A tale of two Bartlein barrels - Cryo treatment?

[TimK]

I have the two barrels pictured. Both are 1-7 Bartlien blanks, both chambered and profiled by Compass Lake with their CLE chamber. The fatty is 12.5", the other is 11.5"

The load is 77 TMK's over 23.0 g of 8208 XBR.

The first 5 shot groups out of both barrels are equivalent, roughly 5/8". Great, right? If I shoot say 5 consecutive groups (2 minutes between groups) on the lighter profile barrel, I get group sizes that go roughly like this:
#1 - 5/8"
#2 - 1"
#3 - 1.5"
#4 - 2"
#5 - 2.5"

I've never gone beyond 5 groups, so I don't know how that story ends. If the barrel is allowed to cool, it goes back to 5/8". I've repeated the test 3 times.

The heavy barrel is much, much better. I only tested it once, but the groups never opened up beyond 1" (acceptable for my purpose) and in truth it put 4 into 5/8" with one opening up the group everytime. There was some mirage that day, so the flyers might be optically induced.

I really want the lighter profile to work. The fatty is a full 1/2# heavier, and this is going on a rifle that's going to get carried for 50-60 miles in the Sniper Adventure Challenge. Finally to my questions:

Should I just expect that lighter profile to perform as it does? Would that be considered typical?

Might having the light one cryogenically stress relieved improve it's performance?

For reference, the diameter up to the gas block on the heavy barrel is 0.860". The lighter one is 0.800".

Edited to add that the heavy profile has about 1K rounds down it. The light profile maybe 400.

 

[rlsmith1]

Following. If you were to have your barrel cryo treated, where would you send it?

 

[Huskydriver]

Were both barrels used in the same receiver set?

Any cans or brakes used?

 

[dms416]

I had something very similar happen.

It was a "medium" weight CHF FN contracted barrel...almost identical to your skinny barrel there. Other specimens of the EXACT same spec stayed at whatever their base accuracy 1MOA or 2MOA whether it was hot or cold. This one in particular started was able to hold 10-rounds 0.85-0.90", and would subsequently disperse in ALL directions after 12-15 rounds fired gradually working out with the last 5 rounds of a 30 round magazine would be in excess of 4" for 5 rounds. Cold it would go back to sub-MOA and repeat the same results.

Hopefully you have better luck getting a helpful response...

 

[TimK]

Both barrels in the same receiver. All else was identical.

 

[OREGUN]

Had a barrel cryo treated at 300 below

300 Below, Inc. - 300 Below, Inc.

Ready to Lower Maintenance Costs? Treat the metal in your tools and equipment with ourproprietary cryogenic process. Reduce metal stress and fatigue Metals ...

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It was done BEFORE chambering/machining…guy doing the chamber seemed to think cryo first was the way. Not sure it made any difference. I don’t think this will solve your problem but that’s where I would start if you want to pursue cryo.

 

[Huskydriver]

Both barrels in the same receiver. All else was identical.

Cans or brakes used?

 

[TimK]

Brakes on both barrels. Same brake actually, one in 5/8-24 the other 1/2-28.

 

[bfoosh006]

Have you tried shimming / Loctiting in the lighter profile ? That might help with more consistent heat transfer.

Or are both a thermal fit ?

And I would lap / true the receiver face as well... can't hurt.

All other heat related things checked ? Gas tube enters freely into the gas key after heating up ?

Kinda seems like something is gradually heating up and messing with your barrel.

 

[_Windrider_]

@Frank Green what do you think about cryo?

 

[Rudy Gonsior]

View attachment 7916143

I have the two barrels pictured. Both are 1-7 Bartlien blanks, both chambered and profiled by Compass Lake with their CLE chamber. The fatty is 12.5", the other is 11.5"

The load is 77 TMK's over 23.0 g of 8208 XBR.

The first 5 shot groups out of both barrels are equivalent, roughly 5/8". Great, right? If I shoot say 5 consecutive groups (2 minutes between groups) on the lighter profile barrel, I get group sizes that go roughly like this:
#1 - 5/8"
#2 - 1"
#3 - 1.5"
#4 - 2"
#5 - 2.5"

I've never gone beyond 5 groups, so I don't know how that story ends. If the barrel is allowed to cool, it goes back to 5/8". I've repeated the test 3 times.

The heavy barrel is much, much better. I only tested it once, but the groups never opened up beyond 1" (acceptable for my purpose) and in truth it put 4 into 5/8" with one opening up the group everytime. There was some mirage that day, so the flyers might be optically induced.

