I need advice on neck turning

[JimSC]

I will be necking up some 6.5 Grendel brass to 30 Caliber. The rifle has a .330 neck and the die has a .225 bushing. My plan is to use a 7mm expanding mandrel followed by a 30 caliber mandrel with some Imperial wax. Then size and measure the neck followed by turning it to a .010 neck wall thickness for .003 neck tension. Is that the correct order?

 

[AlNyhus]

My suggestion is to not cut to a specific thickness. Rather, adjust your cutting tool incrementally until you get to the diameter you want as measured over the pressure ring of a seated bullet of the type you're going to use. The neck tension will be whatever it is....adjust accordingly by changing neck bushings as you test.

Good shootin'. -Al

 

[JimSC]

My suggestion is to not cut to a specific thickness. Rather, adjust your cutting tool incrementally until you get to the diameter you want as measured over the pressure ring of a seated bullet of the type you're going to use. The neck tension will be whatever it is....adjust accordingly by changing neck bushings as you test.

Good shootin'. -Al

It's a new (to me) rifle and the die came with only the .225 bushing so it seems to me that to get the .003 tension I have little choice other than .010 wall thickness. Thanks for the comments however, they have motivated me to purchase a .224 and a .226 bushing this week.

 

[AlNyhus]

Jim...it's obviously a 30 Grendel you're working with. If you're using a flat based .30 cal. bullet as is typically used for 100-300 BR use, the bullets pressure ring is going to run from .3083-.3088 depending on the bullet maker.

With the .330 chamber neck in mind, your .010 neck thickness will result in a loaded round that measures .3283 (.3083 p/r) for a neck clearance of .0017. With a .3088 p/r, you'll be at .3288 for a neck clearance of .0012. Again, these are mathematical projections...it's darn hard to nail something that close and have any sort of margin to work with. That's why I cut necks to the loaded dimension I want. The actual neck thickness is fairly meaningless. Then you adjust the neck tension up or down with the bushings.

Hope this helps. -Al

 

[liljoe]

JimSC, listen to what Al is saying. He is a very accomplished score shooter and knows the 30 cal stuff well.

Joe Hynes

 

[JimSC]

The reason I mentioned .010 neck wall thickness is the rifle came with 50 pieces of brass and the dies. I am using Berger 115gn flat base bullets which measure .308 on the bearing surface. Sized brass without the bullet .325 and when loaded .328 which leaves .002 for expansion when fired. Neck wall thickness measures between .010 to .0101 or .0102. I tried doing a load workup the other day but only managed to get 4 groups of 3 rounds in to get some velocities before the rain started. Keep in mind this is my first time ever shooting a benchrest rifle and the recoil of this .30 cal surprised me. My bench technique and recoil management sucks. I found out the hard way it's a hand full when the scope bit me. It is completely different than shooting a 6 BR prone and I will need some practice.

 

[AlNyhus]

It's pretty unusual to have a .30 cal BR bullet that goes .3080 on the shank.

The Berger 115's I have are .3082 with a .3083 pr, the various BIB's are .3083 and .3085-6-7 on the p.r. and my own measure .3083 and .3085 on the p.r.

I also tried a 'big girl' .3088 shank/03091 p.r. Melonited die.

Again, for what it's worth. -Al

 

[rocketron]

It's a new (to me) rifle and the die came with only the .225 bushing so it seems to me that to get the .003 tension I have little choice other than .010 wall thickness. Thanks for the comments however, they have motivated me to purchase a .224 and a .226 bushing this week.

i hope your bushing size is a typo.

 

[jackieschmidt]

Listen to Al. The most important dimension is what the loaded round measures and how much actual clearance the neck has in the chamber.

Personally, I think under .002 overall clearance is a little too tight for a 30 cal. I get the best performance with between .002 and .003 actual clearance. What you will get with too little clearance is an occasional pressure spike, causing the shot to take a mind of it’s own. This is something you want to avoid in a score rifle.

 

[JimSC]

i hope your bushing size is a typo.

yes it was, the actual # is .325

Listen to Al. The most important dimension is what the loaded round measures and how much actual clearance the neck has in the chamber.

Personally, I think under .002 overall clearance is a little too tight for a 30 cal. I get the best performance with between .002 and .003 actual clearance. What you will get with too little clearance is an occasional pressure spike, causing the shot to take a mind of it’s own. This is something you want to avoid in a score rifle.

the brass came in yesterday afternoon and I turned a few, seated bullets and did lots and lots of measuring. I ended up at .0095 wall thickness which gave me a .03275 finished round. I use a Starrett dial so the ten thousandths on the finished round is a approximation, but the needle is about half way between the 7 and the 8. BTW the brass is Starline, once I am satisfied with my neck turning I will step it up to Lapua and also will be switching from Bergers to Bibbs so I get to do the calculations all over again. Now if the rain will just stop and I can get to the range to work on my bench/recoil management technique.

thanks to all for the advice and suggestions
Jim

 

[AlNyhus]

To add to what Jackie has said....I found the best accuracy with a bit looser neck clearances. It was hard to tell at 100 yds but testing at 200 yds. clearly showed better accuracy with .003 neck clearance. Going to .004 didn't improve the accuracy but it didn't hurt it, either. This was with barrels from Krieger, Bartlien, Lilja and Rock (Lederer era, non-5R rifling). The testing was extensive and proven with multiple guns.

The Grand Aggs are won at 200 yds so that's where the majority of testing happened.

Sounds like you've got a good handle on things. Don't be bashful about neck tension and jam, at least when you start testing. -Al

 

[JimSC]

I'm learning, made it to the range this morning. Chronoed some more, still have the long range mindset and looking for flat nodes. Got some nice 3 round bugholes, will see if the loads hold up at 200 with 5 shot groups next trip. BTW took my drummers stool and with the proper seating height the recoil was a lot easier to manage

 

[INShooter]

You mentioned using a dial to measure. If you are going to measure tenths, consider getting a 0-1” micrometer.

 

[AlNyhus]

Got some nice 3 round bugholes, will see if the loads hold up at 200 with 5 shot groups next trip.

A good way to get on the tune quickly is:

Using wind flags:

- A neck bushing .004 under what a loaded round measures over the pressure ring. .003 will work but a .004 is better to start.
- .015-.020 'jam/seat' on the bullet (adjust the seating stem .015-.020 longer than when the rifling marks just disappear on the bullet)
- Lower end powder load to start and go up by .3's gr. until the vertical is gone. Keep going up on the power...you'll see the vertical come back in and then go away as you continue to go up. You should find at least two 'no vertical' nodes.

Once you find this, you can back the bullet up .005 at a time and see what happens. Then, lighten up the neck tension if you like.

Good shootin" -Al

 

[JimSC]

@ InShooter - the dial calipers with .001 resolution are used for outside and inside neck measurements, I have a ball mike for neck wall thickness with .0001 resolution
@ AlNyhus - good advice. I am thinking of doing the entire load workup from scratch a second time with five round groups shot at 200 yards over flags now that I am more familiar with the rifle and feel more comfortable at the bench with it. I really enjoyed shooting it today

 

[Brians356]

Hope this helps.

"Hope springs eternal."
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