Gunsmithing Barrel wear question

[socal-338]

Hi all,
I have a Barret MRAD in 338 lapua with 250 rounds through it. After the first 50 rounds (Factory Hornady 285 grain match), I measured the chamber and started to use my own loads. I measured the chamber again after 250 rounds (200 of my own loads) and the chamber length has increased by 0.004". Is this normal?

Some notes about the measurement: I believe my measurement accuracy is +/- 0.001" The Brass used for the measurement is a Hornady Lock-N-Load overall gauge modified case (i.e. never fired). The shoulder is 0.004" shorter that a fired case. Im using a Hornady Lock-N-Load Overall Length Gauge for the measurement.

Some information about my loads: Bullet is a Sierra match king 300 gr. Hornady brass. Powder is H1000 using 85 grains. Im getting 2610 fps with an average SD of 12 fps. The loads are 0.010" off the lands and groves. Accuracy on average is 0.7 MOA

Some information about my cleaning: I normally shoot 50 rounds between cleanings. Hopies #9, I run a wet patch first, wait 10 min, then use a brass brush with 10 strokes (20 passes), switch the tip to a Jag, dry patch to get the crud out, wet patch, followed by another 3 or 4 dry patches. Last but not least, some gun oil on a patch and run it through for storage. When Im ready for the next range visit, I run a dry patch on the jag to remove any excess oil.

Thanks,
Phil

 

[Supersubes]

Sounds about right to me.

 

[Quickshot]

My guess is that your chamber didn’t grow. Your once fired brass from the first 50 rounds just wasn’t fully fire formed. I use a Hornady style comparator zeroed on the go-gauge used to chamber the rifle. I chamber my barrels 1 thousandth over go-gauge and the head space closes down a bit after the barrel is torqued. So, I've noticed that the brass needs to be fired twice to match the go-gauge length.

Cheers,

 

[DAVETOOLEY]

My guess is that your chamber didn’t grow. Your once fired brass from the first 50 rounds just wasn’t fully fire formed. I use a Hornady style comparator zeroed on the go-gauge used to chamber the rifle. I chamber my barrels 1 thousandth over go-gauge and the head space closes down a bit after the barrel is torqued. So, I've noticed that the brass needs to be fired twice to match the go-gauge length.

Cheers,

What he said.

 

[socal-338]

I agree that the fired Hornady brass takes more than one firing to be fully "fire formed", but both measurements were done with the unfired Hornady compairitor brass. I'm I missing something?

 

[Supersubes]

.004 isn’t much, and there may be some error in your measuring, but your barrel life is perhaps 2000-2500 rounds. Certainly you’d have some measurable wear. Just one reason why I like loads with some jump, so I don’t have to adress it so often.

 

[Bradu]

Another thing to add, did you use the same bullet for both measurements? That's important if you want accurate results.

 

[socal-338]

Bradu,
Both were Sierra Match King 300Gr, but is was not the same bullet. This time, I have put the measuring bullet aside for reuse in future measurements - Im still learning. Another possibility is how much force was on the bullet when engaging the L&G. I used a cleaning rod and the Hornady Lock-N-Load Overall Length Gauge to toggle the bullet back and forth to determine when it was touching the L&C. Human touch could have added to the error?

Phil

 

[Bradu]

You can have some variation depending on the pressure used when using the hornady gauge. I don't think I would be concerned with the small variation that you would see from that, you are only talking a couple thousandths. Definitely use the same bullet from here on out for best results.

 

[Sheldon N]

Quick clarification... "chamber length" would refer to the length of the part of the chamber that constrains the brass... ie. shoulder dimension. That won't change over the life of the barrel. It appears that you are talking about throat erosion where the lands are moving farther out as the barrel wears. That's why you're getting some confused answers.

0.004 of throat erosion after 250 rounds in a 338 sounds totally normal to me. It will continue to wear as you shoot it.