Gunsmithing Throat Erosion in a 6 Creedmoor

[PinesAndProjectiles]

I'm running the Berger Hybrids in my 6 Creed. When the barrel was new, I measured 2.192" CBTO to the lands.

I have just hit the 700 round mark, and now have a new lot of bullets. So, first step is check the CBTO with the new lot.

With the new lot, I'm measuring 2.210, meaning,
1. The throat has eroded .018"
2. The new lot is .018 longer than the old lot

I have none of the first lot to measure, so that's out. Is it possible to have that much erosion at 700 rounds?

 

[V-Ref]

It'd be nice to have a bullet from the original lot so your comparing apples to apples

.001-.005 per 100 rounds depending on frequency/intensity of your shooting string sounds about right to me.

What powder? And what bullet/velocity?

You'll have quite a variance in folks experience with this, between powders used, bullet weights/twists how hard folks are running handloads vs factory, shooting string length/intensity, cleaning intervals, HBN vs naked etc....

 

[PinesAndProjectiles]

Thanks VRef. I'm using H4350 and shooting about 3075 fps. I've read Berger lot consistancies can vary quite a bit, but have never experienced it myself.

 

[gknutson]

I shot hornady 105 bthp and H4350 at 3030 fps from a .243 win. with a 1-8 kreiger and this is line with what I saw. The erosion seemed to speed up after 1300 rounds.

Also this was match type shooting 6-10 rounds in 2 minutes or less.

 

[V-Ref]

Example: 6 Comp Match. 115 DTACs/110 SMK. H1000/H4831/RL26 3050 fps. .016ish at 520 rounds. PRS shooting string length/intensity. White patch cleaned after every 100 rounds/match whatever's more.

 

[PinesAndProjectiles]

Good info, thanks!

 

[whatsupdoc]

Yea it sneaks up on you, so now after every second or third outing while I am cleaning the rifle I check the throat so I can make any seating adjustments.

 

[gknutson]

Yea it sneaks up on you, so now after every second or third outing while I am cleaning the rifle I check the throat so I can make any seating adjustments.

And before long your rounds won't fit in a mag. Nothing money (a new barrel) won't fix.

 

[PinesAndProjectiles]

And before long your rounds won't fit in a mag. Nothing money (a new barrel) won't fix.

If this was about money, I would have went 308!

 

[Blowby]

6mm Creed
DTAC 115 BN coated.
H4350 41.1
MV 2967@65 deg.

Distance to lands 2.275 (new)

2.281@84 +.006
2.282@205 +.007
2.283 @240 +.008
2.288 @395 + .013

471 rounds now but I haven't checked to see where it is.

 

[V-Ref]

6mm Creed
DTAC 115 BN coated.
H4350 41.1
MV 2967@65 deg.

Distance to lands 2.275 (new)

2.281@84 +.006
2.282@205 +.007
2.283 @240 +.008
2.288 @395 + .013

471 rounds now but I haven't checked to see where it is.

Excellent data points above.

So Blowbys 6 Creed/4350/115HBN/at 2967 is on a .0034/100 round throat erosion pace.

My 6 Comp Match/RL26/115Naked/at 3050 is on a .0031/100 round throat erosion pace.

Between measurement methods, lots of bullets with ogive variation, HBN/Moly/Naked bullets, barrel steel, cleaning regimes, firing string length/intensity....this should demonstrate how one guys experience with one caliber might mean something different for YOU in YOUR gun regarding barrel throat erosion. And also how some cartridge cases spurn legends of great barrel life vs others..that somehow because of shoulder 10-15 deg of shoulder angle, +.150 in neck length, somehow get around Newtons action/reaction LAW of physics. Higher exterior ballistic performance is inversely proportional to barrel/throat life in my experiences.

A couple more wildcards to consider...I've seen the erosion rate change during the life of the barrel...

And then I dunno how to quantify fire cracking in first 6-12" of rifling, other than results on the target.

 

[whatsupdoc]

My 6.5 Creed is not any better .009 erosion at 327 rounds.

 

[davere]

My 6.5 Creed did .026 in 1500 rounds, which is about half what you guys are seeing in 6mm calibers on this thread, and a good bit better than whatsupdoc's - just for reference, not intended to be argumentative.

