Keyholing Supersonic??? Help??

[masblackbelt]

Alright guys, I'm new here so bear with me. I went to the range this weekend and shot some handloads I hadn't used much before. They were 110gr Vmax loads. I noticed every round was keyholing at 7-10 yards. So without anything else to shoot besides Barnes rounds, I loaded a few up. Also 110gr handloads, they shot and grouped fine from my rifle. Any idea why this could be happening? My only two guesses are that either 1) the Vmax load had 17.5gr H110 behind it just for plinking, while the Barnes 110gr TacTX had 19.5gr H110 behind it. And I just wasn't pushing the Vmax hard enough. Or 2) the shorter Vmax round needed to be seated out further because it is a shorter projectile, however they were loaded to the Hornady COAL recommendation in their reloading book. Any ideas? It confused the heck out of me.

[plant.one]

i wonder if you're getting a good concentric seating.


roll a few of them on the bench...

look for wobble on the tip of the bullets


also can you give us more details about both the firearm and the reloads themselves?

[masblackbelt]

I'll check concentricity... I usually seat the bullet, then rotate 90 degrees and seat again to help aid in concentric rounds. The firearms is a built AR with a 10.5in 1/8 twist FN CHF barrel that PSA sells. Has a lantac EBCG, SilencerCo ASR muzzle brake, and keyholed with both the SilencerCo Omega on and off with the Vmaxs (Thank goodness no baffle strikes). The load is using converted LC brass, CCI small rifle primers, 17.5gr H110, seated to COAL of 2.050, no crimp. I use RCBS small base dies. When I got home I pulled a bullet and verified the charge, also verified that the bullets were not undersized (They mic .308 exactly with a Starrett mic.)

[rebel]

Are you crimping, seating hard when reloading them or anything else that could damage the very fragile jacket on the v-max?

[masblackbelt]

Not that I know of... I don't generally crimp (these are not crimped), and I de-bur and brush the case mouth before loading. Seating doesn't seem to require excessive force. The one bullet I pulled did not appear to have any damage to the jacket. I'm hoping to find time this weekend to load up some more at the same charge as the Barnes rounds to test. Thought I might try and check my jump to the rifling as well.

Pretty frustrating issue really, I don't think I've ever heard of super sonic rounds keyholing in 300blk due to the fast twist rates. Maybe the problem is that I've ticked off the 300blk gods because that particular load costs less than 50 cpr.

[dellet]

I would forget conventional wisdom for loading an AR and load like a bolt action or even the dreaded Bench rifle.

If you full length size and use a small base die, then load a real short bullet to a short COL, the round flops around in the chamber like a fish in a bucket of hot water. The Barnes shooting better might be a clue, it at least had the tip of the bullet in the rifling allowing it to at least get a good start down the barrel.

Make up a case trimmed 1.370-75" so you can find the lands with the V-max, but you will probably need to seat it .100-.120" in the neck just to keep it from falling out when shooting. From memory, in my chambers, I think there is less than .050" left in the neck at touch.

Minimally size your fired cases, since there is so little shoulder, keep it as long as possible. If you compare your converted and fired datum lines, you might find more than .020" difference

You might also pull the bolt out of the carrier and check for copper on the backside of the bolt. That would be an indication of the bullet being shaved.

[masblackbelt]

Thanks Dellet! That sounds like a pretty solid approach. Gonna try to really devote some time to figuring out the issue over the weekend. Hopefully I'll learn something in the process! If I get it figured out, I'll definitely post it up on here.

[popper]

Vmax works fine in my 10" pistol, chopped brass. Base 1/2 in the neck. H110, Not nearly as hot as your load. KAK 1:8 barrel. FCD crimp. Too lazy to run out to get OAL but they are short of mag length by 1/4"

[masblackbelt]

Well, I spent some time this weekend working on the issue. Tried to take Dellet's advice. Made some minty fresh brash to 1.375 and set the sizer die up .005" with a feeler gauge. Rifle didn't want to chamber that, so set the sizer die all the way down, and pushed the shoulder back to normal spec. Still didn't want to chamber, so I went ahead and trimmed them back to spec since it wouldn't chamber the longer brass. Went ahead and loaded up some vmaxs at the hotter Barnes charge weight, and went to try them out. Guess what? Couldn't get the rifle to duplicate the keyholing with the original load. So I've figured nothing out so far. I think for future loads I'm going to load them a little longer, since the 300blk has such a long free bore and the vmaxs are so short. I'll continue to keep an eye on it, and see what happens. Not sure I'm going to shoot the rest of what I've got loaded through my can just to be safe.

Tldr; maybe I'm just going crazy...

[dellet]

Well, I spent some time this weekend working on the issue. Tried to take Dellet's advice. Made some minty fresh brash to 1.375 and set the sizer die up .005" with a feeler gauge. Rifle didn't want to chamber that, so set the sizer die all the way down, and pushed the shoulder back to normal spec. Still didn't want to chamber, so I went ahead and trimmed them back to spec since it wouldn't chamber the longer brass. Went ahead and loaded up some vmaxs at the hotter Barnes charge weight, and went to try them out. Guess what? Couldn't get the rifle to duplicate the keyholing with the original load. So I've figured nothing out so far. I think for future loads I'm going to load them a little longer, since the 300blk has such a long free bore and the vmaxs are so short. I'll continue to keep an eye on it, and see what happens. Not sure I'm going to shoot the rest of what I've got loaded through my can just to be safe.

Tldr; maybe I'm just going crazy...

The chamber should allow for a length of 1.374"+, but that will depend on the base to Datum measurement being at max to keep from headspacing off the rim of the neck. Basically the chamber needs to allow for a neck length on brass trimmed to max length of 1.368". You can see it in the chamber drawing below.

The .335" diameter of the neck stops at 1.378"



It is easier to see on a reamer print



In your case, if it stuck with a .005" feeler gauge, the shoulder was still too far back or short. You needed teh shoulder farther forward, maybe a .010-.015" shim.

The cartridge datum line should be 1.0707" min, 1.0818 max. My guess is that with the die screwed all the way down it's closer to 1.06. This is where a comparator or some other way to measure base to datum is a big help.

At least you have the keyholing worked out, but I think you're setting the shoulders back much more than needed. Accuracy could probably be improved some.