I really want the lighter profile to work. The fatty is a full 1/2# heavier, and this is going on a rifle that's going to get carried for 50-60 miles in the Sniper Adventure Challenge. Finally to my questions:

Should I just expect that lighter profile to perform as it does? Would that be considered typical?

Might having the light one cryogenically stress relieved improve it's performance?

For reference, the diameter up to the gas block on the heavy barrel is 0.860". The lighter one is 0.800".

Edited to add that the heavy profile has about 1K rounds down it. The light profile maybe 400.

There is a reason sniper system tend to run heavy barrels, light weight barrels can be accurate BUT the chances of you having POI shifts as it heats is high.

Honestly a 1/2lbs difference is an easy choice given the confidence of performance.

 

[brianf]

its been talked about enough and pretty much agreed upon,

cryo doesnt do much of anything

possibly help/aid the chambering and even thats up for debate

no one in the BR, F-class winners circle is a cryo every barrel guy

not saying they are the be and end all of rifles but if it gives them a edge everyone would immediately jump on board

 

[KYAggie]

Question: What is the course of fire in the Sniper Adventure Challenge? Is it as rigorous as your test, or will you be able to let the barrel cool between strings to the point that the lighter one would work?

I don’t have any experience with this possible suggestion, but I wonder what turning the heavier barrel down or fluting it would do to your test string above?

Other than that I would say work out with a heavier rifle so this one feels lighter with the heavy barrel during the competition.

 

[Scttschnd]

I had a new Wilson barrel melanited to try it for the next rebarrel for my primary upper to see if it will hold up to cut rifle barrel round count. Curious to see the life of it for XTC and shooting to 600 yds if it holds up more than the usual 2600-3600 rounds before pulling them off.

 

[Frank Green]

@Frank Green what do you think about cryo?

Honest opinion! More B.S. than anything else.

Here is what I tell people.....and have maintained this since the beginning of the cryo thing.

In reality it does nothing for accuracy and or barrel life or how the barrel cleans. To me that goes back to the quality of the barrel period!

Our material starts out heat treated and double stress relieved to begin with. The austenite in the material is what retains the stress. Cryo is basically an artificial aging process is how it was described to me. It will help transform the austenite over to martensite which is more stress free. With out cutting up and analyzing every single piece of material there is no way to really no how much austenite is left over. So the less there is of it.....the less of an effect the cryo will have on the material.

A good example back when we we're doing a lot of cryo to our material. We did an order for a half a dozen 7mm f Class barrels for Warner tool. Same heat lot. I had half the heat lot cryo'd. We made Al's barrels half and half. One of the barrels bowed so bad during turning that I wouldn't send it to Al let alone anyone else. Guess what! It was one of the cryo'd blanks. So there is no guarantee with it in my opinion.

If you have a barrel that is giving you problems and you don't have $700 to rebarrel the gun...and if you can get the barrel cryo'd for say $50. Knock yourself out. Give it a try but I will say it's a band aid. It might stop the bleeding and it might not.

I cannot tell you how many lots of steel we played with where we would do the whole lot or half the lot and tracked them the best we could. Again we cannot tell a difference.

Back when I was at Krieger we offered a 2nd cryo after the blank was done and we did cryo all of our steel before any machine work at the time as well. I do remember two barrels after they had been shot and send in for a 2nd cryo...didn't shoot good afterwards. I'm talking a sub half minute barrel/gun that dropped to like 1moa. Why? Beats me! Two pieces out of a several hundred is a real small number but it happened.

Goes back to what I said earlier here.... In reality it does nothing for accuracy and or barrel life or how the barrel cleans. To me that goes back to the quality of the barrel period!

Later, Frank

 

[TimK]

Have you tried shimming / Loctiting in the lighter profile ? That might help with more consistent heat transfer.

Or are both a thermal fit ?

And I would lap / true the receiver face as well... can't hurt.

All other heat related things checked ? Gas tube enters freely into the gas key after heating up ?

Kinda seems like something is gradually heating up and messing with your barrel.

Your question prompted me to remember that the heavy barrel has a +0.001 barrel extension and is a thermal fit. The light one is not. I’ve glued several barrels in recent years with no discernible effect. Couldn’t hurt to try it again, I suppose. The receiver face was already trued.

 

[Huskydriver]

Your question prompted me to remember that the heavy barrel has a +0.001 barrel extension and is a thermal fit. The light one is not. I’ve glued several barrels in recent years with no discernible effect. Couldn’t hurt to try it again, I suppose. The receiver face was already trued.

Well ..... That was important info lol...I would suggest shimming the extension and if you wanna go all out shim and loctite 620