel mounting, could be that the barrel extension is not flush in the face of the upper receiver barrel socket, or you could have bent the upper  receiver barrel socket by over torque'g the barrel nut during the install.
View Quote


The initial install was very low on the torque value.  Thought that was a problem so I torqued to the next gas tube hole.  Same problem.  Truing/ re-facing tool from Midway will be here Friday and I will try that.  
I don't have a lathe to check barrel straightness.
Link Posted: 8/1/2014 7:12:47 PM EDT
[#9]
Thanks for all the thoughts.  

I bought a lapping tool and worked on the front of the receiver.  I was nervous but noticed it was not actually flat/ true.  As the compound was working, I could hear the "high" spot getting worked more until it evened out.  

I also added some Loctite to the barrel extension after seeing that done in several other forums.

A side affect of the lapping was a reduced torque value on the barrel nut.  It was mid range compared to my previous jobs doing this so the lapping slightly reduced what I thought was a bit heavy torque on the nut.

I had just enough time to stop by the range and run 4 rounds between appointments.  4 shots within 1.25 inches at 100 yards.  No flyers or first shot high.  I really need to get back out when I can not rush through.  I feel better but taking a little more time will make me feel better.  All in all, I don't know if it was the "truing" or the barrel torque or the Loctite.  If I had more time I would have forgone the Loctite to see if it mattered.

I did have this in another section and will copy there.

I will update when I can slow down and try it again.  Hope this helps someone else!
Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
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