neck clearance

[Brad from ND]

I just started turning necks for my new 308 last night and I just want to check with you guys to make sure I'm giving myself enough clearance. I've turned necks before to true them up, but not for a tight neck chamber where clearance is an issue.

My reamer has a .339 neck and my turned brass is right at .3355, leaving me 3.5 thou clearance. Is this enough?

Thanks

 

[Shynloco]

From my way of thinking (and I'm not claiming to be an expert), but I would think your necks have plenty of clearance. I usually look for .002 - .003 as optimum in my rifle that has a dedicated throat.

 

[AlNyhus]

Brad, what does the neck o.d. measure with a bullet seated (across the bottom of the bullet)?

Good shootin'. -Al

P.S. When checking your neck o.d.'s when they con=me off the turner, make sure and debur the mouth of the neck and then hit it with a bit of 0000 steel wool to remove any 'fuzz' that can skew the measurements. A quick wipe around the nentire neck length with some 0000 steel wol helps remove some of the minute ridges that form, as well.

 

[Brad from ND]

I thought that I heard .003 was enough but I just wanted to make sure.

All, I'll seat a bullet and measure tonight. My necks all measured .308 inside after turning so I figured it would be good but I like the idea of double checking with a seated bullet. I also steel wool all of the necks to smooth them out and debur afterwards so that is not an issue.

Thanks guys!

 

[BoydAllen]

Just to be clear, the best tool for measuring loaded round necks, over the bullet, is a 1" mic. that measures to .0001. The reason that measuring necks without a bullet doesn't get you there is that the neck expands when the bullet is seated, and of course it is this difference between the diameter of a neck before and after seating a bullet that holds the bullet in place. Also, if you don't have a neck mic. If you measure the bullet with the mic., subtract that from the loaded neck measurement, and divide that by two, you will have an accurate measurement of the average thickness of your turned neck. Of course this does not tell you as much about an unturned neck, because it will be thicker on one side than the other.

 

[Brad from ND]

With a bullet seated, we are right at .336 in a .339 neck. .003 clearance which I would think is perfect.

Now, I tried using my modified case to check coal to the lands and my chamber is so tight that my modified case won't fully chamber. Virgin Lapua brass drops right in though. Dangit.....

 

[Shynloco]

Now, I tried using my modified case to check coal to the lands and my chamber is so tight that my modified case won't fully chamber. Virgin Lapua brass drops right in though. Dangit.....

Brad,
That problem MAY be the base of the modified brass and has nothing to do with the necks. I ran into that problem when a friend gave me some LC Match brass and I couldn;t get it to fullu chamber in a my tight chamber. After measure the base of that brass, I discovered it was .001 LARGER than the Lapua Brass I'd been shooting in this rifle. Got me a Redding Small Base die set it to my usual shoulder settings as on my regular Redding FL die and BINGO, problem solved by simply reducing the size of the base by .001. Shot some test 5 shot groups yeterday and the groups were all in the .2's and .3's at 100 yds off the Benchrest position in a .308. BTW, gotta also watch those necks just in case you are half neck sizing and leaving a slight bludge behind the sized area and the shoulders...a tight chamber won't allow you to chamber that configuration if your tolerance is in the .002 range.

 

[Brad from ND]

It is the base. I'm not gonna spend $30 on a small base die just to size my modified case though. I'll just use one of my turned cases and set a bullet in a close the bolt. The necks are right at 308 so it will lightly hold a bullet to give me my depth.

 

[Steve Blair]

I use .0045" clearance in caliber .30, both .308 Win and .300 WSM. My testing shows more consistent accuracy. The cases are annealed every firing, so cold working the neck is not an issue. Chamber neck diameter is Ø.337" and loaded rounds are Ø.3325". Case necks are .012" wall thickness. I shoot long, heavy bullets in both cartridges and that may be a factor.

 

[Shynloco]

It is the base. I'm not gonna spend $30 on a small base die just to size my modified case though. I'll just use one of my turned cases and set a bullet in a close the bolt. The necks are right at 308 so it will lightly hold a bullet to give me my depth.

Brad,
Tell you what, if you want, send me your modified cases and I'll resized the bases, run them through my regular Redding .308 die for added measure. measure the necks with my RCBS Precision Mics, trim them to 2.005 and send them back to you for final Neck sizing. The only expense to you would be the mailing@ $6.80 USPS. Obviously no charge on this end to you. So if you want, PM me for my mailing address. Just another way for you to be able to use that brass. It's up to you.

Alex

 

[Brad from ND]

Thanks Alex but I just remembered that my friend's brother-in-law just started loading for a 308 DPMS so I should be able to use his die. I'll let you know if I need it done. I appreciate the offer.

 

[Shynloco]

Brad,
No problem. But if you need help, give me a holler because it isn't a problem that can't be overcome either way.

Alex