Big Al Posted February 8, 2015 Report Share Posted February 8, 2015 Guys, Ive got some new Lapua brass for my 20BR which after necking down from 6BR has an overall length for all 100 cases of 1.545" +/- 0.001" Below is a print of the reamer that was used to cut my chamber, you will see the distance to the end of the neck is 1.570" so my question is do these cases need a further trim or is 0.025" enough clearance? Link to comment Share on other sites More sharing options...
The Gun Pimp Posted February 8, 2015 Report Share Posted February 8, 2015 No - 25 thou. is plenty. My 6PPC BR chamber is 1.5 inches and I trim all my brass to 1.485 inches. This will last/grow all season with needing a further trim (about 35 firings). In an ideal world, I'd trim 'em to 1.490 inches - but that would mean another trim partway through the season. Link to comment Share on other sites More sharing options...
Big Al Posted February 8, 2015 Author Report Share Posted February 8, 2015 No - 25 thou. is plenty. My 6PPC BR chamber is 1.5 inches and I trim all my brass to 1.485 inches. This will last/grow all season with needing a further trim (about 35 firings). In an ideal world, I'd trim 'em to 1.490 inches - but that would mean another trim partway through the season. Excellent concise info, thanks very much. I was guessing that so long as you had enough clearance to stop the case neck being crimped onto the bullet and a bit more to allow for stretch then everything is good? As you can see my neck diameter is .235, a loaded round without any neck turning is .2325 so things are quite tight. Do you think it would be best to leave things as they are or would a slight neck turn help any? - if so to what diameter neck? Link to comment Share on other sites More sharing options...
onehole Posted February 8, 2015 Report Share Posted February 8, 2015 Excellent concise info, thanks very much. I was guessing that so long as you had enough clearance to stop the case neck being crimped onto the bullet and a bit more to allow for stretch then everything is good? As you can see my neck diameter is .235, a loaded round without any neck turning is .2325 so things are quite tight. Do you think it would be best to leave things as they are or would a slight neck turn help any? - if so to what diameter neck? I believe they reckon 2 thou neck clearance is ok in the serious benchrerst scene and probably 3 thou a more sensible approach.Observing my own findings with the 6BR 3 thou is definitely a better place to be considering fouling can take up some space over a few rounds in the field without cleaning.If you have access to the actual reamer used to cut your chamber it would be good to get your "smithy" to ream a piece of barrel to check fit and original freebore for reference. Even a slight neck turn to be able to build absolutely concentric ammo is really worthwhile in my opinion.Perfect and repeatable launch is most desirable,,,,,,O Link to comment Share on other sites More sharing options...
gunner Posted February 9, 2015 Report Share Posted February 9, 2015 Al im just thinking about neck turning your neck downed brass, as if you have used a bushing die they only size about ¾ of the neck . This leaves a slight larger proportion just before the shoulder ! If you then turn them going just into the shoulder you may end up with a shallow enternal donut , abit like the start of case head separation before the case separated etc ! Im in this connundrum with my 223/20 prac brass right now ! Any ideas anyone ? Link to comment Share on other sites More sharing options...
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