Gunsmithing Chamber out of spec

[BillyGoatMachine]

So I had a .260 barreled action that I purchased new sometime last year. Trued 700 action with a Mike Rock barrel. Supposed to be a tack driver right? Well I did a bunch of load development for it and it never shot better than 1 moa, and consistently shooting 1.5-3.0 moa. I probably put about 50-70 rounds through it before I gave up. I've since been building my own rifles on my lathe and decided to take a look at things now that I have more experience. First thing I checked was headspace. It chambered my go gauge with a stripped bolt without resistance. Next I popped in the no go and it chambered. I then preceded to add layers of scotch tape and the no go finally didn't chamber on the fourth layer!!!!! The horror I tell you! So the chamber is .008-.010 to large. Not cool, but really how dangerous is this? I am basically wondering if I am extremely lucky to still have my face intact after firing it during load development? Also, would an oversize chamber cause these accuracy issues? I'm assuming yes….I'm obviously not going to fire this rifle again the way it is. I'll either set back the shoulder and tenon length until the headspace is correct, or contact the smith I got it from.

 

[LRI]

Headspace, while important, isn't nearly the "black angel of death" that its often made out to be.


Lets go back in history and look at some stuff that's current to this very day.


Hatcher's notebook states that you need around .05" of firing pin protrusion. YET when you pick up any once fired piece of brass you (at best) see only around .02 to .027" of striker indentation on the primer.

Why the extra .025" -ish of striker exposure?

Jump into the 1st world war. The 03 Springfield was being made by everyone/anyone at the height of production. Is it realistic to think every barrel was HS to a value that we as chooter's like to see?

Only if you smoke the gaunjjj right?

The HS was all over the place. .05" of striker protrusion ensured the thing went bang so that Germans took dirt naps.

In a "fire and forget" scenario it's a number, it's not a 10 commandment.

Where it does have the ability to really hurt guns/shooters is when were at the reloading bench.

Say our rifle is .01" on HS from the zero value of the GO gauge. You shoot it and then take your shells home to size and gas back up. Due to a poor apprenticeship when learning to load, you make the mistake of FL sizing your brass back to original cartridge specifications.

Now you shoot again and the thing blows out another .008 to .01" from the standard specification. It's important to understand that the brass didn't grow .02". It can't cause the chamber is .01 deep from zero. What did happen though is the brass got stretched at the web on the 1st go around. The striker hit the primer, pushed the case forward to either the shoulder/bullet stopped it and caused the primer to get things rolling. The gap at the head/bolt caused the case to stretch like taffy at the webline. That material was robbed and can never be replaced. Brass is a metal. It's not an accordion.

Each time you shoot/size a case from a rifle that's out of proper HS tolerance you run the risk of stretching that web like the prom queen. How many times can you get away with this before it splits the head right off the case? That's a very open question dependent upon a number of variables outside of what your really asking.

The way around it is you load the ammo to the gun. Bump your shoulder just enough to get the thing to run well. FL resize only when they get stubborn. This is reloading 101. It ensures the case stays as close to chamber specs as possible to prolong brass life.

It doesn't solve the problem and in no way am I saying that HS doesn't matter. (my little disclaimer)

What I am stating is that if you bought a gun (like you did) and things are a mess there's two options. One, send it off and have it brought back into the right HS value (or fix it yourself) OR you CAN just work your ammo to where that stretch only occurs once. (the other thing you could do is drop the ejector out of the action, gas up your loads long to ensure the bullet is jammed tight in the lands so that the case head is firmly seated against the bolt, fire form your cases, and size them very carefully to mitigate the tendency of the case to stretch at the web.


Like I said, it's not the killer its often made out to be, but it can lead to damage/injury if one fails to understand what is really going on.


Hope this helps.

C.

 

[HodgdonExtreme]

^Perfect textbook answer.

Thread closed.

 

[wtopace]

You can always dial it in on your machine and shave off the back of the tenon the 0.008-0.01" that you have extra (you'll likely also need to deepen the bolt nose recess and push back the tenon shoulder as well).

Just make sure you go slow and measure often if you don't have the original reamer that was used (or you might get yourself an ever bigger project).

The joys of doing your own machine work... it's just metal, cut it up and make it the way you want it.

 

[BillyGoatMachine]

Headspace, while important, isn't nearly the "black angel of death" that its often made out to be.


Lets go back in history and look at some stuff that's current to this very day.


Hatcher's notebook states that you need around .05" of firing pin protrusion. YET when you pick up any once fired piece of brass you (at best) see only around .02 to .027" of striker indentation on the primer.

Why the extra .025" -ish of striker exposure?

Jump into the 1st world war. The 03 Springfield was being made by everyone/anyone at the height of production. Is it realistic to think every barrel was HS to a value that we as chooter's like to see?

Only if you smoke the gaunjjj right?

The HS was all over the place. .05" of striker protrusion ensured the thing went bang so that Germans took dirt naps.

In a "fire and forget" scenario it's a number, it's not a 10 commandment.

