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Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by crowTrobot, Sep 15, 2004.
I'm just learning to neck turn. How do you know how much to take off???
first of all if you are turning necks for a
factory chamber or SAAMI spec. I would recommend just turning enough to make them uniform but if you are turning necks for a tight neck chamber I would recommend .002-.003 under neck dimension. I have turned too .001 but every once in awhile you will get one that doesn't chamber.
I tell my customers to follow these steps. This for turning to fit a tight necked chamber.
Take a fired case from your chamber. Measure the expanded neck diameter, say for example you have a 6mm-06 with a fired neck diameter of .2755".
Now take a dumby round loaded with the bullet you have decided to try. With this bullet loaded in an empty, unprimed case, measure the neck diameter with a seated bullet.
Say that measurement comes out to .2750".
Basically you have 0.0005" total clearance for your case to release the bullet on firing. Total clearance is not the real figure we want to look at, we want to know how much actual distance will be between the bullet and the case when fired.
To find this you simply divide the total clearance by two and this will give you the actual clearance all around the bullet and case neck when fired.
So in this case it would be 0.00025". Much to tight. As a rule of thumb, the absolute minimum actual clearance youwant is 0.00075" between the bullet and case.
This translates to 0.0015" total clearance. Anything tighter then this will result in possible pressure problems from bullet diameter variations as well as variations in the necks you cut. While small there will be variations.
Like I said, I believe this is the absolute tightest you should have.
I much prefer to have 0.001" clearance on each side of the bullet and on big game rifles 0.0015" to 0.00175" is preferred as hunting bullets are generally not held to the strict tolerances of match bullets.
If you have to remove alot of brass, remember that you will get more accurate cuts if you take off a little at a time. This will depend onteh turning tool you have but I prefer to take off 0.00075" to 0.001" at the most per cut. Makes for a much more accurate case neck.
If you are just turning your necks to improve concentricity and neck tension from load to load. Find the thinnest neck in the lot of brass you have. Use some common sense here. IF you have 500 rounds of brass and 475 of them are 0.015" thick or more in teh neck but there are a couple that are 0.012" thick. DO NOT TRIM THE ENTIRE LOT TO 0.0115" to true all of them up.
USe the thin necked cases for sight in loads or something else. This will save you hours on teh bench as well as save on your turning tool as well.
When you do turn jsut for better consistancy, take off, 0.0005" at a time. Remember that there will be 0.0005" taken off both side for a total of 0.001" off the total diameter of the neck.
Only cut enough to jsut true up the case necks.
If you take off to much with a SAAMI spec neck, you will actually negatively effect the accurcy of your load because the neck will be very loose. Only take off enough to true the neck up and thats it.
Also, if you make the neck to thin in a standard chamber, you will increase the work hardening of the case neck as a result of the greater stretching on firing and necking down when resizing. This will result in premature case neck splitting.
Something youreally do not what when you jsut spent all that time carefully turning your necks.
Hope this helps some,
Fifty Driver as always provided excellent advice on neck turning, and 30 years ago, wish I had him to give advice, when like you I embarked on turning necks for the first time.
However, there is one aspect which doesn't seem to have been mentioned, and hopefully it might prevent you getting caught like I did when neck turning my cases on my .22/284 in 1972, and later with my .224 Clark in 1988.
I believe that you should measure the dimensions of the case neck after sizing the case with both/either the neck sizing die and full length sizing die.
The danger is that you might (like I did the first time with both the 22/284 and .224 Clark) take off too much brass in cleaning up the neck, and then find that the sizing die has no effect.
This creates the situation where you have no neck tension, and the bullet after seating will slide up down the neck. I have learnt from experience that hundreds of grains of powder are a nightmare to remove from the chamber when in the field.
If you find that sizing die does not work after turning the case necks to give the desired clearance of about .001 per side (as Fifty Driver mentioned), then apart from taking off less brass, you will have to get a die custom made to fit your circumstances.
As an example, I now do the following measurements with the case necks on each rifle that I own so that I know what is happening. The measurements of the case necks (Remington) on my 22/250 AI after using an RCBS neck sizing die:
Diameter without expander ball- .2465
Diameter with expander ball - .2515
Diameter of loaded case neck- .2530
Diameter of fired case neck - .2555
Although I am not turning the case necks on this rifle, if I did, obviously I would not want to turn then under .1375 inch thickness or the neck sizing die would not work with the expander ball in place.
Good luck, and hope the above helps. Regards, Brian.
Isn't that what they make bushing dies for?
What I do is divide neck into quarters and measure each and whatever is the smallest thats what I turn the necks to. Sinclair Int will say if only difference is .001 no need to turn necks of course that is on a factory rifle. I use only bushing type dies so I'm more concerned with neck tension than most. I've never found a hard and fast rule on neck turning for a factory rifle except don't cut more than the thinness side. If my high side was .016 low was .014 I turn my neck .0141. I also use a feeler gauge to set my neck turner and have some over sized mandels from Sinclair sure help from having the neck binding on the turner even using wax. I also use two neck turner one for the first and another for the final and have found the Hart and Pumkin best for the final and Sinclair and K&M for the first. Holland shooting supply makes a pretty nice ball mike for the necks can measure all the way down. Don't know what caliber you are turning for but after firing and see what that measurement is might want to try some nickle case they have alittle thicker neck I've got a 22-250AI and 6mmremAI and found some nickle case and have almost made a tight neck out of those case. One of the most important thing to remember on turning necks you will increase the flow of brass up the neck and get the (dreaded donut)so need to get an inside neck reamer and do that from time to time. Most tight neck rifles are between .008/.010 neck thickness and that cover from the 22,6mm,6.5 and 30 cal. I started turning neck in that late 70's for some Br rifles and the equipment sure has gotten better. Well good luck.
