6BRA Heavy bolt lift

[Rehner23]

Hello everyone, I’ve done a lot of reading on this forum, but this is my first post.
I recently had a 6 BRA built with an Impact precision action and Krieger barrel.
The gun shoots great so far, but I’m getting a pretty heavy bolt lift, even with loads that would be considered light… I’ve been ladder testing loads between 29.6 - 30.5 H4895, which is giving me muzzle velocities from 2760-2880 with a 105 Berger hybrid. The bolt lift always seems to be heavy, maybe a little more with the hotter loads but not significantly.
I’m shootings Lapua brass, which I did fire form, but I really didn’t pay too much attention to the bolt lift when fire forming.
At the moment I don’t know the reamer spec that was used to chamber the barrel.
Other than the bolt lift there doesn’t look to be any other signs of over pressure.
Any suggestions for me!??
Thanks!

 

[mikecr]

Is it heavy lifting as in popping extraction, or run out of headspace?
That is, what do measurements show?
Why do you think it's an over pressure sign?

 

[Rehner23]

I’m not sure what a “popping” extraction is, but I would say running out of headspace would make sense.
As far as other over pressure concerns.. I don’t have any flattening of the primers, no ejector marks in the brass, no protruding firing pin strikes.
I’ve bumped all my shoulders .002”, and I tried 10 rounds bumped .004-.005”, 5 rounds of 29.6, 5 rounds of 30.4… no difference at all in the bolt lift, still heavy.
My fired brass measures 1.546” overall length.

 

[docmusk19]

Are your cases and chamber clean?
I had a similar issue with a 6br. Wiping my loaded rounds down with rag/splash of brake cleaner and making sure my chamber was clean completely fixed the issue.

I also made sure I was scrubbing out any carbon ring that could have been forming.

 

[Rehner23]

I have, my barrel and chamber where cleaned thoroughly after each range session, and I give my cases a quick wipe after sizing.

 

[docmusk19]

Hmm. Bummer.

Humor me here - wipe down your loaded round and let it air dry right before you shoot.

I wipe down after sizing, but I know my fingers get grimey etc as I continue through my brass prep. The experience with my 6br taught me to wipe down right before I shoot. My range is in the back yard. I seat my bullet, wipe it down, and it’s dry by the time I get to my bench.

I use a pistol rod with an oversized swab (and another splash of brake cleaner) for my chamber. .410 sized swab I think

 

[docmusk19]

I don’t know if you have a bore scope, but that’s the best way to check on a carbon ring. They can be rascals to get out of there, especially if you aren’t using a bronze brush.

Alright, I’m done beating a potentially dead horse here. I just know I had this exact same issue that was resolved with confirming 100% I did all of the above.

 

[G Liles]

I have, my barrel and chamber where cleaned thoroughly after each range session, and I give my cases a quick wipe after sizing.

What are you using to clean the lube off your cases?

 

[G Liles]

I don’t know if you have a bore scope, but that’s the best way to check on a carbon ring. They can be rascals to get out of there, especially if you aren’t using a bronze brush.

Alright, I’m done beating a potentially dead horse here. I just know I had this exact same issue that was resolved with confirming 100% I did all of the above.

I thought I was getting my barrel clean until I bought a borescope, it taught me that a clean patch doesn’t mean you have a clean barrel!

 

[Rehner23]

I do have a Borescope, it sure looks clean..
It only has 300 rounds down it now too.
I clean with boretech with patches, then boretech on a nylon brush about 20 times back and forth, then patches until they come clean. I haven’t seen any carbon ring develop in the chamber.
I just wipe the case with a towel after sizing..
I use Hornady one shot.. I’ve never had an issue before with it.

 

[G Liles]

After sizing I wipe off cases with rubbing alcohol, there can’t be any lube left on the case or you will have pressure signs, also it’s summertime and 30.5 is high.

 

[DeltaBravo]

I had the same thing happen a week or so ago. First couple of shots and the bolt almost wouldn't open. I wiped the chamber clean and dry and it was gone. Maybe your chamber had a tad bit of lube on/in it, especially since you wiped the ammo before hand?

 

[Rehner23]

I will try that, I knew that 30.5 is getting high, but with speeds still under 2900 I didn’t think it was too much.
But no difference in feel from 29.6 which is under 2800..

 

[G Liles]

How long is your barrel, I’m running a 30” Brux, 29.8 H4895 @ 2950, 103 Vapor Trails, CCI 450, Laupa brass.

 

[Rehner23]

27” Krieger, 4 groove.
CCI 450, Lapua brass. 105 Hybrid

 

[Clancy]

27” Krieger, 4 groove.
CCI 450, Lapua brass. 105 Hybrid

I’ve got a 25” right now and anything over 30.3 is very warm, anything over 30.5 is crazy hot. I settled on 2870 from 30.1 grains because I just wasn’t going to get to that 2925 node safely.

For what it’s worth, H4895 can vary a bunch from lot to lot so comparing charge weights with other shooters isn’t always best practice.

The extra 3-5” is where we are missing out on the extra velocity, and I’d bet on case lube being the culprit on the heavy bolt lift if you’re not cleaning your cases with alcohol.

One other thing, take your bolt apart and clean the inside thoroughly. I had some build up in mine in my last BRA where some of the parts had kinda worn in. After cleaning, apply a little grease where needed and only put a tiny amount of something like wd-40 on the spring and pin.

Let us know how it works out.

 

[Rehner23]

I’ve got a 25” right now and anything over 30.3 is very warm, anything over 30.5 is crazy hot. I settled on 2870 from 30.1 grains because I just wasn’t going to get to that 2925 node safely.

For what it’s worth, H4895 can vary a bunch from lot to lot so comparing charge weights with other shooters isn’t always best practice.

The extra 3-5” is where we are missing out on the extra velocity, and I’d bet on case lube being the culprit on the heavy bolt lift if you’re not cleaning your cases with alcohol.

One other thing, take your bolt apart and clean the inside thoroughly. I had some build up in mine in my last BRA where some of the parts had kinda worn in. After cleaning, apply a little grease where needed and only put a tiny amount of something like wd-40 on the spring and pin.

Let us know how it works out.

I will, I’m going to really clean my next bunch of brass and chamber before going out, I would think that’s where the problem is, because like I said, at 29.6 running under 2800 it was just as sticky. So I don’t really think it’s an over pressure issue.
I appreciate all the input.

 

[Clancy]

I will, I’m going to really clean my next bunch of brass and chamber before going out, I would think that’s where the problem is, because like I said, at 29.6 running under 2800 it was just as sticky. So I don’t really think it’s an over pressure issue.
I appreciate all the input.

You bet. Check your lugs for galling as well. I stop and clean then reapply grease to my lugs every 10-20 rounds when fireforming.

By the way, how is it shooting?

 

[Kracken McGraw]

Have you seen the video of Speedy cleaning where he shows to put something like a big shotgun patch over a brush to dry out the chamber as last step?
I put the patch over a bore mop.

 

[Rehner23]

You bet. Check your lugs for galling as well. I stop and clean then reapply grease to my lugs every 10-20 rounds when fireforming.

By the way, how is it shooting?

It shoots great, I’m definitely not a competition bench rest shooter!, but my best group is about .175, and seems to average about .3 from 100