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Post by selectw on Jun 6, 2015 10:54:37 GMT -8
I'm working on a 6mm Creedmoor build using an Aero upper and Blackhole barrel. I have two issues: 1. the tip of the bullet (Berger 105gr) is striking the throat of the barrel, preventing feeding Here's a picture i.imgur.com/3x8PTaZ.jpg<a href="http://imgur.com/3x8PTaZ"><img src="http://i.imgur.com/3x8PTaZ.jpg" title="source: imgur.com" /></a> 2. the case is being badly dented by the feed ramp during feeding Here's a picture i.imgur.com/uqDhDfB.jpg<a href="http://imgur.com/uqDhDfB"><img src="http://i.imgur.com/uqDhDfB.jpg" title="source: imgur.com" /></a> There is a pronounced ridge between the barrel feed ramp and upper, that you can see here: i.imgur.com/Hjfq6Kz.jpg<a href="http://imgur.com/Hjfq6Kz"><img src="http://i.imgur.com/Hjfq6Kz.jpg" title="source: imgur.com" /></a> I tried different mags, and different cartridge OALs, neither of which helped. Do I have a bad barrel? Theories? Suggestions? Thanks for the help |
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Post by GLSHOOTER on Jun 6, 2015 11:10:16 GMT -8
Ritch has an AR10 perhaps he can chime in. I don't know enough about them to speak with any authority on the feeding of them. . What little I've read would have me thinking the magazines are riding too low n the lower or that the lips need tweaked to let the round set higher.
Out of curiosity what brand is the lower?
Greg
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Post by selectw on Jun 6, 2015 11:24:50 GMT -8
DPMS lower.
I do have an Aero lower to build up if that's a potential solution.
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Deleted
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Post by Deleted on Jun 6, 2015 12:50:40 GMT -8
I can't tell for sure, but it looks like your magazine needs to have the feed rails opened up on the front end. The loaded round is sitting to flat in relation to the chamber. It needs to be pitched up slightly.
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Post by selectw on Jun 6, 2015 14:18:20 GMT -8
I tried 4 different mags, all of which work fine with the .308 upper I also have.
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Post by GLSHOOTER on Jun 6, 2015 14:28:38 GMT -8
Possibly since it's a shorter round it is going have to rotate and come up faster as it exits the magazine lips. We see that in the 264 LBC vs the 6.8. Just supposition on my part but my logic is kicking in and that is dangerous.
Greg
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Post by selectw on Jun 6, 2015 22:20:40 GMT -8
The more I look at the way rounds are (not) feeding, the more convinced I am that there is an issue with the barrel feed ramp angle and/or the barrel chamfer.
I have also tried different OALs and different feed lip angles (tilting the mags). The bullets are not even close to feeding.
I think I need to send the barrel back to BlackHole to fix it.
I wonder what bullet profile BH used in testing their 6mm Creedmoor barrels?
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Deleted
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Post by Deleted on Jun 7, 2015 5:45:14 GMT -8
Your feed ramps are fine. You are trying to feed at the WRONG angle. Open the front of the feed lips on your magazine. The round is sitting to flat. It needs more angle toward the chamber. The other problem is: VLD bullets are hard to feed from any AR style magazine. This happens in both AR 15's and AR 10's. The bullet actually gets caught and wedges it's self between the lugs on the feed ramps.
The fix is to adjust your magazine so the bullet contacts the feed ramp higher up. You can also open the feed ramps a little with a Dremmel and polish the edges.
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Post by selectw on Jun 7, 2015 15:51:39 GMT -8
I'll give it a try. Does this mean bending the small metal tabs at the front of the magazine upwards a little? Or working on the much larger tabs towards the rear of the mag?
Also, I assume this adjustment is not possible with my polymer Pmags?
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Post by GLSHOOTER on Jun 7, 2015 16:33:39 GMT -8
I'll give it a try. Does this mean bending the small metal tabs at the front of the magazine upwards a little? Or working on the much larger tabs towards the rear of the mag? Also, I assume this adjustment is not possible with my polymer Pmags? Yes you are basically working on the first, front, 1/3 of the magazine feed lips. No need to adjust the back. A link to how it is done. Applicable to your issue. You can also Google Tweaking Feed Lips. 458socomforums.com/index.php?topic=311.0No go on the plastic mags. AFAIK. Greg |
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Post by selectw on Jun 11, 2015 21:11:31 GMT -8
Tweaked feed lips do now have the gun feeding. It took quite a large bend on the forward half of the lips (not the 5/1000 some have mentioned) to get close to the right angle.
I fired 10 test rounds at the range and found the neck of the brass was being gouged by the lugs. I took the barrel off and filed the high points off the lugs, which fixed that problem.
However, I am still seeing the tip of the 105 bullet being dinged as it feeds. This may be caused by the barrel extension chamfer, or by the lugs. It's not affecting feeding, but is sure to affect accuracy. Any suggestions?
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Post by GLSHOOTER on Jun 12, 2015 5:31:52 GMT -8
You might let copper wash build up on the lugs and see where they are hitting. I know I routinely round the back edges of the lugs on mine any time I start getting markings/scratches on the bullet.
That tweak amount will vary from gun to gun and mag to mag. The big frame guns have varied heights in the magazine height up in the top as the catches are all over the place and so are the cuts on the body. Obviously that will change the tweak somewhat.
I'm looking forward to an accuracy report.
Greg
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Post by selectw on Jun 12, 2015 17:20:55 GMT -8
I shot two groups today at 100 yards as part of the continued function testing of the rifle. I do not think I was shooting well, and didn't take a lot of time over it:
Group 1: .637" ctc, 5 rounds
Group 2: .186" ctc, 3 rounds
This was with 105 Bergers, 41.2gr H4350, 2.782 OAL, once fired Hornady brass, FGMM primers
So, the rifle has accuracy potential.
I've tweaked the feed lips on two mags. They fed with the exception of the first round which jammed on the chamfer on the end of the barrel. I'm not sure why this happened.
I am seeing two light score lines on the case neck, which are probably from extraction. I could take the barrel off again and do some more filing of the back side of the lugs. Its not bad, and may go away as the rifle wears in.
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Post by GLSHOOTER on Jun 12, 2015 18:28:52 GMT -8
I just reach in with a dremel and a cratex polishing point to break the edges.
Greg
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Post by selectw on Jun 13, 2015 9:34:41 GMT -8
I will do that.
The remaining issue I have is that extraction is REALLY hard.
Whether it's a new round (Copper Creek), a reload using a new case, a reload with a once fired case, or just a new case, I can't get it out without tapping the buttstock on the ground.
I've thoroughly cleaned the chamber.
Is it possible that the chamber is too tight?
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