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Bumped shoulder back too far

 
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  #1  
Old 05-18-2011, 07:50 PM
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Location: Australia
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Bumped shoulder back too far

I sized 200 lapua 223 cases and loaded 100 of them last week. Loaded them up with my usual load of 24.9gr of ar2208 (varget) and 75gr vld's. Running them through the chrony 2 days ago I've lost about 40-50 fps, the bolt is a tad sticky and is a little harder to eject. Primers are flat as a pancake as well. I'm still using the same batch of powder and same seating depth. I'm guessing I have bumped the shoulder back too far resulting in a head space issue. What would be the easiest way to fireform the brass back? I have 85 loaded and 100 sized and primed. Have been reading of using a fast burning powder and some form of case filler for the empties, what about the 85 I have loaded.
Cheers for the help
Ben
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  #2  
Old 05-18-2011, 10:10 PM
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Re: Bumped shoulder back too far

The most likely causes are
(a) mixed up load data
(b) scale not calibrated
(c) cases need trimming
(d) bullet seating depth changed from jump to jam

Otherwise, I'd want to know if I had a headspace issue before messing around.

There are a couple of ways to check and cross-check.

A very crude check would be to remove the firing pin and apply layers of tape to the case head to see how many layers it takes before you begin to feel the bolt crushing the tape as it closes. This is by no means precision testing because it requires more feel than something solid and tape isn't all created with equal thickness. So, you would need a mic or caliper to measure the tape thickness to get an idea.

Secondly, you can get a set of Hornady Lock and Load Headspace inserts for your calipers and measure the case length from the datum line to see if the cases are within SAAMI specs. If so, and IF your chamber is also within specs, then you should be good to go.

Thirdly, use HNL headspace gauge to measure some of the loaded/unfired cases to the just fired cases and see how much they've grown.

Headspace gauges will tell you if the chamber's in spec.

I would be inclined to use several methods and cross-check and if there's any doubt, take it to a gunsmith.

Hopefully, it's something simple.

Be safe.
-- richard
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  #3  
Old 05-19-2011, 04:12 AM
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Re: Bumped shoulder back too far

Just pulled a few of the loaded rounds, powder was fine, checked the scale with the 20 gram weight provided it was spot on, case trim length is fine and seating depth was good as well. Just ordered the lock n load headspace inserts should be here early next week. The first 200 rounds I loaded for this gun were fine no signs of pressure at all and fine with factory ammo.
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Old 05-19-2011, 07:48 AM
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Re: Bumped shoulder back too far

"What would be the easiest way to fireform the brass back?"

Chamber 'em. Point down range and pull the trigger. ??
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  #5  
Old 05-19-2011, 08:10 AM
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Re: Bumped shoulder back too far

Quote:
Originally Posted by boomtube View Post
"What would be the easiest way to fireform the brass back?"

Chamber 'em. Point down range and pull the trigger. ??
So it won't damage the rifle?
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  #6  
Old 05-19-2011, 09:23 AM
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Re: Bumped shoulder back too far

I kinda gather that maybe the cases were new and unfired; correct? A quick way to check your case headspace when compaired with once fired case that have not be resized, is to get your hands on a roller bearing inner race that has either a .312" to 8mm I.D. These are very square and can be bought at mosy any bearing outlet store for about $5 (they are actually better than the ones that come in the kits). But on the otherhand you would have to bump the shoulder back about .025" to see a significant spike in pressure, and even then they might even ignite the primer. I suspect the real problem is in the seating depth and running a near max load. Take five or ten rounds and seat the bullets about .015" deeper, and see if it helps.
gary
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  #7  
Old 05-19-2011, 10:05 AM
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Re: Bumped shoulder back too far

I would put some tape on the back of one of the loaded cases and chamber it, adding tape till it will not chamber to see just where the shoulder is at. I do this all the time with mine to double check, I was having a similar issue with a Savage 270 WSM with new brass and found that I had about .013 head space on new cases. It would show pressure signs like very flat primer and bolt lift from the case slamming back in the chamber.
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