20 practical AR shoots poor from magazine

[hogpatrol]

Just a data point and to each his own, but in over a thousand rounds out of a 20P AR, I've never crimped one and never had a jam, dinged brass, misfire or accuracy issue from not crimping. Brass is Remington and IMI with .002 neck tension, bullets are 32s and 40s, Redding dies. Upper is the ones sold by Robert Whitley, lower is a Del-Ton. I use 10 round magazines only.

 

[Logbuilder35]

Just a data point and to each his own, but in over a thousand rounds out of a 20P AR, I've never crimped one and never had a jam, dinged brass, misfire or accuracy issue. Brass is Remington and IMI with .002 neck tension, bullets are 32s and 40s, Redding dies. Upper is the ones sold by Robert Whitley, lower is a Del-Ton. I use 10 round magazines only.

This thing has me scratching my head,I shot a group in the 3’s with it Sunday feeding one at a time then put a mag in and it opens up to an inch or better,keep the info coming we will get it figured out,thanks.

 

[GrocMax]

Remove the mandrel from a 204 collet neck sizer die and make a spacer (flat washer) or shorten the base of the die .080" to fit 223 neck to shoulder length cases.

 

[Fast14riot]

I had a 24" BHW 20P and never had an issue with accuracy mag feeding from 10rd Pmags. I never crimped. I did run about .003" neck tension with LC brass. I shot 32vmax at 4100, 40vmax at 3800 and 39gr TNT at 3800.

Polish the feed ramps, maybe check the ejection pattern, if on the over gassed side the impulse from the carrier slamming back can also cause bullets to move in the magazine.

 

[Oso]

This thing has me scratching my head,I shot a group in the 3’s with it Sunday feeding one at a time then put a mag in and it opens up to an inch or better,keep the info coming we will get it figured out,thanks.

As some others have mentioned. The fact that the rifle's performance changes dramatically means that something is happening to bullet when being fed from the magazine...it may be the magazine feed or it may be the force/speed of the loading process. You'll need to make some observations to determine if the bullet tips are being deformed (striking the feed ramp), which could lead to inconsistent performance...larger groups. There is also the chance that the change in performance could be result of the changes to the amount of bullet jump, which could be effected by either bullet being pushed back into case when contacting the feed ramp (long jump scenario) or bullet being pushed forward into the lands by the momentum of the BCG slamming forward (short or no jump scenario).

You can do a bolt slam test to check the neck tension. Before you head to the range use your calipers and measure the OAL of several loaded rounds (10-15). Record the measurements on paper as well as writing it with Sharpie on the actual case body (easy to keep track). Load two (2) bullets in your magazine with the first one being a sacrifice round (to be shot) and the second one being a "Measured OAL" round. Insert magazine with 2 rounds and rack the bolt. Fire the first round (sacrifice) and then carefully unload the rifle removing the "Measured OAL" cartridge from the chamber. Now re- measure its OAL, record it and compare to its original starting length. Repeat this process with the other Measured OAL rounds and see if there is any pattern of movement or physical changes to the bullet tips.

If the OAL has increased then the bullet is being pushed forward as the bolt slams the cartridge into the chamber.
If the OAL has decreased then the bullet is being slammed into the feed ramp seating the bullet deeper into the case. Check for irregularities / deformity to the tip of the bullet, which could cause inconsistent performance (aerodynamics) from one shot to the next.
Monkey Wrench - there is always the chance that both of these things are happening in quick succession.


Final Note: Not sure how long you're loading the rounds. I have seen people load near max magazine length, which can cause the bullet to bind or jar against the front of magazine during recoil.

 

[hogpatrol]

This thing has me scratching my head,I shot a group in the 3’s with it Sunday feeding one at a time then put a mag in and it opens up to an inch or better,keep the info coming we will get it figured out,thanks.

What bushing are you using and what's your loaded round diameter?

 

[searcher]

My first .20 Practical barrel was chambered for me by a friend gunsmith who is very proficient in pistol and bolt gun work but had not done many A/R's. My gun jambed each time I released the bolt. Seemed the sharp bullet tip was slamming into a squared shoulder on the extension which has to be properly beveled to otherwise prevent this. I pulled out my Dremel tool and grinded a nice bevel, then polished it. Problem solved. If you are using a good magazine, properly sized ammo in a properly cut and head-spaced chamber, I'd really look at what your bullet is encountering on the way in.

 

[bobcat93]

The 20 practical AR.. Mine shoots like a laser beam.. I had big problems getting it to run with a short barrel.. I messed around for about a year then I took one size drill bit larger then the gas port and opened it up a little (I did put a wooden dowel rod in the barrel before drilling.. THAT FIXED It.. I do have an adjustable gas block that helps also..

Sounds like low gas pressure to me

 

[Coyotefurharvester]

I am hoping when my new barrel shows up and I assemble(have all the other upper parts) that it Will not be over gassed. My guess is almost closed adjustable gas block setting.