Bump shoulder back

[gunmutt]

So I have purchased a Redding comp type s full length small base seating die for my ar loads. I set it up and was able to push the shoulder back .005 for most of my once fired lc brass. Unfired rounds are .010 longer than fired. Well I have several onced fired that pushed back .010. when I place a brand new case in the die it is .010 shorter than it was. Am I doing something wrong or will this variation not really matter.
Fyi- this case is for a bull barrel 20" ar for target/training shooting.

 

[K22]

.010" is too much set back. Ideally, for bolt rifles, you should set the shoulder back of a fired case from the specific rifle that you are loading for, .001 to .002". Over sizing can cause head separation and must be avoided.

If a new cases chambers without resistance there is no need to set the shoulder back. If you want to size to uniform new cases set the sizing die so that the shoulder is not set back assuming the new cases chamber without resistance.

 

[gunmutt]

.010" is too much set back. Ideally, for bolt rifles, you should set the shoulder back of a fired case from the specific rifle that you are loading for, .001 to .002". Over sizing can cause head separation and must be avoided.

If a new cases chambers without resistance there is no need to set the shoulder back. If you want to size to uniform new cases set the sizing die so that the shoulder is not set back assuming the new cases chamber without resistance.

Okay for for sake of explaining lets say my unfired new brass measures .460 and fired measures .470. Now since this is an AR I am wanting to bump back to .465, which I did for most cases but some bumped back to .460. I am not bumping back new unfired cases, only fired cases.

 

[DocDoc]

Okay for for sake of explaining lets say my unfired new brass measures .460 and fired measures .470. Now since this is an AR I am wanting to bump back to .465, which I did for most cases but some bumped back to .460. I am not bumping back new unfired cases, only fired cases.

.010 bump every time and you are headed for a case head separation in short order.

 

[Shynloco]

.010 bump every time and you are headed for a case head separation in short order.

That's if the round will even chamber fully and then fire. Mine will not with a .010 bump.

Alex

 

[Rsadams]

Just did some in my ar tonight I only bump the shoulder back .003 or so and it works fine.. As stated above 010 is alot. Keep an eye on it.. On some factory remington 55gr fmj the shoulders at 1.457 and when fired its 1.460 so I just bump them back to .457 , most range brass.I pick up is around these specs also. I wonder why yours is .470??? Am I just reading your post wrong maybe? Are you getting a good read off your bump gauge? I use the hornady and have to do some serious twisting and looking to get a proper read..

 

[gunmutt]

I am getting a .010 difference in the once fired and fresh brass. I am looking for a .223 wylde no-go gauge to see if maybe my chamber is too deep, but usgi field gauge would not work. Guess I have a deep chamber

 

[Rsadams]

I haven't been doing this as long as most here thats for sure. These guys know their stuff. But that's what I was thinking also.. Most range brass I pick up which is normally once fired lake city fired at my local private range seems to measure in the spec I listed. These are fired out of many ar15s not just mine but they all seem to be about in the same range as far as fired head space goes..

When I was starting to only bump back .003 I measured a bunch of mine,range pickups and factory to get an idea of what was going on. Only Becouse the crappy Remington ammo shot pretty decent out of my gun and I kinda wanted to clone a few, and see the results. It shot better and had half the SD as the factory ammo.. I hope you get it figured out, I will keep watching your thread it has got me wondering also..

 

[K22]

For semi-auto's the ideal shoulder set back is .002 to .003". Again, if you oversize the cases eventually you will create a head separation which can be dangerous.

 

[ireload2]

Then back up your die in the press. Look at the length of the underscore _ character on your screen. It is about .040 long.
Put a Sharpie pen mark on the OD of your die and on top of the bushing. When you rotate the die about .040 (1mm) to the right on the OD you will move it about .001 back. So .04 inch X 5 = .200 inch on the OD of the die will back it up .005 inches.
You might check out a Wilson case gauge for the 5.56. You can check your fired cases and get a good idea of the chamber length. Then you can check the sized cases in the same gauge. I prefer measuring instruments but if you don't have them or have little experience with them the Wilson gauge is pretty simple to use and it is instantly visible.

I am getting a .010 difference in the once fired and fresh brass. I am looking for a .223 wylde no-go gauge to see if maybe my chamber is too deep, but usgi field gauge would not work. Guess I have a deep chamber

 

[Fast14riot]

I bump mine .002-.003 and don't have issues feeding from the magazine. I'd be surprised if the shoulder didn't collapse at .010 bump.