Where it does have the ability to really hurt guns/shooters is when were at the reloading bench.

Say our rifle is .01" on HS from the zero value of the GO gauge. You shoot it and then take your shells home to size and gas back up. Due to a poor apprenticeship when learning to load, you make the mistake of FL sizing your brass back to original cartridge specifications.

Now you shoot again and the thing blows out another .008 to .01" from the standard specification. It's important to understand that the brass didn't grow .02". It can't cause the chamber is .01 deep from zero. What did happen though is the brass got stretched at the web on the 1st go around. The striker hit the primer, pushed the case forward to either the shoulder/bullet stopped it and caused the primer to get things rolling. The gap at the head/bolt caused the case to stretch like taffy at the webline. That material was robbed and can never be replaced. Brass is a metal. It's not an accordion.

Each time you shoot/size a case from a rifle that's out of proper HS tolerance you run the risk of stretching that web like the prom queen. How many times can you get away with this before it splits the head right off the case? That's a very open question dependent upon a number of variables outside of what your really asking.

The way around it is you load the ammo to the gun. Bump your shoulder just enough to get the thing to run well. FL resize only when they get stubborn. This is reloading 101. It ensures the case stays as close to chamber specs as possible to prolong brass life.

It doesn't solve the problem and in no way am I saying that HS doesn't matter. (my little disclaimer)

What I am stating is that if you bought a gun (like you did) and things are a mess there's two options. One, send it off and have it brought back into the right HS value (or fix it yourself) OR you CAN just work your ammo to where that stretch only occurs once. (the other thing you could do is drop the ejector out of the action, gas up your loads long to ensure the bullet is jammed tight in the lands so that the case head is firmly seated against the bolt, fire form your cases, and size them very carefully to mitigate the tendency of the case to stretch at the web.


Like I said, it's not the killer its often made out to be, but it can lead to damage/injury if one fails to understand what is really going on.


Hope this helps.

C.

The nerve you have Mr. Dixon! Coming into all of my threads and answering my questions with superb clarity! One last question. Would the excessive headspace cause the accuracy issues I was seeing?
Thank you

You can always dial it in on your machine and shave off the back of the tenon the 0.008-0.01" that you have extra (you'll likely also need to deepen the bolt nose recess and push back the tenon shoulder as well).

Just make sure you go slow and measure often if you don't have the original reamer that was used (or you might get yourself an ever bigger project).

The joys of doing your own machine work... it's just metal, cut it up and make it the way you want it.

This is one option. I talked to the smith and he wants it back to verify. But honestly I'm not sure if I want to go that route when I can do the work myself. But yeah, without the original reamer, it will take some time especially without a DRO.

 

[300sniper]

it will take some time especially without a DRO.

People still make parts just fine without DROs. I doubt a DRO would save more than a couple minutes to set the shoulder, counterbore and tenon face back a few thousandths.

 

[wtopace]

it will take some time especially without a DRO.

I don't have a DRO and I cut tenons and chamber barrels all the time =) I plan to get a DRO, but it's largely for production parts, for 1 offs a magnetic indicator on the ways is invaluable and works perfectly.

 

[BillyGoatMachine]

I don't have a DRO and I cut tenons and chamber barrels all the time =) I plan to get a DRO, but it's largely for production parts, for 1 offs a magnetic indicator on the ways is invaluable and works perfectly.

This is how I've been doing it so far. I just assumed the DRO would speed things up a bit. Also my other question still looms. Would the oversize chamber cause the accuracy issues the barreled action was having? I can get all my other rifles to shoot great with my reloads except this one.

 

[wtopace]

This is how I've been doing it so far. I just assumed the DRO would speed things up a bit. Also my other question still looms. Would the oversize chamber cause the accuracy issues the barreled action was having? I can get all my other rifles to shoot great with my reloads except this one.

I'm no expert here because I cut my chambers to spec, but if you take an AI (improved cartridge) as an example, the shoulders blow out during the first firing from the factory case to make the 40 degree shoulder, and the rifles are still usually tack drivers during this process. Eg: I insert a .243 Win case into my .243 AI rifle, shoot a 5 shot group at 100 yards and get a great group. During that round of fire, all case shoulders are "unsupported" while they are changing shape. I would assume yours are doing a similar thing.

Although, take this with a grain of salt, because the AI change is created with a pre-existing bearing surface (both cases head space off the bottom of the shoulder, so the .243 Win is technically touching at the base of the shoulder in the .243 AI chamber).

I would bet your accuracy issues might be from bullet seating depth, powder selection, bullet selection or shooter skill (sorry, I have to say it to be fair). Have you tried different loads?

 

[BillyGoatMachine]

I'm no expert here because I cut my chambers to spec, but if you take an AI (improved cartridge) as an example, the shoulders blow out during the first firing from the factory case to make the 40 degree shoulder, and the rifles are still usually tack drivers during this process. Eg: I insert a .243 Win case into my .243 AI rifle, shoot a 5 shot group at 100 yards and get a great group. During that round of fire, all case shoulders are "unsupported" while they are changing shape. I would assume yours are doing a similar thing.

