Cut away view of my chamber on 6.5 Creedmoor 3000 rounds down the tube

[hognuts]

Here is a picture of my chamber on Rock MTU contour 1/8 twist barrel with approximately 3000 rounds down the tube. The barrel was still accurate, just losing velocity, (had to add an additional 2 MOA elevation at 700 yards, 1.5 at 500 etc)









Had several case head separations from running a batch of old brass, you can see the heat ring around where the case head had separated in the rear of the chamber...this mill is going to come in handy for many many things!!

 

[RobertB]

Awesome, where you shooting factory ammo the whole time?

 

[RTH1800]

Lot of that factory ammo comes in old brass.

 

[WildBill3/75]

thanks for sharing

 

[hognuts]

No, they are handloads. 139 grain Scenar, 2.82" OAL, 41.6 Grains H4350...2820-2840ish velocity (when tube is fresh) It had bled off to sub 2700 fps levels towards the end.

 

[hognuts]

The case head separations were my own fault, I pushed brass well beyond its limits...in fact I had intentionally loaded a bunch of "wore out" brass to take to a Wyoming match last summer and was a little skeptical about it, but I got away with it, so I did the logical thing and tried it again!

 

[hognuts]

That wasn't my big issue though, I was just losing velocity and having to add elevation to my dope. The rifle was still accurate, just a little on the slow side.

 

[RobertB]

Lot of that factory ammo comes in old brass.

True, but in my defense a lot of people still just clone the factory. Just as I do. I hotrod some of my cartridges but I always shoot factory load in my creedmoor.

 

[RobertB]

But that's not really much hotter than the factory though is it? Factory 140s call for 41.5 of 4350. I don't know how much the 139 scenars would change it. I wouldn't think much but I maybe wrong/

 

[The Gump]

That's badass! Thanks for sharing.

 

[hognuts]

I really don't think 3000 is bad for barrel life compared to others I have seen. It definitely does not get babied.

 

[Boltfluter]

I really don't think 3000 is bad for barrel life compared to others I have seen. It definitely does not get babied.

Based on what I have seen I think that is very good barrel life. I have seen tactical rifles that have smoked a 6.5 x 47 barrel in as little as 1500 rounds.

Paul

 

[TexasGunTrustLawyer]

Okay, what am I looking at? Or what am I supposed supposed to be noticing?

Anything in particular?

 

[hognuts]

Based on what I have seen I think that is very good barrel life. I have tactical rifles that have smoked a 6.5 x 47 barrel in as little as 1500 rounds.

Paul

Yeah, we don't really "push the envelope" with velocities but I have seen a few guys start bleeding velocity closer to the 2K mark. I have put this up on a few forums and alot of the responses were asking "what happened" It was just used too much when it was new!

 

[hognuts]

Okay, what am I looking at? Or what am I supposed supposed to be noticing?

Anything in particular?

The area in front of the chamber is eroded from normal wear and tear and some of the gasses start leaking around your bullet and the muzzle velocity suffers.

 

[ashiha]

The area in front of the chamber is eroded from normal wear and tear and some of the gasses start leaking around your bullet and the muzzle velocity suffers.

Is that why it seems the lands are so far out?

 

[hognuts]

Yes sir.

 

[Notso]

Those are very cool pictures. I would love to see a factory new or new-ish chamber for a comparo.

 

[cmh2007]

Okay, what am I looking at? Or what am I supposed supposed to be noticing?

Anything in particular?

The complete lack of rifling for almost 2 inches, typically bad juju for accuracy. Also note the ring at the back of the chamber is burning from case head separations, possibly pitting the chamber on that area

Sent from my SAMSUNG-SGH-I747 using Tapatalk

 

[hognuts]

send me one and i will cut it open! Actually I think we may be able to do that we do have some new "take off" barrels from new hunting rifles that were "donor actions" I will see what I can do there.

 

[TheBelgian]

Cool share!! Keep pushing tho

 

[hognuts]

send me one and i will cut it open! Actually I think we may be able to do that we do have some new "take off" barrels from new hunting rifles that were "donor actions" I will see what I can do there.

 

[Jim B in CO]

Can that barrel be set back? (Cut off the milled part and re-chamber farther forward.)

 

[hognuts]

Could be if there is enough "shank" material left, not sure on this one especially now that it has been milled. I know a buddy of mine had got a few blanks with "extra long" shank" area at the chamber end that could be set back by cutting off the entire threaded portion that connects to the action, it is my belief however that if you don't have one of those blanks with the generous shank area, that you have to "pick up the threads on the orignal tennon (threaded part of the barrel where it attaches to the action) and only cut off a small amount so that the chamber is in the thicker "shank" portion of the barrel to support the pressures in the thicker portion of the blank.

 

[Ledzep]

Can that barrel be set back? (Cut off the milled part and re-chamber farther forward.)

I can't find the specs for MTU contours right now. It just depends on if there is enough material left, after he cuts away the milled section, then a shank for the recoil lug and threads for a shoulder against the recoil lug, and if the area is thick enough for chamber pressures.