Start by only taking off .001 or .002 at the most. Taking off to much can result in the case neck spliting after firing or low neck pressure when you resize the fired case. Remember to use a case neck thickest gage and don't be to concerned if the turning does not turn the complete neck most do not. Then check for bullet run-out after seating the bullet and correct as necessary. Remember to turn your necks before trimming as this wiil true up the necks with the cutting head. Hope this helps. Capt kurt
First off, how you go about determining how much to trim is exactly opposite for factory and tight neck guns.
IF it is factory chamber you need to know what is the actual fired case diameter at the neck unless you have a cerrosafe chamber cast to measure. Many factory necks are .008-.010 over loaded round size with unturned necks already. Guess what, neck turning .001 off is not going to help you diddly squat with that large a neck. Total waste of time. If you are only .003-.004 it is really questionable then.
Factory 30 cal with an actual .348 neck, which is on the small side anyway .348 minus .308 gives you . 040 or .020 per side. Very few cases are over .016 at most. That gives you .008 total clearance. Now unless your cases are showing over .003 variance from side to side, IMO total waste of time to neck turn .002 off to make even larger neck variance of .010-.012 in a factory chamber. Think of it as putting a nascar engine in a Yugo. That is not going to work like you want and for all practical purposes impossible to measure an realistic difference in a factory size chamber and barrel. Answer, buy better brass RWS, Lapua etc.
And you are going to need at least .003 neck tension on a loaded round for magazine hunting rifle as minimum or the bullet can and will move under recoil in the neck.
This also means you will often have to go to a standard bushing die or send your non bushing die to Jim Carstenson at JLC precision in Iowa (www.6mmbr.com and under "Tools") for him to convert it to a neck bushing. Cost is about $45 and week turn around. You have to be able to get the neck tension and standard dies often will not give it to you after neck turning. You do not need a custom die, just a bushing die with the correct bushing to give you the proper neck tension.
Now some will state cleaning up factory cases .002 gives more uniform neck tension (in a sloppy chamber). Well maybe, but after 3-4 firings your uniform neck tension has gone to pot and is in actuality all over the map unless you anneal anyway and still in a sloppy chamber. Hell of lot of work for nothing. Been there done that. Wanna try it, get a set of pin gauges and see which ones fit in what necks after resizing that 4th time. the actual variance WILL be .0005 to .002 on the neck.
Now if it is a tight neck gun, you cannot safely fire a case without neck turning it first so no way normally to measure an actual fired case on a new tightneck gun. Even if you could, it is a totally meaningless measurement anyway. Fired cases will expand to chamber neck diameter and then shrink some upon firing. You in reality want to know what is the actual "loaded" bullet/case diameter that will fit safely in that neck.
EXAMPLE: 300 WSM with minimal tight neck of .338 with brass of .015-.017 and .308 bullet equals a loaded round of at least .338 to .342 with zero clearance. Not a good situation and it routinely will not even chamber. .338 is not even real tight for a 30 cal either. They are often .334.
In a tight neck gun, you are actually guided by the neck diameter of the chamber, not the fired case. Take the reamer neck diameter say .338 neck for a 30 cal, subtract .308 from it to get .030 or .015 per side with zero clearance. You need a min of .001 per side so that gives you a final turned neck of .014 thickness maximum.
You will not be able to take off over .002-.003 per cut and do it cleanly. I always set first cut to leave about .0015 per side. Trim all cases with the intial cut first.
Adjust your cutter for the final cut and use either power screwdriver or power neck turner at 120 to no more than 180 rpm. final cut is slow and clean. put the cutter each time on bag of ice or in bowl of cool water/alcohol to cool it between cases. The reason for that is your cutter head and mandrell will heat up and expand as you turn and that expansion will give you as much as .0005 or more variance if you do not cool it. Been there and done that.gun)
Word of caution, these measurement numbers are ballparks to work from. For example a 30 cal bullet has a pressure ring and often pushes the case out past what the nubers add up to such as .0015 each side and .308 should be .338 loaded round but it might come up to .3085 or more, hence the minimum clearance of .001-.0015 per side.
Do you really want to lose the buck or elk of a lifetime to a bullet/case jamming with one little piece of dirt on a hunt? Seen it do it and the barrel actually had to be taken off to get the bolt out an only one little piece of dirt. gun)
It is also a very wise practice to do only one case, load it, measure and see what you really have before doing a 100-200 cases.
Wanna guess how I know that one?
Old rule measure twice and cut once definitely applies. Go back to previous statement about doing one case.