 

[hereinaz]

My 6.5 Creed did .026 in 1500 rounds, which is about half what you guys are seeing in 6mm calibers on this thread, and a good bit better than whatsupdoc's - just for reference, not intended to be argumentative.

How hot are you running your 6 creed? I am going to build one as soon as my Nucleus ships.

 

[davere]

How hot are you running your 6 creed? I am going to build one as soon as my Nucleus ships.

I'm running 6.5, not 6. I'm likely switching to 6 creed after this year, though, thus my interest in the thread ;-)

 

[sanpedroranch]

Just finished building a 6mm CrMr has anyone tried running slower burning powders with 105+ gr pills. We all know the H4350 is not easiest to get. I've read the 6mm CM runs H1000 or 7828 but haven't done much investigation on the cartridge. Just trying to get an idea. I went with 6 CrMr over 243 and 6ai this time because of barrel life expectancy but now wondering if it really will make a difference. I try to not run my rifles hot, but sometimes that best node is on the high side of the spectrum.

 

[my human host]

Just finished building a 6mm CrMr has anyone tried running slower burning powders with 105+ gr pills. We all know the H4350 is not easiest to get. I've read the 6mm CM runs H1000 or 7828 but haven't done much investigation on the cartridge. Just trying to get an idea. I went with 6 CrMr over 243 and 6ai this time because of barrel life expectancy but now wondering if it really will make a difference. I try to not run my rifles hot, but sometimes that best node is on the high side of the spectrum.

If you're talking 6mm Creed, I was able to get to 2975fps with H1000 and Ramshot Magnum out of a 27 inch Shilen. Wasn't satisfied with the accuracy or ES (around 40 fps), so I stuck with H4350 and a 95 grain Sierra tipped match king at 3225fps. To be fair, the inaccuracy and ES may not have been a result of the powder, but rather an issue with bullet to barrel fit, neck tension, wrong primer, etc...

 

[Greene]

I have been running 6cm for several years in PRS competitions. Depending on where I am in the match cycle I pull between 1500-1800 rounds. Yes the 6mm has more throat erosion than 6.5 etc. but I don’t get bent out of shape chasing lands with the 105 hybrids over every little change.

New my ogive COAL was 2.149”
Now at 567 rounds after last weeks comp 2.193”.

Did some testing with Alpha Munitions New SRP brass. Same load, never touch the seating die etc. so jumping extra .040” over my original seating depth. Here is a pick of the results. 5 shots at 740yds.

 

[V-Ref]

I have been running 6cm for several years in PRS competitions. Depending on where I am in the match cycle I pull between 1500-1800 rounds. Yes the 6mm has more throat erosion than 6.5 etc. but I don’t get bent out of shape chasing lands with the 105 hybrids over every little change.

New my ogive COAL was 2.149”
Now at 567 rounds after last weeks comp 2.193”.

Did some testing with Alpha Munitions New SRP brass. Same load, never touch the seating die etc. so jumping extra .040” over my original seating depth. Here is a pick of the results. 5 shots at 740yds.

Nice shooting

What powder/velocity/barrel. My math says that's around .007 per 100 rounds, a bit on the quicker side of the spectrum. Cant argue with results on the target. I'm primarily interested in learning if the cooler powder/lower pressure theory has substance to it regarding barrel longevity.

Sidebar...quick thoughts on the Alpha brass? Interested in the SAUM stuff they talked about releasing later this year.

 

[Greene]

Nice shooting

What powder/velocity/barrel. My math says that's around .007 per 100 rounds, a bit on the quicker side of the spectrum. Cant argue with results on the target. I'm primarily interested in learning if the cooler powder/lower pressure theory has substance to it regarding barrel longevity.

Sidebar...quick thoughts on the Alpha brass? Interested in the SAUM stuff they talked about releasing later this year.

I run special short chamber so that could be part of it. H4350 3120fps with 41.6gr. Bartlien barrel. This is also with hard match use. 200-300 rounds per weekend. Have 2 big matches and a 1 day match on it.

Alpha brass seems to be doing great. Very consistent...