I'm stumped...bolt won't close

[Frank Green]

Just to chime in, this barrel WAS NOT chambered by Bartlein. This was done by a gunsmith nearly a decade ago.

I think the real culprit was a carbon ring and a tight chamber. I cleaned the carbon out again just for good measure and did some load development this morning. Looks like a Bartlein doing Bartlein things...thanks @Frank Green for your excellent work

View attachment 8747789

any of those powder charges will work!

 

[patriot07]

any of those powder charges will work!

My first Bartlein but most certainly not my last...

 

[tacoman69]

Are you sure the bullets measure .2638"/.2639".

Are you sure your mic or measuring tool is properly calibrated and reading correctly?

I ask not to be offensive at all but more often than not what you measure and what you use vs what tools the manufacturer has and uses the measurements are not even close.

Think of this for a minute... let's say your reamer actually cut undersize by a couple/few tenths. Let's say the reamer actually cut the throat at .2642". Then let's say your bullets are actually measuring .2642". Your size on size. Bullets could be in spec but the throat is undersize and causing your issue.

I don't recall or know offhand the actual spec. Hornady makes the 140 ELDM's to. Usually a bullet maker has a standard spec for a given bullet. I'm guessing here so bear with me and don't call Hornady and say... Frank said So!

Let's assume Hornady makes those bullets to a min spec. of .2640" with a tolerance of +.0002". That could give you bullets in the same lot measuring from .2640" to .2642".

Even if the reamer is spec'd at .2645". Now let's say the bullets measure .2642". That doesn't leave a whole lot for clearance per side. Total it leaves you only .0003" total clearance on the diameter. Your numbers start to stack and presto... you have issues.

I've seen it with 300AAC as well. The clown that spec'd the chamber spec'd the throat at .309" diameter. Well guess what they did.... they spec'd the bullet could be as large as .309" diameter and I've actually measured reference ammo where the bullets measured .309" diameter. Then a brand new reamer we had cut the throat at .3088" to .3089". Guess what? The rounds wouldn't go into the chamber. The rim thickness of the case actually stuck out of the chamber around .050"! Pressure jumped 6k psi on a pressure test barrel and velocity jumped like 75fps. on the spec reference ammo.

I'm kinda going through this and have a question. Typically a tight chamber will get worse over time as carbon builds? It won't get better as it gets "worn in" right? I got a 6cm prefit for a kids hunting rifle build. Wanted to shoot factory ammo Black 105 BTHP and 108 ELDM as I don't reload. Barrel headspaced fine so I cycled the 105s through it but it seemed very tight when trying to close the bolt and they cycled very poorly. I could see rifling marks on the extracted bullets. I had two lots of 108s that cycled through it too. One lot cycled better than the other, still not great but better than the 105s. both lots didn't have rifling marks but had marring on the bullets similar to others are posting. I finally got to the range and they shot and cycled not ideal. Nothing got stuck but if I wasn't super deliberate and firm with the bolt though it wouldn't feed great. Not ideal for a kids gun or hunting rifle. Wind was blowing 20+ so wasn't able to get true idea for precision but it seemed acceptable. I'm assuming somethings undersized though and think it will get worse with more carbon so I should probably send it back. your thoughts?

 

[Frank Green]

I'm kinda going through this and have a question. Typically a tight chamber will get worse over time as carbon builds? It won't get better as it gets "worn in" right? I got a 6cm prefit for a kids hunting rifle build. Wanted to shoot factory ammo Black 105 BTHP and 108 ELDM as I don't reload. Barrel headspaced fine so I cycled the 105s through it but it seemed very tight when trying to close the bolt and they cycled very poorly. I could see rifling marks on the extracted bullets. I had two lots of 108s that cycled through it too. One lot cycled better than the other, still not great but better than the 105s. both lots didn't have rifling marks but had marring on the bullets similar to others are posting. I finally got to the range and they shot and cycled not ideal. Nothing got stuck but if I wasn't super deliberate and firm with the bolt though it wouldn't feed great. Not ideal for a kids gun or hunting rifle. Wind was blowing 20+ so wasn't able to get true idea for precision but it seemed acceptable. I'm assuming somethings undersized though and think it will get worse with more carbon so I should probably send it back. your thoughts?

Well you bring up another variable that I didn't think of at the time.

Being box ammo.... they can or do have a seating tolerance on overall length. So it's entirely possible if some rounds the bullets are seated a little longer could be touching the rifling as well. I'm assuming this is all box Hornady ammo? If so I don't know they're tolerance on seating o.a.l. of the rounds but know one spec for 300WM (not Hornady ammo or Hornady spec. so don't think that's what I'm saying here) has a tolerance of +/-.050". That's a pretty big range

What spec reamer was used to cut your chamber? Saami min spec.... or some custom match spec.? I ask because this can affect seating depth and where the bullet might or might not touch the rifling.

How many times was the reamer used? The first thing that goes on a reamer is the throat... even if you using a roughing reamer the finish reamer the throat area is cutting all the time and as it wears the throat diameter will typically cut undersize even if it appears to but cutting cleanly.

Saami min spec reamers for 6CM is suppose to cut the throat at a .2435" diameter.

Which brings us back to... what is the bullet diameters you have and overall seating length?

So you could have a compounding problem/issue... carbon build up, reamer spec, ammo spec. Follow me?

How are you cleaning it and with what and how often (in between number of rounds fired)?

Factory gun or custom build?

Right now more questions than answers.

If it's a custom build... I'd ask your gunsmith for a copy of his reamer print for the reamer he used to chamber the barrel... who made the reamer and as well as how many times has the reamer been used? Tell him what is going on and ask him about sending it back for him to look at if it was a custom build.

Also if a custom build...who made the barrel and to what spec was the bore made to? I ask this because if it's a tight bore spec barrel.... that could be adding to your issue and another variable.

Later, Frank
Bartlein Barrels