Semi auto neck tension

[Bull81]

just curious what you fellas opinion is regarding neck tension for semi auto rifles (AR 15 mainly). I usually have good results with my bolt guns with around 1 to 1.5 thousands neck tension. I have a good load sorted out for a precision AR but no matter what powder combo or charge weight I can't seem to bring the SD's down to what I like to see there's always one or two rounds out of 10 that will vary enough to throw my SD's up above 10fps usually closer to 15. I thought about reducing the neck tension and running a light crimp to try and help remedy this problem. Any thought from the hide?

 

[digrazir]

I like to run about .005 in a gas gun to prevent the bullet from accidentally get jammed deeper in the case causing an over pressure situation. Safety, function and accuracy in that order with a semi-auto. I discard semi-auto brass after 3 firings. Nothing wrong with your SDs being 15fps...Ray

 

[wxl]

For my M1A using LC brass I prefer ~0.004" tension

 

[918v]

You should increase, not reduce, neck tension for a semi auto otherwise the bullets will set back during feeding.

 

[GhengisAhn175]

Test different neck tensions until you don't get setback from chambering

what works for one person necessarily won't work for the other due to buffer spring, mass of BCG, etc

 

[Bull81]

I'm getting good results now with about .002 neck tension and a light crimp. Brought my SD's down to 7.2 for 15 rounds. Thanks for the replies fellas

 

[redbullitt]

.004 here in my ar 10. Same for ar 15 generally. No issues.

 

[JCCinOhio]

I've been trying .003" with a light crimp, or .004 and no crimp, still playing around with what works best.. but in both my ar-15 and .308 ar I was having the opposite problem of setback, the OAL was increasing when the round was chambered. I guess the action that would push the bullet back would be the BCG pushing it into the feed ramp. Maybe I have good feed ramps, dunno. But what's making the OAL grow is that last thrust of the BCG throwing the round in the chamber and it coming to a dead halt. Kind of like an impact bullet puller. I'd load two rounds, shoot the first, and let the second chamber, then take it out and measure it. Had a few expand .010" from chambering in the .308 (massive BCG). That was with .002" neck tension. Factory rounds also grow about .002 -.005" in the .308, and .001-.002" in the AR-15 (some brands, not all).

 

[Niles Coyote]

I tried stopping bullet movement in my 6.5 Creedmoor last match season and came to the conclusion no amount of neck tension was going to stop movement. What I did find is that with .002-.003"neck tension and a very light crimp with a lee factory crimp die will keep the bullet slip consistent and fliers stopped.

 

[918v]

There is more to neck tension and bullet pull than just the diameter. What affects bullet pull Just as much are the condition of the inner neck surface, neck hardness, and the direction of brass springback.

 

[mpk1996]

i'm running between 4-5 thou depending on the cartridge. I think the 1.5-2 is too light for a gas gun. of course the chance of it getting stuck is pretty small being limited to AR mag length rather than the longer AICS or single loading. I actually think there is more of a chance of the bullet getting shoved it while feeding into the chamber. but, the result is the same, you need more tension (or crimp)

 

[RA223MM]

Is this the neck tension you are using for your precision semis or just for plinking?

 

[BigBlastin300win]

Sorry to kick and old thread but I am in the same boat. When I let the bolt catch go it will seat the bullet 0.001 longer. I have right at 0.003 neck tension. I really dont want to crimp. Im hoping my adjustable block will help is cycle smoother.....seeing as I never like hitting the bolt catch I pull the charing handle back and do it that way. First time loading a gasser any help would be appreciated

 

[918v]

.001” is inconsequential

 

[Feniks Technologies]

Sorry to kick and old thread but I am in the same boat. When I let the bolt catch go it will seat the bullet 0.001 longer. I have right at 0.003 neck tension. I really dont want to crimp. Im hoping my adjustable block will help is cycle smoother.....seeing as I never like hitting the bolt catch I pull the charing handle back and do it that way. First time loading a gasser any help would be appreciated

Ya, as stated, .001 won’t matter. Especially if it’s consistently doing the same.

 

[LakuNoc]

Have same issues.
When i let bolt go my bullet will go forward .003 sometimes .002 sometimes .004 this is 6.5CM with .003 neck tension.
Any idea why is doing this?

Any help appreciated

 

[LakuNoc]

Sorry to kick and old thread but I am in the same boat. When I let the bolt catch go it will seat the bullet 0.001 longer. I have right at 0.003 neck tension. I really dont want to crimp. Im hoping my adjustable block will help is cycle smoother.....seeing as I never like hitting the bolt catch I pull the charing handle back and do it that way. First time loading a gasser any help would be appreciated

Did you ever figure this issue out?