Does .005" seating depth error matter?

Not necessarily a charge ladder as we aren’t looking at group size or shape more so location related to the charges on each side.
We have a seating window that’s perhaps.005 wide so once you’ve gone outside the window YES this can certainly invalidate any seating group type testing.
Hope that helps ya

Are you loading .300 BO? LOL, no; not a bit.

In a factory barrel. . . hairy edge of just maybe.

.30BR for a benchrest gun, sure that might matter.

Keep in mind, any but the most premium target bullets will have that much variation in ogive-to-base and ogive-to-tip.

edwardware said:

Keep in mind, any but the most premium target bullets will have that much variation in ogive-to-base and ogive-to-tip.

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Sometimes that's just the variation in seating stems...

Just remember, however... tolerances stack.

Pertaining to the context of the question: If you are getting COAL change due to chambering, in or out, you do not have enough neck tension. Period. Your ignition reliability is in question, at best.

As to the question itself: yes, 5 thou may be sufficiently enough change to influence your load performance. In some cases, that might mean a destructive, catastrophic over pressure event, or it might be as small as a slight shift in POI or velocity - or might be small enough that your well developed load doesn’t shift appreciably within the expectations of your application.

COAL also should not by your critical dimension for almost all bullets. BTO is the critical dimension. Nothing touches the tip except the target.

Remington factory rifle ammo is doing good to keep the cannelure within the general vicinity of the case mouth- the last box of .270 150 gr Core-Lokts I opened were awful.

Sallgood

The Precision Rifle Blog had a nice series talking about bullet jump recently:

https://precisionrifleblog.com/2020/04/28/bullet-jump-research-and-load-development-tips/

Read it for yourself, but they found that the throat erodes 0.004 to 0.007" per 100 rounds fired. If you are in a situation where 0.005 matters, then you're going to have to change your seating depth every 100 rounds or so. They actually recommend seating farther off of the lands, which might not be as precise, but maintains consistency for a much longer period.

Building off of that, I recently did a test with .223 and 80 SMK's. I loaded 10 rounds each from +0.035, 0.025, 0.015, 0.005, and 0.005 jam. Results were so good with the loads seated off of the lands that I chickened out and didn't shoot the jammed bullets. The group size and chrono statistics were so close between loads that I don't see any reason to go closer than 0.025 or 0.035. YMMV

Is this a semi auto or bolt gun? Bullet set back can be caused by too little neck tension. However, if its a bolt, and you are seeing a .005 bullet set back by just chagrining the round, that would not be caused by too little neck tension unless you are running no neck tension. My guess is that your bullets are hitting the lands (start of the rifling) when the round is chambered causing the bullet to be pushed back into the case. Many precision loader purposely load into the lands because that's where their rifle shoots that bullet most accurately. However, when developing charges, this can cause HUGE pressure spikes that can be very dangerous at max charges. At the very least, its likely going to throw off your ladder testing. If this is the case, you are better off loading rounds at a safe distance from the lands (maybe .030 to .030) for you ladder testing and then play with seating depth to tighten up your groups

As previously mentioned, COL (Case overall length) is less important than BTOL (Base to ogive length) because every bullet has a slightly different shape and what you are really concerned about is where the bullet actually contacts the rifling ( which is at the ogive, not the tip)

How did you determine your COL? Do you have a comparator (Like a Hornady) to check the length of your chamber? If not, this is essential to precision reloading. Not only do you need to make sure you are loading to the correct CBTO of your chamber, but once you find a good powder charge, then you will start loading cartridges at different CBTOs to determine the optimum bullet jump for your bullet/powder charge/chamber.

Since bullets vary in ogive shape, each will have a different MAX CBTO. This can even vary greatly with the same bullet from lot to lot depending on the brand of bullet It is important to measure your chamber with the bullet you are loading to determine MAX CBTO and then go from there.