Had it been done before the milling, yes, definitely. Could have cut it back, then recut everything. I don't know if you'd get back enough velocity to make it worth it, though.

 

[jbell]

That is pretty much it. Setting a barrel back will or should I say may extend the barrel life but not take it back to new. It is usually just better to have a new barrel installed.

Cool pics thanks for sharing. I have seen this threw a bore scope but never had a chance to cut one open and get eyes on. I would like to do that a some point.

 

[dcnyli]

Great photos, thank you for sharing these!

 

[mackdrvr]

I'm curious.
#1 - Did the lands and grooves go all the way back to where the case mouth is?
#2 - If yes, when loading a fresh round into the chamber was the projectile already into the l&g?
#3 - I thought there was supposed to be a small/tiny distance between the projectile, and the l&g?
When looking at the last picture it looks like if you laid a fresh round in there the smooth spot in front of the case in where the bullet should be. I understand throat erosion, and how it happens, but I've never seen it like this before. I'm just trying to get an understanding of where the l&g start in relation to a chambered round. Sorry for the lame questions, but I'm just looking for a little knowledge in regards to the relationship of projectile to l&g distance/location. Thanks.

 

[dcnyli]

You are referring to the "free bore" correct?

 

[mackdrvr]

You are referring to the "free bore" correct?

Yes, but is that what is in these pictures in front of where the case sits? I'm getting confused.

 

[338RUM runner]

Is that what they call a "gain twist" , the farther the bullet goes down the barrel the more twist it gains. Split my old 7 mag (1800rds) with a saw and no rifling for the first 8", I knew it was bad but was surprised at how much was gone. Thanks for the post, Anyone else cut one open.

 

[Layton]

Setting a barrel back will or should I say may extend the barrel life but not take it back to new. It is usually just better to have a new barrel installed.

+1. Given you are only saving the cost of a new blank, setting back is really not worth it unless you have no choice. Dumping the same dollars on a used barrel with a hope and prayer isn't a wise investment IMHO.

L

 

[flatland1]

Never have milled one to expose the chamber/throat, but have done a CeroSafe chamber cast on a 6XC that a customer brought in after putting 3000+rds through it. Found no evidence of lands left out to 3" from the front of the chamber - no wonder accuracy had dropped off just a tad bit... This guy is a pretty good customer - doesn't shoot matches anymore, but loves to take a few rifles out and put beau coup rounds downrange. Honestly, I'd get bored $hitless doing the kind of shooting he does, but whatever - different strokes for different folks.

 

[Ledzep]

I'm curious.
#1 - Did the lands and grooves go all the way back to where the case mouth is?
#2 - If yes, when loading a fresh round into the chamber was the projectile already into the l&g?
#3 - I thought there was supposed to be a small/tiny distance between the projectile, and the l&g?
When looking at the last picture it looks like if you laid a fresh round in there the smooth spot in front of the case in where the bullet should be. I understand throat erosion, and how it happens, but I've never seen it like this before. I'm just trying to get an understanding of where the l&g start in relation to a chambered round. Sorry for the lame questions, but I'm just looking for a little knowledge in regards to the relationship of projectile to l&g distance/location. Thanks.

1: No, not likely. There was probably about 1/4" (roughly, I'm guessing) of free bore (lands cut away, no rifling) when the barrel was freshly chambered.
2: Can't answer that one. Depends on how long he was seating his bullets.
3: There is. Remember, however, that each land is only .004" tall. So as the bullet goes forward from the bearing surface into the ogive, everything from the point where the diameter is .256" (in the case of .264 cal bullets) forward to the meplat doesn't ever engage rifling, and can "overlap".

Basically the throat (ramp from no rifling up to a series of full lands) doesn't have to be the length of an exposed section of bullet (as it sits in the case), in front of the bullet as it sits in the chamber. It can start roughly where the bearing surface (the part that is .264" diameter) ends, and the "ramp" on each land is a similar shape to the ogive of the bullet, so there is very minimal standoff necessary.

As hot 50,000-60,000psi gases and copper are released into the beginning part of the rifling, it slowly erodes, and the throat moves farther and farther forward in the rifling. In the case pictured above, the freebore section is now closer to 3/4" long.

edit to add: The lands that you see starting in that picture are likely not as tall as they used to be (.004"). I'd guess they're much shallower now, and don't reach their full height for a few inches down the bore.

The lands generally don't wear down nearly as fast towards the muzzle. This is why you'll see M1 Garands and other old rifles with two values- ME (muzzle erosion) and TE (throat erosion). ME is almost always less than TE. Obviously because the gases have cooled and the bullet is already engraved by the time it gets to the muzzle.

 

[dj_taboo]

Thanks for sharing!
Thats some interesting perspective.

 

[TexasGunTrustLawyer]

Thank you. Now i know what I am seeing.

