Possible brass processing issue causing poor accuracy

[jumbopanda]

Recently I picked up a Dillon 1050 with Ammobot, and I'm trying to load large quantities of reasonably accurate 5.56 ammo with it. For several range trips, I was frustrated to discover that I couldn't get my reloads to reliably shoot better than 2.5-4 MOA from my LMT MRP. Now I realize that this isn't a match rifle, but I do think it should be able to do 1.5 MOA on average.

 

My first thought was that my brass was the culprit; I had been using a bunch of old mixed brass with varying headstamps and number of times loaded. I eventually bought some virgin brass (RUAG brand if it matters) and found that it was extremely consistent in weight, length, and headspace. The case mouths were even nicely chamfered. I reloaded it right out of the bag without doing any kind of processing, except for slightly flaring the case mouth with a Lyman M die for ease of bullet seating. These rounds were loaded on the 1050 autodrive with the same die setup as my previous loads. After tinkering with a few bullets and powders, I noticed a significant accuracy improvement, and some loads would shoot 1.25-1.5 MOA. 

 

Thinking that having new, consistent brass solved my problems, I gathered up the once fired RUAG brass and processed them using my usual setup which is as follows:

 

1. Decap

2. Dillon RT1200 trim and size

3. Neck expand to .223" with a Sinclair carbide expander stem

4. Corn cob tumble to remove lube

 

I then loaded this brass again with the same loads that performed well during the previous range trip. Much to my surprise, I was not able to replicate the same group sizes. In fact, this ammo only seemed marginally more accurate than the mixed brass bulk loads that I had started out with. I would say 2.5 MOA was about average.

 

This past weekend, I went out again and shot more groups using ammo loaded in once and twice fired RUAG brass. The accuracy was crappy. But then I brought out a few rounds that had been loaded in virgin brass, and accuracy immediately improved. After seeing numerous ~2.5 MOA groups all morning, I immediately shot four groups in a row that ranged from 1.15 to 1.5 MOA. 

 

So this leads me to believe that there's something very wrong with my brass processing procedure. I checked many samples of my processed brass and didn't notice any that were improperly headspaced or had noticeably severe neck runout, at least based on a rudimentary check spinning the rounds in between the slots of my mini mill's table with a test indicator. What else could the problem be?

Edited November 6, 2018 by jumbopanda

[Chills1994]

Got a welder?

 

 

Got access to a welder?

 

If so, a block or two of steel, a drill press to drill 4 dimples, 4 pieces of steel slingshot ammo, a mag base, and a dial indicator of some sort, and you will be in business:

 

 

I did eventually buy a commercially available concentricity gauge.

 

I discovered the pre-processed brass I was buying had runout at the neck.

 

I resized some cases and ran them through a Lyman M die.

 

That straightened out the cases.

 

 

 

 

 

[SweetToof]

You did list  "Dillon RT1200 trim and size" so you are sizing after you trim? Because that is definitely not the best order, sizing will re-shape and thus slightly lengthen the case (which is why trimming is necessary) so if you are sizing after the trim you will have problems.

[jumbopanda]

26 minutes ago, SweetToof said:

You did list  "Dillon RT1200 trim and size" so you are sizing after you trim? Because that is definitely not the best order, sizing will re-shape and thus slightly lengthen the case (which is why trimming is necessary) so if you are sizing after the trim you will have problems.

Those are done simultaneously...the RT1200 die is a sizing die, except that it doesn't have a neck expander.

[anbrumm]

Most people still re-size before running into the trimmer.

[12glocks]

Try and take the mandrel out and load a few rounds just as a test or instead of the expander mandrel try a resizing die instead of the madrel. A runout gauge is an idea with merit, the Sinclair tool is popular and I have no regrets with mine.

[SweetToof]

21 hours ago, jumbopanda said:

Those are done simultaneously...the RT1200 die is a sizing die, except that it doesn't have a neck expander.

 

18 hours ago, 12glocks said:

Try and take the mandrel out and load a few rounds just as a test or instead of the expander mandrel try a resizing die instead of the madrel. A runout gauge is an idea with merit, the Sinclair tool is popular and I have no regrets with mine.

 

Ok yes I would try removing the expanding mandrel, sounds like the only thing that may have introduced issues.

 

How necessary is it to even expand the mouth further? Have you tried seating bullets without it? The 1050 sizes the neck at the swage station and then slightly flares at the powder drop, the drop must be adjusted to travel just below where you would get a full stroke, so that the powder funnel *barely* flares the mouth. 

[12glocks]

57 minutes ago, SweetToof said:

 

 

Ok yes I would try removing the expanding mandrel, sounds like the only thing that may have introduced issues.

 

How necessary is it to even expand the mouth further? Have you tried seating bullets without it? The 1050 sizes the neck at the swage station and then slightly flares at the powder drop, the drop must be adjusted to travel just below where you would get a full stroke, so that the powder funnel *barely* flares the mouth. 

I think it is best t o expand the case mouth.  I have tried loading a few just off a Dillon trimmer and nothing bad happened.  It will be intersting jut to see if your groups shrink a lot.  If not it was probably not the mandrel.

 

Tell us about your load and how does factory ammo shoot?

[Chills1994]

I resized some of my pre-processed brass with an RCBS X die....with the mandrel in...until I stuck a case.

 

Trying to drill the case head with a handheld drill rammed the drill bit right into the decapping rod/mandrel.

 

It boogered it up pretty good.

 

So I removed the X die mandrel entirely.

 

Then I resized with just the X die body.

 

On my 650 with station #2 dedicated to the powder through die...and station #3 open (I use a mechanic's inspection mirror and a flashlight to see that the case is appropriately charged with powder.), so that leaves station #4 for bullet seating.

 

Welllll....not opening the mouth/neck back up led to little copper shavings landing on the shell plate.  These were with boattail SMK's.  So while straightening the cases's necks helped with accuracy, I thought a bullet sppinning so fast missing part of its jacket wasn't ideal.

 

So I bought the Lyman M die....

 

And that has made all the difference...

 

 

[fbzero]

For me, my accuracy increased when I started using the Lyman "M" Die after the size/trim operation.  Here's my process, which easily gets MOA ammo with 69gr SMK's and mixed year Lake City brass.  These are intended to be loaded quickly with minimal work for 3gun, not ultimate accuracy.  Personally, I'm not messing with all the extra case prep for a sport that doesn't require the utmost accuracy.

1.  Clean used brass.
2.  Run it through my 1050 .223 processing toolhead.  This has a universal deprime die, hold-down/swage station, followed by RT-1200 size/trim, then a Lyman "M" Die in the last station.

3.  Tumble to remove lube and any brass shavings.

4.  Load on 650 press.  Universal deprime(to get any media out of the flash hole), powder drop, bullet drop, seat, crimp.

5.  Case gauge.  I generally only get 1 that barely fails per 200 rounds or so, but I'd rather catch it before a match than on the timer.

 

Edited November 10, 2018 by fbzero