Inconsistent Datum Lengths Measurements

[Halimar]

I am new to reloading. My first act was to de-prime, stainless steel wash, and then full length re-size some 223 Rem once-fired brass (Remington and Lake City '09) using a LEE Classic press and RCBS X-Die. The brass had been cycled through an AR-15, and will be fired from the same rifle after they are reloaded.

After re-sizing the brass I used a Redding Instant Indicator Comparator to sort it by datum length. When doing this I found that by rotating each case on the case holder and then remeasuring the datum length, I oftentimes obtained readings with anywhere from a .001 to .0015-inch difference in length. (I sorted the brass based on the longest length.)

Is this difference in datum length on the same case normal? If not, can anyone tell me what I did wrong?

Thanks.

 

[hogan]

New to handloading?

Damn guy, you really rush into a hobby, don'tcha!

Strikes me that you are overthinking this stuff way too much. You're .223 brass was fired in an AR-15? You better be sizing that stuff back at least .003" and .004" is better to be sure of complete chambering. Maybe if you're shooting a benchrest setup Custom built varmint or highpower gun you can go a bit tighter, but you seem to have high expectations of Rem & LC brass.

What you might want to watch with your Redding dial chamber gauge is the variation in length. Look at a batch of Virgin brass and evaluate them for consistent length. Record the average, or keep track of 5 or 10 pcs of brass and load and shoot them normally in your rifle. Then evaluate the dimension of your fired brass and note the Before & After numbers. You need to size .004 under the longest dimension.

Are you using hard cup primers? Would be a bitch to do all this work and have a soft primer slamfire on you. Rem 7-1/2 benchrest primers are great in AR-15s. Soft primer and minimum sized fired brass in a magazine fed situation could be a Big Problem. At very least chambering problem could give you a misfire.

Might want to read Glen Zediker's books on The Competitive AR and/or his handloading book so you understand all the variables when handloading precision ammunition intended for AR-15. I've yet to read his handloading book but the loading sections in each of the 2 Competitive AR books is very good.

Nice to have the shiniest brass on the block, but isn't really necessary. Nice to know the info a dial indicating case gauge can impart, but only to setup your sizing die. A quality setup AR-15 shooting precision handloads is a thing of joy. Zediker probably has some tips on his website. Another member here, Robert Whitley of 6mmAR.com is also a great resource on precision techniques for AR platform.

Good luck!

 

[BoydAllen]

What you are seeing is normal and should not be a problem. As the previous poster wrote, gas guns need more shoulder bump than bolt. The variance that you see is caused by slight differences in case hardness and small differences in how much lube is on each case. Dwell time at the top of the ram stroke also is a factor. At the level that you are seeing it, you can ignore it.

 

[bozo699]

I am new to reloading. My first act was to de-prime, stainless steel wash, and then full length re-size some 223 Rem once-fired brass (Remington and Lake City '09) using a LEE Classic press and RCBS X-Die. The brass had been cycled through an AR-15, and will be fired from the same rifle after they are reloaded.

After re-sizing the brass I used a Redding Instant Indicator Comparator to sort it by datum length. When doing this I found that by rotating each case on the case holder and then remeasuring the datum length, I oftentimes obtained readings with anywhere from a .001 to .0015-inch difference in length. (I sorted the brass based on the longest length.)

Is this difference in datum length on the same case normal? If not, can anyone tell me what I did wrong?

Thanks.

Halimar,
Welcome to the forum and to the world of handloading What the other two posters have said is spot on, I would like to add one other thing, I am a fan of redding products but the instant indicator isn't one of them, I had the same problem as you have been finding, you will notice each time you run the press up it will show a difference on the indicator, with some experimenting you will find a happy medium but it just wasn't accurate enough for me and they are cartridge specific so they become VERY expensive if you own very many rifles, I found the Larry Willis tool to be the answer for me, very consistent, very affordable. If you think the datum point measurements vary on the Redding try sorting bullets or loaded round oal measurements do you still have hair?? you won't have if you use it for that!
http://larrywillis.com/ best of luck to you.
Wayne.

 

[jhord]

I got all hot and bothered about the same subject a year or so ago. Boyd said the same thing to me, and he was right. You will have to try very hard to get them all less than .001" difference. My goal is .0005" but it's tough, even shooting all the same brass, annealed and so forth. For an AR, the results you are getting are just fine assuming the longest ones chamber properly. Shoot them and be happy.

 

[Halimar]

Thanks for the very helpful responses.