 

[mackdrvr]

1: No, not likely. There was probably about 1/4" (roughly, I'm guessing) of free bore (lands cut away, no rifling) when the barrel was freshly chambered.
2: Can't answer that one. Depends on how long he was seating his bullets.
3: There is. Remember, however, that each land is only .004" tall. So as the bullet goes forward from the bearing surface into the ogive, everything from the point where the diameter is .256" (in the case of .264 cal bullets) forward to the meplat doesn't ever engage rifling, and can "overlap".

Basically the throat (ramp from no rifling up to a series of full lands) doesn't have to be the length of an exposed section of bullet (as it sits in the case), in front of the bullet as it sits in the chamber. It can start roughly where the bearing surface (the part that is .264" diameter) ends, and the "ramp" on each land is a similar shape to the ogive of the bullet, so there is very minimal standoff necessary.

As hot 50,000-60,000psi gases and copper are released into the beginning part of the rifling, it slowly erodes, and the throat moves farther and farther forward in the rifling. In the case pictured above, the freebore section is now closer to 3/4" long.

edit to add: The lands that you see starting in that picture are likely not as tall as they used to be (.004"). I'd guess they're much shallower now, and don't reach their full height for a few inches down the bore.

The lands generally don't wear down nearly as fast towards the muzzle. This is why you'll see M1 Garands and other old rifles with two values- ME (muzzle erosion) and TE (throat erosion). ME is almost always less than TE. Obviously because the gases have cooled and the bullet is already engraved by the time it gets to the muzzle.

Thanks dude. Great information. That is the clarification I was looking for.

 

[xdeano]

Would you be able to take a good up close picture of the throat and lands.

Deano

 

[steve123]

You have me curious now Hognuts.

I'm going to go do the same thing to my old 6x47 barrels.

 

[ntexaslongshot]

very cool, thanks for posting.

i too, would be interested in a closeup pic of the throat area.

 

[Killswitch Engage]

The creedmoor match chambers usually have approx .170-.172 freebore. The regular reamer spec is .190 I think. So anything past that is throat erosion...

 

[mkollman74]

Cool pics. Thanks for sharing.

 

[milo 2.0]

That is pretty much it. Setting a barrel back will or should I say may extend the barrel life but not take it back to new. It is usually just better to have a new barrel installed.

I've seen barrels set back that came back shooting better than when first chambered. But in Hognuts case, with velocity loss, the barrel is toast.
Also one must figure in cost, if you're paying for a full chamber job, and may have to repaint, a new barrel is the only logical option. The cost of a setback should be discussed with the smith at the time the gun is first built, then one can plan.

Bill, you probably could have gotten more life out of the barrel with more powder, or a powder switch to maintain velocity, as long as it was accurate. But that chamber ring, if it actually cut into the metal, was just going to cause premature CHS in your new brass.
To me, that's just normal throat wear, and a jump tolerant bullet would have been fine. I shot a 7mm saum up to 2 1/2" of freebore, still was shooting lights out, cut 2 1/2' off for setback, came back shooting better, and maintained velocity.

Of coarse you get the good times, wont mention my 6.5x47 that was dumping the velocity daily at 1600 rds, and paid a premium to set back, still trying to get it to work!!

 

[308Gunner]

That is pretty cool, thanks for posting

 

[hognuts]

I will get some pics closer of the throat area and set a round in there so you can see where the Ogive is in relationship to where the lands and grooves are. We load ours to 2.82" OAL which should be just a few thousandths off the lands with the reamer we are using.

Milo, We talked about setting this one back, but I didn't want to if I wasn't going to the full life out of it I didn't want to dick with it, figured I would just screw a new one on and run with it. We have had pretty good luck with the Creedmoor as far as not being picky between barrels. My 6.5 SAUM was a different story, that thing took 800+ rounds of load development before I got it to shoot....a story for another time when we both have a drink in our hand!

 

[milo 2.0]

Nuts, you did the right thing, hope I didn't convey opposite message.

 

[Jim B in CO]

...Rock MTU contour 1/8 twist barrel with approximately 3000 rounds down the tube.

Anyone have an idea of how many rounds until a .308 barrel would be eroded that badly? Maybe 7,000 or 8,000?

 

[Killswitch Engage]

Depends on the load and strings of fire etc. could be as soon as 4-5k

 

[milo 2.0]

I'm curious.
#1 - Did the lands and grooves go all the way back to where the case mouth is?
#2 - If yes, when loading a fresh round into the chamber was the projectile already into the l&g?
#3 - I thought there was supposed to be a small/tiny distance between the projectile, and the l&g?
When looking at the last picture it looks like if you laid a fresh round in there the smooth spot in front of the case in where the bullet should be. I understand throat erosion, and how it happens, but I've never seen it like this before. I'm just trying to get an understanding of where the l&g start in relation to a chambered round. Sorry for the lame questions, but I'm just looking for a little knowledge in regards to the relationship of projectile to l&g distance/location. Thanks.

Try find a reamer diagram somewhere, it'll answer a lot.

 

[rubicon_unlimited]

I will get some pics closer of the throat area and set a round in there so you can see where the Ogive is in relationship to where the lands and grooves are. We load ours to 2.82" OAL which should be just a few thousandths off the lands with the reamer we are using.

Looking forward to seeing these!