Lands evaluation

[deer_hunter132]

This is a 7 mm Remington Magnum that we've had some accuracy issues with. The kahles getting fixed ended up being step one after we figured out the scope was an issue. 150 grain soft points off the shelf and some 120 grain Nosler ballistic tips that I hand loaded with IMR 4198 shoot the same relative point of impact. 139 SST whether it's hand loaded or off the shelf, shoot about 7 and 1/2 in to the right in comparison, roughly the same elevation, at 200 yards. I decided to run the borescope through the gun and see what I had. The lands area was quite difficult to get clean but I finally was able to. What I saw was that there's only two grooves that the lands actually extend all the way to end of the chamber. How common is this or is this possibly some of our accuracy issues? Here is a video upload of the lands area.

 

[Pickettpuncher]

What accuracy issues are you experiencing?

 

[huntnful]

Yeah that’s a crooked ass chamber. Factory rifle?

A crooked chamber can potentially shoot well, but it’s definitely not ideal, and can certainly cause accuracy issues.

That’s a garbage barrel as far as I’m concerned though.

 

[deer_hunter132]

What accuracy issues are you experiencing?

Groups havent been great. Sometimes it's shooting something that's still good enough and then it'll throw out a flyer and just make you scratch your head. One outing to the next and it seems like it shoots a bit different. 100yd powder test with 139gr sst. IMR 4350 59 grains to 61.5 grains I believe. The two 59.5gr happen to be touching so I loaded up some more of those at the range and tried seating them deeper. I started as close to the lands as I could get and be mag length which was somewhere between .020 and .030 iirc. That was on another Target and it was just all over the place bouncing left and right like two and a half inches. The other picture with the yellow tape was the 120 grain that I loaded and shot at 200 yards. It was a little windy that day so some of that could be because of wind I think.

 

[deer_hunter132]

Yeah that’s a crooked ass chamber. Factory rifle?

A crooked chamber can potentially shoot well, but it’s definitely not ideal, and can certainly cause accuracy issues.

That’s a garbage barrel as far as I’m concerned though.

Yes it is a factory Browning A bolt with the boss. What's also weird, is he said that he put a friend's suppressor on it and it shot tighter than it ever had. But I wasn't there to see what the grouping was, he's okay with minute of deer as long as he's able to kill deer which somehow he's always able to pull it off.

 

[wind gypsy]

Those are some ugly lands and the chamber does not appear to be centered or concentric with the bore.

My interpretation of the saami min chamber drawing is that if it was a concentric chamber and the barrel groove and reamer were to spec, you'd have no lands make it to the end of the chamber.

 

[deer_hunter132]

Those are some ugly lands and the chamber does not appear to be centered or concentric with the bore.

My interpretation of the saami min chamber drawing is that if it was a concentric chamber and the barrel groove and reamer were to spec, you'd have no lands make it to the end of the chamber.

View attachment 703584

Well if your interpretation is correct then it's quite a bit off center. I'll have to check my 7 Mag when I get home, I know the other calibers that I have, have the lands going pretty close to the end at least from what I remember.

 

[wind gypsy]

Freebore Diameter: 0.2845
Groove Diameter: 0.2837

Thus there should be no grooves or lands in the freebore unless there is a depth tolerance of the groove that allows it to be deeper. That said, less than a thousandth on a longer chamber like a magnum is pretty dang small. I haven't bore scoped a bunch of factory chambers but I bet that is pretty common.

 

[deer_hunter132]

Dad said the gun was always like a 4in gun at 200yds. Cant say im Surpised. My 80's savage was cut straight lol
Browning says the gun is out of warranty. Purchased around 2003.
They said ship it to them and they will look it over; maybe give a 40% discount on a new rifle.
Gun shop he bought it from said they will ship it, but be warned they might take a year to get a resolution. Guess we shall see.
Being the chamber doesnt meet sammi specs, imo thats a legal liability for them.

 

[Wapiti1]

I'm going to question if the chamber is crooked or if the lands have been worn smooth from cleaning without a bore guide. I see a lot of longitudinal scratches in that video that make me wonder. I also don't see any machining marks from the reamer in there. Even on old chambers you typically see transverse striations from the reamer in the neck/throat area.

