Gunsmithing Sticky Freebore??

[308plinker]

I recently acquired a rifle chambered in 6.5cm. From overall condition, and based on borescope and overall visual inspection, I would have to assume this rig was not run hard and put up dirty. Anyway, I went thru my usual load workup, and as I was getting my bto for seat depth, I encountered something strange. I must remind everyone that I used my preferred method of firing pin removal and hand fitting with a case modified to allow bullet to slip in neck. That said, as I feed the bullet in chamber and approach the throat, I hit what I can only call a “sticky” throat. That is to say I definitely hit a stop, but it’s not a hard stop. Push a little harder and I go another .060-.080” and hit a solid wall. Here’s the problem, that first “sticky” wall has the entire bearing seated to the top of the neck. Also broke out the OAL gauge just to make sure it wasn’t the bourbon talking! Lol. Only Ogive to tip above case rim. I didn’t give this much concern at first, and seated .020” off the second hard stop, but after a short ladder test I’m now getting pressure signs well under max load, and my velocity is in the 2,650 range. I know I’m well under max as I’m not getting a good seal around neck when firing. Filthy necks on case upon extraction. I know I’m spiking, heavy bolt, extractor marks on rim, flattened primers. I know I’m seated in that “sticky” area, and it has to be the cause of my pressure spikes.
Here’s my initial thought, but wanted opinions. Could this have happened from a dull finish reamer? One that was a couple of barrels past too sharp to get a clean cut throat? My next question would be can I resolve this without pulling the barrel and using a 6.5 throater? At this point the rifle isn’t safe to shoot. Any help would be greatly appreciated!

 

[linedrive301ft]

Possible carbon ring. If you have a scope look for this problem. Just found one on a 223 yesterday. I was getting false readings and hard chambering.

 

[Sheldon N]

Sounds like a carbon ring to me too. I'd give it a try cleaning it with some CLR (yes the household calcium lime rust remover). It's strong stuff and pretty acidic but it attacks carbon like no other. Soak a patch and stick it in the throat and let it sit for half an hour then bronze brush to scrub, repeat if necessary. I don't like using CLR regularly but for this kind of problem it does the job great.

 

[Supersubes]

Is it a custom gun, or a factory rifle?

 

[linedrive301ft]

I agree with Sheldon N on this. I have done this process and it worked as he has said.
Have you noticed any scratches on the bullet just above the neck?

 

[ShtrRdy]

A carbon layer is likely, but another check would be to measure the diameter of the bullets your using. In the CM chamber there isn't much room between the bullet diameter and the free bore diameter. About 0.0005". So the bullet needs to be right at 0.264".

 

[Bradu]

I have a brand new barrel that has this issue. I'm assuming it was a worn reamer, you can see rub marks on the bullets.

 

[308plinker]

Not carbon ring. You could eat sushi off of this surface. I scrub my bores with serious OCD. I shoot F/TR primarily, and 600 and 1,000 are my specialty. I’m leaning toward a dull reamer. Don’t want to dump on smith, gonna give him a chance to make it right. It would be different if I were chasing lands. This is the opposite. It’s really weird. I’ve seen this before years ago. If I seat where I touch I’m so deep in the case I can only see ogive above case mouth. Pretty frustrating to say the least. Called smith a few weeks ago and documented problem. I believe he will make it right. Sucks because now I have to send him a barreled action that will be out of service for 6 weeks plus.
I have a friend who’s a top shelf smith, but I believe a condition like this should be owned by the builder.
To the question of custom or not. This is a Shiny like new TL3 DLC’d with Bartlein heavy Palma 23” that I shoot suppressed. Sitting in a Manners that has one of the prettiest bed jobs I’ve seen. Had to ream out a spot for the Jewell safety arm to articulate. Other that that, she’s a keeper. Was grasping at straws here, but thought I’d give it a try. Thanks for chiming in fellas, means a lot.

