Checking for proper shoulder bump in AR

[fatelvis]

After reading here, how to figure for a proper shoulder bump in a bolt rifle, (thanks to all who contribute teaching) I was wondering the procedure you use for an AR rifle. It doesn’t seem to have the smooth bolt travel like a bolt rifle, (at least in my AR). Should I strip the bolt of ejector and extractor? Should I try a sized piece of brass by riding the bolt home using the buffer spring? Thanks again!

 

[2506]

With the ARs to get them to function properly you probably need to forget about shoulder bump sizing like you can do with a bolt rifle. At least that has been my experience. FL size for reliable function in the slam bang actions.

 

[jepp2]

Should I try a sized piece of brass by riding the bolt home using the buffer spring?

To make sure you have an adequate shoulder bump, I separate the upper and just slide the bolt forward using my finger tip until it closes on the sized brass. I don't find it necessary to remove the ejector or extractor to do this. It is kind of a "feel". But I normally size for around 0.003" from the case head to datum that will give resistance when closing the bolt.

On my AR's, I find the headspace to be remarkably similar. However when I compare that with the range brass I scrounge, there is a lot of variation.

 

[10at6]

I size -3 or 4 thou with a Mo's gauge

 

[Milo 2.0]

If the brass is coming out of your chamber, find a tool to measure the bump needed, bump .003-005" and call it a day.
I watched a guy fire 223 ammo with an 18 thou bump and I was envious of the accuracy I saw downrange from it. Even after wondering how it was even firing.

 

[fatelvis]

The reason I am asking, and it is outlined in another post/question of mine, is that my fired brass’s shoulders are .0135” longer than unfurled factory Fed ammo. After bumping the shoulders .005”, The bolt still didn’t seem to close on the sized brass. This made me think that my testing procedure was wrong.

 

[_Raining]

The reason I am asking, and it is outlined in another post/question of mine, is that my fired brass’s shoulders are .0135” longer than unfurled factory Fed ammo. After bumping the shoulders .005”, The bolt still didn’t seem to close on the sized brass. This made me think that my testing procedure was wrong.

Maybe the base is not sized enough or the die is not long enough to make it to the base of the case without excessively bumping the shoulder. Try measuring the base of the fired brass, sized brass with 5 thou bump, and factory ammo and see what the differences are. I personally won't be able to provide advice based on those numbers as I am not familiar with reloading for semi autos but that info may help someone else provide a better response.

 

[Zero333]

Take the ejectors out and make sure the extractor moves freely over the rim.

 

[fatelvis]

It’s for a 224 Valkyrie, if that has any bearing on the matter.

 

[Richard Coody]

To make sure you have an adequate shoulder bump, I separate the upper and just slide the bolt forward using my finger tip until it closes on the sized brass. I don't find it necessary to remove the ejector or extractor to do this. It is kind of a "feel". But I normally size for around 0.003" from the case head to datum that will give resistance when closing the bolt.

On my AR's, I find the headspace to be remarkably similar. However when I compare that with the range brass I scrounge, there is a lot of variation.

+1 this works

 

[Rsadams]

.003 bump back should do the trick.... I don't load that caliber , but I do use small base dies for extra insurance in automatics especially if used for self defense purposes....

 

[Fast14riot]

I dont load 224V, but I do load for multiple 6.8spc uppers, I use .003" shoulder bump. Loads just fine.

 

[natdscott]

If the brass is coming out of your chamber, find a tool to measure the bump needed, bump .003-005" and call it a day.
I watched a guy fire 223 ammo with an 18 thou bump and I was envious of the accuracy I saw downrange from it. Even after wondering how it was even firing.

Take note here that Milo said he WATCHED a guy firing that stuff, despite itself.

Milo wouldn't lie down behind that kind of thing....

 

[Milo 2.0]

The reason I am asking, and it is outlined in another post/question of mine, is that my fired brass’s shoulders are .0135” longer than unfurled factory Fed ammo. After bumping the shoulders .005”, The bolt still didn’t seem to close on the sized brass. This made me think that my testing procedure was wrong.

.005" may be a little much for Valkyrie brass, no use ruining it. Being it is done, seat 5 bullets in unprimed-unpowdered case, put them in a mag and run the slide like it is supposed to run. I bet it chambers, if not, it is on the base end and a diff set of issues.

 

[searcher]

Yes - you might need short base dies if the shoulder bump was more than what the fired case was measuring. Some people try to test an A/R chambering by "gently" allowing the chamber to close. To function properly - the charging handle needs to be release in the full rear position and allowed to snap forward. That momentum is needed to allow for bolt rotation and proper lockup. That said - I was shooting with a buddy and he said every time he tried to unload live round - it was pulling the bullet and spilling powder in the chamber and trigger group. I measured his fired brass against loaded brass and was surprised to see that each time the bolt slammed forward - it was pushing the over-length shoulders back .006" in order to lock up. It actually created some great shooting ammo, however unsafe it was. Not once did the bolt fail to lock up on the hundreds of rounds he had fired. And that was on a rifle with a "low power" mainspring installed. The point is that the force of bolt momentum when closing will usually push the shoulder forward on an A/R where the brass should have been pushed back a bit more. Naturally - this is likely to happen much more with brass that was not originally fired in your gun and you are sizing to fit your gun when the measuring error occurred. I'm thinking if you fired that brass prior in your gun - let the bolt snap forward as you should - and have a reasonably clean gun -you likely need short base dies.

 

[fatelvis]

I just started sizing brass and checking it in my chamber, as Jepp2 suggested. I needed to grind about .015" off the shellholder in order to get enough bump, but now I'm pushing them back between . 004-.005" , and the bolt is closing by hand. (I needed to size it that much, in order to reliably close the bolt). Once again, thanks Guys!