Help...anyone ever have a throat tighten w/use?

[DougH9]

I'll try to keep this short & sweet:

I have a new 30-338 rifle (M70 & Krieger bbl.). When I got it I noticed a couple light scratches on chambered bullets, just past the neck. There was no resistance going in or out, and I thought they were burrs that would fire out.

I put 100 rounds through it, and it shoots great, tested out to 600 yards.

Well, today I go out to shoot & verify zero, and I notice that it is hard to chamber a round. I shoot anyway and it shoots ok. Then I try to extract a live round, and the bullet sticks! (this is the same everything-bullet, seating depth, etc.)

At home, I examine bullets that are extracted, and they have a full, circular, burnished ring around them. They are not hitting the lands, but are sticking in the throat. It appears that the throat has tightened up on it's own!

I thought about fouling, but have scrubbed it good, and shining a light inside it reflects back like a mirror.

Can anybody shed some light on this?

Thank you for any help. Doug

 

[sewwhat89]

I would suspect some carbon fouling. That is my differential diagnosis.

 

[DougH9]

Stephen...that's what it seems to have been.

This morning I took a dummy round and threaded an old M14 cleaning rod into the primer pocket. I put a little fine polishing compound on the bullet ogive, and twirled it by hand around in the "tight spot" for a while. Cleaned out the compound, and my normal lenght loads now chamber fine.

I have never seen anything like this. It only has 100 rounds through it, and I always cleaned it well (scrub with bronze brush and solvent, plus Sweet's for the copper).

The powder is H-1000, and it appears to burn clean.

 

[ewallace]

Carbon in a tight through would be my first guess. I would use wipe-out brushless bore cleaner and let it sit over night or 50 BMG solvent on a good brush should get it out.

 

[ewallace]

You could also use JB bore paste or Flitz and just work it in the problem aria first 2" of barrel on a jag and cleaning patch.

 

[Fiftydriver]

I would agree with the carbon fouling comment.

How often are you cleaning your rifle or at least removing the carbon fouling?

One other area to look at, how tight is your throat in comparison to the bullet diameter that you are using? Ya want 1/2 thou total clearance or so over actual bullet diameter.

Kirby Allen(50)

 

[DougH9]

It seems to have a pretty tight throat ( I have no way to measure it). This is my first "tight chambered" rifle, so this is new to me. I usually go to the range and fire 5-15 rounds max, then clean well with bronze brush. It appears that brushing alone is not enough (I sound like a dentist!)

I like the idea of soaking with a carbon disolving solvent...what is the best out there?

I also though of putting a cordless drill on a brush, and going at it like that.

 

[jwp475]

Take a wet patch wrapped around a jag and start at the chamber end and slowly push into the throat if there is carbon build up here can feel it as you push the jag through this rough spot and as you pass it you will notice it takes less resistance to push the jag.If you feel this then I would say carbon build for sure

 

[Stormrider]

The best carbon remover I have used is Wipe Out. Spray it in let it sit and patch it out. Great stuff. Can even let it stay for 24 hours if you have a really stubborn problem and it won't hurt anything. Also takes out copper and powder fouling.

 

[sewwhat89]

[ QUOTE ]
I like the idea of soaking with a carbon disolving solvent...what is the best out there?

[/ QUOTE ]

Go to your local GM dealer and get some GM TEC. It will cut the carbon out like no other. Just use some good common sense with this one as it has some potent chemicals in it. I have heard good reports from folks that have used Carbon Cutter from Break Free and that have used SLiP2000.

SLiP2000

Carbon Cutter

 

[reed mosser]

I agree Gm top engine cleaner really cuts the carbon. I also have had excellent luck choke and carb cleaner. It only $2 to $3 a can. I clean with carbon cutter first then let wipe out set in the bore over nite. /ubbthreads/images/graemlins/ooo.gif