 

[Twitchy]

Are you using virgin brass? I've run into the same "symtoms" thinking the reamer was bad, but it was the brass. I was using brass from my last barrel (different reamer) and the area just above the case head wasn't sized back down enough with my dies. I ended up needing a small base die and everything came back together.

 

[021411]

Welcome to my world. My build has an awfully short throat. I called the smith and they said nothing was wrong even though I gave them what I measured. “User error” they said. It shoots lights out though but I hit pressure signs quick. I wanna say worn reamer as well.

 

[308plinker]

I used virgin brass....and I know where you’re going. I remove my firing pin and hand feed many cases before I load to verify head space. Now, Just my personal experience, but I’ve never seen 0 headspace cause a pressure spike. I keep hearing people say they do, but I have many rifles I can chamber a fired case in with no shoulder bump and they show no pressure signs whatsoever, and you couldn’t drive a cunt hair between shoulder/chamber, but there is some gap there...all cases springback. I have seen it all when it comes to pressure, from cases too long and crimping bullets when chambered, to bullets jammed so deep in rifling that if having to unload, instant powder dump in action. To that end, just for peace of mind I FL size new Lapua cases and verify length before I ever seat a primer. My first thought was “Flash pressure” due to a large gap of air in case. But, this is so random it’s creepy. It’s almost like the throat is oblong shaped. Meaning I can fire a round 3 grains under max and get pressure, the next load could be 1 grain under and no pressure. There’s no consistency with this. If I had to guess, I’d say that the lands are undercut a few 10 thou on one side, but not on the other, or the chamber isn’t concentric to the bore, which I’ve seen before and is normally a non issue. My loaded rounds aren’t 100% concentric. I may have 1-4 thou of runout depending...don’t go giving me the business about bullet runout. I turn every new Lapua case neck I run through my rigs, and use Redding bushing dies. Could it be better, yes. Would I go insane and become an alcoholic trying to get rid of it....Absofreakinlutely! Anyway, I will follow up with final results of this weird situation. If I have to eat some crow it won’t be the first time! Tastes like chicken at this point in my life!

 

[Terry Cross]

Lead diameter could be the culprit.

HSS reamers can have a very rapid wear rate around that area. If the reamer has much wear, it could certainly cut a beautiful chamber with an out of spec lead coming into the throat.

We ran into this years ago with 95' Palma reamer running 0.3084" lead diameters and cutting lots of chambers.


./

 

[308plinker]

I understand the throat will erode with firing, but if the lead is that much out of spec, would trying to wait until it's "fired" out be an option, I just don't see it? I can run Berger 130 OTM's seated back with enough bearing above neck rim to make it work. But that just pisses me off as I bought 500 each of 140 Berger Hybrids and 140 ELD-M's. I have another 6.5CM that I can load for, but again.....that's bullshit. Pardon my anger, but this is a condition that should have never made it out of a shop. Again, I'm not going to throw this shop under the bus as I believe everyone should be given the opportunity to make things right. I'm just hoping there's an alternative to pulling the barrel. I don't think I have another choice at this point.........but would like to hear any options available if you guys would be so kind as to offer up suggestions......regardless of how "off the wall" they may sound.

 

[Terry Cross]

IF the lead diameter is the culprit, you will have to put up with a PITA and spend a fair amount of money on ammo just to "shoot out" the barrel.

IF the lead diameter is the culprit, you should be able to return to the builder for easy fix with freshened up reamer. The builder may even be able to clean it up without removing the barrel.

.

 

[308plinker]

This sounds like the direction to go. Will follow up with smith tomorrow and see what he suggests. I can see this getting missed with a go gauge. How would a smith catch this condition before calling a build good? Setting headspace is one thing, verifying a clean leade is another animal altogether. One would think a dull throat portion of a reamer would offer some indication of being dull during the process aside from more effort per pass. I can see this happening more often than is documented. I’d like to know how many barrels were pulled because of this condition. I guess there’s no way to really know....