Bullet Keyholing

[Tornado_Racing]

I've got a Spike's Tactical SL-15 that I built from the ground up. The gun has roughly 6k through it. 3k Tula 55 grain steel and 3k various 55-75 grain brass (XM193, M855, M856, 5.56 Winchester, .223 Federal, .223 TAP). The gun has a 14.5" lightweight chrome molly 1/9 barrel, carbine gas system w/DD low pro GB, Spike's M16 BCG, ST-T2 buffer, Tubb flatwire buffer spring inside a MilSpec buffer tube. All parts are still stock factory with no replacements added and has been flawless since day one.

Up until last weekend all brass would eject around 2 o'clock and steel would eject around 4 o'clock with no issues related to the build. While at the range Saturday I noticed my steel was ejecting at 2 o'clock and the last 10-15 rounds started keyholing (400 fired) at 25 yards. The keyholing was after a 30 round mag dump as well.

The week before I did some hot/cold barrel testing on various brass to test grouping. 75 grain TAP would group very tight with a cold barrel and XM193 would spread. When the barrel got hot (2x 30 round mag dumps) the results were just the opposite. TAP was showing a larger group and XM193 produced a very tight group. Steel was spreading hot or cold regardless.

I have read that a worn out barrel will case keyholing, but with only 6k fired and the unusual 2 o'clock case ejections I wonder if it's ammo related or if it's something else in the gun. I am very concerned about this so by all means please post your experiences/opinions. You guys are the pros here and have always looked to ya'll for advise.

Tony


ETA: Spell Check

[Blankwaffe]

Read gotm4's post at the bottom of this thread.May be of assistance to you.
https://www.m4carbine.net/showthread.php?t=53390

[Tornado_Racing]

Read gotm4's post at the bottom of this thread.May be of assistance to you.
https://www.m4carbine.net/showthread.php?t=53390

Awesome..............and thank you for the link. I'll try that and see what happens. Been looking to swap the FH to a FSC 556 anyway!

[HelloLarry]

6,000 round through a plain chrome moly barrel?

That barrel is toast!

[Tornado_Racing]

6,000 round through a plain chrome moly barrel?

That barrel is toast!

Does this mean my barrel is shot out and has to be replaced after only 6k?

[5pins]

If you do a lot of mag dumps then yes a barrel can where out a barrel after six thousand rounds.

I would give it a deep cleaning and than try it with different ammo.

[ForTehNguyen]

I would give the gun a huge cleaning first to make sure its not grime related.

if it indeed is worn out, a hammer forge barrel might be worth changing to since it seems you do a lot of shooting. However tho theres been some midlengths that have shot over 30k in non hammer forge barrels with no keyholing.

[Tornado_Racing]

Thanks for the info guys, I'm gonna put it through a serious cleaning and then head back to the range this weekend.

[ralph]

It is indeed possible the barrel is toast..I did the same thing with my first AR,(bushmaster) lots of mag dumps..5000 rnds later accuracy is gone, keyholing, yup, just a few mag dumps too many. In my case, a new barrel and I was back in business..Now, to the OP..you said in your post the barrel in question was a chrome moly barrel. If it's not chrome lined, you may be able to save it..you'd have to pull the barrel and have it rechambered..very probably the throat is toast,Usually the rifling itself is in good shape, If the throat it self is gone, rechambering/rebarreling are your only options. I don't know how much this would cost, But if it was me,I'd use this opportunity to upgrade to a higher quality barrel if possible. I'd consider either a CHF barrel from DD, BCM, or a Noveske barrel, and maybe back off the mag dumps..

[sinister]

If you've been doing magazine dumps your barrel's probably toast by 6,000.

Any keyholing at all at 25 meters means the barrel's gone. If you shoot at 200 and 300 yards you'll either see bigger patterns or groups, or have un-called flyers and misses.

The are two ways to check -- one cheap, the other requires some work.

Clean the barrel well -- barrels wear at the throat where the bullet ogive first meets rifling grooves. You can find a throat erosion gage which drops in from the rear or has an angled handle and fits in from the ejection port. It'll go in a certain distance depending on how it was originally chambered. You won't know what it gaged as new, but it'll give an idea of how far the bullet jumps smoothbore from the case mouth until it touches or engages the first rifling land.

Throat erosion:

http://accurateshooter.wordpress.com...sion-revealed/

Simple gage:



A little more accurate but more expensive:



The most effective way is to get a gunsmith to borescope your barrel so you can see with your own eye (if it's a good borescope record it on tape or CD/DVD) how the heat from gases pushing the bullets out of the case mouths have eaten away your rifle's throat, smoothed the beginning of the land, and if GI how much chrome has been worn away from both lands and grooves.

Stick the borescope in from the muzzle and you can see how much of the gas port hole has been worn away. Gas port erosion will give you an idea of how many rounds have been down your gun and does not affect weapon functioning -- kind of like looking at tooth and gum wear on a dog, horse, or deer carcass.

Borescoping:

http://www.gradientlens.com/precisionshooting.asp

http://www.stevekershawfirearms.co.u...embarrels.html

Borescoping a Remington hammer-forged factory barrel:

http://www.6mmbr.com/f/Lilja_BoreScope_VID.wmv