Moly bullets & neck tension

[marchboom]

I have read numerous articles on using moly coated bullets and one stated that because the moly bullet has less friction than non-coated bullets it is better to use more neck tension to keep it from moving just from the pressure developed by the primer. More neck tension would hold the bullet until the powder started burning and that would move the bullet. In my 22-250 I use moly coated Sierra 53 gr. bullets over AA2015BR powder and consistently get .400" groups.

Before I start experimenting with reduced neck tension has anyone here done any testing in this area? Any opinions pro or con?

Thanks.

 

[1shot]

I moly all the bullets for my competition calibers and use .002 neck tension on all of them. 6BRX, 6SLR, 6.5GWI, 284 Shehane, 308.
I hope this helps,

Lloyd

 

[mikecr]

Higher/Lower bullet-neck friction makes no difference to results. You can go back & forth between clean and WS2 coated (slipperiest stuff in the world) and tune & MV will hold just the same.

Moly is nowhere near as slippery as WS2, but drops MV a bit. This is special to moly in that some of it vaporizes in the blast, lowering combustion heat in doing so.
Whether a primer alone can eventually push bullets doesn't matter. If there was powder between them, that powder would raise case pressure way faster than the primer alone.

 

[Ccrider]

Expect a drop in velocity that you may have to tune for. You will not know until you try and it will vary from barrel to barrel.

 

[searcher]

Higher/Lower bullet-neck friction makes no difference to results. You can go back & forth between clean and WS2 coated (slipperiest stuff in the world) and tune & MV will hold just the same.

I agree with this statement when shooting my target rifles and using very light neck tension (which I do whether using moly or not). When applying more tension such as a lot of people do for hunting rifles - and much more tension for shooting semi-auto, I find that I will use more powder to achieve same tune as compared to not using moly. And it doesn't seem to make much difference as to the load or the rifle. I thought I'd throw that in there as it WILL make a difference to tune if using a load which requires more tension than normally used in a bolt target gun. In my heavily-tensioned .223-6PPC sized cartridges, that usually amounts to 2/10th to 3/10 grain of powder to bring the moly load to the same velocity as non-moly. That difference is enough to put most loads on the verge of - or being out of tune, in my own experience. Best way to find out is to shoot your load for effect on a target - and confirm velocity change (if any) on chrono.

 

[1shot]

This thread got me to wondering about varying the amount of neck tension, so yesterday I loaded up 3 rounds each of my FT-R 308 load in ,001, .002, .003, and .004. neck tension. Yes, I know they were only 3 shot groups but I found there was no appreciable difference in the groups with any of the loads.
(43.3 H-4895; Berger 200-20x Wolf SR-M primer, Peterson brass)
I hope this helps,

Lloyd

 

[mikecr]

This thread got me to wondering about varying the amount of neck tension, so yesterday I loaded up 3 rounds each of my FT-R 308 load in ,001, .002, .003, and .004. neck tension. ""I found there was no appreciable difference in the groups with any of the loads.

#1 Your INTERFERENCE is not TENSION.
#2 Seating bullets expands necks to the same interference (zero) regardless of your downsizing.

Neck tension is spring back force against an area of bullet bearing (force x area).
It is directly adjusted through sizing LENGTH (your area adjustment).

 

[marchboom]

This thread got me to wondering about varying the amount of neck tension, so yesterday I loaded up 3 rounds each of my FT-R 308 load in ,001, .002, .003, and .004. neck tension. Yes, I know they were only 3 shot groups but I found there was no appreciable difference in the groups with any of the loads.
(43.3 H-4895; Berger 200-20x Wolf SR-M primer, Peterson brass)
I hope this helps,

Lloyd

Good info. Thanks for the effort you put into this.

 

[Ccrider]

#1 Your INTERFERENCE is not TENSION.
#2 Seating bullets expands necks to the same interference (zero) regardless of your downsizing.

Neck tension is spring back force against an area of bullet bearing (force x area).
It is directly adjusted through sizing LENGTH (your area adjustment).

So, what is happening when my groups with N133 get better as I increase neck tension? Uh, I meant decrease bushing size?

 

[mikecr]

Probably something as imagined as whatever you think causes your brass sooting issue...

 

[Ccrider]

Probably something as imagined as whatever you think causes your brass sooting issue...

Maybe. But there are quite a few people on this site, unlike me, that actually know what they are doing that say that N133 shoots better with more neck tension. Do you think they are just imagining too?

Btw. Not trying to be flip. Don’t have time to waste like that. Just trying to understand what you are saying. Is it that neck tension does not matter if the load is otherwise properly tuned?