I'm using Sierra's 5th Edition Rifle and Pistol Manual of Reloading Data” section dedicated to reloading gas operated rifles for guidance. Hogan, it did explain the part about the need to use hard primers. I have some CCI Small Rifle Military No. 41s that I'll use in assembly of the cartridges. It also talked about setting the shoulder back an ample distance from once-fired brass to allow the reloaded case to feed. And it stated how important it is to properly follow both of these steps - re-size cases and use appropriate primers – as together they are a recipe for slam-fires. A few years ago someone told me about a guy who had borrowed a friend’s AR-15 to take shooting at a US Forest Service shooting range. The thing went off on a string of slam-fires. As the story was told, he ended up being convicted for possession of an automatic weapon in spite of his attorney having a paid professional witness testify otherwise. I don't know if the story is true or not, but it sure got my attention since I sometimes shoot at a USFS range.

I already had the book, "The Competitive AR-15: The Ultimate Technical Manual” on my Midway wish list from when I'd seen it referenced elsewhere. But with your recommendation, I'm going to give it a close look and will probably buy it for the reloading information alone.

As far as the stainless steel wash, I must admit that I do like shiny brass, though I had read that it is not known to help accuracy. But the principal reason I went with a Thumler’s Tumbler and stainless steel media was to avoid airborne lead and any other possible contaminants. Before my wife and I restored our 90-year old house, we studied the “art” of stripping paint. We learned that the best way to avoid exposure to lead poisoning is to avoid converting old lead paint to dust, which can easily become airborne. I'm using copper/gilded bullets, and I understand that most modern primers no longer contain lead, but I thought it best to just short the whole problem to ground and go with a wet wash.

And BoydAllen, I did compress the LEE Classic handle all the way to the lock position and held it there until I counted to three. After reading jhord’s comment, I'm thinking that's why I didn't have a larger still range of readings. I'm further inclined to agree with bozo699’s suggestion that there are be better (and less expensive) ways to measure these things.

Anyway, I was totally perplexed at how the heck – after having been so careful – I had managed to press a thousandth of an inch "screw" pattern into the shoulder of once-fired cases. Now I know.

Thanks.

 

[LIUNA]

This reminds me of my experience this week, I was shooting up a load with my bolt action, and had two misfires, and inconsistency shooting results. so when I got home I checked my chrony results, still confused, I started checking my datum lengths, and found .0010 to .0015 shorter than normal. It was obvious that I was negligent when setting up my fl sizer, But my problem was when I re sized my cases I had bumped the shoulder back too much. So, I will now be more careful when setting up my fl sizer, and measure before and after to obtain the proper results. I knew I had to correct these short cartridges. I loaded up 20 gr of varget powder and stuffed cotton in the case and fired each cartridge, which brought the case's back to proper chamber length. so everything came back to normal shooting accuracy.

 

[bozo699]

This reminds me of my experience this week, I was shooting up a load with my bolt action, and had two misfires, and inconsistency shooting results. so when I got home I checked my chrony results, still confused, I started checking my datum lengths, and found .0010 to .0015 shorter than normal. It was obvious that I was negligent when setting up my fl sizer, But my problem was when I re sized my cases I had bumped the shoulder back too much. So, I will now be more careful when setting up my fl sizer, and measure before and after to obtain the proper results. I knew I had to correct these short cartridges. I loaded up 20 gr of varget powder and stuffed cotton in the case and fired each cartridge, which brought the case's back to proper chamber length. so everything came back to normal shooting accuracy.

Liuna,
.001-.0015 most people can't even measure LOL just kidding but really I only bump my shoulders .001 on my bench rest rifles and .002 on hunting rifles, did you by chance mean .010-.015 because that would be a lot!! but not .001
Wayne.

 

[243winxb]

, did you by chance mean .010"-.015"

This much shoulder set back will cause misfires. Plus, if brass is annealed, making it too soft, this can be a problem. The strike of the firing pin can set the shoulder back as much as .010" with a soft shoulder, causing a misfire. If the round fires, you will never know the shoulder was set back by the firing pin. Bolt action rifle. The auto's bolt can set back the loaded rounds shoulder on chambering by .001" if the head to datum line is longer than the chamber. This would vari with brass of a different hardness.

 

[bozo699]

, did you by chance mean .010"-.015"

This much shoulder set back will cause misfires. Plus, if brass is annealed, making it too soft, this can be a problem. The strike of the firing pin can set the shoulder back as much as .010" with a soft shoulder, causing a misfire. If the round fires, you will never know the shoulder was set back by the firing pin. Bolt action rifle. The auto's bolt can set back the loaded rounds shoulder on chambering by .001" if the head to datum line is longer than the chamber. This would vari with brass of a different hardness.

I know that/That is why I brought it up, but .001 longer then you wanted wouldn't,.
unless of course you wanted .009 but got .010 ;D
Wayne.