Pressures using neck sealant

[Basic user]

Have a pressure question using neck sealant. If you seal your necks, and let it sit for a while, what does that do to your pressure inside? Like for example, the older milsurp rounds that are sealed with asphalt then crimped hard-how are those rounds not super hot because of that?
Also, on sort of the same subject; 'stiction', the phenomena that Glen Zediker spoke about in his book. He said that when you handle that bullet, the oils in your skin have an acid in in it, and that will cause the two dissimilar metals to react and corrode, and kind of galvanic weld themselves together.

If you want to seal your rounds, should you reduce the neck tension a little to compensate?

 

[whatsupdoc]

Never heard of a reloader sealing their bullets.

 

[MarinePMI]

It's done by some of the factories. It doesn't affect pressure per se, it affects the pressure curve. Because of the sealant, it requires more pressure to force the bullet from the neck. A by-product of this is more consistent neck "tension". It's why many forms of belt fed machine gun ammo will have the bullets "sealed"; it reduces stoppages by increasing the consistency of ignition. Or so a Chief Engineer at a large ammo manufacturer told me, when I asked about primer sealant once....

 

[918v]

Have a pressure question using neck sealant. If you seal your necks, and let it sit for a while, what does that do to your pressure inside? Like for example, the older milsurp rounds that are sealed with asphalt then crimped hard-how are those rounds not super hot because of that?
Also, on sort of the same subject; 'stiction', the phenomena that Glen Zediker spoke about in his book. He said that when you handle that bullet, the oils in your skin have an acid in in it, and that will cause the two dissimilar metals to react and corrode, and kind of galvanic weld themselves together.

If you want to seal your rounds, should you reduce the neck tension a little to compensate?

You should develop your load using neck sealant as one of the ingredients. Also keep in mind that factory new brass has different properties than resized brass which greatly affects bullet release.

 

[RegionRat]

+1 agree with 918v

If you run neck sealant, your load development should include it up front.
It does raise the pressure about 4KSI versus skipping it.

Mil-Spec ammo includes it for traditional reasons that include passing water submersion testing, so those also have primer sealant.

how are those rounds not super hot because of that?

The whole recipe is a system and includes the neck tension, the crimp, and the sealant, among other things.

If you want to seal your rounds, should you reduce the neck tension a little to compensate?

No, not really. Brass prep is still important for functional reasons and to make the ammo sturdy against chambering. You don't want to think of the sealant as something to hold the bullet. Let the neck tension do that work, just like you don't assume a crimp will do that job either.

 

[Basic user]

+1 agree with 918v

If you run neck sealant, your load development should include it up front.
It does raise the pressure about 4KSI versus skipping it.

Mil-Spec ammo includes it for traditional reasons that include passing water submersion testing, so those also have primer sealant.

The whole recipe is a system and includes the neck tension, the crimp, and the sealant, among other things.

No, not really. Brass prep is still important for functional reasons and to make the ammo sturdy against chambering. You don't want to think of the sealant as something to hold the bullet. Let the neck tension do that work, just like you don't assume a crimp will do that job either.

So that neck sealer sitting there for say a few years, does nothing to increase overall tension on that bullet?

 

[918v]

No, it increases bullet hold when it cures and then maintains it.

 

[Basic user]

Gotcha. So if Ive determined that say the hold on the bullet at three thousandths interference fit works perfect, then I'm assuming I should lower that a bit to compensate for the additional hold the neck sealant's going to give me.

 

[Rocketmandb]

So if Ive determined that say the hold on the bullet at three thousandths interference fit works perfect, then I'm assuming I should lower that a bit to compensate for the additional hold the neck sealant's going to give me.

Anything that inhibits (or enables) bullet movement will have some effect on pressure (either up or down).

 

[918v]

After reworking your load with the sealant you should try different amounts of neck tension to see how it affects your accuracy.

 

[RegionRat]

So that neck sealer sitting there for say a few years, does nothing to increase overall tension on that bullet?

When we tested for performance from long term storage, versus accidental extreme exposure, or suspect lots, we found that there are changes in the pull forces but they still typically shoot to the accuracy standards unless the ammo is very damaged.

In terms of the role of brass prep and neck tension, crimp, and sealant, you can hardly detect the effects of long term ammo stored properly, but you can detect ammo stored poorly or over exposed as in containers sitting in the desert sun too long.

If the neck sealants leaked, there were shifts in the stats of the pressure and velocity, but those "failures" were statistical meaning a good share were still at the correct average. If the gas and propellants were very dry due to sealant failure, the velocity goes up regardless of the pull force. If the humidity of the powder charge or gas was high, the ammo slowed regardless of the pulls force.

My advice to individuals is to protect your ammo as much as possible from shocks and water. Pay attention to the humidity (water content) of your powder when loading, and study your neck tension tolerance as well.

Several ammo specs are available on the internet and you can study them if you are interested. They include the QC issues of how we look at neck tension or pull force with respect to brass prep, sealant, and crimp.

Keep in mind, Mil-Spec ammo is not match ammo, but it is still pretty good stuff in my opinion after considering some of the commercial junk. You can do a lot worse than real M193 for example of commercial 55 grain ball ammo.

In terms of plinking, hunting, competition, or defensive context, with the proliferation of things like force-gage arbor seaters, or the AMP Press, it is easy for a reloader to study the overall window of "neck tension" or seating force that matters to their recipe.

When you develop your recipe, play with the neck tension sans sealant at first. See where the level that matters begins and ends, and then introduce sealant and see if the charge needs to be adjusted. Some loads are picky and sensitive, some are very forgiving. YMMV

 

[Basic user]

Understood. Thanks for the perspective guys.