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How many "thou's" of neck tension are you guy's using in your 6.5 Grendel gas gun's???
I don't crimp....
I don't crimp....
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5 thousandths is good without crimp or mild compression of the powder in gas guns.
Have run as low as 2 thousandths in an M1A and AR when running compressed loads without bullet setback in the ones I measured at least and had good accuracy results. -
Redding recommends a bushing .001" less than the neck size of your loaded round I believe.Comment
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+1.
Both sets of dies I use; Redding and Forster permit no more than .001 neck tension. At the start I was getting all sorts of vertical stringing and large group sizes. Took a while to figure out it was neck tension in a violent action.
Don't know if imposing neck tension is better before or after loading the bullet but for me the crimp die (tensioning after loading the bullet) was the cheapest and most convenient solution at the time. If I knew how critical neck tension is in an auto action way back I probably would go the way you are thinking...sort the tension out before loading the bullet.Comment
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I measure a given manufactures loaded ammo at the neck and subtract .001 to determine the bushing size. Different manufactures will have slight variations in wall thickness so it pays to check. If you are buying unloaded brass, make up five dummy loads (no powder or primer) and measure the OD at the neck to determine bushing size. I've loaded thousands of rounds of various calibers and this has always worked. There are exceptions where neck tension won't hold the projectile in place, and these require a crimp. An example would be my .454 Casull. Without a good crimp, the bullet will move in the brass under recoil, potentially causing a pressure spike or jamming the cylinder. Regarding the 6.5 Grendel, the .001 calculation will work well and provide adequate tension to keep everything in place, regardless of bolt or gas gun.Comment
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When selecting bushing dies agree on the .001 final size dimension for bottle necked cartridges. This is an after bullet seating measurement
If using the non bushing dies such as Hornady and RCBS where the expander ball on the decaping rod determine the neck tension .004 to .005 work well providing enough tension for a semi auto. This is a pre-seating of the bullet measurement. The tighter tension can achieved by making the expander ball smaller by putting it in a drill and using fine sane paper to polish off the needed amount needed to expand for what neck tension you want.
On straight walled cases for revolvers and rifles a good roll crimp is needed to ensure the bullet does not move with recoil in the cylinder or magazine. In the revolver handguns where the bullet has to go through the rest of the cylinder and into the forcing cone there is a large jump and the crimp helps increase pressure to get the slow for handgun powders burning more efficiently.Last edited by kmon; 05-29-2016, 02:25 PM.Comment
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I'd think that the full length bushing sizing dies would be ideal for the Grendel on the AR platform, and a good alternative to reducing the expander ball diameter. When using the typical rule of 0.001" smaller busing, and accounting for brass spring-back, it seems like the neck tension would be very light, based on my experience with other calibers. I think some experimenting with bushings, probably in the 0.002-0.004" range, would produce more neck tension that could be more accurate than crimping.Comment
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While a bushing die may be good for getting the neck diameter small enough to be useful prior to running the expander ball through, the final diameter will continue to be the ball diameter less spring back.
Since the idea is to cause some yielding to be sure of controlling the final dimension, the inside diameter will be the same independent of the bushing die diameter.
Bottom line, increasing tension will require either a smaller diameter ball or crimping.
If, like me, one does not like crimping, the first step is to reduce the ball diameter. If adequate tension develops with the smaller ball and the standard FL size die, smile and be happy that you are minimizing cod work on your brass!shootersnotes.com
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Some use a mandrel and then a bushing die with no expander ball.Comment
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I use the REDDING - TYPE S BUSHING FULL DIE without the expander die. Redding say fit to include both an expander ball and a decapping pin retainer. This die without bushing or stem also sieves as a body/bumb die.Comment
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Neck reduction of .001" is for bench rest bolt guns only. You need a minimum of .002" to .004" for a gas gun. An AR will really slam a cartridge into the chamber. You should not have a neck tension problem with standard dies. If you set the shoulder back .003" when case sizing and and have a minimum of .002" neck tension you will never have a problem. I know this works as I loaded thousands of rounds in AR15"s and AR10"s without a problem.
GreyfoxComment
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100% correct!! Pay no attention to the confusion that came before.Originally posted by Greyfox View PostComment
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Yes. I agree.Originally posted by Greyfox View Post
I am annealing my brass now, and I use a full length sizing die from Forster.
Thanks.Comment
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