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View Full Version : My Semi Auto precision rifle build and some questions.



Alaskapopo
10-11-2013, 01:14 PM
http://i59.photobucket.com/albums/g299/355sigfan/Semi%20Auto%20rifles/Precisionrifle_zps44c2ccbc.jpg (http://s59.photobucket.com/user/355sigfan/media/Semi%20Auto%20rifles/Precisionrifle_zps44c2ccbc.jpg.html)

This gun has given me some challenges. When I first got the barrel installed it would not cycle. I sent it to ADCO to open the gas port and to pin the gas block on for me. It came back and worked better but still not 100%. I tried a lower mass buffer to help and a lighter buffer spring. But still no joy. I then sent the barrel to Krieger and they opened the port a big more. I went back to a full mass rifle buffer but kept the lighter spring. Rifle ran fine at first but I would get cases stuck in the chamber. The same cases that got stuck would feed and cycle fine in my other AR's. I learned about a small base rifle sizing die and that fixed that problem. Then my zero wandered. I tighten everything on the mount and checked the scope 's zero stop lock screws and after doing that the zero remained good so far knock on wood. I am still getting failures to feed where the bullet nose hangs up on the feed ramp with one of my loads using 77 grain SMK's. The problem got worse the more I shot the rifle. I was thinking it may still not have enough gas but the bolt locked back at the end of the magazine each time with no issues. I tried a full power recoil spring and the problem got worse. Love how its shooting for accuracy now but I need to get the reliability in line. Any ideas.
Also is there any downsides to using a small base dies to size the brass in my other rifles that don't need it. I was thinking of making ammo specific for the Krieger barrels chamber so I don't fix what is not broke with my other ammo for my other AR's. I know this is too much scope for a gun like this but I have the same scope on my precision bolt action build and love it and Vortex does not make another Razor in a more appropriate size (3-15 etc)
Pat

DocGKR
10-12-2013, 03:05 AM
How does it run on quality factory ammo?

Alaskapopo
10-12-2013, 02:19 PM
How does it run on quality factory ammo?

I don't know I really don't have much but I can give it a try. In my other guns my reloads were more accurate than Federal match and had a better velocity spread and standard deviation. The two loads I am using is
24 grains of N140 behind a 77 grain SMK and 21.8 grains of N135 behind a 77 grain SMK velocity on both is about the same around 2650.
pat

DocGKR
10-12-2013, 02:34 PM
I am more concerned about functional reliability than accuracy when using factory ammo--if it runs perfectly on factory ammo, that will rule out any issues with gas, chamber, buffer, etc...

LittleLebowski
10-12-2013, 03:00 PM
Have you tried a different BCG?

Alaskapopo
10-12-2013, 04:41 PM
Have you tried a different BCG?

No just swapped in a new bolt. I could try a different carrier.
Pat

Alaskapopo
10-12-2013, 04:42 PM
I am more concerned about functional reliability than accuracy when using factory ammo--if it runs perfectly on factory ammo, that will rule out any issues with gas, chamber, buffer, etc...

Got it makes sense.
pat

TGS
10-12-2013, 04:45 PM
No just swapped in a new bolt. I could try a different carrier.
Pat

You checked the gas key though, right?

Alaskapopo
10-12-2013, 05:08 PM
You checked the gas key though, right?

Yes its good I staked it myself with a MOAKS tool.
Pat

LittleLebowski
10-12-2013, 05:39 PM
So, it sounds like the problem is the rounds are not being fed at the right angle or the bolt is feeding them with too much force. Can you check magazine seating insofar as to how it compares to known good ARs in your safe?

Maybe it's feeding at the wrong time?

Alaskapopo
10-12-2013, 08:54 PM
So, it sounds like the problem is the rounds are not being fed at the right angle or the bolt is feeding them with too much force. Can you check magazine seating insofar as to how it compares to known good ARs in your safe?

Maybe it's feeding at the wrong time?

I will check. Someone also told me to polish the feed ramps on the barrel extension.
Pat

LittleLebowski
10-12-2013, 09:46 PM
Are the rounds that don't feed getting deformed?

Alaskapopo
10-12-2013, 10:43 PM
Are the rounds that don't feed getting deformed?

No but the bullet is caught on the middle of the feedramp.
Pat

BWT
10-13-2013, 09:13 AM
I assume M4 Feed ramps?

LittleLebowski
10-13-2013, 10:02 AM
Tried different mags?

Odin Bravo One
10-13-2013, 10:38 AM
I would seriously consider Doc's recommendation as the first step......

If that isn't it, then it is at least ruled out. However, it has been my experience with 70's to 80's that if they are not assembled properly, they won't feed properly.

The rest of the suggestions are spit balling, and in order to PID the actual issue, you need to focus on one single thing at a time, and not change multiple elements of the equation at once.

Alaskapopo
10-14-2013, 01:22 AM
I assume M4 Feed ramps?

Nope rifle extension and receiver.
Pat

Alaskapopo
10-15-2013, 08:02 PM
My ammo loaded with the small base die worked great. Only issue that remains is a wandering zero. Going to send the scope in for a check up and try a different mount. What happens is when Ifirst start shooting the group is about 1 inches higher than the zero after 25 rounds or so it starts to walk back down. Good groups but wandering zero. I thought I had it licked by tightening everything but still have the issue.
Pat

MSparks909
10-15-2013, 10:38 PM
Barrel nut torqued to spec? Is it a rifle length gas system? Fixed or adjustable gas system? And I'm assuming it has M4 feed ramps?

As suggested, get 100 rounds or so of XM193/855 and run it through. See how that goes. Also, what's your OAL on your 77gr. loads? Anywhere close to max OAL?

Alaskapopo
10-16-2013, 01:34 AM
Barrel nut torqued to spec? Is it a rifle length gas system? Fixed or adjustable gas system? And I'm assuming it has M4 feed ramps?

As suggested, get 100 rounds or so of XM193/855 and run it through. See how that goes. Also, what's your OAL on your 77gr. loads? Anywhere close to max OAL?

As I said earlier no m4 feedramps this is a rifle build. OAL is under max on ammo, Barrel nut torqued to 40 pounds. Thinking about increasing that. Gun functions now for reliability as of today after using small base sizing die. Fixed gas system. Do have wandering zero. I wonder if that could be a function of the barrel nut torque.
Pat

Alaskapopo
10-16-2013, 03:35 PM
update on the zero moving issue. Called Vortex and described my problem and they guessed which scope mount I had. They told me that mount does not work well with their scope. I ordered a JP mount which is built around the Razor based on their suggestion.
pat

Alaskapopo
10-29-2013, 03:13 AM
Got the new JP mount. I like it better as the scope is lower to the bore and more where I am used to it being vs the ADM mount. Still reliable. Accuracy today was .65 moa. Will post a pic later.
pat