Although you may not be loading VLD style bullets, here is a helpful article to explain seating depth and how to determine what works best in your rifle.

https://bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/

BTW - the purpose of ladder testing is not to determine the tightest groups. Its to determine where the accuracy node is for a particular powder / bullet combination. You can tighten up your groups once you find the optimal charge by tuning the seating depth and testing primers. This article on OCW might help:

http://optimalchargeweight.embarqspace.com/

Have fun and be safe!

Yup... than as previously mentioned, you are not running enough neck tension. I usually have to load with at least .003 to .004 neck tension in my ARs.

If you are already running at least that much, then could there still be some case lube in the necks?

Are you putting a crimp on the cases?
If not maybe a light crimp will help.

azrocks said:

Guess it's basically the same question as asking "How much variance in bullet seating depth is acceptable before it causes measurable differences in group size?"

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Question that should be asked is how much variation in neck tension and resulting bullet movement affect powder burn efficiency and chamber pressure build to influence maximum average chamber pressures and muzzle velocities. If you are not looking for utmost accuracy, .005" may not matter for shorter distances to target but if you are wanting accuracy at longer ranges, .005" movement of bullet is sign of poor neck tension that should be addressed.

Varminterror said:

If you are getting COAL change due to chambering, in or out, you do not have enough neck tension. Period. Your ignition reliability is in question, at best.

As to the question itself: yes, 5 thou may be sufficiently enough change to influence your load performance. In some cases, that might mean a destructive, catastrophic over pressure event, or it might be as small as a slight shift in POI or velocity - or might be small enough that your well developed load doesn’t shift appreciably within the expectations of your application.

Click to expand...

Good point.

Many bench rest/long range match shooters turn necks to produce consistent brass thickness for more consistent neck tension which in turn produces more consistent pressure build. If you have poor neck tension, you can kiss accuracy goodbye no matter how consistent your powder charges are.

(While you are loading .300 BLK, when loading for pistol calibers, especially small internal case volume 9mm case, neck tension and bullet setback is particularly pertinent as inconsistent neck tension can not only affect accuracy but significant bullet setback can create over pressure situations)

Varminterror said:

COAL also should not by your critical dimension for almost all bullets. BTO is the critical dimension. Nothing touches the tip except the target.

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Another good point.

Bullet length and ogive (bullet nose profile) can vary quite a bit depending on brand and bullet type and when looking at COAL consistency, you are actually looking at distance from start of rifling/lands to ogive and use of comparator is more pertinent.

(For pistol calibers, especially for straight walled semi-auto calibers that headspace on case mouth, distance from start of rifling to bearing surface/bullet base that engages the rifling and bullet seating depth are more pertinent with consideration given to resized case length variation - Shorter length case should be used to set OAL)

And it's good that you are checking for "chambered COAL" as many reloaders focus on "finished COAL" only. It doesn't matter what your "finished COAL" consistency is to accuracy. What matters for accuracy is "chambered COAL" if you are looking for utmost consistency of your rounds and smallest group size.

(And for semi-auto pistol calibers that bumps the nose of rounds on the feed ramp with availability of bullet diameters that can vary, "chambered COAL" is significant to accuracy and .005" seating depth can matter - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4)

Ruger 15151 said:

I usually have to load with at least .003 to .004 neck tension in my ARs.

If you are already running at least that much, then could there still be some case lube in the necks?

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Good point.

This myth busting thread showed lube type used could affect neck tension and bullet setback (or forward in your case) - https://www.thehighroad.org/index.p...affect-on-neck-tension-bullet-setback.834035/

As Ruger15151 posted, are you checking to see if there is residual lube inside the case neck?

Are you getting any bullet "forward" with factory ammo?

can you go over your sizing process so we can get a better idea of what is going on here? also, when, and how, do you clean the cases?

murf

azrocks said:

What I don't know is the best way to address it. Some of mentioned turning down the expander ball in a drill, but this makes me nervous

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Buy an extra expander so modifying it won't make you nervous.