bullet to barrel clearance

[cocowboy]

not sure which part of the forum to post this question, but here goes.... since we are limitied to bullet seating depth on an AR-15 based on magazine depth, I measured the actual amount of set back my bullets have in relationship to the lands and grooves on a recent upper. There is .100" jump.. That seems huge as many of my bolt guns run anywhere from .005" to .0010" jump... Should I be concerned about that gap?
cocowboy

[Irving]

There is a reloading subforum. From what I've researched, this is not a problem for .223 for this platform. Hopefully someone else comes along with more detailed info as to why.

[Little Dutch]

Long distance shooters often load their bullets to a depth that is too long for the magazine. Improved accuracy and probably a heavier bullet being the reason. They buy a single shot follower for their magazine and load them one at a time.

[Gman]

Reliability and tight tolerances rarely go hand-in-hand.

[ray1970]

That one-thousandths doesn?t leave much room for error on that bolt gun.

[theGinsue]

Moved thread to the Ammunition, Ballistics and Reloading forum.

[XC700116]

It's not an issue, there are normally multiple bands or nodes of seating depth that a barrel/bullet combination will like, much like powder charge. I have gone away from seating bullets close to the lands on my bolt guns and search out a bullet that will jump at a bare minimum of .030" and honestly the more jump tolerant the better, because I run up to 300 rounds of ammo through a bolt gun in a weekend at a big match I need that cushion to keep it stable throughout the match. I take the same approach to loading for my gas guns. I start at a comfortable seating depth that doesn't bind in the magazines, and then test in increments of .010" deeper until I find the node that it likes. If the bullet I test won't perform in those circumstances, I switch to another and test again until I find what works and is stable.


Here's a good article that explains it in detail in regards to a specific bullet "known" for being finicky and needing to be seated either jammed or very close to the lands.

https://bergerbullets.com/vld-making-shoot/

[Tim K]

Listen to XC, he’s exactly right.

There are nodes associated with jump distance. The are on the order of 0.060” apart. Shawn (XC) can correct that number if I’m recalling it incorrectly.

[XC700116]

Listen to XC, he’s exactly right.

There are nodes associated with jump distance. The are on the order of 0.060” apart. Shawn (XC) can correct that number if I’m recalling it incorrectly.

I've found it to be completely dependent on the bullet, I've found some that are just a PITA no matter what you do, and some like a 142 SMK, or 139 Scenar that seem to shoot well no matter where you put them. Some bullets have bands in the .060" range and some go to the .100" range. That said the process looks the same.

I typically test seating depth at 3-4 different charge weights at the same seating depth to find the most stable seating depth.

Example: I load up a group of say 22.0 gr, 22.3 gr, 22.6 gr and 22.9 gr all seated at the same depth, the next group is seated .010" deeper, and the next at .020" deeper and so on. I shoot those groups and you will typically see a trend of growing or shrinking group size as you approach the sweet spot in the seating depth. I want a bullet to perform well over at least a .030" spread in seating depth. If it doesn't I will look for a different bullet that will. I don't have the time or inclination to be constantly tuning my loads as the throat erodes and I will sacrifice BC if need be to get a good consistent bullet.

I'm intentionally inducing the charge weight error to find the most compliant seating depth. Then once known I will note how far off the lands that is so as the throat of the barrel erodes I can keep my ammo in the sweet spot by measuring the distance to the lands and adjusting COAL appropriately.

Then after all the bullet selection seating depth stuff is known, I will test charge weights and powders to get the best combination of group size and velocity stability.

Also for the OP, keep in mind a lot of bullets simply aren't designed to be shot in an AR platform due to length vs bearing surface. For instance a 75 ELDM while seemingly fitting for a 223 AR, they won't work, no matter what you do from the magazine. They are too long to actually be seated in the case and fit the magazine while the case neck is still actually gripping the bullet. Hornady built the 73 ELDM just for the AR15 because of this.

I find I can make most bullets shoot without issue in my bolt guns. Gas guns due to the constraints of the magazines sometimes won't. It's just part of the deal. I tested 5 different bullets in my 224 Valkyrie before finding one that works to my standards. There are some known good bullets out there that just seem to shoot well in most guns, so if you want to skip a lot of headaches I'd recommend those, even though they may not be the best BC, best value etc. For example Hornady 75 gr BTHP, Sierra 69 and 77 SMK's tend to shoot well in almost any 7-8 twist 223 gas gun. Maybe not great, but good.