Throat Erosion

[TimP]

I have 200 rounds down a new Krieger chrome Molly .243 Win barrel and my OAL is now .018 longer. My initial length 2.124 was measured with Sinclair's seating depth tool and a new unfired piece of brass as a starting point for seating depth with the new brass. At first I thought that fire forming the new brass to the chamber was the reason. I then took an unfired case and the original test bullet and came up with the same 2.142 OAL.
I am shooting 37.7 gr of IMR 4350, DTAC 115gr bullet and 210M primer. Is .018 excessive after 200 rounds or is it normal to see that much difference in OAL.

Thanks in advance, Tim

 

[bheadboy]

it sounds like a lot, however, it is possible there was some roughness in the throat that went away fast, and now you have the true "cllean" throat, this is why many folks will "shoot in " a bbl.

Watch and see if the throat continurs to grow or has settled down. i will bet it has settled down and now grows much slower

Bob

 

[gmorganal]

Ditto on bob's opinion. Your barrel's throat is much smoother now that some of the cutting marks left from the reamer have been worn down.

 

[TimP]

Makes sense guys. I am going to check it every 50 rounds and see what happens.

Thanks again, Tim

 

[fdshuster]

Tim: As said above, it's normal to initially get what seems like a lot of erosion, especially with a 243.

The leade area in the throat is smoothing out & once that is done it will settle down somewhat, but the problem of fire-cracking can start to appear as early as 400 rounds fired. I watched it happen with my borescope & it is not pretty.

Three 243 barrels, (Douglas, 2 Shilens) were toast at an average, documented 1400 rounds.

Check out the article on the home page about overbore cartridges & note where the 243 places.

 

[TimP]

fdshuster, read the article it gives me a better understanding. This forum provides a wealth of information. I am allready starting to see some indications of fire cracking. I guess I should order up another barrel because 1200 - 1400 rounds will come quick. The good thing for now is the barrel is consistently shooting in the high 3's and low 4's

Thanks, Tim

 

[lpreddick]

i just now posted the same question and suspicion mentioned here under reloading...didn't read this series of comments before doing so. my increase was only .010 thous and i suspected the leade "smoothing out or polishing" or whatever. thanks,,,i am not loosing my mind, after all.

 

[fdshuster]

TimP: More bad news is that I began to see a drop-off in accuracy beginning around 800 rounds, with all 3, 243 barrels. First indication of something wrong was the occassional throwing of a wild shot, maybe one out of 10 shots, then later 2 or 3 out of 10, and by around 1400 rounds they would not even hold moa w/ 5 shots at 100 yds. Still good for knocking down a deer, but not any type of precision like hitting a g'hog at any distance.

Great ctg. if you "need" it, but not one of my favorites.

 

[matthewusmc8791]

Tim: As said above, it's normal to initially get what seems like a lot of erosion, especially with a 243.

The leade area in the throat is smoothing out & once that is done it will settle down somewhat, but the problem of fire-cracking can start to appear as early as 400 rounds fired. I watched it happen with my borescope & it is not pretty.

Three 243 barrels, (Douglas, 2 Shilens) were toast at an average, documented 1400 rounds.
Check out the article on the home page about overbore cartridges & note where the 243 places.

IF these barrels were toast at 1400, what were your group sizes and at what ranges???

If you were shooting .3moa and then grew to .5moa at 1400rounds whats wrong with that??

Is this rifle a bench rest rifle? did you toss barrel and rechamber?

243s are hot, but unless its benchrest, shooting a CONSISTANT 1/2moa is good shooting. 5" group @ 1000yds

 

[Dgd6mm]

When Frank said more bad news, he said MOA 5 shot group at 100 yards. Meaning with all that goes on in the next 900 yards, 10 MOA would be hard to do, more then likely not even possible. Also it was just going to get worse from there. I've seen some bad stuff in .243's that have been pushed on the hard side , it appears rapidly.