Although, take this with a grain of salt, because the AI change is created with a pre-existing bearing surface (both cases head space off the bottom of the shoulder, so the .243 Win is technically touching at the base of the shoulder in the .243 AI chamber).

I would bet your accuracy issues might be from bullet seating depth, powder selection, bullet selection or shooter skill (sorry, I have to say it to be fair). Have you tried different loads?

To death. All combinations of H4350, Varget, another powder can't remember, Barnes TSX, 139g scenar, Berger 140 VLD, and Southwest remanufactured reloads. All shoot the around the same with one load of H4350/scenars that I got one group under an inch. All three rifles I've chambered (7mmSaum, 308, 260), plus my Gap TR, Warner 260, ext ext all shoot well under 1/2 moa when I do my part. Hell, I can shoot better groups with my AR10's. No offense taken as we all have bad days at the range, but not every time out.

Forgot to mention. Originally I shot the rifle with a Manners EH3 I bedded myself and a NF 2.5-10x. Thinking that maybe that was under weight and under magnified for groups, I swapped it over to a Mcree chassis and a NF 3.5-15x with the most minuscule of improvement.

 

[jonaddis84]

If one were so inclined, you can actually gain velocity over a properly headspaced barrel by chambering it deep. You would HAVE to make sure youre only bumping the shoulders .002, but you do gain case capacity. But like Chad said, no real telling when/if that initial web stretch will come back to bite you with a separation. I tested this out once with a 6.5CM, with a 21" barrel headspaced +.006 I was able to get I think 80-90fps faster before the equal amount of pressure on a +.001 chamber. Same exact barrel.

Dont take this as advice to do so, but as mentioned above, excessive headspace is bad, but not the end of the world.

To answer your accuracy question. If you were bumping the shoulders .002 or more past factory spec, that means the case is having to grow some .008" or more, so yeah I could see you having accuracy problems. Try loading a few of your once fired pieces of brass, just neck size it, and see if it groups.

Also make sure you arent shooting 140 amax with a lot ending in 190 or 191, that could also be your issue.

 

[xringaccuracy]

Where that chambers stands, once fired brass means that, may be stretched to its gills. In rifle building we all seek to remove variables. A good chamber is one of them. Probably not going to blow up but we all want things right. Set it back meaning cut the tennon off and start from scratch. You may find you have a great but shorter barrel. Another thing to think of is load developement. I dont mean go crazy shooting 100 rounds but all rifles like what they like. Most are within what some other identical rifle likes but a little tweaking to find its sweet spot.

 

[RonA]

it will take some time especially without a DRO.

Just order an 18" camshaft degree wheel and install it on your carriage handle with a magnetic pointer. Then you can divide the Z axis travel per rotation by 360 to get how many thousandths per degree of rotation. There will be about 5/32" between degree marks on an 18" wheel so you should be able to guestimate just a couple of thousandths. DRO's just spoil creativity.

 

[MikeeBooshay]

If one were so inclined, you can actually gain velocity over a properly headspaced barrel by chambering it deep. You would HAVE to make sure youre only bumping the shoulders .002, but you do gain case capacity. But like Chad said, no real telling when/if that initial web stretch will come back to bite you with a separation. I tested this out once with a 6.5CM, with a 21" barrel headspaced +.006 I was able to get I think 80-90fps faster before the equal amount of pressure on a +.001 chamber. Same exact barrel.

Dont take this as advice to do so, but as mentioned above, excessive headspace is bad, but not the end of the world.

To answer your accuracy question. If you were bumping the shoulders .002 or more past factory spec, that means the case is having to grow some .008" or more, so yeah I could see you having accuracy problems. Try loading a few of your once fired pieces of brass, just neck size it, and see if it groups.

Also make sure you arent shooting 140 amax with a lot ending in 190 or 191, that could also be your issue.

If you do this, you can try seating the bullets long for the first firing, with a little decent neck tension. It will be a hard jam in the lands, don't overdo the powder, you are just fire forming. Having the round headspace on the lands for the first firing, will keep brass stretch lower, you are more just blowing out the shoulder. It is very similar to making 6PPC brass, you want to move the shoulder forward, by thinning the neck shoulder area a bit, it's usually thicker there anyway.

Make a resize gauge from a barrel stub, then you can measure how much you are setting the shoulder back when you resize. .001 is plenty, and will help case life a lot.

 

[jsthntn247]

There are some competition shooters out there that run their headspace over .030 too long so they can have extra case capacity. They still have their faces because you probably seen them before in magazines.

 

[BillyGoatMachine]

There are some competition shooters out there that run their headspace over .030 too long so they can have extra case capacity. They still have their faces because you probably seen them before in magazines.

.030" over huh?? Now that's going to stretch some brass!

 

[bward]

Think about a BRX. That's a blow out of .100" and the brass still lasts forever if you size it correctly. The amount of blowout on the first firing is a non issue.


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