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Posted: 6/26/2012 3:56:06 PM EDT
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I have recently built AR15/10's in my first custom chamberings - 6mm DTI and 257 DGR
Both of these use brass that is necked down 6.8 SPC and 260 Rem. It has been suggested that I turn the necks down for max accuracy and I have never done this before. I have Forster trimmer and am not overly impressed. Can anyone reccommend an outside neck trimmer they are happy with? |
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In your case Not really required IMO for an AR.
If you neck up it creates a donut at the neck. The thicker brass at the shoulder is moved into the neck area and can cause problems. In that case if the chamber is not set up for it, you need to neck turn. Its not fun and believe me unless you are shooting competition its probably a waste of time, and it takes a lot of time. |
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A long time ago a sage ol' bench shooter steered me away from the Forster type case trimmer and toward the L.E. Wilson type.
It's a simple, beautiful little device that is more precise than the Forster style. The cases are held in a shell holder which rides on two precision rails. In addition to the trimmer cutter there is an inside neck reamer available. I have not used the reamer but it swaps out with the trimmer cutter head. The site is deeper than it appears at first glance. There are some product videos. LE Wilson Sinclair is one of their dealers. LE Wilson @ Sinclair Int'l Use the search function to drill down to what you want. If you're going to turn necks be very careful about neck tension. If you are not planning on single-loading, bullet set-back in the magazine due to recoil is a hazard to always keep in mind. |
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Quoted:
I have recently built AR15/10's in my first custom chamberings - 6mm DTI and 257 DGR Both of these use brass that is necked down 6.8 SPC and 260 Rem. It has been suggested that I turn the necks down for max accuracy and I have never done this before. I have Forster trimmer and am not overly impressed. Can anyone reccommend an outside neck trimmer they are happy with? I have the Forster case trimer that I added the neck turning cutter to and I will say I'm not sure I'm happy with it but I just started turning. I made cases for a little wildcat using .223 brass and the final necks on the FL sized cases was too large in diameter for the chamber so I had to turn. A long time ago I did the same thing but reamed the inside of the necks and was not happy with the necks –– they were not true. My big problem using the Forster neck turner on the case trimmer is it's recommended that you make two passes if there's a lot of brass to remove. I didn't realize that and tried to do it all in one shot. The good point about turning the necks is it cleans up any out-of-roundness besides allowing the brass to fit the chamber correctly. This is the actual article from the 6mm benchrest site Neck turning info –– I wish I had see it before I started. There is a lot of good info and the fellow uses the hand held trimmer –– wish I had seen this article before I started. |
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Guaranteed you will not shrink your groups any appreciable amount with a basic AR
unless your brass is way out of whack.. The tolerances are just not tight enough in an AR. You would probably get more accuracy by replacing your barrel with a match grade barrel and working your loads and load Lapua bullets with the right powder. Now if you go to a good bolt action, Kreiger barrel, top scope and mount assembly, shooting say a 6mm BR in a bedded stock, Weigh and sort your brass, same for bullets then yes, neck turning would make a difference especially if its a tight neck chamber. You also need a scale that will weigh down to one or two pieces of powder. When you are chasing fractions of an inch you have to do everything. I remember reading about one bench shooter on 6mmBR that used a Jukie machine on all his brass to find internal defects then weigh sort etc. I think he was shooting 1.5" groups at 600 yards with a 22 dasher. Another bench shooting family, that would weigh and sort everything brass and bullets. Shoot their test groups for the upcoming match. The shells that shot the tightest, low SD/ED would be sorted out for the match and those were the cases they used for the match. Over all for normal shooting I think its a waste of time to neck turn. If you do everything else then okay. Neck turning is an incredible PIA for me. I hate it. |
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I have to agree with the forum on the concept of low returns for a typical AR.
Your brass would have to be really bad to see a performance benefit for a typical AR. The only other reason to do this for an AR is for the example of wanting to use a single case wall thickness for batch reloading purposes to achieve consistent neck tension and case life. If for example, you encountered a case wall thickness that was on the order of 0.002" thicker due to brand change or runout, you may want to turn just enough to bring it in line with your other batches. This way, the size die is working roughly the same on all your batches. The problem is more common in 30 caliber brass and it isn't unusual to see folks turn everything down to 0.013" or even 0.012" wall thickness. This makes the size button or die selection the same for all their batches. You don't always need to turn 100% since some brands and batches may be just fine as they are. BTW, I have the Forster tool as well as others and didn't find a real difference in the finished cut when all was said and done. In fact, once I started using a small power drive on the Forster it was better than using the other tools by hand since all I have to do is get a rhythm going with mounting the piece in the collet. I still use the K&M for small batches and it is a fine tool. I find the key to be my custom pilots which allow me the best sliding fit for the batch. You can order custom expand mandrels and pilots which aid in the turning process. I also use the Imperial lube to keep the friction down. |
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Sorry I did not respond, I was out of town for a couple weeks.
I am far from an expert but my impression is that these are pretty good barrels: Shilen select on the 6mm DTI and a Brux heavy varmint on the 257 DGR Mike at DTech suggested that I would see best return on my time by turning off a small amount to ensure consistent thickness. I use these strictly for bench shooting at paper and p-dogs so I am looking for better accuracy than the normal AR user. I got 0.64" 5 shot group at 100 with the first loads I tried (70 BK's and Benchmark) so I am hopeful I can whittle that in half with some different powder and bullets. I have not shot the 257 DGR yet as the dies are on back order. I am still on the fence as this looks like a lot of work and the consensus here seems to be for me to not bother. As always I appreciate all the good advice I get from this site. |
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