Not that it couldn't be a crooked chamber, but there are some details in the video that make me think otherwise.
Jeremy

 

[wapitibob]

I've never seen a barrel that smooth and shiny.

 

[SDHNTR]

I'm going to question if the chamber is crooked or if the lands have been worn smooth from cleaning without a bore guide. I see a lot of longitudinal scratches in that video that make me wonder. I also don't see any machining marks from the reamer in there. Even on old chambers you typically see transverse striations from the reamer in the neck/throat area.

Not that it couldn't be a crooked chamber, but there are some details in the video that make me think otherwise.
Jeremy

My thought exactly.

 

[deer_hunter132]

I'm going to question if the chamber is crooked or if the lands have been worn smooth from cleaning without a bore guide. I see a lot of longitudinal scratches in that video that make me wonder. I also don't see any machining marks from the reamer in there. Even on old chambers you typically see transverse striations from the reamer in the neck/throat area.

Not that it couldn't be a crooked chamber, but there are some details in the video that make me think otherwise.
Jeremy

Why is there lands in the freebore at all though? It shouldnt be there at all according to Sammi spec.
Even if it was from cleaning, how would you get four land " rifling grooves" to wear evenly in distance from the chamber?

 

[BBob]

Why is there lands in the freebore at all though? It shouldnt be there at all according to Sammi spec.

^^^ Exactly!
Freebore is .1142" so all lands should be roughly (and evenly) that far away from the end of the chamber. It looks to me that is not the case so I say offset chamber. No it'll never shoot as well as it possibly could with a correct chamber. Happens a lot in factory barrels. I have a Howa Mini at the moment with the same. It shoots okay for it's purpose but not like it should.

 

[deer_hunter132]

I would have never figured a rifle costing what it did would have failed, his scope either.
Its wild.
Learn something new every day.

 

[Koda_]

I never thought I would hear about someone with the same problem. At least mine isnt a nice Xbolt.
Mine is a cheap PSA 223 wylde barrel. It holds about 1.25 moa... but I dont really spend a lot of time with this rifle.

I dont know how barrels are made to understand how it could happen. Dont they cut the lands after the chamber is reamed? Its hard to imagine how only a couple of lands would be formed in the freebore area but not all the lands.

 

[BBob]

Dont they cut the lands after the chamber is reamed?

No, the opposite. Barrel blanks are generally drilled, reamed, some are honed at this stage, rifled and then the chamber is added. Rifling can be by various methods but most aftermarket are button rifled or cut rifled. Some large manufacturers use hammer forging and on some of those the chamber is hammered in along with everything else at the same time.

There are various methods to ream the chamber and if the barrel reamer alignment isn't correct it can easily result in an offset chamber aka non-concentric chamber aka non-concentric throat, etc... There are various methods for reamer alignment before and during chambering. That discussion can get quite lengthy and can be quite contested as to how to go about it.

 

[Koda_]

No, the opposite. Barrel blanks are generally drilled, reamed, some are honed at this stage, rifled and then the chamber is added. Rifling can be by various methods but most aftermarket are button rifled or cut rifled. Some large manufacturers use hammer forging and on some of those the chamber is hammered in along with everything else at the same time.

There are various methods to ream the chamber and if the barrel reamer alignment isn't correct it can easily result in an offset chamber aka non-concentric chamber aka non-concentric throat, etc... There are various methods for reamer alignment before and during chambering. That discussion can get quite lengthy and can be quite contested as to how to go about it.

I can see it being a lengthy explanation and probably no need since I and most here will never make a barrel. But its just hard to understand how the chamber reamer would miss 2 lands in the freebore area, especially cutting in between them.

 

[BBob]

its just hard to understand how the chamber reamer would miss 2 lands in the freebore area

Trust me it's easier to F-up than you'd think

especially cutting in between them.

You're picturing the operation wrong. When chambering the reamer doesn't cut between anything. It just removes material in a circular fashion like a basic drill bit.

 

[Koda_]

You're picturing the operation wrong. When chambering the reamer doesn't cut between anything. It just removes material in a circular fashion like a basic drill bit.

I do understand that part of it, thats why its so hard to imagine how the reamer would leave only 2 lands behind...