Heat Cracking? ( Am I a had lad ) ?

[hunter54]

My question/concern is with a AR15. I know if there are any barrel answers it would be on this forum. Ive been shooting and reloading for 20+ years but just got a Bore Scope 2 years ago. (Maybe a mistake) :

A NEW Bushmaster Predator with chrome moly tube. Shot and cleaned 6X using MC-7, Shooters copper remover, and JB's. At this point NO color was showing on my copper remover patches after laying in the barrel for 10 minutes. Bore scoped it and could see a very faint color in throat area, but that was it. (I figured the barrel was broke in)

Shot 20X and cleaned. This was done 5X

This now made a toal of 105 shots down the tube.

Shot 35 rounds and cleaned MC-7, Shooters copper remover and JB's.

This now makes 140 rounds down tube.

During break in shooting I never let the barrel get HOT. However...

Went to the range yesterday and forgot my cleaning rods. Put 85 rounds down range with NO cleaning, with the last 15 rounds the barrel was pretty darn warm. (Ok....HOT). I didn't really see this as a big deal in that in Highpower competition ( of which I participate , the barrels get HOT (and very dirty in an 80 round match. All of my AR's have had stainless barrels until this one. This gun now has a grand total of 225 down range.

Ok...got home and did my usual cleaning.with the exception of the JB's.I then bore scoped it. Seemed to be an excessive amount of the black stuff in the throat and a bit ahead of it. Did a good short stroking with JB's. Scoped again and the barrel interior is PERFECT...... (with the exception of the throat and a bit ahead of it).

What i see now is what appears to be the dried lake bed look (not much but some) in the barrel lands right at the start of the rifling (throat). I probably wouldn't have even seen this had I not got it so clean with the JB's. I also checked the throat by using my Stoney Point tool. The throat length has increased .oo4 from when the gun was first fired.

Alrighty....What do you think? Is all or most of this normal? Do I have anything to be concerned about? Darn bore scope !

 

[chino69]

Fire cracking

I started breaking in a new match grade barrel .243 AI with a 1 in 12" twist. After just forty rounds there was the start of small fire cracking lines at the neck/throat juncture. By contrast, I started breaking in a new match grade barrel, same barrel maker, in .308 with a 1 in 12" twist with no firecracking after 80 rds. Alot has to do with the restriction and pressure associated with the round.
Chino69

 

[Mike Swartz]

I have a .30BR with a Shilen barrel on it and 1680 recorded rounds through it that is just beginning to show a tiny bit of fire cracking in the throat. As Chino69 said, the intensity of the round makes a big difference.

Mike Swartz

 

[HovisKM]

I reread his post a little closer and I need to clarify and ask a question. Is the barrel just a chome moly barrel or a Chrome lined barrel. My answer previously is for chrome lined barrels only. Firecracking in chrome moly and stainless barrels is normal and the answers that Mike and Chino gave are correct.

Hovis

 

[hunter54]

I reread his post a little closer and I need to clarify and ask a question. Is the barrel just a chome moly barrel or a Chrome lined barrel. My answer previously is for chrome lined barrels only. Firecracking in chrome moly and stainless barrels is normal and the answers that Mike and Chino gave are correct.

Hovis

Hey Fellas.
Thanks for the input !

The barrel is standard chrome moly. (Not Lined)

Went to the range this evening and shot some VERY tight groups. Whatever the cracking is, it hasn't affected it enough to hinder its intended purpose.

I'm glad to hear that this cracking is more or less normal.
Thanks again!!

 

[Octopus]

Other things being equal the slower powders will cause more erosion in the barrel. Some powders produce more heat in the barrel than others.

What powder and primers were you using?

 

[hunter54]

Other things being equal the slower powders will cause more erosion in the barrel. Some powders produce more heat in the barrel than others.

What powder and primers were you using?

RL15 with 69gr Match Kings (break in rounds) The break in though is pretty much done now. 23.5 grs of RL10 and 50gr Vmax for hunting. This particular load has shot very well in most of my guns.I was always a real H335 and WW748 fan but they are pretty dirty. The other powders mentioned just seem to burn cleaner and are more accurate with the above bullets, in this particular gun. (Thus far). Almost forgot.... Primers used with 69 gr load were Rem. 7 1/2. Primers being used now are primarily WW

 

[Octopus]

You will not find them in most reloading books but I have had good luck with the VV powders.

My experience is the VV powders produce less barrel heating than most of the other powders. Ball Powders and triple base powders usually produce more heat than others.

The VV N-135 with 55 and 60 Gr V Max tips shoot tight in my Stoner M-4. (223 with 16+ barrel) N-133 works nice also.

I have used a lot of the Rem 7 1/2 primers in my ARs. OK but the Win primers seem to be a little better. With commercial bullets even with my bull barrel rifles most of my aggs are 0.5 or better. Primers and powders all seem to work if the mix is correct. If your barrel and scope are up to it you can get better accuracy with the Berger or most of the custom match bullets. Using my 36X Leupold scopes, Berger or Watson bullets I can some time agg down to about 3/8 with the AR-15. To get down to this you will need a flat block on the bottom of the round forearm. I screw on a 3" X 6" Iron wood block 1" thick so the forearm fits into my standard bags on the front rest.