Help diagnose shilen barrel issue

[bani]

Hoping someone can help diagnose a problem I'm having with a shilen barrel.

While my CBI 260rem barrel is at the gunsmith having some work done, I swapped my backup barrel on - a prefit Shilen 260rem bull barrel from NSS.

I started working on handloads, used the hornady tool to measure the lands for some hornady amax 140gr. And set my seater for .020 off.

All was well with the rounds until I tried chambering them. Bolt required a lot of force to close, and also a lot of force to extract the round. This was with the ejector pin removed from the bolt btw.

Upon inspection, the projectiles have a scuff mark on one side. Unchambered rounds off the reloading press are pristine.

Measured runout, under .001". Just to make sure, I used the hornady concentricity tool to get some rounds dead on 0.000". And tried chambering them. Same deal - scuff on one side.

So I tried chambering some ABM 260rem match ammo, it chambered perfectly, little force required on the bolt, and zero marks on the projectile. I measured the projectile diameter - 0.2635". Measured my amaxes and they were 0.264".

I took a bore brush and cleaned the ever living crap out of the chamber. Then tried chambering a round, same problem.

So I am pretty sure the problem is not:

* dies scuffing the projectile
* runout
* jamming into the rifling
* ejector forcing rounds to scrape the chamber
* dirty chamber

Anyone seen this problem before? What else could the problem be?

http://i.imgur.com/BfBcNHa.jpg

[Mozella]

I haven't experienced your exact problem, but I had something similar happen with a brand new Shilen Savage prefit. I had trouble setting up my seating depth data using the Hornady tool. The test case didn't want to chamber easily. Likewise, chambering ammo was difficult and extracted cases showed scuff marks on one side about halfway down the case, similar to the marks on your bullet. My ultra cheap borescope wasn't good enough to see what was wrong but it seemed as though there was a rough spot in the chamber, most likely an artifact from the chambering process.

I fabricated a home made device to hone and then polish the chamber; problem solved. I find that a bit disappointing because I paid for a "match select" barrel and it seems as though a rough spot in the chamber should not get by their quality control process. The good news is that once I honed and polished the chamber, the barrel now shoots very well. I regret not using a good borescope so that I could know for sure what the problem actually was.

Perhaps you have a similar defect in the throat area of your barrel. I'm not a gunsmith, I just pretend to be one in my reloading room so I can't offer advice on how to correct a potential defect in the throat area. You might want to consult with a real gunsmith and/or take a look with a real borescope to see if you can detect a flaw of some kind.

You say this is your back up barrel. Is it new or have you used it before? Did it work OK before? If so, it seems doubtful that it's a fault of Shilen. If it's new, perhaps they can help. Have you called Shilen and/or sent them your photo? By the way, nice photo.

[MRCHIRO]

Ditto was about to say about the same thing (rough spot). I have some dull reamers for this exact reason that I bought for dirt cheap.


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[Deadshot2]

It appears that the scuffing is occurring in the freebore and since you say it's on one side I would go back and look closely at runout. If you have a tight freebore it's ID can well be only a few "tenths" more than bullet diameter. If your runout is .001" or less that sounds good but consider that the ID of the freebore could be as little as .0002" larger than bullet diameter. A lot of Match chambers average ~.0005" on the reamer drawing but if the reamer has worn or been sharpened that dimension can shrink. A snug freebore helps with accuracy but being snug like that can also become a problem if it's a little rough, dirty, or the ammo has even small amounts of runout.

Since it's a new barrel perhaps a patch around a bore brush, some J-B Bore Brite, and a cordless drill, and polish the neck and freebore area in the chamber.

Another one of those times when a borescope/borecam is really helpful.

[RustyShackle]

I suppose you could also make a quarter turn on the barrel and see if the problem is still present and or if it has clocked with the barrel.

[strut64]

I started having problems with measurements being inconsistent using the Hornady tool. I believe in my case it may have been due to erosion of the throat during use.. I studied a suggestion I found on the Nosler website. As a result I have been more satisfied that I got more consistent results. For what ever reason, it appears to me that you are seating too deeply. I do continue to use the comparator tools to measure the CBTO( cartridge base to ogive )

[bani]

For what ever reason, it appears to me that you are seating too deeply.

what makes you say that?

[Scott Evans]

C'mon, don't start two threads on the same subject.

[Robinhood]

C'mon, don't start two threads on the same subject.

Jim loves to spend time combining threads.