 

[Alex Wheeler]

I can tell you from 1000's of rounds group testing at 1000 yards that the interference fit (bushing size) has a large effect on accuracy even far past the yield point of brass. Yes, you can see a difference between .005 nt and .006 nt. on the target. Its a fact. I always cover a powder charge window with different bushings because they can move the tune slightly but usually not much. Neck friction itself (seating force) seems to have little effect on groups, but some neck lubes will ruin accuracy in my experience. Every time I test different neck lubes I see pretty small differences on target, except neolube. That stuff will reduce seating force more than any other lube I have tested, and its ruined accuracy every time I have tried it. I think it may be so slick the primer could be moving the bullet. But Im sure someone out there loves it and has it working for them.

 

[BoydAllen]

#1 Your INTERFERENCE is not TENSION.
#2 Seating bullets expands necks to the same interference (zero) regardless of your downsizing.

Neck tension is spring back force against an area of bullet bearing (force x area).
It is directly adjusted through sizing LENGTH (your area adjustment).

I have seen unmistakable differences in accuracy trying different bushings with no other change with VV133 in a 6PPC. Also, it is common knowledge that jam is longer as bushing size is decreased, within the limit of the elasticity of the brass. The commonly used definition of neck tension for reloading is the difference in the OD of a case neck before and after a bullet is seated, in the area of the pressure ring, if there is one.

 

[mikecr]

Jam length changes with greater interference due to greater seating force (not greater neck tension).
The only time greater interference makes a difference to tension is when you're sizing length exceeds seated bullet bearing. In this case, there remains interference, binding against the bearing-base junction.

Otherwise, with partial length bushing sizing, bullet seating simply expands interference straight to zero, and then minus spring back from there if you were to pull the bullet. Spring back in 24cal is about ~1/2thou.
Try it yourself. Seat a bullet, measure neck OD, pull the bullet, remeasure OD. Bout ~1/2thou right?
You might also notice through this testing that it makes no difference if your interference was 2thou, or 6thou, or 10thou. The bullet just re-expands that(which bullets are not designed for),,, and apparently you do not have that interference you thought you had.

As far as 6PPC, I'm sure notions go to the razor thin conditions needed for 6PPC expectations. I've seen zero basis otherwise. But the competitive pressures there, and things supporting that center, leave little for meaning to the rest of us.

Think anything other than extreme underbore for a minute and consider what really means what. How stuff actually works -regardless of your result expectations.
Then go back to the tiny 6ppc world and understand that it works the same there to. That is, there are reasons that go a little deeper than 'it worked', or 'it didn't work' on target.

Neck tension is local hoop tension force springing back against an area of bullet bearing.
It's not interference, and not frictional seating/pull forces, but pounds per square inch (PSI) gripping (trying to squeeze) our bullets.
If you think not -prove it. Bring the logic.

 

[Alex Wheeler]

We do not understand everything. It would be nice, but we dont. Many cases like the 300 wsm, 6 bra/dasher, 300 Norma imp, ext have shown accuracy improvement going well past the yield point of the brass in regard to neck tension. Its not posted, but I would bet if you polled most successful LR BR shooters more are over .002" than under. Test it at distance, if you can't see a difference in bushings past .002 the rifle is not shooting good enough.

 

[BoydAllen]

It seems to me that insisting on a definition of neck tension that is different than common usage of the term is like proclaiming yourself to be an independent dictionary. Accepted definitions come from commonly understood meanings, and their frequency of use. In reloading if someone says he is using .002 neck tension, we know that he means that the case neck expands by that much in the area of the bullet shank, when a bullet is seated. Beyond that after being so picky about word choice it actually seems funny to say that something does not matter because it requires the best equipment to see the difference, especially on a web site that is ostensibly about the finer points of accuracy. The thing that can mislead us on this is that there are differences between powders as far as sensitivity to what is commonly referred to as neck tension. If one's experience is with a mediocre rifle loaded with a powder that does not respond much to differences in degree of neck sizing, one might be tempted to regard this as a universal truth. It isn't.

 

[urbanrifleman]

Higher/Lower bullet-neck friction makes no difference to results. You can go back & forth between clean and WS2 coated (slipperiest stuff in the world) and tune & MV will hold just the same.

Moly is nowhere near as slippery as WS2, but drops MV a bit. This is special to moly in that some of it vaporizes in the blast, lowering combustion heat in doing so.
Whether a primer alone can eventually push bullets doesn't matter. If there was powder between them, that powder would raise case pressure way faster than the primer alone.

Agreed.